1,068 results on '"SUBMARINE fans"'
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2. Distribution patterns and controlling factors of beach bars in Qinghai Lake, NW China.
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Biao Peng, Zhengjian Xu, Xiaowan Chen, Yonghua Zhao, Chaojin Lu, Xiaomng Sun, and Hao Wu
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WATERSHEDS ,SUBMARINE fans ,HYDROCARBON reservoirs ,BRAIDED rivers ,SEDIMENTATION & deposition ,WIND waves ,BEACHES ,PROVENANCE (Geology) ,GEOLOGY - Abstract
The significance of beach-bar reservoirs, which are intricately linked to unconventional hydrocarbon reservoirs, has gained increased attention. This study elucidates the complex mechanisms governing the formation, spatial distribution, and morphological characteristics of beach bars in Qinghai Lake, NW China, highlighting the interplay of lake-level fluctuations, wind wave dynamics, sediment provenance, and terrain gradient. Our findings reveal that large-scale lake-level fluctuations primarily dictate the initial formation settings of beach bars, while small-scale fluctuations refine their internal stratification and sedimentary features. Wind wave dynamics play a critical role in defining suitable depth zones for beach bar development, influencing their morphology and resulting in distinct sedimentary characteristics across different lake zones. Furthermore, the study categorizes beach bars into three main systems based on sediment provenance--bedrock, alluvial fan (fan delta), and braided river systems--each exhibiting unique compositional and structural attributes. Terrain gradient around the lake significantly affects beach bar formation, with areas having a gradient less than 0.7° being particularly favorable. This research advances our understanding of lacustrine beach bar dynamics, offering insights into their potential as indicators of past environmental conditions and their implications for hydrocarbon exploration. The comprehensive analysis of controlling factors provides a foundation for predicting beach bar distribution and contributes to the broader field of sedimentary geology by integrating multi-disciplinary approaches to study lacustrine sedimentary processes. [ABSTRACT FROM AUTHOR]
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- 2024
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3. New cold seep sites on the continental slope southwest to Svalbard.
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Bellec, V. K., Chand, S., Knies, J., Bjarnadottir, L. R., Lepland, A., Sen, A., Thorsnes, T., Ketzer, Marcelo, Jin, Jiapeng, and Yang, Jinxiu
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COLD seeps ,CONTINENTAL slopes ,SUBMARINE fans ,GAS seepage ,OIL seepage ,DOLOMITE ,EARTH sciences ,GLACIAL landforms - Abstract
We discovered seafloor features such as bacterial mats and carbonate crusts typical for active methane seeps on the continental slope southwest of Svalbard. These features are associated with two main northwest-southeast trending morphological structures that are oriented parallel to the regional continental slope. Both structures occur at c. 800 m water depth, at the boundary between the Storfjorden trough mouth fan to the south and the Hornsund trough mouth fan to the north, which suggests a loading related fluid seepage. The main structure displays depressions and ridges forming a crater in its center. Other occurring features include small sediment mounds, domes often covered by bacterial mats, and hummocky seafloor colonized by siboglinid tubeworms. Free gas bubbles were spotted close to the centre and plumes along the rims of the structure. Thick carbonate crusts indicate a long seepage history in the center of the structure and on top of the ridges. The sources of the seeps are likely to be Miocene old organic-rich deposits, or Paleocene hydrocarbon reservoirs. [ABSTRACT FROM AUTHOR]
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- 2024
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4. Effect of Seismicity and Tectonic‐Glacial Interactions on Submarine Megaslides.
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Gulick, Sean P. S., Reece, Robert S., Sawyer, Derek E., Christeson, Gail L., and Horton, Brian K.
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SUBMARINES (Ships) , *ICE streams , *SHEAR strength , *SEDIMENTATION & deposition , *SUBMARINE cables , *SUBMARINE fans - Abstract
Enhanced sedimentation at glacial margins can produce submarine megaslides (>10,000 km3). We report a single megaslide in the Surveyor Fan, Gulf of Alaska. Minimum extant size is ∼16,124 km2 in area and ∼9,080 km3 in volume. Slope failure occurred ∼1.2 Ma at the onset of the mid‐Pleistocene transition (MPT). With accretion along the Aleutian‐Alaska Trench, the original volume is conservatively ∼16,280 km3, with only a 140 km run‐out due to its blocky, high shear strength nature. We suggest the megaslide was triggered by a major sediment influx at the onset of the MPT, when glacial‐interglacial cycles shifted from 41 to 100 Kyr. The absence of repeat megaslides may reflect a changing balance between seismic strengthening and sediment flux, where later sedimentation driven by cross‐shelf ice streams results in thin, fluidized, non‐cohesive slides. Continued accretion of the Surveyor Fan and megaslide also reduces critical wedge taper, further inhibiting major failure. Plain Language Summary: Sediment flux at glacial margins can produce submarine slides >10,000 km3 in size (megaslides). We report a single megaslide in the Surveyor Fan, Gulf of Alaska. Minimum extant size is ∼16,124 km2 in area and ∼9,080 km3 in volume. Failure occurred ∼1.2 Ma at the onset of the mid‐Pleistocene transition (MPT). Due to accretion along the Aleutian‐Alaska Trench, the original volume is conservatively ∼16,280 km3, but with only a 140 km run‐out due to its blocky, high shear strength nature. We suggest the megaslide was caused by the initial major sediment flux at the onset of the MPT, and that afterward only fluidized, thin, and non‐cohesive slides occurred. This is due to changing balance between seismic strengthening and sediment flux, and accretion of the Surveyor Fan and megaslide which reduces the critical wedge taper inhibiting major failure. Key Points: World's Fifth largest mapped megaslide documented beneath Surveyor Fan Gulf of AlaskaTiming of slope failure linked to onset of mid‐Pleistocene glacial intensificationAbsence of later failures due to changing balance of sediment flux/seismic strengthening and negative feedbacks from critical wedge processes [ABSTRACT FROM AUTHOR]
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- 2024
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5. Mid to late holocene alluvial fans activity at the southern sector of sierra de gredos in central Spain: Climate literature review, OSL and topographical analysis.
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Muñoz-Salinas, Esperanza, Castillo, Miguel, De Pablo, Nuria, Palacios, David, Sanderson, David, and Cresswell, Alan
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ALLUVIAL fans , *LITERATURE reviews , *AGGRADATION & degradation , *OPTICALLY stimulated luminescence , *FLOOD risk , *HOLOCENE Epoch , *SUBMARINE fans , *MORPHOTECTONICS - Abstract
Alluvial fans are rapidly evolving landforms sensitive to changes in tectonic and climatic conditions. Their study provides useful information to unravel the landscape evolution of lowlands and mountainous regions where sediment transported by rivers originates. The chronology of alluvial fan deposits is crucial for the flood risk assessment of those populations settled on this type of dynamic landform. Here we provide (1) a review of the literature concerning climatic reconstructions for the Sierra de Gredos, (2) optically stimulated luminescence (OSL) ages and (3) topographical analysis to reconstruct the recent events that built-up the alluvial fans of the southern sector of Sierra de Gredos (Central Spain). The area is tectonically active and has a relatively simple lithology given by a deformed and fractured Paleozoic granite massif that was heavily eroded by Quaternary glacial advances. Our OSL results indicate that the recent build-up events span from ca. 5 ka up to the end of the 19th century. The chronology of events is consistent with the climatic change reported for Central Spain, where humidity seems to be a primary control in the recent activity of the alluvial fans. Additionally, topographic analysis on a 5-m-resolution LIDAR DEM help us to propose that, tectonics have been a major control of Gredos alluvial fans in a long-term scale, longer than the Holocene but, since the mid-Holocene to the present, climate is a primary control on their landscape evolution. We conclude that current climatic conditions favor fan degradation for the Gredos alluvial fans rather than sediment transport and fan aggradation. The present study emphasizes the necessity of supplementing OSL chronologies with other long-term geochronological techniques to confine the constructive periods of fans for the entire Holocene. [ABSTRACT FROM AUTHOR]
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- 2024
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6. How is particulate organic carbon transported through the river-fed Congo Submarine Canyon to the deep-sea?
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Hage, Sophie, Baker, Megan L., Babonneau, Nathalie, Soulet, Guillaume, Dennielou, Bernard, Jacinto, Ricardo Silva, Hilton, Robert G., Galy, Valier, Baudin, François, Rabouille, Christophe, Vic, Clément, Sahin, Sefa, Açikalin, Sanem, and Talling, Peter J.
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SUBMARINE valleys ,COLLOIDAL carbon ,SUBMARINE fans ,TIDAL currents ,TURBIDITY currents ,MARINE sediments ,ESTUARIES ,OCEAN mining - Abstract
The transfer of carbon from land to the near-coastal ocean is increasingly being recognized in global carbon budgets. However, a more direct transfer of terrestrial carbon to the deep-sea is comparatively overlooked. Among systems that connect coastal to deep-sea environments, the Congo Submarine Canyon is of particular interest since the canyon head starts 30 km into the Congo River estuary, which delivers ~7 % of the total organic carbon from the world's rivers. However, carbon and sediment transport mechanisms that operate in the Congo Canyon, and submarine canyons more globally, are poorly constrained compared to rivers because monitoring of deep-sea canyons remains challenging. Using a novel array of acoustic instruments, sediment traps and cores, this study seeks to understand the hydrodynamic processes that control delivery of particulate organic carbon via the Congo Submarine Canyon to the deep-sea. We show that particulate organic carbon transport in the canyon-axis is modulated by two processes. First, we observe periods where the canyon dynamics are dominated by tides, which induce a background oscillatory flow (speeds of up to 0.15 m/s) through the water column, keeping muds in suspension, with a net upslope transport direction. Second, fast-moving (up to 8 m/s) turbidity currents occur for 35 % of the time during monitoring periods and transport both muddy and sandy particulate organic carbon at an estimated transit flux that is more than ten times the flux induced by tides. Remarkably, organic carbon transported and deposited in the submarine canyon has a similar isotopic composition to organic carbon in the Congo River, and in the deep-sea fan at 5 km of water depth. Episodic turbidity currents, together with background tidal currents thus promote efficient transfer of river-derived particulate organic carbon in the Congo Submarine Fan, leading to some of the highest terrestrial carbon preservation rates observed in marine sediments globally. [ABSTRACT FROM AUTHOR]
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- 2024
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7. Landscape response to tectonic deformation and cyclic climate change since ca. 800 ka in the southern Central Andes.
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Orr, Elizabeth, Schildgen, Taylor, Tofelde, Stefanie, Wittmann, Hella, and Alonso, Ricardo
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ALLUVIAL fans ,CLIMATE change ,ALLUVIUM ,SURFACE stability ,LANDSCAPES ,AGGRADATION & degradation ,MILANKOVITCH cycles ,SUBMARINE fans - Abstract
Theory suggests that the response time of alluvial channel long-profiles to perturbations in climate is related to the magnitude of the forcing and the length of the system. Shorter systems may record a higher frequency of forcing compared to longer systems. Empirical field evidence that system length plays a role in the climate periodicity preserved within the sedimentary record is, however, sparse. The Toro Basin in the Eastern Cordillera of NW Argentina provides an opportunity to test these theoretical relationships as this single source-to-sink system contains a range of sediment deposits, located at varying distances from the source. A suite of eight alluvial fan deposits is preserved along the western flanks of the Sierra de Pascha. Farther downstream, a flight of cut-and-fill terraces have been linked to eccentricity-driven (100-kyr) climate cycles since ca. 500 ka. We applied cosmogenic radionuclide (
10 Be) exposure dating to the fan surfaces to explore (1) how channel responses to external perturbations may or may not propagate downstream, and (2) the differences in landscape response to forcing frequency as a function of channel length. We identified two generations of fan surfaces: the first (G1) records surface activity and abandonment between ca. 800 and 500 ka and the second (G2) within the last 100 kyr. G1 fans record a prolonged phase of net incision, which has been recognised throughout the Central Andes, and was likely triggered by enhanced 100-kyr global glacial cycles following the Mid-Pleistocene Transition. Relative fan surface stability followed, while 100-kyr cut-and-fill cycles occurred downstream, suggesting a disconnect in behaviour between the two channel reaches. G2 fans record higher frequency climate forcing, possibly the result of precessional forcing of climate (ca. 21/40-kyr timescales). The lack of a high-frequency signal farther downstream provides field support for theoretical predictions of a filtering of high-frequency climate forcing with increasing channel length. We show that multiple climate periodicities can be preserved within the sedimentary record of a single basin. Differences in the timing of alluvial fan and fluvial terrace development in the Toro Basin appears to be associated with how channel length affects fluvial response times to climate forcing as well as local controls on net incision, such as tectonic deformation. [ABSTRACT FROM AUTHOR]- Published
- 2024
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8. Diagenetic Impact on High-Pressure High-Temperature Reservoirs in Deep-Water Submarine Fan Sandstone of Qiongdongnan Basin, South China Sea.
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Hu, Lin, Luo, Wei, and Ma, Benben
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SUBMARINE fans , *SANDSTONE , *RESERVOIRS , *SCANNING electron microscopes , *CLAY minerals , *LEAD , *PALEOGEOGRAPHY , *SOIL compaction - Abstract
The diagenetic evolution of sandstone is very complicated under the conditions of high temperatures and pressures in deep-water, deep-buried regimes, which have great influence on reservoir quality. This study investigates the typical reservoir target of Neogene deep-water, submarine-fan sandstones under high-temperature, high-pressure regimes in the Qiongdongnan Basin, South China Sea. Utilizing a thin section, scanning electron microscope (SEM), mineral geochemistry combined with burial history evolution, complex diagenetic events, and main controlling factors of the sandstone in the Neogene Meishan Formation were determined. The results show that the evolution of sandstone reservoirs is initially controlled by depositional framework compositions and subsequently modified by eogenetic and mesogenetic alterations during progressive burial. Eogenetic alterations mainly include the following: (1) mechanical compaction; (2) dissolution of feldspar; (3) low-Fe calcite cementation. Mesogenetic events were identified as the following: (1) dissolution of feldspar; (2) ferroan calcite and ankerite formation; (3) precipitation of quartz and clay mineral. Mechanical compaction is greatly influenced by the original depositional framework composition, and sandstone samples enriched in high contents of detrital clay matrix always experienced extensive mechanical compaction. Different phases of carbonate cement during different diagenetic regimes lead to continuous destruction on reservoir porosity. The dissolution of unstable feldspar minerals during eogenetic and mesogenetic environments leads to the development of secondary porosities and would enhance the quality of the reservoir. Overpressure formation is pervasively developed owing to early disequilibrium compaction and subsequent natural gas charging. Only well-sorted sandstones with low contents of detrital clay matrix could resist early mechanical compaction, lead to ample residual original porosities, and then undergo extensive mineral dissolution to generate sufficient secondary porosities. Subsequently, these porosities would be effectively protected by overpressure formation. Poor-sorted sandstones with high contents of detrital clay matrix would experience strong mechanical compaction and extensive destruction of original porosities. Thus, these sandstones are difficult to have significant dissolution and are unable to be effectively protected by overpressure formation. Therefore, the interplay between the original framework composition and the corresponding diagenetic pathways coupled with overpressure formation would result in strong reservoir heterogeneity for the deep-buried sandstones during progressive burial. [ABSTRACT FROM AUTHOR]
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- 2024
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9. Revisiting the Çüngüş Formation, a controversial tectono-stratigraphic unit in front of the Southeast Anatolian Suture Belt.
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ILGAR, Ayhan, TUNCAY, Ercan, BOZKURT, Alper, ERGEN, Ali, ESİRTGEN, Tolga, and AYDIN, Ayşegül
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SUBMARINE fans , *SUTURES , *TURBIDITES , *MUDSTONE , *SUTURING , *SUTURE zones (Structural geology) - Abstract
The turbiditic succession containing exotic blocks of various sizes deposited in the Çüngüş Basin, has been previously identified as the Çüngüş Formation in front of the Southeast Anatolian Suture Belt, Türkiye. These turbiditic sediments, dated as Eocene-Early Miocene, were interpreted as the lowermost allochthonous tectono-stratigraphic unit thrust over the Lice Formation during the Miocene within the Çüngüş-Hakkari nappes. In this study, the stratigraphical, sedimentological, palaeontological, and structural features of the Çüngüş and Lice formations are examined and reinterpreted within a basin model. Both formations consist of sandstones, siltstones, mudstones, and subordinate conglomerates, indicating ramp-fringe palaeochannel, submarine fan, and basin-floor turbidite facies associations. In the northern part of the basin, just in front of the suture belt, volcanic, metamorphic, and ophiolitic rocks and nummulitic limestones are included as blocks and tectonic slices within the turbidite succession. Based on nannoplankton analysis, both Çüngüş and Lice formations are assigned an Early Miocene age. The sedimentary facies associations filling the Çüngüş Basin are transitional from proximal to distal facies. The thrust in the previous maps separating the Çüngüş and Lice formations cannot be confirmed in the field. Based on our field observations and age data, we interpret that the Lice and the Çüngüş formations deposited continuously within the Çüngüş Basin that was opened as a foreland basin by flexural subsidence of the Arabian Autochthon under the crustal load of the Pütürge-Bitlis Massifs and the Maden Complex during the Early Miocene. The turbidite deposits containing exotic blocks in the north of the basin are interpreted as wedge-top deposits of the foreland basin, while those in the south are considered foredeep deposits. [ABSTRACT FROM AUTHOR]
- Published
- 2024
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10. Evolution from shallow‐water deltas to fluvial fans in lacustrine basins: A case study from the Middle Jurassic Shaximiao Formation in the central Sichuan Basin, China.
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Yang, Tian, Li, Xiaofang, Yang, Yu, Wen, Long, Cao, Zhenglin, Wang, Xiaojuan, Zhang, Shaomin, and Liang, Qiangshao
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ALLUVIUM , *SUBMARINE fans , *PALEOPEDOLOGY , *ZIRCON analysis , *LITHOFACIES , *FLUVIAL geomorphology , *PETROLOGY - Abstract
Distinguishing between shallow‐water delta and fluvial fan deposits in the subsurface of lacustrine basins is challenging due to their similar depositional characteristics and distribution patterns. This study focuses on the Middle Jurassic Shaximiao Formation in the central Sichuan Basin using core observations, seismic analyses, petrology analyses, zircon analyses, palaeoclimate indicators and palaeocurrent analyses to address this issue. Fifteen sedimentary lithofacies and eight lithofacies associations were established, corresponding to channelized fluvial deposits, non‐channelized fluvial deposits and shallow‐water delta deposits. Shallow‐water deltas are dominated by channels and mouth‐bar complexes with grey, red and green interbedded mudstone. Shingled seismic reflection, green mud clasts, small burrows and wave ripples are common with occasional palaeosols. Fluvial fans are dominated by channels and crevasse‐splays with pink colour and accompanied by red coloured floodplain deposits. Bright spot seismic reflection, red mud clasts, big burrows, current ripples and palaeosols are common. The increased uplift of the Dabashan Mountains controls the palaeocurrent direction, promoting the evolution from a shallow‐water delta in relatively humid environments to a fluvial fan in relatively arid environments. The channel widths in shallow‐water deltas are wider than those in fluvial fans, whereas the opposite applies for the channel amalgamation rate. Highly frequent channel‐width variations are controlled by short‐cycle climate fluctuation, corresponding to chemical index of alteration value fluctuations in different sandstone groups. The channel width in the relatively humid environments is wider than that in arid environments for both shallow‐water deltas and fluvial fans. It is likely that the sedimentary evolution from shallow‐water deltas to fluvial fans is relatively common in lacustrine basins in relatively arid environments with wide and gentle slope landforms. [ABSTRACT FROM AUTHOR]
- Published
- 2024
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11. Evolution of submarine canyons and hanging-wall fans: insights from geomorphic experiments and morphodynamic models.
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Lai, Steven Y. J., Amblas, David, Micallef, Aaron, and Capart, Hervé
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SUBMARINE valleys , *SEDIMENTATION & deposition , *LONG-Term Evolution (Telecommunications) , *SUBMARINE fans , *TIDAL basins , *MORPHOTECTONICS , *GEOMORPHOLOGY - Abstract
Tectonics play a significant role in shaping the morphology of submarine canyons, which form essential links in source-to-sink (S2S) systems. It is difficult, however, to investigate the resulting morphodynamics over the long term. For this purpose, we propose a novel experimental approach that can generate submarine canyons and hanging-wall fans on continuously evolving active faults. We utilize morphometric analysis and morphodynamic models to understand the response of these systems to fault slip rate (Vr) and inflow discharge (Q). Our research reveals several key findings. Firstly, the fault slip rate controls the merging speed of submarine canyons and hanging-wall fans, which in turn affects their quantity and spacing. Additionally, the long profile shapes of submarine canyons and hanging-wall fans can be decoupled into a gravity-dominated breaching process and an underflow-dominated diffusion process, which can be described using a constant-slope relationship and a morphodynamic diffusion model, respectively. Furthermore, both experimental and simulated submarine canyon–hanging-wall fan long profiles exhibit strong self-similarity, indicating that the long profiles are scale independent. The Hack's scaling relationship established through morphometric analyses serves as an important link between different scales in S2S systems, bridging laboratory-scale data to field-scale data and submarine-to-terrestrial relationships. Lastly, for deep-water sedimentary systems, we propose an empirical formula to estimate fan volume using canyon length, and the data from 26 worldwide S2S systems utilized for comparison show a strong agreement. Our geomorphic experiments provide a novel perspective for better understanding of the influence of tectonics on deep-water sedimentary processes. The scaling relationships and empirical formulas we have established aim to assist in estimating volume information that is difficult to obtain during long-term landscape evolution processes. [ABSTRACT FROM AUTHOR]
- Published
- 2024
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12. Optimization of Double-Closed-Loop Control of Variable-Air-Volume Air-Conditioning System Based on Dynamic Response Model.
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Li, Duanzheng, Ahmat, Mutellip, Cao, Hongqing, and Di, Fankai
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ENERGY consumption of buildings ,SUBMARINE fans ,DYNAMIC models ,DYNAMICAL systems ,AIR conditioning ,ENERGY consumption ,THERMAL insulation - Abstract
Control strategies for variable-air-volume (VAV) air conditioning significantly affect both the air quality within buildings and the consumption of building energy. Current control techniques effectively regulate room temperature using feedback on temperature discrepancies, yet they also elevate the wear on terminal devices and boost the energy usage of the supply fan. In this paper, the hysteresis and inertia parameters of end air valves and supply fans under two seasonal conditions are derived from experimental data. Aiming at the problems of frequent switching of the end air valve, long total switching stroke, and high energy consumption of the air supply fan, a fuzzy PI regulation method is proposed based on the original pressure-independent series PI regulation, which effectively solves the above problems. Initially, data on how room temperature reacts to changes in air supply fan speed and the position of end air valves during winter and summer were gathered. Following model identification, parameters for various seasonal conditions were determined. Secondly, the roles of different components in the variable-air-volume regulation process were investigated. Investigations revealed that within pressure-independent variable-air-volume control, the supply fan and end air valve emerged as the primary subjects of the study. A double-closed-loop control with the speed control of the supply fan as the outer loop and the opening control of the end air valve as the inner loop was adopted. Compared with the traditional serial PI regulation, the room temperature error of this method was increased, but it reduced the total stroke of the valve by more than 43%, which greatly reduced the valve's loss and noise and saved more than 2.7% of the energy consumption of the air supply fan. [ABSTRACT FROM AUTHOR]
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- 2024
- Full Text
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13. Architecture of Fluvial and Deltaic Deposits Exposed Along the Eastern Edge of the Western Fan of Jezero Crater, Mars.
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Mangold, N., Caravaca, G., Gupta, S., Williams, R. M. E., Dromart, G., Gasnault, O., Le Mouélic, S., Paar, G., Bell, J., Beyssac, O., Carlot, N., Cousin, A., Dehouck, E., Horgan, B., Kah, L. C., Lasue, J., Maurice, S., Núñez, J. I., Shuster, D., and Stack, K. M.
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ALLUVIUM ,LAKE sediments ,MARS (Planet) ,SUBMARINE fans ,BOULDERS ,SANDSTONE ,LUNAR craters - Abstract
Early observations from the Perseverance rover suggested a deltaic origin for the western fan of Jezero crater only from images of the Kodiak butte. Here, we use images from the SuperCam Remote Micro‐Imager and the Mastcam‐Z camera to analyze the western fan front along the rover traverse, and further assess its depositional origin. Outcrops in the middle to lower half of the hillslopes comprise planar and inclined beds of sandstone that are interpreted as foresets of deltaic deposits. Foresets are locally structured in ∼20–25 m thick, ∼80–100 m long, antiformal structures interpreted as deltaic mouth bars. Above these foresets, interbedded sandstones and boulder conglomerates are interpreted as fluvial topset beds. One well‐preserved lens of boulder conglomerate displays rounded clasts within well‐sorted sediment deposited in overall fining upward beds. We interpret these deposits as resulting from lateral accretion within fluvial channels. Estimations of peak discharge rates give a range between ∼100 and ∼500 m3 s−1. By contrast, boulder conglomerates exposed in the uppermost part of hillslopes are poorly sorted and truncate the underlying beds. The presence of these boulder deposits suggests that intense sediment‐laden flood episodes occurred after the deltaic foreset and topset beds were deposited, although the origin, timing, and relationship of these boulder deposits to the ancient lake that once filled Jezero crater remains undetermined. Overall, these observations confirm the deltaic nature of the fan front, and suggest a highly variable fluvial input. Plain Language Summary: Early observations from the Perseverance rover of the Kodiak butte suggested a deltaic origin for the western fan of Jezero crater. Here, we use images from the SuperCam Remote Micro‐Imager and the Mastcam‐Z camera to analyze the western fan front along the rover traverse, and further assess its origin. We observe strata in the lower part of the fan front that we interpret as deltaic deposits formed below water in a lake. The strata of the upper part of the fan front contain sediments interpreted as fluvial deposits formed under various fluvial regimes, with some of them being deposited by the rivers that also fed the Jezero paleolake. Overall, these observations confirm the deltaic nature of the fan front, and suggest a highly variable fluvial input. Key Points: New observations from the Perseverance rover of the western fan front confirm a deltaic originDeltaic foresets in the lower fan front are organized as antiformal structures interpreted as delta mouth barsSandstones and conglomerates in the upper part of the fan front suggest a highly variable fluvial input [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
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14. Unidirectional and combined transitional flow bedforms: Controls on process and distribution in submarine slope settings.
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Taylor, William J., Hodgson, David M., Peakall, Jeff, Kane, Ian A., Morris, Emma A., and Flint, Stephen S.
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SLOPES (Physical geography) , *TOPOGRAPHY , *SUBMARINE fans , *OCEAN bottom , *SUBMARINES (Ships) , *MUD , *EROSION - Abstract
Mixed grain‐size bedforms comprise alternating sand‐rich and poorly sorted mud‐rich laminae and bands. These bedforms have been identified in distal submarine settings formed underneath unidirectional flows. This study documents mixed grain‐size bedforms in a proximal submarine slope setting formed beneath both unidirectional and combined flows. Core and outcrop data with well‐constrained palaeogeographical context are used to describe two types of mixed grain‐size bedform. Type A bedforms comprise mud‐rich current ripples and low‐amplitude bed‐waves with alternating concave and planar sandstone–mudstone foresets that pass into mud‐rich troughs, and aggradational sinusoidal laminasets. Type B bedforms consist of sandstone–mudstone laminasets that comprise rounded, biconvex ripples with sigmoidal‐shaped foresets and swale and hummock‐like laminasets and banded sets. These bedforms occur in channel‐margin, internal‐levée and external‐levée, intraslope and disconnected lobe environments, and represent 27 to 63% by stratigraphic thickness of the studied successions. They are interpreted as deposits of clay‐rich transitional flows, whose depositional style is governed by the balance of cohesive and turbulent forces, and the rate of flow deceleration. Type B bedforms are further interpreted as combined transitional flow deposits, resulting from flow deflection and ponding processes by seabed topography. Upward and lateral transitions between different bedforms create distinct bedform sequences, demonstrating progressive spatio‐temporal transformations in flow properties and their topographic interactions. By using a well‐constrained palaeogeographical setting, mixed grain‐size bedforms are shown to be situated close to sites of erosion into muddy substrates, abrupt losses in confinement, and/or changes in slope gradient. These bedforms demonstrate that flow transformation and transitional flow behaviour are not restricted to distal submarine settings. Furthermore, mixed grain‐size bedforms are not a diagnostic criterion for bottom currents, because such flows cannot account for the high mud content in laminasets, or the interlamination of sand and mud. [ABSTRACT FROM AUTHOR]
- Published
- 2024
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15. Fossilized autogenic responses of grain‐size transition to sediment supply and water discharge: Alluvial fan experiments.
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Shin, Haein, Kim, Wonsuck, Lee, Hyojae, Johnson, Joel P. L., and Paola, Chris
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ALLUVIAL fans , *WATER supply , *SEDIMENTS , *SEDIMENT transport , *SUBMARINE fans , *GRAIN size - Abstract
Autogenic feedbacks can produce large‐scale, organized stratigraphic patterns in alluvial fans, but autogenic depositional signatures of specific upstream boundary conditions remain challenging to interpret. Here, a combination of theory, experiment and field application is used to explore how autogenic lithofacies changes can be interpreted as stratigraphic indicators of upstream boundary conditions. Six experiments were conducted to test the effects of sediment supply and water discharge rates on autogenic advance and retreat of the lithofacies boundary (grain‐size transition) in an alluvial fan with two dominant grain sizes. Migration of the grain‐size transition caused a short‐term zigzag pattern in the grain‐size transition position in the dip‐directional deposit section. For each experiment, time‐lapse images and laser topographic scans of the fan surface and stratigraphic cross‐sections of the final deposits were used to quantify characteristic timescales of autogenic processes. Timescales for fan‐margin migration, surface wet‐fraction change and grain‐size transition migration generally shorten as sediment supply rate increases and water discharge rate decreases. Increasing the sediment supply rate shortens the duration of the fluvial sediment storage and release cycle, producing higher frequency zigzags in the grain‐size transition trajectory. Increasing the water discharge tends to widen channels and lengthens the duration of the fluvial sediment storage and release cycle, constructing lower frequency zigzags in the grain‐size transition trajectory. Increasing the water discharge also enables more sediment to transport further downstream during release events, leading to higher magnitude zigzags in the grain‐size transition trajectory. These relationships between upstream boundary conditions and the grain‐size transition trajectory demonstrate how autogenic stratigraphic signals could be used as a tool to infer relative changes in boundary conditions. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
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16. The Hakcheon-Chogok Megaturbidite in the Miocene Pohang-Youngduk Basin, SE Korea: high-gradient slope failure probably triggered by a giant tsunami wave.
- Author
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Son, Junghee, Cho, Soonmi, and Hwang, In Gul
- Subjects
- *
ROGUE waves , *MIOCENE Epoch , *TSUNAMIS , *SUBMARINE fans - Abstract
In ancient records, discrimination of specific triggering events from sediment gravity flow deposits is very difficult, due to multiple interactions between triggering events and similar sedimentary characteristics. For this study, we introduce the Hakcheon-Chogok Megaturbidite (HCM) in the Miocene Pohang-Youngduk Basin (PYB), providing an opportunity to differentiate the triggering events. This megaturbidite is over 70 m thick in the proximal part and less than 4 m thick in the distal part. The diachronous stratigraphic position and distinct coarser sediments than those of the underlying and overlying successions suggest a large-scale slope failure of the fine-grained foreset (more than 2 km3). The occurrence of exotic granitic boulders, originating from the basement rock, more than 1 km west of the present fan-apex, is indicative of extreme sea-level run-up. The dispersal pattern and paleocurrent direction suggest that the HCM flowed to the northeast, irrespective of the local depositional slope which show a radial distribution from the fan-apex. The distribution pattern almost perpendicular to the strike of the NW-SE trending transfer fault suggests that the HCM was triggered by a reflection flow of giant tsunami wave, resulting in a large-scale failure of high-gradient (> 15° in slope angle) fandelta slope. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
17. Spatiotemporal variations in emission and particulate matter concentration outside a concentrated layer feeding operation.
- Author
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Yang, Xiao, Li, Zongyang, Wang, Chaoyuan, Wang, Shaojie, Hu, Qian, and Lu, Yujian
- Subjects
- *
PARTICULATE matter , *HENS , *HUMIDITY , *VENTILATION , *SUBMARINE fans - Abstract
A year-round monitoring of Particulate Matter (PM) less than 2.5 μm in aerodynamic diameter (PM 2.5) and Total Suspended Particulate (TSP) from a conventional cage laying hen house was conducted to reveal their spatiotemporal variations of concentrations downwind of tunnel fans. The PM Emission Rate (ER) and the correlations between PM with meteorological parameters and ventilation rate were studied. Ten self-developed Particle Concentration Monitoring Units were distributed to multiple horizontal (2, 25, and 50 m) and vertical (2 and 5 m) locations for PM examination. Four PM 2.5 concentration categories were classified: good (0–35 μg m−3), moderate (35–75 μg m−3), unhealthy (75–150 μg m−3), and very unhealthy (150–350 μg m−3). Annual and monthly percentages of PM 2.5 and TSP sampling hours for each category were calculated. Significant temporal variations in ER were observed, with monthly average ER ranging from 0.05 to 0.86 mg d−1 hen−1 for PM 2.5 and 1.40–8.90 mg d−1 hen−1 for TSP. Approximately 10–40% of PM 2.5 sampling hours exceeded 75 μg m−3, while no TSP concentration was higher than the recommended threshold. The monthly percentage for the "very unhealthy" PM 2.5 category was higher in winter, whereas the highest monthly percentage for the 800–1,200 μg m−3 TSP category was found in summer. Higher PM 2.5 concentrations were prone to be observed at further sampling points, while higher TSP concentrations were mostly detected near the fans or on both sides of the sampling area. PM 2.5 and TSP were positively correlated with ambient temperature and ventilation rate, while negatively correlated with relative humidity. • The emission rate of particulate matter in laying hen house had seasonal variations. • PM 2.5 concentrations at further locations downwind of fans were prone to be higher. • TSP concentrations near the fans were prone to be higher. • Hazardous PM 2.5 concentrations were more frequently observed in winter. • PM 2.5 and TSP were correlated with meteorological parameters and ventilation rate. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
18. Platform Evolution in an Oligo–Miocene Back‐arc Basin: An Example from the Central Iran Basin.
- Author
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SHARIFI‐YAZDI, Masoud, ENAYATI, Amirhossein, SALEHI AGHDAM, Jamal, BAHREHVAR, Mohammad, and REZAEI, Seyed Mustafa
- Subjects
- *
BACK-arc basins , *SILICICLASTIC rocks , *HYDROCARBON reservoirs , *FACIES , *SUBMARINE fans , *PLANT succession - Abstract
The Qom Formation is the most important hydrocarbon reservoir target in Central Iran. The Qom platform developed in a back‐arc basin during the Oligo–Miocene due to the closing of the Tethyan Seaway. This formation consists of a variety of carbonate and non‐carbonate facies deposited on a platform ranging from supratidal to basin. A combination of tectonic and eustatic events led to some lateral and vertical facies variations in the study area. Six third‐order depositional sequences and related surfaces were identified regarding vertical facies changes in the studied sections of this Oligo–Miocene succession. According to all results and data, this succession was initially deposited during the Chattian upon a distally steepened ramp of siliciclastic‐carbonate composition, including the Bouma sequence. Then, from the late Chattian to the Aquitanian, the platform changed into a homoclinal carbonate ramp with a gentle profile. With respect to tectonic activity, this phase was a calm period during the deposition of the Qom Formation. Finally, a drowned carbonate platform and a rimmed shelf emerged during the Burdigalian, terminated by the continental deposits of the Upper Red Formation. Regarding all geological characteristics, three main tectono‐eustatic evolutionary phases have been recognized in the Qom back‐arc basin. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
19. 2D numerical modeling of intense bedload-transport processes at confluences of mountain rivers and steep tributaries.
- Author
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Holzner, Johannes, Ostrander, Théo St. Pierre, Andreoli, Andrea, Mazzorana, Bruno, Comiti, Francesco, and Gems, Bernhard
- Subjects
POINT cloud ,COMPUTER simulation ,HYDRAULICS ,SEDIMENT transport ,FLUMES ,SUBMARINE fans ,MOUNTAIN soils - Abstract
The presented work deals with the numerical modeling of intense bedload-transport processes at confluences of mountain rivers and steep tributaries. Steep tributaries are characterized by having high transport capacities which supply large amounts of sediments to the confluence zone, where due to the sudden change in slope and the local hydraulic conditions, intense deposition can occur. The objectives of this study are to understand the potential applications and limitations of 2D numerical simulations for modeling these processes. The calibration of the applied 2D numerical model (BASEMENT, Basic Simulation Environment, v2.8) is based on comparing high-density point clouds of the confluence morphology at the end of flume experimental runs with numerical results. The calibrated numerical model is then used to test different discharge ratios and to investigate depositional patterns and mechanisms. The results show that key morphological features such as the confluence fan, the bank-attached bar and the scour hole can be accurately reproduced, showing that 2D numerical simulations are a valuable tool for modeling the complex interactions between morphodynamics and hydraulics at river confluences. Additionally, it is shown that the confluence morphology of steep tributaries and mountain rivers is strongly influenced by the sediment concentration in the tributary channel and the discharge in the main channel. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
20. Optimization of Impeller Structure Parameters of a Centrifugal Fan in a Powered Air-Purifying Respirator Power System.
- Author
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Zhao, Xintong, Guan, Jianhui, Wang, Tianyu, Liu, Xinyu, Xu, Qingao, and Zhou, Jie
- Subjects
RESPIRATORY protective devices ,IMPELLERS ,COMPUTATIONAL fluid dynamics ,AIR pressure ,SUBMARINE fans - Abstract
As the core power element of a centrifugal fan, the impeller's structural parameters are important factors affecting the aerodynamic performance of the fan. Therefore, to improve the aerodynamic performance of centrifugal fans, in this study, we take the Powered Air-Purifying Respirator (PAPR) power system as the object of research and use a combination of computational fluid dynamics (CFD) and experimental validation to investigate the effects of the number of blades, blade inlet angle, blade outlet angle, blade height, and blade thickness on the aerodynamic performance of the fan. A five-factor, four-level orthogonal test table L
16 (45 ) was selected to obtain the optimal combination of structural parameters for the impeller. In addition, in order to identify and visualize the features of the vortex, Q Criterion Normalized is applied to the simulation on the basis that the minimum pressure appears in the vortex core. In this study, Q Criterion Normalized is used to compare the internal vorticity of the prototype with that of the optimized prototype. The results show that (i) the order of influence of each parameter on the aerodynamic performance of the centrifugal fan is blade height > blade outlet angle > blade inlet angle > number of blades > blade thickness; (ii) the optimal combination of the structural parameters is number of blades 48, blade inlet angle 80°, blade outlet angle 120°, blade thickness 0.6 mm, and blade height 23 mm; the optimized prototype has an increase in air pressure of about 10%, an increase in air volume of about 31%, and an increase in efficiency from 49.61% to 53.57%; (iii) the intensity of internal vortices in the optimized prototype is weakened, the size of vortices and the number of vortices are reduced, and the homogeneity of the flow field is also improved. [ABSTRACT FROM AUTHOR]- Published
- 2024
- Full Text
- View/download PDF
21. Sedimentary Characteristics and Basin Evolution of a Compartmentalized Foreland Basin—Internal Ionian Zone, Western Greece †.
- Author
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Vakalas, Ioannis, Tripsanas, Efthymios, Tzimeas, Constantinos, and Konstantopoulos, Panagiotis
- Subjects
- *
SEDIMENTARY basins , *SUBMARINE fans , *FLYSCH , *MUDSTONE , *FACIES , *EVOLUTIONARY models - Abstract
This study is based on the detailed sedimentological analysis of eleven sections and one well through the late Eocene–Oligocene flysch formation of the Internal Ionian Zone (IIZ) in Western Greece. The sections are spread from the northern parts of Epirus to the north and Aitolokarnania to the south. Sedimentological data combined with biostratigraphic analyses resulted in a five-stage evolutionary model for the basin. Unit I corresponds to the lower part of the examined sections, indicating the onset of clastic sedimentation. Regarding depositional environments, it is regarded as a basin plain where lobe distal fringe accumulations occur. Unit II consists almost exclusively of heterolithic facies, marking the advance of a lobe complex system. Massive sandstone facies dominate unit III and can be considered a more proximal submarine fan system. Unit IV reflects a calm period of the basin, where mud-dominated heterolithics and hemipelagic mudstones were deposited. Hemipelagic mudstone facies with intervals of heterolithics, conglomerates, and deformed and massive sandstone facies characterize unit V. The architecture resembles a slope system incised by canyons and channels. The sand-rich intervals in Units III and V could act as the most favorable reservoir levels. In contrast, the sand-rich intervals in Unit II are considered less promising due to their higher heterogeneity. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
22. Neogene evolution of the margin adjacent to the La Plata River Delta (Pelotas Basin): Sedimentary pathways and the origins of the Rio Grande Cone.
- Author
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Tagliaro, Gabriel, Britzke, Adolfo, Gama, Mateus A. C., Bauli, Pedro, Negrão, André P., and Jovane, Luigi
- Subjects
- *
NEOGENE Period , *CONTINENTAL margins , *MIOCENE Epoch , *SEDIMENTATION & deposition , *SUBMARINE fans , *SEDIMENTS , *PLIOCENE Epoch - Abstract
Continental margins that exhibit high terrigenous input are generally located near deltas that are capable of transporting large quantities of sediments into the basin. However, in rare cases, high terrigenous sedimentation occurs in regions deprived of major riverine systems where the sedimentary pathway is enigmatic. One such case is the Neogene of the Pelotas Basin of Brazil and Uruguay, adjacent to the La Plata River mouth. Since the Miocene, anomalous sedimentation formed a giant progradational wedge, the Rio Grande Cone, one of the largest submarine fan-like features on Earth. To understand the Neogene evolution of the margin and the origins of the Rio Grande Cone, here we present a seismic-stratigraphic framework based on well-logs and 2D seismic data. Three depositional environments are identified: (1) on the shelf, upper Miocene to Pliocene fluvial channels delivered sand deposits on the mud-dominated shelf; (2) on the slope, sediment instability resulted in structural deformation and multiple phases of mass transport deposition and (3) on the lower slope and basin floor, large contourite drifts formed by sediment reworking. We classify the Rio Grande Cone as a megaslide complex, due to its depositional and structural setting. Local deltaic systems were active on the shelf in the Neogene, but the limited size of their paleo-drainage systems in comparison to the volume of sedimentation in the margin suggests that an additional sedimentary pathway existed. In this sense, the demise of an epicontinental sea over the La Plata Basin during the Neogene likely enabled the input of large volumes of fine sediments into the margin, via the La Plata plume water. We suggest that the desiccation of this epicontinental sea and the intensification of ocean currents since the middle Miocene explains the anomalous Neogene terrigenous influx into the SW Atlantic margin. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
23. Reconstructing the Zama (Mexico) discovery source to sink palaeogeography, Part II: Sediment routing from the Late Miocene shelf-margin to deepwater basin.
- Author
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Snedden, J. W., Rowan, M. G., Stockli, D. F., Albertson, M., and Pasley, J.
- Subjects
- *
MIOCENE Epoch , *SEDIMENTS , *SHEAR zones , *RESOURCE exploitation , *DIAPIRS , *SUBMARINE fans , *PALEOGEOGRAPHY , *TURBIDITY - Abstract
The Late Miocene source terrane tectonic history in the southern Gulf of Mexico Basin, as informed by detrital zircon geothermochronology data, supports a detailed regional palaeogeographic reconstruction from palaeoshoreline to the deepwater Zama minibasin of the Sureste salt basin. Seismic mapping points to a trio of pathways that converge upon two entry points into the Zama minibasin, illuminating how sediment gravity flows transit a complex seascape defined by shallow salt bodies. Consideration of empirical scaling relationships within and between segments of this sediment dispersal system allows for testable predictions of Upper Miocene submarine fan-runout lengths over basin exploration areas. Distances from the reconstructed shelf-margin to the Zama wells vary around 100 km, an increase of 20% over a straight-line distance as flows likely navigated around extant salt stocks, walls and sheets. This 100-km fan length is about 40% of the reconstructed minimum palaeo-river length, within predicted ranges for smaller source-to-sink systems in tectonically active areas (25 to 50%). The estimated fan-runout distance can be extended even further basinwards, considering the contemporaneous passage of the mobile Chortis block along the Tonala shear zone, expanding the Palaeo-Rio Grijalva drainage network during the Tortonian. These Late Miocene deepwater systems linked to the Palaeo-Rio Grijalva differ substantially from onshore Mexico-sourced turbidity flows feeding into the axis of the north-trending Veracruz Trough. Textural data from wells here suggests these systems were less effective at larger grain transport and sorting. Local (intrabasinal) variations are also evident within the Zama minibasin, as well data (image logs and cores) indicate that axially oriented sediment gravity flows involved fewer high-density turbidities, depositing lower net-to-gross sandstones and thicker shales than those flowing transverse to the basin axis from a southeastern basin entry point. These interpretations will guide both local exploitation of these economic resources and could also support future exploration for analogous salt-influenced deepwater reservoir systems in the Sureste basin and globally. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
24. High-frequency temporal variability of provenance signal in the submarine fan with the narrow shelf: Insights from sediment delivery and formation of late Triassic Zhuoni fan in the northeastern Paleo-Tethys Ocean.
- Author
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Mingxuan Tan, Haonan Sun, Yilin Fu, Haonan Cui, and Chengcheng Zhang
- Subjects
- *
SUBMARINE fans , *PALEOGEOGRAPHY , *OROGENIC belts , *HEAVY minerals , *SEDIMENTS , *OCEAN , *TURBIDITES - Abstract
The submarine fan with a narrow shelf is usually reactive to environmental signal propagation; however, source-to-sink functioning can be further complicated by several allogenic forcings. Here, we document the high-frequency provenance variations and different sediment delivery models recorded in the late Triassic Zhuoni fan developed in the northeastern Paleo-Tethys Ocean, mainly based on process-based sedimentological and provenance study of the Panyuan section in the West Qinling area in the northeastern margin of Tibetan Plateau. High-, low-density turbidites, hybrid event beds and hyperpycnites are distributed in the lobe-dominated submarine fan succession. Field sedimentological evidence from surrounding outcrops suggests that shelf-edge failure was the main cause of most high-and low-density turbidites with the overall absence of submarine slides or slumps, whereas the narrow shelf configuration together with late Triassic humid pulses is favourable for the occurrence of flood-related hyperpycnites in the Zhuoni fan. Detrital zircon grains (N = 6; n=123-272) generally have Palaeozoic-Mesozoic ages (ca. 350-250 Ma and 500-400 Ma) and Neoarchean-Paleoproterozoic ages (ca. 2100-1750 Ma and 2600-2400 Ma), but they can be further categized into three age groups due to different proportions of Precambrian age populations. The results demonstrate that the potential source areas may include the South and North Qinling Orogenic Belt, Qilian Orogenic Belt, different segments of North China Craton and the tectonic junction area between the Qinling and Qilian Orogenic Belts. The temporal changes in provenance signals, which are reflected by both the detrital zircon age spectra and heavy mineral assemblages, indicate different contributions of those sources in response to sea-level fluctuation. It could thus give rise to temporal variations between reactive and buffered source-to-sink sediment delivery models of the Zhuoni fan, despite the overall narrow shelf configuration. The development of the lowstand Zhuoni fan was directly related to extrabasinal hyperpycnal delivery from the river mouth and its high-frequency provenance variability recorded different efficiencies of signal transfer through the onshore catchment with significantly influence of temporal storage, fluvial rejuvenation or even regional climate variability. The highstand submarine fan was thought to be formed by shelf-edge failure with sediment buffering in the shelf region, which was associated with a strong magnitude of provenance mixing. Our work provides a new perspective for deciphering the different origins of deep-water sediment delivery in response to high-frequency sea-level and climate changes. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
25. Sedimentology and sequence stratigraphy of shallow and deeper marine Miocene deposits: A case study from the St. Paul and Gebel El-Zeit blocks, Gulf of Suez, Egypt.
- Author
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El-Azabi, Mounir H.
- Subjects
- *
SEQUENCE stratigraphy , *MARINE sediments , *FACIES , *SEDIMENTOLOGY , *GRABENS (Geology) , *SUBMARINE fans , *CLIMATE change , *TIDAL flats , *ROCK slopes - Abstract
Marginal and deeper marine facies typify the Miocene exposures along the western margin of the Gulf of Suez rift basin. The stratigraphic setting of these facies is a subject of debate and confusing at best. Integrative sedimentological and sequence stratigraphic study of successions exposed in the St. Paul and El-Zeit blocks provides insight into the lateral relationships between the two facies and their evolution, a topic that is not fully understood. The St. Paul block, located at the basin margin, has thin shallow marine facies, while the succession of El-Zeit block, situated near the basin axis, consists of basal conglomerates, thin shallow marine carbonates, thick deeper marine shale and marginal evaporites. The facies architecture of these successions is interpreted as belonging to two different depositional models: a fan-delta/lagoon system followed upwards by an alluvial fans/sabkha-tidal flat system in the St. Paul hangingwall basin, and carbonate-siliciclastic-evaporite systems on the hangingwall dip-slope ramp of El-Zeit block. These models may help understanding the sedimentary history of other similar blocks in the rift basin. The studied facies show many striking features such as deposition during tilting of fault block, abrupt facies and thickness variations, coarse clastic shedding, erosion channel filling, onlapping of high standing blocks and evaporite accumulation. These features are the result of major tectonic events that triggered the formation of unconformities at different hierarchical levels during the late early to middle Miocene. These unconformities subdivide the Miocene facies into five depositional sequences separated by basin-wide erosional boundaries. This division greatly improves the age control of marginal marine facies. It affords new insight into the evolution of marginal marine facies along the western margin of the basin in relation to deeper facies in the basin centre. Facies and thickness changes in these tectonically induced sequences indicate that basin floor irregularities, subsidence rates, climatic changes, variable sediment influx, sea-level/brine-level changes and basin isolation/connection to the Mediterranean Sea are also important factors responsible for their evolution. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
26. Sedimentary architecture of submarine lobes affected by bottom currents: Insights from the Rovuma Basin offshore East Africa.
- Author
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Mei Chen, Shenghe Wu, Ruifeng Wang, Jiajia Zhang, Pengfei Xie, Min Wang, Xiaofeng Wang, Qicong Xiong, Jitao Yu, and Miramontes, Elda
- Subjects
- *
DENSITY currents , *OLIGOCENE Epoch , *SUBMARINE fans - Abstract
The influence of bottom currents on submarine channels has been widely recognized, for instance, by the formation of asymmetric channel-levee systems and drifts. In contrast, it is often considered that submarine lobes can be only reworked by strong bottom currents and are not affected by bottom currents during their deposition. In this study, we analyse the potential effect of bottom currents on different hierarchical lobe architectures that formed during the lower Oligocene in the Rovuma Basin offshore East Africa. We characterize the stacking patterns, morphology and connectivity of different hierarchy lobes using well data and three-dimensional seismic data. We found no direct influence of bottom currents on the lobe complexes and single lobes that show a unidirectional stacking pattern that is opposite to the direction of bottom currents. Lobe elements in single lobes display vertical accretion with no obvious relationship with bottom currents. Additionally, the first deposited single lobe morphology presents an asymmetric shape, with a thicker lobe margin on the downstream side of the bottom currents, but this is due to an initial low topography on the downstream side rather than bottom currents. The architectural distribution reflects that the topography present before the depositions of the submarine lobes was controlled by previous asymmetrical channel-levee systems formed by the synchronous interaction of bottom currents and gravity flows. This asymmetric topography controls the subsequent deposition of lobes and results in the migration of single lobes in the upstream direction of bottom currents. Although weak to moderate bottom currents may not be able to substantially rework submarine lobes, our results demonstrate that they may control the geometry and evolution of submarine channels and thus indirectly affect the thickness and migration of lobes in more environments than previously thought. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
27. Controls on sedimentation in a deep-water foredeep: Central Pindos foreland basin, western Greece.
- Author
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Botziolis, Chrysanthos, Maravelis, Angelos G., Catuneanu, Octavian, and Zelilidis, Avraam
- Subjects
- *
SUBMARINE fans , *MARINE sediments , *SEDIMENTATION & deposition , *AXIAL flow , *OLIGOCENE Epoch , *SEDIMENTARY facies (Geology) , *FACIES - Abstract
This study provides a sedimentological, stratigraphic and palaeocurrent investigation of Upper Eocene to Lower Oligocene deep-sea fan deposits found in the central part of the Pindos foreland basin in western Greece. According to facies analysis, the examined succession at Amfilochia area has 13 sedimentary facies and 10 facies and sub-facies associations. Depositional elements include abyssal plain pelagics, outer fan, inner fan, and slope deposits. Outer fan sediments are classified as lobe-axis, lobe-off-axis, lobe-fringe, and distant lobe-fringe deposits, while inner fan sediments are classified as channel-fill, crevasse-splay, internal and external levee deposits. The stratigraphic study shows an upward shift from abyssal plain pelagics to outer, inner fan, and finally slope deposits, implying submarine fan system progradation and progressive infilling of a deep-water sediment depocentre. The sediments were deposited in the foredeep of the Pindos foreland system and correspond to the system's underfilled stage, when sedimentation was unable to exceed the accommodation provided by lithospheric flexure. They point to deposition near the onset of the Pindos orogen, after the closure of the Pindos basin because of the collision of the Apulian with the Pelagonian microplate during the Cretaceous-Palaeogene period. Palaeocurrent data from sole marks show bipolar directions associated with two distinct spreading sub-marine fan deposits. As a result, the study region was split into Upper (major SE-direction flow) and Lower (major NW-direction flow) parts, indicating that axial flows were predominant during sediment deposition. However, as the deposition of the elements continued, the progradation of both systems constrained the space accommodation because of the increased basin sediment supply and forced an increase in the degree of basin confinement that changed the compensational to aggradational stacking pattern. The goals of this research are to develop an updated facies model for these deep-sea fans as well as a robust correlation framework for the various stratigraphic units in the central Pindos foreland basin. This research also connects the stratigraphic development of deep-sea fan deposits to the evolutionary phases of the Pindos foreland system, providing fresh insights into the palaeogeographic circumstances in the Pindos foreland basin. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
28. Spatial distribution and variability of lobe facies in a large sand‐rich submarine fan system: Neoproterozoic Zerrissene Group, Namibia.
- Author
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Nieminski, Nora M., McHargue, Tim R., Gooley, Jared T., Fildani, Andrea, and Lowe, Donald R.
- Subjects
- *
SUBMARINE fans , *FACIES , *SUBMARINE topography , *SEDIMENT transport , *RIVER sediments , *SEDIMENTARY facies (Geology) , *DESERT plants - Abstract
The deposits of the upper Neoproterozoic Zerrissene Group of central‐western Namibia represent a large siliciclastic deep‐water depositional system that showcases the intricacies of facies and architectural relationships from bed‐scale to fan‐system‐scale. The lack of vegetation in the Namib Desert and regular east–west repetition of folded stratigraphy (reflecting ca 50% tectonic shortening) provides quasi‐three‐dimensional exposure over a current area of approximately 2700 square kilometres. The Brak River Formation, the middle sand‐rich unit of the Zerrissene Group, consists of nearly 600 m of strata exposed in multiple parallel continuous outcrops up to ca 10 km in length and oriented obliquely to depositional dip. Ten stratigraphic sections are correlated ca 32 km (ca 64 km restored) across the basin and offer exposure comparable in scale to modern submarine fans. Six sedimentary facies are identified and grouped into four facies associations that represent axial‐to‐marginal portions of deep‐water lobes in an unconfined submarine fan system. Spatial facies patterns, regional thickness variations, and palaeocurrents indicate that Brak River Formation sediments were transported primarily from the north to south–south‐west through a trough‐like basin, and deposited within an unconfined basin plain at the junction of the Adamastor and Khomas oceans. The unique outcrop exposure and extent permits the documentation of system‐scale architecture and basin configuration of the Brak River submarine fan system. A transition from the sand‐rich lower Brak River Formation to more intercalated mudstone‐dominated intervals in the middle and upper Brak River Formation is interpreted to record a change from aggradational to compensational stacking of lobe deposits. This records the evolution of a large submarine fan as it filled the subtle seafloor topography and became less confined at the system‐scale. The documentation of these deep‐water deposits from centimetre‐scale to basin‐scale provides a new model for a system with extensive long‐distance transport of sand‐rich sediment gravity flows to submarine lobes without apparent channelization. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
29. Discovery of Prevalent Ciliophora, Discoba, and Copepoda Protists in Deep Sea Water by In Situ Nucleotide Extraction.
- Author
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Xu, Peikuan, Yang, Ming, He, Lisheng, Zhang, Hongxi, Gao, Zhaoming, Jiang, Yuelu, and Wang, Yong
- Subjects
SEAWATER ,COPEPODA ,PROTISTA ,DETECTION of microorganisms ,HYDROSTATIC pressure ,CILIATA ,DEEP-sea animals ,SUBMARINE fans - Abstract
Deep-sea eukaryotic microorganisms play a vital role in degrading organic matter and geochemically cycling elements in the deep ocean. However, the impact of sampling methods on detection of these microorganisms under high hydrostatic pressure remains uncertain. In this study, we compared a traditional water sampling method using a Niskin bottle, an in situ microbial filtration and fixation method (ISMIFF), and a multiple in situ nucleic acid collection (MISNAC) method to exhibit differences in the community structures that were collected at ~590–3100 m in the South China Sea (SCS). The classification and biodiversity indices of 18S rDNA Illumina sequencing reads from the V9 variation region revealed higher diversity for MISNAC DNA absorption column samples compared to others. Importantly, the relative abundance of Ciliophora (19.49%), Copepoda (23.31%), and Diplonemea (10.67%) was higher in MISNAC adsorption column samples, while Retaria (48.86%) were dominant in the MISNAC membrane samples. This indicates that MISNAC columns might collect more DNA in situ for the naked protists, while Retaria with a carbonate shell were more likely retained on the membrane. In conclusion, MISNAC is an effective method for DNA collection of deep-sea eukaryotic microorganisms and provides valuable materials for studying deep-sea microbial ecosystems. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
30. Extending morphometric scaling relationships: the role of bankfull width in unifying subaquatic channel morphologies.
- Author
-
Hasenhündl, Martin, Bauernberger, Lena Sophie, Böhm, Christoph, Miramontes, Elda, and Skarke, Adam
- Subjects
SUBMARINE fans ,TURBIDITY currents ,SUBMARINE valleys ,INFRASTRUCTURE (Economics) ,SEDIMENT transport ,DATA harmonization - Abstract
Subaquatic channels, situated in lakes, fjords, submarine canyons and on deep-sea fan systems, exhibit diverse morphometric characteristics controlled by sediment transport processes, particularly turbidity currents. These processes play a significant role in transporting sediment, organic carbon, nutrients, and pollutants and pose hazards to critical infrastructure. This study examines a balanced set of subaquatic channels across various settings, sizes, and locations, employing novel data harmonization techniques to address biases toward larger channels. The analysis reveals consistent scaling relationships, particularly the dominant role of bankfull width, influencing bankfull depth, cross-sectional area, wavelength, and amplitude. The aspect ratio (width-to-depth) emerges as a significant parameter, reflecting a necessary channel compactness to maintain turbidity currents. Meandering development reveals relations between width, wavelength, and amplitude, with a preference for specific ratios. Meandering is most pronounced at channel beginnings, transitioning to straighter forms downstream, potentially influenced by flow dynamics and flow confinement. The study broadens the understanding of subaquatic channel evolution, emphasizing the importance of bankfull width and providing insights applicable across settings and scales. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF
31. Sedimentary architecture and evolution of a Quaternary sand-rich submarine fan in the South China Sea.
- Author
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Entao Liu, Detian Yan, Jianxiang Pei, Xudong Lin, and Junfeng Zhang
- Subjects
SUBMARINE fans ,LEVEES ,SEDIMENTATION & deposition ,PETROLEUM prospecting ,NATURAL gas prospecting ,GAS hydrates ,NATURAL gas in submerged lands ,WATER depth - Abstract
Investigating the sedimentary architecture and evolution of sand-rich submarine fans is vital for comprehending deep-water sedimentary processes and enhancing the success rate of hydrocarbon resource exploration. Recent drilling activities in the Qiongdongnan Basin, northern South China Sea, have unveiled significant gas hydrate and shallow gas potential. However, exploration in this area faces substantial challenges due to the limited understanding of sandy reservoirs. Leveraging extensive newly acquired extensive 3D seismic data (~9000 km²) and well data, our study reveals five distinct deep-water depositional systems in the Quaternary Ledong Formation, including a submarine fan system, mass transport deposits, deepwater channel-levee systems, slope fans, and hemipelagic sediments. Notably, the targeted sandrich submarine fan lies within the abyssal plain, situated at a water depth of 1300-1700 m. This fan exhibits a unique tongue-shape configuration and a SW-NE flow direction within the plane and spans an expansive area of ~2800 km² with maximum length and width reaching 140 km and 35 km, respectively. Vertically, the fan comprises five stages of distributary channel-lobe complexes, progressing from Unit 1 to Unit 5. Their distribution ranges steadily increase from Unit 1 to Unit 3, followed by a rapid decrease from Unit 4 to Unit 5. Our results suggest that the occurrence and evolution of the submarine fan are primarily controlled by sea level fluctuation, confined geomorphology, and sediment supply. Specifically, sea level fluctuation and sediment supply influenced the occurrence of the submarine fan. Concurrently, the confined geomorphology in the abyssal plain provided accumulation space for sediments and shaped the fan into its distinct tongue-like form. In contrast to the deepwater channels within the deepwater channel-levee systems, the distributary turbidite channels within the submarine fan are marked by lower erosion depth with "U" shapes, greater channel width, and higher ratios of width to depth. The comparative analysis identifies turbidite channels as the focal points for offshore gas hydrate and shallow gas exploration in the Qiongdongnan Basin. Furthermore, the temporal evolution of submarine fan offers valuable insights into Quaternary deep-water sedimentary processes and hydrocarbon exploration within shallow strata of marginal ocean basins. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF
32. A deep-marine ichnofossil assemblage from the Tertiary-age Algeciras Formation and related units, Campo de Gibraltar Complex, Southern Spain.
- Author
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McCann, Tom
- Subjects
- *
MUDSTONE , *SANDSTONE , *CHONDRITES , *OLIGOCENE Epoch , *SUBMARINE fans , *GREENHOUSES - Abstract
The Tertiary-age deep-marine succession cropping out between Tarifa and Algeciras can be subdivided into two units, namely the Late Eocene-?Early Oligocene Getares Unit and the overlying Oligocene-?Early Miocene Algeciras Formation. These strata comprise six sedimentary facies, ranging from thick-bedded sandstones to mudstones. The depositional settings are variable, comprising sandstone/calcarenite packages with intercalated mudstones and marls. The lowermost coarse-grained package is the Getares Unit (fan-fringe setting). This is overlain by the thick-bedded sandstones of the Algeciras Fm (channel, channel-margin setting) which pass upwards into more laterally-extensive beds (sheet-like lobe). Sediments were derived from a coastal setting to the north, as evidenced by occasionally abundant plant remains, from direct fluvial input (hyperpycnal flow). Within this succession, 34 ichnogenera (48 ichnospecies) have been recorded, including, Belorhaphe, Capodistria, Chondrites, Circulichnis, Cochlichnus, Cosmorhaphe, Desmograpton, Gordia, Halopoa, ?Helicorhaphe, Helminthopsis, Helminthorhaphe, Imponoglyphus, Lorenzinia, Megagrapton, Oldhamia, Ophiomorpha, Palaeophycus, Paleodictyon, ?Phycodes, Phycosiphon, Planolites, Protopaleodictyon, Protovirgularia, Scolicia, Skolithos, Spirophycus, Spirophyton, Spirohaphe, Taenidium, Teichichnus, Thalassinoides Urohelminthoida and Zoophycos. Of the ichnofossil assemblages that were defined, most are concentrated in the fan-fringe (Getares Unit; 74%) and channel/channel-margin (lowermost Algeciras Fm; 41%) settings, with a marked reduction in the sheet lobe system (uppermost Algeciras Fm; 9%). The ichnofaunal assemblage from the Tarifa-Almeria section represents the Nereites ichnofacies, or more specifically, the Paleodictyon and Nereites subichnofacies, both typified by abundant graphoglyptids. Deposition in the Algeciras-Tarifa region commenced with the mudstones underlying the Getares Unit followed by a sandstone package (fan fringe; Punta de Getares), indicative of fan progradation. Subsequent mudstones suggest a phase of quiescence before the deposition of the thick, sandy hyperpycnites in the lower part of the Algeciras Fm (Punta del Carnero I & II) where deposition was probably related to flooding events in the source rivers to the N. These were subsequently overlain by the Tarifa area lobe sediments. Deposition of the succession coincided with the transition from a Greenhouse to an Icehouse climatic regime (Eocene-Oligocene) and this change may be reflected in the marked reduction in ichnofaunas moving from the lower (Punta del Carnero) to the upper (Tarifa) Algeciras Fm. [ABSTRACT FROM AUTHOR]
- Published
- 2023
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33. RECONSTRUCTING LATE QUATERNARY ENVIRONMENTS IN THE NILE VALLEY USING AQUATIC AND TERRESTRIAL MOLLUSCS.
- Author
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Williams, Martin
- Subjects
- *
SAND dunes , *SUBMARINE fans , *MOLLUSKS , *OPTICALLY stimulated luminescence , *VALLEYS , *EARTH sciences , *LAST Glacial Maximum - Published
- 2023
34. Conditions of submarine levéed channel inception: Examination by flume experiments.
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Poppeschi, Justine, Nakata, Kazushi, and Naruse, Hajime
- Subjects
- *
FLUMES , *SUBMARINE topography , *SUBMARINES (Ships) , *COMPOSITION of sediments , *SUSPENDED sediments - Abstract
Submarine levéed channels are often observed in submarine fans, although submarine fans without continuous levéed channels are also common depending on the composition of supplied sediments, particularly the proportion of muddy/sandy materials. However, parameters governing the inception of levéed channels have not yet been studied. Furthermore, depositional levéed channel topography has not been simulated in experimental flumes in any previous study conducted with dilute flows (flow concentration <10%). Herein, four experimental series were conducted (Series A, B, C and D) to simulate depositional submarine channels and to study their formative conditions. A mixture of sediment and saline water was used in the experiments, and both the width of an outlet diffuser and flow discharge rate were varied in the experimental series. A topography composed of a channel with two ridges resembling natural depositional submarine channels with levées was formed in all experiments. Comparisons between the experimental topographies and natural submarine fans revealed that two of the four experimental series produced channel levées with length to width ratios similar to those produced by natural systems. An experiment with half the outlet size produced a channel two times deeper (4.5 cm against 2.0 cm and 2.2 cm) as compared to other experiments. The flow discharge rate and outlet width were half of those observed in Series A and B. Furthermore, salt was removed from the initial mixture for one of the experiments, resulting in high natural levées with a short channel. This study demonstrated that dilute flows could form purely depositional channel levées without precursor or resultant erosive features. In addition, results revealed that the formation of submarine channels is related to two factors: channel width and muddy suspended sediment. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF
35. Deep‐water sand transfer by hyperpycnal flows, the Eocene of Spitsbergen, Arctic Norway.
- Author
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Grundvåg, Sten‐Andreas, Helland‐Hansen, William, Johannessen, Erik P., Eggenhuisen, Joris, Pohl, Florian, and Spychala, Yvonne
- Subjects
- *
EOCENE Epoch , *TURBIDITY currents , *SAND , *TURBULENT flow , *TURBULENCE , *SUBMARINE fans , *FLUVIAL geomorphology , *MASS-wasting (Geology) - Abstract
Flood‐generated hyperpycnal flows are dense, sediment‐laden, turbulent flows that can form long‐lived, bottom‐hugging turbidity currents, which undoubtedly transport large volumes of fine‐grained sediments into the ocean. However, their ability in transferring sand into deep‐water basins is debated. This study presents sedimentological evidence of sandy hyperpycnal flow deposits (hyperpycnites) in a series of basin floor lobe complexes associated with a progradational shelf margin in the Eocene of Spitsbergen, Arctic Norway. Four coexisting types of sediment gravity flow deposits are recognized: (i) sandy hyperpycnites deposited by quasi‐steady hyperpycnal flows; (ii) turbidites deposited by waning, surge‐type turbidity currents; (iii) hybrid event beds deposited by transitional flows; and (iv) mass transport deposits emplaced during rare slope failures. The abundance of thick‐bedded massive sandstones, frequent bed amalgamation, the distribution of hyperpycnites across the lobes and the abundance and systematic occurrence of plant‐rich hybrid event beds and associated climbing ripple cross‐laminated beds in the lobe fringes, suggest that hyperpycnal flow was the most important mechanism driving lobe progradation. Shelf‐edge positioned fluvial channels linked to the basin floor lobe complexes via deeply incised, sandstone‐filled slope channels, suggest that rivers fed directly onto the slopes where their dense, sand‐laden discharges readily generated quasi‐steady hyperpycnal flows that regularly reached the basin floor. The composite architecture and complex waxing–waning flow facies configuration of the hyperpycnites is consistent with sustained and concomitant suspension and traction deposition under fluctuating subcritical to supercritical conditions. Similar sandstone beds occur on the clinoform slopes, indicating that the hyperpycnal flows operated likewise on the slope. Plant‐rich hybrid event beds indicate transformation of initially turbulent flows by relative enrichment of clay and plant material via progressive sand deposition to such an extent that it suppressed turbulence. The multi‐faceted character of the hyperpycnites reported here, challenges traditional beliefs that hyperpycnites assumingly preserve the waxing–waning signal of single‐peaked floods. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF
36. Alluvial development during climate fluctuations depicted with spectral decomposition of the Middle Triassic to Lower Jurassic post‐rift succession in the Horda Platform (Norway) and the impact on reservoir properties.
- Author
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Würtzen, Camilla L., Hassaan, Muhammad, Anell, Ingrid M., Nystuen, Johan Petter, Faleide, Jan Inge, and Midtkandal, Ivar
- Subjects
- *
ALLUVIAL fans , *MARINE transgression , *LANDSCAPE changes , *TRIASSIC Period , *SUBMARINE fans , *SEDIMENTOLOGY , *FACIES , *FLUVISOLS , *ESTUARIES - Abstract
For the first time, this study presents interpretations of alluvial fans in spectral decomposition RGB Blends, analysed in seismic time slices from the Middle Triassic to Lower Jurassic stratigraphical interval of the Horda Platform (northern North Sea). The time slices record a shifting alluvial fan front, fluvial variability, uplift and erosion and reveals depositional elements that may set the common conception of the geological development of this area during the Early–Middle Mesozoic up for discussion. Results show that the Upper Triassic Lunde Formation in the eastern margin of the Horda Platform was characterized by the deposition of coalesced alluvial fans. A variable extent of the fan front through the Upper Triassic is linked to interplaying allogenic factors: uplifted source areas in the aftermath of Early–Middle Triassic rifting determined sediment availability; climate transitioning from arid to semi‐humid, with increasingly fluctuating precipitation, controlled sedimentation, and run‐off; provenance dictated bulk sedimentology and affected prevailing alluvial processes. An overall retreat of the fan system through the Late Triassic coincided with a significant change in landscape characteristics at the transition into the overlying Statfjord Group. Uplift and initial tilting of the Horda Platform caused landscape degradation and the formation of plateaus and incised valleys, contemporaneous with increased humidity and marine transgression, forming estuaries. The shift in depositional style has implications for reservoir properties, creating complexity and heterogeneity in terms of facies distribution and connectivity, which may benefit potential CO2 storage. Upper Triassic alluvial fan development in the Horda Platform (northern North Sea) depicted through spectral decomposition of seismic time slices Enhanced level of seismic stratigraphic interpretation with RGB blending Impact of allogenic factors on alluvial depositional development Implications of alluvial variability on reservoir properties [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF
37. Lower Eocene carbonate ramp clinoforms of the southern Tethys; Zagros Foreland Basin, SW Iran: Sequence stratigraphy architecture, basin physiography and carbonate factory controlling parameters.
- Author
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Nikfard, Mohammad
- Subjects
- *
SEQUENCE stratigraphy , *GEOMORPHOLOGY , *EOCENE Epoch , *SUBMARINE fans , *CARBONATES - Abstract
Excellent cliff exposures in the Khush‐Ab and Chenareh anticlines (Zagros Foreland Basin, SW Iran) offer a good opportunity to document stratal geometries, paleofacies heterogeneity, depositional architecture and depositional cycles of the Lower Eocene sedimentary basin system. These unique outcrops containing six logged sections have been studied across a large‐scale transect, covering ca. 10 km of continental (Kashkan Formation), carbonate‐dominated platforms (Taleh‐Zang Formation) and submarine fan to basin‐floor settings (Amiran and Pabdeh formations). Field observations of the bedding geometries revealed a set of NE–SW oriented carbonate ramp clinoforms (clinoformal units 1–4) with sigmoidal cross‐sectional shapes and an internal fore‐stepping architecture. Based on detailed facies analysis, six facies associations (FA) were identified (FA.I to FA.VI), which are interpreted to have been deposited laterally in the continental, proximal to distal and deep‐water settings of a distally steepened carbonate ramp. According to the stratal stacking pattern, bounding surface, facies architecture and internal makeup of carbonate clinoforms, four H‐F‐cycles (cycle I–IV) corresponding to a lower hierarchical rank (fourth‐order cycle) were recognized and nested within the regressive stacking pattern (HST) of a higher hierarchical rank (third‐order sequence). These H‐F‐cycles are arranged in three segments (bottomset, foreset and topset) of each clinoformal unit. Higher rank transgressive blocks (TST) discriminated each clinoformal unit by up‐deepening sets of the H‐F‐cycle V. In total, five third‐order depositional sequences were identified. The sequence, stratigraphic framework and internal makeup of this carbonate platform indicate that these carbonate sloping successions are the type of accretionary carbonate ramp clinoforms that display an ascending ramp‐slope break trajectory. Evolutionary episodes of biogenic communities, climatic change, local tectonic movements, physical processes (e.g. waves and storms) and water depth gradient are major forcing parameters that controlled the carbonate factory and depositional geometry of this Lower Eocene succession; however, carbonate‐producing organisms and eustatic sea‐level fluctuations played the first role, and local tectonic movements in response to tectonic activities of the Zagros Foreland Basin played the second role. As a result, Taleh‐Zang carbonate platforms are rich in diverse assemblages of LBFs without fragments of coral and red algae, which appear to be a consequence of a hothouse state that diminishes the global thermal gradient, weakens pycnoclines and thereby limits the turbulence. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF
38. Seismic geomorphology of the basin floor area in the Northern North Sea: evolution of the Frigg submarine channels and their influence on sediment distribution.
- Author
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Harishidayat, Dicky and Kiswaka, Emily Barnabas
- Subjects
GEOMORPHOLOGY ,SUBMARINES (Ships) ,SUBMARINE fans ,SEDIMENTATION & deposition ,GEOMORPHOLOGICAL mapping ,SEDIMENT control - Abstract
The Frigg Field, located in the Viking Graben of the Northern North Sea, contains complex submarine fan successions. Based on an interpretation of wellbores and seismic datasets with varying quality, previous works reported these successions to be characterized by submarine channels-infills. However, there are limited studies on the evolution history of these channels and their influence on sediment distribution. This study has combined the interpretation of wellbores and 3D seismic datasets to establish the spatial evolution of the submarine channels and their influence on sediment distribution. Petrophysical approaches, core studies and seismic attributes analysis were used to accomplish this work. Results show that the development of the Frigg fan complex was influenced by regional tectonics and sea level fluctuations that triggered sediment gravity flows. These gravity flows followed approximately N–S to NE–SW, E, and NW–SE trending submarine channels. Deposition began with the N–S to NE–SW trending channels that were followed by the eastward flowing submarine channel. The system with three major channels (NE–SW, E, and NW–SE) followed before the N–S to NE–SW trending system re-emerged. The final phase of deposition had the NE–SW, E and NW–SE trending channels. The revealed submarine channels facilitated the deposition of sediment lobes identified based on seismic attribute maps showing the geomorphology of the basin floor area during different periods. The observed geomorphological features show that the submarine channels became dominant during the deposition of the upper Frigg interval and their influence decreased toward the distal basinal areas. This suggests that the mapped submarine channels controlled sediment distribution in the study area. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF
39. Debris‐flow fan development and geomorphic effects in alpine canyons under a changing climate.
- Author
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Hou, Weipeng and Yu, Guo‐An
- Subjects
SUBMARINE fans ,MASS-wasting (Geology) ,DEBRIS avalanches ,ALLUVIAL fans ,REMOTE-sensing images ,CANYONS ,RIVER channels - Abstract
Debris flows in alpine environments are prone to occur in the context of global climate change (i.e., elevated air temperature and higher frequency of strong precipitation events). (Alluvial) Fans often develop at the outlet of tributaries after high‐intensity debris flows. Most debris‐flow fans in alpine canyon areas extend directly to the main river channel and become the forefront of the interaction between the tributary gully and the main river channel. Clarifying the development processes/dynamics, evolutionary mechanisms and driving factors of alluvial fans would shed light on understanding the geomorphological effects and genesis of river valleys in alpine canyon areas. Here, we report the development of debris‐flow fan at the outlet of the Tianmo Gully, a formerly hazard‐free but currently hazard‐active tributary of the Parlung Tsangpo Basin, Southeast Tibet, where debris flows have occurred frequently in the last two decades. Combining remote‐sensing images, DEM data, UAV aerial photography, RTK topographic survey and other fieldwork, the development processes and morphological characteristics of the Tianmo fan under the influence of four large debris flows were analysed. Both primary events (described as episodic debris‐flow events characterized by high‐magnitude mass movement) and secondary events (corresponding to perennial stream flow processes with much lower sediment concentrations) affected the development of the Tianmo fan. Episodic debris‐flow events drastically shape the macroscopic morphology of the fan, with rapid deposition and expansion of the fan body, whereas perennial stream flow processes slowly modulate the fan during the intermittent period between debris flows, mainly with gradual retrogressive incision and lateral migration of flow channel on the fan body. Influenced by the strong sediment‐transport process of debris flows and the alluvial fan development, the planform of the Parlung Tsangpo River evolved from a relatively narrow and single‐thread pattern to an alternating‐wide‐and‐narrow pattern, with a corresponding staircase‐like longitudinal profile. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF
40. Field-Measurement of Surface Wind and Sediment Transport Patterns in a Coastal Dune Environment, Case Study of Cala Tirant (Menorca, Spain).
- Author
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Mir-Gual, Miquel, Pons, Guillem X., Delgado-Fernández, Irene, and Smyth, Thomas A. G.
- Subjects
SAND dunes ,VEGETATION boundaries ,WIND speed ,COASTAL zone management ,SEDIMENT control ,TOPOGRAPHY ,SUBMARINE fans ,SEDIMENT transport - Abstract
Blowouts are integral features of coastal dune fields. Their presence enhances both geomorphological and ecological diversity and enables the movement of sand by wind. Their role as a 'transport corridor' may be, however, considered negative from a coastal management perspective in heavily touristic areas, where the existence of blowouts close to the foredune can enhance the loss of sediment from the beach. This paper investigated the relationship between airflow dynamics and patterns of sediment transport from the beach to established dunes through a trough blowout located on the foredune. Seven three-cup anemometers were used to measure wind speed and direction over a 24 h sampling period at a frequency of 1 min under onshore (parallel to the blowout axis) medium and high wind speeds (max of 17.9 ms
−1 ). To measure sediment transport, a total of 12 vertical sand traps were located at three positions along the length of the deflation basin. The results indicated that small amounts of sediments went into the blowout from the beach and that the highest rates of sediment remobilization took place within the deflation basin. These results highlight two processes: (a) flow channelization induced by the blowout topography caused an increase in wind speed and sediment transport toward the depositional lobe, and (b) the presence of embryo dunes and herbaceous vegetation at the beach–blowout boundary effectively reduced the amount of sediment transport from the beach to the landform. The results confirmed the significant role that vegetation plays in controlling sediment movement and conserving the beach–dune system. [ABSTRACT FROM AUTHOR]- Published
- 2023
- Full Text
- View/download PDF
41. Chloride exchanges between oceanic sediments and seawater: Constraints from chlorine isotopes.
- Author
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Agrinier, Pierre, Gieskes, Joris, Subbarao, Gowtham, Bardoux, Gerard, and Bonifacie, Magali
- Subjects
- *
CHLORINE isotopes , *PORE fluids , *SEAWATER , *SEAWATER composition , *SEDIMENTS , *SUBMARINE fans , *WATER disinfection - Abstract
We investigate the chlorine isotope disequilibrium between chlorides in pore fluids and chlorides in seawater and infer its consequences for chlorine isotope exchange between ocean sediment pore fluids and seawater. We illustrate our methodology with pore fluids from two IODP drilled to depths of ≈1000 m (U1456 and U1457) in the Indus River fan dominated by clay-detritus sediments of the western Himalayas. At these two sites, the concentrations of chloride and sodium ions do not show significant changes with depth and remain very close to those of seawater. As a function of depth, however, chlorides show a progressive decrease in 37Cl (downto −2.5 and −1.4 ‰ respectively), while Ca2+ increases and Mg2+ decreases, as commonly observed in clay-rich oceanic sediments. The rate of the δ37Cl decrease is correlated to the lithology and sedimentation rate. Examining the chlorine budget on these two sites, we conclude that: (1) Most of the chlorine (≥96% of the total Cl) is contained in the pore fluids as chlorides, while the chlorine stored in the other sinks (minerals or organochlorine) is generally very minor (representing <4% of the total Cl). (2) These other sinks are too small to sequester the lost 37Cl-enriched chlorine, which could compensate for the decreased δ37Cl of the chlorides observed in the pore fluids (assuming that the pore fluids originally had chlorides with the chlorine isotopic composition of seawater, δ37Cl = 0 ‰). (3) This lost 37Cl-enriched chlorine has been released from the sediment into the overlying seawater, with fluxes of about 20 mol of chloride per square metre per kiloyear. In order to evaluate the consequence of this unbalanced on a global scale, we extend this chlorine budget analysis to 22 other oceanic sites drilled by IODP in a variety of tectonic environments. It is estimated that worldwide oceanic sediment pore fluids contain 1 × 1020 mol of chloride with mean δ37Cl at −2.3 ± 0.1 ‰ and mean chlorinity at 0.290 ± 0.055 mol Cl- per kg of sediment. Most of the calculated values of the lost 37Cl-enriched chlorine flux are between 3.5 and 45.6 mol of chloride per square metre per kiloyear (mean value of 18.3 mol Cl.m−2.kyr−1), corresponding to a typical chloride exchange time between sediments and seawater of between 5.5 and 71 Myr with a mean value of 14 Myr. Importantly, in oceanic sediments, a relationship between the δ37Cl of the chlorides in their pore fluids and the nature of the detrital minerals (smectite, illite, kaolinite, carbonate, quartz, ...) may exists. This relationship should be modulated by the detrital input from the continents to the oceanic sediments and should therefore be a consequence of the climatic conditions on the continents (mainly rain, temperature). The δ37Cl of the seawater should vary according to these detrital inputs. The expected range of variation would be between −0.3 and +0.3 ‰. This is consistent with the range of δ37Cl in seawater predicted by the study of evaporites deposited since 2 Ga (Eggenkamp et al., 2019). [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF
42. Carbonate submarine fan deposits of the Mississippian Lake Valley Formation, Sacramento Mountains, New Mexico.
- Author
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Bishop, James, Bachtel, Steve, Thompson, Jesse, Miller, Cody, Ryan, Brooks, Sullivan, Morgan, and Jobe, Zane
- Subjects
LAKE sediments ,SUBMARINE fans ,SEDIMENTARY rocks ,SEDIMENTATION & deposition ,PETROLEUM reservoirs ,CARBONATES ,GEOMORPHOLOGY - Abstract
Deep‐water carbonate deposition is relatively poorly understood but an area of vigorous research in academia and industry, where these deposits are a significant component of many unconventional petroleum reservoirs. Recent studies of modern deep‐water carbonates have highlighted the wide variety of depositional processes, sediment types and resultant geomorphology; however, well‐documented outcrops of ancient systems, their rock types and architecture are relatively sparse. The Mississippian Lake Valley Formation provides world‐class exposures of slope‐basinal carbonate deposits. The Tierra Blanca and Doña Ana members comprise submarine fans that are >14 to 20 km in length, >5 km wide, and exposed in strike and dip view, affording a unique opportunity to constrain the architecture, rock types and sedimentary processes. Tierra Blanca and Doña Ana sedimentation was dominated by crinoids shed from an up‐dip platform and supplemented by sediments sourced locally from Waulsortian mounds. Depositional processes include turbidity flows, debris flows and hybrid sediment‐gravity flows. The Tierra Blanca submarine fan thins towards its lateral flanks and distal fringe, where deposits become more mud‐dominated, gravelly grain‐supported flows are less common, and fewer beds have scoured bases. In proximal settings, bed tracing complemented by measured sections allow mapping of stratal surfaces and identification of stories, elements and complexes. The Tierra Blanca evolved from more unconfined to confined deposition. Point‐sourced deposition of the Tierra Blanca fan required a funnelling mechanism, probably due to bathymetry created by Waulsortian mounds or possibly a platform margin re‐entrant. Outcrop exposures illustrate that younger Doña Ana submarine fan deposits onlap onto, and compensationally stack with, the thickest portions of the antecedent Tierra Blanca fan. These outcrops illustrate both similarities and differences between carbonate and siliciclastic gravity flow deposits. Similarities include comparable deposit types, depositional processes and architecture; differences relate to hydrodynamics of carbonate grains, funnelling mechanisms for point‐sourced deposits and sequence stratigraphic forcing. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF
43. Silica‐Bearing Mounds and Strata in the Southwest Melas Basin, Valles Marineris, Mars: Evidence for a Hydrothermal Origin.
- Author
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Rogers, Emma R., Qualizza, Briar R., Heidenreich, Joseph R., Dawson, Henry G., and Horgan, Briony H. N.
- Subjects
MARS (Planet) ,HIGH resolution imaging ,DIGITAL elevation models ,WATERSHEDS ,SUBMARINE fans ,LAKE sediments ,SILICA - Abstract
A small basin on the Southwest (SW) margin of Melas Chasma in Valles Marineris, Mars, hosts a variety of previously identified sedimentary fans and layered strata hypothesized to have been formed by one or more paleolakes. This basin also contains light‐toned layered mounds that have distinct spectral absorption bands consistent with amorphous hydrated silica (e.g., opal). While the general morphology and mineralogy of these features and the basin itself have been previously characterized, the formation mechanism of the hydrated silica features and their temporal relationships with the proposed paleolake remain to be determined. We use Compact Reconnaissance Imaging Spectrometer for Mars visible through short‐wave infrared reflectance spectra (0.35–2.65 μm) and High Resolution Imaging Science Experiment digital terrain models and images to analyze the stratigraphic location and morphology of the opaline silica‐bearing features in the SW Melas basin. We find that the basin hosts fourteen high‐relief "mounds," eight low‐relief "patches," and two extended layers within the sedimentary strata that are light‐toned, fractured, and often exhibit hydrated silica‐like spectral signatures. We hypothesize that the mounds are spring deposits formed by sub‐aerial hydrothermal activity, while the patches and layers correspond to sub‐lacustrine hydrothermal activity. The varied elevations of the mounds and patches indicate at least one fluctuation of lake level in the basin during its history. The combination of contemporaneous hydrothermal and lacustrine activity to form silica‐cemented sedimentary deposits in a nutrient‐rich subaqueous environment would have been conducive to forming and preserving biosignatures in the SW Melas basin. Plain Language Summary: A small basin within Valles Marineris, the largest canyon system on Mars, is thought to have contained one or more lakes in its ancient past. This lake basin also contains signs of opal and other minerals that suggest the interaction of water with the rocks present in the basin. While the different features and minerals of the study site have been previously described, there are still many outstanding questions on how these features were formed and how they relate to the lake activity also seen in the basin. We use various orbital instruments on the Mars Reconnaissance Orbiter to answer these questions. We find that there are two different opal‐bearing features, which we separate into "mounds" and "patches," as well as some opal‐bearing sedimentary layers. The structure and mineralogy of these features indicate that hydrothermal activity was potentially contemporaneous with the ancient lakes, and that the variable features can be attributed to varying lake levels. The combination of lakes and hydrothermal activity may suggest that this basin had the right conditions for life to form and be preserved in this area. Key Points: Hydrated silica is present in a population of light‐toned mounds and patches consistent with subaerial and subaqueous hydrothermal springsNearby lake sediments are also silica/sulfate‐bearing, suggesting that the paleolake and hydrothermal activity were contemporaneousSubaqueous hydrothermal systems in Valles Marineris would have created a highly habitable environment with high biosignature preservation potential [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF
44. Lacustrine sedimentation by powerful storm waves in Gale crater and its implications for a warming episode on Mars.
- Author
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Heydari, Ezat, Schroeder, Jeffrey F., Calef, Fred J., Parker, Timothy J., and Fairén, Alberto G.
- Subjects
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GALE Crater (Mars) , *STORM surges , *MARS rovers , *SEDIMENTATION & deposition , *MARS (Planet) , *IMPACT craters , *SUBMARINE fans - Abstract
This investigation documents that the Rugged Terrain Unit, the Stimson formation, and the Greenheugh sandstone were deposited in a 1200 m-deep lake that formed after the emergence of Mt. Sharp in Gale crater, Mars, nearly 4 billion years ago. In fact, the Curiosity rover traversed on a surface that once was the bottom of this lake and systematically examined the strata that were deposited in its deepest waters on the crater floor to layers that formed along its shoreline on Mt. Sharp. This provided a rare opportunity to document the evolution of one aqueous episode from its inception to its desiccation and to determine the warming mechanism that caused it. Deep water lacustrine siltstones directly overlie conglomerates that were deposited by mega floods on the crater floor. This indicates that the inception phase of the lake was sudden and took place when flood waters poured into the crater. The lake expanded quickly and its shoreline moved up the slope of Mt. Sharp during the lake-level rise phase and deposited a layer of sandstone with large cross beds under the influence of powerful storm waves. The lake-level highstand phase was dominated by strong bottom currents that transported sediments downhill and deposited one of the most distinctive sedimentological features in Gale crater: a layer of sandstone with a 3 km-long field of meter-high subaqueous antidunes (the Washboard) on Mt. Sharp. Bottom current continued downhill and deposited sandstone and siltstone on the foothills of Mt. Sharp and on the crater floor, respectively. The lake-level fall phase caused major erosion of lacustrine strata that resulted in their patchy distribution on Mt. Sharp. Eroded sediments were then transported to deep waters by gravity flows and were re-deposited as conglomerate and sandstone in subaqueous channels and in debris flow fans. The desiccation phase took place in calm waters of the lake. The aqueous episode we investigated was vigorous but short-lived. Its characteristics as determined by our sedimentological study matches those predicted by an asteroid impact. This suggests that the heat generated by an impact transformed Mars into a warm, wet, and turbulent planet. It resulted in planet-wide torrential rain, giant floods on land, powerful storms in the atmosphere, and strong waves in lakes. The absence of age dates prevents the determination of how long the lake existed. Speculative rates of lake-level change suggest that the lake could have lasted for a period ranging from 16 to 240 Ky. [ABSTRACT FROM AUTHOR]
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- 2023
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45. Environmental and Human Impact on Gully Erosion Recorded in Fan Sediments: A Case Study of the Vilnius area, Lithuania.
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Smolska, Ewa, Szwarczewski, Piotr, Česnulevičius, Algimantas, and Mažeika, Jonas
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SEDIMENTS , *EROSION , *RADIOCARBON dating , *SUBMARINE fans , *SEVENTEENTH century , *MIDDLE Ages , *HUMAN activity recognition - Abstract
Geomorphological and sedimentological research carried out in the vicinity of Vilnius (SW Lithuania) aimed to determine the age and stages of development of gullies in relation to climatic conditions and human activity. Two gullies located on the northern slope of the Vilnia river valley were examined in detail. The sedimentological features of the sediments which form fans at the mouths of the gullies were analysed. Three main lithological units were distinguished. On the basis of radiocarbon datings, the beginning of gully erosion was determined to be in the Middle Ages. This process began with intensive settlement in this area. Further stages of a cutting which were distinguished include early modern times and the period from the seventeenth century to the present day. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
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46. Tectonic and climatic controls on carbonate sedimentation in active orogen proximal lakes, Cenozoic Qaidam Basin, northern Tibetan Plateau.
- Author
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Guo, Pei, Wen, Huaguo, Li, Changzhi, and Wei, Yan
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CARBON isotopes , *OXYGEN isotopes , *CLIMATE change , *CENOZOIC Era , *GLOBAL warming , *STRONTIUM isotopes , *SUBMARINE fans , *LAKES , *OROGENIC belts - Abstract
Palustrine‐lacustrine carbonates of the well‐dated Xichagou section (ca. 43 to ca. 13 Ma) next to the active Altyn Tagh Fault (ATF) are investigated in terms of abundance, lithofacies, strontium, carbon and oxygen isotopes, to differentiate tectonic and climatic controls on the evolution of intermontane lakes in the Tibetan Plateau. Volumetrically dominant siliciclastic strata document five depositional stages: mid‐Eocene alluvial fan (onshore), late Eocene fan delta (nearshore), Oligocene semi‐deep lake (offshore), early Miocene braided fluvial delta (nearshore) and mid‐Miocene fluvial plain (onshore). Carbonates are most abundant in the middle three lacustrine stages and contain various lithofacies, including calcretes, microbialites, grainstones and marlstones. Oxygen isotopes show two positive excursions (−1.17‰ and −2.59‰) at the first nearshore and late offshore stages, indicating two relatively saline stages linked to the Eocene and late Oligocene global warming climates. Carbon isotopes show a positive excursion (from −4.0‰ to +2.9‰) at the middle semi‐deep lake stage and meanwhile strontium isotopes of carbonates show a large negative excursion (from 0.7120‰ to 0.7113‰), both in response to the early Oligocene global humid and cooling climate and resultant lake expansion at the Qaidam Basin. Except for this lake expansion event, the first‐order lake transgressing, shallowing and regressing evolution at the Xichagou section were not consistent with Cenozoic global climatic change trends. Instead, the two‐stage strike‐slip faulting of the ATF probably induced the northeastward and eastward migration of basin depocenter and resulted in the lake transgression‐regression at the Xichagou section. The widespread presence and relatively minor variation in oxygen isotopes (from −7.5‰ to −7.0‰) of early Miocene microbialites in the northern Tibetan Plateau suggest a warm climate and a low relief before ca. 15 Ma. [ABSTRACT FROM AUTHOR]
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- 2023
- Full Text
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47. The Modern Nile Delta Continental Shelf, with an Evolving Record of Relict Deposits Displaced and Altered by Sediment Dynamics.
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Frihy, Omran E. and Stanley, Jean-Daniel
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CONTINENTAL shelf , *HEAVY minerals , *SEDIMENTS , *RIVER sediments , *CARBONATE minerals , *SUBMARINE fans , *SAND waves , *EROSION , *COASTS - Abstract
The most extensive coverage of surficial sediment samples collected to date on Egypt's Nile Delta coast and shelf is needed to better define sediment dispersal patterns across this setting's rapidly eroding margin. Changes in time are now induced by River Nile sediment cutoff by dams, sea level rise, marked shelf subsidence, and regional climate changes, which have altered the amounts and components of sediments; these require replacement, along with the implementation of more effective coastal protection measures. Multiple computer-generated offshore maps depict the distributions and proportions of sand, silt, and mud; the mean grain size and standard deviation (sorting); heavy mineral concentrations; and carbonate content. Heavy mineral lobes at the coast and offshore identify former Nile branch sites. Channel lobes extending seaward resulted from their progradational phase and from the delta's altered sedimentation from the early to late Holocene. The progressive deposition and erosion of these fossil fluvial lobes, and of two active Nile channels, selectively removed their quartz and less dense minerals, thus concentrating heavy minerals on the coast and inner shelf. The prolonged dispersal of original sediment effluence from relict and recent Nile tributaries induced variable depositional patterns on the present shelf. These coastal depocenters, along with extensive sand, silt, and mud from shelf sediments, were reworked further seaward and dispersed by bottom currents, thus masking most previous onshore-to-offshore transport patterns. The major surficial features document long-term responses to the diverse dispersal that influenced the shoreline to the outer shelf deposits from the Pleistocene to the present. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
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48. Properties of Conglomerates from the Middle Ordovician Dongchong Formation and Its Response to the Yunan Orogeny in the Yunkai Area, South China.
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Wang, Zhihong, Li, Zhihong, Niu, Zhijun, Li, Chu'an, Chen, Hao, Lin, Xiaoming, Hu, Kun, and Yao, Huazhou
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- *
OROGENY , *CLASTIC rocks , *GEOCHRONOMETRY , *LITHOFACIES , *SUBMARINE fans , *PALEOGEOGRAPHY , *CONGLOMERATE , *PROVENANCE (Geology) - Abstract
The strata in the Shita Mountain, Yunkai region, are predominantly composed of clastic rocks with intercalated limestones. However, the precise stratigraphic age remains uncertain due to the scarcity of fossils. Previously, conglomerate layers in this region were considered indicative of the Yunan Orogeny during the Cambrian–Ordovician transition. However, through the identification of 12 lithofacies types and 5 lithofacies combinations in the conglomerate layers of the Shita Mountain section, it has been confirmed that these layers represent a fan delta depositional environment characterized by debris flow, traction flow, torrent, and rock flow. Based on the presence of brachiopod fossils dating to the Early–Middle Ordovician, we propose a novel two-episode model for the Yunan Orogeny. The first episode corresponds to submarine fan deposition, while the second episode involves tectonic uplift and a short-term sedimentary hiatus. Further analysis of the detrital zircon provenance reveals a strong affinity among the Yunkai area, India, Antarctica, the Lhasa, the Himalayas, Southern Qiangtang, and Western Australia during the Early–Middle Ordovician transition under the Gondwana assemblage background. [ABSTRACT FROM AUTHOR]
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- 2023
- Full Text
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49. Alluvial fan and fan delta facies architecture recording initial marine flooding in the Mio‐Pliocene syn‐rift sequence of the Fish Creek‐Vallecito Basin, southern California.
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Alasad, Rawan, Olariu, Cornel, and Steel, Ronald J.
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ALLUVIAL fans , *FACIES , *SUBMARINE fans , *FLOODS , *WATER depth , *MARINE animals , *MARINE sediments , *SHORELINES , *CHEMOSTRATIGRAPHY - Abstract
The timing and character of the initial marine flooding of extensional basins has implications for their tectonic history. Yet, the recognition of such flooding is difficult along rift basin margins due to the dominance of coarse‐grained systems and the lack of marine fauna. This study conducts detailed facies and stratigraphic analysis of a Mio‐Pliocene alluvial fan and fan‐delta succession in the Fish Creek Vallecito Basin in southern California. Our goal is to characterize the marine flooding surface, determine the paleogeographic position of the shoreline and estimate the magnitude of relative base‐level rise that occurred during the marine incursion associated with the opening of the Gulf of California. Our results show that the flooding of the Elephant Trees alluvial fans is often marked by an abrupt lithologic and facies change from meter‐scale boulder‐rich subaerial debrites (proximal alluvial fan facies association) to centimetre‐scale granule‐rich subaqueous debrites, ripple‐laminated sandstones and mudstones (prodelta facies association). By delineating the zone of transition between the subaerial and subaqueous facies, we place the initial flooding paleo‐shoreline 4 km up the alluvial fan's paleo‐depositional slope. Considering alluvial fan slope gradients between 1° and 5°, this 4 km transgression would require an estimated 70–350 m of water depth during the initial marine incursion. Interfingering of fan‐delta deposits with subaqueous marine and planktonic‐rich evaporites suggests that the basin was below sea‐level after, and perhaps even before, the marine flooding. Subaerial subsea‐level basins exist in Death Valley and the Salton Trough today within similar extensional and transtentional tectonic regimes. This subaerial subsea‐level interpretation might explain the high magnitude and abrupt relative base‐level rise recorded by the facies transitions in the Fish Creek Vallecito Basin. These results suggest that the Fish Creek Vallecito Basin underwent significant extension during its early and nonmarine depositional phase, allowing it to reach subsea‐level elevations. The tectonic history of the Fish Creek Vallecito Basin maybe similar to other extensional basins where rapid subsidence allows the accumulation of nonmarine strata below sea‐level prior to the marine flooding, then restricted and deep marine strata immediately after flooding. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF
50. Sedimentary characteristics and depositional model of hyperpycnites in the gentle slope of a lacustrine rift basin: A case study from the third member of the Eocene Shahejie Formation, Bonan Sag, Bohai Bay Basin, Eastern China.
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Yang, Tian, Cao, Yingchang, Wang, Yanzhong, Cai, Laixing, Liu, Haining, and Jin, Jiehua
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EOCENE Epoch , *TURBIDITY currents , *GRABENS (Geology) , *SEDIMENTATION & deposition , *SEDIMENT transport , *SUBMARINE fans , *SEDIMENTARY basins , *LEVEES , *EROSION - Abstract
Hyperpycnal flow deposits, one of the most important deep‐water gravity‐flow deposits in lacustrine basins, have become the research focus in recent years. However, the sedimentary characteristics and depositional model of hyperpycnal flow deposits in lacustrine basins remain unclear due to the differences of depositional settings between lacustrine and marine environments. Hyperpycnal flow deposits observed in the middle of the third member of the Shahejie Formation (Es3z) in the Bonan Sag, Bohai Bay Basin, Eastern China, provide a rare case study to reveal the characteristics and depositional model in lacustrine basins. For the first time, detailed core analysis, high‐resolution 3D seismic data, petrology and grain size analysis were used to unravel the characteristics and depositional model of hyperpycnal flow deposits in this study. Twelve lithofacies, six bed types and four bedsets (corresponding to feeder channel, distributary channel, levee and lobe) were recognized from detailed facies analysis. Plant fragment, an important identification mark for hyperpycnal flow deposits, can be classified into three types: completely broken plant fragments, partially broken plant fragments and complete leaves. The proximal part of the deposit develops a small amount of scattered and completely broken plant fragments in massive or spaced stratified pebbly sandstone and massive sandstone due to strong erosion of sustained high‐density turbidity current. The medial part of the deposit is dominated by laminated partially broken plant fragments in planar laminated or rippled sandstone due to suspended settling of sustained high‐density turbidity current and quasi‐steady low‐density turbidity current. Layered partially broken plant fragments with some complete leaves are common in the upper part mud rich division of hybrid event bed and laminated siltstone in the distal part of the deposit. The distribution pattern of hyperpycnites is controlled comprehensively by palaeogeomorphy and sediment supply. Palaeogullies determine the provenance direction of hyperpycnal flow. The formation of synsedimentary faults and troughs control the transport routing patterns. Local micro‐palaeogeomorphy and depression areas further restrict the distribution of sand bodies. During the early stage of deposition with insufficient sediment supply, sediments are transported to the deep basin along confined faulted troughs forming elongated sandy bodies. During the late stage of deposition with sufficient sediment supply, sediments are transported to the deep basin without confinement accumulating fan‐shaped sandy bodies. This study offers insight for enhancing the recognition criteria of hyperpycnites, as well as their depositional model in lacustrine basins. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF
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