Search

The mechanisms for the deposition of the Cambrian carbonate sedimentary successions remain controversial. The carbonate‐dominated successions (Stage 3 to Stage 10) are well developed in the North China Craton and they are commonly thought to represent a platform setting because of the flat top. In this study, we propose a new scenarioi, that the Cambrian successions in North China are more likely a carbonate ramp rather than a platform. Detailed sedimentological investigation for the Cambrian rocks in the Yanshan area (Stage 4 to Stage 10) reveals a total of 21 lithofacies which can be grouped into 7 facies associations, including sabkha and mixed tidal flat, shoal, carbonate tidal flat, tidal flat on shoal, protected lagoon, mid‐ramp and outer ramp to shelf basin. Sequence stratigraphy analysis of the Cambrian in the Yanshan area reveals nine third‐order depositional sequences, which shows an overall second‐order transgression. A number of sedimentary characteristics, including the gentle depositional slope, abundant open marine deposits, scattered shoals and microbial mounds, absence of slump or gravity flow sediment, domination of subtidal facies cycles and widespread deposits that formed below the storm wave‐base, indicate that the Cambrian sediments in the Yanshan area were deposited in an intracratonic carbonate ramp depositional system. This intracratonic carbonate ramp includes inner ramp, mid‐ramp, outer ramp and shelf basin facies belts, with the inner ramp exhibiting sub‐facies corresponding to tidal flat, protected lagoon and shoal sub‐facies. Sequence stratigraphy analysis indicates that relative sea‐level changes, corresponding to these nine third‐order sequences, show synchronous with the global sea‐level change across the studied sections. This consistency implies that eustatic sea‐level changes could have been a major factor for the sequence stacking patterns in the Yanshan Area. [ABSTRACT FROM AUTHOR]

The Portfjeld Formation, as originally defined, is the lowermost lithostratigraphic unit of the mainly Lower Palaeozoic Franklinian Basin in southern Peary Land, central North Greenland. The unit crops out semi-continuously from Valdemar Glückstadt Land to Nordenskiöld Fjord but is also recognised locally in northern parts of Peary Land and Wulff Land (western North Greenland). Regionally, it provides a key record of the early, pre-break-up history of the basin. The type succession in southern Peary Land has thus been the focus of recent biostratigraphical, sedimentological and geochemical study. This has demonstrated the composite nature of the unit, a lower interval (c. 190 m thick) of carbonate ramp deposits of Neoproterozoic (late Ediacaran) age being overlain at a karstic unconformity by a shallow marine, mixed carbonate–siliciclastic interval (c. 100 m thick) of probable earliest Cambrian age. Lithostratigraphic revision of this succession is presented here. The Portfjeld Formation throughout North Greenland is elevated to the rank of group, and two new formations are defined in this group in southern Peary Land and immediately adjacent areas: the Ediacaran carbonate-dominated unit is referred to the Slusen Formation, the upper mixed siliciclastic–carbonate unit to the Glaciologelv Formation.

The Dalan Formation is a carbonate sequence of Upper Permian age, which was widely deposited in Persian regions. Dalan Formation has been studied in the underground section of Kish 2, 1 and B2 wells of Kish Island gas field. Petrographic studies and facies analysis led to the identification of 12 microfacies deposited in a single-slope carbonate ramp and in 4 sedimentary sub-environments, including intertidal, lagoon, bariier and open sea areas. The important diagenesis processes that have affected the carbonate rocks of the Dalan Formation include micritization, cementation, anhydritization, compression, dolomitization and dissolution. Diagenesis minerals obtained in these deposits include three types of dolomite with replacement texture, two types of dolomite with cement texture, two types of anhydrite and two groups of calcite cement. Replacement type dolomite generally improves the reservoir quality and anhydrite reduces the reservoir quality by creating a layer by creating an obstacle in the path of hydrocarbon movement. Intercrystalline, interparticle and sheared porosity is the best type of porosity in the whole rock. The reservoir rocks were divided into 4 categories (RRTs-1 to RRTs-4) based on the analysis of the drilling core (SCAL data) and the description of thin sections. The first category is the best reservoir rock for storing and producing hydrocarbons, and the quality reservoir decreases towards the fourth category. According to the available data, the sedimentary environment cannot completely create the necessary conditions for the formation of reservoir-quality rocks, but mainly the final diagenesis along with diapirism determines the reservoir or non-reservoir formation. [ABSTRACT FROM AUTHOR]

As a result of a deep burial depth (> 6.5 km), the depositional history of the Early to Middle Ordovician carbonate platform in the Shuntuoguole Low Uplift (Tarim Basin, NW China) has been difficult to unravel, leading to problems in understanding the controls of the facies distribution, particularly in terms of petroleum exploration. Integrated with geophysical surveys, detailed sedimentological observations document the platform evolution and show that a carbonate ramp system developed in the Shuntuoguole Low Uplift during the Early-Middle Ordovician, with twelve lithofacies types arranged into two facies associations, including peritidal to semi-restricted subtidal and open-marine subtidal facies. Based on the tempo-spatial distribution of lithofacies, seven third-order depositional sequences are identified, each composed of a transgressive lower package and a regressive upper part. Their sequence boundaries are commonly characterised by a transitional zone with no obvious subaerial exposure features. The correlation of relative sea-level (or accommodation space) changes derived from the vertical stacking pattern of facies with the global sea-level curve of Haq and Schutter (2008) and sea-level oscillations of coeval successions worldwide suggests that eustatic sea-level fluctuations were the overriding factor controlling the development and evolution of this carbonate ramp during the Early-Middle Ordovician. Meanwhile, regional or local tectonic subsidence and environmental factors (e.g. palaeoclimate and prevailing wind) also exerted an influence on the depositional processes of the Shuntuoguole Low Uplift over this time interval. [ABSTRACT FROM AUTHOR]

This study focuses on the paleontological content of the middle Eocene (Bartonian) carbonate–siliciclastic sediments of the Capo Mortola Calcarenite Formation from Olivetta San Michele (Liguria, Italy). Along the succession, there are significant paleoecological changes triggered by the variation in neritic input as a consequence of tectonic and climatic instability. Among microfossils, nummulitids prevail, followed by orthophragmines, smaller benthic, and planktonic foraminifera, whereas mollusks and ichnofossils are the most abundant macrofossils. The sudden changes in the benthic communities due to the progressive increase in fluvial input are recorded throughout the sedimentary succession. An increase in water turbidity caused stressful conditions for autotrophic taxa, reducing their size and abundance. In contrast, filter feeders became dominant, suggesting an increase in dissolved and suspended nutrients. Ichnological analysis shows environmental fluctuations controlled by the transport of neritic material offshore, thus confirming the general deepening trend of the studied succession. In the upper part of the succession, we recorded an alternation between gravity flows and marly sediments that are interpreted as short-term alternations between low and intense precipitations. The gravity flows yield taxa such as larger benthic foraminifera (LBF), smaller benthic and planktonic foraminifera, mollusks, and corals. In turn, marls display only a few LBF and abundant smaller benthic and planktonic foraminifera. In these intervals, the increase in planktonic foraminifera also suggests a deepening of the carbonate ramp coinciding with a reduction of light that did not favor the development of LBF. These changes are probably related to the climatic dynamics that occurred in the Bartonian in the western Tethys. [ABSTRACT FROM AUTHOR]

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]

Characterization of pore systems is a key to better understand the heterogeneity of reservoir quality. However, the complicated pore types and pore facies of carbonates in the Hartha Formation of X Oilfield remain poorly understood. In this study, we recognized pore types and explored the impact of depositional environment and diagenetic alterations on pore facies and reservoir heterogeneity. Six types and nine subtypes of pore facies displaying various physical properties and fossils are classified based on the proportion of depositional pores, fabric‐ and non‐fabric‐selective pores. The distribution of pore facies are controlled by the interaction between depositional environment and diagenesis: (i) the depositional environment has an impact on the primary pore types mainly through different lithology and fossils. Micro‐interparticle pores and intraparticle pores of foraminifera are dominated in lagoon, middle ramp and outer ramp, while interparticle pores between grains are dominated in rudist shoal. Rocks deposited in medium‐ to low‐energy shoal contain interparticle pores between grains, micro‐interparticle pores and intraparticle pores of foraminifera. (ii) Major diagenetic events that modify pore types include micritization, fabric‐selective dissolution, cementation, compaction and non‐fabric‐selective dissolution. Micritization facilitates the development of micro‐interparticle pores, while compaction can cause the loss of interparticle pores between grains and micro‐interparticle pores. Cementation destroys not only interparticle pores between grains but also intraparticle pores of foraminifera. Fabric‐ and non‐fabric‐selective dissolution are the main causes for increasing the volume of pores. (iii) The intensity of the diagenetic event is linked to rock composition, rock fabric and palaeotopography that are controlled by depositional environment. Thus, the distribution of pore facies related to the environment is established, which can provide insights for areas lacking cores and adjacent fields with similar settings. [ABSTRACT FROM AUTHOR]

Copyright of Iraqi National Journal of Earth Sciences is the property of Republic of Iraq Ministry of Higher Education & Scientific Research (MOHESR) and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In NW Tunisia, the lateral facies equivalents of the mid-Eocene (Bartonian) “Reineche Limestones” member of the shaley Souar Formation, which constitute a proven reservoir hydrocarbon bearing in Gulf of Gabes, are still poorly known and characterized in NE Tunisia and the Salt Dome zone. Recent sedimentological investigations conducted on: (1) the “Reineche Limestones” member in its type locality in NE Tunisia and (2) three correlative sections, first described herein NW Tunisia, allow improving our knowledge about the Middle Eocene biofacies distribution as well as their depositional environment at a regional scale. Fossil assemblages, rock texture, and fabrics lead to the characterization of eight micro-biofacies (Mf1–Mf8) corresponding to “shoal” inner ramp and middle-to-outer ramp depositional settings. This study demonstrates that the Bartonian carbonates of NE Tunisia bear LBF-dominating assemblages and subordinate planktic and small benthic foraminifera, gastropods, algae, and echinids are indicative of marine ramp context under oligotrophic conditions. However, correlative successions from NW Tunisia are represented by relatively thinner carbonate intervals, including either skeletal limestone facies or phosphorite-rich carbonates. The first facies type, dominated by LBF assemblages, suggests the same depositional conditions as the “Reineche limestones”. The phosphorite-rich carbonate facies is characterized by the presence of peloids, bone fragments, lithic components with subordinate nummulitids, planktic and small benthic foraminifers, diversified open marine fauna, and fine siliciclastic grains, all suggesting oxic–sub-oxic conditions favorable for phosphorite genesis. The Bartonian phosphorite-rich carbonate of northwestern Tunisia represents a good example of phosphatic sediment production and accumulation during the latest episode of the Paleogene phosphatogenesis around the paleohigh structures of the Salt Dome zone in the south-Tethyan margin of Tunisia. [ABSTRACT FROM AUTHOR]

The chronological and paleoenvironmental settings of the Sirenia-bearing strata in the Zagros Basin of Iran were studied in four sections. These sections, located in the Izeh (Asmari Formation), Interior Fars (Gachsaran Formation), and Coastal Fars (Mishan Formation) zones of the Zagros Basin, were investigated for the details of their micropaleontology, biostratigraphy, and microfacies. A total of 113 thin sections were analyzed. Fossils from the Asmari Formation and the Gachsaran Formation were younger (Burdigalian), while those from the Mishan Formation were older (Aquitanian). Thirteen carbonate microfacies were identified in three facies belts; tidal flat, inner ramp, and middle ramp. The tidal flat facies association included mudstone microfacies. Inner ramp facies association consisted of bioclast with porcelaneous tests wackestone, peloid and miliolids packstone to grainstone, bioclast and miliolids wackestone to packstone, benthic foraminifera grainstone, red algae with bryozoan and miliolids wackestone to grainstone, and echinoid and miliolid packstone to grainstone facies. Middle ramp facies association was comprised of red algae and meandrous coral packstone to rudstone, coral floastone, bioclast and bryozoan wackestone to packstone, echinoid and bryozoan packstone, bryozoan and benthic foraminifera wackestone to packstone, and echinoid and bioclast wackestone facies. A shallow carbonate ramp was identified as the habitats of sea cows in the Aquitanian-Burdigalian of the Zagros Basin. [ABSTRACT FROM AUTHOR]

Based on the latest drilling cores, thin sections, and 3D seismic data, types, features, and evolution processes of Cambrian–Ordovician carbonate platforms in the Gucheng and Xiaotang areas are studied, and favorable exploration zones in this area are also discussed. There are two types of carbonate platforms developed in the Cambrian–Ordovician in the Gucheng–Xiaotang area, namely, carbonate ramp and rimmed platforms, and the evolution process of the platform in the Gucheng area is different from that in Xiaotang area. In the Early Cambrian, the study area was a homoclinal carbonate ramp. During the Middle to Late Cambrian, it evolved into a rimmed platform, with 5 phases of mound shoals developed. In the southern area, mound shoals were in progradational arrangement and the third and fourth stages of mound shoals suffering exposure and further developed abundant karst vugs. In the northern area, the mound shoals appeared in a superposition of aggradation–weak progradation, the third, fourth, and fifth stages of mound shoals suffered exposure and dissolution, and the platform slope developed gravity flow deposits. In the Early to Middle Ordovician, the southern area gradually evolved into a distally steepened carbonate ramp, where retrogradational dolomitic shoal developed; while the northern part experienced an evolution process from a weakly rimmed platform to a distally steepened carbonate ramp, and developed two or three stages of retrogradational mound shoals. The high-frequency oscillation of sea level and local exposure and dissolution were beneficial to the formation of mound or shoal reservoirs in platform margin and ramp, and the configuration of these reservoirs with low energy slope–basin facies source rocks could form good oil-gas enrichment zones. The dolomitic shoal in the Ordovician platform ramp is the practical exploration field for increasing reserve and production in the Gucheng area. The mound shoal at the Cambrian rimmed platform margin is the key exploration object in the Xiaotang area. In addition, the Cambrian slope gravity flow deposits can be taken as the favorable exploration fields in the study area.

The Gramame and Maria Farinha formations were deposited in the Paraíba Basin during the Maastrichtian-Danian interval, recording the paleoenvironmental evolution during the opening of the Atlantic Ocean. Despite well-investigated, there is still a need to better understand the bioturbation record and the represented ecological conditions during the deposition of these units. This study investigates the ichnofauna of the carbonate facies recorded in the Itamaracá-1IT-03-PE well in the Paraíba Basin, Brazil, focusing on the paleoenvironmental characteristics that influenced this carbonate ramp. The ichnologic analysis allowed to identify environmental stress based on the limited variation in the diversity and complexity. The identified Palaeophycus-Asterosoma and Asterosoma suites suggest low to moderate energy levels, minimal fluctuations in sedimentation rates, and a relatively stress in salinity that persisted for a long period. Variations in δ13C and δ18O values during the Maastrichtian interval corroborates changes in temperature and bioproductivity, reflecting an increase in freshwater influx during this period, which affected paleoenvironmental conditions and trace fossil diversity mainly due to changes in salinity. • Ichnofossil suites from the carbonate ramps and K-Pg boundary. • The trace fossil suites suggest low to moderate energy environments with stable sedimentation rates. • The suites make it possible to identify environmental stress based on the limited variation in the diversity of ichnofossil. [ABSTRACT FROM AUTHOR]

The deeply buried (>8 km) end-Ediacaran Qigebrak Formation dolostones in the Tarim Basin, China, have significant petroleum potential, but have experienced multi-stage dolomitization that has resulted in the occurrence of diverse dolomite phases. The features and origins of the different dolomite types were merely investigated, which hinders an in-depth understanding of the complex dolomitization processes. This paper presents an integrated petrological, geochemical (C–O–Sr isotope and in situ trace element), fluid inclusion microthermometric, and dolomite U–Pb dating study of outcrop and core samples, to investigate the dolomitization mechanisms, and the nature and evolution of the dolomitizing fluids. The results indicate the occurrence of early dolomitization triggered by seepage–reflux of mesosaline seawater, which retained the primary marine geochemical properties of most of the matrix dolomite. Subsequently, during early diagenesis, fibrous dolomite cement was precipitated from marine porewaters, which have similar geochemical characteristics to the matrix dolomites. Following this, during intermediate-depth burial diagenesis in the Ordovician, fine-to medium-crystalline dolomite cements formed at temperatures of 80–117 °C in association with dissolution–reprecipitation of the matrix and early fibrous cements or diagenetic interactions with clay minerals of the lower Cambrian Yurtus Formation shales. During deep burial diagenesis and dolomitization in the Carboniferous, coarse-crystalline dolomite cements formed at temperatures of 104–138 °C from saline brines enriched in middle rare earth elements. Saddle dolomites, formed by hydrothermal dolomitization (162–184 °C) that was closely related to Permian–Triassic volcanic activity, have positive Eu anomalies and depleted δ18O values, that resulted from the mixing of basinal brines with 87Sr-enriched hydrothermal fluids. This study provides a detailed description of multiple dolomitization events in deep time that affected deeply buried dolostones. • Multi-stage dolomitization occurred from the near-surface to deep burial depths. • The dolomitization history and diagenetic fluid evolution were determined. • Pervasive reflux dolomitization was caused by weak seawater evaporation. [ABSTRACT FROM AUTHOR]

Based on the latest drilling core, thin section, 3D seismic, well logging data as well as exploration results, the sequence stratigraphy and sedimentary microfacies of the Middle—Lower Ordovician carbonates in Gucheng area, and their controlling effects on the development of reservoir were examined by the theories and methods of fine carbonate sedimentology. The results show that the Middle—Lower Ordovician in Gucheng area is a set of typical carbonate ramp deposits, which can be divided into 10 microfacies in 4 subfacies as follows: back ramp, inner shallow ramp, outer shallow ramp, and deep ramp. The back ramp subfacies consists of muddy-dolomitic flat and dolomitic lagoon microfacies; it is dominated by lamellar micrite dolomite tight in lithology. The inner shallow ramp subfacies includes dolomitic shoal and dolomitic flat in shoal top and dolomitic flat between shoals microfacies; it is mainly composed of crystal dolomite with metasomatic residual structure, as well as abundant karst vugs and intercrystalline pores. The crystal dolomite has an average porosity of 4.36%. The outer ramp subfacies includes medium—high and low energy grain shoal and inter-shoal microfacies; it is dominated by sandy limestone, oolitic limestone, and micrite limestone with few pores. The deep ramp subfacies is dominated by low-energy argillaceous deposits, with local presences of storm shoal microfacies. The Lower—Middle Ordovician has six third-order sequences from bottom to top, among which sequence (SQ3) represents the third member of Yingying Formation. The main reservoir has three fourth-order high-frequency sequences. Apparently, the favorable reservoir in the study area is jointly controlled by sedimentary microfacies and high frequency sequence in the carbonate ramp. The former controls the primary pore structure, and the latter controls the intensities of karstification exposure and dolomitization in the penecontemporaneous period. The dolomitic shoals and top dolomitic flats of different stages, superimposed and connected into favorable reservoirs of considerable scale like “platform margin”, are favorable exploration facies in the carbonate ramp.

The mid-Holocene sea-level highstand is a well-known phenomenon in sea-level science, yet the knowledge on the highstand's spatial and temporal distribution remains incomplete. Here we study the southwest coast of the Arabian-Persian Gulf where a mid-Holocene sea-level highstand and subsequent sea-level fall may have occurred due to the Earth crustal response to meltwater load. Sea-level indicators were established using standard facies analysis and error calculations, then constrained through glacio-isostatic adjustment (GIA) modelling and though procedures based on Gaussian Process and exponential decay analysis. This work allowed to identify the highstand at 1.6 ± 0.4 m occurring 6.7–6.0 ka, in excellent agreement with GIA model results. The subsequent shoreline migration followed the geophysical constraint by prograding in line with the sea-level fall until around 3 ka. Then, the strength of the external control weakened and internal processes, in particular sediment binding through microbial activity, started controlling the geometry of the accommodation space. [ABSTRACT FROM AUTHOR]

Silicified ostracods from the Tin Mountain Limestone provide new information regarding the Carboniferous paleontology of the Death Valley Region, California, USA. Acid maceration of marine limestones yielded the following ostracods: Acratia spp., Bairdia quasilecta, Bairdia sp. cf. B. orientalis, Ceratobairdia sp., Kirkbya panamintensis sp. nov., Rectobairdia sp. cf. R. legumen, and Silenites sp. This is the first report of Ceratobairdia and Silenites from the Tin Mountain Limestone. These ostracods occupied a carbonate ramp environment that formed during a major Paleozoic transgression. The ostracods played an important paleoecological role, likely as benthic marine scavengers in a shallow marine biotope along the northern shores of Pangea. [ABSTRACT FROM AUTHOR]

The lithofacies architecture and depositional evolution of the Lower Mississippian (Tournaisian) Pekisko Formation in the subsurface of the Hawk Hills area in northwestern Alberta have been established by integrating detailed core work and well log data. The formation is composed of skeletal-peloidal limestones and argillaceous limestones that were deposited along the northern flank of the Peace River Embayment, a semi-restricted and tectonically active oceanic re-entrant located along the western margin of Laurasia at low paleolatitude. Lithofacies associations recognized in the study area include the outer ramp to slope (LA 1), outer ramp (LA 2) and mid ramp (LA 3), which are stacked into three decameter-scale, deepening-upward and aggradational cycles that are of regional extent and have meter-scale deepening and shallowing-upward trends. A previously unrecognized paleosol horizon at the top of decameter-scale cycle 2, indicating widespread subaerial exposure of the ramp, is interpreted as a sequence boundary that divides the Pekisko and Shunda formations in the study area (and possibly elsewhere in the Peace River Embayment) into two third-order sequences, each consisting of transgressive and highstand systems tracts. The Pekisko Formation in the study area is interpreted to represent a low-energy, temperature-stratified ramp that was mainly homoclinal, but with transient, distal steepening occurring in the southern part of the study area. Ramp deposition was strongly affected by basement-fault reactivation causing differential subsidence and uplift in the Peace River Embayment. The paleogeography and paleoceanographic conditions of the embayment favored upwelling currents and development of a temperature-stratified ramp, as well as the formation of heterozoan carbonate deposits and mid ramp facies of predominantly packstones and wackestones. This depositional scenario is atypical, as most other documented examples of the Pekisko Formation and other Lower Mississippian ramp successions in western North America and western Europe are characterized by moderate to high-energy, mid to inner ramp facies deposited in open-ocean conditions. The results of this study contribute to an improved understanding of the range of depositional settings along the western margin of Laurasia during the Early Mississippian and demonstrate the applicability of the thermocline-stratified ramp model, with some modification, to ramps in semi-restricted embayments and other low energy settings. • Subsurface data analyses establish depositional evolution of a Mississippian ramp. • Heterozoan carbonates dominated low-paleolatitude, temperature-stratified ramp. • Semi-restricted embayment resulted in low-energy ramp facies. • Depositional patterns strongly influenced by basement fault reactivation. • Implications for a low-energy, temperature-stratified ramp model [ABSTRACT FROM AUTHOR]

During the sedimentary period of the Ordovician Yingshan Formation, the carbonate platform of the Gucheng area in the Tarim basin was characterized by a distally steepened ramp. Relative sea-level changes exerted a strong influence on the shoal facie dolomite reservoirs of the 3rd Member of the Ordovician Yingshan Formation (the Ying 3 member), sedimented in the context of a shallow water environment on the carbonate ramp. However, previous studies that lacked high-frequency sea-level changes in the Gucheng area prevent further dolomite reservoir characterization. The current work carries out systematic sampling based on the continuous core from the upper and middle parts of the Ying 3 member in two newly drilled exploration wells (GC17 and GC601) and a series of geochemistry analyses, such as C-O isotope, Sr isotope, and rare earth elements (REE), which helps to investigate the features of the shoal facies dolomite reservoir development against high-frequency sea-level changes. With the help of Fischer plots of these two wells, high-density δ13C data (sample interval is about 0.272 m) were merged to construct a comprehensive curve, contributing to characterizing the high-frequency sea-level changes of the upper and middle parts of the Ying 3 member in the Gucheng area and validating the relationship between the pore-vug vertical distribution and high-frequency sea-level changes. Results revealed that the porosity of dolomite reservoirs increased when the high-frequency sea-level fell and decreased when it rose. Furthermore, the karst surface can be found at the top of the upward-shallowing cycle during the high-frequency sea-level falling; the pore-vug reservoirs are concentrated below the karst exposure surface, and porous spaces are more developed closer to the top of the cycle. The high frequency sea-level curve built in this study can be used as a standard for further research of regional sea-levels in the Gucheng area, and this understanding is highly practical in the prediction of shoal facies carbonate reservoir in carbonate ramp. [ABSTRACT FROM AUTHOR]

The Ediacaran is a period characterized by the diversification of early animals and extensive neritic carbonate deposits. These deposits are still not well understood in terms of facies and carbon isotope composition (δ13C). In this study we focus on the Tamengo Formation, in southwestern Brazil, which constitutes one of the most continuous and well-preserved sedimentary record of the late Ediacaran in South America. We present new detailed lithofacies and stable isotopes data from two representative sections (Corcal and Laginha) and revise the paleoenvironmental and stratigraphic interpretation of the Tamengo Formation. The Corcal section consists of neritic deposits including shallow-water limestone beds, alternated with shale and subordinate marl beds. These facies yield specimens of the Ediacaran fossils Cloudina lucianoi and Corumbella werneri. On the other hand, the Laginha section shows more heterogeneous facies, such as impure carbonates, breccias, marls, and subordinate mudstone beds, as well as no evidence of Corumbella werneri. The stable carbon isotope record is also different between the two sections, despite belonging to the same unit. The Corcal section displays higher and more homogeneous δ13C values, consistent with those of Ediacaran successions worldwide. The Laginha section, instead, displays more variable δ13C values, which suggest the influence of local and post depositional processes. The difference between the two sections was attributed to the different distance from the shore. We propose that the difference is due to topographic variations of the continental platform, which, at the Laginha site, was steeper and controlled by extensional faults. Therefore, the Corcal section is a better reference for the Tamengo Formation, whereas the Laginha is more particular and influenced by local factors. Besides, the lithofacies associations of the Tamengo Formation are like those of the Doushantuo and Dengying formatios, in South China, with no significant biogenic carbonate buildups, and different from those of other important Ediacaran units, such as the Nama Group in Nmibia and the Buah Formation in Oman. Our work highlights the complexity and heterogeneity of Ediacaran carbonate platforms and of their carbon isotopic composition. In addition, we characterize the Corcal section as a possible reference for the Ediacaran in South America.

Oligo-Miocene depositional succession of the Zagros Basin is one of the most significant petroliferous systems in the Middle East. This study deals with facies analysis and paleoenvironmental reconstruction of the shallow-water carbonate successions (Asmari Formation) outcropping in the northwest of Zagros Basin. The Asmari carbonate system has been formed by larger benthic foraminifera (LBF), subordinate red algae, mollusks, bryozoans, echinoids, and corals. According to detailed facies analysis, fifteen depositional facies have been recognized in a carbonate ramp environment whose level changes from the aphotic zone to the upper part of the euphotic zone. The shallower euphotic inner ramp components include imperforate benthic foraminifera and mollusks associated with subordinate components of coral patch reefs. The deeper euphotic zone is characterized by wackestones-packstones, mixed perforate, and imperforate LBF. The higher-energy parts on the platform margin are represented by ooids and robust foraminifera-rich grainstones. The oligophotic zone is represented by coral patch reefs in the proximal parts, larger hyaline foraminifera, and coralline red algal debris in the deeper oligophotic zone. The aphotic zone is characterized by the abundance of planktonic foraminifera, and subordinately by small benthic foraminifera, echinoids and mollusks. Tectonic activities that affect the light conditions and sea-level fluctuations are important factors in the production of skeletons and the spatial distribution of carbonate factories. [ABSTRACT FROM AUTHOR]

The Eocene represents the last greenhouse interval before Present. The maximum warming during the early Eocene was followed by a long‐term cooling trend culminating in the Antarctica glaciation at the base of the Oligocene. Superimposed on this long‐term cooling trend there is a prominent transient warming event known as the middle Eocene climatic optimum (MECO) occurring during the early Bartonian. The carbonate ramp succession cropping out in the Argentina Valley (Maritime Alps) offers new insights on the evolution of shallow water realms during this time interval. This ramp displays two main facies belts, middle and outer ramp. The middle ramp is recorded by larger benthic foraminifer floatstone to rudstone, passing to Solenomeris branches and nodule floatstone to rudstone evolving to branching coralline algal floatstone. The outer ramp is dominated by bioturbated marly wackestone to packstone alternating with larger benthic foraminifer floatstone with a silty matrix. The investigated ramp was affected by continuous dispersion and reworking of the skeletal components as other Tethyan Eocene ramps. During the Eocene, the Alpine foreland was influenced by fine terrigenous input controlling the trophic conditions and promoting seawater stratification and the development of a strong pycnocline, for which many perturbations could propagate as internal waves. The reworking of skeletal components of the ramp has been ascribed to the action of internal waves. The switch of carbonate production from a carbonate factory dominated by larger benthic foraminifera to a factory in which the encrusting foraminifer Solenomeris was the main carbonate producer biota, is indicative of a radical change in palaeoenvironmental conditions affecting the early Bartonian. The acme of Solenomeris often coincided with the crisis of carbonate producers during intervals of an evident deterioration of environmental conditions. In this case the acme is probably related to the adverse conditions linked to the (MECO) warming event. Finally, the drowning of the nummulitic ramp has been caused by light reduction for the photo‐dependent biota due to progressively increasing depth linked to flexural subsidence of the foreland plate, and minor efficiency of the aphotic carbonate factory. [ABSTRACT FROM AUTHOR]

Since their first occurrence in the late Cretaceous, seagrasses have played a major role in carbonate production and sedimentation across shallow‐water and nearshore environments, sustaining a prolific carbonate factory and contributing to sediment accumulation through the combination of baffling and trapping effects. Most reported Palaeogene seagrass occurrences developed in oligo−mesotrophic shallow warm‐water habitats and are characterized by distinct associations of small and larger benthic foraminifers adapted to low terrigenous influence. This study describes a number of seagrass episodes interbedded in the Bartonian (middle Eocene) of San Fausto–Lazkua area (Navarra region, North Spain), within a nearshore to inner‐ramp succession that, in spite of being deposited under general transgressive conditions, was highly influenced by terrigenous supply from the adjacent land. Up to twelve different seagrass bed intervals occur interbedded in a cyclical manner with high‐energy nearshore siliciclastics and inner ramp bioclastic carbonates rich in mesophotic−oligophotic foraminifers and heterozoan biota (red algae, echinoderms, bryozoans). Seagrass deposits exhibit typical unsorted textures, abundant bioturbation and moderate to high terrigenous content, and comprise a characteristic skeletal association of epiphytic foraminifers, red algae and, most particularly, of abundant encrusting acervulinids, commonly with distinct hooked and tubular growth forms. This abundance of suspension‐feeders relative to autotrophs and mixotrophs may be indicative of temperate waters, although the taxonomic diversity of the foraminiferal assemblages in both seagrass and non‐seagrass embedding deposits supports the interpretation of shallow, warm‐water conditions. The studied seagrass deposits provide evidence that high siliciclastic supply and associated nutrient input may determine the occurrence of temperate‐like seagrass deposits in warm‐water settings, analogous to extensive heterozoan carbonate production in modern shallow‐tropical environments. Thus, the identification and correct interpretation of past seagrass‐vegetated environments are crucial for reconstructing palaeoecological conditions in ancient shallow‐marine environments. Therefore, in comparison with carbonate‐dominated environments, the mixed terrigenous−carbonate seagrass deposits are volumetrically less important, presenting a more irregular, patchy distribution, and a skeletal assemblage dominated by heterotrophs, regardless of the water temperature. [ABSTRACT FROM AUTHOR]

One of the strategic ways of the old oil-producing regions is to further prospecting for potentially promising areas for hydrocarbon. One of these exploration areas is the Volga-Ural region. These reservoirs consist of Carboniferous carbonate rocks, which contain high viscous hydrocarbons and are characterized by complex facies architecture and reservoir properties influenced by diagenesis. The high degree of facies variability in the studied area does not allow reliable distribution of potential reservoir rocks not only between different areas but even within the same oil field. Based on textural and compositional features of carbonate facies, 5 main facies associations were identified and characterized with respect to the depositional settings in the Bashkirian basin. The facies associations correspond to: distal middle ramp facies, open marine proximal middle ramp facies, high-energy innershoal facies, inner ramp facies of restricted lagoons, facies of affected by subaerial exposures. From west to east in the study the following trends in facies characterare identified: 1) a decrease open marine middle ramp facies and in the total thickness of the Bashkirian sections; 2) an increase in evidences of sub aerial exposures; 3) a decrease in the proportion of potential reservoir rocks. A general shallowing of the depositional setting was identified in an eastward direction, where potentially promising reservoir facies of shallow high-energy environments were replaced by facies of restricted lagoon and facies affected by subaerial exposures and meteoric diagenesis (palaeosols, dissolution). The applied approach based on detailed carbonate facies analysis allows predicting the distribution of potentially promising cross-sections within the region.

Lithological characteristics and results of the lithofacies analysis of carbonate deposits in the most complete section of the Upper Uk Subformation of the Riphean stratotype (northern part of the Bashkir Anticlinorium, southern Urals) are presented. The subformation is divided into the following members or sequences (from the bottom to top): Yuryuzan, Medved I, Manaysu, and Medved II. The subformation bottom occurs at the base of a huge stromatolite buildup. The Yuryuzan member is characterized by the thin-columnar branching stromatolites Patomella. The Medved I and Medved II members are represented mainly by bioherms consisting of the columnar-branching stromatolites Linella, interbiohermal rocks, and local packets of layered granular limestones found only in the lower member). The Manaysu member comprises layered (mainly cyclic) deposits with abundant molar tooth (MT) structures. The growth of the Yuryuzan member stromatolites occurred most likely in the upper subtidal-peritidal zone within the inner carbonate ramp under the influence of siliciclastic-bearing currents. Stromatolite buildups in Medved I and Medved II members were formed as a part of wide facies belts below the normal wave base (inner/middle ramp boundary) but within the photic zone. Layered limestones in the Medved I member are periodic storm current deposits. Environments of the inner ramp and upper middle ramp dominated during the deposition of Manaysu sediments with signatures of the influence of normal and storm waves. The sequence including the upper part of the Lower Uk Subformation, as well as the Yuryuzan and Medved I members of the Upper Uk Subformation, reflects a progressive deepening of the basin. The later slowdown in the rate of sea level rise (or fall) fostered the change in facies and the formation of the shallow-water Manaysu member. Subsequently, the transgressive trend appeared again, resulting in the formation of Medved II member. The upper boundary of the Uk Formation corresponds to a major break in the geological record associated with global glaciation. [ABSTRACT FROM AUTHOR]

As an important exploration target in the Sichuan Basin, the Lower Triassic Feixianguan Formation has been previously interpreted to be deposited in the trough-platform margin system according to the genetic model of classic lithofacies paleogeography. However, this model does not apply to the northwestern Sichuan Basin. Accordingly, this study proposed a new genetic model that highlighted the carbonate ramp based on the outcrop sections, drilling and logging data, and seismic sections. A large-scale regional regression was found to occur in Sichuan Basin at the end of the Late Permian, leading to the evolution of the original Kaijiang-Liangping Trough into a very shallow tidal flat/lagoon environment at the beginning of the Early Triassic. The sedimentary pattern during the Early Triassic was different from that during the Late Permian. A total of six long-term cycles (LSC1-LSC6) were identified within the Feixianguan Formation. The deposition of LSC1-LSC3 witnessed the filling of the trough to a large extent, and the depositional periods of LSC4 and LSC5 were the main shoal-forming periods. The Feixianguan Formation in the study area was speculated to be deposited in the continuous continental carbonate ramp. With the intensified uplifting of the Longmenshan island chain and the Kangdian ancient land on the northwestern margin of the Upper Yangtze Platform, a large number of terrigenous materials were input into the study area from west to east, leading to the continuous eastward migration of the carbonate facies belt during the deposition of the Fei 1 and Fei 2 Members. Meanwhile, large-area inner-ramp shoal bodies were formed during the deposition of LSC5. It became possible to find a giant gas reservoir belt in the Feixianguan Formation of the northwestern Sichuan Basin and the results of this study provide a new complement to the existing classic trough-platform margin shoal-forming model. [ABSTRACT FROM AUTHOR]

The upper Turonian–Maastrichtian Kawagarh Formation represents a thick sequence of carbonates in the Kalachitta Range, Pakistan and it is the only stratigraphic record of Late Cretaceous sedimentation in northwestern Lesser Himalayas. Global sea-level marks a gradual fall of ∼40 to 50 m during the deposition of the Kawagarh Formation. This study is based on detailed outcrop and petrographic investigations of six stratigraphic sections exposed in Kalachitta Range. Carbonate grains are dominantly composed of pelecypods, oysters, trigonia and plankton distributed in a micritic groundmass. Five microfacies, (1) Planktonic Mudstone, Wackestone and Packstone Microfacies, (2) Pelecypodic Planktonic Mudstone and Wackestone Microfacies, (3) Pelecypodic Wackestone and Packstone Microfacies, (4) Marl Microfacies and (5) Dolostone Microfacies, were identified using distribution of faunal types and matrix. Based on faunal paleoecology, microfacies analysis and sedimentary structures, a shallow open-marine, northward-dipping ramp model has been proposed for the deposition of the Kawagarh Formation beginning with a transgressive cycle, which also corresponds to global sea-level rise, and possibly terminated by uplift owing to initial collision of the Indian Plate with the Kohistan-Ladakh Arc at the end of the Cretaceous. Paleontological and paleoecological evidence is used to develop a shallow, open-marine ramp deposition model for the Kawagarh Formation. The initiation of Kawagarh sedimentation with transgression in the late Turonian synchronise with global sea-level curve. Sedimentation was terminated by initial collision of the Indian Plate with the Kohistan-Ladakh Arc. [ABSTRACT FROM AUTHOR]

Two stratigraphic sections (Arjooieh and Firoozabad) of the Mymand anticline, located in the Interior Fars sub‐basin of the Zagros Mountains, were measured and sampled, in order to document sedimentological characteristics, microfacies types and paleo‐seagrasses indicators of the Oligocene succession (Asmari Fm.). Planktonic and benthic foraminifera and coralline red algae are the principal fossils from these strata. Foraminifera are represented by the following families: Soritidae, Peneroplidae, Austrotrillinidae, Alveolinidae, Planorbulinidae, Discorbidae, Lepidocyclinidae, Amphisteginidae, Rotaliidae, Nummulitidae and Globigerinidae. Nine microfacies types were recognized, namely planktonic foraminifera‐peloidal packstone (MF1), bioclast nummulitid/Nerorotalia/Amphistegina packstone‐grainstone‐rudstone‐floatstone (MF2), Neorotalia‐echinoid coralline red algae packstone‐grainstone (MF3), coral boundstone (MF4), coral/coralline red algae rudstone‐floatstone‐packstone‐grainstone (MF5), diverse imperforate foraminifera bioclast packstone‐grainstone (MF6), peloid wackestone‐packstone‐grainstone (MF7), fenestrated mudstone and microbial mats (MF8) and anhydrite (MF9). MF1 indicates an outer ramp, MFs 2‐4 represent a mid‐ramp and MFs 5–9 are interpreted as inner ramp environment. Paleo‐seagrass indicators consisting of foraminifera, hooked and tabular forms of coralline red algae and corals. They were identified in MFs 5 and 6, reflecting the presence of vegetated environments within the mid/inner ramp setting. The Mymand anticline was dominated by the outer ramp environment at the start of the Rupelian. Mid to inner ramp environments prevailed during the Rupelian. The Chattian corresponds to the spread of the inner ramp setting over the Mymand anticline. [ABSTRACT FROM AUTHOR]

Detailed microfacies analysis and sequence stratigraphic architecture of the Bajocian- mid-Callovian Samana Suk Formation exposed in the Hazara Basin, Lesser Himalaya of Pakistan, were examined. The formation reveals deposition on a carbonate ramp under variable low to high energy environments, such as carbonate mud-flats, lagoon, barrier/shoals, and open-marine setting. The stacking pattern of facies association depicts the change in depositional style in response to sea-level fluctuations. Vertical distribution of recognized facies allows dividing the Bajocian- mid-Callovian strata into one major sequence of second-order hierarchy with superimposed four cycles of third-order genetic sequences (DS1-DS4), bounded above and below by type-one unconformity. The succession comprised of the Bajocian- early Callovian Transgressive System Tract (TST) and early-mid Callovian Highstand System Tract (HST) differentiated by maximum flooding surface. It is reasonable to compare at least Bajocian- early Callovian retrogradational cycle (TST) with long-term global eustatic reconstruction suggesting eustatic change as a primary control on regional shoreline movement. Later, the sea level tends to drop toward the middle of Callovian, forming a prograding Highstand System Tract (HST). These HST deposits record a significant retreat of shoreline toward the termination of mid-Callovian, which ultimately led to regional uniformity above the Samana Suk Formation. This cycle indicates deflection from global sea-level signatures ascribes to regional tectonics in the region. For the first time, this study signifies the importance of regional tectonics overwhelming the global eustatic record of middle Jurassic carbonates in the region. [ABSTRACT FROM AUTHOR]

Nummulite facies are known to be a good indicator of Eocene shallow-water paleoenvironments. Nummulitic limestones are widespread in the Lower Eocene of Armenia—the Tethys/northern Peri-Tethys transition zone, but they are studied insufficiently so far. The objective of this work was an integrated study of Lower Eocene deposits in the typical Urtsadzor section (Ararat region, Armenia): detailization of the stratigraphic subdivision based on larger benthic foraminifers (LBF); restoration of sedimentation settings based on the facies analysis and tectonic conditions of the basin origin, and evolution in the Early–Middle Eocene by studying the rock fracture system and formational analysis. For the first time, the Ypresian shallow benthic zones SBZ 9-10 and SBZ 10-11 of the Tethyan Chronostratigraphic Scale were identified in Kotutz and Sevan formations—an important contribution to the development of a modern stratigraphic chart of Armenia. Restoration of depositional settings based on the microfacies analysis was accomplished for Lower Eocene carbonate rocks of Armenia for the first time. Nine microfacies were determined and interpreted in the Ypresian part of the Urtsadzor section. Evolution of paleobiocoenoses represented mainly by nummulites, orthophragmines, and red algae was traced through the section. A transgressive succession of microfacies types was revealed from the littoral to lower–middle parts of the middle ramp. Comparison of the section with the adjacent Shagap and Landzhar sections allowed us to estimate the facies variability of rocks and the main direction of transgressional expansion. Ypresian LBF in paleobiocoenoses of southern Armenia are similar to the Peri-Tethyan varieties at the generic and specific level, and distinguished from the Tethyan biocoenoses by the absence of porcelaneous foraminifers (alveolinids and soritids). The South Armenian Ypresian paleobiota is distinguished from the assemblages in northern Armenia and northern Peri-Tethys by the abundance of red algae remnants. Wide Late Ypresian transgression resulted in the proliferation of LBF in the shallow oligotrophic basins, and their hydrological differences provoked the diversification of biocoenoses. The study of jointing systems in nummulitic limestones healed with aluminous products of karstification demonstrated that the jointing was formed at the Early/Middle Eocene transition due to the northeastern to sublatitudinal tension during uplift of the southern rift shoulder of the emerging Middle Eocene Shirak–Sevan–Megri rift. Rifting was preceded by the Early Eocene attenuation of tectonic activity and expansion of a wide carbonate sedimentation basin with development features typical of pre-rift basins. [ABSTRACT FROM AUTHOR]

The Aptian carbonate Dariyan Formation (Shu'aiba equivalent) is one of the most important oil reservoirs in the Zagros Basin and the Persian Gulf (South and Southwest of Iran). The Dariyan Formation with mainly carbonate facies overlies the Gadvan (Hawar) Formation and is overlain by the Kazhdumi (Nahr Umr) Formation. Despite the reservoir importance of the Dariyan Formation, it seems that not much detailed work has been done about the facies characteristics, diagenetic processes and reservoir quality of this formation in the east of the Persian Gulf Basin of Iran. By using the new and valuable data obtained from the core, this study focused on the identification of microfacies, diagenetic processes, determining the sedimentary environment, biostratigraphy and reservoir characterization of this formation in one of the wells of Reshadat oilfield in the southeast of the Persian Gulf. The results obtained from microfacies study, led to the identification of seven carbonate and one mixed carbonate-clastic microfacies that were deposited in four facies belts including the inner ramp, middle ramp, outer ramp, and deep basin. Uniform facies changes and the absence of reef-forming organisms such as rudists and its replacement by Lithocodium algae with the ability to form patch reefs indicate the homoclinal carbonate ramp environment. The study of benthic and planktonic foraminifera, as well as algae, led to the identification of five biozones, which indicated the Aptian age for this formation. Based on petrographic study, the Dariyan Formation is affected by diagenetic processes such as Cementation, dissolution, mechanical and chemical compaction, dolomitization, bioturbation and pyritization. Correspondence of porosity and permeability data of the cores and petrophysical logs indicates that the reservoir quality of the Dariyan Formation in the studied field was affected by facies, and diagenesis factors. Reservoir characterization has revealed that the high quality zone is located in the intervals containing Lithocodium algae. In the Lithocodium -bearing facies (boundstone-floatstone) the presence of many interconnected pores and cavities in the skeletal network structure of Lithocodium / Bacinella algae have created a suitable reservoir quality and a permeable facies. [Display omitted] • Based on core data, geological and reservoir studies were carried out on the Dariyan Formation (Aptian) in southeast of the Persian Gulf. • Sedimetological studies of the Dariyan Formation revealed the eight microfacies belong to the homoclinal ramp environment. • By combining core studies and petrophysical logs, intervals with suitable reservoir quality were identified. • Lithocodium -bearing intervals were evaluated as the best reservoir zones. [ABSTRACT FROM AUTHOR]

Facies analysis and paleoenvironmental reconstruction of the Burdigalian to Langhian Asmari Formation, outcropping in the Khorram Abad Anticline, in the north-west of the Zagros Basin allow us to interpret the carbonate ramp history during the Early–Middle Miocene time span. The biota producing sediments in this system are dominated by the rhodalgal and echinofor skeletal-grain associations. Based on the facies distribution and paleoecology of the biotic content, the ramp is divided into three parts: inner, middle and outer ramp. The inner ramp is further subdivided into an inner zone where the main components include imperforate benthic foraminifera and molluscs associated with subordinate coral patch reefs, and an outer shallow-water zone dominated by wackestones–packstones with benthic foraminifera and coralline red algae facies. A shoal belt dominated by coralline red algae, benthic foraminifera, and coral fragments occurs in a distal inner ramp position. The middle ramp is characterized by rhodoliths, crustose red algal wackestone and thinly branching corals associated with encrusting foraminifera in proximal parts, and coralline red algal with larger benthic foraminifera and bryozoan colonies in the deeper oligophotic zone. The outer ramp includes proximal parts dominated by bryozoans, echinoids and molluscs with subordinate planktonic foraminifera and the distal part characterized by planktonic foraminifera and deep epifauna and infauna benthic foraminifera. Changes in trophic conditions and sea-level fluctuations, which are related to tectonic activities, seem to be the important factors in skeletal production and the spatial distribution of carbonate factories.

A metre-scale thick siltstone–sandstone lobe is described within the Dapingian outer ramp argillaceous limestone facies of the Baltoscandian palaeobasin. This bed is referred to as the Volkhov Oil Collector in previous studies due to its hydrocarbon accumulation potential. It formed on the palaeoslope of the regional Jelgava Depression, which represents an elongated axial region of the deepest part of the Ordovician Baltoscandian sedimentary basin. Sedimentological and petrological analysis of this siliciclastic bed in core sections shows that it was deposited as a result of a single event of turbidite flow. The internal structure of the turbidite bed follows the classical Bouma divisions of the turbidite sequence model. The triggers of this single siliciclastic turbidite bed within a tectonically inactive shallow carbonate basin are analysed. It is concluded that a rare tsunami might have eroded and transported sediments in suspension from land to shallow sea. Suspension fallout would have evolved into a density flow and later into a turbidity current that travelled into the deeper parts of the basin, depositing siliciclastic material at the slope of the Jelgava Depression. The occurrence of the Volkhov Oil Collector turbidite bed on the tectonically relatively stable and flat-bottomed Baltoscandian palaeobasin suggests that turbidite events can take place in rare cases also in epicontinental environments.

During the sedimentary period of the Ordovician Yingshan Formation, the carbonate platform of the Gucheng area in the Tarim basin was characterized by a distally steepened ramp. Relative sea-level changes exerted a strong influence on the shoal facie dolomite reservoirs of the 3rd Member of the Ordovician Yingshan Formation (the Ying 3 member), sedimented in the context of a shallow water environment on the carbonate ramp. However, previous studies that lacked high-frequency sea-level changes in the Gucheng area prevent further dolomite reservoir characterization. The current work carries out systematic sampling based on the continuous core from the upper and middle parts of the Ying 3 member in two newly drilled exploration wells (GC17 and GC601) and a series of geochemistry analyses, such as C-O isotope, Sr isotope, and rare earth elements (REE), which helps to investigate the features of the shoal facies dolomite reservoir development against high-frequency sea-level changes. With the help of Fischer plots of these two wells, high-density δ13C data (sample interval is about 0.272 m) were merged to construct a comprehensive curve, contributing to characterizing the high-frequency sea-level changes of the upper and middle parts of the Ying 3 member in the Gucheng area and validating the relationship between the pore-vug vertical distribution and high-frequency sea-level changes. Results revealed that the porosity of dolomite reservoirs increased when the high-frequency sea-level fell and decreased when it rose. Furthermore, the karst surface can be found at the top of the upward-shallowing cycle during the high-frequency sea-level falling; the pore-vug reservoirs are concentrated below the karst exposure surface, and porous spaces are more developed closer to the top of the cycle. The high frequency sea-level curve built in this study can be used as a standard for further research of regional sea-levels in the Gucheng area, and this understanding is highly practical in the prediction of shoal facies carbonate reservoir in carbonate ramp.

This contribution reports an ichnological study of the well-exposed strata belonging to the Chefar El Ahmar Formation, located in the Saoura Valley (Ougarta Range, Northwestern Algerian Sahara). This unit consists mainly of irregularly alternating shale and limestone with some intercalated sandstone. The data reflect hemipelagic to pelagic carbonate ramp character, episodically interrupted by internal waves in an extra-tempestite context. The ichnological analysis suggests a low bioturbation intensity. Eight ichnotaxa documented represent the Cruziana ichnofacies: Alcyonidiopsis, ?Balanoglossites, Chondrites, Nereites missouriensis, Neonereites biserialis, Palaeophycus, Thalassinoides and Zoophycos, distributed in an irregularly manner dominated by a Zoophycos-Chondrites assemblage in the lower part (units "a", "b", "c" and bottom part of unit "d"), a Zoophycos-Chondrites-Alcyonidiopsis-?Balanoglossites-Nereites missouriensis-Thalassinoides assemblage in the middle part (unit "d" and lower part of unit "e") and a Chondrites-Alcyonidiopsis-Nereites missouriensis-Neonereites biserialis-Palaeophycus assemblage in the upper part (major part of unit "e" and unit "g"). The distribution of these trace fossils frame the major bioevents represented in this section. They are more frequent above and below the bioevent levels while rare to absent in the crisis beds themselves. The control was evidently provided by palaeoenvironmental conditions (including bathymetry, oxygenation and nutrient supply), as a result of the general deepening of the northern Gondwana carbonate platform from the late Emsian to the early Frasnian, due to the major transgression during the Middle Devonian. [ABSTRACT FROM AUTHOR]

The characterization and comprehension of buried reservoirs receive remarkable benefits from detailed studies of outcropping analogues which help to define the architecture of the buried sedimentary units and their petrophysical features. In particular, modern 3D techniques of geological data analysis can better constrain the geological mapping process and reveal the geometry of the sedimentary units with complex lateral and vertical relationships. By means of the 3D Move software, we define the sedimentological and stratigraphical relationships between lithostratigraphic units of the Bolognano Formation, outcropping in the northernmost sector of the Majella Mountain (Central Apennines, Italy). The study area belongs to the Apulian carbonate platform and the Majella Mountain represents the northward outcropping portion of its margin. The sedimentary succession of the Majella Mountain consists of Upper Jurassic to upper Miocene limestone and dolostone deposits. In the investigated area, outcropping deposits mainly belong to the Oligo--Miocene Bolognano Formation characterized by five lithofacies associations and representing a carbonate ramp developed in a warm subtropical depositional environment within the oligophotic to aphotic zone. The Bolognano Fm. represents, due to its specific hydraulic properties (e.g. porosity and permeability), an outcropping analogue of worldwide common reservoirs (i.e. porous calcarenite deposits of a carbonate ramp formed by benthic foraminifera such as lepidocyclinids, nummulitids, red algae, corals). In the study area, several geological units of the Bolognano Fm. are characterized by abundant hydrocarbon (bitumen) occurrences infilled within the high-porosity of the cross-bedded calcarenites ascribed to the Chattian and Burdigalian interval. The geological field mapping of the area and the visualization of the geological data in a 3D environment show that the unit formed by mid-ramp calcarenites (Lepidocyclina calcarenites 2 unit, Chattian--Burdigalian) increases in thickness towards the NE (basinward) direction as a consequence of sediment shedding from inner ramp. Our study illustrates how the geological mapping and the visualization and analysis of geological data in a 3D environment of the northernmost sector of the Majella Mountain confirms depositional models of the Bolognano Formation and represents a valid tool for the characterization of the lateral stratigraphic relationships within this formation, and hence of its potential hydrocarbon occurrences. [ABSTRACT FROM AUTHOR]

The Late Jurassic is a peak time of diversification of reefs with corals, stromatoporoids, calcareous and siliceous sponges, and microbialites during the Phanerozoic. This study focuses on the Callovian–Kimmeridgian carbonate succession of eastern Sardinia, deposited at tropical latitudes on the European passive margin that recorded from the late Oxfordian the evolution from a coated grain-dominated to a reef-bearing carbonate ramp. The coated grain-dominated carbonate ramp (phase 1; Callovian–middle Oxfordian) includes inner ramp ooidal shoals and peloidal packstone in the middle-to-outer ramp. The overlying reef-bearing ramp (phase 2; late Oxfordian–late Kimmeridgian) is characterized by three types (1–3) of bioconstructions. The distribution of these build-ups along the middle-to-outer ramp depositional profile reflects bathymetric parameters, related to the interplay of water energy and light penetration. Type 1 build-ups developed in the proximal middle ramp and consist of 45 m thick, 100 m wide, coral-stromatoporoid boundstone associated with coral–stromatoporoid rudstone–grainstone. Type 2 build-ups, colonizing deeper environments in the middle ramp, are lens-shaped coral–calcareous sponge–diceratid boundstone including stromatoporoids and chaetetid sponges, 1–2 m thick and 3–4 m wide, associated with bioclastic packstone–grainstone. Type 3 lens-shaped calcareous and siliceous sponge–coral–microbialite boundstone build-ups (1 m thick and a few metres wide) formed in lower energy, distal middle-to-outer ramp settings. The evolution of the eastern Sardinian carbonate ramp reflects the Oxfordian–Kimmeridgian spread of the coral–sponge-microbialite reefs along the Tethyan European passive margin. [ABSTRACT FROM AUTHOR]

Global controls on the oceanographic influences on the nature of carbonate factories are broadly understood. The details of the influences of changes in temperature and nutrients across individual carbonate shelves are less well constrained, however. This study explores spatial and temporal variations in chemical oceanography along and across the Yucatan Shelf, a modern carbonate ramp, and how these factors relate to variable bottom character, sediment and sediment geochemistry. In‐situ sensors and remote‐sensing data indicate the sporadic presence of cool, upwelled water with low dissolved oxygen and elevated Chlorophyll‐a. This current‐driven, westward flow of upwelled water is most evident in a zone just offshore of the northern peninsular shoreline, but its influence wanes ca 75 km offshore and as the shore turns southward. The impacts of this water mass include a transitional photozoan–heterozoan assemblage with biosiliceous components, relict grains and common thin Holocene sediment accumulations nearshore; further offshore are coralgal reefs and expansive sand plains. Geochemical proxies of bulk sediment, including high δ18O and elevated HREE/LREE (heavy rare‐earth element/light rare‐earth element) ratios near, and downcurrent of, the upwelling source, are interpreted to represent the signal of nearshore, westward movement of the cool and nutrient‐rich, upwelled water. Collectively, these data emphasize how local processes such as upwelling and longshore transport can variably influence carbonate sediment accumulations and their geochemical signatures, both along and across individual shelves. These data and insights provide an analogue for the influences of spatial variability of water masses in the geological record, and for accurate interpretation of stratigraphic changes of sedimentary and geochemical proxy data in carbonate archives. [ABSTRACT FROM AUTHOR]

The present study investigates the microfacies and source rock potential of the Eocene Nammal Formation in the Nammal Gorge Section, western Salt Range, Pakistan. The Nammal Formation consists of light grey to creamy color limestones, olive green to grey shales and light grey marls. Twelve rock samples of limestone were collected for microfacies analysis and nine samples of limestone and shale were analyzed for determination of Total Organic Carbon (TOC) content and source rock potential of the Nammal Formation. Thin section studies of rock samples revealed four microfacies, i.e., mudstones, wackestones, wackestones to packstones and packstones. Microfacies analysis showed that intraclast, planktons and some small benthic foraminifera, pelecypods and opperculina are present in the Nammal Formation. The type of microfacies and abundance of planktons suggest deposition on a carbonate ramp platform within outer neritic to distal shelf environment in the study area. The Nammal Formation presents a coarsening upwards trend and rise in sea level during its deposition. The average TOC value of nine samples of shale is 0.0812 which shows very little organic matter and poor source rock potential of the Nammal Formation.

The Fort Munro Formation is 200-m-thick mixed carbonate–siliciclastic succession of Late Cretaceous (Campanian) age exposed at the Rakhi Nala Section, Sulaiman Range, Lower Indus Basin, Pakistan. The Fort Munro Formation is representing thin- to thick-bedded limestone with interbedded marls, shale and sandstone. Detailed microfacies analysis revealed the recognition of 15 microfacies types (11 carbonate and 4 sandstone). These facies were deposited on both inner and middle ramp platform. The inner ramp sediments are more widespread than the corresponding middle ramp including open-marine, skeletal shoals, semi-restricted, carbonate sand shoals and banks and lagoon depositional environments. The uppermost part of the Fort Munro Formation has received sufficient amount of siliciclasts, thereby producing a sandstone texture. These siliciclasts indicate the tectonic uplift, which thereby increases the source area rejuvenation. Therefore, a mixed carbonate–siliciclastic, moderately storm-dominated homoclinal ramp depositional environment is suggested for the Fort Munro Formation. [ABSTRACT FROM AUTHOR]

Appraisal of the volumes of fluid in a carbonate reservoir will typically require a reliable predictive model. This can be achieved by combining studies of well‐exposed carbonate successions with 3D models in order to obtain reliable quantitative data. In this paper, we present a detailed outcrop study and a 3D porosity model of a well‐exposed Oligocene carbonate ramp (Salento Peninsula, southern Italy) to investigate the nature of small‐scale facies and porosity heterogeneities. Porosity and permeability in the ramp carbonates appear to be controlled by the original mineralogy of skeletal components and by depositional textures. The aims of the study were therefore to identify the factors controlling porosity development in an undeformed carbonate ramp; to model the scale‐dependent heterogeneities characteristic of the facies associations; and finally to produce a 3D model of the porosity distribution. The upper Chattian Porto Badisco Calcarenite which crops out along the coast of the Salento Peninsula consists of six lithofacies ranging from inner ramp deposits to fine‐grained outer ramp calcarenites. The lithofacies are: inner ramp small benthic foraminiferal wackestone‐packstones associated with (i) sea grass meadows (SG) and (ii) coral mounds (CM) consisting of coral bioconstructions with a floatstone/packstone matrix; middle ramp (iii) large rotaliid packstones to wackestone‐packstones (LR), (iv) rhodolith floatstone‐rudstones (RF), and (v) large lepidocyclinid packstones (LL); and (vi) outer ramp fine‐grained bioclastic calcarenites (FC). A total of 38 samples collected from six stratigraphic sections (A, B, D, J, E, LO), measured in the Porto Badisco ravine, were investigated to discriminate the types of porosity. Effective and total porosity was measured using a helium pycnometer. The 3D porosity modelling was performed using PETREL™ 2016 software (Schlumberger). Four main types of porosity were recognized in the carbonates: interparticle, intraparticle, vuggy and mouldic. Primary porosity (inter‐ and intraparticle) is limited to middle ramp lithofacies (LL and LR) and outer ramp lithofacies (FC), whereas secondary porosity (vuggy and mouldic) was present in both inner ramp lithofacies (CM and SG) and middle ramp red algal lithofacies (RF). In the Porto Badisco carbonates, stratigraphic complexity and the distribution of primary porosity are controlled by lateral and vertical variations in depositional facies. Significant secondary porosity was produced by the dissolution of aragonitic and high‐magnesium calcite components, which are dominant in the sea‐grass and coral mound facies of the inner ramp and in the rhodolith floatstone‐rudstones of the middle ramp. 3D models were developed for both effective and total porosity distribution. The porosity models show a clear correlation with facies heterogeneities. However of the two models, the effective porosity model shows the best correlation with the 3D facies model, and shows a general increase in effective porosity basinwards in the middle ramp facies. [ABSTRACT FROM AUTHOR]

Barrier islands are important landforms in many coastal systems around the globe. Studies of modern barrier island systems are mostly limited to those of siliciclastic realms, where the islands are recognized as mobile features that form on transgressive coastlines and migrate landward as sea‐level rises. Barrier islands of the 'Great Pearl Bank' along the United Arab Emirates coast are the best‐known carbonate examples. These Holocene islands, however, are interpreted to be anchored by older deposits and immobile. The mid‐Holocene to late‐Holocene depositional system at Al Ruwais, northern Qatar, provides an example of a mobile carbonate barrier island system, perhaps more similar to siliciclastic equivalents. Sedimentological and petrographic analyses, as well as 14C‐dating of shells and biogenic remains from vibracored sediments and surface deposits, show that after 7000 years ago a barrier system with a narrow back‐barrier lagoon formed along what is now an exposed coastal zone, while, contemporaneously, a laterally‐extensive coral reef was forming immediately offshore. After 1400 years ago the barrier system was forced to step ca 3 km seaward in response to a sea‐level fall of less than 2 m, where it re‐established itself directly on the mid‐Holocene reef. Since that time, the barrier has retreated landward as much as 1000 m to its current position, exposing previously‐deposited back‐barrier lagoonal sediment at the open‐coast shoreline. In modern neritic warm‐water carbonate settings mobile barrier island systems are rare. Their construction and migration may be inhibited by reef formation, early cementation, and the relative inefficiency of sourcing beach sediments from open carbonate shelves. Carbonate barrier island systems likely formed more commonly during geological periods when ramps and unrimmed shelves predominated and in calcite seas, when meteoric cementation was minimized as a result of initial calcitic allochem mineralogy. As with their siliciclastic analogues, however, recognition of the influence of these transient landforms in the rock record is challenging. [ABSTRACT FROM AUTHOR]

A major global marine transgression occurred during the Callovian to Early Kimmeridgian, which was interrupted locally by a hiatus during the Late Callovian to Early Oxfordian. The transgression may have been a major driver for extensive coral buildup development in the Oxfordian. The depositional hiatus may be related to a combination of eustasy, local tectonic activity and hinterland movements, highlighting the potential influence of tectonism on sedimentary evolution in sedimentary basins. Whilst a regional Late Callovian-Early Oxfordian hiatus has been recorded extensively in the Tethys realm, this study has improved the biostratigraphic and sedimentary record from Morocco, and for the first time documents the Late Callovian-Early Oxfordian depositional hiatus in the Atlantic realm. Detailed sedimentary facies analysis of Callovian to Oxfordian carbonates and siliciclastics (Ouanamane Formation) demonstrates a major transgression from continental and coastal sediments, through oolitic mid-inner ramp deposits, brachiopod-rich middle ramp deposits, and ultimately to outer ramp marls, sharply overlain by Middle Oxfordian coral buildups across the basin. Repeated hard- and firmgrounds and bioturbated bed tops highlight transgressive surfaces traceable basinwide, which suggests low sedimentation rates in the upper Ouanamane Formation. Localized siliciclastic input is evidence for episodes of erosion in the same interval. Collection of new fossil specimens (ammonites, brachiopods, echinoderms, foraminifera) and revision of existing fossil material suggest this interval corresponds to a hiatus or condensed section in the Callovian-Oxfordian transition. The uppermost part of the Ouanamane Formation is of early Middle Oxfordian age and is directly overlain by Middle Oxfordian coral buildups. Onset of buildup construction is considered synchronous based on the new biostratigraphic data. Observations in Moroco compare with the sedimentary evolution around the Tethys, and in particular with the Arabian Plate. The Callovian-Oxfordian depositional hiatus corresponds to eustatic sea level changes, which were possibly driven by global cooling, and was likely overprinted by local tectonics. • Revised biostratigraphy of the Callovian-Oxfordian succession on the Atlantic margin of Morocco. • Upper Callovian-Lower Oxfordian condensed section or hiatus, consistent with regression recognized in the Tethyan realm. • Overlying Oxfordian coral buildups have a basal Middle Oxfordian age. [ABSTRACT FROM AUTHOR]