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The Neoproterozoic Panium Sandstone Formation of the Kurnool Group (India) offers a unique scope for understanding regressive depositional history in a Neoproterozoic clastic shoreline. It is divided into two 'Systems Tracts' namely forced regression and lowstand. Process-based facies and paleo-environmental analysis identified twelve different facies types; grouped under four facies associations (FA I–IV) belonging to both continental and shallow-marine domains viz. distal braided fluvial, swash bar-foreshore runnel, upper shoreface bar-trough, and lower shoreface bar-interbar. Whereas the fluvial deposit (FA I), sharply and erosionally overlying the argillaceous shelf succession of the Owk shelf shale, represents the product of forced regression, the wave-dominated shallow marine deposits (FA II, III and IV) record the depositional history of lowstand in the coastline. A basin ward transition from unconformity (base of FA I) to correlative conformity (base of shallow marine deposits FA II, III, and IV) is documented. The shoreline had a north-northwest to south-southeast alignment and the north-eastward flowing fluvial system met the shoreline at a high angle. Detrital zircon geochronology from the Panium fluvial sandstone allowed documentation of Paleoproterozoic (~2050 Ma–1800 Ma) and Mesoproterozoic (~1500 Ma to ~1200 Ma) age clusters, in addition to earlier documented age clusters from the Banganapalle alluvial sandstone present at the basal part of Kurnool succession. The new age data suggest an addition of new provenances and in turn, tectonic intervention behind the regression in the Kurnool coastline that triggered Panium deposition. Further, the Paleoproterozoic age cluster, obtained from the Panium fluvial deposit, helped in the justification of solitary zircon grain occurrences within the Owk Shale, as described in earlier studies. [Display omitted] • Neoproterozoic Panium sandstone bears a regressive depositional history. • Panium sandstone was deposited during forced regression and lowstand system tracts. • U Pb age data suggest the addition of new provenance in course of Panium deposition. • The provenance was shifted from NNW to SSW during Panium deposition. • Tectonic perturbances reversed local basin slope and introduced addition of new provenance. [ABSTRACT FROM AUTHOR]

Understanding the factors that control the temporal and spatial evolution of the Lower Triassic Buntsandstein Group, eastern France, is important not just for palaeoenvironmental reconstruction but also because it is an important reservoir for the lithium-rich geothermal brines in the Upper Rhine Graben region. The interval of interest in this study, the Lower Grès Vosgien Formation (LGV), is made up of c. 200 m of clastic deposits of mixed fluvial and aeolian origin. Given the proximity between the outcrops and the areas of mineral and heat exploration, this region offers a unique opportunity for quantitative analysis and correlation between outcrops and reservoirs. The LGV is the thickest Formation in the Buntsandstein Group. However, hitherto, no detailed architectural analysis has been published to reveal the controlling factors of its depositional elements. In this study, high-resolution facies analysis was applied to thirteen outcrops, and a core, to quantify fluvial and aeolian depositional architectures, and to comprehend palaeoenvironmental conditions during their deposition. Two facies associations were identified. The fluvial channel facies association, composed mainly of sandstones deposited in poorly confined, occasionally ephemeral channels, corresponds to 93 % of the total thickness. The analysis of >800 sets of strata characterised by lower-, transitional-, and upper-flow regime sedimentary structures, distributed within different architectural elements, enabled the distinction of temporal and spatial variabilities, and an estimate of fluvial palaeohydraulic characteristics. The wind- and water-laid facies association, which accounts for 7 % of the total thickness, records an architecture controlled by a fluctuating water-table level, and ephemeral floods. Results revealed that aeolian dunes and sand sheets accumulated in distinct temporal moments. The vertical trends, recorded in the core, indicate an upward increase in the frequency of intercalations between the two facies associations, and a decrease in the occurrences of thicker cross-bedded sandstone sets of fluvial origin, which, associated with the overall retrogradational stacking pattern of the LGV, is interpreted as the preserved record of a large distributive fluvial system (DFS). The occurrence of laterally extensive aeolian deposits, overlying fluvial deposits, is often associated by authors with periods of relatively more arid conditions at a regional scale. However, evidence indicates channel belt avulsion as an alternative interpretation for the establishment of the two facies associations. The findings enhance the knowledge about the depositional controlling factors in braided fluvial and aeolian systems, and improve predictive models that account for reservoir heterogeneity in accumulated successions of this type. [ABSTRACT FROM AUTHOR]

The sequence-stratigraphic analysis of continental and shallow marine successions is a helpful tool for investigating the cyclicity of the sedimentary record. A similar approach is adopted in the present study to illustrate the composite cyclothemic facies architecture that characterizes the Piacenzian strata of the southern Valdelsa Basin (Central Italy). Specifically, we integrated facies analysis, paleopedology, paleobiology of marine mollusk assemblages and biostratigraphy to assess the response of geomorphic, sedimentary and biotic systems to Piacenzian multifrequency relative sea-level fluctuations. This integrated approach resulted in the definition of a composite sequence-stratigraphic framework that includes a hierarchy of units ranging from the elementary to the composite depositional sequences, referred to the 5th to 3rd order cycles of sea-level fluctuations, respectively. A correlation with the Piacenzian oxygen isotopic signature of glacial and interglacial stages and related sea-level fluctuations associates the cyclic development of fluvial, coastal and shallow marine depositional systems to the mid-Piacenzian Warm Period and to the subsequent transition to the Gelasian. Thus, the glacio-eustatic control prevailed on the development of the described multi-scale cyclical pattern of sedimentation, compared to the role played by the deformation of the Northern Apennines orogen. • The Valdelsa Basin is one of the larger hinterland basins of the Northern Apennines. • The Piacenzian part of the latest Messinian-Gelasian basin fill is a composite cyclothem. • Depositional, paleobiological and paleopedological features mark the cyclical pattern. • Sequence stratigraphy is used for ranking the different-scale depositional cycles. • Glacio-eustatic fluctuations were the main forcing on the sedimentary cyclicity. [ABSTRACT FROM AUTHOR]

Three iron oxides-rich microsphere types (Type I to III) were detected in an Holocene 17 m-thick stratigraphic succession located in the Iberian Range (NE Spain). Lithofacies features indicate that the studied materials were generated in an alluvial-dominated setting, with a channeled area fringed by floodplain zones. During high water levels and high-energy floods, gravels and sands deposited in the active area and in lateral overbank areas. In these lateral areas, mud settling took place when flood decreased and then anoxic conditions could be reached due to microbial oxidation of organic matter and the low permeability of the marly sediment. X-ray diffraction (XRD) analysis of 32 samples and microtextural observation of 10 samples by Field Emission Scanning Electron Microscopy (FESEM) revealed the occurrence of Fe oxi-hydroxides microspheres showing different surficial structure. These microspheres are pseudomorphs after pyrite framboids although the formation of some primary Fe oxy-hydroxides aggregates cannot be rejected. Pyrite framboids genesis in sediments underlying oxic-dysoxic water column would have been favored by anoxic conditions reached in lateral overbank areas after main flooding, involving the activity of Fe reducing bacteria and sulfate-reducing bacteria (SRB), given the high SO 4 = availability provided by the highly mineralized groundwater from the upstream Baños de Ariño spring. Subsequent change to oxic conditions during the exposition of the floodplain enhanced the transformation of pyrite into Fe oxy-hydroxides, as well as in microenvironments around cracks and roots. Pyrite oxidation likely took place with the implication of neutrophilic iron oxidizing Bacteria and Archaea living in microaerophilic conditions, as well as cyanobacteria, given the close association of Fe oxides framboids with microbial features. In addition, pyrite and/or Fe oxi-hydroxides framboids from marl levels could have been incorporated to sand sediments during further overbank flooding episodes. Under these new oxic conditions pyrite oxidation would have been favored and even the formation of primary Fe oxy-hydroxides. [ABSTRACT FROM AUTHOR]

Abstract Seismically active fault zones receive a great deal of attention due to their potential for quantification of seismic hazards. Zones with low slip rates pose a challenge, however, since their poor topographic expression is related to difficulties in the quantification of fault movement. This study focuses on the Dobrá Voda Depression, an area with the highest level of seismic activity in the Western Carpathians. The Quaternary tectono-sedimentary evolution of the small intramontane basin was investigated with the use of facies analysis of cores, dated with the use of cosmogenic nuclide depth profiles (10Be, 26Al and 36Cl), together with 26Al/10Be burial dating and radiocarbon dating. A set of archived boreholes and geoelectric survey data was used for the correlation of results with those from new boreholes across the depression. Four facies associations were distinguished: (FA1) Colluvial deposits that comprise subaerial debris flows and mudflows; (FA2) Fluvial deposits with high sediment supply: accommodation ratio, composed mostly of sandy-gravelly channel fill facies; (FA3) Fluvial deposits with low sediment supply: accommodation ratio, consisting mostly of floodplain muds, overbank heterolithic facies and minor sandy-gravelly channel fills; and (FA4) Swamp deposits, which are mostly made up of peat. Geochronological results suggest that the studied part of FA3 was deposited before 1.0 Ma due to a rise in the base level following a major incision event. Overbank-dominated deposits of FA3 covered an incision surface, resulted in a difference of ca. 65 m of elevation of these strata, which represents the minimal thickness of FA3. The second phase of incision was related to reactivation of Miocene normal faults resulting in further topographic differentiation. The initiation of fault activity is recorded by the deposition of colluvial FA1 before ca. 250 ka. FA2 accumulated between ca. 160 and 100 ka, mostly at the toes of slopes bounding the fault scarps on the basin margins. The last documented phase of evolution represents an increase of accommodation, which was connected to the deposition of Holocene peat in swamps as well as floodplain muds of FA4 above FA2. The observed settings imply that variation between incision and accumulation in a scale of hundreds of thousands of years is characteristic for low relief tectonically active zones. The presented research demonstrates the significance of sedimentological analysis for reconstruction of tectonic evolution in areas with low slip rate activity. Highlights • Depth profile exposure dating of 10Be, 26Al and 36Cl applied together with 14C dating. • Accumulation in the area was interrupted by two phases of incision at >1 Ma and 250–100 ka. • Reactivation of normal faults and topographic differentiation during 250–100 ka. • Overbank/channel fill ratio and alluvial/colluvial deposition changes driven by base level shifts. • Accumulation-incision alteration characteristic for moderate relief tectonically active zones. [ABSTRACT FROM AUTHOR]

Abstract Environmental interpretations of subsurface fluvial successions are commonly based on facies observations from core and are often attempted by generalist geologists by reference to classic facies models. However, for fluvial channel deposits, the value of observations on lithofacies proportions for interpretations of depositional environment has yet to be assessed quantitatively. Here, a test is presented that is based on a comparative study of facies data from 77 reaches of 46 modern rivers. The analysis is undertaken on datasets from published case studies stored in a sedimentological database, with consideration of causes for observational bias, and with particular attention paid to sandy lithofacies. The observed variability in the proportion of facies assemblages in the channel deposits of sandy river systems is quantified for classes of environments categorized according to channel pattern (braided, low sinuosity, meandering), climatic setting (arid to perhumid), and discharge regime (ephemeral to perennial). By capturing the variability in facies organization within fluvial systems of certain types, these outputs serve as facies models that provide a measure of uncertainty to sedimentological interpretations. Concurrently, the statistical analysis presented enables a test of the significance of relationships between the relative proportions of channel lithofacies and parameters that either represent controlling factors (e.g., water-discharge characteristics) or covariates (e.g., channel pattern). For classes of river systems grouped by channel pattern, climate, and discharge regime, emerging features of facies organization can be identified. Statistically, it is observed that relationships exist (i) between channel pattern and the frequency of the preserved expression of bedforms, and (ii) between controls on river hydrology (climate, discharge regime and seasonal variability) and the record of upper and lower flow-regime conditions. Thus, the results corroborate existing qualitative facies models in some respects. However, observations of the relative dominance of facies in channel deposits demonstrate limited value for interpretations or predictions in subsurface or outcrop studies, as variability within each type of depositional system is significant. Corehole data of fluvial channel deposits may be commonly overinterpreted. [ABSTRACT FROM AUTHOR]

Abstract Interflag sandstone laminae are thin, silty to sandy, layers between thicker sandstone beds, and a new name for sedimentary structures recently called "shims", and "microbial mat sandwiches", from Ediacaran fossil localities of Nilpena, South Australia. They have been regarded as structures unique to Precambrian marine environments, but both the age and environmental associations are reinterpreted in this study. Interflag sandstone laminae from Eocene (Wasatch Formation, Colorado, U.S.A.) and Pennsylvanian (Mansfield Formation, Indiana, U.S.A.) fluvial levees and scroll bars were studied in the field, and by means of petrographic thin sections and granulometry. Climbing translatent ripples and distinct grain size distributions are evidence that interflag sandstone laminae were eolian, whereas intervening flagstones were deposited by fluvial traction currents. Other evidences of exposure to wind include microbial earth textures, shallow cracking structures, zibars, setulfs, root traces, and insect trackways. Other evidences of flagstone deposition in traction currents include intraformational claystone breccias, oscillation and current ripples, and microbial mat textures. Similarly distinct beds can be seen in modern sandy river levees, such as the Murchison River of Western Australia and Green River of Utah (U.S.A.). These observations reveal that interflag laminae are created by exposure and wind-drift, but flagstones are produced by floods. Quartzose flagstones of demonstrable marine origin, with fossil brachiopods and trilobites, have also been examined, but lack interflag sandstone laminae. Interflag sandstone laminae are evidence of alternating flood and wind, only known from fluvial environments, and are further support for the idea that Ediacaran vendobionts from South and central Australia, and Namibia lived on land. Graphical abstract Unlabelled Image Highlights • Interflag sandstone laminae is a new name for sedimentary structures called "shims". • Interflag sandstone laminae are not unique to Precambrian marine rocks. • Examples are described from Ediacaran, Pennsylvanian, and Eocene fluvial levee facies. • In modern rivers, interflag sandstone laminae form by wind-drift between flood beds. [ABSTRACT FROM AUTHOR]

Spring-related carbonates are valuable repositories for information on physical and biotic environments of the past. However, for Mesozoic and earlier records, their use is limited due to their low preservation potential and difficulties in accurate identification of the carbonate type. This study aims to characterise the source of carbonate clasts preserved as thin beds of cross-bedded grainstones in Late Triassic, siliciclastic fluvial deposits, the Maleri Formation, Pranhita-Godavari rift basin, India. The microfabric and stable isotopic compositions of the grainstones and thin and discontinuous beds of impure limestones of this formation are presented here. These features help in identifying the freshwater carbonate-precipitating environments that existed in an ancient continental rift basin, though such deposits are not primarily preserved in this case. The microfabric of the carbonate grains provides evidence for carbonate precipitation in aquatic environment related to karstic springs. Taking together the microfabric, stable isotopic compositions, as well as the associated geological and palaeontological information, it could be shown that the calcium carbonate precipitation took place in palustrine pools related to tufa-like spring systems and in alluvial swamps under a pluvial climatic setting. This research, thus, demonstrates that carbonate grains derived from spring-related carbonate deposits, formed mainly near the margins of rift basins, can be incorporated into nearby siliciclastics. If interpreted correctly, they can be used in reconstructing ancient karstic carbonate environments, even when in situ primary record is not preserved – therefore making it possible to access the information stored in freshwater carbonates. [ABSTRACT FROM AUTHOR]

Studies of distributive fluvial systems and their preserved successions envisage the distribution and orientation of architectural elements to be primarily controlled by channels radiating outward from fan apices, in many cases along an elongate basin margin. Conceptual models for such systems account for the downstream dynamics of the fluvial network, but with limited consideration of temporal geomorphic variations, resulting vertical organisation of architectural elements, or of the interplay of factors controlling system dynamics. To understand the external and internal architecture of distributive fluvial systems, and the factors that influence their sequential facies organisation, a sedimentary succession of the proximal portion of an Upper Cretaceous, semiarid, distributive fluvial system, located at the north-eastern margin of the Bauru Basin (Southeast Brazil), has been analysed in detail. Three fining- and thinning-upward fluvial sequences are identified, forming an interval separated at the top and the bottom by two palaeosol profiles. Each sequence is formed of channel and floodplain deposits. Two types of channel deposits are identified. One is composed of stacked sets of small-scale dune deposits, suggesting perennial and steady fluvial regime, associated with more humid climate periods. The other is composed of large-scale sets indicative of flattened dunes associated with unsteady and fast-changing fluvial flow, formed in quasi-supercritical flow regime conditions, associated with drier climate periods. The vertical alternation of these two types of channel deposits records the accumulation of a fluvial succession that responded to high-frequency, climate-induced cyclic change in boundary conditions. Two palaeosol profiles, at the top and at the bottom of the succession, indicate temporary interruptions and cessation of the fluvial sedimentation, likely related to avulsion of the fluvial belt. Thus, the studied succession reveals high-frequency climate-induced allogenic sedimentary cycles that occur within a long-period autogenic geomorphologic-induced sedimentary cycle. This work suggests that the internal architecture of the channel deposits can be used as a climate proxy, and that climate and geomorphology act jointly as notable factors to control the vertical organisation of distributive fluvial systems. [ABSTRACT FROM AUTHOR]

Fluvial floodplains established prior to the greening of continents have long been overlooked, despite their relevance for landscape reconstructions in deep time. The record of fluvial overbank sedimentation dates back as far as the Mesoarchean, and mature assemblages of floodplain landforms had already developed at least by the early Palaeoproterozoic. In this review, a critical assessment of pre-vegetation floodplain processes and deposits is carried out through literature compilation and detailed descriptions of case studies. Pre-vegetation floodplains were variably composed of floodbasins, splay complexes (including crevasse- and distributary-channel fills and related splay lobes) and, in minor proportion, by channel levees. The hydrology of ancient floodbasin environments, mainly inferred from the occurrence or lack of evaporite features, is particularly topical and, once critically tested against other palaeo-environmental indicators, can be related to climate or catchment physiography. Pre-Silurian floodplains preferentially developed in rift basins prone to restricted drainage, where low-gradient axial depressions experienced limited stream power and accumulation of cohesive fines. Since supercontinents prone to host mature intracratonic basins first appeared in the Palaeoproterozoic, a causal relationship is established between the rise of modern-style plate tectonics and fluvial floodplains. By comparison, pre-vegetation overbank records are sparse in foreland, syn-orogenic, or passive-margin basins, where higher gradients and ocean-ward bypass of cohesive fines would have enhanced reworking by adjacent channels. These features are analogue to modern non-vegetated floodplains, with examples drawn from both arid endorheic drainages (Death Valley, California; Salar de Uyuni, Bolivia), and humid exorheic drainages (coastal plains of southern Iceland). Future developments in pre-Silurian sedimentology will help addressing lingering questions related to, for instance, the biogeomorphology of microbial mats and the morphogenetic variability between floodplains developed in different latitudinal climate belts. [ABSTRACT FROM AUTHOR]

Extant, planform-based facies models for alluvial deposits are not fully fit for purpose, because they over-emphasise plan form whereas there is little in the alluvial rock record that is distinctive of any particular planform, and because the planform of individual rivers vary in both time and space. Accordingly, existing facies models have limited predictive capability. In this paper, we explore the role of inter-annual peak discharge variability as a possible control on the character of the preserved alluvial record. Data from a suite of modern rivers, for which long-term gauging records are available, and for which there are published descriptions of subsurface sedimentary architecture, are analysed. The selected rivers are categorized according to their variance in peak discharge or the coefficient of variation ( CVQ p = standard deviation of the annual peak flood discharge over the mean annual peak flood discharge). This parameter ranges over the rivers studied between 0.18 and 1.22, allowing classification of rivers as having very low (< 0.20), low (0.20–0.40), moderate (0.40–0.60), high (0.60–0.90), or very high (> 0.90) annual peak discharge variance. Deposits of rivers with very low and low peak discharge variability are dominated by cross-bedding on various scales and preserve macroform bedding structure, allowing the interpretation of bar construction processes. Rivers with moderate values preserve mostly cross-bedding, but records of macroform processes are in places muted and considerably modified by reworking. Rivers with high and very high values of annual peak discharge variability show a wide range of bedding structures commonly including critical and supercritical flow structures, abundant in situ trees and transported large, woody debris, and their deposits contain pedogenically modified mud partings and generally lack macroform structure. Such a facies assemblage is distinctively different from the conventional fluvial style recorded in published facies models but is widely developed both in modern and ancient alluvial deposits. This high-peak-variance style is also distinctive of rivers that are undergoing contraction in discharge over time because of the gradual annexation of the channel belt by the establishment of woody vegetation. We propose that discharge variability, both inter-annual peak variation and “flashiness” may be a more reliable basis for classifying the alluvial rock record than planform, and we provide some examples of three classes of alluvial sediment bodies (representing low, intermediate, and high/very high discharge variability) from the rock record that illustrate this point. [ABSTRACT FROM AUTHOR]

Two episodes of intense flooding and sediment movement occurred in the Westmorland Stream alluvial system near Caveside, Australia in January 2011 and June 2016. The events were investigated in order to better understand the drivers and functioning of this composite alluvial system on a larger scale, so as to provide awareness of the potential hazard from future flood and debris flow events. A novel combination of methods was employed, including field surveys, catchment morphometry, GIS mapping from LiDAR and aerial imagery, and hydraulic modelling using RiverFlow-2D software. Both events were initiated by extreme rainfall events (< 1% Annual Exceedance Probability for durations exceeding 6 h) and resulted in flooding and sediment deposition across the alluvial fan. The impacts of the 2011 and 2016 events on the farmland appeared similar; however, there were differences in sediment source and transport processes that have implications for understanding recurrence probabilities. A debris flow was a key driver in the 2011 event, by eroding the stream channel in the forested watershed and delivering a large volume of sediment downstream to the alluvial fan. In contrast, modelled flooding velocities suggest the impacts of the 2016 event were the result of an extended period of extreme stream flooding and consequent erosion of alluvium directly above the current fan apex. The morphometry of the catchment is better aligned with values from fluvially dominated fans found elsewhere, which suggests that flooding represents a more frequent future risk than debris flows. These findings have wider implications for the estimation of debris flow and flood hazard on alluvial fans in Tasmania and elsewhere, as well as further demonstrating the capacity of combined hydraulic modelling and geomorphologic investigation as a predictive tool to inform hazard management practices in environments affected by flooding and sediment movement. [ABSTRACT FROM AUTHOR]

Stream-dominated alluvial fans are formed by the periodic channel avulsion running on their surfaces and are characterized by the downstream changes in hydrodynamics of stream flows and flood frequency. The spatial variations in hydrodynamics also control the sedimentation on the floodplain, which is important for sediment dispersal patterns on the stream-dominated alluvial fans as they feed back into channel avulsion processes. To understand the influence of downstream changes in hydrodynamics on the floodplain sedimentation and associated channel avulsion processes, we studied the Cretaceous Duwon Formation in the southern part of the Korean Peninsula. The Duwon Formation unconformably overlies the Paleoproterozoic basements and consists of gravelly braided stream deposits (FA-1), sandy braided stream deposits (FA-2), and calcretes-bearing floodplain deposits (FA-3). Close to the basements, FA-1 shows the radial paleoflow patterns, and the size of sediments and the ratio of channel to floodplain deposits decrease downstream over a relatively short distance (<7 km). This indicates that the Duwon Formation was deposited in the stream-dominated alluvial fans under arid to semi-arid climatic conditions, which can be classified into the proximal, medial, and distal zones. In the medial zone, the floodplain deposits are composed of the underlying, purple-colored sandstones and the overlying, compensational stacked crevasse channel and splay deposits (ca. 19 m thick) with the unsystematic paleoflow directions, finally overlain by the sandy braided stream deposits. In contrast, in the distal zone, the floodplain fines are composed of homogeneous clay and silt with calcretes and vegetation traces. These floodplain fines are interbedded with and overlain by the progradational stacked, coarsening- and thickening-upward trending, crevasse channel and splay deposits (ca. 18 m thick) with the constant paleoflow directions to those of the overlying sandy braided stream deposits. In the medial zone, a relatively large volume of discharge of the stream floods resulted in the frequent overbank flooding via the multiple breaching points and the concomitant growth of alluvial ridges by the combined effects of in-channel bed aggradation and compensational stacked crevasse channel and splay deposits resulted in a shift in the flow pathway of the sandy braided streams. In the distal zone, the floodplain fines containing calcretes and vegetation traces suggest the longer periods of non-deposition, providing sufficient time for the vegetation development. Once the channel levees collapsed, the vegetated channel levees stabilized the breaching point, and the breaching point progressively incised by the multiple flooding events, causing susceptibility to overbank flooding. Crevasse channel flows via the breaching point and associated overbank floodwaters led to a continuous supply of the coarse-grained sediments stacking on the cohesive, vegetated floodplain fines, with an increase in the cross-floodplain topographic gradient. As a result, crevasse channels were able to advance the distal floodplains, resulting in the development of progradational stacking pattern. With the cross-floodplain topographic gradient, the deposition of these erodible overbank flooding sediments on the cohesive, vegetated floodplain fines provided an alternative route for the parent channel, resulting in channel avulsion. Thus, this study suggests that downstream changes in hydrodynamics and associated floodplain sedimentation are important for channel avulsion and hence control the sediment dispersal patterns of coarse-grained sediments on the stream-dominated alluvial fans. [ABSTRACT FROM AUTHOR]

The properties of sediment grain shape provide valuable information about the transport mechanisms in different sedimentary and geomorphological environments. With the emergence of new, high-resolution analytical techniques, it has become possible to quickly examine the grain shape properties of a large number of individual mineral grains. In this study, we used automated image analysis (Malvern Morphologi G3SE-ID) to investigate mineral particles of four sediment types from different depositional environments (sand sheet (1), floodplain (2) and fluvial channel deposits (3), Pleistocene infilling material of sand wedges (4), n = 20) in the Carpathian Basin (Central Europe). Our primary objective was to identify quantitative key variables that can help objectively distinguish certain geomorphological environments located in the Carpathian Basin. In our analysis and data processing (which included techniques such as hierarchical cluster analysis, Wilks' λ, Kruskal–Wallis, multivariate analysis of variance and principal component analysis) we focused on four variables related to grain shape: circularity (form), convexity (surface texture), solidity (roundness) and elongation (form). The form of sedimentary grains depends largely on the physical properties of their source area, while the roundness depends on the energy of the transport medium and the distance of transportation. Surface texture or convexity can change in a relatively short time in a fluvial environment. The study revealed that distinguishing geomorphological environments can be achieved by analyzing the circularity, convexity and solidity parameters of the sediment grains. Based on the established grouping, the analyses carried out with hundred repetitions showed that high sensitivity circularity, convexity and solidity variables were the most effective attributes regarding Kruskal–Wallis test statistics that provided significant (p < 0.001) results between the analyzed sedimentary environments, while the elongation was not able to provide significant results between the grouped samples. Statistical analyses of the MANOVA test with hundredfold repetitions showed significant differences between the derived groups. Wilks' λ test statistics and PCA showed that convexity and high sensitivity circularity discriminate the groups. Separate analyses of aeolian and fluvial sediments have been carried out. The Kruskal–Wallis analysis of variance showed the significant differences considering all four variables, and differences were also significant in the case of the MANOVA test. Wilks' λ test statistics and PCA showed that convexity, high sensitivity circularity and solidity discriminate the groups. According to our results, the circularity parameter can provide information about the transport distance, while the solidity parameter can indicate the transport energy. The convexity parameter can serve as an indicator of both transport distance, as well as post-depositional processes. Some infilling materials underwent multiple transport processes, including high energy aqueous, wind transport mechanisms, and the post-depositional alteration process (frost weathering), while others originated from sand-sheet covered areas (active during Pleistocene glacials). The solidity parameter proved effective in separating sediments with similarly high convexity values (smooth surface), which were, in our case, from recent aeolian and fluvial environments. This result was due to the investigated fluvial sediments that inherited their form and low level of roundness from their source area. Our research supports that aeolian transport is more effective in rounding the grains than the aqueous environment. Using automated static image analysis producing statistically stable results with hundreds of analyzed mineral grains provides useful indicators for paleogeographical reconstruction studies by investigating paleo and recent sediments. • The high HS circularity values can indicate a longer transport distance. • The solidity factors can be used to identify relative transport energy. • The convexity variable may indicate the post-depositional process. • The low level of roundness can be inherited from the source environment. • Automated static image analysis produces statistically robust results on mineral grains. [ABSTRACT FROM AUTHOR]

The origin and evolution of clay minerals in sedimentary basins are usually influenced by changes in depositional hydrochemistry. The formation and preservation of rare fibrous magnesium-rich clay minerals, like sepiolite, are of interest in the Chobe Enclave, northern Botswana, as it occurred in a siliceous-rich intra-cratonic basin. New X-ray diffraction (XRD) data, scanning electron (SEM) and transmission electron (TEM) microscopy analyses, as well as geochemical data, are used to study the origin of authigenic sepiolite and the sub-environments related to its formation in the Chobe Enclave. The paleoenvironment record during the Late Pleistocene to Holocene demonstrates that the deposition in the region was preceded by an aluvial fan/fluvial deposits in humid conditions. The upper-basin catchment yielded a clay assemblage, including kaolinite and minor smectite amounts, now preserved in the Chobe as a detrital phase. The alluvial fan deposits were later overlain by deposits from lacustrine/palustrine environments where significant hydrochemical changes took place: during these changes, a fibrous clay mineral (authigenic sepiolite) formed in shallow lake/marshes in a closed system with low energy, under the influence of magnesium-rich and alkaline waters. The mineralogical and geometrical (diagenetic) relationships between the palustrine deposits (carbonate facies) and sepiolite point to a sequence of precipitation from an evaporitic system in which calcite, sepiolite, and finally amorphous silica follow one another. In addition, although the sepiolite parent solution was enriched from a water source concentrated in Mg2+, the presence of Ba2+ ions also emphasizes some spells of hydrothermal activity. • Sepiolite is observed in a siliceous-rich intra-cratonic basin of northern Botswana. • Sepiolite formed in a closed alkaline system with magnesium-rich waters. • Sepiolite belongs to a sequence of precipitation from an evaporitic system. • This sequence is composed of calcite, sepiolite, and finally amorphous silica. • The presence of Ba2+ ions emphasizes some spells of hydrothermal activity. [ABSTRACT FROM AUTHOR]

The Yellow Cat Member of the Cedar Mountain Formation in Poison Strip, Utah, USA, consists of stacked, erosionally bounded alluvial sequences dominated by massive mudstones (lithofacies Fm) with paleo-Vertisols. Sediment bodies within these sequences grade vertically and laterally into each other at pedogenic boundaries, across which color, texture, and structures (sedimentary vs. pedogenic) change. Slickensides, unfilled (sealed) cracks, carbonate-filled cracks, and deeper cracks filled with sandstone; the latter features suggest thorough desiccation during aridification. Thin sandstones (Sms) in some sequences, typically as well as laminated to massive mudstones (Flm) with which they are interbedded in some cases, are interpreted as avulsion deposits. The termini of many beds of these lithofacies curve upward, parallel to nearby pedogenic slickensides, as the features we call “turnups.” Turnups are overlain or surrounded by paleosols, but strata sheltered underneath beds with turnups retain primary sedimentary fabrics. Turnups were produced by movement along slickensides during pedogenesis, by differential compaction alongside pre-existing gilgai microhighs, or by a combination of both. Palustrine carbonates (lithofacies C) appear only in the highest or next-highest alluvial sequences, along with a deep paleo-Vertisol that exhibits partially preserved microrelief at the base of the overlying Poison Strip Member. The attributes of the Yellow Cat Member suggest comparatively low accommodation, slow accumulation, long hiatuses in clastic sedimentation, and substantial time intervals of subaerial exposure and pedogenesis; it appears to be distinct among the members of the Cedar Mountain Formation in these respects. [ABSTRACT FROM AUTHOR]

The Winton Formation of central Queensland is recognized as a quintessential source of mid-Cretaceous terrestrial faunas and floras in Australia. However, sedimentological investigations linking fossil assemblages and palaeoenvironments across this unit remain limited. The intent of this study was to interpret depositional environments and improve stratigraphic correlations between multiple fossil localities within the preserved Winton Formation in the Eromanga Basin, including Isisford, Lark Quarry, and Bladensburg National Park. Twenty-three facies and six repeated facies associations were documented, indicating a mosaic of marginal marine to inland alluvial depositional environments. These developed synchronously with the final regression of the Eromanga Seaway from central Australia during the late Albian-early Turonian. Investigations of regional- and local-scale structural features and outcrop, core and well analysis were combined with detrital zircon provenance signatures to help correlate stratigraphy and vertebrate faunas across the basin. Significant palaeoenvironmental differences exist between the lower and upper portions of the preserved Winton Formation, warranting informal subdivisions; a lower tidally influenced fluvial-deltaic member and an upper inland alluvial member. This work further demonstrates that the Isisford fauna is part of the lower member of the preserved Winton Formation; whereas, fossil localities around Winton, including Lark Quarry and Bladensburg National Park, are part of the upper member of the Winton Formation. These results permit a more meaningful framework for both regional and global comparisons of the Winton flora and fauna. [ABSTRACT FROM AUTHOR]

Crevasse-splay deposits form a volumetrically significant component of many fluvial overbank successions (up to 90% in some successions).Yet the relationships between the morphological form of accumulated splay bodies and their internal facies composition remains poorly documented from ancient successions. This work quantifies lithofacies distributions and dimensions of exhumed crevasse-splay architectural elements in the Campanian Castlegate Sandstone and Neslen Formation, Mesaverde Group, Utah, USA, to develop a depositional model. Fluvial crevasse-splay bodies thin from 2.1 m (average) to 0.8 m (average) and fine from a coarsest recorded grain size of lower-fine sand to fine silt away from major trunk channel bodies. Internally, the preserved deposits of splays comprise laterally and vertically variable sandstone and siltstone facies associations: proximal parts are dominated by sharp and erosional-based sandstone-prone units, which may be structureless or may comprise primary current lineation on beds and erosional gutter casts; medial parts comprise sets of climbing-ripple strata and small scale deformed beds; distal parts comprise sets of lower-stage plane beds and complex styles of lateral grading into fine-grained floodbasin siltstones and coals. Lithofacies arrangements are used to establish the following: (i) recognition criteria for crevasse-splay elements; (ii) criteria for the differentiation between distal parts of crevasse-splay bodies and floodplain fines; and (iii) empirical relationships with which to establish the extent (ca. 500 m long by 1000 m wide) and overall semi-elliptical planform shape of crevasse-splay bodies. These relationships have been established by high-resolution stratigraphic correlation and palaeocurrent analysis to identify outcrop orientation with respect to splay orientation. This permits lateral changes in crevasse-splay facies architecture to be resolved. Facies models describing the sedimentology and architecture of crevasse-splay deposits preserved in floodplain successions serve as tools for determining both distance from and direction to major trunk channel sandbodies. [ABSTRACT FROM AUTHOR]

Multiproxy analysis of detrital minerals is a powerful tool for unravelling the source-to-sink evolution of syn-rift sedimentary basins that represent important depositional settings during major rift events. The Cenozoic Resende half-graben in SE Brazil is a classic example of a syn-rift basin developed under oblique extension, which preserves evidence of tectonic episodes and palaeoclimatic conditions during the opening of the Atlantic. Sediment in the basin was sourced from the surrounding basement rocks, which to the faulted margin consists of older Proterozoic orthogranulites and orthogneisses, whilst to the flexural margin is characterised by Neoproterozoic passive margin paragneisses. Cretaceous intra-plate alkaline stocks crop out at the western edge and in the central-south basement of the basin and represent a distinct provenance fingerprint. This study uses new detrital zircons U–Pb ages combined with previously published elemental and Nd and Sr isotopic data to characterise the sedimentary provenance of Eocene alluvial deposits and to understand how sediment sourcing has changed throughout the evolution of the basin. U–Pb detrital zircon analyses from samples collected across the Resende Basin are presented herein. Samples yield a spread of detrital age spectra from the Archaean to the Cretaceous. Precambrian zircons range from ca. 3228 Ma to ca. 542 Ma. Cretaceous zircons yield ages between ca. 138 Ma and ca. 67 Ma. The sediment source location is interpreted by comparing the yielded detrital zircon spectra with the age spectra of zircons from the basement rocks. The dominance of detrital zircons yielding ages of ca. 1500 Ma and ca. 1000 Ma is interpreted to be sourced from the Neoproterozoic basement rocks to the flexural border of the half-graben. Cretaceous zircons from samples with whole rock εNd 40Ma > −10 are found in both the western and eastern portions of the half-graben but not in the central portions. It is interpreted that an along-axis fluvial system was responsible for a small increase in the compositional maturity of the Resende sandstones from west to east, resulting in the progressive dilution of Cretaceous alkaline igneous detritus along the basin axis. Preserved metamorphic rims in zircon grains indicate low transport abrasion, suggesting that Cretaceous zircons in the eastern depocentre could be associated with other small proximal sources. U–Pb zircon analyses and Nd and Sr isotopes provide reliable insights regarding sediment provenance and transport processes, whilst element geochemistry supplies evidence for hydraulic sorting effects. Consequently, the data represents a more robust estimation of the provenance patterns of the Resende Basin, showing chemical and geochronological differences that support the division of the basin into three depocentres (western, central, and eastern) connected by a longitudinal fluvial system sourced mostly by sediments coming from the south-western flexural border. This study highlights the usefulness of using multiple provenance proxies to unravel the complex development of rift basins, assessing multiple source terrains and the variable degrees of mixing in sedimentary basins. [Display omitted] • Unravelling syn-rift sedimentary basins' source-to-sink behaviour • U–Pb detrital zircon dating reflects proximal source areas in a continental rift basin. • Palaeogeographic reconstruction and the role of a longitudinal fluvial system [ABSTRACT FROM AUTHOR]

Modern subaerial catastrophic mass-wasting (rockslides, rock avalanches) are identified as being huge bulky masses with a surface littered with boulders to blocks. The identification of partly preserved deposits of 'fossil' subaerial catastrophic mass-wasting, in contrast, requires assessment of deposit fabrics. In the Alps, within the synorogenic Gosau Group (Turonian to Ypresian) that accumulated in an oblique-convergent setting, we had identified a 'megabed' (Wäschkogel megabed) up to 95 m thick that is interpreted as a vestige of a subaerial rock avalanche deposit. This megabed is an extremely poorly sorted, disordered, clast-supported deposit of sand- to boulder-sized dolostone fragments from an upper Triassic succession that comprises the local bedrock. In the megabed, numerous clasts display crackle, jigsaw and mosaic fabrics with fitted subclast boundaries. The matrix is a lithified gouge of fragmented dolomite crystals. In its upper part, the megabed displays very thick planar parallel stratification. Across strata, no change in sediment fabric is discerned. The distinctive features of the megabed, i.e., the sharp intercalation between fluvial deposits, large bed thickness with a uniform fabric, abundant clasts fractured in situ, and the gouge matrix all indicate that the megabed and lateral correlatives accumulated from a rock avalanche. The planar stratification in the upper part of the megabed is interpreted as a dynamic feature produced by internal simple shear during a terminal phase of rock avalanche propagation. Bedrock geology and the distribution of other Gosau Group deposits in the area suggest that the rock avalanche propagated along a SSW–NNE striking incised valley. This is the first identification of a subaerial rock avalanche deposit in the Gosau Group. Our case study may help to consolidate the awareness of deposits of fossil subaerial catastrophic mass-wasting. [ABSTRACT FROM AUTHOR]

Tertiary, syn-rift clastic reservoirs offer a unique opportunity to investigate the pivotal role of depositional and early diagenetic controls on reservoir quality. The Al Wajh Formation is a vital exploration target for petroleum in the Red Sea, and is characterized by early, near-surface diagenetic signatures. An integrated petrographic-mineralogical study is conducted to assess the role of depositional factors (e.g., sand grain size and clay matrix) and early diagenetic overprints on reservoir quality. The Al Wajh sandstones are primarily subarkose and lithic arkose, deposited in alluvial fan, braided fluvial, and nearshore environments. Braided fluvial sandstones of the formation have the best quality reservoirs (average porosity: 23.2 %; average permeability: 3025 mD) because of medium to coarse grain size and small proportion of clay matrix, whereas the nearshore sandstones form reservoirs of far lower quality (average porosity: 12.6 %; average permeability: 486 mD) owing to predominantly finer grain size and higher proportion of clay matrix. Clay volume between 10 and 20 % generally reduces the reservoir properties to <10 % porosity and 100 mD permeability. Compaction and grain dissolution are the major near-surface, early diagenetic processes that have strongly affected the sandstones reservoir quality. High mechanical compaction has been recorded in sandstones characterized by abundant matrix content and ductile rock fragments. Dissolution of labile grains (e.g., feldspars) has created secondary, intragranular porosity of up to 13.5 % (average 4.7 %). Kaolinite is the primary authigenic pore-filling clay in the continental units of the formation, whereas detrital and authigenic smectites are the key pore-filling clays in the nearshore units of the formation. Grain-coating smectite (up to 18.7 %; average: 7.1 %) was mainly emplaced through mechanical infiltration and has the potential for inhibiting quartz cementation should deep burial occur. The findings of the study can be utilized for modelling reservoir quality in the subsurface analogue of the Al Wajh Formation in the Red Sea or elsewhere, thereby improving reservoir quality prediction. • Reservoir quality is controlled by depositional facies and diagenesis. • Compaction is the main driver for porosity loss in the sandstones than cementation. • Braided fluvial facies have the best reservoir quality, whereas nearshore facies have the poorest reservoir quality. [ABSTRACT FROM AUTHOR]

Valley-fill terraces and fluvio-lacustrine sediment successions were investigated for the nature and type of soft-sediment deformation structures (SSDS) in the Alaknanda Valley of the Garhwal Himalaya. Based on their morphologies, sediment characteristics and comparison with existing data on SSDS, these features are classified into seismic and aseismic categories. The study indicates that, despite the terrain being in the seismically active domain of the Central Himalaya, the majority of the deformation structures seem to have been generated aseismically. We attribute their genesis to uneven loading, slope failure and, most importantly, turbulent flow and sudden loading by flash floods. The study suggests that a cautious approach is needed before assigning a seismic origin to deformation structures in sediments deposited in high-energy fluvial systems. [ABSTRACT FROM AUTHOR]

The recognition of seismically induced soft-sediment deformation structures (SSDS) in sedimentary successions characterized by different facies, and hence by different rheology, is challenging. This is the case for high porosity and high permeability aeolian facies interbedded with muddy wet interdune deposits and alluvial conglomerates and sandstones. Several types of SSDS have been studied in two exposures of the Upper Pliocene (2.9–2.6 Ma) sediments of a fault-bounded intracontinental aeolian dune field in the Teruel Basin (Iberian Chain, eastern Spain). Among SSDS, load and fluid-escape structures, apart from several animal tracks, have been recognized. Those structures show an irregular distribution through the studied stratigraphic sections, being scarce in homogenous aeolian sands and frequent in water-related facies. A detailed study of the distribution and geometry of SSDS and their relationships with respect to the stratigraphic architecture and facies has allowed a critical discrimination of trigger mechanisms, i.e. biological or physical overloading vs. earthquakes. The seismically induced structures are concentrated into seven deformed beds, showing an uneven lateral distribution and geometry closely controlled by the hosting sedimentary facies and their rheology. These seismites resulted from liquefaction during moderate earthquakes (estimated magnitude from 5.0 to 6.8). The most probable seismogenic source was the Sierra del Pobo normal fault zone, located 2 km to the East. Results show how an appropriate recognition of sedimentary facies is crucial to understand the lateral variability of seismites in sedimentary environments characterized by sharp facies changes. [ABSTRACT FROM AUTHOR]

Floodplain deposits are abundant in low-gradient dryland river systems, but their contribution to connected reservoir volumes has not yet been fully acknowledged due to their poor detectability with typical wireline log suites and relatively-lower reservoir quality. This study presents an analysis of stacked crevasse splays in the distal part of the Miocene Huesca fluvial fan (Ebro Basin, Spain). Vertical stacking of crevasse splays implies local aggradation of the active channel belt. Lateral amalgamation of crevasse splays created an elevated rim around their feeder channel, raising its bankfull height. Subsequent crevasse splays were deposited on top of their predecessors, creating sand-on-sand contact through incision and further raising the active channel belt. This process of channel-belt super-elevation repeated until an upstream avulsion occurred. Amalgamated crevasse splays constitute connected reservoir volumes up to ~ 10 7 m 3 . Despite their lower reservoir quality, they effectively connect channel deposits in low net-to-gross fluvial stratigraphy, and hence, their contribution to producible volumes should be considered. Unswept intervals of amalgamated crevasse splays may constitute a secondary source of natural gas. Their interval thickness can serve as a proxy for feeder-channel dimensions, which can in turn be used to estimate the degree of stratigraphic connectivity. [ABSTRACT FROM AUTHOR]

Fluvial fans in the rock record are inferred based on critical criteria such as: downstream grain-size fining; evidence for drainage fractionation along bifurcating channels; increasing fluvial-aeolian interaction in the basinward direction; and radial palaeoflow dispersion. Since pre-vegetation fluvial rocks often lack heterolithic alluvium and channelisation at the outcrop scale, the recognition of pre-Silurian fluvial fans has, so far, not been straightforward. This research proposes a sedimentary model for the Alderney Sandstone Formation of Channel Islands (UK), so far considered as a fine record of early Palaeozoic axial-fluvial sedimentation. Here, outcrop-based and remote-sensing analysis of the formation's type-section reveal the interaction of fluvial and aeolian processes, expressed by the alternation of: compound fluvial bars enclosing macroform surfaces, related to phases of perennial discharge; fluvial sandsheets containing antidunal forms and soft-sediment deformations, related to seasonal (i.e. flashy) discharge; and aeolian bedforms overlying thin stream-flow deposits. An up-section increase in aeolian deposits is accompanied by the shrinking of fluvial bars and minor-channel cuts, suggesting that drainage was fractioned along smaller channels terminating into marginal aeolian environments. Together with a propensity towards more dispersed values of fluvial cross-set thickness up-section (again due to discharge fractionation along intermittently active channels), these features depict an aeolian-influenced fluvial fan. This work discusses a set of criteria for the identification of fluvial fans in pre-vegetation environments. In doing so, it also explores possible parallels to modern environments, and underscores the potential of integrated outcrop and remotely sensed observations on ancient fluvial rocks and modern sedimentary realms. [ABSTRACT FROM AUTHOR]

The significance of rip-up clasts as sandstone framework grains is frequently neglected in the literature being considered as accessory components in bulk sandstone composition. However, this study highlights the great value of muddy and dolomitic rip-up clast occurrence as: (a) information source about low preservation potential from floodplain deposits and (b) key element controlling host sandstone diagenetic evolution and thus ultimate reservoir quality. High-resolution petrographic analysis on Triassic fluvial sandstones from Argana Basin (T6 and T7/T8 units) highlights the significance of different types of rip-up clasts as intrabasinal framework components of continental sediments from arid climates. On the basis of their composition and ductility, three main types are distinguished: (a) muddy rip-up clasts, (b) dolomitic muddy rip-up clasts and (c) dolomite crystalline rip-up clasts. Spatial distribution of different types is strongly facies-related according to grain size. Origin of rip-up clasts is related to erosion of coeval phreatic dolocretes, in different development stages, and associated muddy floodplain sediments. Cloudy cores with abundant inclusions and clear outer rims of dolomite crystals suggest a first replacive and a subsequent displacive growth, respectively. Dolomite crystals are almost stoichiometric. This composition is very similar to that of early sandstone dolomite cement, supporting phreatic dolocretes as dolomite origin in both situations. Sandstone diagenesis is dominated by mechanical compaction and dolomite cementation. A direct correlation exists between: (1) muddy rip-up clast abundance and early reduction of primary porosity by compaction with irreversible loss of intergranular volume (IGV); and (2) occurrence of dolomitic rip-up clasts and dolomite cement nucleation in host sandstone, occluding adjacent pores but preserving IGV. Both processes affect reservoir quality by generation of vertical and 3D fluid flow baffles and barriers that compartmentalize the reservoir. These findings may provide quantitative useful data for the better understanding of reservoir quality in analogous hydrocarbon-bearing basins such as the Bay of Fundy, Nova Scotia (Canada). [ABSTRACT FROM AUTHOR]

Soft-sediment deformation (SSD) structures preserved in sedimentary successions can record significant seismic events which occurred during or right after deposition. The integrated analysis of sedimentary facies, depositional architecture, and SSD data can determine the relative temporal relationship between deposition and deformational events, and reveal the origin and mechanisms involved in the deformation and the resulting structures. The São Paulo Formation in southeastern Brazil preserves Cenozoic alluvial deposits which characterize most of the geology of the homonymous metropolis area. This succession preserves fluvial channel and floodplain deposits, with associated debris-flow dominated alluvial fan deposits, and preserves abundant SSD structures in a wide range of dimensions and morphologies. These deformation structures include small- and large-scale folds, multi-scale vents of varied geometries, ball-and-pillow structures, and clastic dykes. Here we provide an integrated analysis of sedimentary facies, depositional architecture data, and SSD data from the São Paulo Formation, in order to discuss the deformation mechanisms and plausible triggering mechanisms responsible for the development of such structures. Our interpretation is that SSD structures in the São Paulo Formation were likely triggered by a Cenozoic meteor impact recorded by a crater near the study area. • Multi-style and multi-scale soft-sediment deformation structures can be preserved in fluvial deposits. • The São Paulo Formation records multiple soft-sediment deformation structures. • Integrated analysis of soft-sediment deformation structures, sedimentary facies, and depositional architecture. • Soft-sediment deformation in the São Paulo Formation was triggered by a Quaternary meteor impact. [ABSTRACT FROM AUTHOR]

Alluvial fan deposits record important information about paleoclimate, tectonic setting, and paleogeography that can be deciphered with detailed sedimentological analysis. The late Messinian Chaabet Et Tabbela Formation, in the western part of the Kechabta Basin in northern Tunisia, shows excellent examples of alluvial fans deposited during the latest phase of the Messinian Salinity Crisis, the Lago Mare event. This exposure provides the opportunity to investigate terrestrial depositional conditions during this period. The Chaabet Et Tabbela Formation was investigated through sedimentological logging and detailed facies analysis at eight locations. Sixteen facies types were identified and interpreted along with variation in clast compositions. These facies were further grouped into four facies associations: (1) proximal alluvial fan, dominated by gravity-driven processes, (2) medial alluvial fan, which mainly comprises a mix of debris flow and high-sediment load streamflow deposits, (3) distal alluvial fan, which consists of laterally continuous sheetflood and subordinate channels deposits, and (4) playa and floodplain, which are made of red mudstones with calcareous paleosols. Clast composition of these fan deposits comprises Triassic, Jurassic, and Cretaceous bedrock suggesting that sediment was sourced from the surrounding Maghrebian mountain chain. Two laterally adjacent alluvial fans were identified along the N-S Messeftine Fault. These fans have prograded during the Late Messinian, with an estimated radius of ca 2 km. The evolution of these alluvial fans is related to a complex interplay of allogenic processes. The uplift related to intra-Messinian tectonic event and climate variation contributed to the formation of these fans during the late Messinian. Although, these deposits are relatively limited in extension, similar continental deposits form synchronously in different marginal Mediterranean basins during the Lago Mare stage, suggesting that the alluvial fans of the Chaabet Et Tabbela Formation should be placed in a context of regionally change climactic and paleogeographic conditions. [ABSTRACT FROM AUTHOR]

The Plio-Pleistocene Tilatá Formation records a tectonic paleo-lake system in the Colombian Andes. This unit exhibits recurrent episodes of volcanism and diatomite deposits. Outcrop-based facies analysis of eight stratigraphic sections varying in thickness from 4 to 40 m indicates variations in the sediment supply, accommodation space, climatic conditions, water depth, and organic activity. Fourteen sedimentary facies are grouped into three facies associations (FAs) representative of alluvial, fluvial, and lacustrine settings. FA1 (alluvial fan deposits) corresponds to conglomerates, sandstones, and subordinated mudstones. FA2 (mixed fluvial system) represents sandy conglomerates, cross-bedded/massive sandstones, organic-rich mudstones, lignites, and diatomaceous mudstones. FA3 (lacustrine) comprises mainly organic-rich mudstones, diatomites, laminated sandstones, and tephra layers. The Upper Tilatá Formation reflects the evolution of an overfilled to a balanced-fill lake with a progradational-retrogrational-progradational stacking pattern. The organic facies revealed variations in the origin of the Amorphous Organic Matter (AOM) from aquatic to terrestrial, indicating episodes of shallowing when terrestrial conditions dominated. Seven families, eight genera, and eleven diatom species were identified in diatomites and diatomaceous mudstones, mainly in the lacustrine facies. The most abundant species was Aulacoseira ambigua , suggesting moderate energy in the water column (turbulence), solar light availability for photosynthesis, and mesotrophic to eutrophic conditions. The sedimentological record implies that bedrock, fluvial, pluvial, and volcanic input played a decisive role in nutrient supply for the proliferation of diatoms in the paleo-lake. This scenario is concordant with similar Quaternary depositional systems in northern South America. • Plio-Pleistocene diatomites are recorded in a lake system in the Colombian Andes. • Eleven diatom species were identified with an abundance of Aulacoseira ambigua. • Tectonics, pluviosity, and drainage damming caused the development of an intermontane paleo-lake. [ABSTRACT FROM AUTHOR]

A grain shape analysis of sandy deposits has implications for determining the processes that affect grain shape. So far, most methods of carrying out a grain shape analysis are based on the subjective estimation of the researcher. The purpose of this study is to indicate the shape parameter/parameters that best differentiate sand grains, and to compare the results with those that have been obtained by the Krumbein method. We determined the shape parameters of sand grains (size range from 0.71 mm to 1 mm) using photos of two-dimensional images of particle projections onto a plane. The photos were taken under an optical microscope and were then subjected to an image analysis. We selected six shape parameters that best differentiate the studied sand grains, based on the criteria of: i) the monotonicity of parameter value, which changed depending on the categorization of the grains to the successive Krumbein roundness classes, and ii) the statistical significance of differences between the optical parameter values in the individual Krumbein classes. We selected three circularity parameters ( θ 1 , θ 4 and θ 5 ) and three surface structure parameters ( κ 3 , κ 4 and κ 6 ). None of these shape parameters allowed the direct categorization of a particle into a particular Krumbein roundness class. Nevertheless, despite the fact that an unambiguous characterization of deposits is not possible, this method can be helpful in identifying the origin of deposits. Moreover, it is possible to develop more advanced methods (e.g., based on artificial intelligence tools), which would allow an unambiguous categorization based on the determined shape parameters. [ABSTRACT FROM AUTHOR]

The Paleocene Paskapoo Formation in western Canada is composed of several hundred meters of fluvial strata that were deposited in an actively subsiding retro-arc foreland basin adjacent to the southern Canadian Cordillera. Here, we utilize newly available subsurface data from down-hole gamma-ray well logs to reconstruct the large-scale fluvial stratigraphy and depositional history of the Paskapoo Formation in the central portion of the Cordilleran foreland basin in Alberta. Paleocene fluvial strata in this region contain several notable characteristics, including variable degrees of channel sandstone amalgamation, regionally-variable stratigraphic architecture, and a large fan-shaped sandstone unit that emanated from the adjacent fold-thrust belt. Fluvial channel sandstone bodies are abundant and amalgamated near the base of the formation in the southern portion of the basin, but become less apparent in the northernmost 100 km of the basin. The middle interval of the Paskapoo Formation, characterized by abundant mudstone with isolated channel sandstone bodies, is prevalent across the entire study area. The upper portion of Paskapoo Formation is dominated by a large (5000 km 2 ), north-northwest trending, laterally continuous sandstone in the northern portion of the basin that abuts against the fold-thrust belt and fans outward into the basin. This feature is interpreted as either a distributive fluvial system or a fixed-outlet river system that experienced repeated avulsions. This area of the fold-thrust belt may be the site of a long-lived fluvial outlet. The variable degree of sandstone amalgamation in the Paskapoo Formation suggests two different modes in the relative ratio of accommodation to sediment supply. Periods of rapid subsidence, likely associated with thrust emplacement in the adjacent fold-thrust belt, resulted in mudstone-dominated successions with isolated sandstone bodies, whereas tectonically inactive periods, associated with less subsidence, resulted in amalgamated sandstone units. The principal stratigraphic features reconstructed from the data in this area can be used to better understand and predict fluvial stratigraphy within other foreland basins. [ABSTRACT FROM AUTHOR]

Earthquake-induced liquefaction phenomena are commonly observed at shallow depths or at the ground surface above Holocene alluvial deposits. Nonetheless, a high-resolution examination of the relationship between surface manifestations and alluvial stratigraphy has been rarely attempted. In this study, we provide a detailed subsurface model from a selected sector of the southern Po Plain affected by widespread liquefaction processes triggered by the 2012 Emilia-Romagna seismic crisis. We report a comprehensive sedimentological and CPT-based characterization of the Terre del Reno subsoil and investigate how the stratigraphy controls earthquake-induced liquefaction phenomena. The main facies associations making up the alluvial subsoil constitute the basic elements of the liquefaction system, herein named host, source and sedimentary cap. Their subsurface distribution documents the presence of fluvial bodies prone to liquefaction beneath the earthen levees and across an area dominated by flat muddy floodplain deposits with no physical evidence of paleochannels at the surface. In addition, our observations suggest that vertical and lateral changes in stratigraphy control the mode and location of liquefaction evidence at the surface in both settings. In particular, the relative thickness of fluvial channel bodies vs. channel levee deposits (source–seal couplet) appears to control the severity of sand ejection at the surface. Our findings also suggest that vertical and lateral discontinuities within source layers prevent the occurrence of widespread liquefaction features. Conversely, lateral spreading effects and differential underground hydrostatic pressure at the interface between saturated and less permeable units are accountable for repeated sand ejection along surface fractures. This case study constitutes a unique natural laboratory thanks to the quality and density of available data. However, we emphasize that a similar approach can be useful to promote source-layer identification in areas characterized by poor or sparse data and to mitigate liquefaction hazards in urban areas built on alluvial plains. [Display omitted] [ABSTRACT FROM AUTHOR]

The Ash Hollow Formation (AHF) of the Ogallala Group is an important sedimentary archive of the emergence of the Great Plains and it contains major groundwater resources. Stratal patterns of constituent alluvial lithofacies demonstrate that the AHF is much more heterogeneous than is commonly assumed. Very fine- to fine-grained sandstone dominate overall, chiefly lithofacies Sm (massive to locally stratified sandstone). Stacked, thin sheets of Sm with accretionary macroform surfaces are common, indicating that many sandstone architectural elements originated as compound-bar deposits in dominantly sand-bed streams. Channel forms are difficult to identify and steep cutbanks are absent. Multiple units of lithofacies Sm show dense, and sometimes deep, burrowing by insects well above water tables under ancient floodplains. Massive, pedogenically modified siltstones (Fm), which compose floodplain fine architectural elements, are subsidiary in volumetric abundance to sandstones. Paleosols in these siltstones lack evidence for well-developed B horizons and advanced stages of maturity. Thin lenses of impure carbonate and laminated mud (lithofacies association Fl + C), which appear in most exposures, are deposits of ponded water in abandoned channels. Paleosols, ponded-water elements, and large vertebrate burrows in both Sm and Fm indicate that episodes of floodplain deposition, bar accretion, and channel filling were regularly followed by intervals of nondeposition on floodplains and by channel migration and abandonment. This study documents a major downdip change in the Ogallala Group overall, from source-proximal gravelly successions in the Wyoming Gangplank and deep, narrow paleovalley fills extending eastward into the Nebraska Panhandle. The lithofacies composition, stratigraphic architecture, and stratal dimensions of the AHF in the present study area are compatible with the planform geometries and floodplain soils of modestly-sized, sandy, low-sinuosity braided streams in Nebraska today, namely the modern North, South, and Middle Loup Rivers, rather than being the signatures of “big rivers.” [ABSTRACT FROM AUTHOR]

The Berrazales carbonate spring deposit is a small outcrop constituted mainly by cascade-like geometries. Four main facies have been identified: fibrous dense macrocrystalline formed by rapid degassing under high-flow conditions; framestones of coated plant moulds formed in moderate energy flow favoured by the presence of biogenic support; micrite/microsparite are primary precipitates in which crystalline aggregates nucleated on organic filaments and/or EPS; banded micrite-coarse crystalline were the result of alternating physically, chemically and biologically induced precipitation in areas of varying flow-velocities. Most facies underwent different degrees of micritization processes. Micrite is distributed as thin lines penetrating the crystals, as irregular patches or as micrite layers. In the first case organic filaments penetrate crystals, suggesting that micritization is mainly biogenically driven. In the latter cases micritization is caused mostly by partial dissolution. Microbe participation in micrite formation increased micrite MgCO3 content in comparison with coarse crystalline facies. Isotopic analyses show positive δ13C values (+2.63 and +4.29‰ VPDB) and negative δ18O (−5.65 and −4.48‰ VPDB) values. Positive δ13C values clearly indicate “deep-sourced” fluids. The Berrazales spring deposit studied here very probably is a small part of a larger carbonate building that was largely eroded by fluvial incision. Calculations of spring water temperature give a range from 20°C to 35°C, characteristic of a cold to warm spring favouring precipitation of calcite and important biogenic activity (framestones). Although the study deposit has textural characteristics of tufas, proving that the CO2 sourced from deep fluids, it should be considered as thermogene travertine, being one more example of the difficulty of using those terms for ancient sedimentary deposits. Carbonate spring deposits, very rare in the Canary Islands, are good archives of recent volcanic activity, fluvial processes and vegetation regimes prevailing in the islands in recent times. [ABSTRACT FROM AUTHOR]

Abstract: The evolution and controls on lithofacies distribution in ancient fluvio-paralic successions have been the focus of many studies. However, the evolution of ancient continental-scale fluvio-paralic depositional systems is not well documented due to a lack of suitable outcropping or subcropping examples. Features inherent to continental-scale fluvial systems, such as low overall gradients and large distances separating source from sink are likely to have a strong influence on vertical and lateral lithofacies evolution. During the Early Cretaceous a vast fluvio-paralic system drained the interior of the north Gondwana continent, terminating at approximately the present day coastline of North African/Saharan platform, and extending for >1500km across the margin. In the Murzuq Basin, ~600km from the shelf edge, extensive outcrops of Lower Cretaceous (named the Messak Fm) comprise ~300m of fluvio-paralic sediments. Correlation with more distal equivalent outcrops on the northern margin of the Ghadames Basin presents an excellent opportunity to assess facies development of a large-scale continental system, and clearly illustrates the effects of limited accommodation availability. For the first time, we identify evidence of marine influence in the Murzuq Basin during the early Cretaceous and interpret this as the record of transgressions associated with the regionally well-documented early Aptian sea level rise. The distribution of fluvial and paralic facies is interpreted to be controlled by a combination of limited accommodation availability, repeated relative sea level rises, and autocyclic fluvial processes. Relative sea level rises were able to rapidly inundate large parts of the Gondwanan margin due to the low gradient of the platform, but transgressive facies distribution and preservation were restricted due to the balance between sediment supply and limited long-term accommodation availability. Thus, while relative sea level exerts a strong influence in such a setting, marine-influenced deposits are likely to be relatively rare. The Messak Fm provides a clear example of how sediments preserved by a large-scale low-gradient fluvial system do not necessarily reflect the relative balance of depositional controls. [Copyright &y& Elsevier]

This study elucidates the geological and physical factors that produce polymodal grain size distributions in two dunes systems in southeastern Oaxaca, Mexico. The dune systems are characterized by (1) small embryo vegetated, transverse and undeveloped dunes; and (2) tall types identified as barchanoid, parabolic, climbing and falling dunes. We performed a best-fit statistical Weibull distribution model with data obtained by laser granulometry to determine the polymodal trends of the coastal dune sands distribution. Polymodal distributions in small dunes arise from coarse and fine-grained sands mainly derived from the erosion of alluvial deposits composed of granitic and metasedimentary rock fragments (e.g., schists, orthogneiss and paragneiss). The medium- to fine-grained sands result from wind deflation, producing a heavy mineral lag. Conversely, the polymodal grain size distributions in the tall dunes are mainly derived from the physical weathering of granites, andesitic-tuff-lava flow marine sandstones (ATLMS), alluvial deposits, and metasedimentary rock fragments (e.g., schists, orthogneiss and paragneiss) due to the frequent storms and intense winds. We constructed binary plots of grain size parameters to compare the dune sand systems in Oaxaca with some others in Mexico. Based on the sedimentary results and the Weibull distributions, we conclude that the grain sizes of the coastal dune sands from Oaxaca, Mexico, are controlled by the sand composition, wind patterns, hydrodynamic conditions, weathering effects, and physical characteristics, regardless of the dune geomorphology. Evidence of multicycle aeolian transport of sand particles in the Oaxaca coastal dunes is supported by the compositional framework of the sands and the roundness of sand grains. [Display omitted] • Oaxaca's coastal dunes in Mexico develop under complex geological and physical conditions. • The Weibull analysis supports the polymodal distributions in the Oaxaca's coastal dune sands. • Dune morphology seems not to control the diversity in grain sizes of the coastal dune sands. [ABSTRACT FROM AUTHOR]

The late Paleocene to earliest Eocene sedimentary record in the eastern Tremp-Graus Basin (southern Pyrenees, Spain) consists of a mud-prone fluvial succession informally known as 'Upper Red Garumnian', which is dominantly composed of non-channelized deposits interspersed with fluvial channel bodies. The succession records evidence of variations in water discharge at multiple temporal scales. One-hundred-and-eighty sand-prone and conglomeratic bodies present within otherwise fine-grained deposits have been examined by facies and architectural-element analyses. These have been assigned to four distinctive types: (i) simple and (ii) compound channelized deposits, (iii) multilateral and multistorey elements, and (iv) sediment gravity-flow deposits. Simple and compound channel bodies represent deposits of channelized high-energy flows associated respectively with single floods or multiple events occurring in the same channel belt. Multilateral and multistorey elements are associated with sedimentation in longer-lived channel belts. An increase in the occurrence of these latter elements through the stratigraphy can be related to changes in tectonic and/or climatic drivers, heralding a change in facies architecture that signifies a shift to perennial discharge conditions and incised-valley backfilling. This is itself followed by a marked change in architectural style in a part of stratigraphy recording the Paleocene-Eocene Thermal Maximum (PETM), when variations in precipitation regime and/or intrabasinal characteristics (e.g., vegetation) related to this event favoured the lateral migration of channels, causing the development of laterally extensive coarse-grained bodies. Floodplain sediments comprise (i) heterolithic deposits accumulated in the vicinities of the fluvial channels where riparian ecosystems were developed, and (ii) overbank mudstones with variable degree of pedogenesis, especially associated with wetting and drying cycles in areas of the floodplain located distally away from fluvial channels. This succession records the importance of water-discharge variations in the evolution of alluvial systems: it displays facies arrangements recording the effects of highly variable discharge in ephemeral to perennial channels, as well as variations in stratigraphic architecture testifying to longer-term hydrological changes in the late Paleocene and earliest Eocene. • Facies and architectures of Paleogene alluvial strata of the Tremp-Graus Basin (Spain) demonstrate flow processes. • The succession records discharge variability at multiple temporal scales. • Stratigraphic variations are interpreted in terms of allogenic forcing by climate and base level. [ABSTRACT FROM AUTHOR]

Abstract: The impressive 2000m thick conglomerates of the Bucegi Formation exposed in the southernmost part of the Eastern Carpathians were interpreted initially as large alluvial fans, and later suggested to be deposited as deepwater submarine-slope deposits. However, the routing system of the coarse sediment transfer from the source area to the deepwater slope (source-to-sink analysis) has not been explained and the mechanisms involved in the shelf sediment storage and bypass onto the slope have not been discussed. The present research on the Albian Bucegi Formation has provided the following new insights on their source-to-sink aspect: (1) that the Upper Member of the Bucegi Formation, with its frequent channelized and sheet like fine conglomerates and sandstones, contrasts greatly with the Middle and Lower members of deepwater slope and basin-floor origin. The Upper Member is interpreted as fluvial and shallow-marine deposits that were temporarily stored and reworked on a ‘shelf’, albeit a narrow one, bridging the area between the deforming hinterland and the deepwater slope deposits; (2) the Upper and Middle members are genetically linked and developed through the basinward migration of a large-scale (hundreds of metres in amplitude) clinoform with relative flat-lying topsets and slightly steeper (few degrees), coarser grained slopes that built out to the south and southeast; a configuration that is common along continental margins and also generally along all types of deepwater basin margins; (3) the Middle Member contains a range of submarine, sediment density flows that vary from high-density, mobile debris flows to lower-density sandy turbidites. The sediment textures (sorted grain populations) inherited from the shelf ‘sorting factory’ can to some extent still be recognised in the slope stratigraphy; and (4) the large (10–20m diameter) carbonate and metamorphic olistoliths that are ubiquitous on the shelf and (to a lesser extent) slope, reflect the steep gradients and very active tectonic setting of the fractured and thrusted hinterland, from which these outsized blocks were transported onto the adjacent shelf. The now-proposed, narrow shelf platform of the Albian Bucegi basin margin thus functioned to temporarily store sands and gravels, to distinctly sort some of this sediment, and to eventually bypass both sorted and new flood-generated, unsorted materials onto the slope. Compared with other basin margins, this Albian Bucegi margin was extremely coarse grained because of its proximity to the actively deforming mountain range, to a fractured basement that produced more gravel than sand, to the great sediment flux from steep short rivers, and to the narrowness (10–20km) of the shelf. [Copyright &y& Elsevier]

Abstract: Calcareous tufa, as well as other types of continental carbonates, are largely sensitive to climate variations. As a consequence, the relationship between climate variations and tufa deposition is relatively well known and calcareous tufa deposits are often used as a reliable climatic proxy in many geological settings. Conversely, the response of tufa to tectonics and uplifting processes is relatively poorly known, due to their genetic independence from geothermally heated groundwater springs and associated tectonic-controlled upwelling conduits in tectonically active settings. The aim of this paper is to describe a peculiar stratigraphic succession where calcareous tufa deposits are closely associated and interbedded with coarse-grained clastic deposits. The study area is located in southern Tuscany (Massa Marittima), where extensional tectonic processes, responsible for the emplacement of magmatic bodies at shallow crustal levels, have been active from Pliocene to Quaternary age, and caused a diffuse uplift as well as local volcanic eruptions and hydrothermal fluid circulation. The succession described in the paper recorded phases of calcareous tufa-dominated deposition (i.e. overall, medium/low hydrodynamic energetic settings) repeatedly interbedded with coarse-grained clastic fluvial sediments which testify an abrupt change in both the energy of the depositional environment and the sediment supply. Nevertheless, during the phases dominated by clastic sedimentation, tufa deposition was not inhibited as it would be expected for climate-influenced settings, suggesting that the observed stratigraphic settings were a consequence of a local uplift of the catchment area. These findings indicate that calcareous tufa deposits could be a sensitive proxy to tectonics when they are associated with coarse-grained clastic deposits, in a geological setting where the origin of the clastic sediments cannot be explained by autocyclic or climate-induced factors. [Copyright &y& Elsevier]

Abstract: During the Early Pleistocene, fluvial, alluvial and aeolian depositional systems interacted in the central Ebro Basin, Spain, constructing wide alluvial plains over a Neogene evaporite substratum. Fluvial sediments, mainly longitudinal gravel bars and channels, are interdigitated with gravel mass flow and distal mudflat deposits. Aeolian sedimentation is registered as aeolian dunes and sand sheets. Episodes of fluvial deposition alternated with periods of alluvial fan progradation and aeolian deposition. These changes are related to climate-driven water availability. Stratigraphic units and deformation structures show synsedimentary karstification of the evaporite substratum that, although karst was not restricted to any particular climate scenario, was probably favoured during periods of high water availability. Karstification conditioned the development of local sedimentary depocentres which, in turn, influenced the distribution of sedimentary subenvironments as well as the accumulation and preservation of aeolian dunes and lacustrine–palustrine deposits. Stratigraphic architecture shows that thickening of the series due to karst subsidence did not occur homogeneously, but was controlled by diachronous subsidence resulting in numerous angular unconformities. In subsiding karst areas transport capacity was reduced and sediment preservation increased. [Copyright &y& Elsevier]

Abstract: Submarine channels with intricate meandering patterns and extensive levees are recognized as products of density-driven flows known as turbidity currents. Compared to the fluvial meandering channels, understanding of the flow and morphodynamics of submarine channels is limited. In this paper, we present experimental results on the morphodynamic and stratigraphic evolution of a submarine channel from sedimentation due to the passage of successive flow events. A pre-formed sinuous channel with multiple bends, a trapezoidal cross section, and an initial thalweg slope of 0.43° was emplaced in a large tank. A total of 29 runs, each lasting an hour, were made by releasing heavier fluids containing salt and silica powder at a constant rate in the tank filled with fresh water. The overbank flow was restricted to curvature-induced flow stripping. The following observations were made from the experimental measurements; (i) asymmetric channel cross sections developed due to higher deposition rates on the outer bank of the channel bends, (ii) an apron or sediment wedge with overlain bedforms appeared near the channel entrance that prograded and aggraded with successive runs, (iii) overbank flow due to flow stripping at bend apices resulted in lobe-shaped deposits, (iv) a higher concentration of solute resulted in flow confinement, and (v) the flow velocity during later runs increased due to channel narrowing and steepening of the gradient. [Copyright &y& Elsevier]