Shallow-marine massive sandstone sheets as indicators of palaeoseismic liquefaction — An example from the Ordovician shelf of Central Bolivia
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Siliciclastic
<p>The interplay between carbonate production and siliciclastic input in marine mixed depositional systems results in spatially complex distribution of facies. In this study, we investigate this interplay in a lacustrine setting to explore hypotheses for the facies distribution and stratigraphic architecture in such settings. The Yacoraite Formation (Maastrichtian-Danian) is a mixed lacustrine carbonate-siliciclastic succession within the Salta Group in the Salta rift Basin (Argentina). The Yacoraite Fm has been thoroughly characterized in the southern part of the basin (Met&#225;n-Alemania sub-basins), whereas the northern sub-basin of Tres Cruces, focus of this study, remains largely understudied. In this project we applied high-resolution stratigraphic and sedimentological analyses to characterize in detail the depositional environment and the stratigraphic architecture of the Yacoraite Fm. Facies are mainly represented by lacustrine marginal and littoral associations. The facies associations, their distribution and stacking pattern are interpreted to reflect deposition in a predominantly shallow water balanced-fill lake basin type. Littoral and sub-littoral facies associations are dominated by oolitic, skeletal and microbial carbonates, frequently intercalated with fine-grained siliciclastic facies, ranging from mudstones and siltstones deposited in mudflats, shoreline sandstone deposits and distal profundal shales. The Yacoraite Fm is tentatively subdivided in two intervals. The lower part (lower 100 m) is characterized by carbonate-dominated facies, showing a marked and regular cyclicity, with metric-scale sequences of carbonate-dominated facies overlying fine-grained siliciclastics and mudstone-wackestone. These cycles are interpreted as shallowing-upwards cycles, composing the regressive hemicycles of metric-scale Transgressive-Regressive (T-R) cycles. These cycles are often asymmetric and result from lacustrine expansion-contraction cycles, controlled by climatically influenced lake-level fluctuations. The middle-upper part (m 100 to 220 circa) is dominated by siliciclastic facies and is characterized by a decrease in regularity of cyclicity, with high frequency T-R cycles being asymmetric and often lacking the transgressive hemicycles. Frequent desiccation cracks and tepees mark the top of the regressive hemicycles in the middle to upper part, indicating repeated sub-aerial exposures. Our observations are in line with the hypothesis that alternating phases of deposition between clastic-dominated facies and carbonate-dominated facies are the result of climatically driven lake-level fluctuations. Carbonate production is enhanced during arid climatic phases (lake contraction), whereas siliciclastic-dominated facies are mainly deposited during humid phases, coeval with an increase of water inflow and sediment input into the lake, corresponding to expansion phases. Based on our sedimentological and stratigraphical analysis the evolution of the lake system has been inferred, with the identification of two lake stages in the evolution of the Yacoraite paleo-lake. A first lake stage is characterized by a perennial lake system that progressively changes into a more rapidly fluctuating ephemeral setting; this shift appears to be gradual as there is no clear stratigraphic expression corresponding to the transition itself. Climate appears to be the primary control on the stratigraphic architecture, with rapid lake-level variations resulting in sharp facies transitions from carbonate to siliciclastic facies and prevalently stratigraphic mixing. Compositional mixing is limited to the littoral facies, due to the local presence of siliciclastic input sources by riverine inflows into the Yacoraite paleo-lake system.</p>
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We propose to use the 3D voxel based unsupervised seismic facies classification to identify vertical facies variations within a turbidite reservoir. The technique was applied to a real data from a deep water field in the Campos basin, Brazil, and the results were compared with other classical facies analysis method, with similar results.
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Siltstone clasts are commonly known from turbidites in deep-water successions and have been interpreted to document information regarding depositional processes of host sandstones. Here we studied formative processes of siltstone clasts on the basis of size and fabric of siltstone clasts and of host sandstones.Although siltstone clasts generally exhibit imbrication dipping to upslope directions regardless of depositional features of host sandstones, their size, density, and position in a turbidite bed are variable in response to vertical variations in grain size and grain fabric of host sediments. Therefore, the variation in size, density, and position of siltstone clasts in a single turbidite bed is interpreted to be controlled by temporal variations in the relative rates of suspended-load fallout during a single depositional process of sandstone beds from turbidity currents.
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Siltstone clasts are commonly known from turbidites in deep-water successions and have been interpreted to document information regarding depositional processes of host sandstones. Here we studied formative processes of siltstone clasts on the basis of size and fabric of siltstone clasts and of host sandstones.Although siltstone clasts generally exhibit imbrication dipping to upslope directions regardless of depositional features of host sandstones, their size, density, and position in a turbidite bed are variable in response to vertical variations in grain size and grain fabric of host sediments. Therefore, the variation in size, density, and position of siltstone clasts in a single turbidite bed is interpreted to be controlled by temporal variations in the relative rates of suspended-load fallout during a single depositional process of sandstone beds from turbidity currents.
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Siltstone
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Lithostratigraphy
Sequence (biology)
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Abstract Submarine or sub-lacustrine lobe deposits are important reservoirs, but the fan fringe deposits form heterogeneities within deep water fan deposits. Fan fringe facies records the complex sediment gravity flow types. By understanding of the bed types and flow mechanisms, we can identify the fan fringe deposit, which aids in the reconstruction of deep water fan and reservoir evaluations. The Jiucaiyuanzi and Dalongkou sections in the West Bogda Mountains preserve well-exposed 536-m and 171-m thick successions, respectively, of a deep water lacustrine depositional system from the Middle Permian Lucaogou Formation. Bed types of the Lucaogou Formation include high-density turbidite, low-density turbidite, incomplete Bouma-type turbidite, hybrid event beds, and slump deposits. The Lucaogou Formation is interpreted here as a fan fringe facies due to the thin bed thickness that characterize turbidites and hybrid event beds, as well as the predominance of the isolated sheet architecture. Previous studies suggest that these deposits were considered as deposited in a deep water setting due to the absence of wave-related structures. The presence of abundant mud clasts in massive medium-coarse grained sandstone beds reflects the significant erosional capability and interactions between high-density turbidity currents and lake floor. The fan fringe facies here contains amalgamated and thick-bedded homolithic facies (~ 30%) and thin-bedded heterolithic facies (~ 70%). The examination of the bed type is of wider significance for facies prediction and reservoir heterogeneity in the sub-lacustrine fan fringe facies.
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Abstract The Batocrinidae are characteristic faunal elements in Lower Mississippian shallow-marine settings in North America. Recent delineation of objectively defined genera allows a reexamination of batocrinid species and their distribution in the Fort Payne Formation (early Viséan, late Osagean), a well-studied array of carbonate and siliciclastic facies. The Fort Payne batocrinid fauna has 14 species assigned to six genera, plus hybrid specimens. Magnuscrinus spinosus (Miller and Gurley, 1895a) is reassigned to its original placement in Eretmocrinus . Hybrid specimens (Ausich and Meyer, 1994) are regarded as Eretmocrinus magnificus × Eretmocrinus spinosus . Macrocrinus casualis is the dominant species of Macrocrinus in the Fort Payne, and M . mundulus and M . strotobasilaris are recognized in the Fort Payne Formation for the first time. Magnuscrinus cumberlandensis n. sp. is named, 13 species are designated as junior synonyms, the name for the hybrid specimens is changed to Eretmocrinus magnificus × Eretmocrinus spinosus , and the previous occurrences of two species in the Fort Payne are rejected. The Eastern Interior Seaway was a mixed carbonate-siliciclastic setting with both shallow- and deep-water epicontinental sea facies ranging from relatively shallow autochthonous green shales to deep-water turbidite facies. Dizygocrinus was restricted to shallow-water carbonate and siliciclastic facies, Eutrochocrinus was restricted to shallow-water carbonate facies, and Magnuscrinus was restricted to deep-water facies. Species distributions varied from Abatocrinus steropes , Alloprosallocrinus conicus , Macrocrinus mundulus , and Uperocrinus nashvillae , which occurred throughout the Eastern Interior Seaway, to species that were restricted to a single facies. Eretmocrinus magnificus , Alloprosallocrinus conicus , and Uperocrinus robustus were the dominant batocrinids in the Fort Payne Formation. UUID: http://zoobank.org/703aafd8-4c73-4edc-9870-e2356e2d28b8
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Carbonate platform
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Siliciclastic
Submarine canyon
Continental Margin
Carbonate platform
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Upper Cretaceous mixed carbonate-siliciclastic sequences are among the most important targets for hydrocarbon exploration in the Moghan area, located in the eastern Para-Tethys Basin. Despite of their significance, little is known about their facies characteristics and depositional environments. Detailed facies analysis and paleoenvironmental reconstruction of these sequences have been carried out in eight surface sections. Accordingly, four siliciclastic facies, eight carbonate facies and one volcanic facies have been recognized. Detailed facies descriptions and interpretations, together with the results of facies frequency analysis, standard facies models and Upper Cretaceous depositional models of Para-Tethys Basin, have been integrated and a non-rimmed carbonate platform is presented. This platform was affected by siliciclastic influx, in the form of coastal fan delta and submarine fans in the shallow- to deep-marine parts, respectively. This model is interpreted to be shallower in the central and northeastern parts of the Moghan area. Toward the southeast and southwest, this shallow platform turns into deep marine settings along steep slopes without remarkable marginal barriers.
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