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This study offers new insights into the internal architecture of shallow marine carbonate sediments deposited in an epeiric sea formed on a broadly flooded passive margin continental shelf. The Ullayah Member of the Late Jurassic Hanifa Formation is exposed along the Tuwaiq Mountain Escarpment in Central Saudi Arabia and serves as an example. High‐resolution drone imagery over a 4 × 4 km2 wadi system, measured‐sections and thin‐section petrography are utilized to develop the three‐dimensional architecture of the lagoonal sediments deposited in an inner‐ramp setting. Parasequence sets have been mapped on the digital outcrop models that demonstrate a high degree of lateral and vertical thickness variability associated with stromatoporoid/coral buildups and inter‐buildup sediments. The stromatoporoid/coral buildups have been interpreted to be deposited during the late Transgressive Systems Tract and Highstand System Tract. The positive relief developed by the stromatoporoid/coral buildups resulted in hydrodynamic acceleration of currents in the inter‐buildup areas, which limited sediment deposition. The incomplete filling of the inter‐buildup areas led to an undulating topography, which significantly influenced depositional architecture in the next parasequence set. This theme of sediment filling, also referred to as compensational stacking, was repeated over the next two parasequence sets, with an overall decreasing accommodation towards the late highstand, eventually levelling the uneven topography at the top of the Ullayah Member. The study offers insights into the processes of sediment accumulation in an inner ramp lagoon and/or on a flat‐top shallow marine epeiric carbonate shelf. Although accumulation is cyclic, neither strict facies patterns nor uniform cycle thicknesses can be discerned on a kilometre scale. This insight potentially provides a reason for the frequently debated correlation of cycles and facies patterns in carbonate sequences in shallow epeiric seas. [ABSTRACT FROM AUTHOR]

Abstract This study aims to interpret and document the depositional architecture styles and sequence stratigraphic framework of the Ash Shumaysi Formation in the Jeddah‐Makkah region, the west‐central part of Saudi Arabia, and presents an example of rarely discussed, local‐scale sub‐basins (half grabens). It also shows the relationships between synchronous sedimentary processes and pre, syn and post‐rift conditions. The described lithofacies and their facies associations indicate the presence of seven architectural depositional styles: proximal‐distal braided fluvial, meandering fluvial (point bar), crevasse splay, floodplain, estuarine and lacustrine. A proposed depositional model for the Ash Shumaysi Formation is drawn. The Ash Shumaysi Formation forms a second order depositional sequence, which is organised into two third order depositional sequences (sequences I and II) bounded by three sequence boundaries. Each third‐order sequence encloses the low accommodation systems tract and high accommodation systems tract. The low accommodation systems tract represents the coarse‐grained, braided‐distal fluvial facies developed during low accommodation space associated with high sediment supply (high discharge). The high accommodation systems tract encloses the fine‐grained deposits of point bar, estuarine and lacustrine facies that reflect the creation of significant accommodation space and low sediment supply (low discharge). Vertical and lateral variations of the inferred depositional architectural styles, sequences and systems tracts reflect that tectonic forces and climate are the main controlling factors during deposition of the Ash Shumaysi Formation, although base‐level changes in response to sea‐level changes cannot be ruled out.

This study aims to interpret and document the depositional architecture styles and sequence stratigraphic framework of the Ash Shumaysi Formation in the Jeddah‐Makkah region, the west‐central part of Saudi Arabia, and presents an example of rarely discussed, local‐scale sub‐basins (half grabens). It also shows the relationships between synchronous sedimentary processes and pre, syn and post‐rift conditions. The described lithofacies and their facies associations indicate the presence of seven architectural depositional styles: proximal‐distal braided fluvial, meandering fluvial (point bar), crevasse splay, floodplain, estuarine and lacustrine. A proposed depositional model for the Ash Shumaysi Formation is drawn. The Ash Shumaysi Formation forms a second order depositional sequence, which is organised into two third order depositional sequences (sequences I and II) bounded by three sequence boundaries. Each third‐order sequence encloses the low accommodation systems tract and high accommodation systems tract. The low accommodation systems tract represents the coarse‐grained, braided‐distal fluvial facies developed during low accommodation space associated with high sediment supply (high discharge). The high accommodation systems tract encloses the fine‐grained deposits of point bar, estuarine and lacustrine facies that reflect the creation of significant accommodation space and low sediment supply (low discharge). Vertical and lateral variations of the inferred depositional architectural styles, sequences and systems tracts reflect that tectonic forces and climate are the main controlling factors during deposition of the Ash Shumaysi Formation, although base‐level changes in response to sea‐level changes cannot be ruled out. [ABSTRACT FROM AUTHOR]

Sedimentary processes of marine turbidite systems under sea-level changes have been the focus of deep-water sedimentology. Compared with well-studied marine basins, the products of deep-water sediment gravity flows responding to lake-level changes in closed lacustrine basins are still poorly understood. In this study, we integrate cores of 10 exploratory wells, logs of 280 development wells, 3D seismic data and geochemical elements from the Eocene Dongying Depression, Bohai Bay Basin, East China to investigate sedimentary mechanisms and depositional architecture of lacustrine turbidite systems under lake-level changes. The studied strata are divided into three parasequence sets (PSS4 ~ PSS2), corresponding to early highstand normal regression with ascending trajectories, late highstand normal regression with flat trajectories, and forced regression with descending trajectories, respectively. From early highstand normal regression to forced regression, the ratios of Fe/Mn and U/Th reveal that the humid climate shifted to the arid climate. More lithofacies clues indicate that turbidites in highstand normal regression were triggered by river floods, whereas counterparts in forced regression were related to sediment failures. There are different architectural features of turbidite systems in three regression stages. PSS4 developed a series of channel belts within which individual channel elements are aggraded vertically. PSS3 is composed of a channelized lobe formed by individual distributary channels migrating laterally. PSS2 is characterized by a suite of compensational stacking debrite tongues. Climate forcing is a crucial factor controlling depositional architecture of the turbidite systems. A relatively humid climate during highstand normal regression led to rising lake-level and frequent floods, which are conducive to the formation of hyperpycnal-fed channel-lobe systems. Nevertheless, during forced regression under an arid climate, the strong progradational clinothems were prone to failure and sediment remobilization, resulting in debrite tongue complexes. This study highlights depositional differences of lacustrine turbidites during regression stages under the control of climate. Meanwhile, it also provides a new predictive model for deep-water hydrocarbon exploration and production in lacustrine basins worldwide. • Lacustrine turbidites in highstand normal regression were induced by river floods. • Lacustrine turbidites in forced regression were triggered by sediment failures. • Lake-level changes control stacking patterns of lacustrine turbidite systems. • Climate forcing controls triggering mechanisms of lacustrine turbidites. [ABSTRACT FROM AUTHOR]