Sedimentology of the Upper Pennsylvanian organic‐rich Cline Shale, Midland Basin: From gravity flows to pelagic suspension fallout

Abstract

Although deep‐water fine‐grained sedimentary rocks comprise approximately two‐thirds of the stratigraphic record, the transportation and depositional processes are poorly understood compared with their shelf counterparts. This study reports the range of fine‐grained sedimentary rock lithofacies, transport, and depositional processes and cyclicities recorded in deep‐water deposits on the basis of three continuous cored wells from the Upper Pennsylvanian Cline Shale, Midland Basin, USA, with the goal of elucidating general principles that can inform synthesis depositional models for deep‐water fine‐grained sedimentary systems. A combination of sedimentological, petrographic and bulk geochemical analysis has defined seven lithofacies that stack in a repeated pattern to constitute ca 8 to 20 m thick composite cycle sets. The lower unit of each composite cycle set is characterized by basal siliciclastic‐rich lithofacies interpreted to record dilute, low‐density turbidity currents, potentially derived from hyperpycnal input which grade upward into carbonate‐rich lithofacies interpreted as debris‐flow deposits or pelagic suspension deposits. The upper unit of each composite cycle set is characterized by basal carbonate‐rich lithofacies interpreted as debris‐flow deposits or pelagic suspension deposits which grades upward into siliciclastic‐rich lithofacies interpreted to record dilute, low‐density turbidity currents, potentially derived from hyperpycnal input. The cyclicities recorded in the Cline Shale are believed to be controlled by high‐amplitude glacioeustatic sea‐level fluctuation (mean: ca 100 m). The siliciclastic‐rich lithofacies, potentially derived from hyperpycnal turbidity flows, were deposited during sea‐level lowstand, when siliciclastic sediment‐transport systems extended across the wide Eastern Shelf and deltas developed at the shelf margin. Carbonate‐rich lithofacies are interpreted to be deposited from debris flows or pelagic suspension fallout during sea‐level highstand when carbonate platforms were developed on the surrounding shelves. The prevalence of sediment density flow deposits, even in distal basin floor environments, challenges the conventional model that deep‐water fine‐grained sedimentary rocks are dominantly background sedimentation.

Shale Lithofacies and Sedimentary Environment of the Third Member, Shahejie Formation, Zhanhua Sag, Eastern China

“…Most shale lithofacies categorizations have mainly been based on lithology and sedimentary structures (Abouelresh and Slatt, 2012;Peng, 2021;Peng et al, 2021).…”

“…Lithofacies is the most important indicator of the sedimentary characteristics and environments of shale. The most important parameters for lithofacies description are lithology, sedimentary structures and their combinations (Loucks and Ruppel, 2007;Katz et al, 2014;Peng, 2021;Peng et al, 2021). The Es3 member in the Zhanhua Sag shows typical shale lithology, sedimentary structure and combination characteristics.…”

“…In addition to some geochemical parameters revealing physical and chemical properties of the water column, lithofacies analysis is a very important tool to reconstruct sedimentary environments (Macquaker and Gawthorpe, 1993;Loucks and Ruppel, 2007;Bohacs et al, 2014;Lazar et al, 2015;Bhattacharya et al, 2016;Li et al, 2018). Many researchers have studied lithofacies packages and characteristics of shale in various sedimentary basins from the perspectives of mineralogy, structure, biological facies and structural characteristics (Macquaker and Adams, 2003;Hickey and Henk, 2007;Liu et al, 2012;Abouelresh and Slatt, 2012;Roban and Dobrinescu, 2012;Yang et al, 2016;Zhang et al, 2018;Peng, 2021;Peng et al, 2021). For example, three lithofacies were recognized in the Barnett Shale in the Fort Worth Basin, Texas, which involved some sedimentary processes such as hemipelagic mud plumes, dilute turbidites, and debris flows (Loucks and Ruppel, 2007).…”

“…Mudstone and shale can serve as sources, seals of hydrocarbons, even as economic reservoirs. Worldwide, much attention has been paid to research into the sedimentary characteristics of mudstone and shale (Peng, 2021Zhu et al, 2021). With the exploration for unconventional hydrocarbons, it has been observed that shale deposits in a relatively deep water environment have complicated mineral compositions, sedimentary structure, sedimentary sequences, sedimentary dynamic processes and sequence stratigraphic architecture, etc.…”

Molecular dynamics simulation of the surface wettability of typical minerals in shale

“…As a result of the interaction of the surface tension of each phase, the wetting phase fluid preferentially attaches to the surface of solid particles and occupies narrow pore channels, whereas the nonwetting phase fluid tends to flow into the middle of pores. The hydrophilicity of organic matter and clay minerals will affect the distribution and fluidity of the water phase in pores of different scales, thus affecting the continuity and fluidity of oil (Li et al, 2020; Peng, 2021; Yassin et al, 2016; Zhang et al, 2023). If the shale reservoir is lyophilic, crude oil can be adsorbed or wetted on the pore throat surface of the reservoir.…”