Highstand sublacustrine fans: The role of a sudden increase in sediment supply

Abstract

Contrary to widely used traditional sequence-stratigraphic models, highstand sublacustrine fans developed in the deep-water environment in the middle of the third member of the Eocene Shahejie Formation (Es3z, 42-40.5 Ma), Dongying Sag. Using four cores and 3D seismic data, we describe the sequence stratigraphy frameworks, sediment characteristics, depositional elements, and depositional model of the Liangjialou highstand sublacustrine fan. The Es3z is a complete third-order sequence stratigraphic, bounded by T4 at the top and T6 at the base. Between T4 and T6, there is the maximum flooding surface (MFS) distributed from proximal to distal of the system in the third-order stratigraphic sequence. Therefore, the Liangjialou Fan at the top of the Es3z, between MFS and T4, is a typical highstand sublacustrine fan as determined from seismic data. This highstand sublacustrine fan is characterised by gravel to fine-grained sand, abundant amalgamation surfaces, and crude stratifications common in coarsegrained structureless-to normal-graded sandstones. Climbing ripples and thin laminae rich in plant debris are common in inverse-then normal-graded sandstones. Channel-levee, channel-lobe transition zone, and lobes developed in this highstand sublacustrine fan, with clear internal progradation stacking patterns caused by hyperpycnal flow. The sudden increase in sediment supply in an accommodation decrease situation and the narrow shelf width are the primary controlling factors for forming highstand sublacustrine fans. In the late stage of the highstand systems tract, gravity-flow deposits caused by hyperpycnal flow are developed from another new point source to form this highstand sublacustrine fan.Hyperpycnal flow in lacustrine basins can transport coarse-grained sediments with the help of strong flood energy and steep slopes. Gravity flow deposits in lacustrine basins are not confined by sequence stratigraphy frameworks, and many additional areas of sand caused by hyperpycnal flow could be found in lacustrine basins.

Variability of sequence architecture in a rift margin controlled by tectonic activity: The Eocene Dongying Depression, Bohai Bay Basin, China

“…Flood-triggered deep-water systems (marginal subaqueous fan systems) and fan delta systems are well documented on the rift margin (Kra et al, 2022;Liu et al, 2022;Yang et al, 2023). These depositional systems are characterized by multi-depocenters and a variety of stacking patterns along the border of rift margin (Li et al, 2019(Li et al, , 2021.…”

Origin, Migration, and Characterization of Gas in the Xinglongtai Area, Liaohe Subbasin (Northeast China): Insight from Geochemical Evidence and Basin Modeling

“…This is particularly evident in lacustrine basins with substantial tectonic evolution and changes in sedimentary systems [41,42]. Within the Shahejie Fm, known for its deltaic-lacustrine and lacustrine-turbidite depositional environments [9,16,[43][44][45][46], we have identified six potential source rock types: Sublacustrine-Fan Mudstones (SFM), Fan-Delta Mudstones from the Western slope (FDM-W), Fan-Delta Mudstones from the Eastern slope (FDM-E), Semi-Deep Lake Mudstones (SDLM), Shallow Lake Mudstones (SLM), and Nearshore Subaqueous Fan Mudstones (NSFM).…”

Sedimentary characteristics and depositional model of hyperpycnites in the gentle slope of a lacustrine rift basin: A case study from the third member of the Eocene Shahejie Formation, Bonan Sag, Bohai Bay Basin, Eastern China

“…In contrast, the narrowed definition of hyperpycnal flow refers to quasisteady low-density turbidity current caused by flooding (Mulder & Alexander, 2001;Yang et al, 2019Yang et al, , 2020. Due to high-frequency of occurrence, long duration, thick and stable distribution of sediments and long transporting distance, hyperpycnal flow deposits are of great significance in the geological record and the formation of conventional and unconventional oil and gas reservoirs in deep-water environments (Mulder et al, 2003;Petter & Steel, 2006;Talling, 2014;Wilson & Schieber, 2014;Yang et al, 2017Yang et al, , 2020Yang et al, , 2023Zavala & Arcuri, 2016).…”

“…Previous research have demonstrated that deep‐water gravity‐flow could be triggered by the collapse of pre‐existing deposits (Mutti et al, 2009; Plink‐Bjӧrklund & Steel, 2004; Talling, Paull, & Piper, 2013). However, numerous research works have shown that flooding, as a common mechanism, plays an important role on the formation of deep‐water gravity‐flow (Lamb & Mohrig, 2009; Mulder et al, 2001, 2002, 2003; Mutti et al, 2009; Petter & Steel, 2006; Piper & Normark, 2009; Yang et al, 2023; Zavala, 2020; Zavala & Arcuri, 2016). Gravity‐flow deposits caused by flooding, are termed as hyperpycnal flow deposits or hyperpycnites (Mulder et al, 2003; Zavala, 2020).…”