A giant lacustrine flood‐related turbidite system in the Triassic Ordos Basin, China: Sedimentary processes and depositional architecture

Abstract

Turbidites have been regarded as an important sedimentary infilling component in both oceans and lakes, but limited studies have been performed on the mechanisms governing the initiation and development of lacustrine turbidite systems. The present study offers unique insight into the controls and potential extent of ancient lacustrine turbidite systems by an investigation of the Triassic Ordos Lake, where a large turbidite system had been traced across >25 653 km 2 . This article shows by comparison that the Triassic Ordos Lake turbidite system is larger than all known modern and ancient lacustrine counterparts. The exceptionally large intracontinental sag basin provided a relatively unconfined environment for the development of the turbidite system, explaining its vast extent. Extraordinary flood events formed during the Carnian Pluvial Episode facilitated continuous sediment supply into the turbidite system, supporting its accumulation. Lacustrine flood-related turbidity currents travelled as sediment-laden turbulent flows, showing an increase in the proportion of suspended-load deposits and a decrease in the proportion of bed-load deposits downstream from the river mouth. Five architectural elements have been revealed, reflecting a distinctive assemblage of erosional bedforms and depositional bedforms in channel-lobe systems, and their recognition criteria were established. This study changes the traditional understanding of lacustrine turbidite systems, generally interpreted as having smaller sizes, and demonstrates likewise in the lacustrine realm, that extreme flood events can generate a world-class deep-water turbidite system, which can even be comparable with its submarine counterparts. This study also confirms that the combination of lowgradient slopes and a long-lived, mixed-load, prograding fluvial feeder system can produce exceptionally large-scale deep-lake flood-related turbidites. Furthermore, it has implications for the prediction of facies and reservoir quality in ancient lacustrine turbidite systems.

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

“…Hyperpycnites in depression basins have been widely reported, such as that in the Ordos Basin (Chen et al, 2021; Xian et al, 2018; Yang et al, 2017), and the Songliao Basin (Dou et al, 2021; Pan et al, 2017) in China. This study demonstrated that there are many differences between hyperpycnites in rift basins and depression basins (Yang et al, 2020).…”

“…This study demonstrated that there are many differences between hyperpycnites in rift basins and depression basins (Yang et al, 2020). Hyperpycnites in depression basins are usually dominated by fine‐grained sandstone, with distinct channel‐lobe system and long transport distance more than 100 km (Chen et al, 2021; Dou et al, 2021; Pan et al, 2017; Xian et al, 2018; Yang et al, 2017). However, hyperpycnites in rift basins are characterized by a wide range of grain size range from gravel to fine‐grained sands (Figure 3) (Liu et al, 2021; Yang et al, 2019, 2020; Yuan et al, 2019).…”

“…In lacustrine rift basins, hyperpycnal flows are more likely to occur because of strong tectonic activity, small basin area, low water density, large terrain height difference and development of small rivers (Chen et al, 2021;Dou et al, 2021;Mulder et al, 2003;Mulder & Chapron, 2011;Pan et al, 2017;Soyinka & Slatt, 2008;Xian et al, 2018;Yang et al, 2017Yang et al, , 2020Zavala, 2020;Zavala et al, 2006Zavala et al, , 2011. It thus provide a natural laboratory to resolve the controversies about the identification marks and transport evolution processes of hyperpycnal flow deposits.…”

Deep‐water sand transfer by hyperpycnal flows, the Eocene of Spitsbergen, Arctic Norway

“…For these reasons, hyperpycnal flow deposits (‘hyperpycnites’) are commonly described from various lacustrine and glacio‐deltaic successions, reflecting the favourable conditions for dense underflows to form in these environments (e.g. Nemec et al ., 1999; Zavala et al ., 2006; Girard et al ., 2012; Yang et al ., 2017; Cao et al ., 2018; Bellwald et al ., 2020; Chen et al ., 2021). Despite recent developments in the surveillance of naturally occurring turbidity currents (Clare et al ., 2016; Azpiroz‐Zabala et al ., 2017; Hage et al ., 2019; Maier et al ., 2019; Heijnen et al ., 2020; Heerema et al ., 2022; Pope et al ., 2022; Talling et al ., 2022), monitoring data of hyperpycnal flows in the marine realm is relatively sparse.…”

“…In addition, there is a growing body of literature describing hyperpycnites in ancient and modern submarine lobes, suggesting that hyperpycnal flows may transfer sand into deep‐water environments (e.g. Mutti et al ., 2003; Bourget et al ., 2010; Zavala et al ., 2012; Warrick et al ., 2013; Chen et al ., 2021). This is enigmatic, because it has been shown that hyperpycnal flows entering marine basins typically deposit their sandy load near the river mouth (e.g.…”