Controls on the stratal architecture of lacustrine delta successions in low‐accommodation conditions

Abstract

Lake-delta deposits in low-accommodation conditions are only a few metres thick and in some cases non-existent. Fluvial channels occur in many cases directly on top of fine-grained lacustrine deposits with delta deposits apparently missing. The geomorphology and stratigraphy of modern deltas in Lake Eyre, Australia, and Lake Chad in Africa indicate that delta shorelines can develop in lakes, but in many cases build out into low-accommodation settings due to highly dynamic lake-water levels. This work suggests that low-accommodation is critical in the development of lacustrine delta deposits and that high (frequency and magnitude) rates of lake-level change result in 'telescoping' deltas, the deposits of which are thin but extensive. The telescopic deltas have conformable beds, but with abrupt vertical facies changes; this apparent stratigraphic contradiction is the result of long horizontal distance translation of the depositional system. Details of two lacustrine units, in Uinta Basin in the USA and Junggar Basin in China, both of which show characteristics of telescoping, are used to develop a process based stratigraphic model for the deposits of such lake deltas. Lacustrine facies comprise cross-stratified, ripple crosslaminated, structureless or graded and sharp-based sandstone beds, mudstone (structureless, laminated, rippled, rich in organic content), carbonate mudstone, ooid packstone and stromatolites. Three facies associations are critical for lake delta stratigraphy: channelized distributary deposits that occur in the delta topset; lake plain deposits that represent the fluvial overbank deposits and the subaerially exposed (at low lake level) lake deposits; and fine-grained, lacustrine deposits. A key corollary of the proposed low-gradient, telescoping lacustrine delta model is that broad and shallow channels dominate the system, but that decimetre to metre thick, gently dipping delta-front beds form subtle deposits along the margins of the lakes. These delta depocentres migrate basinward and landward at high rates (tens of kilometres each year), building thin (metres) but laterally extensive (tens of kilometres) sandstone units through multiple transgression-regression cycles.

Development and controlling factors of shale lithofacies cycles in a continental rift basin: A case study of Es4u in the Boxing Subsag of Dongying Sag, Bohai Bay Basin, China

“…The present results show that the typical Milankovitch cycle exists in many lacustrine deposits (Szurlies, 2007;Machlus et al, 2008;Abels et al, 2009;Walters et al, 2020). The Milankovitch cycle was also found in some continental deposits in China, such as the Late Cretaceous in the Songliao Basin (Wu et al, 2014) and the Middle Permian Lucaogou and Jingjingzigou formations and Late Triassic Yanchang Formation in the Ordos Basin (Zhang et al, 2019;Olariu et al, 2022). In the Jiyang Depression of the Bohai Bay Basin, the cyclical sedimentary records of the Paleogene Kongdian Formation include color meter-scale cycle, graded meter-scale cycle, and non-graded meter-scale cycle, which have been proved to be controlled by the Milankovitch cycle (Tan et al, 2015).…”

Multiple sediment source infill in a low-accommodation basin: implications for the late Paleozoic sediment routing system in the southeastern Ordos Basin

“…In the upper transgressive or highstand systems tracts (Figure 16), the mass sediments were transported by multiple S2S systems, which led to an overfilling process in the basin with low-accommodation space. Referring to the study of Olariu et al (2021), the low tectonic subsidence rate limits the rise in the accommodation space. Thus, we infer that the fine-grained sediments occupied the accumulation space in the sink area.…”

“…The above two types area characterized by high relief, while the last one is presented as a limited accommodation space area. Due to low-accommodation space, sediments are hardly preserved, and S2S system reconstruction is more difficult (Allen & Fielding, 2007; Spengler & Read, 2010; Halla et al 2020; Olariu et al 2021). Furthermore, basins with low-accommodation space are characterized by rapid and frequent lake level changes (Allen & Fielding, 2007; Olariu et al 2021), which may complicate the reconstruction of the S2S system.…”