The coupled evolution of depositional systems and paleo-redox conditions was recorded in terminal Ediacaran sedimentary succession in the Tarim Block, NW China

The terminal Ediacaran was a critical period in Earth history due to the coincidence of climate change, seawater chemistry variability, biological innovation, and tectonic activity. The Wushi-Aksu area in the NW Tarim Block contains widely distributed terminal Ediacaran outcrops, providing important sedimentological and paleoenvironmental information. A detailed investigation of the Ediacaran Xiaoerbulake-Xigou (XG) and Shayilike (SA) outcrop sections in the NW Tarim Block identified 14 types of lithofacies: mudstone (F1), sandstone (F2), conglomerate (F3), mixed siliciclastic-dolomicrite (F4), mixed siliciclastic-dolograinstone (F5), mixed siliciclastic-dolo-oolite (F6), dolomicrite (F7), dolograinstone (F8), dolo-oolite (F9), planar-wavy stromatolitic dolomite (F10), domal stromatolitic dolomite (F11), stratiform-like thrombolitic dolomite (F12), domal thrombolitic dolomite (F13), and foamy microbial dolomite (F14). A model of the depositional evolution of the Ediacaran Qigebrak Formation in the study area was established, which indicates a shift in the depositional system from an early mixed carbonate-siliciclastic tidal-flat environment to a late carbonate platform, and the Tabei massif was confirmed as the provenance of terrigenous detrital input in early mixed tidal flats. The Ce anomalies of the carbonate fraction ranged from negligible (Ce/Ce* = 1.18 +/- 0.18) in the lower mixed carbonate-siliciclastic system to clearly negative (Ce/Ce* = 0.74 +/- 0.10) in the upper carbonate-platform facies, indicating the progressive oxidation of shallow seawaters. The coupled evolution of depositional systems and paleo-redox conditions may explain the positive anomaly of similar to 7 parts per thousand in the lower part of delta C-13(carb) profiles (i.e., in the mixed carbonate-siliciclastic facies). In the early mixed carbonate-siliciclastic system, terrigenous input provided nutrients, enhancing primary productivity and increasing the burial of organic carbon in the suboxic environment, resulting in an increase in C-13 levels in seawater and a positive (delta)13C(carb) anomaly. This study highlights the contribution of regional sedimentary environments to the positive (delta)13C(carb) anomaly, indicating that caution is necessary in its application in global Ediacaran correlations.