The Late Triassic Sequence-Stratigraphic Framework of the Upper Yangtze Region, South China

Abstract

In the transitional period between the Middle and the Late Triassic, the Indochina orogeny caused two tectonic events in South China: (1) the formation and uplift of the Qinling‐Dabie orogenic belt along the northern margin of the South China Plate, due to its collision with the North China Plate; and 2) the development of a 1300‐km‐wide intra‐continental orogen in the southeastern part of the South China Plate, which led to a northwestward movement of the foreland thrust‐fold zone. These tectonic events resulted in the ending of the Yangtze Platform, and were a stable paleogeographic factor from the Eidacaran to the end of the Middle Triassic. This platform was characterized by the widespread development of shallow‐water carbonates. After the end of the Yangtze Platform, the upper Yangtze foreland basin (or Sichuan foreland basin) was formed during the Late Triassic and became a accumulation site of fluvial deposits that are composed of related strata of the Xujiahe Formation. In western Sichuan Province, the Xujiahe Formation overlies the Maantang Formation shallow‐water carbonate rocks of the Xiaotangzi Formation siliciclastic rocks (from shelf shales to littoral facies). The sequence‐stratigraphic framework of the Upper Triassic in the upper Yangtze foreland basin indicates a particular alluvial architecture, characterized by sequences composed of (1) successions of low‐energy fluvial deposits of high‐accommodation phases, including coal seams, and (2) high‐energy fluvial deposits of low‐accommodation phases, including amalgamated river‐channel sandstones. The spatial distribution of these fluvial deposits belonging to the Xujiahe Formation and its relative strata is characterized by gradual thinning‐out, overlapping, and pinching‐out toward both the east and south. This sedimentary record therefore expresses a particular sequence‐stratigraphic succession of fluvial deposits within the filling succession of the foreland basin. The sequence‐stratigraphic framework for the Upper Triassic in the Upper Yangtze region provides a record of the end of the Yangtze Platform and the formation of the upper Yangtze foreland basin.

Digging into the ancestral stocks of Jurassic lineages: ostracods (Crustacea) from Carnian (Late Triassic) sponge mounds from the Maantang Formation (South China)

“…It is tentatively dated to the Norian (Wu, 1989;Li et al, 2003) but diagnostic fossils are missing (Deng et al, 1982;Wu, 2009) so that its basal part could be of Tuvalian age (Shi et al, 2017). The remaining part of the Xiaotangzi Formation is made of fluvial sandstone with common horizontal, cross and ripple bedding (Wu, 1989;Mei and Liu, 2017). This formation contains rare macrofossils and few ammonoid fragments for age attribution.…”

Application of Strontium Isotopic Stratigraphy to Dating Marine Sedimentary Units: A Case Study from the Permian Stratotype Section in Southern China

“…The northern margin of the Upper Yangtze was adjacent to the Mianlue Ocean in the Permian period (Fig. 2b), and was a passive continental margin of the ocean (Feng et al, 1997;Dong et al, 2015;Dong and Santosh, 2016;Mei and Liu, 2017;Qu et al, 2018). During the initial Qixia stage, a widespread marine transgression in the Yangtze region submerged the Yangtze plate, which led to the formation of carbonate rocks on the Middle Permian stable platform (Feng et al, 1993;Yang and Feng, 2000;Zhu et al, 2004;Li et al, 2020).…”

New Discovery of Neocalamites from the Upper Triassic Daheba Formation in West Qinling, Northwest China

“…Neocalamites is a common plant fossil from the Triassic to the Middle Jurassic. Neocalamites fossils are commonly found in coal-bearing sedimentary rocks of Rhaetian stage from South China and the Yanchang Group from North China (Mei and Liu, 2017). Moreover, the fossils also distribute in the Late Triassic such as the Babaoshan Group in Dulan and Darigemole Group in Gangcha of Qinghai Province, the Haojiagou Formation in Turpan and the Taliqike Formation in Kuche of Xinjiang.…”