The Ordovician Retroarc Foreland Basin on the Yangtze Block Linked to the Final Assemblage of Gondwana

Abstract

Amalgamation of the Yangtze and Cathaysia blocks in the context of Gondwana assembly in the early Paleozoic has been addressed for decades, but the far-field effects on the Yangtze Block during the amalgamation remain unclear. In this study, we outline the sequence stratigraphic framework of the Ordovician succession in the central-upper Yangtze Block and analyze provenance records in sandstone compositions, distributions, and detritus zircon U-Pb dating. The Ordovician succession in the central-upper Yangtze Block is subdivided into six third-order sequences, which were deposited mainly in a carbonate platform with restricted sediments in Tremadocian to early Floian stages, mixed terrigenous-carbonate deposits in mid- to late Floian stages, and open circulation sediments in Dapingian to middle Katian stages. These sequences show the central-upper Yangtze Block experienced syn-tectonic deformation with northeast-trending long-wavelength uplift and depression alternatively and the depocenter shifting from the east during Tremadocian to mid-Floian stages to the southwest in late Floian to early Hirnantian stages. Provenance data indicate that detritus in the Ordovician succession was mainly from the northern India and Kangdian paleohighland to the southwest of South China Block. Incorporating the depositional and deformation variations, we propose a retroarc foreland basin that was developed on the South China Block in response to final suturing between the South China Block and East Gondwana at Sanya suture zone. The South China Block was thus involved in the global tectonics of the Gondwana supercontinental cycle during the Ordovician.

Reservoir characteristics and genesis of the Lower Ordovician Tongzi Formation in central Sichuan Basin, China

“…Due to the Late Cambrian Orogeny in South China (referring to Yunan Orogeny in Chinese literatures), the Upper Cambrian was exposed and formed the unconformity between the Upper Cambrian Xixiangchi Formation and the Lower Ordovician Tongzi Formation (Zhu et al, 2015). In addition, the top surfaces of Hunghuayuan, Linhsiang and Wufeng formations are defined as unconformities (Tang et al, 2022).…”

“…Stable isotopic compositions of dolostones from the Tongzi Formation are characterized by the enrichment with respect to δ 18 O (Tao et al, 2022), indicating the dolomitization fluids originated from evaporative environments. South China Block Frontiers in Earth Science frontiersin.org was located around the equator during the Ordovician, and gypsum were developed in the Lower Ordovician Taching Formation at the southwest of Yangtze Block (Tang et al, 2022), both of which suggest a geologic setting dominated by evaporation. Therefore, it is prone to forming a restricted and evaporative lagoon surrounded by shoals, providing penesaline seawater to cause reflux dolomitization of shoal grainy sediments (Figure 8).…”

Differences of Organic Matter Types of High Maturity Marine Organic-Rich Shale from Wufeng-Longmaxi Formation: Implication for Shale Gas “Sweet Spots” Prediction

“…Due to the convergence of the Cathaysian ancient land and the Yangtze plate, the latter in the Middle Ordovician developed as a foreland basin (Liu et al, 2021; Tang et al, 2022). In the Early Silurian, due to the enhancement of compression, the Chuangzhong uplift, the Qianzhong paleouplift, and the Xuefeng uplift were formed successively, which changed the sedimentary environment of the Sichuan Basin and its surrounding areas into a limited deep-water environment surrounded by paleouplift.…”