Petrography and Geochemistry of the Upper Triassic Sandstones from the Western Ordos Basin, NW China: Provenance and Tectonic Implications

Abstract

Petrographic and geochemical characteristics of the Upper Triassic sandstones in the western Ordos Basin were studied to provide insight into weathering characteristics, provenance, and tectonic implications. Petrographic features show that the sandstones are characterized by low‐medium compositional maturity and textural maturity. The CIA and CIW values reveal weak and moderate weathering history in the source area. The geochemical characteristics together with palaeocurrent data show that the northwestern sediments were mainly derived from the Alxa Block with a typical recycled nature, while the provenance of the western and southwestern sediments were mainly from the Qinling‐Qilian Orogenic Belt. The tectonic setting discrimination diagrams signify that the parent rocks of sandstones in the western and southern Ordos Basin were mainly developed from continental island arc, which is closely related to the evolution of the Qinling‐Qilian Orogenic Belt. However, the sandstones in the northwestern Ordos Basin show complex features, which may be resulted from a typical recycling process. Overall evidence from petrography, geochemistry and sedimentology, together with previous researches suggest the Kongtongshan and Helanshan areas were the southwestern and northwestern boundary of the Ordos Basin, respectively, and there was no clear boundary between the Hexi Corridor Belt and Ordos Basin, where a large, uniform sediment dispersal system developed during the Late Triassic.

A Late Palaeozoic disconformity in the Moqinwula area: Insights into the tectonic evolution and basement nature of the Junggar Block, NW China

“…However, recent studies have suggested that the Bogda-Harlik arc resulted from the northward subduction of the North Tianshan Ocean (Chen, Xiao, et al, 2019;Zhang et al, 2018;Zhao et al, 2022). Additionally, on the northern side of Karamaili ophiolite, the Yemaquan arc contains widespread Devonian arcrelated volcanic rocks (An et al, 2021;Zhao, Liao, Xiao, et al, 2018). In contrast, contemporary sedimentary rocks were deposited on the southern side of the Karamaili ophiolite (Bai, Chen, Zhu, & Fen, 2018;Li et al, 2009;Zhang et al, 2021;and this study).…”

“…The Junggar Terrane is separated from the Chinese Altai Orogen to the north by the Iraqi ophiolite belt, and from the North Tianshan Belt to the south by the Kangguertag-Dacaotan ophiolite belt (Li et al, 2020; F I G U R E 2 Devonian to Early Carboniferous stratigraphic columns in the northern Junggar Block and southern East Junggar Belt, showing the principal rock types, fossil assemblages and sample positions. The Zircon U-Pb age data are from Huang et al (2012), Zhang et al (2013Zhang et al ( , 2021, Bai, Chen, Zhu, and Fen (2018); Bai, Chen, Tang, and Zhang (2018), Zhao, Liao, Xiao, et al (2018) and this study. Stratigraphic projection sites are indicated in Figure 1.…”

“…The intrusive rocks in the Dulate-Baytag arc are spatially widespread and dominated by the Devonian (390-370 Ma) and Carboniferous (330-320 Ma) granitoids (Song et al, 2019;Song et al, 2022). The Yemaquan arc is dominated by Devonian to Carboniferous volcaniclastic rocks, with subordinate Ordovician and Silurian meta-sedimentary rocks and volcanic rocks (Figure 2; Xu et al, 2013;Zhao, Liao, Xiao, et al, 2018). Additionally, the Palaeozoic granitoids are extensively distributed in the Yemaquan arc, such as the Ordovician to Silurian arc-related granite in the Zhifang area (Xu et al, 2020), Devonian diorite in the Taheir area (Xu et al, 2013) and Carboniferous Sujiquan and Huangyangshan A-type granites (Su et al, 2007;Yang et al, 2011).…”

“…To the south of the Yamaoliang Fault, the oldest sedimentary strata are the Miaoergou Formation of the Ordovician Huangcaopo Group, which mainly comprises marine clastic rocks and silty slate interlayered with limestones that contain abundant trilobites and brachiopods (Figure 3b; Long et al, 2012;Zhao et al, 2022). The Lower Silurian Daliugou Formation consists of basalt, basaltic andesite, andesite, tuff and pyroclastic rocks, which unconformably overlie the Miaoergou Formation (Figure 3b; Zhao, Liao, Xiao, et al, 2018;Zhao et al, 2022). The Lower Devonian Hongliugou Formation comprises passive continental marginal facies of carbonates, silicates and terrigenous clastic rocks (Figure 3b; Zhang et al, 2021).…”