Late Carboniferous to Permian paleoclimatic and tectono-sedimentary evolution of the central Ordos Basin, western north China Block

Abstract

The Late Carboniferous to Permian is a crucial time epoch that witnessed multiple-stage icehouse-to-greenhouse transitions and amalgamation of the Pangea supercontinent in geological history. In the North China Block (NCB), a sequence of Late Carboniferous to Permian successions preserves dramatic changes related to these climatic and tectonic shifts. Here, we conducted a comprehensive study of sandstone petrology, mudstone whole-rock geochemistry, and detrital zircon U-Pb geochronology on Late Carboniferous to Permian strata in the Wuqi Oilfield, central Ordos Basin of the western NCB. Mudstone geochemistry and sandstone modal composition data indicate that sediments in the central Ordos Basin were deposited in arc/orogen-related tectonic backgrounds, with sources dominantly from erosion of intermediate-acid rocks. Detrital zircon U-Pb analyses yielded 3 major age populations of 2600–2200 Ma, 2100–1700 Ma, and 470–260 Ma, matching well with a northern Inner Mongolia Continental Arc (IMCA) source instead of a southerly Qinling/Qilian source. Three climate warming events were identified by increased levels of continental weathering. The τNa, CIA, and Ln (Al₂O₃/Na₂O) values manifest two positive increasing events and, by reference, climate warming events, represented by high chemical weathering intensity (e.g., CIA >90 and τNa < −0.96), at ca. 302–298 Ma and ca. 292–290 Ma. The first event coincided with the deglaciation event of Gondwana triggered by the Skagerrak-Centered Large Igneous Provinces (LIPs). The second event was associated with the ca. 290 Ma large-scale glacial retreat in Gondwana that was synchronous with the Tarim LIP, Panjal LIP. The zircon Eu/Eu∗ empirical equation data indicates that the crustal thickness of the IMCA thickened from 40-43 km–50 km between approximately 320 Ma and 285 Ma. The increasing relief of the IMCA was recorded by ca. 280–260 Ma craton-wide sedimentary hiatus in the NCB interior. Subsequently, the high relief of the IMCA led to orographic rain shadow and aridification, which caused the third climate warming event, as indicated by the change in mudstone color from black to red.