Middle Triassic humidification in Southern North China linked to northward propagation of Qinling Orogenic Belt

Abstract

Orogenic uplift can change landscape topography and influence regional climatic conditions. However, it is generally hard to track the causal linkage of regional climate change with orogenesis from geological records due to lack of direct correlations between climatic and tectonic evolution. During the early-middle Triassic, there was a subarid to subhumid climate shift in Southern North China along with the formation of the Qinling Orogenic Belt. To further understand the early-middle Triassic climate shift and its potential linkage with the Qinling orogenesis, two early-middle Triassic successions through the upper Heshanggou to Ermaying formations in the Jiyuan area in Southern North China Basin were studied by sedimentology, paleosols and detrital zircon provenance analysis. The paleosols are characterized by calcareous nodule horizons and have morphological features of calcic paleosols. Based on depth to the calcareous nodule horizon of the observed paleosols, regional precipitation was estimated and showed an increase from less than 420 to more than 800 mm/yr in the lower Ermaying Formation. This climate humidification is accompanied by the fluvial to deltaic facies transition and postdates a significant provenance change recorded by the detrital zircon UPb ages. Detrital zircons from the Heshanggou Formation exhibit two primary UPb age groups of 530–380 Ma and 1100–700 Ma, indicating a dominant provenance from the North Qinling Belt. In contrast, detrital zircons from the Ermaying Formation show three major UPb age groups of 2900–2300 Ma, 2100–1650 Ma, and 330–230 Ma, pointing to a provenance from the Southern Margin of North China. This provenance shift can be interpreted as indicative of the northward propagation of the orogenic uplift. In this context of tectonic evolution, we proposed that the increased precipitation in the Southern North China was related to the orogenic uplift to the south. This study enhances our understanding of the interactions between climate and tectonics from geological record.