Palaeoweathering Conditions, Provenance, and Tectonic Setting of the Early Silurian Longmaxi Formation in the Upper Yangtze Region (Southern China): Evidence from Geochemistry

Abstract

The Longmaxi-1 black shales in the Upper Yangtze region are a vital source rocks in southern China. This study investigates the palaeoweathering conditions, provenance, and tectonic setting of the Longmaxi-1 black shale from an elemental geochemical perspective, ultimately revealing its tectonic setting. The results showed that the Longmaxi-1 black shales in the sedimentary period have the characteristics of primary deposition. The Longmaxi-1 black shales were deposited as a primary deposition under a mainly humid climate. However, fluctuations in climatic conditions were recorded from the bottom to the upper part of the formation. The parent rock of the Longmaxi-1 black shales in the Upper Yangtze region is a mixture provenance, mainly composed of intermediate-acid volcanic lithologies (granite and granodiorite), followed by mature quartzite and basalt. Black shale deposition is related to the tectonic setting of active continental margin and island arc-continent collision. The Cathayian orogenic belts and the North Qiangling orogenic belt may have played a role in the genesis of the Longmaxi-1 black shales within the Upper Yangtze region. This study provides significant clues regarding the reconstruction of the palaeoclimatic and palaeogeographical conditions of the Upper Yangtze region during the Early Silurian period.