High-resolution environmental magnetic study of a paleosol from the upper Permian in Southwest China, and its paleoclimatic implications

Abstract

Paleosols are ancient soils that are formed in non-marine environments and contain valuable information about past climates and environmental changes. They have been extensively studied around the world as paleoclimatic indicators for the Earth's history. However, the systematic study of paleosols from the upper Permian and their corresponding paleoclimatic implications remain poorly understood. In this study, we systematically investigated the rock magnetic and microscopic features of an oxisol bed (∼5.07 m thick) from the upper Permian in Southwest China. Analyses on both outcrop and drill core samples show that the oxisol bed exhibits a systematic lithological transition from the dusky red mudstone in the saprolite subzone to grayish-green and reddish-brown mottled sandy mudstone and silty mudstone in the mottled subzone. In the saprolite subzone, the mineral crystal size is relatively smaller and poorly preserved, and the magnetic-carrying minerals are comprised of abundant micron- and submicron-sized magnetite particles. By contrast, in the mottled subzone, the mineral crystal size (such as quartz) is relatively larger and well-preserved, and the magnetic-carrying minerals are dominated by abundant micron- and submicron-sized hematite particles. High-resolution environmental magnetic analyses suggest that the saprolite subzone was formed in relatively warm and humid conditions with enhanced physical weathering, while the mottled subzone was formed under short-term paleoclimatic events characterized by high temperatures and enhanced chemical weathering. This study represents the first systematic magnetic and microscopic characterizations of paleosols from the upper Permian in Southwest China, shedding new light on the paleoclimatic conditions at the time.