Sedimentary Filling Evolution under Paleoclimate Transition—A Case Study from the Middle Jurassic Zhiluo Formation, Ordos Basin

Abstract

Under a specific tectonic background, the change in paleoclimate can show different facies associations and depositional architecture. The Jurassic China continent was an important region for transforming the Paleotethys tectonic domain to the circum-Pacific tectonic domain, and its paleoclimate information was entirely preserved in the continental sedimentary successions. The Middle Jurassic Zhiluo Formation, in the Ordos Basin, was at just the critical period of paleostructure and paleoclimate transition, preserving considerable sedimentological evidence; however, little sedimentological research has been conducted under the transition. This study reconstructed the sedimentary filling characteristics of the Zhiluo Formation under paleoclimate transition based on field outcrop survey, thin section observation, geochemical indices, stratigraphic correlation, and depositional environment analysis. The results showed that with the paleoclimate change from warm and humid to hot and arid, the sedimentary facies of the Zhiluo Formation were characterised by the change from the braided river/braided river delta in the J2z1-1 sedimentary period to the meandering river/meandering river delta in the J2z1-2 sedimentary period, and finally the change to the meandering river, meandering river delta, and lacustrine in the J2z2 sedimentary period. The combined action of the southern super monsoon effect, the increasing global CO2 concentrations, the moving southward of the East Asian block, and the terrain elevation difference, changed the basin’s climate from warm and humid to hot and semi-arid/arid. This study provides a crucial basis for reconstructing the interplay between paleoclimate and paleotectonics, and guiding sedimentology and paleoenvironment research on East Asia during the Middle Jurassic period.