Geochemical characteristics of the upper carboniferous source rocks in a terrestrial-marine transitional environment from the shuangjingzi area, Junggar Basin: Insights into palaeoenvironment, palaeoclimate, and palaeovegetation

Abstract

The Upper Carboniferous organic-rich sediments record the depositional transition from terrestrial to marine environment across the Shiqiantan Formation-Batamayineishan Formation boundary. The geochemical characteristics of source rocks deposited in such terrestrial-marine transitional environments are not clear. The Late Carboniferous palaeovegetation, palaeoclimate and palaeoredox conditions are comprehensively reconstructed by combining organic petrology, molecular biomarkers, stable carbon isotopes and elemental composition. The molecular composition characteristics and stable carbon isotope compositions suggest a major terrestrial organic matter input with a lesser contribution of algae. Oxic to suboxic conditions for the Late Carboniferous sediments can be inferred from the elemental composition and biomarker proxies. A wet, cool, and seasonal dry climate during the Late Carboniferous can be deduced based on biomarkers, macerals, and spore and pollen records. The Late Carboniferous period is characterized by the enhanced burial of terrestrial organic carbon, coinciding approximately with the intensification of the Late Paleozoic Ice Age. The expansion of terrestrial floras in the Late Carboniferous is likely associated with the Late Paleozoic Ice Age.