Elemental logging evidence for paleoenvironmental reconstruction of the ordovician strata in the Western Ordos basin, China

The Ordovician carbonate succession in the western Ordos Basin, China, represents an important target for unconventional hydrocarbon exploration, particularly shale gas in the Wulalike Formation. In this study, we utilize high-resolution elemental logging data from MJ1 well to reconstruct the paleoenvironmental evolution of the basin and evaluate the controlling factors on organic matter enrichment. Major and trace element distributions reveal distinct geochemical signatures across stratigraphic units, reflecting variations in lithology, productivity, redox conditions, paleoclimate, salinity, and water depth. Proxies such as Al/Ti, Cu/Al, U/Th, Sr/Cu, and Rb/K were applied to infer paleo-productivity, redox state, climate, and bathymetric trends. The results indicate that the Wulalike Formation experienced relatively high paleoproductivity, dysoxic to suboxic redox conditions, semi-arid climate, and moderate water depth, creating favorable conditions for organic matter accumulation. A progressive transgressive sequence is documented from the Sandaokan to Wulalike Formations, with corresponding shifts in facies and geochemical environments. These findings provide new insights into the depositional evolution and hydrocarbon potential of the Ordovician strata in the western Ordos Basin and offer valuable implications for future shale gas exploration strategies.