ABSTRACT The lower Yan'an and upper Yanchang formations in Well Gu208, southwestern Ordos Basin, preserve paleoenvironmental records from the Late Triassic to Early Jurassic. Elemental geochemistry indicates derivation from felsic to intermediate igneous source rocks that originally formed in an active continental margin or island arc setting. Chemical Index of Alteration (CIA) values of 65–85, C‐values > 0.2 and Sr/Cu ratios collectively suggest a semi‐arid to semi‐humid climate with moderate weathering. Low Sr/Ba ( −0.1), elevated Ba/Al (> 0.01) and enrichment in Cu, Ni and Zn reveal dysoxic to anoxic bottom waters, reflecting high primary productivity. From a temporal perspective, the Chang 2 Member experienced dry–wet climatic fluctuations and unstable depositional conditions; the Fuxian Formation transitioned to stable humid conditions with sustained high productivity; and the Yan 10 Member became relatively drier, with slightly reduced anoxia while still maintaining high productivity. Overall, high‐productivity freshwater lakes developed in this intracontinental cratonic basin, and the evolving paleoclimate together with persistent dysoxic to anoxic conditions favoured the potential preservation of organic matter.
Dong et al. (Tue,) studied this question.
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