A comprehensive chemostratigraphic study, including evaluation
of rare earth elements and trace elements, was conducted to explain
the paleoenvironments of the northern margin of the Upper Yangtze
Platform. Trace elements, like Ba, U, V, Cu, and Zn, tended to be
more abundant in these formations than in the upper continental crust.
The authigenic abundances of Al-normalized U and V, as well as the
Th/U and V/Sc ratios, were used as indicators of the redox circumstances.
In the Nanjiang area, the redox circumstances of the bottom water
during the Ordovician–Silurian transition changed from oxic
in the Late Katian to slightly anoxic in the Hirnantian and then gradually
became anoxic in the Early Rhuddanian. In the Chengkou area, the redox
circumstances of the bottom water during the Ordovician–Silurian
transition abruptly changed from oxic in the Late Katian to strongly
anoxic in the Hirnantian and continued to become more anoxic until
the Rhuddanian. The total organic carbon concentrations were well
correlated with the redox circumstances of the bottom water. We conclude
that the transient hydrothermal activity was not widely distributed
during the Late Ordovician–Early Silurian transition, and it
might also have been only a local event in the Upper Yangtze Platform.
The enrichment in organic matter was mostly sourced from the photic
zone and was governed by the redox circumstances of the bottom water.
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