Australia: The Land Where Time Began

A biography of the Australian continent 

The Cryogenian Datangpo Formation, South China - Reconstruction of Palaeo-Redox Conditions and Early Sulphur Cycling

The Datangpo Black Shales, South China, 663-654.5 Ma, were deposited during the interglacial between the Sturtian Glacial and the Marinoan Glacial in the Cryogenian. The palaeo-depositional environment of this black shale horizon has been reconstructed using multi-geochemical proxies, including different iron speciation and relevant ratios (Fe/_HRFe_T, Fe_P/Fe_HR and Fe_T/Al ratios) and concentrations of molybdenum. It is suggested by the ratios of different iron species (Fe_HR/Fe_T > 0.38 and Fe_P/Fe_HR <0.80), that there were overall anoxic conditions (ferruginous) over black shale deposition, though intermittent euxinic (Fe_HR/Fe_T > 0.38 and Fe_T/Fe_HR ≈ 0.80 and oxic Fe_HR/Fe_T < 0.38) intervals could possibly have occurred. It is also confirmed by (Fe_T/Al ≤ 0.51) that the water column may not have been persistently euxinic during the deposition of the black shales of the Datangpo Black Shales, which would reconcile the gradual trend in oxygenation that occurred during this period, as stated above. When compared to the δ³⁴S_PY values in the deep ocean during the Mesoproterozoic, more positive δ³⁴S_PY values may result from a small sulphate reservoir. It is indicated by the small size of the sulphur reservoir, and the concurrent molybdenum enrichment, that in the Cryogenian Period the ocean chemistry was similar to that in the Archean Eon.

Sources & Further reading

1. Feng, Lian-Jun, Xue-Lei Chu, Jing Huang, Qi-Rui Zhang, and Hua-Jin Chang. "Reconstruction of Paleo-Redox Conditions and Early Sulfur Cycling During Deposition of the Cryogenian Datangpo Formation in South China." Gondwana Research 18, no. 4 (11// 2010): 632-37.