Carbon, sulfur, and oxygen isotope evidence for a strong depth gradient and oceanic oxidation after the Ediacaran Hankalchough glaciation

In order to understand spatial variations of stable isotope geochemistry in the Quruqtagh basin (northwestern China) in the aftermath of an Ediacaran glaciation, we analyzed carbonate carbon isotopes (dCcarb), carbonate oxygen isotopes (dOcarb), carbonate associated sulfate sulfur (d SCAS) and oxygen isotopes (d OCAS), and pyrite sulfur isotopes (d Spy) of a cap dolostone atop the Ediacaran Hankalchough glacial diamictite at four sections. The four studied sections (YKG, MK, H and ZBS) represent an onshore–offshore transect in the Quruqtagh basin. Our data show a strong paleobathymetry-dependent isotopic gradient. From the onshore to offshore sections, dCcarb values decrease from 2& to 16& (VPDB), whereas dOcarb values increase from 4& to 1& (VPDB). Both dSCAS and dSpy show stratigraphic variations in the two onshore sections (MK and YKG), but are more stable in the two offshore sections (H and ZBS). dOCAS values of onshore samples are consistent with terrestrial oxidative weathering of pyrite. We propose that following the Hankalchough glaciation seawater in the Quruqtagh basin was characterized by a strong isotopic gradient. The isotopic data may be interpreted using a three-component mixing model that involves three reservoirs: deep-basin water, surface water, and terrestrial weathering input. In this model, the negative dCcarb values in the offshore sections are related to the upwelling of deep-basin water (where anaerobic oxidation of dissolved organic carbon resulted in C-depleted DIC), whereas sulfur isotope variations are strongly controlled by surface water sulfate and terrestrial weathering input derived from oxidative weathering of pyrite. The new data provide evidence for the oceanic oxidation following the Hankalchough glaciation. 2010 Elsevier Ltd. All rights reserved.