1182 / 2019-08-06 10:53:16

Depositional controls on the sulfur isotope of sedimentary pyrite

14、古生物、古地理与古环境 > 专题7：关键地质历史时期地球环境的演变

Sulfur isotope fractionation of authigenic pyrite is mainly controlled by microbial sulfate reduction, but recent studies indicate that the local depositional environment can also affect the composition of pyrite sulfur isotopes, especially in shallow depositional environments. In the shallow unsteady environment, physical reworking and bioturbation lead to reoxidation of sulfides formed in the sulfate reduction zone, which in turn affects the sulfur isotopes of pyrite. The sedimentation process in shallow depositional environment is easily affected by paleoclimate and sea-level changes, causing drastic fluctuations in sedimentation rate, resulting in instability of inputs such as organic matter and active iron, which in turn affects the openness of the diagenetic system and ultimately affects the isotopic value of pyrite sulfur. In addition, the change in sedimentation rate also affects the movement of the sulfate-methane transition zone, resulting in the conversion of organic matter and anaerobic oxidation methane sulfate reduction, producing different sulfur isotope signals.
The study of sulfur isotope of authigenic pyrite within the mud sediments on the inner shelf of the East China Sea provides a good example for depositional control on the formation of authigenic pyrite and its sulfur isotope composition. This area has been well studied on sedimentary process, and is enriched in authigenic pyrite and biogas (CH4) in sediments. Our preliminary findings demonstrate that pyrite sulfur isotope compositions (bulk δ34SCRS & hand-picked δ34Spyr) are sensitive to local environmental evolution and the combined use of these two indicators can provide new insights into C-S-Fe cycling in unsteady environments. Therefore, the ECS is an ideal place to study the sulfur cycle in the marginal sea and is expected to provide new perspective on global C-S-Fe biogeochemical cycle.