69 D32. Geochemistry (Posters)

Sunday, 22 October 2017
9:00 AM - 5:30 PM
Halls 4EF

CARBON, SULFUR AND NITROGEN ISOTOPE CHEMOSTRATIGRAPHY OF EARLY-TO-MIDDLE EDIACARAN IN SOUTH CHINA

Paper number: 69-19
Program: Technical Sessions
Time: 9:00 AM – 5:30 PM

Authors

Abstract

The coevolution of life and environment is highlighted in the recent debate on the possible relationship between ocean oxygenation and animal evolution in the Neoproterozoic. Ediacaran successions in South China are ideal targets for focused and integrated geochemical analysis to infer the impact of redox conditions on evolution and ecology. While previous studies have been focused on shelf sections in the Yangtze Gorges, it is necessary to gain insights from sections in deep-water slope and basinal facies, as well as shallow-water facies sections in western Zhejiang province. Integrated geochemical data, including δ13Ccarb, δ13Corg, δ34Spyr, δ34SCAS and δ15Nsed, from the Lantian Formation deposited in deep-water environments are analyzed. A large spatial gradient of δ13Ccarb is present in the lower Doushantuo/Lantian Formation. This gradient is largely due to the influence of 13C-depleted authigenic/diagenetic calcite cements in organic-rich and carbonate-poor sediments deposited in deep-water facies. A pronounced negative δ13Ccarb excursion in the upper Doushantuo/Lantian Formation, however, is spatially consistent and does not display a > 10‰ depth gradient. The δ34Spyr record seems to show a spatial pattern, with more negative δ34Spyr values in deeper-water facies. The spatial pattern of δ34Spyr is interpreted as evidence for a chemically stratified basin, with predominantly euxinic deep waters where pyrite precipitated in the water column has lower δ34Spyr values. The Lantian and Doushantuo formations do not preserve highly positive δ15Nsed values characteristic of partial denitrification in suboxic environments of modern oxygen-minimum zone. Integrated TOC, TN, δ34Spyr, and Fe speciation data suggest that oscillation between oxic and euxinic conditions is characteristic of the Lantian Formation The prelimentary results established in shallow-water facies through western Yangtze platform keep well consistent with the previous studies in Lantian area.

Geological Society of America Abstracts with Programs. Vol. 49, No. 6

doi: 10.1130/abs/2017AM-301183

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