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GSA Annual Meeting in Indianapolis, Indiana, USA - 2018

Paper No. 192-10
Presentation Time: 9:00 AM-6:30 PM

THE ORIGIN OF BARITE IN THE BASAL EDIACARAN SETE LAGOAS CAP CARBONATE (BAMBUI GROUP, BRAZIL) AND ITS IMPLICATIONS


OKUBO, Juliana1, KLYUKIN, Yury I.2, WARREN, Lucas V.3, BODNAR, Robert J.2 and XIAO, Shuhai2, (1)São Paulo State University, Av. 24A, 1515, Rio Claro, 13506-900, Brazil; Virginia Polytechnic Institute and State University, Virginia Tech, 4044 Derring Hall, Blacksburg, VA 24061, (2)Virginia Polytechnic Institute and State University, Virginia Tech, 4044 Derring Hall, Blacksburg, VA 24061, (3)São Paulo State University, Rio Claro, 13506-900, Brazil

Most Precambrian sedimentary barite has been interpreted to be derived from diagenetic, hydrothermal exhalation, or methane-seepage origins. However, seafloor barite precipitates and void-filling barite cements in basal Ediacaran and post-Marinoan cap carbonates have been interpreted as sedimentary and early diagenetic in origin, and they have been used to infer ocean geochemistry in the aftermath of the Marinoan Snowball Earth glaciation. Barite crystals precipitated syndepositionally from seawater or authigenically from porewaters in direct communication with seawater can potentially offer insights into Neoproterozoic ocean geochemistry. In this study, we analyzed void-filling barite cements from the basal Ediacaran Sete Lagoas cap dolostone in order to determine whether the barite records seawater geochemical signatures (i.e., early diagenetic in origin) and whether it experienced postdepositional hydrothermal alteration. Sete Lagoas barite occurs as veins and as major void-filling cement in multiple horizons, sometimes interbedded with carbonate fans. Barite crystals, commonly forming rosettes, mostly grew both upwards and downwards. Barite is present as radiating bladed crystals, isolated crystals in the matrix, inclusions within carbonate fan crystals and minor void-filling cements, sometimes partially replacing carbonate fans. Previous researchers have reported the sulfur isotope composition of the Sete Lagoas barite range from 25.7 to 32.2 ‰. Preliminary Raman geothermometric data from carbonaceous material show temperatures between 177°C and 291°C, indicating hydrothermal activity. Fluid inclusion data in the barite crystals suggest the salinity of hydrothermal fluids are higher than the seawater. Given the possibility of hydrothermal alteration, caution must be taken when using the Sete Lagoas barite to infer seawater geochemistry and environment in the aftermath of Marinoan Snowball Earth glaciation.

Session No. 192--Booth# 318

T157. Evolving Perspectives of the Precambrian World: Using Combined Theoretical and Applied Approaches to Tackle Problems at the Intersection of Geology, Geobiology, and Geochemistry (Posters)
Tuesday, 6 November 2018: 9:00 AM-6:30 PM
Halls J-K (Indiana Convention Center)
Geological Society of America Abstracts with Programs. Vol. 50, No. 6
doi: 10.1130/abs/2018AM-321382
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