A 600-Million-Year Carbonate Clumped-Isotope Record from the Sultanate of Oman

Abstract

Carbonate clumped-isotope thermometry is a promising technique that has the potential to help decode the significance of the variability of both physical and geochemical compositions of ancient carbonate rocks. This study utilizes a 600-million-year record of marine carbonate rocks from the subsurface and surface of the Sultanate of Oman to explore how burial and exhumation affected the carbonate clumped-isotope thermometer. Samples span 6 km of burial depth, and include calcite and dolomite mineralogies and a range of carbonate rock textures. We find evidence for two broad patterns in the physical and geochemical behavior of carbonate rocks during burial. The first group of carbonates yield water δ^(18)O_(VSMOW) compositions slightly enriched or equal to an expected "ice-free" seawater composition of –1.2‰ and display good to fair textural preservation suggesting that cementation and lithification occurred within tens of meters of the sediment–water interface. Temperatures from the second group sit on the present-day geotherm, yield highly enriched water δ^(18)O_(VSMOW) compositions, and display fair to poor textural preservation. We find no evidence for solid-state reordering in paired analyses of calcites and dolomites. Our results contribute to a growing body of work that indicates that the seawater δ^(18)O_(VSMOW) composition has not changed significantly over 600 Myr and was not –6‰ in the Ediacaran.

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