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Erhardt, Andrea M; Turchyn, Alexandra V; Dickson, J A D; Sadekov, Aleksey Y; Taylor, Paul D; Wilson, Mark A; Schrag, Daniel P (2019): Chemical composition of carbonate hardground cements. PANGAEA, https://doi.org/10.1594/PANGAEA.910001

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Abstract:
Trace metal and isotopic ratios, including some rare earth elements, Mg/Ca, manganese and strontium concentrations, δ¹⁸O, δ¹³C, and ⁸⁷Sr/⁸⁶Sr, were analyzed in the carbonate cements from 17 Phanerozoic carbonate hardgrounds. The sensitivity of the geochemical signal to alteration depends on the geochemical analysis in question and the environmental water-rock ratio. Of these samples, only our modern sample has measurements consistent with primary precipitation from seawater; all other samples precipitated from chemically evolved seawater or were influenced by meteoric water, even if only minimally changed. The more recent samples from the Cenozoic had seawater ⁸⁷Sr/⁸⁶Sr. The Mesozoic samples, in contrast, did not preserve seawater ⁸⁷Sr/⁸⁶Sr, even though the Mg/Ca, δ¹⁸O, and δ¹³C values were consistent with precipitation from seawater. Finally, the Paleozoic samples preserved expected seawater ⁸⁷Sr/⁸⁶Sr, though REE and δ¹⁸O suggest primary precipitation was from evolved seawater. Additionally, we place our results in the context of open vs. closed system precipitation using transects of the Mg/Ca ratios across individual cements. Overall, we stress that one geochemical measurement provides only a partial record of fluid composition, but multiple measurements allow a potential understanding of the seawater geochemical signal.
Keyword(s):
carbonate hard grounds; Mg/Ca ratios; strontium isotopes
Coverage:
Median Latitude: 33.179768 * Median Longitude: 30.709373 * South-bound Latitude: 11.500000 * West-bound Longitude: -117.000000 * North-bound Latitude: 54.566670 * East-bound Longitude: 162.333330
Size:
7 datasets

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