High precipitation rate in a Middle Triassic carbonate platform: Implications on the relationship between seawater saturation state and carbonate production

Three-dimensional geological modeling of the Middle Triassic Latemar carbonate platform is coupled with facies modal analysis to estimate its carbonate precipitation rate (G). The 3D model, strongly constrained by field data, encompasses a specific stratigraphic interval of the platform, bounded by two isochronous surfaces. Modal analysis of thin sections allows estimating the proportion of syndepositional vs postdepositional carbonate in the fades associations of the platform. This, together with the 3D facies distribution in the model that takes into account lateral and vertical fades variability, permits to calculate the volumes of syndepositional carbonate preserved at Latemar between the two considered isochrones. Given the peculiar characteristics of the platform, that does not show evidences of strong dissolution processes or large carbonate mass loss through export in the nearby basins, results can be used to estimate the average precipitation rate of the platform in the considered time interval. This estimate allows discussion in relation to models of ocean water saturation state (Omega) with respect to carbonates in the geological past, and comparison to the calculated precipitation rates of modern tropical coral reef ecosystems at global and reef scale. A high G value is found at Latemar and represents the first empirical confirmation that, in the Triassic, extremes in Omega may have triggered high carbonate precipitation in shallow water settings; moreover, comparison to modern reefs points to a possible common relationship that may link seawater Omega and precipitation rate in carbonate platform ecosystems through geological time. (C) 2016 Elsevier B.V. All rights reserved.