12/12/2024

Dr. Sara Rose Kimmig

16:00 Uhr

Abstract: Dolomite is a predominantly diagenetic mineral that forms by replacing marine calcite and aragonite during burial. Dolomitization requires subsurface fluid flow to deliver Mg and remove product Ca, and only forms abiotically in laboratory experiments at temperatures above ~100°C, equivalent to burial depths of 3 km or greater. Limited sources of Mg at these depths would appear to restrict most dolomite formation to shallow burial depths using seawater as a source of reactive Mg, despite the kinetic limitation imposed by lower temperatures. The Williston Basin in North America is replete with evaporites and dolomites that appear to have formed using Mg from evaporatively concentrated seawater at near surface temperatures. However, two dolomite bodies examined in this study record basin wide gradients in Sr and Mg isotope signatures that are inconsistent with dolomitization by seawater. In this talk, we will investigate the processes that may have created these isotopic gradients and propose a new dolomitization model whereby seepage reflux created early diagenetic protodolomite that was later altered during deep burial by radiogenic Sr and Mg-enriched fluids ascending from the deep structural center of the basin, in contrast to long standing traditional models.