Dolomitization – Question COOne of the puzzles of carbonate diagenesis is that seawater is supersaturated with dolomite, yet nowadays dolomite is rarely directly precipitated. Discuss the strengths and weaknesses of the different mechanisms that have been postulated to explain dolomitization and why it is important to understand them from a hydrocarbon perspective. Introduction Dolomite (CaMg〖(CO_3)〗_2) is found in carbonate rocks of all ages that formed under a variety of conditions, but today it forms only in hypersaline lagoons, lakes and tidal flats. This suggests that most dolomite is of secondary origin as a result of dolomitization: the replacement of calcite or aragonite (CaCO_3) by dolomite soon after deposition or during diagenesis, generally increasing porosity. Dolomition is therefore very important in sedimentology and hydrocarbon exploration, but is not yet fully understood. Numerous models have been proposed to explain its presence and why it does not form everywhere, even if seawater is supersaturated with respect to dolomite (Nichols, 1999; Tucker, 2001). Models of dolomitization Due to the highly ordered structure of dolomite, there are numerous factors that inhibit its precipitation: high ionic strength of sea water, hydration of Mg2+ and low activity of CO3-, even in supersaturated conditions and therefore certain conditions. These are: a sufficient Mg2+ supply that is long-lasting, an initial porosity, a pressure differential for pore fluid migration, and a pore fluid undersaturated in Ca2+. Therefore it is normal that before dolomitization occurs the Mg:Ca ratio must increase, forcing the dolomite out of solution. If these conditions are not satisfied there will be no dolomitization and insertion...... half of the article......, G. (1999). Semettology and stratigraphy (p. 355). Blackwell Science Ltd. Potma, K., Weissenberger, JAW, Wong, P. K., & Gilhooly, M. G. (2001). Toward a sequence stratigraphic framework for the Frasnian of the Western Canadian Basin. Canadian Petroleum Geology Bulletin, 49(1), 37–85. doi:10.2113/49.1.37Tucker, M. E. (2001). Sedimentary petrology (Terza., p. 262). Blackwell Science Ltd. Whitaker, F. F., Smart, P. L., & Jones, G. D. (2004). Dolomitization: from conceptual to numerical models. Geological Society, London, Special Publications, 235(1), 99–139. doi:10.1144/GSL.SP.2004.235.01.05 Whitaker, F. F., and Xiao, Y. (2010). Modeling reactive transport of dolomitization of early burial of carbonate platforms by geothermal convection. AAPG Bulletin, 94(6), 889–917. doi:10.1306/12090909075Wright, V. P. (2009). Review of Sedimentology 1 (p. 152). John Wiley and Sons.