Extensive recrystallization of Cenozoic dolomite during shallow burial: A case study from the Palaeocene–Eocene Umm er Radhuma formation and a global meta‐analysis

Abstract

AbstractRecrystallization of dolomite can alter textural, mineralogical and geochemical attributes used to infer environmental conditions of initial dolomitization. A meta‐analysis of the published literature shows that extensive recrystallization is most common in old and deeply buried dolomites, but data from the Palaeocene–Eocene Umm er Radhuma Formation in Qatar show that this can also happen in geologically young carbonates that have never been deeply buried. Evidence of extensive recrystallization comes from a principal component analysis of published mineralogical and geochemical data that are integrated with new clumped isotope (∆47) measurements and cathodoluminescence petrography. The observations indicate that dolomite stoichiometry and cation ordering correlate with dolomite texture and depth: shallow mimetic dolomites are less stoichiometric and poorly‐ordered whereas coarser and deeper planar‐e and planar‐s to nonplanar dolomites with mottled cathodoluminescence signatures are more stoichiometric and well‐ordered, suggesting they have recrystallized. Dolomite δ18O data (Vienna Pee Dee Belemnite) also covary with texture, as mimetic dolomites have the narrowest range (−0.45‰ to +0.38‰), planar‐e dolomites are generally ≤0‰ (−2.4‰ to +0.68‰) and planar‐s to nonplanar dolomites exhibit the widest range (−2.3‰ to +1.4‰). The principal component analysis results indicate one component with positive loadings for dolomite stoichiometry (+0.752) and cation ordering (+0.813), and negative loading for δ18O (−0.833), trends predicted in recrystallized dolomites. The ∆47‐derived temperatures (32 to 46°C) and δ18Ow (+0.18 to +2.6‰ Vienna Standard Mean Ocean Water) reflect recrystallization by warm, slightly evaporated seawater at shallow depths. In the context of a meta‐analysis of recrystallized dolomites in the literature, this study implies that extensive dolomite recrystallization in Cenozoic dolomites and shallow‐burial conditions is an under‐appreciated phenomenon. The results of this study also demonstrate that initial petrological attributes can be significantly altered after dolomitization, hindering interpretations of past seawater chemistry and environmental conditions of dolomitization.