Preferential dolomitization in Mio–Pliocene bioclastic clinoforms, Bonaire Island, South Caribbean: insights from petrographic and geochemical analyses

Abstract

Selective dolomitization, where certain carbonate components are preferentially dolomitized over others, can be significant in the overall dynamic context of the global magnesium cycle. Thus, the abundance of these components can modify the Mg balance between the ocean and sediments, thereby disrupting the Mg cycle in certain geological times. Selective dolomitization may be connected to the apparent correlation between global dolomitization events in the Neogene and the synchronous rise in species abundance of coralline red algae (CRA), but the underlying issue remains unclear. In the Caribbean islands, excellent examples of Neogene partially dolomitized carbonates containing coralline red algal facies are described to understand selective dolomitization of different components (grains and matrix) by examining the well-preserved outcrop of partially dolomitized Mio–Pliocene carbonates at the Seru Grandi locality on Bonaire Island, in the Caribbean. The degree and timing of selective dolomitization of various carbonate components are assessed using petrographical and geochemical methods. The micrite matrix is dolomitized first, followed by coralline red algal bioclasts, and subsequently all other grains. Dolomite crystals appear to originate from within and immediately around coralline algal fragments, suggesting that dolomite could have initiated from internally sourced Mg of the CRA’s high-magnesium calcite skeleton. Collectively, these observations suggest that selective dolomitization is controlled primarily by reactive surface area of the carbonate components, but it is less clear as to whether there is a dependency on original mineralogy.