The Neogene carbonate succession on the island of Bonaire (Netherland Antilles) shows complex geometries associated with a sequence of depositional and erosional events which reflects the history of this isolated platform and the interaction between eustasy and tectonics. Three major episodes of carbonate platform deposition are defined which show contrasting depositional styles: 1) aggradational platform (Lower-Middle Miocene) with sediments showing a fining-upward trend from mixed coral rudstone to medium-grained coralgal grain/packstone, partly dolomitized and tilted by tectonic deformation; 2) 2 prograding platform (Upper Miocene-Pliocene) which is formed of several shallowingupward prograding units mainly composed of reworked red algal grain/packstone, with significant dolomitization, passing upward to shoreline and aeolian deposits formed of coralgal grain/packstone and large benthic foraminifera grainstone, and 3) flat-topped platform (Pleistocene) with a reefal framework composed of a rich variety of corals in a bioclastic pack/wackestone matrix. These platform episodes exhibit contrasting stacking patterns and are separated by erosional unconformities. Overprinting this depositional succession is a series of Quaternary near-horizontal shoreline erosional terraces and vertical cliffs which have been cut into the island stratigraphy and complicate the stratal field relationships. However, this terrace morphology clearly does not represent depositional episodes, as has been suggested before. The internal architecture of each of the three carbonate platform episodes reflects interaction of the dynamics of sedimentation with allogenic controls. The latter relate to major oceanographic and tectonic events in the region, including changing ocean circulation as a result of the closure of the Panama isthmus, and Caribbean plate dynamics that affected sea-floor and island topography. The Bonaire succession provides a model for understanding and predicting isolated carbonate platform development, as well as architecture, facies and potential diagenetic changes, in an active tectonic setting.

Selective dolomitization of HMC allochems in Neogene carbonates is a common phenomenon. It has been proposed that the higher magnesium concentrations [Mg] in these allochems promotes dolomitization. To directly investigate the effects of [Mg] (reported as mol% MgCO3) in biogenic HMC on dolomitization, high-temperature (200 °C) dolomitization experiments were conducted. Dolomite reaction rate, stoichiometry, and microstructures were tracked during dolomitization for a variety of biogenic HMC reactants, including Goniolithon, Lithothamnion, Lithophyllum, Corallina officinalis, Heterocentrotus mamillatus, and Mellita quinquiesperforata. Solids were characterized using standard powdered X-ray diffraction (XRD) and scanning electron microscopy (SEM). In general, biogenic HMC reactants are progressively replaced by protodolomite products between 2 and 46 hours. In the experiment using Corallina officinalis, no products were detected by XRD after 46 hours. Initial protodolomite products are subsequently replaced by ordered dolomite as the reactions proceed. Dolomitization rate and protodolomite stoichiometry do not correlate with [Mg] of the biogenic HMC reactants. Dolomitized HMC skeletons reliably retain the original microstructure of the HMC reactants, consistent with the microcrystalline mimetic textures observed in nature. These findings collectively suggest that under the conditions investigated, dolomitization is less affected by the concentration of magnesium in the HMC reactants relative to other known factors, such as temperature, reactant mineralogy, organic content, skeletal texture, and fluid chemistry. These results imply that the observed correlation between coralline red algae abundance and global dolomitization events in the Neogene is not driven by the elevated magnesium concentration of the HMC reactants.

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