Evolution of calcite microcrystal morphology during experimental dissolution

ABSTRACT Phanerozoic limestones are composed of low-Mg calcite microcrystals (i.e., micrite) that typically measure between 1 and 9 μm in diameter. These microcrystals, which host most the microporosity subsurface reservoirs, characterized by a variety microtextures. Despite overwhelming consensus diagenetic, origin various textures is widely debated. The commonly reported texture polyhedral rounded interpreted to form via partial dissolution rhombic during burial diagenesis. A proposed implication this model responsible for significant porosity generation. This claim has been previously criticized based on mass-balance considerations geochemical constrains. To explicitly test model, series laboratory experiments were conducted whereby types calcites partially dissolved under constant degree undersaturation, both near far-from-equilibrium. Our results indicate crystals far-from-equilibrium conditions develop edges corners, inter-crystal gulfs (narrow grooves or channels adjacent crystals), few etch pits crystal faces—observations consistent with burial-dissolution hypothesis. Crystals near-equilibrium conditions, contrast, retain sharp corners ledges pits—suggesting occurs more selectively at high-energy sites. observations support longstanding understanding transport-controlled, surface-controlled. also show while may when themselves do not become spherical. By only but nearly spherical continued dissolution. Collectively, these suggest likely from precursor exhibiting an equant texture, rather than euhedral as proposed. Lastly, observation developed after 5% indicates presence such features natural need imply generation occurred.