Dolomite Crystal Architecture: Genetic Implications for the Origin of the Tertiary Dolostones of the Cayman Islands

摘要

Dolostones in the Cayman Formation on Grand Cayman and Cayman Brac, which are the product of two and possibly three phases of dolomitization, are formed of very small (< 100 µm) but architecturally complex dolomite crystals that are characterized by planar and non-planar boundaries, corrosional internal discontinuities, oscillatory low-Ca calcian dolomite (LCD) and high-Ca calcian dolomite (HCD) zoning, and syntaxial (?) overgrowths. The dolomite overgrowths, which grew on earlier formed but corroded rhombs, increased crystal size and modified crystal shape and, hence, caused significant textural modifications. The size and shape of the overgrowths that developed preferentially on those crystal faces that formed the walls of micropores was controlled by the competition for growth space with neighboring crystals. Interpretation of this textural information suggests that the development of planar and non-planar dolomite boundaries crystals is probably related to critical supersaturation levels rather than critical roughening temperatures.