Biogenic carbonate mineralogies through the Phanerozoic

Evidence is rapidly becoming available which indicates that global ocean chemistry has fluctuated with respect to carbonate solubility through Phanerozoic time; the mineralogy of inorganically precipitated carbonate cements appears to have changed as a result. Reported here are new scanning and transmission electron microscopic and ultrastructural evidence together with theoretical calculations that suggest such changes in global ocean chemistry also mediated mineralogic changes in the carbonate skeletons or some organisms. Many groups of organisms are thought to mediate the entire skeletal crystal growth process by actively directing ions into a potentially charged organic matrix, always constructing a specific mineral. A host of other groups of organisms only initiate skeletal crystal growth so that the majority of their skeletal mineral growth is physicochemical, akin to the precipitation of marine cements; inorganic skeletal crystal growth is usually followed by readsorption of these inorganically precipitating crystals by the organism, halting crystal growth and forming skeletons of finished adaptive design. The author propose that physicochemical dominated skeletonizers had heterogeneous primary mineralogies through Phanerozoic time; he further suggests that organisms most susceptible to mineralogic inversion with changing ocean chemistry are those that, by new definition (presented here), are organisms which are the dominant reef builders more » of any given ancient carbonate system. « less