Abstract
Summary Modern carbonate sediments are accumulating in almost all depositional environments except for the very deep oceans. Chemical and physical conditions, however, govern preservation and abundance of carbonate relative to non-carbonate material. Most modern marine carbonate sediments owe their origin to accumulation of bioclastic debris. Rarely can inorganic precipitation be actually proven. Mineralogical analysis of these sediments has shown that deep cold-water carbonates are predominantly low-magnesium calcites; whereas shallow, warm-water shelf deposits are composed predominantly of metastable carbonates (aragonite and high-magnesium calcite) with minor amounts of low-magnesium calcite. Significant quantities of supratidal dolomite has been reported in modern sediments. Diagenesis is taking place in modern sediments; however, only rarely can mineralogical or chemical changes be demonstrated in sediments that have not been exposed to fresh water. If modern shelf sediments are good examples of ancient sediments, almost all limestones have recrystallized.
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