Marine diagenesis of Lower Ordovician carbonate sediments (Dumugol Formation), Korea: cementation in a calcite sea

Abstract

The Lower Ordovician Dumugol Formation exhibits many features that indicate early lithification, such as calcite nodules, hardgrounds, mud-mounds and intraclasts. Detailed observations of these early-lithified features reveal that rapid marine cementation was instrumental in their formation. Marine lithification took place in a low-energy subtidal environmental that was influenced by intermittent storms. Marine cements include syntaxial overgrowth, bladed calcite, fibrous calcite and fine-crystalline equant calcite cements. Syntaxial overgrowths precipitated on echinoderm grains and contributed to rapid marine lithification of echinoderm-bearing sediments. Bladed, fibrous, and fine-crystalline equant calcite cements precipitated in locally suitable sites but their occurrence is limited, and thus played a minor role in marine lithification. Microcrystalline calcites also precipitated in lime mud-rich, fine-grained sediments and participated in rapid marine lithification of the Dumugol sediments. The absence of aragonite allochems and cement, and the predominance of calcite cement, suggest that the Dumugol sea was undersaturated with respect to aragonite, but supersaturated with respect to calcite, which is indicative of a ‘calcite sea’.