Epitaxial calcite cements in Earth history: a cooler-water phenomenon during aragonite-sea times?

Abstract

AbstractEpitaxial calcite overgrowths on echinoderm fragments are important contributors to the rock record during specific time intervals in Earth history (so-called ‘calcite-sea’ times). Such overgrowths also occur throughout the Phanerozoic in heterozoan carbonate associations, where, these cements often form the volumetrically most important cement type. The origin and environment in which this cement forms are controversially debated, reaching from early marine, meteoric, burial to emergence. The formation of epitaxial overgrowth in calcite sea shallow-water carbonates is reported from early diagenetic environments (marine, marine burial and meteoric), whereas for aragonite sea shallow-water heterozoan carbonates generally a later, burial diagenetic environment of epitaxial cement precipitation is stated. Data from the central Mediterranean area (Maltese Islands and Sicily) show that also in heterozoan shallow-water carbonates the main phase of epitaxial cement precipitation can occur early, in the marine, meteoric and marine burial environment. Cementation was not sourced by pressure solution of calcitic grains, which clearly postdates epitaxial cement growth, but by the early dissolution of aragonitic biota. These findings underline the importance of aragonitic components as an early cement source in aragonite-sea time non-tropical/heterozoan carbonates and emphasize the similarity of the diagenetic evolution of these rocks with calcite-sea time tropical carbonates.