EARLY VOID-FILLING CEMENTATION IN DEVONIAN FORE-REEF LIMESTONES (GERMANY)

SUMMARY
Fibrous calcite is the main cement in the voids and cavities of Devonian fore-reef limestones in Germany. Cementation occurs in some cases simultaneously with encrustation by blue-green algae as well as internal deposition of calcarenites and calcilutites. These observations lead to the conclusion that the fore-reef voids were exposed to light and were still in free communication with the sea, when the cementation began. Furthermore, redeposited fragments of former cavity fillings indicate that the formation of cavity-filling fibrous calcium carbonate cement was already completed before the sea-ward erosion took place. It is believed that the precipitation of fibrous calcium carbonate in most of the Devonian fore-reef limestones, which show no signs of dissolution, occurred in a shallow subtidal environment. Only the voids showing larger solution phenomena were probably exposed to fresh water in the inter- to supratidal zone.