Upper Carboniferous-Lower Permian Buildups of The Carnic Alps, Austria-Italy

Abstract A variety of buildup types occur in the upper Paleozoic Auernig and Rattendorf Groups, Carnic Alps, at the present-day Austrian-Italian border, including coral, diverse algal (Anthracoporella, Archaeolithophyllum,Rectangulina,and phylloid green), bryozoan, brachiopod, and sponge buildups. Thin mounds and banks have a diverse fossil association (e.g., Archaeolithophyllum-bryozoan-brachiopod mounds) and occurin siliciclastic-dominated intervals, as do coral buildups. Some of the biodiverse thin mounds occur in stratathat were deposited in cooler water. However, the thickest mounds are nearly monospecific (e.g., Anthracoporellamounds) and grew in carbonate-dominated, warm-water environments. Most of the mounds considered in this paper, particularly algal mounds, grew in quiet-water environments below wave base but within the photic zone. Mound growth was variously stopped by siliciclastic input, e.g., auloporid coral mounds, sea-level rise, e.g., the drowning of Anthracoporellamounds of the RattendorfGroup, influence of cool water, e.g., algal mounds of the Auernig Group overlain by limestone of cool-water biotic association, or sea-level fall, e.g., phylloid algal mounds that were subsequently exposed subaerially. Thereis no indication of ecological succession during mound growth. Growth, dimensions, biotic association, and termination of mounds seem to have been controlled by extrinsic factors, mainly sea level and water temperature. Phylloid algal mounds are similar to those described from other late Paleozoic settings. Auloporid coral buildups, and Rectangulinaand Anthracoporellaalgal buildups, however, have not previously been reported from other regions, although these fossils are described from several localities outsidethe Carnic Alps.