MIS 5a carbonate deposits (MIS 5a) of Capo Colonna (Crotone, Southern Italy): microfacies and biosedimentary processes

Interglacial MIS 5a mixed carbonate and siliciclastic deposits, cropping out along the marine terrace of Capo Colonna (Kr), were studied. Two main bio-sedimentary facies can be recognized: 1) Red algae-dominated decimeter- to meter-scale domal to stratiform bioconstructions (Coralligenous), rich of encrusting red algae, with less bryozoans, serpulids, and encrusting foraminifera; laterally, these are associated to medium to coarse mixed bioclastic grainstone/packstones that also fill most of the cavities of the skeletal framework; 2) Maerl facies, mainly composed of free branches and fragments of red algae immersed in mixed bioclastic medium to coarse grainstone/packstone. In mixed bioclastic sediments of both biofacies, micrite is ubiquitous and generally well preserved. Several typical microbialitc fabrics characterize most of the micrite: aphanitic, peloidal/ dendritic, pseudo-thrombolitic and stromatolitic. Primary marine cements are commonly micritic isopachous rims, whereas vadose and botryoidal are rare. Late diageneses affect all the deposits with dissolution, aragonite conversion into calcite, neomorphic recrystallization of calcite (e.g., micrite to microspar), and precipitation of meteoric dogtooth cements. The primary skeletal framework of the buildups is composed of encrusting red algae, foraminifera, bryozoans, and serpulids, while both primary micritic cement and early indurated microbialites contribute to bind skeletal and detrital components in both biofacies. Physical and biological destructive processes are commonly detected, producing erosional surfaces and dissolution cavities mainly due to endolithic sponges.