Rhodalgal/bryomol assemblages in temperate-type carbonate, channelized depositional systems: the Early Miocene of the Sarcidano area (Sardinia, Italy)

Abstract

AbstractDuring Aquitanian-Burdigalian times, temperate-type carbonate-siliciclastic successions were deposited in basins located on the graben and half-graben along the Oligo-Miocene Sardinia Rift Basin (Sardinia, Italy). In one of these basins, the Isili Basin, rhodalgal/bryomol limestone was deposited in a temperate-type carbonate depositional system in which a shallow carbonate factory, a marginal tributary belt and a main channel were identified. In this paper, the Isili Limestone is described in terms of biogenic components and taphonomic characterization. To understand the palaeoecology of the depositional settings and the related palaeoceanographic controls, the coralline algal assemblages were differentiated according to coralline growth forms, rhodolith shapes, rhodolith inner structure and taxonomic composition. In addition, a first analysis was carried out in order to discriminate among the different bryozoan and mollusc assemblages present in different localities corresponding to different palaeoecological settings. The results obtained provide fundamental support for palaeoenvironmental reconstruction that combines palaeobiological analyses (i.e. rhodolith characteristics, bryozoan growth forms, taphonomic features) with previous physical (sedimentological and geometrical) observations. This allows a more detailed reconstruction of the complex relationships between the different sectors of the sedimentary system: the carbonate factory, the smaller erosive tributary channels and the deeper main channel.