Microbiofacies analysis of Cambrian offshore carbonates from Sardinia (Italy):environment reconstruction and development of a drowning carbonate platform

The Campo Pisano Formation of southwestern Sardinia is represented by an offshore carbonate succession spanning the latest Early to late Middle Cambrian. Paleogeographically, the fauna is characteristic of western Perigondwana, and indicates faunal relations to France, Spain, and Turkey. Microfaunal paleoecology reflects drowning of an isolated carbonate platform at tropical latitudes. Sessile epibenthic filter feeders dominate at the base, succeeded upward by sessile, epibenthic, suspension feeders. Upsection, a shift in the ratio of faunal groups indicates increasing replacement by mobile epibenthos. Autochthonous faunal elements decline near the top where allochthonous taxa become important. In the basal portion of the formation the faunal succession indicates relatively shallow neritic habitats with a moderate influx of suspended sediment, followed by a period of slightly deeper neritic conditions. Probably a shallow bathyal environment was established at the transition to the overlying siliciclastic Cabitza Formation. The bathymetric and ecofacies changes in the Campo Pisano Formation are interpreted as having been caused by a discontinuous rise in eustatic sea-level, probably accompanied by subsidence due to tensional tectonics. The depositional environment was that of a distal open-marine shelf or ramp without strong relief. This interpretation is supported by the lack of significant lateral changes in the fossil assemblages, and an upward deepening of facies. The applied micropaleoecological approach is proven a powerful tool in regional stratigraphy and in the reconstruction of sedimentary realms in the Mediterranean Cambrian, particularly when high-resolution biostratigraphic data and diagnostic sedimentary characteristics are sparse.