Re-sedimented rhodoliths in channelized depositional systems

Abstract

The knowledge of re-sedimented rhodolith deposits has always lagged behind that of in situ deposits, which can be formed in shallow and deeper water carbonate and mixed siliciclastic-carbonate depositional settings. A combination of detailed outcrop analyses from three published case studies reveals a series of palaeobiological and taphonomic signals that are used to identify fossil re-sedimented rhodoliths. The re-sedimented rhodolith deposits of the middle Eocene carbonates in the Venetian area (northeast Italy), the lower Miocene carbonates from southern Sardinia (Italy), and the lower–middle Miocene carbonates from Southern Apennines (southern Italy) are described in terms of rhodolith morphology, coralline algal assemblages, inner arrangement, outer growth-forms, and taphonomic signatures. In all the cases, shallow water rhodolith beds were redeposited to feed offshore deposits through submarine channel systems. The sedimentological features, rhodolith characteristics and taphonomic signatures of the rhodolith deposits are compared from the carbonate factory, through the shelf-margin to the proximal and distal parts of the tributary belt. Within submarine channelized carbonate settings, complex relationship patterns of autochthonous/parautochthonous and allochthonous rhodolith deposits were governed by the interplay of changes in environmental factors such as water energy, light irradiance, substrate characteristics, and residence time on the sediment-water interface.