FACIES AND STRATIGRAPHIC ANATOMY OF A TEMPERATE CARBONATE SEQUENCE (CAPO COLONNA TERRACE, LATE PLEISTOCENE, SOUTHERN ITALY)

摘要

Accurate interpretation of ancient non-tropical carbonate systems requires the development of appropriate facies and sequence stratigraphic models. These models should account for the marked differences in sedimentation style among nontropical carbonates formed under different energy settings. This paper presents data and a conceptual model of the sequence architecture of non-tropical carbonates of moderate energy environments based on the late Pleistocene deposits of Capo Colonna marine terrace (Calabria, southern Italy). These deposits have the advantage of being continuously exposed along a proximal-distal transect across the paleo-shelf and their geometry has not been disturbed by later tectonic activity. They consist of a transgressive-regressive (T-R) cycle whose genesis can confidently be related to one of the interstadial glacioeustatic fluctuations of marine isotope stage (MIS) 5. Eight different mixed carbonate–siliciclastic and carbonate facies are present in the studied sequence. Of these, biogenicdominated facies are invariably made up of skeletal remains of light-independent organisms plus or minus red calcareous algae (the heterozoan association). The relatively young age of the deposits allows calibration of the paleoecological significance of observed facies by direct comparison with modern analogues from the Mediterranean Sea. Four laterally persistent discontinuity surfaces were identified along the transect, and interpreted, from bottom to top, as (1) a basal ravinement surface, (2) a submarine hardground locally acting as a substrate for algal boundstones, (3) a regressive surface of marine erosion, and (4) a surface of subaerial exposure. Sequence stratigraphic analysis indicates that the preserved T–R cycle is asymmetric, with a thicker regressive portion. Highstand deposits can be subdivided into a shore-connected sandy prism and more distal autochthonous and parautochthonous skeletal accumulations and algal boundstones. During forced regression, a thin, sharp-based, strongly progradational unit of calcarenites was deposited above the regressive surface of marine erosion. The deposits of Capo Colonna terrace document the response of non-tropical, moderate-energy carbonate ramps to sea-level fluctuations during icehouse conditions. Their architecture can facilitate the interpretation of other successions from similar settings and provide an end member to be compared and contrasted with high-wave-energy cool-water carbonates.