Evolution and organization of the Sciliar/Schlern carbonate buildup (Triassic Dolomites - Italy).

The Sciliar/Schlern area is the type area of the Dolomia dello Sciliar. Here it’s where the biological origin of ancient carbonate platforms has been recognized for the first time in the Dolomites. This area has been widely studied since the 19th century because of the outstanding outcropping of carbonate platforms: here lateral facies transition and depositional geometries are very well preserved. This allowed us to study composition, architecture and depositional environments of a fossilized reef. In this report we present an integrated stratigraphical and sedimentological study combined with a facies analysis of the area. Our data lead us to better understand the evolution and the growing mode of several different generations of superimposed carbonate buildups from Anisian to Carnian p.p. (Triassic), and the relationships between the inner organization of the carbonate platforms, the margin rim and slope and the correlated basinal facies. The stratigraphic correlations resulted from the lithological data and the facies analysis have been integrated with known and new biostratigraphic data (mostly ammonoids and palynomorphs) in order to build a high resolution bio-chronostratigraphic framework. The result is the remodeling of the evolution of the Sciliar/ Schlern buildup which is the consequence of the growing of different generations of carbonate platforms. The three-dimensional development of each growing phase of the platform seems to be controlled mainly by the rate of accommodation , by the inherited morphology of the previous body and by the variation in basinal sedimentation rate that forces the decrease of the clinoforms’ angle. Another peculiarity of the last phases of the evolution of this platform is the huge number of megabreccias bodies and carbonatic olistoliths (“Cipit boulders”) found in the Alpe di Siusi/Seiser Alp volcanoclastic basinal sediments. These bodies are probably related to frequent displacements which involved both the slope and the reef, testified by several scallops features recognized along the paleo-slope.