CARBONATE SLOPE CLINOFORMS FROM OUTCROP TO NUMERICAL MODEL: THE GROWTH OF THE ROSENGARTEN PLATFORM (MIDDLE TRIASSIC, DOLOMITES, ITALY)

Owing to its spectacularly outcropping slope clinoforms, the Rosengarten in the Dolomites of Northern Italy has long since been a reference model for progradational carbonate platforms. A combination of reverse basin and forward stratigraphic modelling was carried out on the N-S trending platform transect in order to quantify basin dynamics and platform evolution. Data sets for both modelling approaches were derived from existing studies and new detailed analyses on facies architecture and thermal maturity of underlying strata.

The Rosengarten platform is characterised by two major stages of platform evolution with different sets of clinoforms. The first set reveals aggradational, the second progradational sedimentary characteristics. Our reverse basin and forward stratigraphic modelling results show that these two platform stages originate in a temporal change in total subsidence. Spatial variations in total subsidence along the 6km transect were insignificant. During the first stage of platform evolution, high total subsidence rates of up to 1200m/Ma yielded aggradational clinoforms. As total subsidence rates dropped below 400m/Ma, clinoforms with progradational characteristics developed. This maximum in the first stage was pulse-like as it reached from 241.5Ma to 241.2Ma only. Explanations for the sudden stop in subsidence are synsedimentary deep-reaching strike-slip tectonics in the vicinity of the Rosengarten (ca. 10km to the SE) and the subsequent development of a huge magmatic chamber.

Stratigraphic forward modelling was applied to quantify the controlling factors of carbonate platform evolution. In order to replicate the clinoforms and platform architecture, constant carbonate production rates of up to 900m/Ma were necessary. It is therefore evident that at the verge of the Anisian - when platform development launched at Rosengarten - the carbonate factory must have had recovered completely from the P/T biotic crisis. Our results also indicate that sealevel oscillations played a minor role as architects for slope clinoforms. This aspect has implications for the eustatic sealevel curve of the Middle Triassic, which is primarily derived from field data. Variations in total subsidence chiefly controlled the growth mode of the Rosengarten platform and the geometry of its slope clinoforms.