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Abstract: The Evolution of the Mid-Triassic Carbonate System in the Italian Dolomites: Interaction Between Tectonics and Environmental Variations Affecting the Carbonate Factory

M. Stefani, F. van Buchem, A. Bosselini

The Mid Triassic (Anisian-Ladinian) carbonate system in the Italian Dolomites represents an overall 2nd order transgressive/regressive cycle (composed of four 3rd order sequences) which was strongly controlled by regional tectonism. The specific growth patterns of the carbonate platforms (slope angle, facies composition) during this cycle reflect the response of the carbonate factory to the gradually changing environmental conditions.

The organisation at the basin scale bears evidence of tectonic control in (1) the shaping of the topographic landscape by differential subsidence, creating subbasins and relative highs, the latter of which became the nucleation sites of both the "Ansian" and "Ladinian" platforms; and (2) in controlling the accommodation space available for carbonate growth by the changing rate of subsidence. The role of eustatism is difficult to detect at the basin scale, but the overall transgression was also recorded in other Alpine and European basins.

At the facies scale, we found an evolution of the ecosystem over the course of the 2nd order cycle: during general transgression carbonate productivity was high and large amounts of carbonate mud were deposited on generally gently inclined slopes during times of slow relative sea level rise (progradation in "Anisian times"); when subsidence accelerated aggradation occurred of the isolated pinnacle reefs (early "Ladinian"), slopes became steeper (15-30°) and concave but were still very muddy; during general regression, due to a slowing down of the subsidence, the productivity of carbonate mud was very low, and progradation occurred (late "Ladinian") by deposition of carbonate clasts on the now steeply inclined slopes (up to 45°).

AAPG Search and Discovery Article #90956©1995 AAPG International Convention and Exposition Meeting, Nice, France