ABSTRACT: The Interplay of Tectonism and Eustasy in Controlling Carbonate Platform-to-Basin Deposition: Triassic of the Dolomites, Northern Italy

Lyndon A. Yose, Lawrence A. Hardie, Peter Littman

Stratigraphic histories of seven separate Late Ladinian to Carnian platform systems of the Dolomites are compared to help distinguish local tectonic from eustatic controls over platform-to-basin deposition. These platforms are ideal for this type of study in that they are well exposed, relatively undeformed by later Alpine tectonics and each provide and independent case study for regional comparison. Recent workers proposed that these platform-basin systems provide examples of lowstand debris sheets, lowstand wedges, and prograding highstand systems tracts. Published eustatic curves for the Late Ladinian and Carnian have been constructed, in large part, based on these relationships. A problem, however, is that these platforms developed coeval with strike-slip faulting and volcanism, which must have played a major role in their evolution. Also, the proposed sequence models are constructed piecemeal from relationships exposed at a few specific localities and have not been tested at a regional scale.

An important problem in this study is identification of systems tracts in deep-water carbonate environments. For example, carbonate megabreccias used as evidence by others for a global sea level drop near the Ladinian-Carnian boundary are interstratified with platform-derived carbonate sands and muds and may actually represent base-of-slope talus accumulations adjacent to submerged, rather than exposed platforms. Our regional comparison of separate platform histories based on new palynostratigraphic determinations and new interpretations of systems tracts indicates that local tectonic variations (in rates of subsidence and uplift) in combination with competing platform and volcaniclastic source areas during basin filling, have produced significantly different platform-to-basin deposit onal records from one area to the next. However, long-term regional trends in platform development during the late Ladinian and Carnian can be recognized, and may be related to more regional thermo-tectonic processes or eustatic sea level changes.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990