Middle Triassic Paleokarst Surfaces and Associated Stratigraphic Patterns in Platform Carbonates: Evidence from Sedimentology and Diagenesis, Southern Alps, Italy

MUTTI, MARIA, and FLAVIO JADOUL, University of Milan, Milan, Italy

Triassic carbonate platforms are superbly exposed in the Southern Alps. A regional paleokarst surface occurs in the Middle Triassic, at the Ladinian-Carnian stage boundary, and is well recognized throughout the Tethyan region. We describe the characteristics of the paleokarst and the stratigraphic patterns of the strata deposited immediately after the formation of the surface in the Brembana Valley.

The paleokarst cuts up to tens of meters into the underlying Esino Limestone massive platform facies and forms a lens-shaped depression filled by peritidal cyclic facies intensively deformed in tepees. The origin of this geometry can be explained either as a tectonic-controlled feature or as a karst-processes related incised-valley associated to a major eustatic cycle. Depression-filling peritidal facies are intensively deformed in senile tepees and are periodically interbedded with "terra rossa" soils and tend to pinchout at the margins of the depression. Several orders of cyclicity are recognized in peritidal carbonates.

Diagenetic features are exceptionally complex and record a wide variety of superimposing environments ranging from normal marine to early meteoric and can be related to major cyclic stratigraphic patterns. Syndepositional cements form up to 80% of the present rock.

AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)