Sequence Stratigraphy and Systems Tract Development of the Latemar Platform, Middle Triassic of the Dolomites: Outcrop Calibration Keyed by Cycle Stacking Patterns
GOLDHAMMER, R. K., and P. A. DUNN, Exxon Production Research Co., Houston, TX, M. T. HARRIS, University of Wisconsin at Milwaukee, Milwaukee, WI, and L. A. HARDIE, Johns Hopk_ns University, Baltimore, MD
The Middle Triassic Latemar platform (740 m thick, 5-6 km wide) provides a seismic-scale outcrop example of an intact carbonate shelf-to-basin transition, ideal for integrating sequence stratigraphy with facies and cyclic stratigraphy This subcircular, high-relief buildup records two third-order (1 - 10 myr) accommodation sequences within the platform interior: the lower Ladinian sequence (L1-8 myr; 400 m thick) and the upper Ladinian sequence (L2-6 myr; 340 m thick). Sequence L1 developed atop a widespread, low-relief Middle Anisian carbonate bank (60 m thick). Underlying subtidal bank cycles thin upward into the basal, subaerial sequence boundary (type I) reflecting decreasing third-order accommodation; above it, platform-interior facies of sequence L1 retrograde. This results in su erimposition of Ladinian basinal and foreslope facies atop the underlying, horizontal, shallow-water bank along its periphery. The transgressive (TST) and highstand systems tract (HST) of sequence L1 (as well as L2) are marked by long-term, systematic vertical facies changes (subtidal-versus exposure-dominated facies) and variation in stacking patterns of aggradational high-frequency, 20 kyr cycles (progressive thickening-versus thinning-upward) within the platform interior. The maximum flooding surface (MFS) is a marine hardground surface displaying evidence of very slow sedimentation and is the platform expression of the condensed section. A type 2 SB caps sequence L1, marked by an interval of vertically superimposed thin subaerial tepees; beneath this, high-frequency cycles are thinni g-upward, and above they are thickening-upward. Only the transgressive systems tract of sequence L2 is preserved at the Latemar owing to late Ladinian-Early Carnian volcanism and tectonism which terminated carbonate platform deposition.
AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)