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Abstract

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 m.y.) accommodation sequences within the platform interior, the Lower Ladinian sequence (8 m.y.; 400 m thick) and the Upper Ladinian sequence (6 m.y.; 340 m thick). The Lower Ladinian sequence developed atop a widespread, low-relief Middle Anisian carbonate bank (60 m thick). Underlying subtidal cycles of the Middle Anisian bank thin upward into the basal, subaerial sequence boundary of the Lower Ladinian sequence reflecting decreasing third-order accommodation. Above this sequence boundary, platform-interior facies of the Lower Ladinian sequence retrograde. This retrogradation results in superimposition of Ladinian basinal and foreslope facies atop the underlying, horizontal, shallow-water bank along its periphery. The transgressive and highstand systems tract of the Lower Ladinian sequence and transgressive systems tract of the Upper Ladinian sequence are marked by long-term, systematic vertical facies changes (subtidal vs. subaerial exposure-dominated facies) and variation in stacking patterns of aggradational high-frequency, 20 k.y. cycles within the platform interior. The maximum flooding surface in the Lower Ladinian sequence is a prominent surface in a platform interior position that loses its identity laterally into reef margin, foreslope, and basinal facies. A stratigraphically transitional sequence boundary caps the Lower Ladinian sequence, marked by an interval of vertically superimposed thin subaerial tepees. Beneath this interval, high-frequency cycles are thinning-upward, and above they are thickening-upward. At this sequence boundary there is no downward shift in overlying facies, no lowstand wedge in the downdip position, particularly in the case of isolated buildups such as the Latemar, and no erosional hiatus. 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.

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