THE FORESLOPE AND TOE-OF-SLOPE FACIES OF THE MIDDLE TRIASSIC LATEMAR BUILDUP (DOLOMITES, NORTHERN ITALY)

The Latemar buildup was a circular carbonate buildup (4 km wide) with a central platform core (flat-bedded interior platform and massive reef margin) flanked on all sides by slope facies. Steeply dipping (30-35-degrees) foreslope breccias are present adjacent to the margin and flat-lying graded grainstones at the toe of slope. Slope facies relate directly to depositional profile and slope angle. The steeply dipping foreslopes consist of lobate breccia beds that are 25 m thick and a few tens of meters across, and extend tens to hundreds of meters downslope. Some beds are conformably overlain by thinner (< 1 m thick) beds of finer-grained carbonate sediment. The basal surfaces of the breccias are erosional and are anastamosing in both strike and dip views. The breccia talus was derived principally from margin boundstones and deposited by rockfalls and avalanches. Planar clinoforms extend the entire height of the foreslope (hundreds of meters) and bracket depositional units (clinothems) tens of meters thick. Clinoforms appear to be shear surfaces formed during large slope failures (avalanches?). Graded grainstone beds less than 1 m thick are present at the nearly flat-lying toe of slope. These consist of redeposited shallow-water (platform-interior and reef-margin) carbonate sands, some with nodular limestone caps, that are interpreted as proximal carbonate turbidites. Toe-of-slope breccias are the downdip extensions of foreslope breccias and pinch out abruptly basinward. Some slope depositional processes are related to high-frequency (fourth-order and fifth-order) sea-level changes: toe-of-slope graded grainstones correspond to times of platform submergence. In contrast, foreslope breccia was deposited during both platform submergence and exposure. The slope deposits do not record the high-frequency cyclic rhythms identified in shallow-water platform sections. This is attributed to the nature of slope deposition. Downslope talus transport was episodic and localized; graded grainstone beds reflect storm redeposition.