SCALLOPED VS FAULTED CARBONATE PLATFORM MARGINS AND THE ORIGIN OF BASINAL MEGABRECCIAS

SCALLOPED vs FAULTED CARBONATE PLATFORM MARGINS AND THE ORIGIN OF BASINAL MEGABRECCIAS The relationships between carbonate platform margins and adjacent basinal sediments have been studied in Italian carbonate systems of various age, including the Triassic (Ladinian-Carnian) platform slopes of the Dolomite Region, the Cretaceous margin of the Apulia Platform (Montagna della Maiella and Gargano) and the Cenozoic of the Salento Peninsula. Huge megabreccias are present in the Ladinian and Carnian basins of the Dolomites as responses to earthquakes of volcano-tectonic origin. Spectacular seismic-scale outcrops in the Montagna della Maiella allow direct observation of a 1000-m-high escarpment, abruptly separating shallow-water carbonates from slope-to-basin deposits. In plan view, several km-scale amphitheatre-like indentations have been recognized. In the Gargano Peninsula, three major collapse events, during Middle Cretaceous and Middle Eocene, produced extensive and thick megabreccia bodies. Finally, in the Salento Peninsula, several (at least six) carbonate systems (Eocene to Quaternary) are laterally disposed and grafted one upon the other, separated by erosion surfaces and commonly suturing re-entrants in preceding units. These stratigraphic relationships show that: 1) carbonate platform margins are commonly indented and scalloped owing to gravitational collapses, which can be of gigantic proportions; 2) collapses are the main generators of carbonate megabreccias so common in slope and base-of-slope settings; 3) boundaries of carbonate platforms depicted as abrupt and huge subaqueous fault escarpments are basically conceptual models which are very far from the real “geologic world”; 4) massive dismantling of platform margins and associated accumulation of megabreccia wedges may produce in adjacent basin successions a sequence-stratigraphic organization that may have nothing to do with relative sea-level fluctuations; but rather can be simply the result of tectonic dismantling of the platform margin.