PLIOQUATERNARY MEGASEQUENCE GEOMETRY AND ITS TECTONIC CONTROLS WITHINTHE MAGHREBIAN THRUST BELT OF SOUTH-CENTRAL SICILY

Sequence stratigraphy in marine foredeep and thrust-top basins is cont rolled by the conventional variations in eustatic sea-level and sedime ntation rate together with tectonics. Vertical motions reflect combina tions of subsidence due to regional flexure and uplift on local thrust anticlines which act to modify the volume and shape of accommodation space together with syn-depositional slopes. Plio-Pleistocene successi ons on Sicily were deposited in thrust-top and foredeep basins, above and ahead of evolving structures of the Maghrebian fold and thrust bel t. Collectively the sediments represent a single megasequence defined at its base by a maximum flooding surface of earliest Pliocene age fol lowing reconnection with global sea-level at the end of the Messinian. The internal stratigraphy of this megasequence consists of Trubi chal ks, blue marls and a coastal calcarenite package with subordinate sili ciclastic sand. Plankton biostratigraphy allows these facies to be pla ced in a chronostratigraphic framework. Regionally the upper assemblag e progrades away from the orogenic hinterland, recording a tectonicall y forced regression in response to regional uplift from late Pliocene times. This uplift may be associated with isostatic unloading in the o rogenic hinterland due to tectonic collapse of the more internal thrus t sheets. Prior to this, flexure from orogenic loading is inferred to have been sufficient for regional subsidence locally to outstrip uplif t associated with the growth of some thrust structures. For shallow-wa ter facies the competition between thrust-related uplift and flexural subsidence can be investigated from the stacking patterns of paraseque nce sets. For structures developed at greater palaeobathymetries recei ving fine-grained pelagic sediment, active tectonics may be recognized from depositional hiatuses.