Massimo Bernini

Mass-transport deposits in confined wedge-top basins: surficial processes shaping the messinian orogenic wedge of Northern Apennine of Italy

Among the many cases studied of mass-transport deposits in continental margins, the role of basin topography in controlling the types, distribution, architecture and emplacement of such deposits has not been properly remarked. In the western portion of Northern Apennine foothills, masstransport deposits form two composite Messinian mass-wasting bodies that reveal progressive development strictly controlled by basin topography. Extensively analyzed through stratigraphic and structural studies, they form two major elliptical-shaped bodies in map view; maximum 10 kilometres wide, tens of kilometres in length and with estimated volumes of about 250 km3 each, they are elongated parallel to NW-SE oriented thrust fronts. They are coalescing chaotic masses that consist, at the base, of debris flows formed by monogenic gypsum arenite or breccia and decametric blocks of primary gypsum, whereas at the top they are made up of kilometres-wide outliers of pre-gyspum deposits, which slid away from partially preserved headwall scarps. In the external accumulation zone, the mass wasted deposits show imbricate thrust-stacks composed of scraped-off gypsum debris flow deposits. The types, distribution, architecture and emplacement of the studied mass-transport deposits testify the strict control of the wedge-top basins morphology. The internal and steeper flank of the wedge-top basins was representing the depletion zone of sliding masses; whereas, the outer and less steep flank of the wedge-top basins stopped the moving masses and formed the accumulation zones. The relief of the wedge-top basins was progressively modifying during the intra-Messinian tectonic pulse that, affecting the entire Northern Apennine orogenic wedge, triggered the studied mass-transport deposits

Tectonic and Climatic Controls on Sedimentation in Late Miocene Cortemaggiore Wedge-Top Basin (Northwestern Apennines, Italy)

At the foothills of the north-western Apennines, the Cortemaggiore Wedge-Top Basin (CWTB) is bounded by the buried and arcuate Cortemaggiore anticline, to the north, and by the polyphased and complex Salsomaggiore tectonic window, to the south. The CWTB started to form in response to a late Tortonian tectonic pulse that uplifted the Cortemaggiore anticline and established euxinic conditions. A major intra-Messinian tectonic pulse further shortened the CWTB and triggered the emplacement of gravity-driven mass-wasting deposits above which turbiditic, shelfal deposits evolve upward to fluvio-deltaic deposits. The former, Late Messinian hypohaline succession, is characterized by a well-developed cyclical pattern which falls in the range of astronomically-controlled climate changes with precessional periodicity modulated by obliquity and eccentricity periodicity. Tectonic and climate controls on sedimentary succession of the CWTB act at different frequencies. Based on the refined and highresolution late Miocene chronostratigraphy of coeval Mediterranean sedimentary succession, it is possible to time constrain the tectonic and climatic events and their cyclicity. Tectonics control acts at low frequency (order of 2 Myr) and produces major and fast morphologic changes of the basin. Climate acts at variable higher frequency (order of 20–100 kyr); it both distributes laterally and stacks vertically and cyclically the sediment supplied to transport by erosion of tectonically uplifted rocks. The tectonic and climatic controls should have acted concomitantly over the entire Northern Apennines foreland basin system and the Mediterranean area, because cyclicity and depositional characters of late Miocene succession present common features. Tectonic uplift causes basin-wide hydrologic and hydrogeologic changes that might induce increased evaporation; in the CWTB, two drier climate events, corresponding to the lower and upper evaporites of the Mediterranean region, are closely preceded by tectonic pulses. However, during late Miocene, climate changes occurred also outside the Mediterranean region. Thus, it is argued that the 2 Myr is a periodicity common both to tectonics pulses and climate changes; it is a low-frequency cyclicity that, related to astronomical forces, drives simultaneous action of tectonic pulses and climate changes within the CWTB.