DEPOSITIONAL GEOMETRIES AND FACIES ASSOCIATIONS IN AN UPPER CRETACEOUS PROGRADING CARBONATE PLATFORM MARGIN (ORFENTO SUPERSEQUENCE, MAIELLA, ITALY)

Although progradation of platform margins is a well documented process , its timing with respect to sea-level cycles is controversial, This o utcrop study was designed to test the relation between prograding stra tal patterns and sea-level cycles, using a sequence stratigraphic anal ysis and direct investigation of the sedimentological facies associati ons, The upper Campanian-Maastrichtian Orfento supersequence in the Ma iella platform margin is an outstanding outcrop example of a large-sca le prograding carbonate wedge, composed of smaller-scale, vertically a nd laterally stacked sequences, The evolution of the Orfento supersequ ence was characterized by an initial phase of aggradation, followed by progradation, At the scale of the supersequence, basinal aggradation preceded progradation of shallower-water facies, because excess relief had to be buried prior to progradation. Seven depositional facies wer e distinguished on the basis of depositional geometries, stratal patte rns, and sedimentary features, These facies record different depositio nal environments on a low-angle ramp, ranging from deep-water pelagic wackestones to wave-dominated upper shoreface grainstones, Facies dist ributions record the overall transition from pelagic sediments, turbid ites, and megabreccias into progressively shallower-water shoreface co mplexes, The prograding units consist of shingled offlapping sigmoidal complexes, composed of rudstones and grainstones, deposited in shallo w, wave-dominated environments, and their deeper-water equivalents. Si gmoidal sequences are separated by erosive unconformities, which bring upper-shoreface facies into direct contact with underlying lower-shor eface or outer shelf facies, indicating a sea-level fall (forced regre ssion), Meteoric diagenesis associated with the unconformities also su pports lowering of relative sea level, Depositional facies patterns wi thin sequences record a relative rise and highstand of sea level, Repe titive downward shifts bring the shoreline successively farther basinw ard, indicating long-term lowering of sea level during the late stages of progradation, producing downstepping progradation, Our data sugges t that changes in relative sea level, acting on a lo ir angle ramp, co ntrol the overall architecture of sequence distribution, whereas chang es in sediment supply control changes in facies association within eac h sequence.