Turbidite Facies and Facies Associations of Cretaceous and Paleocene Gottero Sandstone, Northern Italy: ABSTRACT

Abstract

Turbidites of the Gottero Sandstone were deposited as a small deep-sea fan in a trench-slope basin. The Gottero is as thick as 1,500 m (4,900 ft), had an original radius of 30-50 km (19-30 mi), and in the early and middle Cenozoic was thrust northeastward onto the Italian peninsula. The Gottero Sandstone is stratigraphically part of the Vara Supergroup, which has an ophiolite at its base and forms one of several stacked allochthonous sheets in the Ligurian Apennines southeast of Genoa. The Gottero, which contains foraminifers ranging in age from Albian to Paleocene that indicate deposition at bathyal depths, consists chiefly of feldspathic sandstone thought to be derived from the largely plutonic Corsican-Sardinian continental block to the southwest. The Gottero rests on ectonically disrupted shale that contains intercalated olistostromes. To the northwest, northeast, and southeast, it pinches out into and is overlain by basin-plain End_Page 512------------------------------ turbidites. An outward-radiating paleocurrent pattern suggests northeastward transport of sand through a single major inner-fan-channel complex, succeeded by radial downfan dispersal to smaller middle-fan channels, outer-fan lobes, and fan-fringe deposits. Sandstone-to-shale ratios are 99:1 in inner-fan-channel deposits, 10:1 in middle-fan-channel deposits, 2.5:1 in middle-fan-levee deposits, 1.3:1 in middle-fan-interchannel deposits, 11:1 in outer-fan-lobe deposits, 2.6:1 in fan-fringe deposits, and 0.25:1 in basin-plain deposits. Orderly and progressive downfan changes in most sedimentary parameters, such as maximum clast size, thicknesses of fining- or coarsening-upward cycles, facies, and facies associations permit the growth history of the fan to be determined. The Gottero Sandst ne provides a useful model for petroleum exploration in small deep-sea fans characterized by a mixture of grain sizes and deposited adjacent to tectonically active, convergent continental margins. End_of_Article - Last_Page 513------------