Neptunian dikes along submarine escarpments: examples from the Jurassic of Monte Kumeta (Sicily)

Along the Jurassic escarpment of Monte Kumeta (western Sicily), the opening of neptunian dikes is related either to extensional tectonics or to dilatation due to down-slope sliding. Crosscutting relationships coupled with biostratigraphic data indicate that at least three generations of fractures formed from Early to Middle Jurassic times. Orientation of dikes similar to the strike of coeval faults, and occurrence of fitted breccia are all considered to be evidence of coeval extensional tectonics, whereas box-shaped cavities are indicative of gravitational down slope sliding of detached rock blocks. During Late Jurassic times anastomosed cracks indicating surficial extension due to downslope creeping of semilithified deposits, suggest gravity as an important controlling factor at that time.