Soft-sediment deformation induced by sinkhole activity in shallow marine environments: A fossil example in the Apulian Foreland (Southern Italy)

Abstract

Soft-sediment deformation structures are exposed in sea cliffs in the lower part of the Calcarenite di Gravina Formation (late Pliocene–early Pleistocene) in the Cala Corvino area N of Monopoli (Adriatic sector of the Apulian Foreland, southern Italy). Deformation affects a thickness of about 5 m involving a lower calcareous–terrigenous sand and gravel unit and an upper heavily bioturbated grainstone and packstone unit. Deformation is absent from the overlying part of the succession. Large-scale soft-sediment deformation structures are collapse features comprising irregularly elongated conical zones of sinking. In vertical section, narrow “drop” zones occur in the lower sandy–gravelly facies and large gentle folds in the upper grainstone–packstone beds. The degree of deformation decreases upwards. Small-scale soft-sediment deformation structures adjacent to the large-scale conical collapse structures are narrow, vertically elongated load structures about 2 m high and 30–50 cm wide that involve only the basal terrigenous facies. The distribution of small- and large-scale soft-sediment deformation structures corresponds closely to zones of fracturing in the underlying Cretaceous limestones, and the elongation directions of soft-sediment deformation structures correspond to the orientation of major fractures in the limestones. The soft-sediment deformation occurred due to collapse associated with karstic sinkhole formation along fractures in the bedrock. Geometrical relationships between deformed and undeformed sedimentary units show that deformation occurred in a shallow marine environment. The structures at Cala Corvino provide a rare outcrop-scale record of sinkhole-induced soft-sediment deformation occurring in a shallow marine environment.