Sequence stratigraphy of a lowstand prograding complex, middle-upper Pliocene Ariano Unit, Potenza Basin (southern Apennines, Italy)

The depositional architecture and the sequence stratigraphy interpretation of middle-upper Pliocene coarse-grained deltas, forming the best-exposed part of the Potenza Basin succession (southern Italy), are discussed in this study. The data document that high-frequency glacio-eustatic sea-level changes and tectonic uplift were distinctive elements on the control of the sedimentary evolution of an Apenninic ‘satellite’ basin. The studied succession forms a lowstand prograding complex (LPC) representing the lowermost element of a 3rd-order depositional sequence, known as Ariano Unit, middle-late Pliocene in age. During the ensuing relative sea-level lowstand, vertical-stacked coarse-grained Gilbert-type braid deltas and coeval shoreface successions prograded several kilometers basinward forming the LPC. The LPC succession consists of coarse-grained prevalent sediments, generally shoaling upwards from offshore mudstone containing pro-delta turbidites to conglomeratic delta foresets and topsets, with laterally coexisting sandstone-dominated shoreface facies. Along the vertical-stacked succession, a key surface of marine transgression, divides the succession into two 4th-order deltaic sequences (P1 and P2), whilst internal changes on the depositional architecture indicate lower-rank composing minor sequences or stratal units. The overall stratigraphy of the 3rd-order Ariano depositional sequences suggests an initial relative sea-level lowstand and a successive rise that generated a major marine flooding surface. A relative sea-level fall followed, resulting in widespread exposure and incision. The internal arrangement of the 4th-order sequences indicates the occurrence of minor relative oscillations (up to the 5th-order) producing distinct deltaic units. The 5th-order units are reciprocally arranged in ‘attached’ and ‘detached’ imbricate-stacked braid-deltas, recording a long stage of sea-level relative lowering, punctuated by short rises and alternated falls of different amplitudes. The interpretation of the depositional architecture of the lowermost part of the Ariano Unit demonstrates that uplift persistently controlled the sedimentation during sequence P1, affecting differently the western margin of the Potenza Basin.