Sedimentation and tectonics in a steep shallow-marine depositional system: stratigraphic arrangement of the Pliocene-Pleistocene Rometta Succession (NE Sicily, Italy)

Abstract

A 160 m thick Pliocene-Pleistocene sedimentary succession, cropping out in NE Sicily (Rometta Succession), was subdivided into three unconformity-bounded units, overlying deformed bedrock: (i) a Middle Pliocene sandymarly R1 unit; (ii) an Upper Pliocene-Lower Pleistocene biocalcarenitic R2 unit; (iii) a Middle Pleistocene mudstone R3 unit. The R2 unit is composed of at least three sub-units, bounded by truncation surfaces, and showing aggradational patterns of strata. Each of these sub-units records a sudden seaward-shifting of the facies tract. A stratigraphic gap of ~870 kyr at the R1/R2 boundary, marks an abrupt change from offshore transition to shoreface environments. A second gap of ~260 kyr at the R2/R3 boundary corresponds to a sudden deepening of the environments, from shoreface to fully offshore. The Rometta units represent three incomplete, tectonically-enhanced depositional sequences. The R1 unit is a HST of a lower sequence, marked at the top by a slightly angular unconformity. The R2 unit is a HST of a younger depositional sequence, aggrading above a ravinement surface. During these relative sea level still-stands, the local tectonic uplift combined with the high-frequency eustatic oscillations, produced three forward-stepping sets of minor sequences within the R2 HST, simulating the typical FSST stratigraphic arrangement. The top of the R2 is bounded by an erosive surface, representing the transgressive surface of the subsequent R3 depositional sequence. The R3 unit is a late TST+HST of a Pliocene-Pleistocene sequence, the LST of which probably occurs basinward. The foresetted R2 biocalcarenites are unimodal in their paleocurrents. This feature resulted from shore-directed wind stress, applied to the water surface and reflected by a steep paleocoast, generating basinward-directed bottom currents.