Sedimentology and sequence stratigraphy of wedge-top clastic successions: Insights and open questions from the upper Tortonian Terravecchia Formation of the Scillato Basin (central-northern Sicily, Italy)

Abstract

An up to 1250m-thick clastic succession, the upper Tortonian Terravecchia Formation (TRV), has been analyzed in detail in the middle-late Miocene Scillato wedge-top Basin grown above an already deformed tectonic stack in the northern Sicilian fold-and-thrust belt. The study involved field-based sedimentological and stratigraphic analyses aimed to determine to what extent both the depositional and sequence stratigraphic evolution of the Scillato Basin have been ruled by syn-sedimentary compressional to transpressional tectonics. Widespread intraformational angular unconformities associated with sudden change of palaeocurrents pattern and successive source area shifting suggest that tectonics acted, at least during the late Tortonian, as a major controlling factor during the sedimentation and generation of the sequential architecture of the basin infill. Six main facies associations were recognized, respectively: 1) gravelly braidplain “A”, (2) alluvial plain with ephemeral ponds “B”, (3) sandy - gravelly river-dominated delta front “C”, (4) brackish prodelta clayey siltstones “D”; (5) prograding delta slopes and delta front “E” and (6) delta top conglomerates and sandstones “F”. These associations are arranged into two main successive depositional systems: (1) the entrenched valley fill system (EVF) and (2) a retrograding to prograding river-dominated delta system (RDS). Both depositional systems and facies associations are arranged laterally and vertically to create a tectonically-induced late Tortonian Trangressive-Regressive cycle developed in a time interval roughly coinciding with the III order, 3.1. eustatic cycle. The Scillato Basin Trangressive-Regressive cycle is internally modulated by a depositional sequence set consisting of four IV order sequences here named LTS1, LTS2, LTS3, LTS4, respectively, bounded by tectonically-enhanced unconformities. The data here shown from the Terravecchia Formation suggest that the Scillato Basin is a good case-study of tectonically controlled sequence stratigraphic evolution and an analogy for similar continental to shallowmarine wedge-top basin infill.