Pliocene–Pleistocene sequences bounded by subaerial unconformities within foramol ramp calcarenites and mixed deposits (Salento, SE Italy)

Abstract

Nine discrete, metre-scale sequences, of Early Pliocene to Middle Pleistocene age, were deposited in the small Novoli graben (Salento peninsula, Puglia, S-Italy). They consist of carbonate and mixed carbonate-siliciclastic sediments, deposited on a slowly subsiding foreland ramp. Skeletal concentrations and intervening less fossiliferous intervals have been examined to provide information on major environmental parameters and infer the dynamics of their changes. Taphonomic and palaeoecological analyses indicate that storm-induced waves and currents, reduced sediment input, and settling behaviour of components were the main factors controlling the features of the various shellbed types. The concentrations were formed below fair-weather wave base in low-stress inner-to-outer shelf environments and are often associated with surfaces or intervals that are characterized by sedimentary condensation. Vertical change in the fossil content within individual cycles indicates water depth changes that were parallel to climatic fluctuations, hence may result from glacio-eustatic sea-level changes. Most sequences are bounded by subaerial, karstic unconformities. Because of the regional setting of low subsidence rate, the record of the relative sea-level fluctuations is incomplete. Episodes of subaerial exposure and concomitant effects of vadose diagenesis are documented by: (i) diagenetic changes leading to hardening of unconformity horizons; (ii) local subvertical solution pits developed in the vadose zone below unconformity surfaces; (iii) networks of polygonal cracks below unconformities; and (iv) infilling of solution pits and polygonal cracks with vadose silt and marine sediment inwashed during transgressions following the subaerial stages. Lower sequences are characterized by tighter cementation and significant increase in moldic and vuggy porosity, due to superimposition of the diagenetic effects of repeated high-amplitude sea-level fluctuations.