CARBONATE PLATFORM PRODUCTION AND EXPORT POTENTIAL RECORDED IN UPPER JURASSIC BASE-OF-SLOPE DEPOSITS (CENTRAL APENNINES, ITALY)

Upper Jurassic base-of-slope and inner-platform carbonate successions have been studied in the Lazio–Abruzzi and northern Campania–Molise sectors of the central Apennines. Based on the analysis of systematic trends in thickness, grain size, lithofacies proportion, and evolution, these successions have been subdivided into decametric depositional cycles. The stacking pattern of these cycles shows a larger-scale stratigraphic organization, corresponding to a long-term cycle entirely encompassing the Upper Jurassic studied interval. Composition of base-of-slope resedimented deposits indicates that they were exported from the inner platform and the reef margin. The inner-platform cycles reflect changes in carbonate production, whereas base-of-slope cycles reflect changes in inner-platform and reef-margin export potential. Biochronostratigraphic tie points allow us to compare production and export patterns recorded by platform and base-of-slope successions. Sedimentary features of the shallow-water cycles indicate that sea level controls the inner-platform production. The correlation between the shallow-water and the base-of-slope sedimentary cyclic record indicates that the inner-platform production and export potential are comparable. The hierarchical architecture of the shallow-water cycles indicates that sea-level fluctuations had two different frequencies (low and high). During low-frequency sea-level fluctuations, inner-platform production and export directly correlate with long-term phases of platform accommodation. During high-frequency sea-level fluctuations, inner-platform production and export depend on whether the shallow-water cycles modulate long-term phases of platform accommodation. The internal organization of base-of-slope depositional cycles shows that, during high-frequency sea-level fluctuations, the inner-platform and the reefmargin sediment export is time-shifted. This export pattern is interpreted as the response of the inner platform size and of the reef biotic system to sea-level fluctuations. During the early stages of platform flooding (early HST), the reef-margin export potential is low, because sediments produced fill the available space. During slowing sea-level rise (late HST), the space created is rapidly filled, allowing the reef margin to gently prograde and its export potential to progressively increase. During both early and late HST, the extent of the innerplatform area is at its maximum, and production and export are high. When emersion takes place on the platform, during the LST, the size of the productive inner-platform area reduces, and the inner-platform input decreases or ceases. The reef margin is forced to prograde basinward, and its export potential records the highest values.