Miocene shallow-water deposits of the northern Apennines: a stratigraphic marker across a dominantly turbidite foreland-basin succession

Abstract

Lower-Middle Miocene shallow-water deposits commonly occur in the piggy-back-basins sequence of the northern Apennines thrust-belt. In contrast, such deposits are restricted to small bodies of reduced lateral extent in the adjacent foredeep succession. Lateral tracing of major unconformities across the two different structural domains allows reconstruction of a common sedimentary evolution for the study area, through the identification of three depositional sequences with an internal arrangement in systems tracts, generally showing lack or scarcity of lowstand deposits. A regional unconformity, marking the erosional truncation of the underlying turbidite deposits, constitutes the base of sequence S1 (Upper Burdigalian). Above mixed carbonate-siliciclastic, shallow-water facies (transgressive systems tract, TST), sequence 51 exhibits a progradational stacking pattern of outer-shelf to inner-shelf and nearshore facies (highstand systems tract, HST). The unconformable lower boundary of sequence S2 (Lower Langhian) is the base of transgressive, glaucony-rich, tide- and storm-influenced nearshore arenites (TST). The maximum flooding surface, showing local concentration of glaucony, records the sharp change from marginal marine arenites to highly bioturbated shelf deposits (HST). A generalized drowning of shelves during the Late Langhian-Early Serravallian is documented by rapid transition to coarse-grained siliciclastic deposits and deepwater marls (sequence S3). Tectonics appear to have exerted a major control on sedimentation, especially at the onset of sequence S1 and during deposition of sequence S3. Conversely, a possible eustatic control may apply for sequence S2.