No abstract

Mixed siliciclastic-carbonate deposits consist of a suite of different types of mixing between the two components, from bed (core-plug) to stratigraphic (seismic) scales, producing a high vertical and lateral lithological variability. Mixed deposits result from the interaction of siliciclastic input and coeval carbonate production controlled by temporal and/or spatial factors. Although mixed deposits are very diffuse in the geological record, studies about these deposits are scrappy and not well encoded. Accordingly, mixed deposits represent a labyrinth for researchers who want to investigate them for the first time.In this paper, different types of mixing (compositional versus strata) controlled by different allocyclic (e.g. sea-level, climate) and/or autocyclic (e.g. depositional processes) factors that operate at different scale are documented. Mixing is recognized and described at three main scales of observation: bed/core-plug scale; lithofacies/well-log scale; and stratigraphic/seismic scale. (i) Compositional mixing reflects the contemporaneous accumulation of the two heterolithic fraction in space and time. This type of mixing is observable at lamina to bed scale, locally producing depositional structures diagnostic for particular depositional environments. (ii) Strata mixing results from the alternation of the two heterolithic fraction in time. This type of mixing is observable at lithofacies to stratigraphic scale and can be related to depositional processes, climatic variations and/or relative sea-level changes.A correct identification of these different types of mixing and the scale of their occurrence is crucial in revealing (i) physical processes that control the sedimentation, (ii) environmental factors that influence the carbonate factory related to the siliciclastic dispersal mechanisms, and (iii) internal heterogeneity of the resulting sedimentary deposit. Furthermore, the petroleum industry is interested to unravel new insights about internal properties of mixed siliciclastic-carbonate systems (e.g., porosity, permeability) and to reconstruct predictive 3D models for the related reservoirs. The correct prediction of internal heterogeneity and the recognition of lateral and vertical compartmentalization have an important impact on hydrocarbon exploration and exploitation.

The Bradanic Trough (southern Italy) is the Pliocene-present-day south Apennines foredeep. It is a foreland basin as subsidence due to westward subduction of the Adria Plate involves the continental crust of the Apulian domain. The infill succession of the Bradanic Trough is characterised by the presence of a long thrust sheet system (the so called 'allochthon') that occupied part of the accommodation space created on the foreland by subduction. The upper part of the infilling succession crops out along numerous sections. About 600 m of the 3-4 km basin-fill succession is exposed as the Bradanic Trough has experienced uplift during Quaternary times. Outcropping successions are mainly characterized by shallow-marine deposits comprising carbonates of the Calcarenite di Gravina Formation, silty clay hemipelagites of the Argille subappennine Formation and coarse-grained bodies of the 'Regressive coastal deposits'. The Calcarenite di Gravina Formation (Middle-Late Pliocene-Early Pleistocene in age) crops out in a backstepping configuration onto the flanks of the Apulian Foreland highs. It displays evidence of strong transgression onto a karstic region previously dissected in a complex horst and graben system. The Argille subappennine Formation (Late Pliocene-Middle Pleistocene in age) succeeds the carbonate sedimentation on the foreland side of the basin and represents the shallowing of the basin in the other sectors of the Bradanic Trough. Toward the Apennines chain, in the wedge-top area of the foredeep, the Argille subappennine Formation covers the allochthon, while in the depocentre (in the foredeep sensu stricto) the same formation overlays turbidite deposits. The latter characterize the deeper part of the successions, and are mainly buried below the allochthon. The Regressive coastal deposits (Early-Late Pleistocene in age) represent the upper part of the succession. They consist of coarse-grained wedges that lie on the hemipelagites of the Argille subappennine Formation in, alternatively, conformable or erosional contact. The wedges of the Regressive coastal deposits stack in a downward-shifting configuration, which indicates deposition during uplift. The Quaternary development of the Bradanic Trough differs from that of the central and northern Apennines foredeep. The latter is characterized by aggradation of shallow-marine and alluvial sediments in a subsiding remnant basin, whose filling records a basin-scale depositional regression. In contrast, the Bradanic Trough is characterized by a basin-scale erosional regression and the last evolutive phase of this sector of the Apennines foredeep is best defined as a cannibalization phase rather than a filling or overfilling phase

No abstract

Tide-dominated depositional systems are very common in macro tidal and meso tidal settings. They are less developed in micro tidal marine areas where sediments are dispersed mostly under the effects of waves and currents. In some specific coastal settings, the influence of the dominant hydrodynamics can be reduced or attenuated by the presence of promontories forming engulfed sectors or by the occurrence of submarine passageways or straits. In these conditions, as well as in micro tidal settings, the tidal influence can be amplified, producing a significant signature in the sedimentary record.A number of tide-influenced deposits can be recognized in the Neogene of the Southern Apennine, Italy, although the Mediterranean area is characterized by minor tidal ranges.Spectacular exposure of middle to upper Pliocene deposits cropping out around Tricarico allows the analysis of the architecture and internal complexities of a mixed bioclastic-siliciclastic succession deposited in a thrust-top basin. Undulations forming along the hinge of an anticline favored the onset of seaway conditions, which produced hydraulic amplification of marine currents flowing towards the chain and subjected to tidal influences.The mixed deposits of Tricarico exhibit prominent large-scale, unidirectional cross stratification and a suite of additional dune-and ripple-bedded structures of various dimensions. Cross stratification can be subdivided into four hierarchical levels based on their increasing degree of internal complexity of different ranks (from first-order to fourth-order sets).Processes invoked for the formation of such a complex suite of larger-and smaller-scale sedimentary structures are related to cyclical events, such as high-frequency sea-level oscillations and tidal cycles of various durations.First-order sets are interpreted as produced by migrating subaqueous dunes along a SSW-NNE-trending seaway at water depths below the wave base. These sets exhibit bed-thickness vertical patterns which have been related to the influence of highfrequency base-level oscillations that occurred during dune accumulation, producing alternating stages of accelerating and decelerating currents. Second-order cross stratification has been interpreted to have formed by dunes with varying sinuosity, superposition, and flow conditions, under the effect of varying current strengths but constant sediment production. Formset successions were produced by large compound dunes and are considered as the expression of low-energy and decaying dune fields that developed during times of decreasing sediment transport.Cross lamination of third-order and fourth-order sets shows series of bundles and couplets of coarser and finer laminae which, at a different scale, recorded repeated cycles of tidal ranges of different amplitudes.These considerations allow us to propose an original depositional model represented by a flood-tidal delta, which questions the absence of macro tidal sedimentation within the purportedly micro tidal oceanographic setting of the Mediterrane...