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Traditional sequence stratigraphic models provide limited understanding of the internal complexity and variability of mixed siliciclastic-carbonate strata accumulated in tectonically active settings. Coeval Lower Pleistocene (Gelasian) shallow-marine, mixed siliciclastic-carbonate depositional wedges accumulated within an active piggyback basin along the southern Italy fold-and-thrust belt are characterized by similar internal architecture of sequences but different stacking patterns. In particular, four coastal wedges (up to 30 m thick each), just a few kilometers (~2 km) apart from each other, show aggradational versus progradational stacking patterns related to their location within a deforming piggyback basin. In all the studied sections, mixed siliciclastic-carbonate strata form isolated sedimentary wedges organized into three vertically stacked transgressive-regressive sequences bounded by sharp flooding surfaces. Aggradational versus progradational internal architecture results from (1) local syndepositional compressive and/or extensional tectonics controlling differential uplift and subsidence, and (2) sediment supply characterized by a combination of intrabasinal and extrabasinal siliciclastics and carbonates. Aggradation occurs in areas showing a balance between both accommodation and sediment supply, and siliciclastic and carbonate fractions. Progradation is typical of supply-dominated areas located close to the active anticline, and dominated by the carbonate fraction. The present work documents the local variability of stratal stacking patterns and sediment supply (siliciclastic-carbonate ratio). We highlight the limitations of using sequence architectures and systems tracts for base-level change and basin reconstructions in tectonically active settings. It is important not only to correctly interpret the stacking pattern, but also to increase our understanding of the type of sediment (siliciclastic vs. carbonate) and sedimentation rate, sedimentation loci, and subsurface predictions. [ABSTRACT FROM AUTHOR]

The 3-km-wide Messina Strait divides Sicily from the Italian peninsula, representing one of the most impressive examples of tide-dominated marine passageway of the central Mediterranean Sea. The tidal hydrodynamics governing the strait results from a semi-diurnal phase inversion between two interlinked wider basins (i.e., the Tyrrhenian Sea to the north and the Ionian Sea to the south), due to the presence of a nodal tidal point in the centre of the strait. This condition, associated with coastal narrowing, causes continuous water exchanges and a local phenomenon of tidal amplification, producing collinear tidal currents up to 3 m s −1 in velocity in the point of tidal maxima of the strait centre. Currents follow bi-directional patterns across the strait, decelerating towards either opposite peripheries because of the progressive enlargement of the cross-sectional areas. Tides exert a relevant influence on the strait bottom, shaping characteristic erosional features, governing the main sediment transport routes and promoting the migration of distinctive bedforms. The textural and dimensional attributes of these bottom features vary according to the current velocity trends and main directions, indicating a specific partition of the strait in individual sedimentary zones. In the Early Pleistocene, analogous conditions established across the same area, and huge quantities of siliciclastic and bioclastic deposits accumulated in the ancient Messina Strait under a similar tidal hydrodynamics. The 250-m-thick strait-fill succession, which is magnificently exposed across the two opposite margins (i.e., Scylla and Charybdis) of the modern passageway, represents a crucial correlative element in supporting the reconstruction of the sedimentary dynamics of the past strait, based on the observation of the modern system. In this work, which represents the second part of a first article focused on the modern Messina Strait, previous stratigraphic data are reviewed and integrated with new sedimentological observations carried out in both onshore and offshore key areas. In particular, outcrop analysis allows distinguishing a number of facies associations, which are described and interpreted by taking into account the correspondent modern depositional strait setting. The results of this study highlight a mutual correlation between the depositional zones detected in the modern Messina Strait and the individual facies associations recognised in the onshore margins. The strait-centre zone represented a bedload parting sector in the ancient system. This zone, which is one of the most difficult environment to detect in ancient straits due to a condensed sedimentary record, is suggested to coincide with a structural palaeo-high, exposed in the southern sector of the investigated onshore area and continuing offshore in the modern strait. This tectonic horst symmetrically separated two opposite highly-depositional zones to the north and to the south, hosting gravel and sand-size siliciclastic and bioclastic deposits, exhibiting diffuse motifs of large-scale tidal cross stratification and a specific vertical facies stacking. These characteristic tidal deposits, which are believed to record the migration of several generations of tidal dunes forming extensive bedform fields in the strait, reflect a tidal asymmetry between flood and ebb currents. Tidal asymmetry is referable to the oceanographic setting observable nowadays in the Messina Strait and deriving from a marked density-driven, water-mass stratification between the two opposite flows. In the ancient system, tidal dunes transited down-current to highly bioturbated fines, including sporadic small-scale tidal cross strata, representing the distal periphery of the Early Pleistocene strait. Here, bedforms followed migration pathways not always reflecting mutually-evasive net-gross sediment transport routes, due to local conditions of current rotation occurring during each tidal phase inversion. During these stages, similar to slack-water periods, currents were weak enough to allow fine sediments to be settled from suspension, reproducing a signature typical of other tide-dominated coastal systems (e.g., estuaries, tidal flats, etc.). These sedimentary zones of the ancient Messina Strait were laterally bounded by tectonically-active margins, where fan deltas, clastic aprons and carbonate wedges developed under the constant interplay between mass-transport processes and tidal currents. The resulting architectural and sedimentary features observable in outcrop reveal impressive similarities with the morpho-bathymetric features nowadays documented in the correspondent strait-margin modern environments. These considerations allow deciphering a general palaeo-environmental reconstruction of the ancient strait which, although suffering of limitations due to a partial preservation of the whole rock record, discloses sedimentary processes and depositional environments of the ancient Messina Strait. The process-based analysis of this field-based case study is crucial in predicting long-term environmental changes and facies migration pathways and improves the state of knowledge on tidal straits, which are the less understood among the most common tidal depositional systems. [ABSTRACT FROM AUTHOR]

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 results 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. [ABSTRACT FROM AUTHOR]

Sandstone tidal cross-strata are the predominant sedimentary feature of strait-fill stratigraphic successions. However, although widely described in numerous studies, tidal strait-fill two-dimensional and three-dimensional cross-strata have rarely been reported to occur in discrete intervals which are laterally adjacent or vertically stacked, and the meaning of this stratigraphic architecture has not yet been fully investigated. Understanding of the processes responsible for changes in the internal features of modern and ancient tidal bedforms is essential in order to predict lateral and vertical heterogeneities in analogous reservoir strata. This facies-based study aims to interpret the three-dimensional to two-dimensional cross-strata transition observed in the lower Pleistocene mixed siliciclastic/bioclastic sandstone filling the Catanzaro Strait, in southern Italy, during a continuous phase of tectonically driven marine transgression. Tidal cross-strata disappear in the uppermost interval of the studied succession, where mudstone strata prevail. This stratigraphic trend is interpreted as the evidence of an important change in the tidal strait hydrodynamics due to a phase of relative sea-level rise. At the beginning of the transgression, three-dimensional tidal dunes migrated throughout the ca 3 to 4 km wide and ca 30 km long, WNW- ESE-oriented Catanzaro Strait, due to strong tidal currents amplified through the seaway and flowing in semi-diurnal phase opposition. As the intermediate phase of transgression enlarged the seaway width, the tidal current strength decreased as tidal water exchange occurred over a larger cross-sectional area. The progressive reduction of the bed shear stress modified three-dimensional tidal dunes into an extensive two-dimensional bedform field. At the end of the transgression, the further widening of the Catanzaro Strait into a ca 10 to 12 km wide marine passageway changed the tidally dominated strait into a non-tidal open shelf. The results of this research suggest the presence of a 'critical cross-sectional area' in the narrowest strait-centre zone which controls the activation and deactivation of tidal current amplification along a marine seaway. [ABSTRACT FROM AUTHOR]

The Miocene Gorgoglione Flysch Formation records the stratigraphic product of protracted sediment transfer and deposition through a long‐lived submarine channel system developed in a narrow and elongate thrust‐top basin of the Southern Apennines (Italy). Channel‐fill deposits are exposed in an outcrop belt approximately 500 m thick and 15 km long, oriented oblique to the palaeoflow, which was roughly south‐eastward. These exceptional exposures of channel‐fill strata allow the stacking architectures and the evolution of the channel system to be analyzed at multiple scales, enabling the effects of syn‐sedimentary thrust tectonics and basin confinement on the depositional system development to be deciphered. Two end‐member types of elementary channel architecture have been identified: high‐aspect‐ratio, weakly‐confined channels, and low‐aspect‐ratio, incisional channels. Their systematic stacking results in a complex pattern of seismic‐scale depositional architectures that determines the stratigraphic framework of the deep‐water system. From the base of the succession, two prominent channel complex sets have been recognized, namely CS1 and CS2, consisting of amalgamated incisional channel elements and weakly‐confined channel elements. These channelized units are overlain by isolated incisional channels, erosional into mud‐prone slope deposits. The juxtaposition of different channel architectures is interpreted to have been governed by regional thrust‐tectonics, in combination with a high subsidence rate that promoted significant aggradation. In this scenario, the alternating 'in sequence' and 'out of sequence' tectonic pulses of the basin‐bounding thrusts controlled the activation of coarse‐clastic inputs in the basin and the resulting stacking architectures of channelized units. The tectonically‐driven confinement of the depositional system limited the lateral offset in channel stacking, preventing large‐scale avulsions. This study represents an excellent opportunity to analyze the stratigraphic evolution of a submarine channel system in tectonically‐active settings from an outcrop perspective. It should find wide applicability in analogous depositional systems, whose stratigraphic architecture has been influenced by tectonically‐controlled lateral confinement and associated lateral tilting. [ABSTRACT FROM AUTHOR]