The Upper Cretaceous Bordighera Sandstone of NW Italy is a coarse-grained, sand-rich elongated turbidite system (ca. 15 x 45 km in outcrop) up to 250 meters thick, interpreted to have been deposited in a trench setting. The siliciclastic succession interfingers with muddy calcareous turbidites, which become more abundant toward the lateral and distal domains. Bed type associations allow the distinction of a proximal channelized domain which transitions to a more distal lobe domain, characterized by abundant mudclast-rich sandstones and by bipartite and tripartite beds with a mud-rich middle or upper division (hybrid event beds).The transition between the proximal and distal domains occurs over a relatively limited spatial extent (ca. 5 km). The presence of lenticular bed-sets made up of coarse grained and mud-poor sandstones throughout the distal domain suggests that distributary channels were present, indicating sediment bypass further down-dip toward the most distal and not preserved parts of the system. Hybrid event beds -commonly associated with distal and marginal fan environments such as fan fringes -are present throughout the lobe domain and extend for up to ca. 30 km in down-dip distance. They are more abundant in the proximal and axial depositional lobe domain and their appearance occurs within a short basin-ward distance from the inferred channel-lobe transition zone. Flow expansion at the termination of the channelized domain and the enhanced availability of cohesive substrate due to the presence of intra-basinal muddy calcareous beds are interpreted as the key controls on pronounced argillaceous sandstone distribution. The abrupt appearance and the persistent occurrence of such beds across an extensive domain have implications for characterizing bed-scale (subseismic) heterogeneity of deep-water clastic hydrocarbon reservoirs.
This is a repository copy of Detrital signatures of impending collision: The deep-water record of the Upper cretaceous Bordighera Sandstone and its basal complex (Ligurian Alps, Italy).
This paper reports the results of a field-based structural investigation of a well-exposed paleo-accretionary prism, which experienced complex deformation in a low-grade metamorphic setting. Field analyses focused on the description of structural fabrics, with the main emphasis upon parameters like the orientation, style and kinematics of foliations, folds and shear zones. We address the research to the south-westernmost part of the Alpine chain, the Ligurian Alps, where, despite their origin as turbidite sequences deposited into the closing Alpine Tethys Ocean, the Helminthoid Flysch Nappes are presently distributed in the outer part of the chain, above the foreland. The new dataset highlights different deformation patterns related to the different spatial distribution of the flysch units. This regional-scale partitioning of strain is hence associated with progressive deformation within a two-stage geodynamic evolution. Correlations among the different orogenic domains allow the proposal of a kinematic model that describes the motion of the Helminthoid Flysch from the inner to the outer part of the orogen, encompassing the shift from subduction- to collision-related Alpine geodynamic phases.
In convergent zones, several parts of the geodynamic system (e.g., continental margins, back-arc regions) can be deformed, uplifted, and eroded through time, each of them potentially delivering clastic sediments to neighboring basins. Tectonically driven events are mostly recorded in syntectonic clastic systems accumulated into different kinds of basins: trench, fore-arc, and back-arc basins in subduction zones and foredeep, thrust-top, and episutural basins in collisional settings. The most widely used tools for provenance analysis of synorogenic sediments and for unraveling the tectonic evolution of convergent zones are sandstone petrography and U–Pb dating of detrital zircon. In this paper, we present a comparison of previously published data discussing how these techniques are used to constrain provenance reconstructions and contribute to a better understanding of the tectonic evolution of (i) the Cretaceous transition from extensional to compressional regimes in the back-arc region of the southern Andean system; and (ii) the involvement of the passive European continental margin in the Western Alps subduction system during impending Alpine collision. In both cases, sediments delivered from the down-bending continental block are significantly involved. Our findings highlight its role as a detrital source, which is generally underestimated or even ignored in current tectonic models.
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