Abstract
Examples of slope channels and canyons being diverted by structurally related sea-floor topography are commonly found both on the modern seabed and in the subsurface, in deep-water fold and thrust belts but their depositional histories have rarely been documented using examples from outcrop. The synthesis of outcrop (original geological field mapping at 1:10,000 scale) and subsurface data sets from the early Pleistocene stratigraphic succession of the Peri-Adriatic basin provides a window into the overall evolutionary pattern of large intraslope turbidite systems that, during the Gelasian (2.58–1.80 Ma), shed Apennine-derived clastic sediments into the adjacent deep-water basin. Trends from mapping and paleocurrent indicators converge to indicate that the sea-floor bathymetric expression of a thrust-related anticline, the north-trending Jesi-Nereto-Zaccheo structure, likely influenced the downslope transport direction of gravity flows and sediment dispersal pattern. During early and middle Gelasian time, coarse-grained turbidite deposition occurred on the western flank of the intraslope anticline by westerly sourced, northward-flowing turbidity currents, indicating that the opposing sea-floor topography was sufficient to cause the diversion of turbidite systems, forcing them to travel near parallel to the east-facing regional paleoslope for significant distances. By very late Gelasian time, the intraslope accommodation space on the western flank of the anticline had filled and turbidites were dispersed through dip-oriented conduits incising across the crest of the underlying structure.
Highlights
Diversion in deep-water channels and canyon courses has been described from a number of modern to very young intraslope turbidite systems where preexisting or developing seabed topography associated with thrust-related folds is present (e.g. Bourget et al, 2011; Chiang & Yu, 2006; Clark & Cartwright, 2009; Kukowski et al, 2001; Mayall et al, 2010; Mountjoy, Barnes, & Pettinga, 2006)
This article deals with four of these turbidite systems exposed at Monte Ascensione, Castignano, Offida, and Montedinove in southern Marche (Figure 1) and focuses on the exceptional opportunity they provide to document, from an outcrop perspective, the important impact of structurally generated bathymetric relief on the routing of gravity currents depositing sand on deep-water basin floors and the long-term evolution of continental slope morphology from a thrust-related stepped slope, to a smooth, healed slope
The 1:20,000-scale geological map of the Gelasian (Pleistocene) slope turbidite systems and enclosing mudstones presented in this study (Main Map) encompasses an area of roughly 125 km2 in the southern part of Marche and was originally mapped at 1:10,000 scale using the topographic maps of the Regione Marche ‘Carta Tecnica Regionale’
Summary
Diversion in deep-water channels and canyon courses has been described from a number of modern to very young intraslope turbidite systems where preexisting or developing seabed topography associated with thrust-related folds is present (e.g. Bourget et al, 2011; Chiang & Yu, 2006; Clark & Cartwright, 2009; Kukowski et al, 2001; Mayall et al, 2010; Mountjoy, Barnes, & Pettinga, 2006). Detailed reconstructions of the tectonic and stratigraphic evolution of the late Miocene– Pleistocene Central Apenninic foreland basin system in the Marche-Abruzzi sector are provided by Artoni (2013) and Bigi et al (2013) This portion of the basin assumed its present-day configuration during the Pliocene and early Pleistocene when, as a result of the progressive eastward propagation of the thrust fronts, the previous foredeep was fragmented into discrete piggyback basins limited on both sides by northward-striking thrust fronts and related folds (Ori et al, 1991). During middle Pleistocene time, this portion of the basin fill succession recorded an overall shallowing-upward trend from slope, through shelf, to coastal and alluvial deposits (Cantalamessa & Di Celma, 2004), indicating that sediment supply exceeded the rate at which accommodation was created in the basin
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