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Facies Distribution and Architectural Characterization of Turbidite Channel Complexes in the Gorgoglione Flysch Formation (Basilicata, Southern Italy)

Abstract

Turbidite channel complexes have received considerable attention in the petroleum industry during the past decade. Spectacular examples of modern deepwater channel systems are now commonly imaged using high resolution 3D seismic data, allowing morphological analysis at scales of tens or hundreds of meters and interpretation of evolutionary histories. However, detailed sedimentological and stratigraphic analysis of ancient turbiditic channel-fill deposits at outcrop scale (spanning seismic to sub-seismic scales,) is essential to integrate the characterization of the reservoir features in analogue oil-bearing successions. A field-based study is presented from the Gorgoglione Flysch Fm, a Miocene turbiditic succession exposed within a piggy-back basin in the Southern Apenninic Chain of Italy. Systematic bed-scale stratigraphic measurements on key outcrops have been integrated with interpretations of sedimentary architecture based on an aerial photographic dataset. The formation includes 10-to-100-m-thick sandbodies, characterized by amalgamated, normally-graded intervals with rip-up mud clasts layers, cross-cutting strata-sets and cross laminations. The sandbodies are systematically offset stacked to form channel complexes that are laterally associated with heterolithic overbank deposits. These latter consist of tabular, thinly bedded fine-grained sandstones and mudstones. The data allow complex internal organization of the lithosomes and the mutual relationships between channel-fill sediments and overbank deposits to be characterized. Palaeocurrent analysis reveals a main palaeoflow direction from NNW to SSE, albeit with subsidiary lateral input. There is an upward evolution from laterally-migrating amalgamated channelised sedimentary bodies into sheet deposits. Those compound geometries and hierarchies within the lithosomes at different scales of observation are also constrained by 3D reconstructions of some key outcrops. The progressive nature of the channel migration, migrating first laterally to the NE and then back to the SW, under net aggradational conditions and without avulsion of the channel to new locations implies that tapered levees were not developed in this setting. At the largest scale the system is laterally confined by tectonically-controlled slopes, and this may have controlled the geometry of the overbank strata, and hence the channel complex migration pattern.