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Seismic-scale fluid migration features in a passive margin setting, Outcrop analogues from the Mesozoic SE France Basin - Field trip INTINARY and INVITATION! IAS OCT 2017



3 Days Field Trip, IAS Congress, Toulouse, October 10 – 12, 2017 This field trip will take place in the SE France Basin, which is filled by an up to 10 km-thick pile of Mesozoic sediments. These sediments accumulated in a deep embayment that opened onto the divergent, then drifting northern margin of the Tethys Ocean. Several organic-rich intervals were deposited during that period, and have locally reached maturity as biogenic or thermogenic (for both oil and gas) source rocks are evidenced by hydrocarbon shows at the outcrop and in boreholes. Although fluid migration study is usually based on petrographic and geochemistry methods, we will introduce in this field trip the concept of ‘outcrop scale fluid migration features’, namely: sand injectites and seep carbonates and to some extent mass-transport deposits. We will discuss for each of these the related fluid pressure regime, its links to the petroleum systems, and inferred seismic analogues of such bodies based on examples from various sedimentary basins. The earliest studied outcrop exposes one of the famous ‘Pseudobioherms’ of the Oxfordian Terres Noires Formation. This spectacular seep carbonate mound (20 m thick) differs in several ways from the ‘classic’ outcrop of Beauvoisin (and other seep carbonates worldwide); the origin of such particularities will be discussed based on facies and petrographic analysis, and linked to hydrocarbon migration mechanisms. Other outcrops are all found in the Aptian-Albian Marnes Bleues Formation. On the edge of the basin, a bluff nicely expose seep carbonates on ca. 200 m long, 150 m height, which allows the description of mappable clustering pattern. The stacked clusters point down to underlying turbidite channels as possible hydrocarbon reservoir leaking up to the sea floor. Sand injectites have connected with thick sandbodies and cross-cutting the encasing marly Marnes Bleues Fm. have been described near Sisteron; their association with dispersed columnar and tubular carbonate concretions will be examined based on geometric relationships from a couple of hundred meters to a few kilometers scales. Finally, a 80-m-thick mass-transport deposit (MTD) will be examined. MTDs are known from geotechnical modeling to detach on intervals of high fluid pressure, making them “fluid indicators” in a wide sense. In addition, the outcrop will raise the issue of the significance of kinematic indicators and highlight some aspects of the mechanical behavior of sediments shortly after deposition. The outcrop presented here will be visited during a 3 days field trip before the IAS Congress, in October 2017 in Toulouse. During the journey we will cross the basin; starting from the NW margin (Vercors) and ending at the foot of the SE margin (Provence). The highlights will include a museum of regional fossils showing world-class specimens.
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