--> Abstract: Contrasting Middle Eocene and Upper Oligocene / Lower Miocene Deep-Water Facies and Processes from Campos Basin, Brazil, by L. M. Arienti, L. F. G. Caddah, E. B. Rodrigues, M. R. Becker, C. J. Abreu, and C. H. L. Bruhn; #90933 (1998).

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Abstract: Contrasting Middle Eocene and Upper Oligocene / Lower Miocene Deep-Water Facies and Processes from Campos Basin, Brazil

Arienti, L.M.; Caddah, L.F.G.; Rodrigues, E.B.; Becker, M.R.; Abreu, C.J.; Bruhn, C.H.L. - Petrobras/E&P/Cenpes

Deep-water facies associations and depositional processes of Middle Eocene and Upper Oligocene/Lower Miocene reservoirs from deep-water Campos Basin are compared on the basis of 1200 m of cores.

The lower part of the Middle Eocene succession is formed by confined lobes (CL) which fill intra-slope troughs and are overlain by a slope-apron section (SA). The troughs are 5 km-wide, over 25 km-long and are filled by up to 100 m of amalgamated very coarse- to fine-grained, unstratified, graded and fluidized sandstones beds, 1 to 5 m thick (Fig. 1). Some beds are capped by laminated and bioturbated siltstones, and show mud intraclasts-rich horizons at the base. This facies association correspond to channelized lobe deposits deposited by confined sandy high-density gravity flows. No lobe fringe or overbank deposits are observed. The slope-apron succession average 110 m in thickness and is mainly composed of debris flow deposits with muddy or muddy/sandy matrix (Fig. 1). Debris flows richer in sandstones and red-algae clasts evolve to graded bioclastic sandy gravels and, further downcurrent, to stratified bioclastic pebbly-sandstones and fine-grained laminated sandstones.

The Oligo/Mlocene reservoirs comprise up to 150 m-thick, and up to 10 Km-wide sand-rich channel complexes (CC). Intraformational conglomerates (8%) deposited by hyper-concentrated flows and unstratified (60%) and traction carpet sandstones (10%), deposited by gravelly and sandy high-density turbidity currents, are the main facies (Fig. 2). Debris flow deposits are rare. Thin-bedded ripple cross-stratified fine-grained sandstones (16%) occur laterally to and at the upper part of the CC and correspond to overbank deposits (Fig.2).

The Lower Miocene reservoirs are composed of 10-60 m-thick, 6-8 Km-wide, and 10->15 Km-long sand-rich lobes (SL), which are formed mainly by poorly-sorted, clean, unstratified, medium to fine-grained sandstones (95%). Thin-bedded, very fine-grained Tbc and Tc Bouma beds are subordinate as the lobes are almost completely formed by sandy high-density turbidite deposits (Fig. 2). Bioturbated, thin-bedded and finely laminated sandstones overlay the lobes and are inferred as bottom-current deposits (Fig. 2). The lower slope feeder systems are filled by channel-overbank complexes or confined sand-rich lobes that are heavily desiccated by 200-600 m-wide 5-15 m-deep sea channels.

Facies association and geometry of the Oligo-Miocene reservoirs indicate a lower slope to basin-floor fan depositional setting while the Middle Eocene turbidite system fills slope valleys connected to the paleo-shelf.

AAPG Search and Discovery Article #90933©1998 ABGP/AAPG International Conference and Exhibition, Rio de Janeiro, Brazil