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Formation MicroScanner (FMS) characterization of a Contourite Depositional System. Insights from IODP Expedition 339 in the Gulf of Cadiz

Johanna Lofi, Aurélie Galvani, Trevor Williams, F. Javier Hernandez-Molina, Dorrik Stow, Estafania Llave, and Exp 339 Scientists

Contourite Depositional Systems (CDS) shaped by bottom current activity have been described in most oceanic basins, specially on the continental slopes and rises. Due to the continuous expansion of petroleum exploration towards deeper water, new attention is paid to CDS. Sandy contourites can present the required characteristics for potential oil-bearing reservoirs. Muddy drifts can conversely act as sealing rocks. Beside an economic light, CDS form sedimentary archives that can be crucial for paleoceanographic reconstructions. Recently, IODP Expedition 339 was conducted in the Gulf of Cadiz in order to investigate the CDS under the influence of the Mediterranean Outflow Water (MOW). Five sites successfully drilled, cored and logged, make this area an ideal ground for testing the contourite paradigm over a 5 Ma long record. The Gulf of Cadiz offers a unique opportunity to determine reliable sedimentary facies characteristics of the interaction between bottom circulation and sedimentary processes, and to characterize CDS from both seismic and well log data, which is essential to provide predictive tools for reservoir identification. During Expedition 339, the Formation MicroScanner (FMS) downhole logging tool provided high-resolution electrical resistivity–based images of borehole walls. Features such as bedding, slump folding and bioturbation can be resolved. A careful analysis of FMS image texture and resistivities has been performed at 2 sites (U1389 and U1390). It allowed recognition of 6 FMS facies, whose vertical extension ranges between several cm and few m. The good core recovery allows core/log integration, showing that FMS facies correlate well with either muddy intervals, muddy contourites or coarse-grained intervals. Mapping the FMS facies at the borehole scale generates synthetic lithological logs with a much higher vertical resolution than with Gamma Ray logs. Moreover, the type of contact (sharp or diffuse) between two successive FMS facies often allows to distinguish bi-gradational contourites from other depositional sequences (eg. uni-gradational contourites, turbidites).

This research project is undertaken as part of IODP Expedition 339.

6 Exp 339 Scientists: Acton G., Bahr A., Balestra B., Ducassou E., Flood R., Flores J-A., Furota S., Grunert P., Hodell D., Jimenez-Espejo F., Kim J. K., Krissek L., Kuroda J., Li B., Lourens L., Miller M., Nanayama F., Nishida N., Richter C., Roque C., Sierro F.J., Singh A., Sloss C., Takashimizu Y., Tzanova A., Voelker A., Xuan C., C.A. Zarikian

AAPG Search and Discovery Article #90161©2013 AAPG European Regional Conference, Barcelona, Spain, 8-10 April 2013