Glide Planes to Turbidites; Deep Water Carbonate Megabreccias, Oligocene, Spain

Agar, S.¹, J. Bova¹, A. Derewetzky², N. Hartley¹, P. Hillock¹, T. Hughes¹, C. Iannello¹, A. Mckerron¹, T. Simo³ (1) ExxonMobil, Houston, TX (2) ExxonMobil, N/A, TX (3) University of Wisconsin, Madison, WI

The Villajoyosa region of the Costa Blanca of eastern Spain provides spectacular outcrops of Oligocene deep water carbonate deposits adjacent to their age equivalent platform. These sediments provide an analogue to sub-surface deposits similar to those observed on seismic in other parts of the world. Members of the ExxonMobil Carbonate Internship Program conducted an integrated field study using photo-pans, measured sections, and aerial photographs to understand the facies, geometries, and processes for application to petroleum exploration.

Facies range from matrix and grain supported mega-breccias to meter scale grainstones and wackestones; organised into repetitive packages. These facies formed as the result of catastrophic failure, turbidity flows and minor hemipelagic sedimentation, respectively. Mega-breccias are laterally discontinuous, bounded by erosional and basal glide planes. The turbidites are laterally extensive, frequently amalgamated and up to several meters thick.

Depositional processes for mega-breccias include seismically and/or gravitationally induced collapse of margin and slope sediments. Turbidites represent background eustatic-controlled deposition with significant bypass of finer-grained turbidites. Syn- or early post sedimentary deformation is common, including compaction, shearing, slumping and related processes. Debrite clast composition reflects the progressive erosion of the platform from margin to interior.

Reservoir quality appears to be limited by poor-sorting, lateral heterogeneity and a lack post-depositional meteoric dissolution, nevertheless, the predominantly grain-dominated succession provides a positive analogue for similar facies elsewhere in the geological record. Fracturing observed in outcrop is another potential mechanism to enhance the ostensibly poor reservoir potential of the section.