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Recognition of Sub-Facies Within a Miocene Canyon and Fan System by Use of Benthic Foraminiferal Assemblages


Rogerson, Michael1, C.J. Van der Zwan2, Brian J. O’Neill3, G.J. Van der Zwaan1, T.J. Kouwenhoven1, George Postma1, H.J. Tijbosch1, Kick Kleverlaan4 (1) Utrecht University, Utrecht, Netherlands (2) Shell International Exploration and Production BV (SIEP), Rijswijk, Netherlands (3) Shell International Exploration and Production Inc, New Orleans, LA (4) Kick Kleverlaan, Sedimentology Consultant, Amsterdam,


The sedimentology and micropalaeontology of an exhumed Miocene age canyon and fan system from the Tabernas Basin (S. Spain) has been investigated. Four sections from the El Buho canyon encompassing proximal canyon, distal canyon and adjacent slope environ­ments have been logged on a centimeter scale and the 150-595mm size range of 174 sam­ples have been examined for their benthic foraminiferal content. Two further sections from the time-equivalent fan have also been investigated, and benthic foraminiferal census data has been collected for a further 28 samples.

The assemblages revealed are similar across all of the environments, but several taxa show sufficiently strong associations with a particular sub-facies to make highly promising potential indicator species. Individuals of Genus Cibicidoides dominate the assemblage in all samples, with the exception of a number of locations within the fan deposits. Here, deep­dwelling infauna dominate, which may reflect enhanced supply of organic matter by trans­port down the canyon, as has been inferred from similar assemblages in the distal parts of modern canyons. Absence from canyon environments of several taxa indicates that these species are not able to adapt to conditions in which sedimentary disturbance is common. Presence of Cassidulina laevigata exclusively within energy minimum zones within the canyon itself indicates a strong preference of this species to a unique environment that is sheltered from direct disturbance and perhaps with highly elevated food supply. In addition, some general assemblage characteristics show significant, apparently environmentally con­trolled, trends.