Benthic foraminiferal recovery after recent turbidite deposition in Cap Breton Canyon, Bay of Biscay

摘要

The vertical distribution of living (rose Bengal stained) benthic foraminifera from three multiple cores from Cap Breton Canyon, Bay of Biscay, France, has been investigated with the objective of monitoring the recolonization and subsequent evolution of the foraminiferal fauna following the deposition of a turbidite layer. The first samples, taken in May 2000 in the axis of Cap Breton Canyon, contained a young turbiditic sequence, most likely deposited during the heavy storm of December 1999. Four months after this sedimentological event, the composition of the living benthic foraminiferal fauna was almost monospecific in the > 150 μ m fraction, which contained mainly Technitella melo, a species which is otherwise very rare or absent in the Cap Breton Canyon and open slope assemblages. This species was accompanied in the 63-150 μ m fraction by adult specimens of Cassidulina carinata and Fursenkoina bradyi, and exclusively juvenile specimens of Bolivina subaenariensis and Bulimina marginata. This fauna represents the first stage of foraminiferal colonization after the turbidite deposition. The samples taken one year later, in June and September 2001, at approximately the same location, contained a more variable foraminiferal assemblage strongly dominated by Bolivina subaenariensis.Foraminiferal assemblages in samples taken just below the successive turbidite sequences contained nearly the same faunal elements as the surface assemblages sampled in 2001. The benthic foraminiferal assemblages from the canyon axis sampled in 2001 show the same composition as other canyon axis faunas dominated by B. subaenariensis. We suggest that the recovery of the foraminiferal faunas in this extremely unstable environment takes about 6-9 months, and that the community structure more or less permanently stays in an early stage of ecosystem recolonization.