Resumen de Changes in the Community Structure of Deep Water Agglutinated Foraminifers across the K/T Boundary in the Basques Basin (Northern Spain)
Wolfgang Kuhnt, Michael A. Kaminski
Two deep-water sections across the K/T boundary in the Basque Basin (the Zumaya and Sopelana sections) have been studied for quantitative changes in agglutinated benthic foraminifera. We provide a taxonomic overview of 52 agglutinated species occurring in the uppermost part of the Maastrichtian pelagic marl and in the K/T boundary clay, which is about 30 cm thinck in the studied sections. Three general types of agglutinated assemblages are observed: 1. Upper Maastrichtian assemblages are dominated by epifaunal detritus-feeders (e. G. Astrorhizids and ammodiscids) and species with a calcareous agglutinated wall (e. G. Spiroplectammina, Dorothia, Gaudryna and Tritaxia). 2. Assemblages directly above the boundary are dominated by faunal species (Subreophax, Ammobaculites, Recurvoides and Saccammina), often showing a typical coarsely agglutinated wall with large quartz grains. Forms with a calcareous agglutinated wall and epifaunal detritus-feeders are rare or abtent. 3. A continuous decrease of Subreophax, Ammobaculites, Recurvoides, Saccammina and a strong increase of the calcareous agglutinating Spiroplectammina and Dorothia are observred in the marly upper portion of the K/T boundary clay. The taxonomic turnover across the K/T boundary does not remarkably exceed normal turnover rates in the Late Cretaceous or early Paleogene. However, marked quantitative faunal changes in deep water agglutinated foraminiferal community structure across the K/T boundary favour a model of drastic decrease in surface productivity and a collapse of the food web for deep-water benthic communitieds at the K/T boundary. Benthic foraminiferal populations slowly recover to background levels over a timespan of at least 50, 000 years following the K/T boundary event.
