Benthic foraminifers in Mesozoic and Cenozoic sediments of the southwestern Atlantic

Benthic foraminiferal assemblages in Mesozoic and Cenozoic sediments were studied at Sites 511, 512, 513, and 514 drilled during Leg 71 in the southwestern Atlantic on the Maurice Ewing Bank and in the Argentine Basin. Benthic foraminifers in almost all stratigraphic subdivisions of Sites 511 and 512 reflect the gradual subsidence of the Falkland Plateau from shelf depths in the Barremian-Albian, when a semiclosed basin with restricted circulation of water masses and anaerobic conditions existed, to lower bathyal depths in the Late Cretaceous and Cenozoic, with an abrupt acceleration at the boundary of Lower and Upper Cretaceous. The composition, distribution, and preservation of Late Cretaceous assemblages of benthic foraminifers suggest considerable fluctuations of the foraminiferal lysocline and the CCD. This is evidenced by dissolution facies and foraminiferal assemblages in which agglutinated and resistant calcareous forms predominated during high stands of the CCD and by calcareous facies in which rich assemblages of calcareous species predominated during low stands. The highest position of the CCD on the Plateau (less than 1500-2000 m) was in the late Cenomanian, Turonian, and Coniacian. In the Santonian and Campanian the CCD was at depths below 1500-2000 meters. At the end of the Campanian the CCD shifted again to depths comparable with those of Cenomanian and Turonian time. In the latest Campanian and the Maestrichtian the CCD was low and nanno-foraminiferal oozes with a rich assemblage of benthic foraminifers accumulated. Foraminiferal assemblages at Sites 513 and 514 in the Argentine Basin also testify to oceanic subsidence from lower bathyal depths in the Oligocene to abyssal ones at present. This process was complicated by the influence of geographical migrations of the Polar Front caused by extensions of the ice sheet in the Antarctic after the opening of the Drake Passage during the Oligocene. In Mesozoic and Cenozoic deposits of the Falkland Plateau and the Argentine Basin seven assemblages of benthic foraminifers were distinguished by age: early-middle Albian, middle-late Albian, Late Cretaceous (including four groups), middle Eocene, late Eocene-early Miocene, middle-late Miocene, and Pliocene-Quaternary. The Albian assemblages contain many species common to the foraminiferal fauna of the Austral Biogeographical Province. The Late Cretaceous assemblage contains, along with Austral species, species common to foraminifers of North America, Western Europe, the Russian platform, and the south of the U.S.S.R. Deep-sea cosmopolitan species prevail in Cenozoic assemblages.

Appendix 7: List of species with their distribution ranges restricted to the corresponding phytogeographical region

Understanding species distribution patterns and the corresponding environmental determinants is a crucial step in the development of effective strategies for the conservation and management of plant communities and ecosystems. Therefore, a central prerequisite is the biogeographical and macroecological analysis of factors and processes that determine contemporary, potential, as well as future geographic distribution of species. This thesis has been conducted in the framework of the BIOMAPS-BIOTA project at the Nees Institute of Biodiversity of Plants, which was funded by the German Federal Ministry of Education and Research (BMBF). The study investigated patterns of plants species richness and phytogeographic regions under contemporary environmental conditions and forecasted future climate change in the area of West Africa covering five countries: Benin, Burkina Faso, Côte d'Ivoire, Ghana and Togo. Firstly, geographic patterns of vascular plant species richness have been depicted at a relatively fine spatial resolution based on the potential distribution of 3,393 species. Species richness is closely related to the steep climatic gradient existing in the region with a high concentration of species in the most humid areas in the south and decreases towards the northern drier areas. The investigation of the effectiveness of the existing network of protected areas shows an overall good coverage of species in the study area. However, the proportion of covered species is considerably lower at national extent for some countries, thus calling for more protected areas in order to cover adequately a maximum number of plants species in these countries. Secondly, based on the potential distribution range of vascular plant species, seven phytogeographic regions have been delineated that broadly reflect the vegetation zones as defined by White (1983). However notable differences to the delineation of White (1983) occur at the margins of some regions. Corresponding to a general southward shifted of all regions. And expansion of the Sahel vegetation zone is observed in the north, while the rainforest zone is decreased in the very south.This is alarming since the rainforest shelters a high number of species and a high proportion of range-restricted or endemic species, despite their relatively small extent compared to the other regions. Finally, the evaluation of the potential impact of climate change on plant species richness in the study area, results in a severe loss of future suitable habitat for up to 50% of species per grid cell, particularly in the rainforest region. Moreover, the analysis of the possible shift of phytogeographic regions shows in general a strong deterioration of the West African rainforest. In contrast the drier areas are expanding continuously, although a slight gain in species number can be observed in some particular regions. The overall lesson to retain from the results of this study is that the West African rainforest should be fixed as a high priority area for the conservation of biodiversity of plants, since it is subject to severe contemporary and projected future threats.