Total number of benthic foraminifera in sediments below the K/T boundary in the Atlantic and Pacific Ocean

Most species of Late Cretaceous deep-sea benthic foraminifera are believed to be cosmopolitan and therefore to exhibit only minor biogeographical differences. In this preliminary report, six Deep Sea Drilling Project (DSDP) sites from different oceans, paleolatitudes, and paleodepths were analyzed for terminal Cretaceous abyssal-bathyal benthic foraminifera in order to investigate their assumed cosmopolitan distribution and the question of whether different faunal compositions are related to time, different paleolatitudes, and/or different paleodepths. The material studied was obtained from the low-latitude Site 465 (Pacific Ocean), and the intermediate-latitude Sites 384 (North Atlantic) and 356, 516, 525, and 527 (South Atlantic). The material analyzed represents a time slice encompassing the last 20-50 k.y. of the Cretaceous. The faunas contain numerous "Velasco-type" species, such as Gavelinella beccariiformis (White), Cibicidoides velascoensis (Cushman), Nuttallides truempyi (Nuttall), Gaudryina pyramidata Cushman, and various gyroidinoids and buliminids. The results contradict the general assumption of the cosmopolitan nature of Late Cretaceous deep-sea benthic foraminifera advocated in the literature. Only about 9% of the taxa identified were found to be truly "cosmopolitan" through their occurrence at all the sites analyzed. On the basis of correspondence analysis and relative abundance data, three assemblages and three subassemblages were recognized: (1) a bathyal-abyssal assemblage [Nuttallinella sp. A, Cibicidoides hyphalus (Fisher), Valvalabamina sp. evolute form, and Gyroidinoides spp.] at the South Atlantic Sites 356, 516, 525, and 527, divided into three subassemblages, namely (a) a middle bathyal subassemblage [Eouvigerina subsculptura McNeil and Caldwell, Truaxia aspera (Cushman), and G. pyramidata] at Sites 516 and 525, (b) a lower bathyal subassemblage [Osangularia? sp., Pyramidina rudita (Cushman and Parker), and Quadrimorphina camerata (Brotzen)] at Site 356, and (c) an abyssal subassemblage [Gyroidinoides sp. C, Hyperammina-Bathysiphon, Gyroidinoides beisseli (White), and Globorotalites sp. B] at Site 527; (2) an abyssal assemblage [Buliminella cf. plana (Cushman and Parker) and Bulimina incisa Cushman] at the North Atlantic Site 384; and (3) a middle bathyal assemblage [Vulvulina sp. A, Osangularia navarroana (Cushman), Alabamina? sp., Bulimina velascoensis (Cushman), Spiroplectammina spp. calcareous forms, and Bulimina trinitatensis Cushman and Jarvis] at the Pacific Site 465.

Benthic foraminiferal number of specimens in Cretaceous samples of various DSDP and ODP Sites (Table 2)

Benthic foraminifera from 24 DSDP/ODP sites were investigated to assess their global horizontal and vertical distribution in the deep-sea environment at the end of the Cretaceous period. The samples analyzed are from the late Maastrichtian and within the planktic foraminiferal Abathomphus mayaroensis Zone from a wide range of oceans and paleolatitudes, including the low-latitude Sites 10 and 384 (Atlantic Ocean), 47, 171, 305, and 465 (Pacific Ocean), the mid-latitude Sites 20, 111, 356, 363, 516, 525, 527, 548, and 605 (Atlantic Ocean), 216, 217, and 758 (Indian Ocean), and the high-latitude Sites 208 (Pacific Ocean), 689,698,700,738 and 750 (Southern Ocean). Correspondence analysis, based on the 75 most common taxa, shows a clear biogeographic trend along the first correspondence axis by arranging the sites in paleolatitudinal order. The assemblages from the Tethyan Realm (i.e., low latitudes) are marked by abundant heavily calcified buliminids (such as Bulimina incisa, B. trinitatensis, B. velascoensis, and Reussella szajnochae) and Aragonia spp., whereas high-latitude faunas are characterized by abundant Alabamina creta, Gyroidinoides quadratus, and Pullenia coryelli. The results indicate that the faunas at low and high latitudes, respectively, were influenced by quite different environmental conditions. This is based on the much higher abundance of infaunal morphotypes at low and mid latitudes compared to high latitudes, suggesting that the biogeographic trend found in the data set coincides with the trophic regime at the various sites. The results also provide support for the hypothesis that postulates two simultaneous sources and mechanisms for deep-water formation during the Late Cretaceous, including warm, saline deep water produced by evaporation at low (equatorial) latitudes in contrast to the formation of cold deep waters at high (southern) latitudes.