Calcareous Nannoplankton from the Western North Atlantic, DSDP Leg 44

Abstract

Calcareous nannoplankton were recovered from all sites and most of the intervals cored during DSDP Leg 44. The locations of the sites are shown in Figure 1. In the samples studied, calcareous nannoplankton assemblages ranged from Upper Jurassic to Quaternary. The zonal and age assignments of the cores are summarized in Table 1. The radiometric ages for the Cenozoic nannoplankton zones follow those of Berggren (1972), with some modifications for the Neogene as suggested by Ryan et al. (1974). The radiometric ages for the Jurassic and Cretaceous zones are from van Hinte (1976a, b). These time scales form the basis for calibration of sedimentation rates when only calcareous nannofossils are found. Several core sequences are of particular interest for calcareous nannoplankton studies. An almost continuously cored sequence of the uppermost Jurassic- Lower Cretaceous was recovered from the Blake- Bahama Basin (Hole 391C, Cores 9-54). Assemblages of Tithonian or upper Kimmeridgian to lower Albian are recognized in succession. On the Blake Nose (Holes 390, 390A, 392A), Barremian to Albian assemblages are separated by a hiatus from upper Campanian to Maestrichtian assemblages. A nearly complete upper Campanian to Maestrichtian sequence was recovered in Hole 390A (Cores 11-14) and coverage continues in Hole 390A (Cores 1-11) in which lower Paleocene to middle Eocene assemblages are present in nannofossil ooze. In the Blake-Bahama Basin (Holes 391 A, Cores 3-20; 391C, Cores 2-3), nannofossil assemblages of lower- upper Miocene were recovered from gravity-flow deposits in association with reworked Cretaceous and Eocene-Oligocene species. Hemipelagic clay from the lower continental rise hills (Hole 388A, Cores 4-11) contains middle-upper Miocene age assemblages. Quaternary assemblages were cored discontinuously in several holes of Leg 44.