Planktonic foraminifer biostratigraphy and paleoenvironmental implications of leg 152 sites (east Greenland margin)

Five sites and eight holes drilled on the East Greenland Margin during Ocean Drilling Program Leg 152 recovered Quaternary to middle Eocene sediments. Planktonic foraminiferal assemblages display generally low diversity; abundance and preservation varies from layer to layer. Several intervals devoid of planktonic foraminifers were identified in middle Miocene through Pliocene, lower upper Oligocene, and Eocene sediments. The more complete sedimentary sequence recovered at Site 918 spans the interval from the Quaternary to the middle Eocene. However, a major hiatus is recorded in the interval that spans the upper Eocene and the lower Oligocene. Two minor hiatuses occur in the lowermost Miocene and probably in the upper part of the middle Miocene, respectively. Paleoclimatic interpretations based on species diversity, changes in assemblages, and comparison with the stable isotope record indicate that several alternating glacial-interglacial episodes occurred during the Pliocene and the Quaternary. These t wo intervals are, however, separated by a warmer episode in the early Pliocene. Cool conditions and glacial episodes also prevailed in the late Miocene, whereas a slight warming probably occurred in the middle Miocene. This period was, however, cooler than the late Oligocene, the early Miocene, and the middle Eocene. These latter intervals were characterized by a warmer climate as indicated by the presence of several warmer water taxa. The first occurrence of Neogloboquadrina pachyderma and the changes in coiling direction of Neogloboquadrina atlantica are also climatically controlled. Comparison with previously drilled sites in the same area indicates that the short early Miocene hiatus and part of the hiatus spanning the late middle Eocene and the early Oligocene identified in Hole 918D may have interregional extensions in the North Atlantic Ocean. INTRODUCTION In this paper I study the biostratigraphy and the paleoenvironmental implications of Quaternary through middle Eocene planktonic foraminifers recovered from five sites and eight holes (914−916, 918, and 919) drilled in the North Atlantic Ocean during Ocean Drilling Program (ODP) Leg 152 (East Greenland Margin). Sites were drilled on the East Greenland shelf along an ideal north-northwest to southsoutheast transect from the inner shelf (Sites 914−917) to the continental rise (Sites 918−919). Figure 1 shows the location of the sites drilled during Leg 152 and some of the sites previously drilled in the North Atlantic. Table 1 shows geographic coordinates, water depth, and penetration at each hole. A Quaternary−Pliocene sequence was recovered from Hole 918A and at Site 919, whereas middle Miocene to upper Oligocene sediments were recovered in Hole 918D. Upper Eocene sediments were recovered in Holes 915A and 916A. The oldest sediments, based on planktonic foraminifers, are considered as early middle Eocene in age (Hole 918D). In the northern Atlantic, extended sedimentary sequences were previously recovered during Deep Sea Drilling Project (DSDP) Legs 12, 48, 49, 81, and 94 and ODP Legs 104 (Norwegian Sea) and 105 (Baffin Bay and Labrador Sea). Berggren (1972), Poore (1979), Murray (1979), Krasheninnikov (1979), Spiegler and Jansen (1989), and Aksu and Kaminski (1989) described the planktonic foraminifers from these legs. Only Holes 407 and 408 (Leg 49) are close to the Leg 152 sites. A summary of the biostratigraphic data obtained and a cor1Saunders, A.D., Larsen, H.C. , and Wise, S.W. , Jr. (Eds.), 1998. Proc. ODP, Sci. Results,152: College Station, TX (Ocean Drilling Program). 2Dipartimento di Scienze della Terra, Universitá di Milano, Via Mangiagalli 34, 20133, Milano, Italia. Present address: ETH-Zentrum, Geologisches Institut, S neggstrasse 5, 8092 Zurich, Switzerland. silvia@erdw.ethz. ch relation with some of the more representative sites drilled in the North Atlantic are reported below. METHODS The present study is based on 1−3 samples per section for each core. Only a few representative core catchers were included. Sample volume was about 10 cm3. In case some specimens would prove suitable for isotope analyses, all samples were soaked in distilled water, washed through >40 μm sieve, and dried at room temperature. Samples were then dry-sieved through >40 μm, 40−150 μm, and >250 μm sieves to obtain three size fractions. They were then studied under a binocular microscope. The three size fractions were obtained to facilitate comparison with previous paleoclimatological studies (Haq et al., 1977; Premoli Silva and Boersma, 1989; Spezzaferri, 1994a). Abundances of single species, groups of species, and other components over total faunal content were estimated in each sample (see Appendix). These include biogenic remains (radiolarians, diatoms, sponge spicules, benthic foraminifers, ostracodes, mollusk and echinoid fragments, and fish remains) as well as inorganic components (red clay, quartz, glauconite, oxides, pyrite, tephra, and dropstones). Seven categories are distinguished and plotted in the range charts. They are VR: very rare (1−3 specimens per sample), R: rare (<10 specimens), C: common (10−30 specimens), A: abundant (30−50 specimens), VA: very abundant (about 50−70 specimens), D: dominant (more than 70 specimens), X: simple occurrence. Planktonic foraminiferal preservation was graded with the following scale: VP: very poor preservation, P: poor preservation, M: moderate preservation, and G: good preservation (Larsen, Saunders, Clift, et al., 1994). Species diversity was estimated counting the number of species present in each sample. The range charts report only samples containing planktonic foraminiferal faunas. However, a large number of the studied samples on-