Cenozoic Calcareous Nannofossils from the Galicia Margin, Ocean Drilling Program Leg 103

Abstract

Ocean Drilling Program Leg 103 occupied five sites on the Galicia margin, northwest of the Iberian Peninsula. Two holes (Holes 637A and 638B) yielded significant Cenozoic sedimentary sections ranging from late Miocene to late Pleis tocene in age. From the nannofossil stratigraphy, one hiatus is recognized in Hole 637A (2.35-2.4 Ma), whereas two hia tuses (one at 1.9-2.6 Ma and another at 3.5-3.7 Ma) are recognized in Hole 638B. Sediment-accumulation rates for the Cenozoic portions of these two holes have been calculated based on the nannofossil datums. The abundance ratios of Coccolithus pelagicus to Discoaster brouweri for Hole 637A show relatively low values and small fluctuations from 2.5 to 6.5 Ma but sharply increase and then widely fluctuate beginning at about 2.5 Ma. This may indicate relatively warmer, more stable surface-water temperatures from 2.5 to 6.5 Ma and cooler, variable surface-water temperatures af ter 2.5 Ma at Site 637. C. pelagicus/D. brouweri ratios from Hole 638B also show a trend of increasing values with time from late Miocene to late Pliocene, but with more fluctuations and a different pattern from that of Hole 637A.

Neogene calcareous nannofossils: western Mediterranean biostratigraphy and paleoclimatology

“…2). Wei et al (1988) also found that the D. brouweri-C. pelagicus ratio decreased sharply after about 2.5 Ma on the Galicia Margin. Another predominantly coolwater interval also occurs in Zone NN13 in Leg 161 holes.…”

“…In the Neogene, however, several discoasters (D. variabilis, D. intercalaris, D. tamalis, and D. asymmetricus) are believed to have preferred cool waters (Bukry, 1981;Rio et al, 1990a). A single discoaster species, Discoaster brouweri, which has a well-established preference for warm waters (e.g., Bukry, 1978, Siesser, 1975Muller, 1985, Wei et al, 1988, was thus selected as the warmwater proxy for this study.…”

“…Using a ratio rather than absolute abundances of the two species avoids potential error caused by variations in the density of specimens sedimented on a slide. Wei et al (1988) also used the ratio of these two species to investigate Neogene water temperatures on the Galicia Margin.…”

Pliocene paleoclimatology at ODP Site 1115, Solomon Sea (southwestern Pacific Ocean), based on calcareous nannofossils

“…In the Neogene, however, several discoasters (D. variabilis, D. intercalaris, D. tamalis, and D. asymmetricus) are believed to have preferred cool waters (Bukry, 1981;Rio et al, 1990b). A single discoaster species, Discoaster brouweri, which has a well-established preference for warm waters (e.g., Bukry, 1978Bukry, , 1981Siesser, 1975;Müller, 1985;Wei et al, 1988) was thus selected as the warm-water proxy for this study.…”

“…Using two species that vary inversely in relative abundance rather than using the absolute abundance of only one species avoids potential error caused by variations in the density of specimens sedimented on a slide. Siesser and de Kaenel (1999) used a similar method of investigation for the Pliocene in the western Mediterranean, and Wei et al (1988) used a ratio of these two species on the Galicia Margin. Samples investigated are plotted against the timescale (Fig.…”