(Figure 1) Silicoflagellates at DSDP Hole 69-504

Diverse and abundant late Miocene to Pleistocene silicoflagellates at DSDP Site 504 can be correlated by tropical biostratigraphic zones and relative paleotemperature values to eastern tropical Pacific reference site DSDP 503A farther to the west. Early Pliocene assemblages, which were poorly known until now, are present and can be correlated locally between DSDP Holes 504, 503A, and 495, using species events associated with the new Dictyocha pulchella Subzone and Dictyocha angulata Subzone. Silicoflagellate relative paleotemperature values show major warming at 4.7 to 5.0 Ma (Cores 45-48), 3.4 to 3.8 Ma (Cores 32-33), 1.5 to 1.7 Ma (Cores 12-16), and 0.5 to 0.8 Ma (Cores 3-6). Major coolings occurred at 5.0 to 5.1 Ma (Core 51), 3.9 to 4.4 Ma (Cores 38-44), and 1.0 to 1.3 Ma (Cores 8-10). The appearance of Dictyocha longa is proposed to replace the asperoid/fibuloid ratio reversal as the bottom of the Dictyocha fibula Zone, because the non-evolutionary ratio reverses several times in the upper Miocene of Hole 503A, and at least once in Hole 504. Three new Pliocene silicoflagellates are defined: Dictyocha concinna Bukry, n. sp., D. helix Bukry, n. sp., and D. tamarae Bukry, n. sp.

(Table 1) Paleomagnetic properties of specimens from DSDP Holes 69-504B and 70-504B

Paleomagnetic and rock magnetic measurements of basalt specimens from DSDP Hole 504B, associated with the Costa Rica Rift, have a mean natural remanence intensity (Jn) between 5 and 10 x 10**-3 gauss, consistent with the presence of a magnetized layer that is 0.5 to 1 km thick, which produces the observed magnetic anomalies. A mean Koenigsberger ratio (Qn) greater than 10 indicates that the remanence dominates the magnetic signal of the drilled section. The susceptibility (x) increases with depth, and the median demagnetizing field (MDF) decreases with increasing depth in Hole 504B, congruent with the downhole increase in the relative abundance of massive flow units. Hole 504B is composed of at least 12 units with distinct stable average inclinations (Is), which probably represent extrusion at times of different geomagnetic field directions and possibly also the effects of faulting. The thickness of basalt associated with these inclination units varies from less than 9 meters to possibly as much as 160 meters. Two relatively thick magnetic units (40 m and 45 m, separated by 100 m) have anomalously high Is values of -53° and -63°, in contrast with the near zero inclinations expected for the equatorial latitude of Site 504. For this reason and because the average inclination of all the magnetic units is skewed to a negative value, it might be that the entire section at Hole 504B was tilted by approximately 30°.

Dinoflagellate cysts in surface sediment samples of METEOR cruises M20/2, M23/1, M34/1, M34/2, M34/3 and M34/4

To enhance the limited information available about the palaeo-ecological significance of calcareous dinoflagellates, we have studied their lateral distribution in surface sediments of the equatorial and south Atlantic between 13°N and 36°S. Calcareous dinoflagellate cysts appear to be widely distributed throughout the studied area. In the surface sediments, concentrations (cyst per gram dry sediment) of the vegetative stage Thoracosphaera heimii are generally higher than that of the (presumably) calcareous resting cysts. Distribution patterns in surface sediments of Orthopithonella granifera (Fütterer) Keupp and Versteegh, Rhabdothorax spp. Kamptner., Sphaerodinella albatrosiana (Kamptner) Keupp and Versteegh S. albatrosiana praratabulated, Sphaerodinella tuberosa var. 1 (Kamptner) Keupp and Versteegh and S. tuberosa var. 2 and the ratios between these species have been compared with temperature, salinity, density and stratification gradients in the upper water column. Rhabdothorax spp. is characteristically present in sediments of more temperate regions characterized by high seasonality. Dinoflagellates producing these cysts are able to tolerate high nutrient concentrations, and mixing of the water column. S. albatrosiana is abundant in regions characterized by high sea surface temperatures and oligotrophic surface water conditions. In contrast, the distribution of S. tuberosa var. 2 is negatively related to temperature. The other cyst species did not show a characteristic pattern in relation to the studied environmental gradients. The ratio of Sphaerodinella tuberosa var. 2 to Orthopithonella granifera can be used for reconstructing the presence of stratification in the upper 50 m of the water column, whereas the ratios of S. tuberosa var. 2 to Sphaerodinella albatrosiana and of O. granifera to Rhabdothorax spp. might be used for palaeotemperature reconstructions. Calcareous dinoflagellate cysts are abundant in oligotrophic areas and may be useful for the reconstruction of palaeoenvironmental conditions.

Humic acids in bottom sediments of the Western Pacific

Elemental composition, functional groups, and molecular mass distribution were determined in humic acids from the Western Pacific abyssal and coastal bottom sediments. Humic acid structure was studied by oxidative degradation with alkaline nitrobenzene and potassium permanganate, p-coumaric, guaiacilic, and syringilic structural units typical for lignin of terrestrial plants were identified in humic acids by chromatographic analysis of oxidation products. Polysubstituted and polycondensed aromatic systems with minor proportion of aliphatic structures were basic structural units of humic acids in abyssal sediments.