Pollen records and age determinations from 2 profiles at Lake Nikolay, Lena Delta

Radiocarbon-dated pollen, rhizopod, chironomid and total organic carbon (TOC) records from Nikolay Lake (73°20'N, 124°12'E) and a pollen record from a nearby peat sequence are used for a detailed environmental reconstruction of the Holocene in the Lena Delta area. Shrubby Alnus fruticosa and Betula exilis tundra existed during 10,300-4800 cal. yr BP and gradually disappeared after that time. Climate reconstructions based on the pollen and chironomid records suggest that the climate during ca. 10,300-9200 cal. yr BP was up to 2-3 °C warmer than the present day. Pollen-based reconstructions show that the climate was relatively warm during 9200-6000 cal. yr BP and rather unstable between ca. 5800-3700 cal. yr BP. Both the qualitative interpretation of pollen data and the results of quantitative reconstruction indicate that climate and vegetation became similar to modern-day conditions after ca. 3600 cal. yr BP. The chironomid-based temperature reconstruction suggests a relatively warm period between ca. 2300 and 1400 cal. yr BP, which corresponds to the slightly warmer climate conditions reconstructed from the pollen. Modern chironomid and rhizopod assemblages were established after ca. 1400 cal. yr BP.

Geochemical analyses of secondary minerals from ODP Leg 115 basalts (Tables 1+2)

Basalts recovered along the Reunion hotspot track on Ocean Drilling Program (ODP) Leg 115 range in age from 34 Ma at Site 706 to 64 Ma at Site 707. They have undergone various degrees of secondary alteration. Within single holes the amount of alteration can vary from a few percent to near complete replacement of phenocrysts and groundmass by secondary minerals. Olivine appears to be the most susceptible to alteration and in some sections it is the only mineral altered. In other sections, olivine, pyroxene and plagioclase phenocrysts, and groundmass have been completely replaced by secondary minerals. Clays are the predominant form of secondary mineralization. In addition to replacing olivine, pyroxene, glass, and groundmass, clays have filled veins, vesicles, and voids. Minor amounts of calcite, zeolites, and K-feldspar were also detected. The clays that filled vesicles and veins often show color zonations of dark, opaque bands near the edges that grade into tan or green transparent regions in the centers of the veins. The electron microprobe was used to obtain chemical analyses of these veins as well as to characterize isolated clays that replaced specific minerals and filled voids and vesicles.

(Table 2) Geochemical composition of suspended matter samples from the northern Dvina River

The results of the analysis of samples of the Northern Dvina River's suspended particulate matter obtained by the sedimentation method from large water volumes in the periods of the spring high water and summer low water are presented. By the method of sequential leaching using different reagents, four fractions have been separated: the F1 is the sorbed complex and carbonates, the F2 is the amorphous hydroxides of Fe and Mn, the F3 is the form connected with the organic matter, and the F4 is the residual or silicate-detrital (inert) form. The data have shown that all ten elements determined were grouped with respect to the ratio of the distinguished forms: F4 is the predominant form for Al and Fe (73-88% of all the forms; however, the summer sample contains only 38% of this form of iron, and F2 is the predominant form for this period with 46.6%). As to Mn, the F1, F2, and F4 are nearly equally distributed in the spring high water samples, and only the F3 form is less important (5.4%). In the summer sample, the manganese sorbed complex is predominant (53.5%); for Cu, Ni, Cr, and Co, the inert F4 form is predominant (60-70%) in the sample of the spring suspended matter. The summer low water suspended matter has a lower F4 contribution (25-45%); for Zn, Pb, and Cd, the equal distribution of the forms in the spring samples is typical, while the summer suspended matter differs by the F2 form's predominance (53-61% for Zn and Pb). The main conclusion from the acquired data is that the geochemical mobility of all the studied elements, except for cadmium, in the summer low water suspended matter is higher than in the spring suspended matter. The more intensive biogeochemical processes in August, the high level of organic matter, and the higher contribution of phytoplankton lead to the intensification of the metals' geochemical activity in the Northern Dvina suspended matter in the end of the summer compared to the spring high water period when the physical processes are predominant over the biogeochemical ones due to the high speeds of the freshened waters flow.

(Table 2) Compressional and shear wave velocites from basalts and sediments of the Atlantic and Pacific Ocean

Compressional (Vp) and shear (Vs) wave velocities have been measured to 1.0 kbar for 14 cores of well-consolidated sedimentary rock from Atlantic and Pacific sites of the Deep Sea Drilling Project. The range of VP (2.05-5.38 km/sec at 0.5 kbar) shows significant overlap with the range of oceanic layer-2 seismic velocities determined by marine refraction surveys, suggesting that sedimentary rocks may, in some regions, constitute the upper portion of layer 2. Differing linear relationships between VP and Vs for basalts and sedimentary rocks, however, may provide a method of resolving layer-2 composition. This is illustra ted for a refraction survey site on the flank of the Mid-Atlantic Ridge where layer-2 velocities agree with basalt, and two sites on the Saya de Malha Bank in the Indian Ocean where layer-2 velocities appear to represent sedimentary rock.

(Table 2) Mineralogy and carbon, oxygen, and hydrogen isotope ratios for secondary mineral samples from igneous rocks from ODP Hole 128-794D

The basaltic rocks of Hole 794D drilled during Leg 128 are strongly altered. Microprobe analyses and XRD spectra on small quantities of matter extracted from thin sections show that primary minerals and glassy zones of the groundmass are totally or partially replaced by clay minerals with chlorite/saponite mixed-layer composition whatever the rock sample considered. This mixed-layer was also identified in veins and vesicles where it crystallizes in spheroidal aggregates. The largest veins and vesicles are filled by a zoned deposit: the chlorite/saponite mixed-layer always occupies the central part and is rimmed by pure saponite. Calcite crystallizes in secondary fractures which crosscut the clayey veins and vesicles. Chemographic analysis based on the M+-4Si-3R2+ projection shows that the chemical composition of the saponite component in the mixed-layer is identical to that of the free saponite. This indicates that the clay mineral crystallization was controlled by the chemical composition of the alteration fluids. From petrographic evidence, it is suggested that both chlorite/saponite mixed-layer and free saponite belong to the same hydrothermal event and are produced by a temperature decrease. This is supported by the stable isotopic data. The isotopic data show very little variation: d18O saponite ranges from 13.1 per mil to 13.5 per mil, and dD saponite from -73.6 per mil to -70.0 per mil. d18O calcite varies from +19.7 per mil to +21.9 per mil vs SMOW and d13C from -3.2 per mil to +0.4 per mil vs. PDB. These values are consistent with seawater alteration of the basalt. The formation of saponite took place at 150°-180°C and the formation of calcite at about 65°C.