Biostratigraphy of selected taxa and radiolarian events in ODP Hole 183-1138A sediments

Well-preserved radiolarian assemblages of late middle Miocene to early Pliocene age are found in Ocean Drilling Program (ODP) Hole 1138A (Cores 183-1138A-12R to 20R), which was rotary drilled into the Central Kerguelen Plateau. The faunas are typical for Antarctic assemblages of this time interval, and the site appears to have been south of the Polar Front during the time period studied. Despite only moderate drilling recovery of the section, most late middle to early Pliocene radiolarian zones are present, although at the sample resolution used, subzones could not be identified. A significant discontinuity in the section is present at the boundary between lithologic Units I and II (between Cores 183-1138A-12R and 13R), corresponding to an interval from at least 4.6 to 6.1 Ma. Mixed late Miocene-early Pliocene assemblages are seen in the base of Core 183-1138A-12R (Sample 183-1138A-12R-3, 20 cm), and the overlying basal Pliocene Tau Zone appears to be absent. It cannot be determined if the discontinuity is due to incomplete recovery of the section and drilling disturbance or if it reflects a primary sedimentary structure - a hiatus or interval of condensed sedimentation.

Methane in waters and bottom sediments of the North (Severnaya) Dvina mouth area in 2004-2006

The mouth area of the North (Severnaya) Dvina River is characterized by a high concentrations of methane in water (from 1.0 to 165.4 µl/l) and bottom sediments (from 14 to 65000 µl/kg), being quite comparable to productive mouth areas of rivers from the temperate zone. Maximum methane concentrations in water and sediments were registered in the delta in segments of channels and branches with low rates of tidal and runoff currents, where domestic and industrial wastewaters are supplied. In the riverine and marine water mixing zone with its upper boundary, locating far into the delta and moving depending on a phase of the tidal cycle, decrease of methane concentration with salinity increase was observed. The prevailing role in formation of the methane concentration level in water of the mouth area pertains to bottom sediments, which is indicated by close correlation between gas concentrations in these two media. Existence of periodicity in variations of methane concentration in river water downstream caused by tidal effects was found.