Distribution of heavy minerals in sediment cores from the Laptev Sea continental margin and the central Arctic Ocean

Focussing on heavy-mineral associations in the Laptev-Sea continental margin area and the eastern Arctic Ocean, 129 surface sediment samples, two short and four long gravity cores have been studied. By means of the accessory components, heavy-mineral associations of surface sediment samples from the Laptev-See continental slope allowed the distinction into two different mineralogical provinces, each influenced by fluvial input of the Siberian river Systems. Transport pathways via sea ice from the shallow shelf areas into the Arctic Ocean up to the final ablation areas of the Fram Strait can be reconstructed by heavy-mineral data of surface sediments from the central Arctic Ocean. The shallow shelf of the Laptev Sea seems to be the most important source area for terrigenous material, as indicated by the abundant occurence of amphiboles and clinopyroxenes. Underneath the mixing Zone of the two dominating surface circulation Systems, the Beaufort- Gyre and Transpolar-Drift system, the imprint of the Amerasian shelf regions up to the Fram Strait is detectable because of a characteristical heavy-mineral association dominated by detrital carbonate and opaque minerals. Based On heavy-mineral characteristics of the potential circum-Arctic source areas, sea-ice drift, origin and distribution of ice-rafted material can be reconstructed during the past climatic cycles. Different factors controlling the transport of terrigenous material into the Arctic Ocean. The entrainment of particulate matter is triggered by the sea level, which flooded during highs and lows different regions resulting in the incorporation of sediment from different source areas into the sea ice. Additionally, the fluvial input even at low stands of sea level is responsible for the delivery of material of distinct sources for entrainment into the sea ice. Glacials and interglacials of climate cycles of the last 780 000 years left a characteristical signal in the central Arctic Ocean sediments caused by the ice- rafted material from different sources in the circum-Arctic regions and its change through time. Changes in the heavy-mineral association from an amphibole-dominated into a garnet-epidote-assemblage can be related to climate-related changes in source areas and directions of geostrophic winds, the dominating drive of the sea-ice drift. During Marine Isotope Stage (MIS) 6, the central Arctic Ocean is marked by an heavy-mineral signal, which occurs in recent sediments of the eastern Kara Sea. Its characteristics are high amounts of epidote, garnet and apatite. On the other hand, during the Same time interval a continuous record of Laptev Sea sediments is documented with high contents of amphiboles on the Lomonosov Ridge near the Laptev Sea continental slope. A nearly similar Pattern was detected in MIS 5 and 4. Small-scale glaciations in the Putorana-mountains and the Anabar-shield may have caused changes in the drainage area of the rivers and therefore a change in fluvial input. During MIS 3, the heavy-mineral association of central Arctic sediments show similar patterns than the Holocene mineral assemblage which consists of amphiboles, ortho- and clinopyroxenes with a Laptev Sea source. These minerals are indicating a stable Transpolar-Drift system similar to recent conditions. An extended influence of the Beaufort Gyre is only recognized, when sediment material from the Amerasian shelf areas reached the core location PS2757-718 during Termination Ib. Based On heavy-mineral data from Laptev-Sea continental slope Core PS2458-4 the paleo-sea-ice drift in the Laptev Sea during 14.000 years was reconstructed. During Holocene sea-level rise, the bathymetrically deeper parts of the Western shelf were flooded first. At the beginning of the Atlantic stage, nearly the entire shelf was marine influenced by fully marine conditions and the recent surface circulation was established.

Radiocarbon ages, d13C values and rare earth element content of sediment cores BP00-23/07 and BP00-07/06

Two bottom sediment cores (BP00-23/7 and BP00-7/6) recovered from the Yenisei transect in the southern Kara Sea are described. Data on their grain size composition, clay and heavy mineral assemblages, and distribution of a large group of chemical elements are presented. Radiocarbon dates based on AMS C-14 method suggest the Holocene age of sediments in the cores. Literature data on physical properties and foraminifers have also been analyzed. The facies affiliation of the lithostratigraphic subdivisions has been unraveled. History of the Yenisei River runoff in the Holocene has been reconstructed on the basis of different indicators.

Composition of bottom sediments from the Isfjord, Western Svalbard

Lithology, heavy mineral associations, and chemical composition of bottom sediments studied in two gravity cores from Isfjord, Western Spitsbergen (Svalbard) accompanied by high-frequency seismic records, provide a new insight on provenance and glaciomarine sedimentation in the fjord from the last deglaciation through Holocene.

Composition of surface layer bottom sediments from the Kem' River estuary, White Sea

Based on grain-size, mineralogical and chemical analyses of samples collected in cruises of R/V Ekolog (Institute of Northern Water Problems, Karelian Research Centre of RAS, Petrozavodsk) in 2001 and 2003 regularities of chemical element distribution in surface layer bottom sediments of the Kem' River Estuary in the White Sea were studied. For some toxic elements labile and refractory forms were determined. Correlation analysis was carried out and ratios Me/Al were calculated as proxies of terrigenous contribution. Distribution of such elements as Fe, Mn, Zn, Cr, Ti was revealed to be influenced by natural factors, mainly by grain size composition of bottom sediments. These metals have a tendency for accumulation in fine-grained sediments with elevated organic carbon contents. Distribution of Ni is different from one of Fe, Mn, Zn, Cr, Ti. An assumption was made that these distinctions were caused by anthropogenic influence.

Composition of Upper Quaternary bottom sediments from the Syrian area of the Mediterranean Sea

Results of a lithological study of bottom sediments in the Syrian region of the Mediterranean Sea during Cruise 27 of R/V Vityaz (1993) are reported. Suspended sediment discharge of the Nile River are of the greatest importance for terrigenous sedimentation in the SE part of the Mediterranean Sea, especially in deep-sea areas. Suspended load entering from the Syrian catchment area plays an important role in formation of recent shelf and slope deposits. Supply of aerosols from Syrian and Arabian deserts was distinguished by the patchiness of surface distribution of quartz. During Late Quaternary accumulation of terrigenous material supplied from both the Syrian and the Nile drainage areas was irregular. Sedimentation was remarkably enhanced during sapropel formation 7000-9000 years BP.

A magneto-mineralogical study of basalt at DSDP Leg 73 Holes

The basalts in Holes 519A, 522B, and 524 were studied for intensity of natural remanent magnetization, magnetic hysteresis, magnetic susceptibility, stability of isothermal remanence, and thermomagnetic behavior. Some of these properties are sensitive to both the composition and the microstructure of the magnetic minerals, others to composition only. Thus it is possible to separate the two effects and to trace the variation of effective magnetic grain size and degree of alteration within a lithologic unit or over a yet larger distance or time interval. The flow in Hole 519A is highly maghemitized at the top, the degree of maghemitization decreasing with depth in the flow. Effective grain size increases with increasing depth. Electron microprobe analysis of the titanomaghemite grains in these samples provides no support for the leaching out of iron during alteration. The pillows and flows in Hole 522B are distributed among a number of cooling units, and no systematic downhole variations are apparent. The inferred magneto-petrology is consistent with the cooling and alteration history that might be expected within the units. The upper and lower sills in Hole 524 are more uniform and have a larger concentration of well-developed magnetic mineral grains than the pillows and flows in Holes 519A and 522B. Maghemitization appears to have developed from the boundaries of the sills that are in contact with the sediments between the sills.

Composition of bottom sediments from the Guinea Basin

Geomorphology of the Guinea Basin is described along with sediments from cores collected on the abyssal plain, within the abyssal hill zone, and in the eastern part of the Chain Fracture Zone. Stratigraphic differentiation of deep-sea sediments was based on diatom analysis, geochemical and lithological data. Holocene and Pleistocene were identified by these criteria. The lower boundary of Holocene is was found from a marked decrease in CaCO3 concentration and total diatom count. Mineral and chemical compositions are given for coarse silt fraction of various Late Pleistocene sediments. It is shown that this facial complex is determined by tectonic position of the Guinea Basin.