Strontium isotopic data for calcareous ooze, chalk, and pore waters from DSDP Hole 590B

A detailed study of strontium isotope variations in Neogene marine carbonate sediments from Deep Sea Drilling Project Site 590B, using techniques that allow the 87Sr/86Sr ratio to be determined to better than +/-0.00001, gives a high-resolution record of the Sr isotopic evolution of seawater. The data show that the rate of change of the marine 87Sr/86Sr ratio has varied significantly even on time scales as short as 1 m.y. Periods of particularly rapid growth appear to follow major marine regressions and probably reflect an increase in the delivery of radiogenic Sr from the continents coupled with a decreased submarine carbonate dissolution rate (greater carbonate compensation depth). Periods of relatively slowly changing 87Sr/86Sr follow major marine transgressions. On the basis of correlations with the marine oxygen isotope record and the times of major continental glacier growth, it is inferred that the effects of sea-level variations are modified by climatic factors that affect the intensity of continental weathering and runoff. The effects of sea-floor generation rate variations are not discernible for the Neogene. The maximum attainable stratigraphic resolution using Sr isotopes is between 0.1 and 2 m.y. for this time period.

Holocene sedimentation in the Strait of Otranto, Mediterranean Sea

An extensive radiograph study of 24 undisturbed, up to 206-cm long box and gravity cores from the western part of the Strait of Otranto revealed a great variety of primary bedding structures and secondary burrowing features. The regional distribution of the sediments according to their structural, textural, and compositional properties reflects the major morphologic subdivisions of the strait into shelf, slope, and trough bottom (e.g., the bottom of the northern end of the Corfu-Kephallinia Trough, which extends from the northeastern Ionian Sea into the Strait of Otranto): (1) The Apulian shelf (0 to -170m) is only partly covered by very poorly sorted, muddy sands without layering. These relict(?) sands are rich in organic carbonate debris and contain glauconite and reworked (?Pleistocene) ooids. (2) The slope sediments (-170 to -1,000 m) are poorly sorted, sandy muds with a high degree of burrowing. One core (OT 5) is laminated and shows slump structures. An origin of these slumped sediment masses from older deposits higher on the slope was inferred from their abnormal compaction, color, texture, organic content, and mineral composition. (3) Cores from the northern end of the Corfu-Kephallinia Trough (-980 to -1,060 m) display a few graded sand layers, 2-5 cm (maximum 30 cm) thick with parallel and ripple-cross-laminations, deposited by oceanic bottom or small-scale turbidity currents. They are intercalated with homogeneous lutite. (4) Hemipelagic sediments prevail in the more southerly part of the Corfu-Kephallinia Trough and on the "Apulian-Ionian Ridge", the southern submarine extension of the Apulian Peninsula. Below a core depth of 160 cm, these cores have a laminated ("varved") zone, representing an Early Holocene (Boreal-Atlanticum) "stagnation layer" (14C age approximately 9,000 years). The terrigenous components of the surface sediments as well as those of the deeper sand layers can be derived from the Apulian shelf and the Italian mainland (Cretaceous Apulian Plateau and Gargano Mountains, southern Apennines, volcanic province of the Monte Vulture). Indicated by the heavy mineral glaucophane, a minor proportion of the sedimentary material is probably of Alpine origin. If this portion is considered to be first-cycle clastic material it reaches the Strait of Otranto after a longitudinal transport of 700 km via the Adriatic Sea. The lack of phyllosilicates in the coarse- to medium-grained shelf samples might be explained by the activity of the "Apulian Current" (surface velocities up to 4 knots) which in the past possibly has affected the bottom almost down to depths of the shelf edge. The percentage of planktonic organisms, and also the plankton: benthos ratio in the sediments is a useful indicator for bathymetry (depth zonation).

Geochemistry of sediments from the mid-oceanic Kolbeinsey Ridge

In order to assess recent submarine volcanic contributions to the sediments from the active Kolbeinsey Ridge, surface samples were analyzed chemically. The contribution of major and trace elements studied differ within the study area. A statistical analysis of the geochemical variables using factor analysis and cluster method allows to distinguish possible sample groups. Cluster method identifies three distinct sediment groups located in different areas of sedimentation. Group 1 is characterized by highest contents of Fe2O3, V, Co, Ni, Cu and Zn demonstrating the input of volcaniclastic material. Group 2 comprises high values of CaCO3, CaO and Sr representing biogenic carbonate. Group 3 is characterized by the elements K, Rb, Cs, La and Pb indicating the terrigenous component. The absolute percentage of the volcanic, biogenic and terrigenous components in the bulk sediments was calculated by using a normative sediment method. The highest volcanic component (> 60% on a carbonate free basis) is found on the ridge crest. The biogenic component is highest (10-30%) in the eastern part of the Spar Fracture Zone influenced by the East Iceland Current. Samples from the western and southeastern region of the study area contain more than 90% of terrigenous component which appears to be mainly controlled by input of ice-rafted debris.

Geochemistry of Loihi Seamount hydrothermal deposits

High-resolution bathymetric surveys, bottom photography and sample analyses show that Loihi Seamount at the southernmost extent of the Hawaiian ëhotspotí is an active, young submarine volcano that is probably the site of an emerging Hawaiian island. Hydrothermal deposits sampled from the active summit rift system were probably formed by precipitation from cooling vent fluids or during cooling and oxidation of high-temperature polymetallic sulphide assemblages. No exotic benthic fauna were found to be associated with the presently active hydrothermal vents mapped.

Eh and pH values in sediments and composition of interstitial waters from the Frolikha Bay, Baikal Lake

Redox conditions and compositions of bottom sediments and sedimentary pore waters in the area of the hydrothermal vent in the Frolikha Bay (Baikal Lake) are under discussion. According to obtained results, the submarine vent and its companion spring nearby on the land originate from a common source. The most convincing evidence for their relation comes from proximity of stable oxygen and hydrogen isotope compositions in the pore waters and spring water. The isotope composition indicates meteoric origin of the pore waters, but their major- and minor element compositions have influence of deep water, which may seep through the permeable faulted crust. Although the pore waters near the submarine vent have specific enrichment in major and minor constituents, hydrothermal discharge at the Baikal bottom causes minor influence on water composition of the Baikal Lake, unlike freshwater lakes in rifts of the East Africa and North America.