Geochemistry and sedimentology of IODP Hole 307-U1317E

The Plio-Pleistocene intensification of Northern Hemisphere continental ice-sheet development is known to have profoundly affected the global climate system. Evidence for early continental glaciation is preserved in sediments throughout the North Atlantic Ocean, where ice-rafted detritus (IRD) layers attest to the calving of sediment-loaded icebergs from circum-Atlantic ice sheets. So far, Early-Pleistocene IRD deposition has been attributed to the presence of high-latitudinal ice sheets, whereas the existence and extent of ice accumulation in more temperate, mid-latitudinal regions remains enigmatic. Here we present results from the multiproxy provenance analysis of a unique, Pleistocene-Holocene IRD sequence from the Irish NE Atlantic continental margin. There, the Challenger coral carbonate mound (IODP Expedition 307 site U1317) preserved an Early-Pleistocene record of 16 distinctive IRD events, deposited between ca 2.6 and 1.7 Ma. Strong and complex IRD signals are also identified during the mid-Pleistocene climate transition (ca 1.2 to 0.65 Ma) and throughout the Middle-Late Pleistocene interval. Radiogenic isotope source-fingerprinting, in combination with coarse lithic component analysis, indicates a dominant sediment source in the nearby British-Irish Isles, even for the oldest, Early-Pleistocene IRD deposits. Hence, our findings demonstrate, for the first time, repeated and substantial (i.e. marine-terminating) ice accumulation on the British-Irish Isles since the beginning of the Pleistocene. Contemporaneous expansion of both high- and mid-latitudinal ice sheets in the North Atlantic region is therefore implied at the onset of the Pleistocene. Moreover, it suggests the recurrent establishment of (climatically) favourable conditions for ice sheet inception, growth and instability in mid-latitudinal regions, even in the earliest stages of Northern Hemisphere glacial expansion and in an obliquity-driven climate system.

Physical properties, mineral and chemical compositions, and accumulation rates of Holocene and Upper Pleistocene bottom sediments from the Sea of Okhotsk

Mineral and chemical compositions and physical properties of diatomaceous clayey-siliceous sediments from the Sea of Okhotsk are studied. Accumulation rates of silica are determined. Their compositional model based on silica content is similar to that of Late Jurassic and Olenekian-Middle Anisian cherts from the Sikhote Alin region. Thickness of Holocene siliceous unit and accumulation rates of siliceous deposits depended on bioproductivity in the upper water layer and seafloor topography. Accumulation rates of amorphous SiO2 (0.05-5.7 g/cm**2/ka) and free SiO2 (0.5-11.6 g/cm**2/ka) are minimal on seamounts and maximal in depressions near foothills. These values match accumulation rates of free SiO2 in Triassic and Late Jurassic basins of the Sikhote Alin region (0.33-3 g/cm**2/ka). Comparison of composition and accumulation rates of silica shows that Triassic and Late Jurassic siliceous sequences of Sikhote Alin could accumulate in a marginal marine basin near a continent.

Tab. 1: Radiocarbon ages of the late Pleistocene and early Holocene of Mecklenburg-Vorpommern and surrounding areas

Several geoscientific projects in the last decade led to a marked increase of radiocarbon dates in Mecklenburg-Vorpommern and in neighbouring areas. The studies were mostly focussed on the genesis of the Baltic Basin and the last termination. In this Paper, a regional collection of 271 radiocarbon dates of the late Pleistocene and early Holocene (ca. 50,000-8,000 14C yr BP) is presented. The dates were calibrated, correlate, and assessed with regard to their credibility. The evaluation of the data is focussed on problems of regional palaeogeography. The age of the last Weichselian deglaciation (deglaciation after the Mecklenburg Advance) is assumed to be around 14,000 14C yr BP through radiocarbon dates from the Pomeranian Bay. This data is ca. 1,000 years older compared to former views. On the other hand, the database allows the dating of late Pleistocene basin sequences from the Baltic coast, This indicates three stratigraphic units for basin areas 0-15 m above sea level - glaciolacustrine sedimentation in the late Pleniglacial, lacustrine and telmatic sedimentation as well as soil formation in the early Lateglacial and Alleroed and aeolian sedimentation in the Younger Dryas. The Younger Dryas in the huge Mecklenburg Bay-Darss Basin NE of Rostock is characterised by lacustrine sedimentation ca. 20 m below sea level ("Baltic Ice Lake"), and by aeolian sedimentation above sea level.

Physical/chemical properties and stable oxygen and carbon isotope records of Holocene to late Pleistocene sediments in the Gela Basin, central Mediterranean Sea

The Holocene Twin Slides form the most recent of recurrent mass wasting events along the NE portion of Gela Basin within the Sicily Channel, central Mediterranean Sea. Here, we present new evidence on the morphological evolution and stratigraphic context of this coeval slide complex based on deepdrilled sediment sequences providing a >100 ka paleo-oceanographic record. Both Northern (NTS) and Southern Twin Slide (STS) involve two failure stages, a debris avalanche and a translational slide, but are strongly affected by distinct preconditioning factors linked to the older and buried Father Slide. Core-acoustic correlations suggest that sliding occurred along sub-horizontal weak layers reflecting abrupt physical changes in lithology or mechanical properties. Our results show further that headwall failure predominantly took place along sub-vertical normal faults, partly through reactivation of buried Father Slide headscarps.

Late pleistocene and holocene sedimentation in the central and eastern Persian Gulf

The sandfraction of the sediment was analysed in five cores, taken from 65 m water depth in the central and eastern part of the Persian Gulf. The holocene marls are underlayn by aragonite muds, which are probably 10-11,000 years old. 1. The cores could be subdivided into coarse grained and fine grained layers. Sorting is demonstrated by the following criteria: With increasing median values of the sandfraction - the fine grained fraction decreases within each core; - the median of each biogenic component, benthonic as well as planktonic, increases; - the median of the relict sediment, which in core 1179 was carried upward into the marl by bioturbation, increases; - the percentages of pelecypods, gastropods, decapods and serpulid worms in the sandfraction increase, the percentages of foraminifera and ostracods decrease; - the ratios of pelecypods to foraminifera and of decapods to ostracods increase; - the ratios of benthonic molluscs to planktonic molluscs (pteropods) and of benthonic foraminifera to planktonic foraminifera increase (except in core 1056 and 1179); - the ratio of planktonic molluscs (pteropods) to planktonic foraminifera increases; - the globigerinas without orbulinas increase, the orbulinas decrease in core 1056. Different settling velocities of these biogenic particles help in better understanding the results : the settling velocities, hence the equivalent hydrodynamic diameters, of orbulinas are smaller than those of other globigerinas, those of planktonic foraminifera are smaller than those of planktonic molluscs, those of planktonic molluscs are smaller than those of benthonic molluscs, those of pelecypods are smaller than those of gastropods. Bioturbation could not entirely distroy this "grain-size-stratification". Sorting has been stronger in the coarse layers than in the finer ones. As a cause variations in the supply of terrigenous material at constant strength of tidal currents is suggested. When much terrigenous material is supplied (large contents of fine grained fraction) the sedimentation rates are high: the respective sediment surface is soon covered and removed from the influence of tidal currents. When, however, the supply of terrigenous material is small, more sandy material is taken away in all locations within the influence of terrigenous supply. Thus the biogenic particles in the sediment do not only reflect the organic production, but also the influence of currents. 2. There is no parameter present in all cores that is independently variable from grain size and can be used for stratigraphic correlation. The two cores from the Strait of Hormus were correlated by their sequences of coarse and fine grained layers. 3. The sedimentation rates of terrigenous material, of total planktonic and benthonic organisms and of molluscs, foraminifera, echinoids and ophiuroids are shown in table 1 (total sediment 6.3-75.5 cm/1000 yr, biogenic carbonate 1.9-3.6 cm/1000 yr). The sedimentation rates of benthonic organisms are nearly the same in the cores of the Strait of Hormus, whereas near the Central Swell they are smaller. In the upper parts of the two cores of the Strait of Hormus sedimentation rates are higher than in the deeper parts, where higher median values point to stronger reworking. 4. The sequence of coarse and fine grained intervals in the two cores of the Hormus Strait, attributed to variations in climate, as well as the increase of terrigenous supply from the deeper to the upper parts of the cores, agrees with the descriptions in the literature of the post Pleistocene climate as becoming more humid. The rise of sea level is sedimentologically not measurable in the marly sediments - except perhaps for the higher content of echinoids in the lower part of core 1056. These may be attributed to the influence of a migrating wave-base. 5. The late Pleistocene aragonite mud is very fine grained (> 50%< 2 p) and poor in fossils (0.5-1.8%) biogenic particles of total sediment. The sand fraction consists almost entirely of white clumps, c. 0.1 mm in diameter (1177), composed of aragonite needles and of detrital minerals with the same size (1201). The argonite mud was probably not formed in situ, because the water depth at time of formation was at most 35 m at least 12 m. The sorting of the sediment (predominance of the fine grained sand), the absence of larger biogenic components and of pellets, c. 0.2-0.5 mm in diameter, which are typical for Recent and Pleistocene locations of aragonite formation, as well as the sedimentological conditions near the sampling points, indicate rather a transport of aragonite mud from an area of formation in very shallow waters. Sorting as well as lenticular fabric in core 1201 point to sedimentation within the influence of currents. During alternating sedimentation - and reworking processes the aragonitic matrix was separated from the silt - and sand-sized minerals. The lenses grade into touches because of bioturbation. 6. In core 1056 D2 from Hormus Bay the percentages of organic carbon, total nitrogen and total carbonate were determined. With increasing amounts of smaller grain sizes the content of organic matter increases, whereas the amount of carbonate decreases. The amounts of organic carbon and of nitrogen decrease with increasing depth, probably due to early-diagenetic decomposition processes. Most of the total nitrogen is of organic origin, only about 10% may well be inorganically fixed as ammonium-nitrogen. In the upper part of the core the C/N-ratio increases with increasing depth. This may be connected with a stronger decomposition of nitrogen-containing organic compounds. The general decrease of the C/N-ratios in the lower part of the core may be explained by the relative increase of inorganically fixed ammonium-nitrogen with decreasing content of organic matter.

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).

Benthic foraminiferal faunas of Miocene to Holocene sediments of ODP Site 184-1143 from the southern South China Sea

Deep-sea benthic foraminiferal assemblages from Ocean Drilling Program (ODP) Site 1143 located in the southern South China Sea (SCS) were investigated to evaluate the relationship between faunal composition patterns and paleoceanographic changes during the last 6 million years (late Miocene to Holocene). We used multivariate statistics (correspondence analysis) to analyze carbon-flux-related changes in assemblage composition of benthic foraminifers. Additional proxies for carbon flux and deep-water ventilation include delta13C records of epifaunal Cibicidoides wuellerstorfi and infaunal Uvigerina peregrina var. dirupta and Melonis pompilioides, benthic foraminiferal accumulation rates (BFARs), diversity indices, and relative abundances of indicator species. We observe three significant benthic faunal changes in the southern South China Sea during the last 6 million years. Strong fluctuations in BFAR and relative abundance of productivity indicator species between glacial and interglacial stages after the mid-Pleistocene revolution (MPR) at approximately 0.9 Ma, indicating stronger seasonal carbon flux fluctuations, are accompanied by the extinction of such species as Stilostomella spp. Increases in carbon flux indicator species are coupled with an overall decrease in benthic foraminifer diversity around 3.0 Ma in the late Pliocene. This may indicate increasing carbon flux in a period of productivity maximum caused by enhanced offshore upwelling from intensified winter monsoon wind strength.

Mineral composition of 0.25-0.05 mm grain size fraction from Holocene sediments of the Baikal Lake

Results of investigations of Baikal bottom sediments from a long core (BDP-97) and several short (0-1 m) cores are presented. It can be shown that Holocene sediments in the Baikal basins consist of biogenic-terrigenous muds accumulated under still sedimentation conditions, and of turbidites formed during catastrophic events. The turbidites can be distinguished from the host sediments by their enrichment in heavy minerals and thus their high magnetic susceptibility. Often, Pliocene and Pleistocene diatom species observed in the Holocene sediments (mainly in the turbidites) point to redeposition of ancient offshore sediments. Our results indicate that deltas, littoral zones, and continental slopes are source areas of turbidites. The fact that the turbidites occur far from their sources confirms existence of high-energy turbidity currents responsible for long-distance lateral-sediment transport to the deep basins of the lake.

Late Miocene to Holocene calcareous nannofossils from ODP sites of Leg 125

During Leg 125 of the Ocean Drilling Program, nine sites were drilled in the Mariana and Izu-Bonin areas. The sediments recovered range in age from early Pliocene to late Pleistocene in the Mariana Region and from middle Eocene to late Pleistocene in the Izu-Bonin region. This contribution concerns the biostratigraphic study of the latest Miocene (CN9b Subzone) to late Pleistocene interval. Aquantitative analysis of all calcareous nannofossil associations was conducted for the interval encompassing late Miocene to the top of the early Pliocene. Moreover, the genera Discoaster, Amaurolithus, and Ceratolithus were quantitatively investigated from the late Miocene to late Pliocene interval. Some bioevents were identified, and variations in the composition of assemblages were linked to climatic changes.

Stable isotope record of benthic foraminifera in late Pleistocene sediments

Variations in the contribution of North Atlantic Deep Water (NADW), relative to North Pacific Deep Water (NPDW), to the Southern Ocean, are assessed by comparing delta13C records from the mid-depth North Atlantic, deep Southern Ocean, and deep equatorial Pacific Ocean. In general, the relative contribution of NADW was greater during interglaciations than glaciations of the past 550,000 years. An increase in the NADW flux to the Southern Ocean since the last glaciation was proposed to have resulted in higher atmospheric CO2 in the Holocene (Broecker and Peng, 1989, doi:10.1029/GB003i003p00215). Glacial-interglacial variations in the proportion of NADW in the Southern Ocean may have also influenced atmospheric CO2 levels over the past 550,000 years. The greatest relative flux of NADW to the Southern Ocean occurred during interglacial stage 11. Faunal data suggest that the North Atlantic polar front and southern Indian Ocean subtropical convergence zone were located farthest poleward during stage 11. Warmth in these locations and a strong southward flux of NADW during stage 11 may be causally linked by the NADW formation process/warm water return route (Gordon, 1986, doi:10.1029/JC091iC04p05037). Time series analysis indicates that delta13C variations in the deep Southern Ocean occur at the same frequencies as the Earth's orbital variations and are coherent and in phase with delta18O. At most, 50% of the glacial-interglacial delta13C amplitude in the Southern Ocean is due changes in the contribution of NADW. The remainder is probably due to mean ocean delta13C changes.

Geochemistry of Pleistocene volcanic rocks in the Mariana Forearc

Geophysical surveys of the Mariana forearc, in an area equidistant from the Mariana Trench and the active Mariana Island Arc, revealed a 40-m-deep graben about 13 km northwest of Conical Seamount, a serpentine mud volcano. The graben and its bounding horst blocks are part of a fault zone that strikes northwest-southeast beneath Conical Seamount. One horst block was drilled during Leg 125 of the Ocean Drilling Program (Site 781). Three lithologic units were recovered at Site 781: an upper sedimentary unit, a middle basalt unit, and a lower sedimentary unit. The upper unit, between 0 and 72 mbsf, consists of upper Pliocene to Holocene diatomaceous and radiolarian-bearing silty clay that grades down into vitric silty clay and vitric clayey silt. The middle unit is a Pleistocene vesicular, porphyritic basalt, the top of which corresponds to a high-amplitude reflection on the reflection profiles. The lower unit is a middle to upper (and possibly some lower) Pliocene vitric silty clay and vitric clayey silt similar to the lower part of the upper unit. The thickness of the basalt unit can only be estimated to be between 13 and 25 m because of poor core recovery (28% to 55%). The absence of internal flow structures and the presence of an upper glassy chilled zone and a lower, fine-grained margin suggest that the basalt unit is either a single lava flow or a near-surface sill. The basalt consists of plagioclase phenocrysts with subordinate augite and olivine phenocrysts and of plagioclase-augite-olivine glomerocrysts in a groundmass of plagioclase, augite, olivine, and glass. The basalt is an island arc tholeiite enriched in large-ion-lithophile elements relative to high-field-strength elements, similar to the submarine lavas of the southern arc seamounts. In contrast, volcanic rocks from the active volcanoes on Pagan and Agrigan islands, 100 km to the west of the drill site, are calc-alkaline. The basalt layer, the youngest in-situ igneous layer reported from the Izu-Bonin and Mariana forearcs, is enigmatic because of its location more than 100 km from the active volcanic arc. The sediment layers above and below the basalt unit are late Pliocene in age (about 2.5 Ma) and normally magnetized. The basalt has schlierenlike structures, reverse magnetization, and a K-Ar age of 1.68±0.37 Ma. Thus, the basalt layer is probably a sill fed by magma intruded along a fault zone bounding the horst and graben in the forearc. The geochemistry of the basalt is consistent with a magma source similar to that of the active island arc and from a mantle source above the subducting Pacific plate.