Composition of bottom sediments from Core SO201-2-101, Shirshov Ridge, Bering Sea

Analysis of lithology, grain-size composition, clay minerals, and geochemistry of Upper Pleistocene bottom sediments from the submarine Shirshov Ridge (Bering Sea) showed that the Yukon-Tanana terrane of the Central Alaska was main source area of the sediments. Sedimentary material was transported by the Yukon River through Beringia up to the shelf break, where they were entrained by a strong north-west sea current. Lithological data revealed several pulses of ice-rafted debris deposition roughly synchronous with Heinrich events and periods of weaker bottom current intensity. Based on geochemical results we distinguished intervals of an increase in paleoproductivity and extension of the oxygen minimum zone. Our results suggest that there were three stages of deposition driven by glacioeustatic sea-level fluctuations and glacial cycles in Alaska.

Petrology and isotope characteristics of basalts from ODP Hole 111-504B

Petrography and isotope geochemical characteristics of H, O, S, Sr, and Nd have been described for basalts recovered from Hole 504B during Leg 111 of the Ocean Drilling Program. The petrographic and chemical features of the recovered basalts are similar to those obtained previously (DSDP Legs 69, 70, and 83); they can be divided into phyric (plagioclase-rich) and aphyric (Plagioclase- and clinopyroxene-rich) basalts and show low abundances of TiO2, Na2O, K2O, and Sr. This indicates that the basalts belong to Group D, comprising the majority of the upper section of the Hole 504B. The diopside-rich nature of the clinopyroxene phenocrysts and Ca-rich nature of the Plagioclase phenocrysts are also consistent with the preceding statement. The Sr and Nd isotope systematics (average 87Sr/86Sr = 0.70267 ± 0.00007 and average 143Nd/144Nd = 0.513157 ± 0.000041) indicate that the magma sources are isotopically heterogeneous, although the analyzed samples represent only the lowermost 200-m section of Hole 504B. The rocks were subjected to moderate hydrothermal alteration throughout the section recovered during Leg 111. Alteration is limited to interstices, microfractures, and grain boundaries of the primary minerals, forming chlorite, actinolite, talc, smectite, quartz, sphene, and pyrite. In harmony with the moderate alteration, the following alteration-sensitive parameters show rather limited ranges of variation: H2O = 1.1 ±0.2 wt%, dD = - 38 per mil ± 4 per mil, d180 = 5.4 per mil ± 0.3 per mil, total S = 562 ± 181 ppm, and d34S = 0.8 per mil ± 0.3 per mil. Based on these data, it was estimated that the hydrothermal fluids had dD and d180 values only slightly higher than those of seawater, the water/rock ratios were as low as 0.02-0.2, and the temperature of alteration was 300°-400°C. Sulfur exists predominantly as pyrite and in minor quantities as chalcopyrite. No primary monosulfide was detected. This and the d34S values of pyrite (d34S = 0.8 per mil) suggest that primary pyrrhotite was almost completely oxidized to pyrite by reaction with hydrothermal fluids containing very little sulfate.

Physical properties of four profiles from the Triassic in Germany

The Norian Steinmergel-Keuper (SMK) represents a low-latitude cyclically-bedded playa system of the Mid-German Basin. We investigated a drilling site (core Morsleben) and sections from marginal positions. Dolomite/red mudstone beds form rhythmic alternations that were associated with varying monsoon activity. Hence, low K/Al ratios of dolomite beds suggest increased chemical weathering of the crystalline hinterland and therefore increased monsoonal rainfall. High K/Al ratios in red mudstone beds reflect increased physical weathering of the hinterlands during dryer periods. Dolomite layers reflect the lake stage (maximum monsoon) while red mudstones indicate the dry phase (minimum monsoon) of the playa cycle. We distinguished five major types of cyclic facies alternations, representing specific facies zones in the playa system. We have implemented spectrophotometry as a tool for high-resolution cyclostratigraphy. The dense sampling increment (up to 1 cm) allows for the recognition of all orbital frequencies. Sediment colour profiles reveal striking hierarchical cycles from semi-precession (SP, 99 kyr) over precession (P, 19.8 kyr) and obliquity (O, 36 kyr) to eccentricity (E1-2 109 kyr; E3, 413 kyr). A significant about 2 Myr-signal is attributed to the longer-term eccentricity E4. One monsoonal (precession) cycle includes two carbonate precipitation events. We propose that stratified mudstone and red mudstone are associated with maximum and minimum monsoon during the transition of the solstices in perihelion and aphelion, respectively. The two carbonate precipitation events were most likely created when equinoxes were in perihelion and aphelion, respectively. A sedimentary semi-precession response cycle is a novel finding for the Norian strata. The obliquity signal is attributed to incoming atmospheric moisture from the northeast of the SMK basin. The E4 cycle controls lake-level changes over long times. Apparently, E4 is responsible whether or not a threshold value is crossed. Bundles of 109 kyr and 413 kyr in red mudstones suggest a dry system with reduced monsoonal activity. In contrast, humid periods reveal thick layers of dolomite beds, indicating that during those intervals the monsoonal activity was strong enough to prevent the playa system from drying out completely.

Composition of sediments, hydrothermal manifestations, interstitial waters, and aeolian material from the TAG Hydrothermal Field and Central Atlantic

The book is devoted to regularities of spatial distribution, mineralogy and geochemistry of hydrothermal and hydrothermal-sedimentary manifestations of the Mid-Atlantic Ridge rift zone.

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.

Chemistry of magmatic samples of ODP Holes 134-832B and 134-833B

New petrographic and compositional data were reported for 143 samples of core recovered from Sites 832 and 833 during Ocean Drilling Program (ODP) Leg 134. Site 832 is located in the center and Site 833 is on the eastern edge of the North Aoba Basin, in the central part of the New Hebrides Island Arc. This basin is bounded on the east (Espiritu Santo and Malakula islands) and west (Pentecost and Maewo islands) by uplifted volcano-sedimentary ridges associated with collision of the d'Entrecasteaux Zone west of the arc. The currently active Central Belt volcanic front extends through the center of this basin and includes the shield volcanoes of Aoba, Ambrym, and Santa Maria islands. The oldest rocks recovered by drilling are the lithostratigraphic Unit VII Middle Miocene volcanic breccias in Hole 832B. Lava clasts are basaltic to andesitic, and the dominant phenocryst assemblage is plagioclase + augite + orthopyroxene + olivine. These clasts characteristically contain orthopyroxene, and show a low to medium K calc-alkaline differentiation trend. They are tentatively correlated with poorly documented Miocene calc-alkaline lavas and intrusives on adjacent Espiritu Santo Island, although this correlation demands that the measured K-Ar of 5.66 Ma for one clast is too young, due to alteration and Ar loss. Lava clasts in the Hole 832B Pliocene-Pleistocene sequence are mainly ankaramite or augite-rich basalt and basaltic andesite; two of the most evolved andesites have hornblende phenocrysts. These lavas vary from medium- to high-K compositions and are derived from a spectrum of parental magmas for which their LILE and HFSE contents show a broad inverse correlation with SiO2 contents. We hypothesize that this spectrum results from partial melting of an essentially similar mantle source, with the low-SiO2 high HFSE melts derived by lower degrees of partial melting probably at higher pressures than the high SiO2, low HFSE magmas. This same spectrum of compositions occurs on the adjacent Central Chain volcanoes of Aoba and Santa Maria, although the relatively high-HFSE series is known only from Aoba. Late Pliocene to Pleistocene lava breccias in Hole 833B contain volcanic clasts including ankaramite and augite + olivine + plagioclase-phyric basalt and rare hornblende andesite. These clasts are low-K compositions with flat REE patterns and have geochemical affinities quite different from those recovered from the central part of the basin (Hole 832B). Compositionally very similar lavas occur on Merelava volcano, 80 km north of Site 833, which sits on the edge of the juvenile Northern (Jean Charcot) Trough backarc basin that has been rifting the northern part of the New Hebrides Island Arc since 2-3 Ma. The basal sedimentary rocks in Hole 833B are intruded by a series of Middle Pliocene plagioclase + augite +/- olivine-phyric sills with characteristically high-K evolved basalt to andesite compositions, transitional to shoshonite. These are compositionally correlated with, though ~3 m.y. older than, the high-HFSE series described from Aoba. The calc-alkaline clasts in Unit VII of Hole 832B, correlated with similar lavas of Espiritu Santo Island further west, presumably were erupted before subduction polarity reversal perhaps 6-10 Ma. All other samples are younger than subduction reversal and were generated above the currently subduction slab. The preponderance in the North Aoba Basin and adjacent Central Chain islands of relatively high-K basaltic samples, some with transitional alkaline compositions, may reflect a response to collision of the d'Entrecasteaux Zone with the arc some 2-4 Ma. This may have modified the thermal structure of the subduction zone, driving magma generation processes to deeper levels than are present normally along the reminder of the New Hebrides Island Arc.

Composition of suspended matter and bottom sediments from the North Dvina mouth area

Grain-size, mineral and chemical compositions of suspended particulate matter (SPM) from waters of the Severnaya (North) Dvina River mouth area during the spring flood in May 2004 is studied. Data published on composition of riverine SPM in the White Sea basin are very poor. The spring flood period when more than half of annual runoff is supplied from the river to the sea in during short time is understood more poorly. The paper considers comparison results of the grain size compositions of SPM and bottom sediments. Data of laser and hydraulic techniques of grain size analysis are compared. Short-period variations of SPM concentration and composition representing two diurnal peaks of the tide level are studied. It is found that SPM is mainly transferred during the spring flood as mineral aggregates up to 40 µm diameter. Sandy-silty fraction of riverine SPM settles in delta branches and channels, and bulk of clay-size material is supplied to the sea. Mineral and chemical compositions of SPM from the North Dvina River are determined by supply of material from the drainage basin. This material is subjected to intense mechanic separation during transfer to the sea. Key regularities of formation of mineral composition of SPM during the flood time are revealed. Effect of SPM grain size composition on distribution of minerals and chemical elements in study in the dynamic system of the river mouth area are characterized.

Geochemistry of ocean floor and forearc serpentinites

We provide new insights into the geochemistry of serpentinites from mid-ocean ridges (Mid-Atlantic Ridge and Hess Deep), passive margins (Iberia Abyssal Plain and Newfoundland) and fore-arcs (Mariana and Guatemala) based on bulk-rock and in situ mineral major and trace element compositional data collected on drill cores from the Deep Sea Drilling Project and Ocean Drilling Program. These data are important for constraining the serpentinite-hosted trace element inventory of subduction zones. Bulk serpentinites show up to several orders of magnitude enrichments in Cl, B, Sr, U, Sb, Pb, Rb, Cs and Li relative to elements of similar compatibility during mantle melting, which correspond to the highest primitive mantle-normalized B/Nb, B/Th, U/Th, Sb/Ce, Sr/Nd and Li/Y among subducted lithologies of the oceanic lithosphere (serpentinites, sediments and altered igneous oceanic crust). Among the elements showing relative enrichment, Cl and B are by far the most abundant with bulk concentrations mostly above 1000 µg/g and 30 µg/g, respectively. All other trace elements showing relative enrichments are generally present in low concentrations (µg/g level), except Sr in carbonate-bearing serpentinites (thousands of µg/g). In situ data indicate that concentrations of Cl, B, Sr, U, Sb, Rb and Cs are, and that of Li can be, increased by serpentinization. These elements are largely hosted in serpentine (lizardite and chrysotile, but not antigorite). Aragonite precipitation leads to significant enrichments in Sr, U and B, whereas calcite is important only as an Sr host. Commonly observed brucite is trace element-poor. The overall enrichment patterns are comparable among serpentinites from mid-ocean ridges, passive margins and fore-arcs, whereas the extents of enrichments are often specific to the geodynamic setting. Variability in relative trace element enrichments within a specific setting (and locality) can be several orders of magnitude. Mid-ocean ridge serpentinites often show pronounced bulk-rock U enrichment in addition to ubiquitous Cl, B and Sr enrichment. They also exhibit positive Eu anomalies on chondrite-normalized rare earth element plots. Passive margin serpentinites tend to have higher overall incompatible trace element contents than mid-ocean ridge and fore-arc serpentinites and show the highest B enrichment among all the studied serpentinites. Fore-arc serpentinites are characterized by low overall trace element contents and show the lowest Cl, but the highest Rb, Cs and Sr enrichments. Based on our data, subducted dehydrating serpentinites are likely to release fluids with high B/Nb, B/Th, U/Th, Sb/Ce and Sr/Nd, rendering them one of the potential sources of some of the characteristic trace element fingerprints of arc magmas (e.g. high B/Nb, high Sr/Nd, high Sb/Ce). However, although serpentinites are a substantial part of global subduction zone chemical cycling, owing to their low overall trace element contents (except for B and Cl) their geochemical imprint on arc magma sources (apart from addition of H2O, B and Cl) can be masked considerably by the trace element signal from subducted crustal components.