Composition of sediment pore water and isotopes in carbonate and benthic foraminifera at DSDP Holes 68-501, 69-505 and Site 69-504

Two sites on the southern flank of the Costa Rica Rift were drilled on DSDP Legs 68 and 69, one on crust 3.9 m.y. old and the other on crust 5.9 m.y. old. The basement of the younger site is effectively cooled by the circulation of seawater. The basement of the older site has been sealed by sediment, and an interval in the uppermost 560 meters of basement recently reheated to temperatures of 60 to 120°C. Although the thickness of the sediments at the two sites is similar (150-240 m versus 270 m), the much rougher basement topography at the younger Site 505 produces occasional basement outcrops, through which 80 to 90% of the total heat loss apparently occurs by advection of warm seawater. This seawater has been heated only slightly, however; the temperature at the base of the sediments is only 9°C. Changes in its composition due to reaction with the basement basalts are negligible, as indicated by profiles of sediment pore water chemistry. Bacterial sulfate reduction in the sediments produces a decrease in SO4 (and Ca) and an increase in alkalinity (and Sr and NH3) as depth increases to an intermediate level, but at deeper levels these trends reverse, and all of these species plus Mg, K, Na, and chlorinity approach seawater values near basement. Si, however, is higher, and Li may be lower. At the older site, Site 501/504, where heat loss is entirely by conduction, the temperature at the sediment/basement contact is 59°C. Sediment pore water chemistry is heavily affected by reaction with the basaltic basement, as indicated by large decreases in d18O, Mg, alkalinity, Na, and K and an increase in Ca with increasing depth. The size of the changes in d18O, Mg, alkalinity, Ca, Sr, and SO4 varies laterally over 500 meters, indicating lateral gradients in pore water chemistry that are nearly as large as the vertical gradients. The lateral gradients are believed to result from similar lateral gradients in the composition of the basement formation water, which propagate upward through the sediments by diffusion. A model of the d18O profile suggests that the basement at Site 501/504 was sealed off from advection about 1 m.y. ago, so that reaction rates began to dominate the basement pore water chemistry. A limestone-chert diagenetic front began to move upward through the lower sediments less than 200,000 yr. ago.

Composition of Quaternary and Neogene-Quaternary sedimentary rocks from the Black Sea

Processes of sedimentation in marine basins locating in the area of interaction of the largest continental plates (African and Eurasian) are under consideration in the book. During the giant tectonic reconstruction of the Tethys Ocean semi-enclosed seas - the Mediterranean and Black originated. Their sedimentary sequence contains a recording of complex history of the Alpine-Himalayan belt. The dramatic history of the seas and their feeding catchments during Cenozoic is described in detail on the base of unique material of coring and deep-sea drilling, as well as a variety of geophysical and geochemical studies. Particular attention is paid to the history of volcanism - terrestrial and underwater - with correlation of ash falls accumulated on the land and in marine sediments.

Composition of hydrothermal massive sulfide deposits from ODP Site 158-957 and Leg 169 sites

Sulfide mineral major and trace element analyses were performed on more than 50 polished slabs representing mineralization from three seafloor hydrothermal massive sulfide deposits. Samples from the Bent Hill and ODP Mound massive sulfide deposits, both on the Juan de Fuca Ridge, can be contrasted with samples from the Trans-Atlantic Geotraverse (TAG) hydrothermal mound on the Mid-Atlantic Ridge. The massive sulfide at Bent Hill is predominantly pyrite and pyrrhotite, with increasing amounts of copper-bearing sulfide minerals at the base of the massive sulfide body and through the stockwork to an interval 200 m below seafloor that hosts high copper mineralization (Deep Copper Zone). ODP Mound contains much more abundant sphalerite and copper-bearing sulfides as compared to either Bent Hill or TAG, which are predominantly pyrite with much less abundant chalcopyrite. Copper-bearing sulfides from the Deep Copper Zone beneath Bent Hill and the lowest sampled interval of ODP Mound are petrographically and chemically similar, but distinct from copper-bearing minerals higher in either sequence.

Age and strontium isotope composition for Cretaceous in DSDP Hole 74-525

Firm stratigraphic correlations are needed to evaluate the global significance of unconformity bounded units (sequences). We correlate the well-developed uppermost Campanian and Maestrichtian sequences of the New Jersey Coastal Plain to the geomagnetic polarity time scale (GPTS) by integrating Sr-isotopic stratigraphy and biostratigraphy. To do this, we developed a Maestrichtian (ca. 73-65 Ma) Sr-isotopic reference section at Deep Sea Drilling Project Hole 525A in the southeastern Atlantic Ocean. Maestrichtian strata can then be dated by measuring their 87Sr/86Sr composition, calibrating to the GPTS of S. C. Cande and D. V. Kent (1993, personal commun.), and using the equation Age (Ma) = 37326.894-52639.89 (87Sr/86Sr). Sr-stratigraphic resolution for the Maestrichtian is estimated as +-1.2 to +-2 m.y. At least two unconformity-bounded units comprise the uppermost Campanian to Maestrichtian strata in New Jersey. The lower one, the Marshalltown sequence, is assigned to calcareous nannofossil Zones CC20/21 (~NC19) and CC22b (~NC20). It ranges in age from ~74.1 to 69.9 Ma based on Sr-isotope age estimates. The overlying Navesink sequence is assigned to calcareous nannoplankton Zones CC25-26 (~NC21-23); it ranges in age from 69.3 to 65 Ma based on Sr-isotope age estimates. The upper part of this sequence, the Tinton Formation, has no calcareous planktonic control; Sr-isotopes provide an age estimate of 66 +- 1.2 Ma (latest Maestrichtian). Sequence boundaries at the base and the top of the Marshalltown sequence match boundaries elsewhere in the Atlantic Coastal Plain (Owens and Gohn, 1985) and the inferred global sea-level record of Haq et al. (1987); they support eustatic changes as the mechanism controlling depositional history of this sequence. However, the latest Maestrichtian record in New Jersey does not agree with Haq et al. (1987); we attribute this to correlation and time-scale differences near the Cretaceous/Paleogene boundary. High sedimentation rates in the latest Maestrichtian of New Jersey (Shrewsbury Member of the Red Bank Formation and the Tinton Formation) suggest tectonic uplift and/or rapid progradation during deposition of the highstand systems tract.

Chemical composition of bottom waters and interstitial waters from sediments and deposits within and outside the Haakon Mosby submarine mud volcano in the Norwegian Sea

On the base of data of Cruise 40 of R/V Akademik Keldysh features of formation of saline composition of interstitial waters from sediments containing free hydrocarbons (methane) and gas hydrates (CH4 x 6H2O) were considered. Chemical composition of the interstitial waters is presented for three zones of sediments from the Haakon Mosby submarine mud volcano: (1) zone of kettles containing free hydrocarbons, (2) gas hydrate sediments, and (3) periphery of the volcano. Abnormally high concentrations of bromine and especially iodine characteristic of the interstitial and particularly of the oil-field waters were found. Because of a great interest in natural gas hydrates found in marine sediments, we obtained a possibility to supplement scarce of available published data with some new information.

Chemical composition of phosphorites, Fe-Mn nodules and crusts, and basalts from the West Pacific

The monograph gives the first systematic description of ore-bearing guyots from the West Pacific. It is mostly based on data obtained in numerous expeditions of Russian vessels during 1984-1992. Ore deposits located on upper parts of all slopes and tops of the guyots include phosphorites associated with cobalt- and platinum-rich ferromanganese crusts. Location, origin and prospecting of mineral deposits are discussed on the base of new data on metallogenic factors (geodynamics, tectonics, magmatism, sedimentation and morphostructures).

Composition of bioclastic sands, carbonates and pyroclastic rocks of the Great Meteor and Josephine Seamounts, eastern North Atlantic

1. Great Meteor Seamount (GMS) is a very large (24,000 km**3) guyot with a flat summit plateau at 330-275 m; it has a volcanic core, capped by 150-600 m of post-Middle-Miocene carbonate and pyroclastic rocks, and is covered by bioclastic sands. The much smaller Josephine Seamount (JS, summit 170- 500 m w. d.) consists mainly of basalt which is only locally covered by limestones and bioclastic sands. 2. The bioclastic sands are almost free of terrigenous components, and are well sorted, unimodal medium sands. (1) "Recent pelagic sands" are typical of water depths > 600 m (JS) or > 1000 m (GMS). (2) "Sands of mixed relict-recent origin" (10-40% relict) and (3) "relict sands" (> 40% relict) are highly reworked, coarse lag deposits from the upper flanks and summit tops in which recent constituents are mixed with Pleistocene or older relict material. 3. From the carbonate rocks of both seamounts, 12 "microfacies" (MF-)types were distinguished. The 4 major types are: (1) Bio(pel)sparites (MF 1) occur on the summit plateaus and consist of magnesian calcite cementing small pellets and either redeposited planktonic bioclasts or mixed benthonic-planktonic skeletal debris ; (2) Porous biomicrites (MF 2) are typical of the marginal parts of the summit plateaus and contain mostly planktonic foraminifera (and pteropods), sometimes with redeposited bioclasts and/or coated grains; (3) Dense, ferruginous coralline-algal biomicrudites with Amphistegina sp. (MF 3.1), or with tuffaceous components (MF 3.2); (4) Dense, pelagic foraminiferal nannomicrite (MF 4) with scattered siderite rhombs. Corresponding to the proportion and mineralogical composition of the bioclasts and of the (Mgcalcitic) peloids, micrite, and cement, magnesian calcite (13-17 mol-% MgCO3) is much more abundant than low-Mg calcite and aragonite in rock types (1) and (2). Type (3) contains an "intermediate" Mg-calcite (7-9 mol-X), possibly due to an original Mg deficiency or to partial exsolution of Mg during diagenesis. The nannomicrite (4) consists of low-Mg calcite only. 4. Three textural types of volcanic and associated gyroclastic rocks were distinguished: (1) holohyaline, rapidly chilled and granulated lava flows and tuffs (palagonite tuff breccia and hyaloclastic top breccia); (2) tachylitic basalts (less rapidly chilled; with opaque glass); and (3) "slowly" crystallized, holocrystalline alkali olivine basalts. The carbonate in most mixed pyroclastic-carbonate sediments at the basalt contact is of "post-eruptive" origin (micritic crusts etc.); "pre-eruptive" limestone is recrystallized or altered at the basalt contact. A deuteric (?hydrothermal) "mineralX", filling vesicles in basalt and cementing pyroclastic breccias is described for the first time. 5. Origin and development of GMS andJS: From its origin, some 85 m. y. ago, the volcano of GMS remained active until about 10 m. y. B. P. with an average lava discharge of 320 km**3/m. y. The volcanic origin of JS is much younger (?Middle Tertiary), but the volcanic activity ended also about 9 m. y. ago. During L a t e Miocene to Pliocene times both volcanoes were eroded (wave-rounded cobbles). The oldest pyroclastics and carbonates (MF 3.1, 3.2) were originally deposited in shallow-water (?algal reef hardground). The Plio (-Pleisto) cene foraminiferal nannomicrites (MF 4) suggest a meso- to bathypelagic environment along the flanks of GMS. During the Quaternary (?Pleistocene) bioclastic sands were deposited in water depths beyond wave base on the summit tops, repeatedly reworked, and lithified into loosely consolidated biopelsparites and biomicrites (MF 1 and 2; Fig. 15). Intermediate steps were a first intragranular filling by micrite, reworking, oncoidal coating, weak consolidation with Mg-calcite cemented "peloids" in intergranular voids and local compaction of the peloids into cryptocrystalline micrite with interlocking Mg-calcite crystals up to 4p. The submarine lithification process was frequently interrupted by long intervals of nondeposition, dissolution, boring, and later infilling. The limestones were probably never subaerially exposed. Presently, the carbonate rocks undergo biogenic incrustation and partial dissolution into bioclastic sands. The irregular distribution pattern of the sands reflects (a) the patchy distribution of living benthonic organisms, (b) the steady rain of planktonic organism onto the seamount top, (c) the composition of disintegrating subrecent limestones, and (d) the intensity of winnowing and reworking bottom current

Composition of suspended matter and bottom sediments from the Atlantic Ocean and its seas

The book summarizes data on distribution and composition of sedimentary material suspended in waters of the Atlantic Ocean and its seas. Results of observations of Soviet and foreign expeditions are given. Distribution of suspended matter in sections across the ocean, as well as in the most studied seas are shown. New data on grain size, mineral and chemical composition of suspended matter are published. Summary of history of investigation of bottom sediments from the Atlantic Ocean from the first scientific cruises to the present is done. A brief description of sediment types in the ocean and a detailed description of Mediterranean Sea sediments are given.

(Table 1) Mineralogical composition of sediments from DSDP Sites 69-504 and 69-505

We discuss the provenance of minerals detected by X-ray-diffraction analyses of sediments of Sites 504 and 505 of Deep Sea Drilling Project Leg 69. These are X-ray-amorphous material, opal-CT, calcite, quartz, feldspar, apatite, smectite, illite, kaolinite, magnetite, maghemite, pyrite, marcasite, barite, sepiolite, and clinoptilolite. Authigenic marcasite and clinoptilolite together with opal-CT are restricted to Site 504, indicating the special diagenetic conditions related to relatively high sediment temperatures at this site. Marcasite formation is likely dependent on the relatively low pH values of <7.1 found in interstitial waters of Site 504 sediments below 50 meters sub-bottom. Clinoptilolite evidently was formed by diagenetic alteration of rhyolitic volcanic glass or smectite plus biogenic silica within the chalk-limestone-chert sequence of Site 504, where opal-CT also reflects a high degree of silica dissolution and reprecipitation. This was a consequence of high temperatures (50-55 °C) at the base of the sediment column.

Composition of Messinian sediments from the Tyrrhenian Sea

The data base for this study is represented by essentially nonevaporitic Messinian sediments recovered at ODP Sites 654, 653, 652, and 656 along the eastern Sardinian margin, and of the overlying early Pliocene oozes. Grain-size distribution, carbonate content, and microscopic observation of the sand size fractions were investigated. Messinian paleoenvironments, documented in the western Tyrrhenian Sea (ODP Sites 654 and 653), provide additional evidence supporting the deep basin desiccation model. A sharp lithologic contrast between early Pliocene pelagic oozes and latest Messinian conformable gypsiferous silts supports this model. The "lago-mare" biofacies was only occasionally observed in the shallowest site and is limited to the topmost part of the Messinian. Sites 652 and 656, lying in the deeper part of the Tyrrhenian and located on the downthrown side of an important eastward dipping fault system known as "Faglia centrale" are characterized by terrigenous sedimentation, with partly recycled minor evaporites. Of special interest is Site 652, where the thickness of the (probable) Messinian is 530 m. Sedimentary characters indicate a permanently subaqueous but nonmarine environment, with turbidites accumulating in a rapidly subsiding basin. According to the model proposed, this basin was fed by continental waters during times of maximum evaporitic draw-down, with temporary marine incursions from the west or southwest when the water level was higher. A basement ridge separated the evaporating pond from this endoreic lake located on the opposite (eastern) margin of the Tyrrhenian Basin, which was then limited to its western part. Post-Messinian reactivation of the "Faglia centrale" is necessary to account for the inversion of the relief.

Composition and age of ores and bottom sediments accumulated within and near the Rainbow hydrothermal field

Results of direct geological and geochemical observations of the modern Rainbow hydrothermal field (Mid-Atlantic Ridge, 36°14'N; 33°54'W) carried out from the deep-sea manned Mir submersibles during Cruises 41 and 42 of the R/V Akademik Mstislav Keldysh in 1998-1999 and data of laboratory studies of collected samples are under consideration in the paper. The field lacks neovolcanic rocks and the axial part of the rift is filled in with a serpentinite protrusion. In this field there occur metalliferous sediments, as well as active and relict sulfide edifices composed of sulfide minerals; pyrrhotite, chalcopyrite, isocubanite, sphalerite, marcasite, pyrite, bornite, chalcosine, digenite, magnetite, anhydrite, rare troilite, wurtzite, millerite, and pentlandite have been determined. Sulfide ores are characterized by concentric-zoned textures. During in situ measurements during 35 minutes temperature of hydrothermal fluids was varying within a range from 250 to 350°C. Calculated chemical and isotopic composition of hydrothermal fluid shows elevated concentrations of Cl, Ni, Co, CH4, and H2. Values of d34S of H2S range from +2.4 to +3.1 per mil, of d13C of CH4 from -15.2 to -11.2 per mil, and d13C of CO2 from +1.0 to -4.0 per mil. Fluid inclusions are homogenized at temperatures from 140 to 360°C, whereas salinity of the fluid varies from 4.2 to 8.5 wt %. d34S values of sulfides range from +1.3 to +12.5 per mil. 3He/4He ratio in mineral-forming fluid contained in the fluid inclusions from sulfides of the Rainbow field varies from 0.00000374 to 0.0000101. It is shown that hydrothermal activity in the area continues approximately during 100 ka. It is assumed that the fluid and sulfide edifices contain components from the upper mantle. A hypothesis of phase separation of a supercritical fluid that results in formation of brines is proposed. Hydrothermal activity is related to the tectonic, not volcanic, phase of the Mid-Atlantic Ridge evolution.

Petrographic description and mineral composition of ODP Site 161-975 sediments

Ocean Drilling Program Site 975 is located near the base of the Menorca Rise in the South Balearic Basin of the western Mediterranean Sea. Coring at this site penetrated the Pliocene/Miocene boundary and recovered a sequence of sediments that represent the final stages of salt deposition and the transition from evaporitic to open marine conditions at the end of the Miocene (Messinian). Detailed petrographic observations and bulk mineralogical analyses by X-ray diffraction form the basis for preliminary interpretations of depositional environments for this section. Gypsum is thought to have been deposited in an evaporating basin below wave base. Cycles consisting of a clay layer overlain by gypsiferous chalk, laminated gypsum, and finally pinch-and-swell gypsum suggest upsection increases in salinity. The gypsum section is overlain by two exotic sand layers thought to mark events of fresher water (marine or meteoric) inflow to the basin. Gypsum deposition terminated and was replaced by inorganic precipitation of micritic calcite with periodic, variable dilution by fine-grained terrigenous sediment. The micritic sediments have fine, slightly wavy, laminations indicating either an algal/microbial mat origin, or varve-like fluctuations in deposition, perhaps in a deep basin. The Pliocene/Miocene boundary falls within an interval of banded micritic silty clays that reflect the final environmental fluctuations during the transition to the open marine conditions of the Pliocene.

Suspended matter in waters of the Kem' River estuary (white Sea) and its composition in July-August 2003 and 2002

On the base of detailed studies in the Keret' and Kem' estuaries (Karelian coast of the White Sea) in 2000-2003 a comparative analysis has been carried out. It includes: salinity and freshening of the water column, variations of suspended matter concentration and its chemical composition, current velocity and zooplankton species composition during flood- and ebb tides.

Mineral composition of 0.1-0.05 mm grain size fraction from the surface layer of bottom sediments in the West European province of the Atlantic Ocean

Rock material sampled from the Mir manned deep-sea submersibles and by dradges, grabs, and sediment cores over a vast area of the North Atlantic was analyzed to show that this material is of continental origin, unlike original rocks of the ocean floor. It is proved to be related to iceberg rafting during Quaternary glaciations. Independent data on distribution and composition of sandy and silty grains in sediment cores also support this relation to the recent glaciation. New criteria for identification of iceberg rock matter in pelagic sediments are presented on the base of analysis of all available data.

Chemical and isotopic composition of seawater and waters from thermal spring sites of the Yankicha Island and Kraternaya Bay

A study of chemical and isotopic composition of coastal thermal springs and waters of the Kraternaya Bay, Yankicha Island, revealed that the total mineralization and concentrations of d18O and d2H decrease from the thermal spring site I to V. These waters are of marine origin with various proportions of local meteoric water. Thermal waters of the site VI have considerably altered chemical and isotopic composition due to high temperatures of surrounding rocks. Base temperatures calculated for this area were 130-200°C. Coastal thermal springs affect isotopic composition of water throughout the bay.