Geochemistry, clay mineralogy and grain size distribution in various sediment cores drilled during ODP Leg 119 on the Antarctic continental shelf off Prydz Bay

Drilling was undertaken at five sites (739-743) on ODP Leg 119 on a transect across the continental shelf of Prydz Bay, East Antarctica, to elucidate the long-term glacial history of the area and to examine the importance of the area with respect to the development of the East Antarctic ice sheet as a whole. In addition to providing a record of glaciation spanning 36 m.y. or more, Leg 119 has provided information concerning the development of a continental margin under the prolonged influence of a major ice sheet. This has allowed the development of a sedimentary model that may be applicable not only to other parts of the Antarctic continental margin, but also to northern high-latitude continental shelves. The cored glacial sedimentary record in Prydz Bay consists of three major sequences, dominated by diamictite: 1. An upper flat-lying sequence that ranges in thickness from a few meters in inner and western Prydz Bay to nearly 250 m in the outer or eastern parts of the bay. The uppermost few meters consist of Holocene diatom ooze and diatomaceous mud with a minor ice-rafted component overlying diamicton and diamictite of late Miocene to Quaternary age. The diamictite is mainly massive, but stratified varieties and minor mudstone and diatomite also occur. 2. An upper prograding sequence cored at Sites 739 and 743, unconformly below the flat-lying sequence. This consists of a relatively steep (4° inclination) prograding wedge with a number of discrete sedimentary packages. At Sites 739 and 743 the sequence is dominated by massive and stratified diamictite, some of which shows evidence of slumping and minor debris flowage. 3. A lower, more gently inclined, prograding sequence lies unconformably below the flat-lying sequence at Site 742 and the upper prograding sequence at Site 739. This extends to the base of both sites, to 316 and 487 mbsf, respectively. It is dominated by massive, relatively clast-poor diamictite which is kaolinite-rich, light in color, and contains sporadic carbonate-cemented layers. The lower part of Site 742 includes well-stratified diamictites and very poorly sorted mudstones. The base of this site has indications of large-scale soft-sediment deformation and probably represents proximity to the base of the glacial sequence. Facies analysis of the Prydz Bay glacial sequence indicates a range of depositional environments. Massive diamictite is interpreted largely as waterlain till, deposited close to the grounding line of a floating glacier margin, although basal till and debris flow facies are also present. Weakly stratified diamictite is interpreted as having formed close to or under the floating ice margin and influenced by the input of marine diatomaceous sediment (proximal glaciomarine setting). Well-stratified diamictite has a stronger marine input, being more diatom-rich, and probably represents a proximal-distal glaciomarine sediment with the glaciogenic component being supplied by icebergs. Other facies include a variety of mudstones and diatom-rich sediments of marine origin, in which an ice-rafted component is still significant. None of the recovered sediments are devoid of a glacial influence. The overall depositional setting of the prograding sequence is one in which the grounded ice margin is situated close to the shelf edge. Progradation was achieved primarily by deposition of waterlain till. The flat-lying sequence illustrates a complex sequence of advances and retreats across the outer part of the shelf, with intermittent phases of ice loading and erosion. The glacial chronology is based largely on diatom stratigraphy, which has limited resolution. It appears that ice reached the paleoshelf break by earliest Oligocene, suggesting full-scale development of the East Antarctic ice sheet by that time. The ice sheet probably dominated the continental margin for much of Oligocene to middle Miocene time. Retreat, but not total withdrawal of the ice sheet, took place in late Miocene to mid-Pliocene time. The late Pliocene to Pleistocene was characterized by further advances across, and progradation of, the continental shelf. Holocene time has been characterized by reduced glacial conditions and a limited influence of glacial processes on sedimentation.

Table 1 Microorganisms, identified with DOGE analysis. 16S rDNA sequences, obtained from sequencing of DOGE bands, were assigned to the corresponding microorganisms

Microorganisms play an important role in the transformation of material within the earth's crust. The storage of CO2 could affect the composition of inorganic and organic components in the reservoir, consequently influencing microbial activities. To study the microbial induced processes together with geochemical, petrophysical and mineralogical changes, occurring during CO2 storage, long-term laboratory experiments under simulated reservoir P-T conditions were carried out. Clean inner core sections, obtained from the reservoir region at the CO2 storage site in Ketzin (Germany) from a depth of about 650 m, were incubated in high pressure vessels together with sterile synthetic formation brine under in situ P-T conditions of 5.5 MPa and 40°C. A 16S rDNA based fingerprinting method was used to identify the dominant species in DNA extracts of pristine sandstone samples. Members of the alpha- and beta-subdivisions of Proteobacteria and the Actinobacteria were identified. So far sequences belonging to facultative anaerobic, chemoheterotrophic bacteria (Burkholderia fungorum, Agrobacterium tumefaciens) gaining their energy from the oxidation of organic molecules and a genus also capable of chemolithoautotrophic growth (Hydrogenophaga) was identified. During CO2 incubation minor changes in the microbial community composition were observed. The majority of microbes were able to adapt to the changed conditions. During CO2 exposure increased concentrations of Ca**2+, K**+, Mg**2+ and SO4**2- were observed. Partially, concentration rises are (i) due to equilibration between rock pore water and synthetic brine, and (ii) between rock and brine, and are thus independent on CO2 exposure. However, observed concentrations of Ca**2+, K**+, Mg**2+ are even higher than in the original reservoir fluid and therefore indicate mineral dissolution due to CO2 exposure.

Zirkon fission track ages of for middle Pleistocene Rangitawa Tephra, New Zealand

Rangitawa Tephra is an important stratigraphic marker in mid-Pleistocene marine and terrestrial sequences in New Zealand and adjacent ocean basins. Zircon fission track ages (ZFTA) on Rangitawa Tephra from five sites in the southern North Island yield mean site ages in the range 0.34 to 0.40 Ma with a weighted mean of 0.35 + 0.04 Ma (1 sigma). On the basis of glass shard major-element chemistry, ferromagnesian mineralogy, ZFTA and similarity of paleomagnetic dates of proposed tephra correlalives in deep-sea cores, it is concluded that Rangitawa Tephra represents a major eruptive event in the Taupo Volcanic Zone most probably associated with eruption of the Whakamaru-group ignimbrites (0.35 0.39 Ma) or less likely the Paeroa Range Group Ignimbrites (0.36 -0.38 Ma). Pollen analyses from two onshore sites, together with regional loess stratigraphy, show that Rangitawa Tephra was erupted during a glacial period. The ZFTA and previously reported oxygen isotope data from DSDP Site 594 indicate that Rangitawa Tephra was erupted near the end of oxygen isotope stage 10.

Stable carbon isotope record of Bahama Bank sediments

The carbon-isotopic composition (d13C) of bulk carbonates, obtained from a transect of sites drilled through platform and periplatform sediments of Holocene to Early Miocene age, has been compared to ascertain whether changes in the d13C can be correlated between sediments of equivalent ages and whether such changes can be related to global changes in the d13C of the dissolved inorganic carbon in the oceans over this time period. Five of the sites were drilled during Leg 166 of the Ocean Drilling Project (1003-1007) in a transect ranging from five km to 25 km away from the platform margin and penetrating sediments of Holocene to Oligocene age that are contained in 17 depositional sequences (A-Q). Two shallow-water sites, Clino and Unda were situated on a extension of the same transect on Great Bahama Bank in a water depth of 10-15 m. With the exception of Unda and Clino, the d13C of the carbonates ranges from +5 per mil in the younger sequences to +1 per mil in the Early Miocene. In each of the sites, the d13C is strongly positively correlated with the percentage of aragonite. As a consequence, the d13C of sequences A through F is strongly correlated, reflecting the decreasing amount of aragonite with increasing depth. In the two platform sites, the d13C is significantly lower in the younger portions of the cores as a result of the influences of meteoric diagenesis during repeated exposure during the Pleistocene. Although the d13C of the individual sequences can be correlated in most instances between the ODP holes, the changes are not related to global changes in the d13C of the oceans which in contrast to the d13C of the platform sediments become isotopically lower towards the present day. Instead variations in the d13C appear to be related to varying mixtures of d13C-rich banktop sediments and pelagic material.

Planktonic foraminiferal stratigraphy of sediments from ODP Leg 173 sites

Planktonic foraminifers recovered from five sites drilled off western Portugal during Ocean Drilling Program Leg 173 are documented. Hole 1065A yielded planktonic foraminifers from Miocene sediments in Sections 173-1065A-1R-1 through 6R-2. Hole 1067A penetrated middle Eocene sediments containing planktonic foraminifers in Section 173-1067A-1R-1 through Lower Eocene planktonic foraminiferal horizons to Section 12R-CC. Hole 1068A yielded planktonic foraminiferal assemblages from middle Eocene sediments at Section 173-1068A-1R-1 to Maastrichtian sediments at Section 173-1068A-15R-3, whereas Hole 1069A contained middle Eocene taxa in Section 173-1069A-1R-1 through Campanian/Maastrichtian forms in Section 173-1069A-15R-2. All of the planktonic foraminifers recovered from these sites are of poor to moderately good preservation and are variable in abundance. Hole 1070A yielded only six planktonic foraminifers, with the assemblages being dominated by benthic foraminifers and fish teeth. The co-occurrence of other microfossil groups, including benthic foraminifers, are only briefly discussed here. The lower Miocene biosiliceous facies recorded in Hole 1065A is considered to be coeval with a similar facies found in onshore sections farther to the east, in southern Spain.

Mineralogy and chemical composition of ODP Sites 129-800 and 129-801

Sites 800 and 801 in the Pigafetta Basin allow the sedimentary history over the oldest remaining Pacific oceanic crust to be established. Six major deposition stages and events are defined by the main lithologic units from both sites. Mineralogical and chemical investigations were run on a large set of samples from these units. The data enable the evolution of the sediments and their depositional environments to be characterized in relation to the paleolatitudinal motion of the sites. The upper part of the basaltic crust at Site 801 displays a complex hydrothermal and alteration evolution expressed particularly by an ochre siliceous deposit comparable to that found in the Cyprus ophiolite. The oldest sedimentary cover at Site 801 was formed during the Callovian-Bathonian (stage 1) with red basal siliceous and metalliferous sediments similar to those found in supraophiolite sequences, and formed near an active ridge axis in an open ocean. Biosiliceous sedimentation prevailed throughout the Oxfordian to Campanian, with rare incursions of calcareous input during the middle Cretaceous (stages 2, 4, and 5). The biosiliceous sedimentation was drastically interrupted during the Aptian-Albian by thick volcaniclastic turbidite deposits (stage 3). The volcanogenic phases are pervasively altered and the successive secondary mineral parageneses (with smectites, celadonite, clinoptilolite, phillipsite, analcime, calcite, and quartz) define a "mineral stratigraphy" within these deposits. From this mineral stratigraphy, a similar lithologic layer is defined at the top of the Site 800 turbidite unit and the bottom of the Site 801 turbidite unit. Then, the two sites appear to have been located at the same distal distance from a volcanic source (hotspot). They crossed this locality, at about 10°S, at different times (latest Aptian for Site 800, middle Albian for Site 801). The Cretaceous siliceous sedimentation stopped during the late Campanian and was followed by deposition of Cenozoic pelagic red clay (stage 6). This deep-sea facies, which formed below the carbonate compensation depth, contains variable zeolite authigenesis in relation to the age of deposition, and records the global middle Cenozoic hiatus events. At the surface, the red clay from this part of the Pacific shows a greater detrital component than its equivalents from the central Pacific deep basins.

Mineralogy and geochemistry of ODP Hole 176-735B minerals

We present a synthesis of some 20,504 mineral analyses of ~500 Hole 735B gabbros, including 10,236 new analyses conducted for this paper. These are used to construct a mineral stratigraphy for 1.5-km-deep Hole 735B, the only long section of the lower crust drilled in situ in the oceans. At long wavelengths, generally >200 m, there is a good chemical correlation among the principal silicate phases, consistent with the in situ crystallization of three or four distinct olivine gabbro bodies, representing at least two major cycles of intrusion. Initial cooling and crystallization of these bodies must have been fairly rapid to form a crystal mush, followed by subsequent compaction and migration of late iron-titanium-rich liquids into shear zones and fractures through which they were emplaced to higher levels in the lower crust where they crystallized and reacted with the olivine gabbro host rock to form a wide variety of ferrogabbros. At the wave lengths of the individual intrusions, as represented by the several olivine gabbro sequences, there is a general upward trend of iron and sodium enrichment but a poor correlation between the compositions of the major silicate phases. This, together with a wide range in minor incompatible and compatible element concentrations in olivine and pyroxene at a given Mg#, is consistent with widespread permeable flow of late melt through these intrusions, in contrast to what has been documented for a 600-m section of reputedly fast-spreading ocean crust in the Oman Ophiolite. This unexpected finding could be related to enhanced compaction and deformation-controlled late-stage melt migration at the scale of intrusion at a slow-spreading ocean ridge, compared to the relatively static environment in the lower crust at fast-spreading ridges.

Stable oxygen and carbon isotope composition of Miocene planktonic foraminifers from the tropical Indian Ocean

Oxygen and carbon isotope records are presented for the planktonic foraminifers Dentoglobigerina altispira and Globigerinoides sacculifer (shallow-dwelling species) and Globoquadrina venezuelana (deep-dwelling species) from Miocene sediments at two Ocean Drilling Program sites, located at depths of near 3000 m, in the western (Site 709) and eastern (Site 758) tropical Indian Ocean. The planktonic isotope record at Site 709 is compared with the benthic isotope record obtained at this site by Woodruff et al. (1990, doi:10.2973/odp.proc.sr.115.147.1990). The isotope stratigraphy is related to the biostratigraphy and the available magnetostratigraphy at the sites. Despite varying sampling density, incompleteness of isotopic records, and the condensed (or even disturbed) nature of parts of the sequences, a number of chronostratigraphic isotopic signals previously recognized in the equatorial Pacific and at other tropical Indian Ocean sites are identified.

Stratigraphy of the Campanian-Maastrichtian boundary in ODP Hole 122-762C

An integrated framework of magnetostratigraphy, calcareous microfossil bio-events, cyclostratigraphy and d13C stratigraphy is established for the upper Campanian-Maastrichtian of ODP Hole 762C (Exmouth Plateau, Northwestern Australian margin). Bulk-carbonate d13C events and nannofossil bio-events have been recorded and plotted against magnetostratigraphy, and provided absolute ages using the results of the cyclostratigraphic study and the recent astronomical calibration of the Maastrichtian. Thirteen carbon-isotope events and 40 nannofossil bio-events are recognized and calibrated with cyclostratigraphy, as well as 14 previously published foraminifer events, thus constituting a solid basis for large-scale correlations. Results show that this site is characterized by a nearly continuous sedimentation from the upper Campanian to the K-Pg boundary, except for a 500 kyr gap in magnetochron C31n. Correlation of the age-calibrated d13C profile of ODP Hole 762C to the d13C profile of the Tercis les Bains section, Global Stratotype Section and Point of the Campanian-Maastrichtian boundary (CMB), allowed a precise recognition and dating of this stage boundary at 72.15 ± 0.05 Ma. This accounts for a total duration of 6.15 ± 0.05 Ma for the Maastrichtian stage. Correlation of the boundary level with northwest Germany shows that the CMB as defined at the GSSP is ~800 kyr younger than the CMB as defined by Belemnite zonation in the Boreal realm. ODP Hole 762C is the first section to bear at the same time an excellent recovery of sediments throughout the upper Campanian-Maastrichtian, a precise and well-defined magnetostratigraphy, a high-resolution record of carbon isotope events and calcareous plankton biostratigraphy, and a cyclostratigraphic study tied to the La2010a astronomical solution. This section is thus proposed as an excellent reference for the upper Campanian-Maastrichtian in the Indian Ocean.

Calcareous nannofossil stratigraphy, nannofossil events and carbon isotopic ratios of ODP Leg 183 sites

Cores from Sites 1135, 1136, and 1138 of Ocean Drilling Program Leg 183 to the Kerguelen Plateau (KP) provide the most complete Paleocene and Eocene sections yet recovered from the southern Indian Ocean. These nannofossil-foraminifer oozes and chalks provide an opportunity to study southern high-latitude biostratigraphic and paleoceanographic events, which is the primary subject of this paper. In addition, a stable isotope profile was established across the Cretaceous/Tertiary (K/T) boundary at Site 1138. An apparently complete K/T boundary was recovered at Site 1138 in terms of assemblage succession, isotopic signature, and reworking of older (Cretaceous) nannofossil taxa. There is a significant color change, a negative carbon isotope shift, and nannofossil turnover. The placement of the boundary based on these criteria, however, is not in agreement with the available shipboard paleomagnetic stratigraphy. We await shore-based paleomagnetic study to confirm or deny those preliminary results. The Paleocene nannofossil assemblage is, in general, characteristic of the high latitudes with abundant Chiasmolithus, Prinsius, and Toweius. Placed in context with other Southern Ocean sites, the biogeography of Hornibrookina indicates the presence of some type of water mass boundary over the KP during the earliest Paleocene. This boundary disappeared by the late Paleocene, however, when there was an influx of warm-water discoasters, sphenoliths, and fasciculiths. This not only indicates that during much of the late Paleocene water temperatures were relatively equable, but preliminary floral and stable isotope analyses also indicate that a relatively complete record of the late Paleocene Thermal Maximum event was recovered at Site 1135. It was only at the beginning of the middle Eocene that water temperatures began to decline and the nannofossil assemblage became dominated by cool-water species while discoaster and sphenolith abundances and diversity were dramatically reduced. One new taxonomic combination is proposed, Heliolithus robustus Arney, Ladner, and Wise.

Correlation of Bolboforma zonation and nannoplankton stratigraphy in the Neogene of the North Atlantic

The Neogene Bolboforma zones established in the North Atlantic have been correlated with the calcareous nannoplankton stratigraphy obtained by investigation of the same samples from DSDP Sites 12-116 (44 samples), 49-408 (76 samples), 81-555 (43 samples) and 94-608 (103 samples). The absolute ages for the zonal boundaries were determined by the paleomagnetic record of Site 94-608. This correlation and the age determinations are additional useful tools to develop a precise biostratigraphy of Neogene sediments in the Northern Atlantic.

Composition of carbonaceous sediments from the Late Jurassic Volgian Basin of the East European Platform (Kostroma Region, Russia)

Lithological, geochemical, stratigraphic, and paleoecological features of carbonaceous sediments in the Late Jurassic Volgian Basin of the East European Platform (Kostroma Region) are considered. The shale-bearing sequence studied is characterized by greater sedimentological completeness as compared with its stratotype sections in the Middle Volga region (Gorodishche, Kashpir). Stratigraphic position and stratigraphy of the shale-bearing sequence, as well as distribution of biota in different sedimentation settings are specified. It is shown that Volgian sediments show distinct cyclic structure. The lower and upper elements of cyclites consist of high-carbonaceous shales and clayey-calcareous sediments, respectively, separated by transitional varieties. Bioturbation structures in different rocks are discussed. Microcomponent composition and pyrolytic parameters of organic matter, as well as distribution of chemical elements in lithologically variable sediments are analyzed. Possible reasons responsible for appearance of cyclicity and accumulation of organic-rich sediments are discussed.

Calcareous nannofossil stratigraphy and datums of sediments from ODP Leg 198 sites

During Ocean Drilling Program Leg 198, Sites 1207, 1208, 1212, 1213, and 1214 were drilled on Shatsky Rise, coring Lower to mid-Cretaceous successions of nannofossil chalk, porcellanite, and chert. Although recovery was poor, these sites yielded an outstanding record of calcareous nannoplankton, providing valuable data concerning the evolutionary succession and paleobiogeography of the largest Cretaceous marine habitat. Mid-Cretaceous sections (Aptian-Cenomanian) were recovered at all sites, and Site 1213 includes an apparently complete Berriasian-Hauterivian section. Biostratigraphic dating is problematic in places because of the absence or rarity of zonal fossils of both Boreal and Tethyan affinity. The majority of nannofossil assemblages are relatively typical of this age, but there are clear differences that set them apart from coeval epicontinental assemblages: for example, Lithraphidites carniolensis is common to abundant throughout and was most likely an oceanic-adapted taxon; the cold- to temperate-water species Crucibiscutum salebrosum, Repagulum parvidentatum, and Seribiscutum primitivum are entirely absent, indicating the persistence of tropical, warm surface water temperatures; and the warm-water species Hayesites irregularis is common. Most striking, however, is the virtual absence of Nannoconus and Micrantholithus, both taxa that were conspicuous and often common components of many Tethyan and Atlantic nannofloras. These forms were almost certainly neritic adapted and usually absent in deep open-ocean settings away from guyots and platforms. Other Tethyan taxa are also absent or rare and sporadically distributed (e.g., Calcicalathina oblongata, Conusphaera spp., Tubodiscus verenae, and Lithraphidites bollii), and factors related to neritic environments presumably controlled their distribution. Site 1213 also records extended Early Cretaceous ranges for species previously thought to have become extinct during the Late Jurassic (e.g., Axopodorhabdus cylindratus, Hexapodorhabdus cuvillieri, and Biscutum dorsetensis), suggesting these species became Pacific-restricted prior to their extinction. Watznaueria britannica may also have been a species with Pacific affinities before reexpansion of its biogeography in the early Aptian. One new genus (Mattiolia) and thirteen new species (Zeugrhabdotus clarus, Zeugrhabdotus petrizzoae, Helicolithus leckiei, Rhagodiscus amplus, Rhagodiscus robustus, Rhagodiscus sageri, Rhagodiscus adinfinitus, Tubodiscus bellii, Tubodiscus frankiae, Gartnerago ponticula, Haqius peltatus, Mattiolia furva, and Kokia stellata) are described from the Shatsky Rise Lower Cretaceous section.

Benthic foraminifera stratigraphy of sediments from ODP Leg 199 sites

Benthic foraminifers from Ocean Drilling Program Leg 199 Holes 1215A, 1220B, and 1221C were examined across the Paleocene/Eocene boundary. Assemblages were studied in 240 samples. The benthic foraminiferal extinction event that correlates with the Paleocene/Eocene epoch boundary was recognized at these sites. Benthic assemblages before the event are characterized by high diversity, but those after the event are low in diversity. An assemblage of agglutinated foraminifers without carbonate cement was recognized at Sites 1220 and 1221. These assemblages were typically found after the event. The discovery of such agglutinated assemblages has never been reported before at this boundary.