1,070 Works

40Ar/39Ar analysis for incremental heating experiments at DSDP Holes 77-537 and 77-538A

R D Dallmeyer
Drilling penetrated pre-Mesozoic crystalline basement beneath abbreviated sedimentary sequences overlying fault blocks in the southeastern Gulf of Mexico. At Hole 538A, located on Catoche Knoll, a foliated, regional metamorphic association of variably mylonitic felsic gneisses and interlayered amphibolite is intruded by post-tectonic diabase dikes. Hornblende from the amphibolite displays internally discordant 40Ar/39Ar age spectra, suggesting initial post-metamorphic cooling at about 500 Ma followed by a mild thermal disturbance at about 200 Ma. Biotite from the...

Maceral distribution, stratigraphic position and vitrinite reflectance at DSDP Hole 81-555

Jane Lund & Walter Riegel
Twenty-four sediment samples from late Paleocene to early Eocene were studied for maceral content, vitrinite reflectance, and spectral fluorescence in order to determine some parameters of the origin and diagenetic history of their organic fraction. The sediments had been obtained at Site 555 of DSDP Leg 81 in the northeastern North Atlantic. The bulk of the microscopically visible fraction is made up of humic materials; inertinites follow as a distant second; and liptinites are exceedingly...

Geochemistry and ages at DSDP Holes 81-552A, 81-553A and 81-555

Andrew C Morton, Richard J Merriman & John G Mitchell
Glauconite-rich sediments have been encountered at two horizons during drilling in the southwest Rockall Plateau. The younger of these horizons lies at the base of a deep-sea ooze sequence and is of early or middle Miocene age. Glauconite formed in situ during periods of nondeposition related to strong bottom-water currents, in water depths of as much as 2500 m - five times greater than previously accepted limits for glauconite formation. The older horizon, of early...

Radiolarian stratigraphy of ODP Leg 138 sites

Theodore C Moore
A group of 46 radiolarian species was used in this study of Leg 138 sites. The recovery of the sections was complete in the intervals that were cored using the APC system and nearly complete in the deeper sections. The northeastern sites (844 and 845) were sampled down through the middle Miocene into the uppermost part of the lower Miocene (middle part of the Calocycletta costata Zone). In the southeastern sites and those of the...

Noble gases sampled from three cruises in the eastern tropical Atlantic

Reiner Steinfeldt, Sebastian Rütten, Jürgen Sültenfuß, Marcus Dengler, Tim Fischer & Monika Rhein
Oceanic upwelling velocities are too small to be measured directly. Deviations of the He-3/He-4 ratio in the mixed layer from solubility equilibrium provide an indirect means to infer vertical velocities at the base of the mixed layer. This method is applied to the Mauritanian upwelling region for data from three cruises in summer 2006 and winter 2007 and 2008. Diapycnal mixing coefficients are estimated from microstructure measurements, reaching from 10**-3 m**2/s over the shelf break...

Magnetic mineralogy and geochemistry of ODP Holes 137-504B and 140-504B samples

Laura B Stokking, Elizabeth A Heise, Janet E Pariso & Simon A Allerton
Leg 140 of the Ocean Drilling Program deepened Hole 504B to a total depth of 2000.4 m below seafloor (mbsf), making it the deepest hole drilled into ocean crust. Site 504, south of the Costa Rica Rift, is considered the most important in-situ reference section for the structure of shallow ocean crust. We present the results of studies of magnetic mineralogy and magnetic properties of Hole 504B upper crustal rocks recovered during Legs 137 and...

Glacier mass balances and elevation zones of Hallstätter Gletscher, Dachstein, Austria, 2006/2007 et seq

Andrea Fischer, Martin Stocker-Waldhuber, Lea Hartl, Klaus Reingruber & Kay Helfricht
The annual glacier mass balance of Hallstätter Gletscher in Austria is measured since 2006-10-01 with the direct glaciological method in the fixed date system (1st October to 30th September of the following year). The accumulation of snow is measured by determination of the water equivalent in 6 snow pits, the ice ablation is measured with 15 stakes drilled into the ice. Results are the annual net mass balance in kg, the total accumulation and ablation,...

Interstitial water chemistry at DSDP Leg 82 Holes

Joris M Gieskes, Kirk Johnston & Marcus Boehm
Interstitial waters were collected at only two sites during Leg 82, Sites 558 and 563. Only very small changes in dissolved calcium and magnesium occur, presumably resulting from reactions in the underlying basement basalts. Dissolved strontium profiles indicate maxima, which can be understood in terms of carbonate recrystallization processes. Data on Sr/Ca in carbonates cannot be used to estimate the extent of recrystallization that has occurred in these sediments.

Chemistry and fluid inclusions of the sheeted dike comples of ODP Holes 137-504B and 140-504B

Deborah S Kelley, David A Vanko & Chifeng Gu
Fluid inclusions in variably altered diabase recovered from Ocean Drilling Program Legs 137 and 140 at Hole 504B, Costa Rica Rift, exhibit fluid salinities up to 3.7 times that of seawater values (11.7 wt% NaCl equivalent) and exhibit uncorrected homogenization temperatures of 125°C to 202°C. The liquid-dominated inclusions commonly are entrapped in zones of secondary plagioclase and may be primary in origin. Fluid salinities are similar to compositions of fluids venting on the seafloor (0.4-7.0...

Platinum group elements and geochemistry of altered oceanic crust of ODP Hole 140-504B

Michael P Gorton, Eva S Schandl & AJ Naldrett
Primary chemical heterogeneity in the sheeted dike complex in Deep Sea Drilling Project Hole 504B makes these rocks unsuitable for conventional mass balance calculations in determining element mobility associated with hydrothermal alteration. Due to the original heterogeneity and variable degrees of fractionation in the dikes, an appropriate reference sample on which calculations can be based is difficult to find. Therefore, the use of incompatible element ratios is developed to evaluate geochemical changes during alteration(s). For...

Petrography and geochemistry of organic matter at DSDP Holes 80-549 and 80-550B

Birgitta Hartung, Prasanta K Mukhopadhyay, Jürgen Rullkötter, Rainer G Schaefer & Dietrich Hugo Welte
Three lower Barremian to middle/upper Cenomanian samples from DSDP Hole 549 and three lower Cenomanian to lower Maestrichtian samples from DSDP Hole 550B were investigated by organic geochemical and organic petrographic methods. The samples came from wells drilled in the area of the Goban Spur in the northeastern Atlantic; they represent gray to greenish gray carbonaceous mud or siltstones from the deeper parts of the Cretaceous sequences penetrated and light-colored chalks from the shallower ones.The...

Monthly air temperatures, snow density and snow and ice thickness at Malcolm Ramsay Lake, North America

Laura C Brown & Claude R Duguay
In northern regions where observational data is sparse, lake ice models are ideal tools as they can provide valuable information on ice cover regimes. The Canadian Lake Ice Model was used to simulate ice cover for a lake near Churchill, Manitoba, Canada throughout the 2008/2009 and 2009/2010 ice covered seasons. To validate and improve the model results, in situ measurements of the ice cover through both seasons were obtained using an upward-looking sonar device Shallow...

Short-term variations in radiolarian faunal dsitribution in the eastern equatorial Pacific

Nicklas G Pisias & Theodore C Moore
Two short time intervals centered at 2.3 and 4.7 Ma were studied to investigate short-term variations in surface-ocean processes as indicated by changes in the radiolarian microfossil population. These time intervals represent two different settings of late Neogene climate. The older interval represents a time when tropical circulation between the Pacific and Atlantic oceans was not blocked by the Isthmus of Panama, whereas the younger interval represents a time when Northern Hemisphere glaciation was present...

Phenotypic evolution in a venerid bivalve species lineage from the late Middle Miocene Central Paratethys Sea: a multi-approach morphometric analysis

Thomas A Neubauer, Mathias Harzhauser & Oleg Mandic
A morphometric analysis was performed for the late Middle Miocene bivalve species lineage of Polititapes tricuspis (Eichwald, 1829) (Veneridae: Tapetini). Specimens from various localities grouped into two stratigraphically successive biozones, i.e. the upper Ervilia Zone and the Sarmatimactra Zone, were investigated using a multi-method approach. A Generalized Procrustes Analysis was computed for fifteen landmarks, covering characteristics of the hinge, muscle scars, and pallial line. The shell outline was separately quantified by applying the Fast Fourier...

Organic geochemistry and Rock-Eval pyrolysis at DSDP Leg 79 and 41 Holes

Gerard Deroo, Jean-Paul Herbin & J Roucaché
Cenozoic and Mesozoic sediments ranging in age from Pleistocene to Early Jurassic/late Triassic were recovered on DSDP Leg 79, off Morocco at Sites 544 to 547 in front of the Mazagan Plateau. The main zone of oil genesis should be reached at Site 547 within the Jurassic section. Organic material of marine origin with good petroleum potential characterizes the late Eocene slumps of Site 547 and originates from reworked organic matter of Cretaceous origin. Organic...

Visual estimates of carbonate particles and coccolith abundance at DSDP Hole 75-530A

Peter H Roth
The upper Albian to Coniacian section (Cores 105 to 89) at Site 530 contains rare and poorly preserved coccoliths at a few levels and fine-fraction carbonate ("micarb") at all the levels studied. Dissolution ranking of the most resistant coccolith species is possible. Changes in the dissolution intensity resulting from variations in the organic carbon and carbonate input seem a likely explanation for changes in the relative abundance of fine-fraction carbonates types.

Results from a stable isotope tracer experiment in Potter Cove, King George Island, Antarctica

Francesca Pasotti, Marleen De Troch, Maarten Raes & Ann Vanreusel
Antarctic meiofauna is still strongly understud- ied, and so is its trophic position in the food web. Primary producers, such as phytoplankton, and bacteria may repre- sent important food sources for shallow water metazoans, and the role of meiobenthos in the benthic-pelagic coupling represents an important brick for food web understanding. In a laboratory, feeding experiment 13C-labeled freeze- dried diatoms (Thalassiosira weissflogii) and bacteria were added to retrieved cores from Potter Cove (15-m depth, November...

Radiocarbon ages and average physical properties of sediment cores obtained during Icebreaker Oden cruise OSO0910

Alexandra E Kirshner, John B Anderson, Martin Jakobsson, Matthew O'Regan, Wojciech Majewski & Frank-Oliver Nitsche
To date, understanding of ice sheet retreat within Pine Island Bay (PIB) following the Last Glacial Maximum (LGM) was based on seven radiocarbon dates and only fragmentary seafloor geomorphic evidence. During the austral summer 2009-2010, restricted sea ice cover allowed for the collection of 27 sediment cores from the outer PIB trough region. Combining these cores with data from prior cruises, over 133 cores have been used to conduct a detailed sedimentological facies analysis. These...

Late Cretaceous volcaniclastic rocks at DSDP Holes 74-525A and 74-528

M Simon & Hans-Ulrich Schmincke
Volcaniclastic rocks of Late Cretaceous age occur in four out of five sites (525, 527, 528, 529) drilled on the crest and the northwest flank of the Walvis Ridge during Leg 74. They are mostly interlayered with and overlie basement in the lowermost 10-100 m of the sedimentary section. Rocks from Holes 525A and 528 were studied megascopically and microscopically, by XRD, and XRF chemical analyses of whole-rock major and trace elements were undertaken. The...

Geochemistry and isotopic ratios of samples from the Tiger gabbroic complex, Northern Victoria Land, Antarctica

Friedhelm Henjes-Kunst, Jürgen Koepke, Andreas Läufer, Solveig Estrada, Glen Phillips, Karsten Piepjohn & Dominique Kosanke
Subduction related mafic/ultramafic complexes marking the suture between the Wilson Terrane and the Bowers Terrane in northern Victoria Land (Antarctica) are well-suited for evaluating the magmatic and structural evolu- tion at the Palaeo-Pacific continental margin of Gondwana. One of these intru- sions is the "Tiger Gabbro Complex" (TGC), which is located at the southern end of the island-arc type Bowers Terrane. The TGC is an early Palaeozoic island-arc related layered igneous complex characterized by extraordinarly...

A magneto-mineralogical study of basalt at DSDP Leg 73 Holes

J Housden, Peter Tucker & W O'Reilly
The basalts in Holes 519A, 522B, and 524 were studied for intensity of natural remanent magnetization, magnetic hysteresis, magnetic susceptibility, stability of isothermal remanence, and thermomagnetic behavior. Some of these properties are sensitive to both the composition and the microstructure of the magnetic minerals, others to composition only. Thus it is possible to separate the two effects and to trace the variation of effective magnetic grain size and degree of alteration within a lithologic unit...

Miocene through Pleistocene dinoflagellates from ODP Site 170-1039

Monica Zegarra & Javier Helenes
Palynological data from offshore Costa Rica, allow us to investigate the relationship between dinoflagellate cyst assemblages and changes in regional oceanic primary productivity. From Miocene to Pleistocene, productivity at ODP Site 1039 was influenced by tectonic drift, as Site 1039 approached the continent, from the Equator to its current position at ~10°N. In addition, dinoflagellate abundance is modulated by regional productivity events, which modified primary productivity, as also indicated by available data on calcareous nannofossils,...

Quaternary planktonic foraminifera of DSDP Hole 72-517

Claude Pujol & Josette M Duprat
Quaternary sediments were recovered at all four Sites at Leg 72. Planktonic foraminifers were abundant and well preserved, especially in the holes shielded from Antarctic Bottom Water (AABW) influence. The fauna belonged to the subtropical province marked by Globigerinoides ruber and to a lesser extent by Globorotalia inflata. Thirty planktonic foraminiferal species were distinguished, and a detailed study of the Site 517 stratigraphy was made.The Quaternary sequence of the Rio Grande Rise was subdivided slightly...

Dinoflagellate cyst assemblages, Mg/Ca based reconstructed temperatures, stable carbon isotopes, and geochemical parameters of sediment core GeoB9508-5

Ilham Bouimetarhan, Jeroen Groeneveld, Lydie M Dupont & Karin A F Zonneveld
In order to investigate a possible connection between tropical northeast (NE) Atlantic primary productivity, Atlantic meridional overturning circulation (AMOC), and drought in the Sahel region during Heinrich Stadial 1 (HS1), we used dinoflagellate cyst (dinocyst) assemblages, Mg/Ca based reconstructed temperatures, stable carbon isotopes (d13C) and geochemical parameters of a marine sediment core (GeoB 9508-5) from the continental slope offshore Senegal. Our results show a two-phase productivity pattern within HS1 that progressed from an interval of...

Chemical and isotopic compositions of zircons from an eclogitized gabbronorite dike at the Gridino village, Northern Karelia

O I Volodichev, A I Slabunov, O S Sibelev, S G Skublov & T I Kuzenko
A comprehensive (mineralogical, geochronological, and geochemical) study of zircons from an eclogitized gabbronorite dike was carried out in order to identify reliable indicators (mineralogical and geochronological) of genesis of the zircons in their various populations and, correspondingly, ages of certain geological events (magmatic crystallization of the gabbroids, their eclogitization, and overprinted retrograde metamorphism). Three populations of zircons separated from two rock samples comprised xenogenic, magmatic (gabbroic), and metamorphic zircons, with the latter found exclusively in...

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