bluuebunny/crossref_metadata_2025_split huggingface dataset:
Hydrothermal inputs at ODP Sites 836, 837, 838 and 839 in relation to Eastern Lau Spreading Centre propagation in the Lau Basin, southwest Pacific
Authors: Hodkinson Richard A. , Cronan David S. 
Published: September 2007

Abstract
Lau Basin Ocean Drilling Program (ODP) Sites 836, 837, 838 and 839 were drilled in basins west of the axial rift zone of the Eastern Lau Spreading Centre (ELSC), south of the Central Lau Spreading Centre (CLSC). Based on the models of basin evolution, Site 836 is thought to be located on ELSC-generated crust while Site 838 is located on pre-existing extended arc terrain to the west of ELSC-generated crust. Sites 837 and 839 are postulated to be close to the boundary separating ELSC-generated and pre-existing crust.
Sediments recovered at all sites comprise late Pliocene to Pleistocene clayey nannofossil ooze containing sparse calcareous turbidites overlying a thick sequence of redeposited volcaniclastic sediments interbedded with hemipelagic clayey nannofossil oozes. All calcareous ooze sections contain hydrothermal ferromanganese oxides.
The hydrothermal flux to the sediments at each site has been assessed using non-detrital Mn+Fe accumulation rates for recalculated, hemipelagic sediment intervals alone in order to remove the effect of sediment redeposition. Site 836 shows a typical mid-ocean ridge up-hole pattern of decreasing accumulation rates with increasing crustal accretion, as expected from its predicted location on ELSC-generated crust. Site 837 shows a similar pattern suggesting its location on ELSC-generated rather than pre-existing western Lau Basin attenuated crust. At Site 839 non-detrital Mn+Fe accumulation rates show an increase up-hole from basement to a peak before decreasing towards surface, reflecting increasing hydrothermal flux to the sediments with the southward propagation of the ELSC past this site and suggesting its location on pre-existing crust west of ELSC-generated crust. For the time-equivalent sediment section at Site 838, non-detrital Mn+Fe accumulation rate patterns are similar to those at Site 839. Although a period of low non-detrital Mn+Fe accumulation rate reflecting lower plume fallout flux prior to ELSC propagation past the site is not seen at the base of the sediment section at Site 838 (as the hole did not penetrate to basement), the accumulation rate patterns seen are not at variance with its postulated location on pre-existing attenuated crust west of ELSC-generated crust.
Mean non-detrital Mn+Fe accumulation rate values are highest at Site 836 with lower mean values at Sites 837, 838 and 839. These values are within the range of those for East Pacific Rise sediments but lower than those for ELSC-propagation-associated sediments at Sites 834 and 835 in the northwestern part of the basin, suggesting that hydrothermal plume fallout associated with the southern, more recently generated portion, of the ELSC was lower than that of the older portion in the north.
Rare earth element anomalies in the Nankai accretionary prism, Japan
Authors: Alexander Jane L. 
Published: September 2007

Abstract
Rare earth element (REE) patterns are often used as provenance indicators, but there is growing evidence that this signal may be distorted by REE mobility. This study focuses on turbiditic and hemipelagic muds from Ocean Drilling Program (ODP) Site 808, drilled in the toe of the Nankai accretionary prism. Most of these muds have a typical shale REE composition, but several samples are enriched in REE. Four of these are associated with hydrothermal deposits, rich in manganese (up to 18% MnO). A further two have minor mineral phases, zircon and florencite, with high REE concentrations. There is also a heavy REE enrichment in one sample from the décollement zone. This has not yet been explained, but it does not appear to have a mineralogical control.
Cyclicity and basin axis shift in a piggyback basin: towards modelling of the Eocene Tremp-Ager Basin, South Pyrenees, Spain
Authors: Nijman Wouter 
Published: September 2007

Abstract
A new database of the Eocene Montanyana delta in the Tremp-Ager piggyback basin of the South Pyrenees is exemplified and discussed. It consists of a grid of nine transverse and five longitudinal stratigraphic cross-sections and structural profiles, some examples of which are shown. Detailed facies maps and a large number of digitized sedimentary logs formed the basis for the stratigraphic correlation of the traverses with a resolution at the scale of 5 m, i.e. the size of minor architectural elements. The correlation was calibrated chronostratigraphically with biostratigraphic and recently published palaeomag data. The database so provides a detailed picture of the geometry, internal architecture and stacking patterns of the increments of basin infilling.
The database allowed recognition and definition of eight megasequences, between 148 and 404 m thick, that are aperiodic, spanning time intervals between 400 and 1400 Ma. Although most of the megasequence boundaries can easily be related to third-order sea-level fluctuations, predominant structural control is indicated by their correlation with sharp reversals in the pattern of basin axis shift in transverse cross-sections of the basin, and with flank unconformities. Several modes of structural control by thrust sheet displacement are proposed. Sea-level fluctuation modified the megasequential architecture accounting, for instance, for extreme progradation as observed in the Castissent Sandstone.
The megasequences are subdivided into a large number of basin-wide cycles, on an average 44 m thick, with a calculated average periodicity of 124 ka approximating the 100 ka of orbital forcing. Aggradational, amalgamated sheet, fan progradational and fluvial expansion cycles are distinguished and correlated with episodes of specific structural and sea-level control. The pattern of stacking of the cycles conforms to the structurally controlled megasequential basin-axis shift on which it is superposed. Climatic fluctuations appear to have played a prominent role only in generating minor subcycles observed in some parts of the basin fill.
This basin analysis is meant to be a step towards 3D numerical tectono-sedimentary modelling of the Tremp-Ager piggyback basin.
Fluid migration during Eocene thrust emplacement in the south Pyrenean foreland basin (Spain): an integrated structural, mineralogical and geochemical approach
Authors: Travé Anna , Labaume Pierre , Calvet Francesc , Soler Albert , Tritlla Jordi , Buatier Martine , Potdevin Jean-Luc , Séguret Michel , Raynaud Suzanne , Briqueu Louis 
Published: September 2007

Abstract
In the frontal part of the south Pyrenean Eocene thrust-fault system, syn-kinematic fluid flow during the early compressional deformation of the foreland basin marls is evidenced macroscopically by the abundance of calcite shear veins within the thrust-fault zones and folds.
The geometry and distribution of the veins are indicative of the mechanisms and kinematics of fluid-deformation relationships, and give assessment of the fluid migration paths. The crack-seal mechanism of formation of the shear veins attests to the episodic nature of fault-slip and associated fluid flow in fractures. The distribution of the veins suggests that the main source of fluid was the dewatering of the overpressured, poorly permeable marls from the thrust footwalls, probably related to both (i) vertical compaction due to burial under thrust sheets and (ii) tectonic horizontal shortening. These fluids drained upwards towards the thrust-fault zones, in which they migrated laterally towards the thrust front due to the anisotropy of the fracture permeability in these zones.

The geochemistry of the vein-filling minerals and their comparison with the geochemistry and mineralogy of the host marls are indicative of the fluid types, fluid origins, fluid-sediment interactions, and fluid migration paths. The δ
34
S and
87
Sr/
86
Sr ratio of the host marl calcite and of the calcite and celestite in the veins away from the thrust-fault zones indicate that the original water trapped interstitially in the marls was Eocene seawater. The elemental composition (Ca, Sr, Mg, Mn, and Fe), δ
18
O, and δ
13
C of the same samples reveal a change of the pore-water composition from marine to formation water during the early burial stage. Fluid-inclusion analyses of the celestite in the veins reveal the presence of a hot, saline ascending fluid restricted to these discontinuities, where it was mixed with the local formation water. These two types of fluids drained towards the thrust-fault zones where they acquired a higher
87
Sr/
86
Sr ratio, probably related to local fluid-sediment reactions. Indeed, dickite precipitated during cleavage formation in the most intensely strained part of the fault zones, and its formation was probably mainly controlled by stress. δ
18
O depletion in the calcite from the structurally highest/innermost thrust-fault zones suggests also the influence of meteoric water derived from the emerged part of the belt in these structures.

The earlier fluid regime in the Ainsa basin was an intergranular (porous) flow regime (compactional flow) allowing for a pervasive isotopic, and elemental exchange of the marls prior to vein formation. With the onset of compressional deformation, channelized flow along tectonic slip surfaces became dominant.
Horizontal shortening control of Middle Miocene marine siliciclastic accumulation (Upper Marine Molasse) in the southern termination of the Savoy Molasse Basin (northwestern Alps/southern Jura)
Authors: Beck Christian , Deville Eric , Blanc Eric , Philippe Yann , Tardy Marc 
Published: September 2007

Abstract
Between the southern Jura and the Subalpine Chains (Bornes, Bauges, and Chartreuse Massifs), the Burdigalian-Langhian-Serravalian tidal siliciclastic ‘Upper Marine Molasse’ (UMM) outcrops in N-S synclines between N-S-trending ramp anticlines separating southward-narrowing synclines. A surface survey and an interpretation of transverse seismic-reflection profiles across the latter confirm that they represent progressively individualized and separated sedimentation areas. Combined seismic configuration and surface geometry show westward migration of depo-axes, and coeval progressive steepening close to each ramp, upon blind thrusts. Several thick earthquake-disturbed layers offer further evidence of a syntectonic sedimentation. A regime of flexure-subsidence prevailing during the Chattian-Aquitanian (the so-called Lower Freshwater Molasse, LFM) was overprinted by thin-skin shortening. The latter, combined with Burdigalian-Langhian higher eustatic sea-level, favoured the accumulation and the preservation of abundant tidal bedforms and sequences, which are generally poorly preserved in stable settings.
Evolution of the western Swiss Molasse basin: structural relations with the Alps and the Jura belt
Authors: Burkhard Martin , Sommaruga Anna 
Published: September 2007

Abstract

The tectonic evolution of the NW alpine front and foreland basin is reviewed in the light of new structural and chrono-stratigraphical data. Seismic-reflection profiles from the Jura fold thrust belt and Molasse basin, surface-geology and thrust-system considerations lead to a complete cross-section of the NW Alpine front including the Helvetic domain. Restoration of this section places individual Cenozoic formations in their approximate palaeogeographic position. ‘Geohistory’ plots are constructed for five profiles along a SE-NW transect. Thrust front, onlap and forebulge advanced at high rates of 10–20 km/Ma
−1
at the onset of foreland basin formation in the late Eocene/ early Oligocene (40–30 Ma). In these early stages, the foreland basin is an underfilled flexural trough with about 100 km width, less than 600 m water depth at the deepest point and less than 200 m of total accumulated sediments. From 30 to 22 Ma, thrust front and ‘pinch-out’ migrate at a decreased rate of about 5 km/Ma
−1
northwestward. The basin width remains constant at around 100 km; an increased total subsidence (
c.
2.7 km) is compensated by sedimentation. At around 22 Ma, the thrust front seems to come to a halt southeast of Lausanne, whereas a strong subsidence trend prevails. After the Serravallian (
c.
12 Ma) the Alpine thrust front jumps by about 100 km northwestward from a position southeast of Lausanne to the external Jura leading to thrust related uplift, deformation and concommitant erosion of the entire basin fill. No new flexural foreland basin in response to the modified thrust- and load-geometry has yet been developed. The present-day Molasse basin is only a small remnant of a much larger foreland basin in a very advanced stage of its evolution.
Reservoir analogue modelling of sandy tidal sediments, Upper Marine Molasse, SW Germany, Alpine foreland basin
Authors: Zweigel J. 
Published: September 2007

Abstract

An outcrop of sandy tidal sediments (Überlingen, Lake Constance) was studied and modelled using the computer-program
heresim
. The distribution of 12 lithofacies types was mapped on photo-panels. Facies-proportion curves and variograms were calculated and used as input parameters for the simulations. Simulations with varying numbers and positions of pseudo-wells showed that already one well is sufficient to achieve a good reservoir image, due to the simple layercake-like arrangement of lithofacies types at the scale of the outcrop (125 m × 15 m). Further, a detailed geostatistical analysis of tidal sandwave deposits revealed a complex, but surprisingly systematic internal structure. Single crossbedded bodies were classified according to their size, foreset orientation, and geometry. The geostatistical analysis revealed vertical alternations of the dominant current direction (ebb and flood) and of the size of cross beds, which could be related to changes in accommodation space.
Automation of stratigraphic simulations: quasi-backward modelling using genetic algorithms
Authors: Bornholdt Stefan , Westphal Hildegard 
Published: September 2007

Abstract
Stratigraphic modelling involves a multi-dimensional parameter-fitting process where a large number of free model parameters are determined by hand in an iterative sequence of educated guesses. This problem can be viewed as an optimization task. It is solved here using a genetic algorithm. The iterative trying and checking process, which previously had to be done manually, is thereby automated. This method is demonstrated to be consistent for a completely defined toy model. Furthermore it is applied to a real problem involving the Eocene to Miocene succession of the Bavarian Molasse Basin.
Numerical modelling of growth strata and grain-size distributions associated with fault-bend folding
Authors: Bezemer Taco den , Kooi Henk , Podladchikov Yuri , Cloetingh Sierd 
Published: September 2007

Abstract
A numerical model is developed to investigate the facies and stratal patterns associated with fault-bend folding in (non-marine) foreland fold and thrust belts. After identifying the basic predicted stratal and facies geometries for a single fault-bend fold the modelling is extended to situations involving multiple folds, changes in displacement velocity, contemporaneous variations in climate and variations in sediment calibre of source material. We show that the orientation of kink-axes of fault-bend folds is of minor influence on the predicted stratal patterns and that variations in displacement velocity and climate may produce resembling, but still distinct facies patterns. The stratigraphic architecture of facies patterns is very sensitive to vergence and sequence of thrusting and may serve as a guide in interpreting the stratigraphic record associated with multiple fault structures. Applied to two natural examples of fault-bend folds, our modelling narrows down the range of interpretations of these structures.
Mathematical models of gas hydrate accumulation
Authors: Rempel A. W. , Buffett B. A. 
Published: September 2007

Abstract
Gas hydrate reservoirs are widespread on the world’s continental margins and in the Arctic, but little is known about the way in which they form. We use conservation principles to derive a set of equations that describe hydrate formation in uniform porous media. Using scaling arguments, we identify the physical processes that are most important to hydrate accumulation in different environments. This knowledge is used to construct models that quantitatively predict the development of hydrate layers under a variety of circumstances. These models compare favourably with recent field observations of hydrates in marine sediments.
Improvements in clathrate modelling II: the H
2
O-CO
2
-CH
4
-N
2
-C
2
H
6
fluid system
Authors: Bakker R. J. 
Published: September 2007

Abstract

Clathrate stability conditions have been modelled for the H
2
O-CO
2
-CH
4
-N
2
-C
2
H
6
fluid system based on all available experimental data. Optimum Kihara parameters are estimated for pure CO
2
, CH
4
, N
2
and C
2
H
6
gas hydrates from using the most accurate calculation of other parameters involved in clathrate modelling, like fugacities, gas solubilities in H
2
O and thermodynamic constants. For mixed gas hydrates of CO
2
-CH
4
, CH
4
-N
2
, and CH
4
-C
2
H
6
excess Gibbs free energy functions are introduced to obtain a good fit to experimental data. The excess Gibbs free energy is described according a modified Margules equation, which depends on mole fraction and temperature.
Synthesis of CO
2
hydrate in various CH
3
CO
2
Na/CH
3
CO
2
H pH buffer solutions
Authors: Lu H. , Matsumoto R. 
Published: September 2007

Abstract

CO
2
hydrates were synthesized in CH
3
CO
2
Na/CH
3
CO
2
H buffer solutions with various pH values and different concentrations to investigate whether the change of pH value can influence CO
2
hydrate formation. The results imply that the change in pH value has a minimum influence on the equilibrium condition of CO
2
hydrate. The equilibrium condition of CO
2
hydrate in the various pH buffer solutions is seemingly controlled by the total concentration of the acetic acid and acetate anion, while Na
+
cation plays a minimum role.
Detection of gas hydrates using downhole logs
Authors: Goldberg D. , Saito S. 
Published: September 2007

Abstract

Downhole logs have proven to be critical in quantifying natural gas hydrates found in marine sediments and the seismic signature associated with free gas below. In recent drilling on the Blake Ridge, the Ocean Drilling Program recorded
in situ
velocity and resistivity logs that reveal an increasing amount of hydrate with depth in the pressure-temperature stability window. The associated increase in shear rigidity (decrease in
V
p
/
V
s
ratio) and decrease in acoustic amplitude over this interval is attributed to the cementation of sediment grains by hydrate, which may also explain the prevalent seismic blanking across the Blake Ridge. In future drilling campaigns, the use of ‘logging-while-drilling’ (LWD) sensors placed just above the drill bit will improve the
in situ
estimation of porosity, lateral variability and hydrocarbon reservoir potential of natural gas hydrates.
Tomographic seismic studies of the methane hydrate stability zone in the Cascadia Margin
Authors: Hobro J. W. , Minshull T. A. , Singh S. C. 
Published: September 2007

Abstract

A seismic study in the Cascadia Margin in June 1993 focused upon the bottom simulating reflector (BSR) around Hole 889B of the Ocean Drilling Program. Extensive wide-angle and normal-incidence data were collected during two deployments of five ocean bottom hydrophones (OBHs). We have applied a new two-dimensional travel-time inversion method to data from one line within the survey. Data from four OBHs and normal-incidence arrivals are inverted simultaneously, and a distribution of P-wave velocities above the BSR is obtained. These velocities are found to be slightly higher than those given by vertical seismic profile (VSP) and sonic log data from Hole 889B, with velocities of 1.83–1.95 km s
−1
occurring immediately above the BSR. Estimates of hydrate concentration derived using two different methods range from 2 to 24% of the pore space. The velocity model provides some support for the existence of a correlation between BSR strength and hydrate concentration above the BSR in this region.
Marine gas hydrate inventory: preliminary results of ODP Leg 164 and implications for gas venting and slumping associated with the Blake Ridge gas hydrate field
Authors: Paull C. K. , Borowski W. S. , Rodriguez N. M. 
Published: September 2007

Abstract

Deep ODP holes on the Blake Ridge (sites 994, 995 and 997; Leg 164) show that sediments within the interval ∼200–450 metres below sea floor (mbsf) contain 1–4% gas hydrate based on interstitial geochemistry, pressure core samples, well logs and borehole seismic data. In addition, a considerable methane gas reservoir also exists below the gas hydrate stability zone in the form of free and dissolved methane. Addition of methane from these deep reservoirs to overlying ocean water (and ultimately to the atmosphere) could have profound geological, geochemical and climatic effects. Pervasive flux of methane to the sea floor via diffusion is unlikely because methane is almost completely consumed by reaction with sulphate at the sulphate-methane interface. Further, sulphate and
87
Sr/
86
Sr profiles suggest that upward advection of potential methane-containing fluids is also unlikely. However, point sources for methane advection to the sea floor do occur. Active methane transport along faults occurs at Site 996, and the methane
13
C isotopic signature indicates derivation from the gas hydrate-bearing and free gas zones below.
14
C data from sediments indicate that the frequency of sediment slumping on the Blake Ridge is higher during the sea-level lowstand associated with the last ice age. Whereas there is no direct evidence that methane exchange is associated with slump events, nor that gas hydrates are necessarily related to the increased slumping frequency, the association between slumps and faults suggest that the amounts of gas escape should be greater during sea-level lowstands.
Geochemistry of gas hydrates and associated fluids in the sediments of a passive continental margin. Preliminary results of the ODP Leg 164 on the Blake Outer Ridge
Authors: Thiéry R. , Bakker R. , Monnin C. 
Published: September 2007

Abstract
Marine sediments containing gas hydrates have been drilled up to a depth of 750 m below the sea floor (mbsf) at the Blake Outer Ridge during the ODP Leg 164. Gas hydrates are present between 190 and 450 mbsf. Shipboard analyses of gases and interstitial waters are interpreted with the help of thermodynamic models for gas hydrates and aqueous solutions. Two aspects of the influence of gas hydrates on the chemistry of associated fluids are investigated here. The first one is related to the methane/ethane ratio, which exhibits a sudden change of trend at the base of the gas hydrate zone. This phenomenon could be due to gas hydrates, which act as a concentration barrier for ethane. The second aspect concerns the presence of interstitial waters less saline than sea water above and inside the gas hydrate zone. This could result from the upward expulsion of saline waters during the compaction of sediments in the gas hydrate zone.
Extensive deep fluid flux through the sea floor on the Crimean continental margin (Black Sea)
Authors: Ivanov M. K. , Limonov A. F. , Woodside J. M. 
Published: September 2007

Abstract

The ANAXIPROBE/TTR-6 Cruise of the Russian R/V
Gelendzhik
in the summer of 1996 resulted in the discovery of a new area of extensive deep fluid flux through the sea floor on the lower Crimean continental margin, within the Sorokin Trough in the Black Sea. The study area is noted for the widespread development of acoustic anomalies in bottom and sub-bottom sediments indicating the presence of gas. Bottom sampling confirmed a high content of gas in the sediments, the presence of gas hydrates and other features normally associated with gas escape. These features include authigenic carbonates with a light carbon isotope composition and bacterial mats. The geochemical data indicate that the gas has in part a thermogenic origin.