bluuebunny/crossref_metadata_2025_split huggingface dataset:
Tracing the evolution of hydrothermal fluids in the upper oceanic crust: Sr-isotopic constraints from DSDP/ODP Holes 504B and 896A
Authors: Teagle D. A. H. , Alt J. C. , Halliday A. N. 
Published: April 2008

Abstract

Whole rock and secondary mineral
87
Sr/
86
Sr determinations from ODP Holes 504B and 896A have been compiled into a profile for the upper 2 km of
in situ
ocean crust to constrain the composition and evolution of recharge and discharge fluids. There is a gradual trend from elevated
87
Sr/
86
Sr whole rock ratios at the top of the crust towards primary MORB compositions at the base of the sheeted dykes. Rocks from the mineralized lava-dyke transition zone have
87
Sr/
86
Sr ratios clustering in the range of black smoker fluids. Igneous and alteration phases are not in Sr-isotopic equilibrium, therefore whole rock strontium isotopic ratios reflect the proportion of secondary minerals and the extent of plagioclase recrystallization. The
87
Sr/
86
Sr of anhydrite directly records the chemical evolution of seawater during recharge. There is a slight decrease in anhydrite
87
Sr/
86
Sr with depth in the volcanic rocks but anhydrite from the lowermost dykes yields diabasic
87
Sr/
86
Sr ratios. Epidotes in cross-cutting veins have higher
87
Sr/
86
Sr than the background alteration recorded by amphibole in the lower dykes. This elevated signature reflects the
87
Sr/
86
Sr of 504B black smoker-type fluids and requires less fluid evolution than the background alteration, suggesting channelling of recharge fluids locally.
Petrological investigations of low temperature hydrothermal alteration of the upper crust, Juan de Fuca Ridge, ODP Leg 168
Authors: Hunter A. G. ,   DP Leg 168 Scientific Party
Published: April 2008

Abstract
Ten sites were drilled across the eastern flank of the Juan de Fuca Ridge during ODP Leg 168 to investigate the nature of ridge-flank hydrothermal circulation and crustal evolution in a region of varying sediment-basement topography. The sites were divided into: (i) the Hydrothermal Transition (HT) transect, a zone of gradually thickening sedimentary cover, extending from the ridge-flank boundary for a distance of 20 km to the east; (ii) the Buried Basement (BB) transect, which consists of uniformly, flat lying basement, capped by a regionally continuous thick sedimentary sequence; and (iii) the Rough Basement (RB) transect, represented by a region of basement highs and troughs, located ∼100 km east of the ridge axis, and capped by a variable thickness of sediment.
Across the flank, a progressive sequence of alteration was recognized, produced as the hydrothermal system evolved from open oxidative conditions involving a slightly modified seawater derived fluid, to a more restricted/closed, non-oxidative environment in which more strongly modified seawater derived fluids interacted with the basement. Alteration commenced with the formation of chlorite at relatively high temperatures in non-oxidative to oxidative conditions, followed by the first wide spread stage of low temperature oxidative alteration with the formation of iron oxyhydroxides and celadonite. Progressive burial, along with continued alteration of the basement, restricted fluid circulation resulting in the formation of saponite ± pyrite over a range of temperatures under non-oxidative conditions. The final stage of alteration is represented by carbonate, which formed under non-oxidative conditions by interaction of strongly modified seawater and the crust.
Drilling of sediment-hosted massive sulphide deposits at the Middle Valley and Escanaba Trough spreading centres: ODP Leg 169
Authors: James R. H. , Duckworth R. C. , Palmer M. R. ,   The ODP Leg 169 Shipboard Scientific Party
Published: April 2008

Abstract
Massive sulphide deposits actively forming from hydrothermal systems within sedimented environments have been drilled during Ocean Drilling Program Leg 169 at two locations along the Juan de Fuca/Gorda spreading centres. The Bent Hill Massive Sulphide and Ore Drilling Program deposits, Middle Valley, include iron- and zinc-rich massive and semi-massive sulphides underlain by a well-developed feeder zone characterized by sulphide impregnations and cross-cutting copper-rich veins. Ridge-parallel normal faulting is probably involved in providing high-permeability pathways for focused discharge at the seafloor, and this is a key element in creating these large ore deposits. In strong contrast, massive sulphide recovered from the Central Hill hydrothermal site, Escanaba Trough, suggests mineralization forms only a thin (5–15 m) veneer over the sediment sequence. Interstitial waters recovered from this area have chlorinities both significantly higher and lower than seawater. The only way to explain this variation is that the fluids contain a hydrothermal component which has undergone supercritical phase separation at depth. Diffuse discharge of hydrothermal fluids through the sediments evidently precludes the formation of a large ore deposit in this area.
Holocene uplift and subsidence of the Helike Delta, Gulf of Corinth, Greece
Authors: Soter Steven 
Published: April 2008

Abstract

The southwestern coast of the Gulf of Corinth, known as Aigialeia, lies in a region of rapid tectonic uplift and extension. Using age and elevation data from raised relic shorelines, and Lambeck’s model for local isostatic sea-level rise, I re-examine the uplift of the coastal footwall block in Aigialeia. The average Holocene uplift rate is 2.4±0.8m ka
−1
, significantly higher than the Quaternary uplift rates associated with the raised terraces near Corinth on the southeastern coast. The footwall movement in Aigialeia consists of coseismic uplift events separating periods of relatively aseismic uplift. A footwall uplift of about 2 m apparently accompanied the earthquake that destroyed and submerged ancient Helike 373
bc
. The city was built on a Gilbert-type fan delta adjacent to the area of raised relic shorelines. Using dated samples from bore holes drilled in the delta, I estimate that the delta itself subsided by at least 3 m during the earthquake. The opposition between gradual uplift and coseismic subsidence events apparently resulted in a relatively small absolute net displacement of the delta during Holocene time.
Late Cenozoic emergence of the islands of the northern Lau-Colville Ridge, southwest Pacific
Authors: Nunn P. D. 
Published: April 2008

Abstract

The Lau-Colville Ridge is part of an island arc abandoned during Pliocene time as a result of development of the back-arc Lau Basin. Throughout much of Plio-Pleistocene time, the ridge subsided, and its volcanic peaks were submerged and cloaked with (reef) limestone. Uplift, mostly during Pleistocene time, caused the northern part of the ridge to emerge by at least 315m. Islands along the northern Lau-Colville Ridge exhibit ten well-defined terraces above
c.
10m whose ages are constrained by those of anomalously young lavas and avian phosphates. Low-level emerged shorelines may be all of Holocene age and exhibit a recurrence interval of coseismic uplift events of 1500 years.
Holocene coastal tectonics in NE Brazil
Authors: Bezerra Francisco H. R. , Lima-Filho Francisco P. , Amaral Ricardo F. , Caldas Luciano H. O. , Costa-Neto Leão X. 
Published: April 2008

Abstract

We have identified two beachrock facies in NE Brazil which can be used as reliable sea-level indicators. Facies (a) represents the lower foreshore and the upper shoreface, being mainly characterized by coarse unsorted sandstones with trough cross-stratification, whereas facies (b) corresponds to sediments deposited on the middle to lower foreshore and is usually characterized by medium to coarse, better sorted sandstones which form seaward-dipping, swash cross beds. The age of the beachrock bodies ranges from
c.
7000 to 1150 cal. a
bp
. Although the relative sea-level record is complicated by oscillations which are probably due to minor climatic changes, it was possible to identify a general rise at
c.
7000 cal. a
bp
which reached its maximum of +2 m
c.
5000 cal. a
bp
and then started to fall to its present level some 300 years later. Our sea-level data are consistent with glacio-hydroisostatic models for the region but dates of 4080 cal. a
bp
on shells in growth position at +5 m above sea level and 2780 cal. a
bp
on a beachrock at sea level east of the Carnaubais fault point to rapid, possibly coseismic, late Holocene emergence.
Carbonate-siliciclastic sedimentation on a high-energy, ocean-facing, tropical ramp, NE Brazil
Authors: Testa Viviane , Bosence Dan W. J. 
Published: April 2008

Abstract

The inner portion of the continental shelf of Rio Grande do Norte State, Brazil has been investigated by Landsat-TM imagery and by scuba diving. The area experiences high-energy, shoreline and shelf-margin parallel currents driven by a combination of oceanic, tidal and wave processes. The high meso-tidal range (<4 m) further distributes the high-energy waters over the entire inner shelf region (0–25 m). This shelf is a high-energy, distally steepened ramp in which the distribution of carbonate and siliciclastic facies belts is controlled by the energy of the environment, the sources of siliciclastic sediment and the Quaternary history of the area. Carbonate sediments are generated throughout the sublittoral zone and are dominated by calcareous red and green algae. Small, low-diversity coral patch reefs occur in shallow areas. Quartz-rich sands form beaches and subaerial longitudinal dunes, and an offshore, submarine, sandstone outcrop interpreted as a former Quaternary shoreline. This sandstone has been eroded during the Holocene transgression to generate quartz sands deposited in a train of transverse dunes migrating parallel to the coast. Longitudinal sand ribbons comprising bioclastic gravelly sands attest to high-energy, shore-parallel currents in the inner shelf. Branching coralline algae (maërl) form stabilized sea-floor areas. Preliminary
14
C dating indicates a Pleistocene highstand period when coarse algal sands accumulated. Holocene lowstand conditions spread quartz-rich sands over the inner ramp area, which were reworked during the Holocene transgression. Present-day erosion, transport and
in situ
carbonate production results in mixing of these earlier carbonate and siliciclastic units. The Brazilian ramp has similar, but narrower morphology, when compared with the distally steepened ramps of the Yucatan and west Florida. All three ramps are swept by coastline-parallel currents. In Brazil, the higher-energy, windward-facing, inner ramp has calcareous algal sands and patch reefs compared with the inner ramps of the leeward-facing Gulf of Mexico examples that accumulate molluscan sands. Outer ramp facies in each example are planktonic foraminiferal oozes.
Cool-water carbonate deposition on the West Shetland Shelf: a modern distally steepened ramp
Authors: Light Janice M. , Wilson John B. 
Published: April 2008

Abstract

The West Shetland Shelf (WSS) is part of a carbonate province ranging through 11° of latitude on the western seaboard of the British Isles. Bioclastic gravels and sands and quartzitic shelly sediments, ranging in thickness from a few centimetres to 2 m have been accumulating since the Flandrian transgression (13 ka
bp
). A storm wave-base is recognized at the shelf margin (200 m) below which deposits are winnowed and reworked by an upper slope northerly-flowing contour current. Samples from a 143 km transect of 15 stations from the south of Shetland to 260 m on the upper continental slope have been analysed. Bivalve molluscs, barnacles and attached serpulids are the major carbonate contributors with bryozoans, gastropods and echinoderms of secondary importance. The free-living serpulid
Ditrupa arietina
and erect branching bryozoans are important sediment contributors on the outer shelf. The deep-water coral,
Lophelia pertusa
, has been recorded from depths of 200–500 m.

The WSS is a distally steepened carbonate ramp shelving at an angle of <1° to the open ocean with continual sweeping of long-period waves, frequent storms and deep-water contour currents.
A review of sediment distributions and processes in Oligo-Miocene ramps of southern Italy and Malta (Mediterranean divide)
Authors: Pedley Martyn 
Published: April 2008

Abstract
Carbonate ramps lying on the divide between the Eastern and Western Mediterranean basins are considered in the context of the facies that dominate their inner to outer ramp profiles. They developed during the final stages of Tethyan ocean closure. Consequently, the ramp successions accumulated within an increasingly microtidal regime. The ramp facies associations are typical of mid- to late Tertiary developments found throughout the old Tethyan belt. A detailed consideration is given to carbonate productivity and location of the carbonate factory, substrate stability, resedimentation mechanisms, and synsedimentary tectonics. Gravity sliding in mid-ramp situations is examined and its importance in maintaining ramp profile is considered. The relative importance of all processes and their bearing on sustainable ramp development in both current-facing and leeward situations is discussed.
Facies architecture and geometry of a prograding carbonate ramp during the early stages of foreland basin evolution: Lower Eocene sequences, Sierra del Cadí, SE Pyrenees, Spain
Authors: Gilham Rodney F. , Bristow Charlie S. 
Published: April 2008

Abstract

This paper describes the Early Eocene sedimentological evolution of the Sierra del Cadí carbonate platform during the early development of the southeastern Pyrenean foreland basin, Spain. The platform developed as a south-facing ramp system located either across the southern margin of a growth anticline within the newly formed basin or along the axial margin of the basin. Sequences I and II both comprise basal transgressive systems tracts (TSTs) dominated by a thick succession of outer ramp lime mudstones, shallowing upwards into a highstand systems tract (HST) of mid- and inner ramp bioclastic shoals, sand banks and lagoonal deposits. In Sequence III the TST comprises a thick, wedge-shaped unit of east to west backstepping, inner and mid-ramp
Nummulites
shoals and lagoonal deposits, progressively overlain by a thick succession of outer ramp lime mudstones and marls of the HST. No lowstand systems tracts are recognized. Sequence boundaries correspond to flooding surfaces which grade basinwards into correlative conformities, interpreted to represent the onset of high tectonic activity in the orogenic wedge and resulting high flexural subsidence across the foreland and drowning of inner ramp regions. TSTs represent continued high flexural subsidence creating accommodation space infilled by high rates of outer ramp sediment accumulation. In Sequences II and III, TSTs show a pronounced west to east thickening, interpreted to represent the effect of variable subsidence across the margins of an uplifting growth anticline within the otherwise flexurally subsiding foreland. Progradational successions that characterize HSTs developed during periods of reduced tectonic subsidence, both within the foreland and in the orogenic belt, allowing the growth and expansion of carbonate ramp facies belts.
Controls on development of Mid-Triassic ramps: examples from southern Hungary
Authors: Török Ákos 
Published: April 2008

Abstract
During Mid-Triassic time the palaeogeographical-tectonic setting of the northern Tethyan passive margin and epicontinental basins favoured the ramp morphology, as broad flat areas were available for flooding and establishment of carbonate sedimentation. Throughout this time, in what is now southern Hungary, homoclinal ramps developed, which also exhibit some evidence of partial distal steepening. The nearly 1 km thick Anisian-Ladinian Muschelkalk carbonates are grouped into six depositional units. In each ramp unit facies types were identified representing coastal sabkhas, inner ramp peritidal facies, backshoal lagoons, oolite shoals, storm to fair-weather influenced mid-ramps, proximal to distal shell beds and low-energy outer ramps. Mid- and inner ramp carbonates make up the majority of the successions. The deepest outer ramp facies correspond to the peak transgression of a second-order Triassic sea-level rise. In the Hungarian Muschelkalk three major transgressive-regressive sequences were identified. In Germany, Poland and Spain much thinner and slightly coarser Muschelkalk carbonate successions were formed in the same Mid-Triassic interval. The major sediment redistribution processes were related to storms that generated coquinas, and mud flow deposits. Slow, early diagenesis and the predominance of unstable muddy substrate led to the formation of small-scale slumps, slides and plastic deformation. The fauna reflects the prevalence of carbonate mud and temporarily high-stress conditions. A non ‘cool water’ origin of this ramp is inferred from the presence of evaporites, early dolomization of inner ramp carbonates, the biota and the palaeogeographical setting. The major controlling factors of Mid-Triassic ramps were the gentle antecedent morphology, the subtropical climate, the high production of carbonate mud and the lack of reef-building organisms, as well as the passive margin setting, which resulted in a moderate and relatively uniform subsidence rate over a wide area.
Middle Devonian reef and mud mounds on a carbonate ramp: Mader Basin (eastern Anti-Atlas, Morocco)
Authors: Kaufmann Bernd 
Published: April 2008

Abstract

The Mader Basin is a palaeogeographical unit of the eastern Anti-Atlas, once situated on the northwestern margin of Gondwana, which was a mid-latitudinal (30–45°S) carbonate province during Devonian time. In this basin, isolated reef and mud mounds are intercalated within a 200–300 m thick Middle Devonian succession. The mounds were established on a 40 km wide, tectonically controlled homoclinal ramp, which developed between an area of uplift (Mader Platform) and another area of strong subsidence (depocentre of the Mader Basin). The bathymetric gradient of this ramp is reflected by a facies pattern varying from shallow ramp to basinal environments and by different faunal associations of the carbonate mounds. The lithology of the Mader Basin carbonate mounds consists of massive, stromatactis-bearing, bioclastic wackestones, with the bulk of the mound volume consisting of microspar. High accumulation rates (0.2–0.8 m/ka) and the purity of mound carbonates (>95% CaCO
3
) compared with the marly inter- and off-mound facies strongly favour autochthonous carbonate production. In addition, several indications (calcimicrobes in the immediate neighbourhood of stromatactis, dark crusts surrounding stromatactis and alignment of stromatactis parallel to the accretionary mound surfaces) suggest a close relationship between microbial carbonate production and stromatactis formation. Microbial communities probably flourished on the mound surfaces, precipitating fine-grained carbonates and consolidating the steep mound flanks by their mucilagenic secretions. Once embedded, these communities decayed and left behind stromatactis cavities, which were subsequently filled by calcite cements. Drowning of the Mader Basin carbonate ramp was caused by progressive deepening related to basinal subsidence, which was superimposed by rapid eustatic sea-level rises. Onlapping of poorly oxygenated basinal waters was the direct cause for the termination of mound growth.
Coevolution of the Earth’s environment and life: Goldilocks, Gaia and the anthropic principle
Authors: Watson Andrew J. 
Published: April 2008

Abstract
Observation suggests that the Earth’s surface environment is maintained by processes in which non-living and living causes are linked inextricably. Once established on Earth, life rapidly became a dominant influence on the evolution of the planetary environment. But life was also shaped by that evolution, constrained and directed by the physical and chemical processes that moulded the planet’s surface. Life and the planetary environment form a closely coupled entity, a view of the Earth as a complex system which is prefigured in the writings of James Hutton.

Hutton compared the workings of the Earth’s surface to the body of an animal, being both wasted and repaired continually. In modern times, James Lovelock has argued that it is a property of this system that it acts to maintain the planet in a habitable condition. Alternatively, perhaps it is pure chance that the planet has always remained hospitable for life — it could just as easily have followed an infinity of different evolutionary paths, many and perhaps most of which would lead rapidly to global extinction. Consideration of the fates of our near-neighbour planets, Mars and Venus, and the dangerous nature of the inner solar system, leads to the conclusion that there is indeed a substantial element of luck involved in the Earth’s biosphere having survived as long as it has. The fact that our own existence is dependent on it having survived makes it nearly impossible to accurately assess
a priori
the probability of survival.

Abstract models such as ‘Daisyworld’ can capture some of the complex behaviour of the Earth-life system. This may include periods of stasis and sudden changes to new states, the stasis being an example of regulatory behaviour where the system is dominated by negative feedback, and the sudden changes being essentially the opposite — brief but traumatic periods where the dominant feedbacks are positive. GEOCARB, a biogeochemical model for the Phanerozoic which links changes in the long-term carbon cycle to planetary temperature, shows examples of both regulatory and destabilizing behaviour in a less abstract system, and suggests that such responses have indeed characterized Earth history.
I conclude that the properties of the Earth-life system are complex and not easily predictable. The longevity of Hutton’s animal (nearly 4 Ga) is no guide to its future life expectancy, and even if the system as a whole lasts many aeons into the future, any given species (such as humans) is most unlikely to.
Studies of post-depositional remanent magnetization and their relevance to the palaeomagnetic record
Authors: Pisarevsky S. A. 
Published: April 2008

Abstract
The results of experiments on the watering of different types of continental Quaternary sediments in the anomalous magnetic field show that it can cause strong changes in the direction of remanence. The direction of acquired post-depositional remanent magnetization is stable to thermal and alternating field (AF) demagnetization. These changes are not related to the chemical remagnetization and are probably caused by mechanical rotations of magnetic particles in the pore spaces. Post-depositional remagnetization, both in nature and after collection of sediment samples, can distort the palaeomagnetic record of geomagnetic excursions, events and polarity transitions, as well as altering the finestructure features, such as the palaeomagnetic record of secular variations.