bluuebunny/crossref_metadata_2025_split huggingface dataset:
Turbidity-current and debris-flow pathways to the Cape Verde Basin: status of long-range side-scan sonar (GLORIA) surveys
Authors: Kidd Robert B. , Hunter Peter M. , Simm Robert W. 
Published: April 2008

Summary
A regional GLORIA survey in the southern Cape Verde Basin identified highly variable patterns of backscattering intensity that were interpreted as resulting from seabed roughness and small-scale slope changes. It was inferred that their origin was linked to turbidity-current pathways across the continental rise. Farther north, a survey of the Saharan Continental Rise SE of Madeira identified even more spectacular changes in backscattering. Follow-up 3.5 kHz echo-sounder surveys together with core-sampling and bottom-camera studies allowed an assignment of acoustic facies to sediment type. In this area turbidity-current channels and deposits have been overrun by long-range debris flows resulting from the late-Quaternary Saharan sediment slide. Preliminary results of a further GLORIA survey that links the previously studied areas with a single swath along the continental rise are reported in this paper. The resulting sonographs show details of submarine-slide-debris-flow complexes on this margin that had previously been mapped from 3.5 kHz records. They extend across the lower continental rise to the plain areas. Others do not extend as far as the lower rise. Debris flows can no longer be thought of as unequivocal indicators of proximality in the geological record.
Organic carbon oxidation and preservation in NW Atlantic continental margin sediments
Authors: Heggie D. , Maris C. , Hudson A. , Dymond J. , Beach R. , Cullen J. 
Published: April 2008

Summary
We present distributions of pore-water inorganic metabolites (nitrate, ammonia, manganese and iron), dissolved organic matter (DOM) including dissolved organic carbon (DOC), nitrogen (DON) and phosphorus (DOP) and solid-phase organic carbon from the Hatteras Abyssal Plain, the Hatteras Continental Rise and Slope and the northern Bermuda Rise areas of the eastern United States seaboard. Organic carbon oxidation rates in the sediments were calculated from models of the pore-water inorganic metabolites and the solid-phase organic carbon distributions. The pore-water model results were consistently higher than rates determined from the sediment organic carbon distribution. This result may reflect an inappropriate use of bulk sediment mixing coefficients in simple solid-phase models to estimate rates of interfacial diagenetic processes. The organic carbon oxidation rates in the sediments were combined with the organic carbon burial rates to assess the particulate organic flux into the sediments, and these results were compared with the particulate organic rain caught in sediment traps. Trap fluxes were consistently higher than model-estimated fluxes. We cannot make an unequivocal interpretation of the organic carbon mass balance, but we suggest that rates of benthic metabolism estimated from inorganic metabolite and sediment organic carbon distributions underestimate rates of organic carbon cycling because some fraction of the particulate organic carbon rain caught in traps is remineralized as DOM. Pore-water enrichments of DOM, DOC and DON were a factor of 5–10 higher than bottom-water concentrations, suggesting a flux of DOM to bottom waters. DOM fluxes to bottom waters contribute to abyssal metabolism in the benthic boundary layer and not to sediment metabolism.
Early Proterozoic Metavolcanic Suites of the Northernmost Part of the Baltic Shield
Authors: Pharaoh T. C. , Warren A. , Walsh N. J. 
Published: April 2008

Summary
Metavolcanic rocks of Proterozoic age occur in three major supracrustal belts in the northernmost part of the Baltic Shield, in Norway and the USSR.

In the west, the
Kautokeino Belt
, and its continuation into the tectonic windows of Finnmark, contains thick sequences of tholeiitic metabasalt the age of which is poorly constrained at present. In the Repparfjord Window, these basalts are strongly enriched in Fe, Ti, LIL and LREE and are chemically similar to modern continental flood basalts. Stratigraphic equivalents in the Alta area and Kautokeino Belt are less enriched in incompatible elements, and more like MORB in composition, although a within-plate setting is indicated by the field evidence. These differences are believed to reflect heterogeneity of the mantle source region, with a locally ‘enriched’ source in the Finnmark windows.

The
Karasjok Belt
of central Finnmark forms the northward continuation of the Kittilä Belt of northern Finland. Amphibolitic rocks derived by metamorphism of tholeiitic basalts dominate the tectonostratigraphy of the greenstone belt. These are associated with metamorphosed komatiitic rocks which have recently yielded a Sm-Nd age of 2.1 Ga. The Karasjok Belt is interpreted as an early Proterozoic supracrustal sequence thrust westwards as an allochthonous sheet during uplift of the Lapland Granulite Complex in the Svecokarelian Orogeny at about 1.9 Ga.

The
Pechenga Complex
of the USSR continues westward into Finnmark, and overlies the Archaean gneisses of the Kola Complex. The Kola Superdeep Borehole penetrated a metamorphosed supracrustal sequence 7 km thick, dominated by basalts and andesites of calcalkaline composition. The MORB-normalized geochemical patterns of these lavas indicate that they were erupted in a mature continental volcanic arc.

The geochemical data support geotectonic models invoking rifting of pre-existing continental crust in the early Proterozoic. Komatiitic liquids were locally able to reach the earth’s surface, but probably only in the rift zones suffering greatest extension. Calcalkaline arc magmatic suites along the western edge of the Kola Craton reflect subduction of‘oceanic’ lithosphere, although no trace of this is preserved along the suture now marked by the Karasjok Belt.
Flow and flow mechanisms in crystalline rock
Authors: Black J. H. 
Published: April 2008

Summary

Recent work on the hydrogeology of crystalline rocks has evolved rapidly from basic data gathering to specific experiments for evaluating details of flow mechanisms. Single-borehole data from around the world are similar and independent of detailed geology and test techniques. It appears that most faults in crystalline rocks have an effective hydraulic conductivity of around 1 × 10
−7
ms
−1
with values for intact rock about five orders of magnitude lower. The porosity of unweathered crystalline rock measured in the laboratory usually varies between 0.1% and 1% with weathered samples attaining up to 15%. When large data sets are considered it is possible to correlate depth and hydraulic conductivity. The interpretation of hydrogeological tests has evolved from basic porous media through fissures bounded by impermeable rock and fissures bounded by permeable rock to networks and channels. Whereas most hydraulic testing is adequately interpreted using the fissured porous medium concept, tracer tests require highly complex fissure network models with channelling. There is growing evidence that groundwater flow is concentrated in a limited network of channels. This seems to apply on both the laboratory and the regional scale.
Tectonic control of desert sediments in rift basins ancient and modern
Authors: Frostick L. E. , Reid I. 
Published: April 2008

Summary

Desert sediments are frequently associated with continental rifts or aulacogens in the stratigraphic record. In this circumstance, rift structure and the timing and magnitude of tectonic events exert an overriding control on the distribution and character of alluvial sediments. Recent advances in the understanding of rift structure make a reassessment of ideas on the relationship between faulting, drainage patterns and alluvial facies distribution timely. Existing models of symmetrical graben with large alluvial fans shed from the footwalls of planar, normal boundary faults do not accord with observations in recent rifts. For example, half-graben dominate the structure throughout the African rifts. Boundary faults are mostly listric and the associated back-tilting of fault-blocks, combined with the doming that frequently accompanies rifting, causes back-shedding of rivers away from the basins. Alluvial fan development at fault scarps is, therefore, limited. The maximum observed fan radius in Lake Turkana is, for example, only 8 km, or 10% of the half-graben width at that point. The supply of sediment to rift basins can be dominated by axial rivers (
eg
Sugata R. flowing into L. Logipi in Kenya, the Awash R. of the Afar in Ethiopia, and the Rhine R. flowing through the Rhine rift), but there are a surprising number of basins that do not have major axial inputs (
eg
L. Tanganyika and L. Malawi in East Africa and L. Baikal in Siberia). In these cases, the importance of smaller, but more numerous rivers draining across the roll-over becomes obvious. These rivers are subjected to rapid changes in base level and longitudinal gradient: movement of a boundary fault alters the geometry of the lake basin and base-level falls as the lake adjusts. This is accompanied by the aggradation of coarse alluvial deposits across the roll-over. Clast size gradients in these deposits are well defined for the region between the basin margin and the main depocentre, with typical measured values of −3 mm km
−1
. During the long, intervening periods of tectonic quiescence these and other deposits are reworked and redistributed downslope and offshore. Deltas build out into the lake, but microstratigraphy reveals that they are not of the classic Gilbert type. Short- and long-term fluctuations in lake level cause large-scale migration of the shoreline so that lake muds and alluvial sands are interdigitated over many kilometres in sequences which vary from a few metres to tens of metres in thickness. A synthesis of detailed work carried out on the sedimentology and geomorphology of a modern rift of the common half-graben type provides a new model of sedimentation that will prove useful in interpreting ancient deposits with hydrocarbon potential.
The diagenesis of the Great Estuarine Group, Middle Jurassic, Inner Hebrides, Scotland
Authors: Hudson J. D. , Andrews J. E. 
Published: April 2008

Summary
The Bathonian Great Estuarine Group consists of sandstones, silty shales and mainly shelly limestones, deposited in micro-tidal brackish lagoons in a warm, seasonal climate. The rocks show, in general, a lack of intense early diagenesis or deep-burial diagenesis, and are thus suitable for the study of shallow-burial diagenetic processes. Early diagenetic changes can be directly linked to depositional environment. They were only important on the lagoon margins, where cyanobacteria flourished in schizohaline ‘algal marsh’ settings and dolomite formed in response to evaporation of low-salinity lagoonal waters. During burial to a few hundred metres, and after initial compaction, cementation by ferroan calcite occurred. This was pervasive in limestones and formed large concretions in sandstones. Quartz and feldspar grains in sandstones were marginally corroded by the porewaters that precipitated calcite, and some feldspars had previously or concurrently suffered partial solution. Aragonitic mollusc shells were replaced by calcite in permeable rocks but remained unaltered in shales. Widespread volcanism in the Palaeocene buried the area beneath basaltic lavas and dykes were intruded. These events produced little metamorphic or burial-diagenetic change, except in close proximity to minor intrusive contacts or in the vicinity of plutons. The evolution of porewaters can be monitored in the carbon and oxygen isotopic composition of diagenetic calcites. After initial burial, they were dominantly of meteoric derivation. Vitrinite reflectance measurements confirm the mild thermal history of most of the sediments, and show the local effects of heating by igneous intrusions.
A new look at the causes and consequences of the Icelandic hot-spot
Authors: Bott M. H. P. 
Published: April 2008

Summary
New support for the hypothesis of a lower mantle plume rising near Iceland comes from recent developments in the theory of whole-mantle convection and is inferred from the large heat input required to support the major topographic swell which affects much of the N Atlantic and Greenland. The associated geoid and gravity highs are interpreted as due partly to the swell and its deep compensation and partly to the pressure anomaly caused by the plume. Rapid lateral migration of partially fused material from the plume in the asthenosphere prior to continental break-up caused the early Tertiary volcanism, with subsequent igneous activity concentrated at the ridge crest to form the Icelandic transverse ridge. Progressive expansion of the upper mantle thermal anomaly in response to pressure, in association with the complexities of plate evolution in this region, may account for the early uplift of S Greenland and later uplift of the Blosseville Kyst region. The low density upper mantle would also be expected to give rise to an anomalously high ridge-push force.
Early Tertiary volcanic rocks in Well 163/6-1A, Rockall Trough
Authors: Morton A. C. , Dixon J. E. , Fitton J. G. , Macintyre R. M. , Smythe D. K. , Taylor P. N. 
Published: April 2008

Summary
Well 163/6-1A, located in the northern part of the Rockall Trough, proved the presence of a thick sequence of extrusive igneous rocks below Upper Palaeocene sediments. K-Ar age dating suggests that the lavas were extruded at approximately 55 Ma. The lava sequence comprises three distinct lithologies. The upper part of the pile consists of olivine tholeiites that show alkalic and picritic tendencies and have a distinct within-plate composition. These are underlain by another group of olivine tholeiites that are much closer in composition to normal mid-ocean ridge basalt (N-type MORB). The Sr and Pb isotopic compositions of the basalts suggests possible contamination by continental crustal material.
The basalts are underlain by a sequence of cordierite-phyric dacites of remarkably homogeneous composition. Their highly aluminous nature, high Ni and Cr contents and their Sr and Pb isotopic compositions indicate that they are not differentiates of a basaltic parent magma, and are considered to have originated by melting of argillaceous and, possibly, arenaceous rocks at depth. Organic-rich black shale lithologies may have been involved.
Biological marker compounds as indicators of the depositional environments of petroleum source rocks
Authors: Volkman J. K. 
Published: April 2008

Summary

Recent studies concerned with the use of biological marker compounds for assessing the source of organic matter in sediments and crude oils are reviewed and critically assessed. Compounds which are indicative of inputs from bacteria and phytoplankton are reviewed as well as some compounds for which origins have not been determined. The use of ratios of C
27
and C
29
steranes for assessing the depositional environment of petroleum source rocks is shown to be particularly open to misinterpretation. Some inferences based on pristane/phytane ratios also need to be reassessed. Areas of research where more studies would be valuable are highlighted.
Palaeolimnology and organic geochemistry of the Middle Devonian in the Orcadian Basin
Authors: Duncan A. D. , Hamilton R. F. M. 
Published: April 2008

Summary
An interdisciplinary study of the Middle Devonian lacustrine laminites from the Orcadian Basin of NE Scotland has enabled the construction of a predictive source-rock model which we have applied to the Moray Firth area.
Parameters characterizing areal source-rock extent, primary organic input, and the depths, salinity levels and redox potential of the depositional water column are discussed, together with the quantity and maturity of the preserved sedimentary organic matter.
On the basis of this model, we suggest that a Middle Devonian component is present in the Beatrice crude (an atypical North Sea oil) in the Moray Firth Basin. This proposal is largely supported by molecular geochemical evidence.
Styles of soft-sediment deformation on a Namurian (Carboniferous) delta slope, Western Irish Namurian Basin, Ireland
Authors: Martinsen O. J. 
Published: April 2008

Summary
Soft-sediment deformation features from a delta-slope succession exposed in the Western Irish Namurian Basin, Ireland, are described and related to three main styles of deformation: (i) slumping, (ii) sliding and (iii) water-escape structures. While (i) and (ii) were formed by near-surface gravitational gliding of sediment, (iii) was formed by mainly vertical motion of sediment and escaping pore fluids. Deformation structures formed by slumping include slump folds and large- and small-scale faults, internal shear surfaces, deformation of early calcareous concretions and boudinage. The slumps were initially dominated by plastic deformation, whereas brittle deformation dominated the late stages. Deformation structures formed by sliding are mainly macroscopic faults, but microfaults and slide folds also formed locally. The slides were at all stages dominated by brittle deformation. Water-escape structures include mud and sand dykes and volcanoes, collapse depressions, mud diapirs and small-scale loading. These structures can be either related to or independent of slumping and sliding. While slumps are not restricted to any particular part of the delta slope, the occurrence of slides is, to a large degree, dependent upon grain size. Mud slides only occur on the muddy upper delta slope, while sand slides are only found on the lower delta slope. Water-escape structures tend to be more common on the lower delta slope.
Controls on internal structure and architecture of sandstone bodies within Upper Carboniferous fluvial-dominated deltas, County Clare, western Ireland
Authors: Pulham A. J. 
Published: April 2008

Summary
Deposition of Upper Carboniferous (Namurian R1-R2) deltas in the Clare Basin, western Ireland, was influenced by a combination of processes: fluvial, basinal (notably waves), synsedimentary deformation, and rapid subsidence rates within the receiving basin. Fluvial processes predominate; consequently the major deltaic sandstone bodies are fluvial channels and fluvial-dominated mouth bars. The internal structure of single channel sandstones reflects high energy tractive processes and aggradation of sands in relatively straight channel reaches. The structure of mouth-bar sandstone bodies reflects a variety of frictional and buoyant river-mouth processes. Depositional processes within the Clare Basin are often overprinted by syndepositional deformation. Delta-front sequences exhibit abundant evidence of synsedimentary faulting, slumping, clay diapirism and gravity sliding. Deformed packets of sediment are up to 60 m thick and over half of all delta-front sequences are disturbed. These processes led to a modification of mouth-bar structure and geometry. Some fault-bounded delta-front sandstone bodies fill fault-induced depocentres. Large, multistorey and laterally composite channel sandstones in the S of the basin may reflect major deformation across the delta plain, related to rapid subsidence and compaction rates. In contrast, the architecture and structure of delta-plain sequences in the N of the basin are consistent with a more stable fluvial-dominated setting.
Facies and development of the Middle Jurassic Brent Delta near the northern limit of its progradation, UK North Sea
Authors: Brown S. , Richards P. C. 
Published: April 2008

Summary
The lithofacies patterns in the Middle Jurassic Brent Group, the principal hydrocarbon reservoir in the UK northern North Sea, are examined in seven wells. The sections, from the area of the Don and Murchison oil fields, record the nature of the Brent Delta near the northern limit of its progradation. Here the deltaic deposits of the Brent Group, which regionally constitute a major regressive-transgressive clastic wedge, progressively lose the interbedded sands and muds of the delta plain which characterize the middle part of the succession further S. This leads locally to a maximum sand-to-mud ratio for the Brent Group reservoir interval.
A regressive storm-wave-influenced marine succession, from offshore transition-zone silts and muds up to hummocky cross-stratified nearshore sand, is overlain in turn by stacked distributary channel sands. Distributary mouth deposits are absent. The interbedded delta-plain succession, where it occurs, exhibits some marine influence and records wave reworking of interdistributary bay or lagoonal sediments. The Brent Group succession is capped by transgressive sands which were deposited in a storm-wave-influenced nearshore environment. Delta-plain drowning is also evident in the gradual marine incursions into distributary channels at the northern limit of the study area.
The character of the delta locally is compared with the nature of the wave-dominated Brent Delta elsewhere on its progradational path. High energy nearshore deposits in both regressive and transgressive phases are widely distributed, but there is a contrast between the dominance of fluvial processes in the study area and the development elsewhere of a barrier island complex in front of a coastal plain.
Tectonic controls on boninite genesis
Authors: Murton B. J. 
Published: April 2008

Summary
Boninites are rare high-MgO and compatible-element-rich basalts that are depleted in incompatible trace elements. Whilst their high magnesium number indicates equilibrium with upper-mantle peridotite, their depleted trace-element geochemistry indicates a highly refractory and depleted source. Many models account for boninite magmatism in destructive margin environments but none has so far explained their erratic spatial and temporal occurrence. Recent studies along the southern Troodos margin have revealed a history of boninite magmatism within a complex supra-subduction zone transform fault. The transform fault boninites form a suite that cross-cuts a less trace-element-depleted magmatic sequence forming the Troodos oceanic crust that was generated at a constructive plate margin.
Melting models demonstrate that the transform fault boninites were probably produced by a 10% melt of the upper mantle which had already been depleted by the extraction of the Troodos crust and mid-ocean ridge basalts (MORB). In contrast with the Troodos crustal sequence, however, the boninites are also enriched in two separate components, selected high field strength elements and large-ion lithophile elements. Such incompatible-trace-element enrichments are unlikely to have survived the earlier source depletion events. Therefore the enrichment of the transform boninites must have been added to their source immediately prior to or during their genesis within the supra-subduction transform environment.

The identification of rapid dilation and transtensional transform displacement along the southern Troodos margin suggests important tectonic factors in the formation and emplacement of boninite magmas. The requirement of an extensional regime and rifting of trace-element-depleted oceanic crust formed above a subduction zone (
eg
extension and rifting of an extended fore-arc region) explains the erratic and rare nature of boninite magmatism.