bluuebunny/crossref_metadata_2025_split huggingface dataset:
Groundwater recharge and pollution vulnerability of British aquifers: a critical overview
Authors: Foster S. S. D. 
Published: April 2008

Abstract
The concept of aquifer pollution vulnerability, and the way it has been developed and incorporated as a central element in British groundwater protection policies, is reviewed in detail. A related question is: do we understand enough about groundwater recharge mechanisms to assess pollution vulnerability realistically and to define necessary protection measures efficiently? Some key remaining areas of uncertainty are analysed in the light of recent research results.
Identification of the source and fate of nitrate contamination of the Jersey bedrock aquifer using stable nitrogen isotopes
Authors: Green A. R. , Feast N. A. , Hiscock K. M. , Dennis P. F. 
Published: April 2008

Abstract

Measured NO
3
−
concentrations in the Jersey bedrock aquifer exceeded 50 mg l
−1
in 67% of groundwaters sampled in June 1995. The δ
15
N values of this dissolved NO
3
−
showed a total range in composition from + 3.6‰ to + 18.4‰ and exhibited a general, island-wide increase from + 4‰ in the centre of the island to + 9‰ towards coastal districts. The majority of the island is intensively cultivated and most of the sites sampled have δ
15
N values of less than + 7‰ (mean = + 7.7‰,
n
= 40) indicative of an agricultural source for NO
3
−
. There is no apparent evidence for point-source contamination from septic tanks. The progressive seaward increase in δ
15
N is attributed to an increasing volume of deeper, denitrified groundwater mixing with shallow groundwater. Values of δ
15
N greater than + 10‰ are restricted to those coastal and valley locations that abstract, due to their low topographic elevation, the greatest proportion of deeper, denitrified groundwater. An alternative explanation is that sewer leakage enhances the observed δ
15
N values in southern urban areas, although this is considered unlikely to be occurring at present.
Groundwater recharge: an overview of estimation ‘problems’ and recent developments
Authors: Simmers I. 
Published: April 2008

AbstractSince the mid-1980s there has been a relative explosion of recharge studies for (semi-)arid regions reported in the scientific literature. It is therefore relevant to assess what we now know and to offer guidance to the water resources development practitioner. This paper summarizes recurring recharge estimation ‘problems’ and reviews some recent advances in (inter alia) estimation techniques and recharge time/space variability.The determination of recharge fluxes in (semi-)arid regions remains fraught with uncertainty; multiple tracer approaches appear to offer the best potential for reliable results in local studies which require ‘at-point’ information. It is also clear that sufficient advances have been made in recent years to show that the value of water balance and Darcian approaches should not be under-estimated. The frequently studied issues of localized recharge and spatial variability need not be a problem if concern is with regional estimates. The key for the practitioner is the project objective; this will dictate whether multiple ‘at-point’ or area-based estimation methods are appropriate. For the latter, a combination of reliable local data, remote sensing, GIS and geostatistical techniques offers considerable promise for a better understanding and determination of recharge over extended areas.
Geology and hydrocarbon occurrences in the Ghadames Basin, Algeria, Tunisia, Libya
Authors: Echikh K. 
Published: April 2008

Abstract
The Ghadames Basin is a large intra-cratonic basin, covering portions of Algeria, Tunisia and Libya. The three countries are independently conducting petroleum exploration in their portions of the basin, using different play concepts and consequently obtaining different exploration results. This paper presents the first published basin-wide view of petroleum stratigraphy and play types. Some 700 exploratory wells have been drilled in the basin, resulting in the discovery of at least 150 oil pools with 9500 MMBO (million barrels of oil) in place. Most wells were located in the structurally higher parts of the basin, with deeper portions being less explored because of shifting dune conditions and an expectation of reservoir thinning into the basin centre. Silurian and Devonian source rocks occur across large parts of the basin and have generated volumes of hydrocarbon orders of magnitude above those discovered. The numerous structural phases (Taconic, Caledonian, Hercynian and Austrian) that have affected the basin have had important implications for depocentre migration, structural style, and for patterns of trap formation, alteration and destruction. The erosion pattern and topography developed on the Hercynian unconformity is a key control on petroleum systems within the basin, controlling the preservation of Palaeozoic hydrocarbons, communication between source and higher reservoirs and patterns of long-distance migration in the Triassic reservoir. For each of the producing plays, an analysis is presented of the geological factors controlling the habitat of hydrocarbons (e.g. the effect of various tectonic phases, the influence of basin-scale facies variations on reservoir quality, and the source rock-reservoir relationship), and is related to the variations that have been observed in exploration success rate and producibility. It is believed that a substantial volume of hydrocarbons still remains undiscovered in a range of trap and play types.
Regional depositional setting and pore network systems of the El Garia Formation (Metlaoui Group, Lower Eocene), offshore Tunisia
Authors: Loucks R. G. , Moody R. T. J. , Bellis J. K. , Brown A. A. 
Published: April 2008

Abstract
The Metlaoui Group was deposited on a broad ramp that deepened to the northeast into the Tethyan Sea. The ramp contains a series of broad facies belts. The inner-ramp facies belt is composed of three facies tracts: (1) Faid sabkha (most landward) characterised by skeletal-poor dolomudstones and wackestones and interbedded evaporites, (2) Ain Merhotta restricted shallow-lagoon facies composed of sparse skeletal wackestones, packstones, and cross-bedded gastropod grainstones; (3) updip El Garia high-energy shoal complex (most seaward) composed of red algal-discocyclinid grainstones and packstones which are locally cross-bedded. The El Garia carbonates in the mid-ramp setting are predominantly composed of large, flat nummulites. Dominant textures are burrowed, mud-poor packstones and poorly sorted or bimodal grainstones. The accumulation was located below fair-weather wave base and above storm wave base, at a water depth estimated to have ranged from 30 to 60 m (middle neritic). The deep-water (deep neritic), outer-ramp Ousselat Member consists of coarse silt- to medium sand-sized nummulithoclastic debris that grades from coarser to finer debris down the ramp. The Bou Dabbous Formation is composed of basinal foraminiferal mudstones, wackestone and packstones deposited by suspension and less commonly by gravity-flow deposition in upper bathyal water depths. Reservoir quality is variable, with most lime packstones and grainstones having moderate to high porosity (related to intraparticle and microporosity), but only poor to fair permeability (generally less than 10 mD). The higher-quality reservoirs have preserved interparticle porosity with permeabilities ranging from tens of millidarcys to several darcys. Permeable nummulitic packstones and grainstones are favoured by the following factors: (1) low abundance of lime mud, (2) low abundance of nummulithoclastic debris, (3) low abundance of echinoderm fragments, (4) moderate sorting, (5) minor precipitation of late burial cements, (6) dolomitization.
Basin evolution and deposition during the Early Paleogene in Tunisia
Authors: Zaïer A. , Beji-Sassi A. , Sassi S. , Moody R. T. J. 
Published: April 2008

Abstract
The marine Paleocene and Ypresian deposits of Tunisia, within the El Haria Formation and the Metlaoui Group, have been intensively studied because of the commercial interest in phosphates and hydrocarbons. This paper presents the latest updates of isochron, lithofacies and palaeogeographical maps, and interprets the patterns identified in light of synsedimentary structure. This reveals a close association between structure, basin geometry and subsidence. Facies distribution during the Early Paleogene is thought to be structurally controlled along basement lineaments. These major fault systems were reactivated several times during the Mesozoic and Tertiary, with the last movements occurring as Neogene and post-Villafranchian events. The structural control of facies is most evident during the Ypresian, particularly along the ‘North-South Axis’ (Nosa) a sub-meridian orogenic segment of Central Tunisia. In this area the Ypresian deposits exhibit a preferred alignment with the Nosa exerting a notable influence on basin geometries and rates of local subsidence. In addition to two large islands indicated in the onshore area of Tunisia, a number of ‘bald’ highs are identified in the offshore, representing original submarine highs. The general pattern across Tunisia throughout the period is of a number of small tectonically controlled basins. The distribution of phosphorites, organic-rich shales and evaporites can be particularly linked to the development of restricted basins during the period.
Kinematics of the Watchet-Cothelstone-Hatch Fault System: implications for the fault history of the Wessex Basin and adjacent areas
Authors: Miliorizos M. , Ruffell A. 
Published: April 2008

Abstract
The Watchet-Cothelstone-Hatch Fault (WCHF) comprises a system of northwest-southeast-trending basement and cover faults that are traceable for at least 40km from the Bristol Channel, southeast into the western Wessex Basin. The west-dipping WCHF displays outcrop and seismic evidence of a complex movement history involving early (Variscan) and late (?Cretaceous or Tertiary) strike-slip, separated by phases of normal extension. In the Variscan basement of North Somerset, the WCHF shows a 14–16km dextral offset to Devonian markers and Variscan fold axes, and can be linked to similar trending faults in South Wales. Offsets to early Permian (and possibly late Carboniferous) rifts indicate a dextral transfer of north-south extension from the Crediton and Tiverton troughs, across the WCHF and into the Wessex Basin. In Mesozoic cover, the WCHF swings to become part of the east-west Central Bristol Channel Fault Zone in the north and Lopen Fault Belt (western Wessex Basin) in the south. This geometry reflects a present-day preservation of a later sinistral movement. The structure of juxtaposed Palaeozoic and Mesozoic successions along the WCHF provides an analogue for what might be expected at the basement-cover contact beneath the Wessex Basin. The existence of Mesozoic cover to the WCHF most likely explains why no Cenozoic pull-apart basins were formed, unlike the Sticklepath Fault (in granites and metamorphic rocks) to the southwest.
Transpression (or transtension) zones of triclinic symmetry: natural example and theoretical modelling
Authors: Lin Shoufa , Jiang Dazhi , Williams Paul F. 
Published: April 2008

Abstract
We describe a natural shear zone with triclinic symmetry, present a general model for triclinic shear zones based on natural examples, and investigate the kinematics and strain geometry within such zones.
In the Roper Lake shear zone in the Canadian Appalachians, the orientation of a stretching lineation is oriented approximately down-dip near the shear zone boundary and becomes gradually shallower towards the centre. The structures in the central portion of the shear zone exhibit approximately monoclinic symmetry where the poles to both the S- and C-surfaces, the stretching lineation on the S-surfaces and the striations on the C-surfaces all plot in a great circle girdle. However, the lineations from the marginal portion do not plot in the same girdle, and the bulk symmetry of the shear zone is triclinic. Theoretical modelling shows that the observed strain geometry can be interpreted by an oblique transpression with a larger ratio of simple shear to pure shear in the centre of the shear zone than in the margin. The latter suggests a higher degree of localization of the zone boundary-parallel movement component relative to the boundary-normal compression component.
We emphasize that, as the imposed boundary displacements for most natural shear zones lie between dip-slip and strike-slip, their movement pictures are generally triclinic; monoclinic shear zones are special end members. Structural data that exhibit monoclinic symmetry do not necessarily mean that they resulted from a monoclinic movement picture; the present modelling demonstrates that a triclinic movement picture with a high ratio of boundary-parallel movement to boundary-normal movement can result in apparent monoclinic structural geometry. The results of the modelling also show that the simple statement made for simple shear zones that stretching lineations will align with, and therefore indicate, the shear direction cannot be extrapolated to three-dimensional transpressional (or transtensional) shear zones.
Tectonic evolution of the Northern Salinian Block, California, USA: Paleogene to Recent shortening in a transform fault-bounded continental fragment
Authors: Tavarnelli Enrico 
Published: April 2008

Abstract
The complex structural setting of the western margin of North America is interpreted to result from oblique convergence of the North American and Pacific plates, accommodated by both right-lateral slip along the San Andreas fault and shortening east and west of it. Strike-slip movements along the San Andreas fault led to the detachment of a continental fragment (the Salinian Block) from the North American margin during early Miocene, and its translation northwestwards for over 300 km. Structural analysis in the Northern Salinian Block, west of the San Andreas fault, reveals a NE-SW-directed shortening accommodated by NW-SE-trending folds and thrusts with a dip-slip kinematic character. The stratigraphic record of progressively younger unconformities affected by both folds and thrusts, as well as the overprinting relationships among these contractional structures, enables us to clarify the tectonic evolution of the region since Paleocene time. The Paleocene to Recent history of the Salinian Block was dominated by strike-slip along the San Andreas fault, and by shortening perpendicular to it. The partitioning between strike-slip and dip-slip movements appears to be controlled by a pre-existing tectonic feature. The results from structural analysis along the Salinian Block are integrated into a deformation model for the western margin of North America, providing additional constraints on the timing of deformation and helping to clarify the role of strain-partitioning processes in the obliquely convergent California margin.
Ocean floor volcanism: constraints from the integration of core and downhole logging measurements
Authors: Brewer T. S. , Harvey P. K. , Lovell M. A. , Haggas S. , Williamson G. , Pezard P. 
Published: April 2008

Abstract
The volcanic architecture of oceanic crust records the diversity in volcanic activity during its development in the neovolcanic zone of individual ridge systems. Potentially there exists a spectrum of lithological architectures which may primarily be related to the spreading rate and the dynamics of individual magma chambers along different ridges. Recent studies have emphasized the observable spatial variations within different neovolcanic zones, although direct extrapolation into the third dimension can only be achieved by the use of drilling results. To study the structure of the volcanic layer it is essential that individual lithologies (sheet flows, pillow lavas and/or breccias) can be discriminated from the core and/or logging results and mapped within the borehole. Unfortunately a problem with the drilling of the volcanic basement during the Ocean Drilling Program has been the generally low (typically c. 25%) and biased core recoveries, which produce an erroneous picture of the lithological diversity of the volcanics. This problem is further compounded by the difficulty in determining the volcanic stratigraphy, particularly when the key information is lost during coring (i.e. boundaries/contacts). Downhole logging provides near continuous records of the physical/chemical properties of the borehole which when integrated with core measurements, yield a detailed picture of the architecture of the volcanic layer. Logging results from ODP Hole 896A are of sufficient quality that sheet flows, pillow lavas and brecciated units can be discriminated and mapped effecively within the borehole. From their distribution it is evident that sheet flows become more abundant in the lower part of the hole, which probably correlates with ridge axis volcanism whereas, the predominance of pillow lava flows (<340 mbsf (metres below sea floor)) in the upper part of the hole, is probably related to off-axis volcanism within the neovolcanic zone.
A novel approach for constraining heat flow histories in sedimentary basins
Authors: Gallagher K. , Morrow D. W. 
Published: April 2008

Abstract
We examine the application of a novel inversion procedure to determine a heat flow history from down-hole thermal indicator data from 2 wells in northern Canada. The approach is based around Occam’s razor in that we attempt to constrain the simplest heat flow history consistent with the observed data. Simple models are defined in terms of the variation about the present day heat flow and the inverse problem is to minimise a combined function of the data misfit, weighted by the individual error on each observation, and the model complexity.
The results obtained for the 2 wells, Pan Am Beaver River YT G-01 and Imperial Island River No. 1 in the Liard Basin, agree with heat flow histories determined from forward modelling. However, the inversion approach discussed provides useful estimates of model resolution and sensitivity. The effect of variations in the data errors and the nature of the forward model are also considered. As we expect intuitively, the quality of the solution depends directly on the quality of the input data and forward model.
Geology of the Sierra de Fiambalá, northwestern Argentina: implications for Early Palaeozoic Andean tectonics
Authors: Grissom Grady C. , Debari Susan M. , Snee Lawrence W. 
Published: April 2008

Abstract

Field mapping in conjunction with structural, metamorphic, and geochronological data document the tectono-thermal history of exhumed deep crustal rocks in the Sierra de Fiambalá, NW Argentina. The range consists of two structural blocks distinguished by different metasedimentary sequences and different grades of metamorphism. Orthogneiss and paragneiss in the northern structural block may have a Precambrian history. Greenschist- to amphibolite-facies metamorphism, intrusion, and injection migmatization affected all rocks at 540–550 Ma. A subsequent event in the Late Cambrian to Ordovician (
c.
515 to 470 Ma) involved amphibolite- to granulite-facies metamorphism, mafic intrusion, and deformation, followed by cooling through mid-Palaeozoic time. The emplacement of Carboniferous (325–350 Ma) post-tectonic granites caused reheating and retrogression that was strongest toward the northeast part of the range.

The Cambrian, Ordovician, and Carboniferous events in the Sierra de Fiambalá were of regional extent as indicated by temporal correlations with events reported for other deep crustal rocks of the northern Sierras Pampeanas. Correlations between periods of intrusion and high-grade metamorphism in the northern Sierras Pampeanas and volcanic-sedimentary events in the adjacent supracrustal exposures confirm that rocks in the northern Sierras Pampeanas formed at deep (10–25 km) structural levels in the early Palaeozoic continental margin of Gondwana.
The granitoids of the Sierra de San Luis
Authors: Llambías E. J. , Sato A. M. , Suárez A. Ortiz , Prozzi C. 
Published: April 2008

Abstract

The Sierra de San Luis consists of Lower Palaeozoic igneous and metamorphic rocks. The granitoids were emplaced between Late Cambrian and Early Carboniferous times, and the most important metamorphic and deformational events occurred during this period. Older metamorphic events have also been recognized but they are poorly constrained. The most important group of granitoids are as follows: (1) Deformed tonalites and granites. The tonalites have a calc-alkaline signature with low La/Yb ratio. They are the Early Famatinian, pre-orogenic, granitoids of Late Cambrian to Early Ordovician age and form part of a magmatic arc. (2) The La Escalerilla granite is a deformed biotite monzogranite and consists of a single elongated pluton; its relation with the other granitoids is not clear. (3) Garnet-biotite-muscovite granodiorites and granites and pegmatites. The granitoids have S-type signatures, with high
87
Sr/
86
Sr and La/Yb ratios. They are possible crustal magmas related to a thickened crust and are interpreted as early- to syn-orogenic. (4) Biotite- and biotite-hornblende granites and minor tonalites of Devonian to Early Carboniferous age. The granites form large, post-orogenic, plutons and batholiths related to crustal uplift, and represent the last igneous activity of the Famatinian cycle (and also of the Palaeozoic era) in the Sierra de San Luis.
Fluid inclusion constraints on conditions and timing of hydrocarbon migration and quartz cementation in Brent Group reservoir sandstones, Columba Terrace, northern North Sea
Authors: Wilkinson J. J. , Lonergan L. , Fairs T. , Herrington R. J. 
Published: April 2008

Abstract
Fluid inclusion data have been obtained from Brent Group sandstones from the Columba Field on the margin of the East Shetland Basin, northern North Sea. Cogenetic primary aqueous and hydrocarbon inclusios trapped during the initial stages of late diagenetic quartz overgrowth are common, indicating that the pore fluid present during the onset of a major phase of quartz-kaolinite(-illite) diagenesis consisted of immiscible saline aqueous and petroleum phases. Similar inclusions are also observed in abundant planar arrays cross-cutting detrital and authigenic quartz. Homogenization temperature and salinity data from the two types of aqueous inclusions are statistically indistinguishable, as are the properties of the two types of hydrocarbon inclusions, suggesting that the same two-phase fluid was present probably throughout the main phase of quartz cementation. Fluid inclusion thermobarometry shows that the majority of the fluids were trapped in the range 104 ± 6°C and 300 ± 33 bars. These data are consistent with either (1) trapping of a warm, over-pressured hydrocarbon + aqueous fluid, probably in thermal and chemical disequilibrium with the host reservoir rocks, derived from a Kimmeridgian source in the deep Viking Graben basin to the east of the reservoir within the period 85–55 Ma, or (2) trapping of a hydrostatically pressured fluid, in thermal equilibrium with the host reservoir rocks, with hydrocarbon ± aqueous fluids derived by lateral up-dip migration from a local Kimmeridgian hydrocarbon source in the East Shetland Basin within the period 65–40 Ma. A maximum duration of 10 Ma for the fluid flow event can be estimated based on a typical burial history model for the area.