bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Southeast Greenland glaciated margin: 3D stratal architecture of shelf and deep sea
Authors: Clausen Lene 
Published: April 2008

Abstract
A seismic stratigraphic study of the Upper Neogene and Pleistocene shelf and deep-sea deposits of Southeast Greenland is presented. The depositional environment was controlled by glacial, turbidity current, and contour current processes. Below the mid- and outer shelf a Tertiary sedimentary wedge, as much as 1.7 km thick, is resting on a seaward-dipping volcanic acoustic basement. A lower marine part is separated by a regional unconformity, SB-A, from two seismic sequences of early Pliocene to Pleistocene prograding clinoforms. SB-A is surmised to represent a seaward-dipping palaeo-relief surface, accentuated by modest submarine erosion related to a sea-level lowering. The overlying two Sequences x and y reflect shelf-edge progradation in front of grounded ice during periods of maximum glaciation. The topset beds of the youngest sequence, possibly of Pleistocene age, are characterized by six or more sub-horizontal, landward-dipping internal unconformities, taken to reflect individual glacial cycles of grounded ice erosion. The present-day shelf is overdeepened, landward dipping, and traversed by troughs. These features are characteristic of a shelf sculptured by grounded ice. The position of the transverse troughs, reflecting the positions of former icestreams, seems to have been more or less permanent since the late Neogene. The shelf progradation has been higher in front of the troughs than in front of adjacent banks, resulting in the development of trough-mouth fans (TMF). The strata continue seawards below the shelf break across a crustal monoclinal flexure to the deep sea. Three seismic sequences have been identified within the late Miocene and Pleistocene deep-sea sedimentary succession on the continental rise. They are bounded by unconformities of mid-Pliocene, early Pliocene, and (?) late Miocene ages. The oldest sequence is interpreted as basin floor fans, probably linked to a sea-level lowstand. The two youngest sequences were deposited from interplay of contour and turbidity currents during glacial periods, and they form large sediment ridges on the sea floor, oriented almost perpendicular to the continental rise, nucleated on the older sequence. Inter-ridge channel-levee complexes recognized within the youngest sequence were deposited from turbidity currents. The major turbidity channels are prolongations of the transverse shelf trough-trough-mouth fan systems. A moat zone, at the base of the continental slope, reflects the position of strong modern contour currents. Appreciable contourite deposition did not commence before the early Pliocene, and was probably linked to glaciation of the shelf and onset or intensification of the Labrador Sea Water deep current.
Recent geological processes in the Central Bransfield Basin (Western Antarctic Peninsula)
Authors: Ercilla G. , Baraza J. , Alonso B. , Canals M. 
Published: April 2008

Abstract
Acoustic character of the near-surface geological features in the Central Bransfield Basin, located between the northwestern Antarctic Peninsula and the South Shetland Islands, are products of recent sedimentary, volcanic and oceanographic processes. A platform, between 250 and 750 m water depth, is characterized by a highly rough surface with prolonged and hyperbolic reflections, which are interpreted as a result of ice-sheet grounding that occurred during the last glacial advance and iceberg scouring. Locally, this surface is draped by thin, stratified sediments deposited from suspension during the present interglacial stage. The upper slope shows prolonged and hyperbolic reflections without subbottom returns that form an irregular surface resembling slide scars and slumped material. Futher downslope, sediments become stratified, and individual, chaotic or semi-transparent slump masses occur locally, within the eroded valleys and in inter-valley areas. Basin sediments are defined by stratified, semi-transparent and chaotic deposits that correspond to a variety of mass-transport, volcanic and oceanographic processes. Mass-transport and volcanic processes develop slump masses, turbidite deposits and volcanic edifices of varying characteristics. The activity of slope-parallel bottom currents builds sediment drifts between the volcanic edifices and the base of the Antarctic Peninsula slope.
Late Glacial to Recent accumulation fluxes of sediments at the shelf edge and slope of NW Europe, 48–50°N
Authors: Hall I. R. , McCave I. N. 
Published: April 2008

Abstract

Data were collected on magnetic susceptibility, volcanic tephra abundance, coarse silt mean grain-size, and total and fine inorganic carbon for a suite of cores collected from the NW European Margin between 48 and 50°N. Age models were constructed based on accelerator mass spectrometry (AMS)
14
C dating and stratigraphy based on δ
18
O of foraminiferal carbonate together with correlatable instantaneous marker horizons of the Vedde Ash and the ‘Heinrich’ layers of ice-rafted detritus. Glacial vertical flux over the transect (2200–4500 m) on the open slope of Goban Spur yields an approximately 15 cm ka
−1
deposition rate. This decreases in the Holocene to a present deposition rate of between 3 and 6 cm ka
−1
. Deposition rates within the Porcupine Seabight are in close agreement with those seen at a similar depth on the open slope, whereas enhanced resuspension and sediment focusing leads to an approximate doubling in the depositional rate of hemipelagic sediment found near the base of King Arthur Canyon. Carbonate burial flux shows a maximum in the early part of isotope stage 2, during the deglaciation (17.5 ka to 12 ka) and in the late Holocene. This is seen at depths shallow enough to suggest it is not due to dissolution. It therefore could reflect enhanced productivity. Changes in current speed inferred from the sortable silt component of the sediment suggest slow currents during isotope stage 2 increasing irregularly through to a maximum just before the Younger Dryas, decreasing sharply in the early Holocene, then increasing again in the late Holocene. Rates of deposition at OM-2K follow this pattern fairly well for much of the time, suggesting lateral flux is important. However, during isotope stage 2 there is high flux of sediment with low current speed, suggesting supply from ice-rafting or directly downslope.
Recharge: the key to groundwater pollution and aquifer vulnerability
Authors: Robins N. S. 
Published: April 2008

Abstract
Recharge is pivotal to understanding the processes by which groundwater pollution can occur. It is implicit in the classification of aquifer units according to their vulnerability to pollution. The management of both groundwater resources and of individual groundwater sources cannot sensibly be undertaken without some knowledge of recharge: its quantity, its seasonality and, above all, the different routes through the sub-soil and the unsaturated zone by which it can occur. However, current estimates of recharge, other than on a research site basis, may be poor, both in the UK and overseas. This volume provides a review of current research into these issues; this introductory paper attempts to highlight the thread throughout all of this work which collectively provides the basic information in support of the current and future management of groundwater resources and sources.
Groundwater recharge and pollutant transport beneath wastewater irrigation: the case of León, Mexico
Authors: Chilton P. J. , Stuart M. E. , Escolero O. , Marks R. J. , González A. , Milne C. J. 
Published: April 2008

Abstract
Agricultural irrigation with wastewater is widely established in Mexico. The city of León is the centre of the Mexican tanning industry, and produces wastewater with a significant component of industrial effluent. The city is one of the fastest growing in Mexico and is highly dependent on groundwater for public supply. Much of this is drawn from aquifers around the city, including those beneath the wastewater area. The sources of recharge to these aquifers and the types of pollutants are reviewed. Regionally, groundwater levels are falling as a result of excessive groundwater abstraction but, within the area of wastewater irrigation, groundwater levels are maintained close to the ground surface. Groundwater sampling from existing boreholes, surface geophysics, soil sampling and the drilling of cored investigation boreholes have been able to characterize a body of shallow, polluted groundwater beneath the wastewater area, and contrast this with the regional groundwater quality. The most immediate threat to public supply from pollutants originating in the wastewater is posed by salinity. The predicted consequences of various management options for reducing the impact of wastewater on the quality of deeper groundwater are briefly discussed.
Recharge components in a semi-arid area: the Sana’a Basin, Yemen
Authors: Alderwish A. M. , Dottridge J. 
Published: April 2008

Abstract

Credible estimates of recharge are essential for assessment of sustainable water resources in semi-arid areas, which rely on groundwater for irrigation and domestic supply. Investigation of the mechanisms and rates of recharge to the aquifers of the Sana’a Basin, Yemen, showed that the main components of recharge are infiltration of surface flows, irrigation return and urban leakage. Limited data and inaccessible, mountainous terrain required the use of robust, low-cost methods of quantifying the recharge components. Infiltration of surface flows from 12 wadis averages 39 Mm
3
a
−1
, with high interannual variation. The recharge was calculated using a combination of a rainfall-run-off model and computation of the water balance for the wadi. Irrigation return flows of 30 Mm
3
a
−1
, 20 to 40% of the water applied, were derived from measurements of soil moisture and matric potential for the three most extensive crops. Urban recharge from mains leakage and seepage through septic tanks was estimated from a well inventory, water supply records and usage rates, as 59% of the water supplied. The total recharge to the aquifers of the Sana’a Basin in 1993 was estimated to be 102 Mm
3
, significantly less than the total groundwater abstraction, of about 184 Mm
3
.
Palaeozoic lithofacies correlatives and sequence stratigraphy of the Saharan Platform, Algeria
Authors: Fekirine B. , Abdallah H. 
Published: April 2008

Abstract
This paper attempts to unravel the interacting effects of eustacy, subsidence and sediment supply in controlling facies distributions in the Palaeozoic of the Algerian craton. These strata, particularly the Cambro-Ordovician section, contain no diagnostic index fossils, and the identification of sequence boundaries is therefore of paramount importance in defining a stratigraphic framework for the region. The wealth of outcrop and subsurface data in the Algerian Palaeozoic enables us to recognize six major sequences, the boundaries of which correspond to major events such as Taconic and Hercynian tectonism, the Ordovician glaciation and global-scale sea-level falls. Formations within these sequences exhibit thickness variations and lateral facies changes that are traceable and predictable in the subsurface. Unconformities of regional extent generally tie to significant facies changes and to inflection points on the global sea-level curve. These trends stem from the high sensitivity of this area, which was structurally stable over most of its Palaeozoic history, to eustatic sea-level fluctuations. The Cambro-Ordovician strata feature a high proportion of coarse clastic rocks, with subtle lateral and vertical facies variations, which were deposited within continental fluvial and shallow marine environments. The Silurian, Devonian and Early Carboniferous sequences show a typical pattern of marginal shallow marine sand belts, which migrate with changing sea-level and pass rapidly into deep marine shales, many of which are organic rich. The Upper Carboniferous strata consist of sediments deposited in continental and restricted basin settings, created as a result of tectonic movements heralding the Hercynian event. With respect to the occurrence of petroleum, the most important reservoirs are found in lowstand tracts in the Cambro-Ordovician and Siluro-Devonian sequences. Thick radioactive marine Silurian and Devonian black shales deposited during major transgressions provide both source and cap-rocks.
Sedimentological and diagenetic controls on Cambro-Ordovician reservoir quality in the southern Hassi Messaoud area (Saharan Platform, Algeria)
Authors: Djarnia Mohamed Robert , Fekirine Berrached 
Published: April 2008

Abstract
The Cambro-Ordovician reservoirs of the Hassi Messaoud area comprise quartzitic sandstones, which rest unconformably on granitic basement and are capped by the Hercynian unconformity. Two sequence stratigraphic cycles are identified: a lower cycle of lowstand, transgressive and highstand deposits, and an upper cycle in which only lowstand deposits are preserved below the Hercynian unconformity. Sandstone of the greates thickness and highest porosity and permeability occur within the lowstand deposits of the two sequences. Petrographic and scanning electron microscope studies were conducted in two wells in the southern Hassi Messaoud area on five sandstone units, to which the following chronostratigraphic terms are applied, from base to top: Ra + Ri lithozones (which contain the bulk of the reserves), Alternance Zone, El Atchane Sandstones and Hamra Quartzite. Reservoir quality is found to bear a strong relationship to clay content and mineralogy. All reservoirs are characterized by an extensive quartz cementation, which reduces porosities to generally below 10%. Permeability is related to clay content and type, with effective permeabilities generally limited to the quartz- and kaolinite-rich Ra lithozone. Permeability is lowest in reservoirs rich in fibrous illite and/or chlorite, such as the Hamra Quartzite. As porosity shows a less direct relationship to matrix mineralogy, there is a poor statistical relationship observed between porosity and permeability. Comparative diagenetic studies carried out within both the oil-bearing and the water-bearing parts of the reservoirs have determined that all the secondary processes occurred under freely operating diagenesis, pre-dating oil emplacement in the structure.
Tectonic controls on the petroleum geology of NE Africa
Authors: Keeley M. L. , Massoud M. S. 
Published: April 2008

Abstract
During the Palaeozoic and early Mesozoic, the NE sector of the African craton remained an entire, integral part of Gondwanaland. It experienced two episodes of intracratonic sagging and marginal cratonic rifting, linked to episodes of strike-slip affecting both the craton interior and its northern margins. Source kerogens accumulated during Palaeotethyan highstands within these sags, across which reservoir clastics prograded during the corresponding lowstands. Such source-reservoir associations are known from the Silurian, Devonian and Carboniferous. The fragmentation of the NE African margin with Mesotethys took place over the period Mid Triassic-Bathonian. From Palestine to Cyrenaica, a rift propagated westwards, detaching crustal terranes along shears that later formed Asia Minor. Deep marine shales within this rift have some proven oil-generating potential. However, the principal Jurassic oil kerogen is found associated with coal swamp-delta clastics, deposited during the Bathonian lowstand, in basins formed between the shears along the new cratonic edge. There is also now evidence for a Mid-Triassic rift penetrating the Sirt Basin from the northwest. Sinistral strike-slip associated with these Mesotethyan shears penetrated deeper into NE Africa during the Late Cretaceous, with subsidence reaching a maximum in the Jebel el Akhdar, Abu Gharadiq and proto-Clysmic Basins, in which rich oil-prone marine source rocks accumulated during the Turonian-Coniacian lowstand. Inversion followed, as the sense of strike-slip reversed with the onset of ‘Syrian Arc’ movements, starting in the latest Cretaceous, and proceeding as a series of pulses into the Late Oligocene. The final phase of ‘Syrian Arc’ tectonics was linked to the opening of the Red Sea and Gulf of Suez Basins, and transtension along the Gulf of Aqaba in the Early Miocene. Falling Miocene sea levels then permitted the accumulation of the restricted ‘Globigerina Marls’ facies within the active graben system of the Gulf of Suez.
Trap architecture of the Early Cretaceous Sarir Sandstone in the eastern Sirt Basin, Libya
Authors: Gras Rutger , Thusu Bindra 
Published: April 2008

Abstract
The Sarir Sandstone is the principal reservoir for oil accumulations in the eastern Sirt Basin in Libya. The main phase of the rifting in this area took place in the Late Jurassic-Early Cretaceous, during which time the Sarir Sandstone was deposited as a non-marine, intra-continental clastic syn-rift sequence. Although successfully explored from 1959 onwards, the prolific eastern Sirt Basin is in a relatively immature stage of exploration regarding wildcat drilling and 3D seismic data acquisition. The most recent phase of exploration, utilizing 3D seismic techniques, revealed a complex structural development. The trap geometries are often related to E-W trending, basement-controlled fault systems, oblique to the NNW-SSE Sirt Basin trend. The fault systems were active during the Sarir Sandstone deposition, giving rise to structural as well as well as combined structural-stratigraphic traps. An increased understanding of trap architecture has led to both re-evaluation of older fields and new discoveries. Complex structural traps exhibiting four-way dip or fault closures, and combined structural-stratigraphic traps, have been successfully explored in recent years, and will continue to provide exploration opportunities. The prospective areas comprise the faulted basin margins and the Sarir Sandstone depositional and erosional edges. Modern geophysical techniques including high-resolution 3D seismic data acquisition are critical in discovering and developing the remaining potential.
The exploration history and controls on hydrocarbon prospectivity in the Wessex basins, southern England, UK
Authors: Buchanan James G. 
Published: April 2008

Abstract
The Wessex basins were formed during Mesozoic extension and were subsequently modified by Cretaceous uplift and Alpine inversion events. The basin geometry and evolution of the area is strongly controlled by the long-lived fault systems which cross the area.
Two primary plays are recognized within the Wessex basins; the Triassic Sherwood Sandstone and the Jurassic Bridport Sandstone. These plays contribute the vast majority of the recoverable reserves in the area. The Triassic play consists of a Sherwood Sandstone Group reservoir, a Liassic mudstone source rock and a Mercia Mudstone Group regional seal. Hydrocarbons were generated from the Late Jurassic to Tertiary in the main kitchen area and migrated into a range of fault-related traps. The main risks on the play are reservoir quality together with the timing and the route of hydrocarbon migration into valid traps.
The Jurassic play consists of the Bridport Sandstone Formation which is also sourced from the Liassic mudstones and the top seal is provided by the Fuller’s Earth Formation. The dominant risk on this play is the extent and quality of reservoir facies. In the onshore domain trap definition, using two-dimensional seismic data, is an additional risk on both plays.
The basins of southern England have been explored for hydrocarbons for over 50 years. The initial phase of exploration focused on the onshore and tested anticlinal structures which had been mapped at surface. Onshore activity reached a peak in the successful drilling by British Gas of the Jurassic and Triassic reservoirs in the Wytch Farm Field in 1973 and 1977, respectively.
The first offshore well in the United Kingdom Continental Shelf (UKCS) was drilled off Lulworth Cove by BP in 1963. More recently, offshore exploration concentrated on fault-related traps within or on the edges of the Portland-Wight Basin. Although offshore activity has been reduced in the last 5 years, the 14th UKCS Licensing Round rekindled interest in the area as companies were awarded previously unlicensed acreage for exploration.
Successful future exploration in the Wessex basins will require a more complete understanding of reservoir development and three-dimensional basin evolution. Future drilling will focus on untested fault bounded prospects and stratigraphic traps with suitable reservoir quality.
The tectono-stratigraphic development and exploration history of the Weald and Wessex basins, Southern England, UK
Authors: Hawkes P. W. , Fraser A. J. , Einchcomb C. C. G. 
Published: April 2008

Abstract
Exploration drilling for hydrocarbons in southern England commenced over 50 years ago prompted by numerous seepages along the Dorset coast and gas shows in water boreholes. The two main depocentres, the Weald and Wessex basins, exhibit many similarities in both tectonic and stratigraphic evolution through Early Triassic-Tertiary times, reflecting the regional influences of Atlantic Margin rift-subsidence processes and subsequent Tertiary (Alpine) inversion tectonics. Given these similarities, the development of the hydrocarbon play system in both these areas can be compared using a common tectono-stratigraphic framework which has been identified and calibrated using well and seismic data. In detail, facies variability recognized within individual depositional units highlights differences in both source and reservoir distribution between the Weald and Wessex areas, which have in turn exerted fundamental controls on the hydrocarbon prospectivity of the two basins. These differences are influenced by the position of major basin-bounding fault systems and by the changing importance of the Cornubian-Armorican and the London-Brabant Massifs as clastic provenance areas through time. Sequence isopachs illustrate the same discrete episodes of rift-related subsidence in both areas. These rifting episodes led to the development of extensional trapping geometries particularly during Late Jurassic-Early Cretaceous times. Subsequent Late Cretaceous thermal subsidence led to the formation of mature source kitchen areas focused within the hanging walls of the earlier extensional faults. Hydrocarbon expulsion from the source kitchen areas ceased during Tertiary uplift and subsequent cooling. Inversion movements on the old extensional faults led to the development of hanging wall anticlines which rely upon remigration mechanisms, including exsolution of gas from uplifted Liassic source rocks, to receive hydrocarbon charge. To date over 300 million barrels of oil and 100 bcf of gas have been discovered.