bluuebunny/crossref_metadata_2025_split huggingface dataset:
Silurian graptolites from Serbia, Yugoslavia
Authors: Pavlović Milena Mihajlović 
Published: April 2008

Summary
Eastern Serbia has black graptolitic shale from early Llandovery to early Devonian times. Tectonic disturbances prevent examination of a continuous sequence, but twenty-four zones have been established with 175 species and subspecies identified. Serbian graptolites and sediments compare well with those in Bulgaria and with the Carpathian-Balkanic Arch in particular, and in general with successions in the Alpine structural province. Closest comparisons can be made with the Bohemian assemblages.
Evidence for changes in Mesozoic and Cenozoic oceanic circulation on the south-western continental margin of Ireland: DSDP/IPOD Leg 80
Authors: de Graciansky P. C. , Wylie Poag C. , Hailwood E. A. , Knox R. W. O’B. , Masson D. G. , Montadert L. , Ravenne C. , Müller C. , Sibuet J. C. , Sigal J. , Snyder S. W. , Waples D. W. , Cunningham R. 
Published: April 2008

Summary

A transect of four coreholes, drilled by the
Glomar Challenger
across the Irish continental margin at the Goban Spur, evidences a dynamic palaeoceanographic regime during the late Mesozoic and Cenozoic. Shallow marine waters invaded the rift-stage grabens of the Goban Spur in the early Barremian. Thereafter, the margin subsided rapidly, producing a pelagic depositional regime by late Barremian time. Deep marine conditions were maintained as sea-floor spreading began in the early Albian, and chiefly pelagic deposition continued to the present.

Among a series of significant post-rift oceanographic changes, one of the most notable is the familiar fluctuation of oxic and anoxic sea-floor environments during the Cenomanian and Turonian. Another marked change took place during the late Palaeocene, when cooler, oxygen-rich, northern bottom waters reached the Goban Spur as a consequence of rifting and sea-floor spreading between Greenland, Rockall Plateau, and Norway. Later during the Cenozoic, the initial production of Antarctic bottom water, several accelerations of polar icecap growth, and fluctuating eustatic sea-level produced a variety of circulatory shifts on the Goban Spur. A particularly significant sedimentological consequence of these interacting processes was the widespread creation of numerous erosional and non-depositional unconformities.
Late Cretaceous anoxic events, sea-level changes and the evolution of the planktonic foraminifera
Authors: Hart Malcolm B. , Ball Kim C. 
Published: April 2008

Summary
This paper investigates the relationship, if any exists, between the evolution of the planktonic foraminifera and the presence of anoxic water masses in the water column. The relationship with changes in sea-level over the expanded Cretaceous shelves is also discussed. New data from DSDP Legs 80 and 95, coupled with that from southern England, north-east England and the North Sea Basin will be used to assess the evolution of the microfauna.
Role of climate in affecting late Jurassic and early Cretaceous sedimentation in the North Atlantic
Authors: Hallam A. 
Published: April 2008

Summary
Both regional and temporal changes in the influx of terrestrial organic matter, siliciclastic sediments and kaolinite are related to climate over the continents adjacent to the opening North Atlantic, reflecting a change from humid to arid and back to humid in North America and Europe, and more persistent aridity in Africa. Small-scale sedimentary cycles of laminated organic-rich and non-laminated organic-poor claystones have previously been interpreted in terms either of periodic influx of detrital plant material, or variations in sedimentation rate. They are here interpreted as the result of periodic stirring of bottom waters related possibly to Milankovich cycles.
Organic geochemistry of Cretaceous organic-carbon-rich shales and limestones from the western North Atlantic Ocean
Authors: Meyers Philip A. , Dunham Keith W. , Dunham Pamela L. 
Published: April 2008

Summary
Organic-carbon-rich black shales are found in Cretaceous sedimentary settings on the North American outer continental rise. Comparison of carbon isotope and molecular biomarker compositions of black shales with adjacent lithologies gives evidence of enhanced preservation of marine organic matter in the darker layers. In middle Cretaceous sequences, the black shales represent short episodes of exceptional preservation of organic materials within an oxygenated, deep-ocean depositional setting. Neocomian black shales show poorer preservation and were deposited within turbiditic carbonates and sandstones, containing large proportions of land-derived organic matter.
The inorganic geochemistry of Cretaceous black shales (DSDP Leg 41) in comparison to modern upwelling sediments from the Gulf of California
Authors: Brumsack Hans J. 
Published: April 2008

Summary
Recent trace element data for sea water and plankton reflect the importance of biological activity for the distribution of these elements in the water column and for their accumulation in sediments underlying areas of high productivity. Many trace metals in sea water are highly correlated to nutrients like phosphate, nitrate, or silica. By considering the ability of an element to be involved in nutrient cycling, as demonstrated by its deep/surface sea water concentration ratio, and its availability in sea water, a relationship between plankton and sea water chemistry is evident.
Fifty sediment samples from the Gulf of California, an area of exceptionally high primary productivity, have been analysed for all major and 15 minor elements, including Cd, Zn, Cu, Ni, Ba, Se, Cr, As, V, Mo, Co, Pb, Tl, and Bi. The ‘excess’ of nutrient and trace elements in upwelling sediments from the Gulf of California reflects the plankton chemistry. Among those elements found enriched in the diatomaceous oozes from the Guaymas Basin Slope relative to average shale are P, S, Mo, Se, Cd, and possibly Bi. For Mo and V an additional accumulation process besides bioconcentration seems to be active during early diagenesis. For these two elements their concentration ratios to aluminum increase with burial depth in the upper 30 cm of the sedimentary column, indicating that sea water seems to be a major source, besides plankton.
The chemistry of Ba in pore-waters and solids is controlled by barite solubility. A front of barite precipitation and dissolution (the ‘barite front’) is moving through the sedimentary column in the depth range of near zero pore-water sulphate, which at a drastic reduction of the sediment accumulation rate would lead to the formation of larger barite crystals or even nodules in this depth range.
Cretaceous black shales from the Cape Verde Basin (Site 367, Cores 17 to 21) are characterized by extremely high (see maximum values in brackets) concentrations of Mo (280 p.p.m.), V (3600 p.p.m.), Zn (7000 p.p.m.), and a number of other trace elements, besides S (7.4%) and organic carbon (35.6%) which cannot be explained by upwelling. If these enrichments are of primary origin, then complete stagnation of the Cape Verde Basin during intervals in Cretaceous time seems likely. The marine environment is metal-poor, therefore stagnation and corresponding low accumulation rates of detrital material would favour the accumulation of organic carbon and trace metals.
Palaeozoic Prospects on the Northern Flanks of the London-Brabant Massif
Authors: Tubb S. R. , Soulsby A. , Lawrence S. R. 
Published: April 2008

Summary
Seismic data across the northern flank of the London-Brabant Massif, between the United Kingdom and the Netherlands, have highlighted some interesting exploration leads in the sub-Permian section. Carboniferous sediments have been affected by low-amplitude Hercynian folding, Mesozoic rift faulting and Cretaceous inversion-related compression and fault re-activation. These effects have created a variety of trap situations in potential Palaeozoic reservoir units. In addition to early Permian Rotliegende sandstones, potential reservoirs are formed by late Carboniferous Barren Measures and Millstone Grit sandstones, Carboniferous Limestone carbonates, and basal or pre-Carboniferous clastics. Also Carboniferous Limestone ‘reef’ developments have been tentatively identified along a paleo hinge-line. A significant stratigraphic break is identified near the base of the Barren Measures in the late Carboniferous which has been designated the ‘Symon Unconformity’. The unconformity and depositional patterns within the Barren Measures are explained by the effect of lateral heat flow on normal basin development in the late Carboniferous. An analysis of well log data has demonstrated that Barren Measures’ sandstones constitute a good reservoir objective. Reservoir quality and sand thickness/frequency increase towards the flanks of the London-Brabant Massif.
Westphalian A and B coals subcrop the Symon Unconformity, and together with the Millstone Grit, onlap the Carboniferous Limestone surface on the flanks of the London-Brabant Massif. The coals constitute a proven commercial gas source which is in direct contact with the recognised potential reservoirs. Maturation studies, based on geochemical analysis, demonstrate that gas-generative maturity is largely dependent on Jurassic burial. The source/migration/entrapment model suggests that conditions have been favourable for gas accumulation in Palaeozoic reservoirs contained within rift-related fault-blocks and more subtle stratigraphic traps.
Gas Prospects in the ‘Midland Valley’ of Northern Ireland
Authors: Illing L. V. , Griffith A. E. 
Published: April 2008

Summary
A substantial sedimentary basin in southeast Co. Antrim is indicated by gravity measurements and has been explored by the Larne-2 geothermal test well which encountered 9395 ft of Permo-Triassic sediments without reaching their base. Porous sandstones near the top of the Sherwood Sandstone occur beneath thick impervious halite horizons in the Mercia Mudstone. Further potential reservoir rocks occur in Lower Permian sandstones below a 370 ft thick Zechstein salt at a depth of about 6000 ft. Potential traps in the form of tilted fault blocks have been indicated by reconnaissance Vibroseis. Suitable source rocks, the remaining essential ingredient for a petroleum prospect, are expected but have yet to be proved.
A similar Permo-Triassic basin is indicated by gravity beneath Lough Neagh. Although covered by thick Tertiary basalts and Lough Neagh Clay, its western margin has been successfully mapped by reconnaissance Vibroseis. The Permo-Triassic here is thinner and is without salt. However, the underlying Carboniferous contains Westphalian and Namurian coals, and geochemical studies confirm their potential to produce gas where suitably buried. There is a good chance that similar Carboniferous strata with coals underlie the Permo-Trias of the Larne Basin of southeast Antrim and provide the source rock for an important gas province.
The Geology of the Rough Gas Field
Authors: Goodchild M. W. , Bryant P. 
Published: April 2008

Summary
The Rough Gas Field was discovered in 1968. It lies in the United Kingdom Continental Shelf blocks 47/3d and 47/8b and produces from the Permian Rotliegendes sandstone in a faulted anticlinal structure. Initial reserves were 384 BCF. The field was on production until 1980 when the British Gas Corporation began developing Rough as a gas storage facility to meet peak season demand in the mid to late 1980’s. Three main facies associations are recognised from core studies of the Rotliegendes reservoir; aeolian sands, proximal fluvial sands and conglomerates, and distal sheet flood sands. The vertical arrangement of these associations within the Rotliegendes sequence define three sedimentary units which represent semi-arid alluvial fan progradation and abandonment. These units can also be recognised on electric-logs and can be correlated across the field. Reservoir porosity and permeability is largely controlled by the texture and mineralogy of the sedimentary facies, with a concomitant diagenetic influence. The geological model of facies distribution and trends in reservoir quality, together with well test data, has been used to optimise future development locations and update reservoir simulation of field behaviour in the storage mode.
Reservoir Geology of the Sean North and South Gas Fields, U.K. Southern North Sea
Authors: ten Have A. , Hillier A. 
Published: April 2008

Summary
Sean North and South, discovered in 1969 and appraised in 1982, are two separate gas reservoirs some 15 km southeast of the Indefatigable field. Located in block 49/25a, they are owned equally by Shell/Esso/Britoil/Union Texas.
The fields are northwest-southeast trending anticlinal structures, separated by a transcurrent fault. The two accumulations, which are mostly fault-bounded, have different gas/water contacts. The Permian Rotliegend reservoir occurs at a depth of around 8300 ft (2500 m) and varies in thickness between 200–265 ft (60–80 m). The reservoir rock consists of aeolian dune sandstones with excellent reservoir properties.
Development drilling started early 1985 from two platforms. Combined recoverable gas reserves are in the order of 425 BCF. First gas is expected to come ashore in October 1986.
Seismic reflections from the lower crust around Britain
Authors: Matthews D. H. 
Published: April 2008

Summary

A cartoon is presented which represents a time-section typical of the first 3000 km of BIRPS profiling over the continental shelf north, west and south of Britain. It shows a Mesozoic sedimentary basin in the hanging wall of a low-angle normal fault zone. The dipping fault reflection merges with layering in the lower crust which appears as several strong but short (
c.
4 km) horizontal reflections between about 6 s two-way travel time and the base of the crust at about 10 s. The uppermost mantle is devoid of reflections except where dipping events extend from the layered lower crust towards the base of the section at 15 s two-way time. The cartoon is justified by reference to examples from profiles.

Discussion states present hypotheses that are being tested. The layering in the lower crust is real and due to lenses of flat-lying foliation about 4 km across and tens of metres in thickness in which the seismic velocity has been reduced by the presence of fluids. Brine has been suggested to account for the electrical conductivity of the lower crust, and carbon dioxide may be associated with granulites. The geometry implies that the lower crust was ductile at the time of faulting, and that the foliation became horizontal during Mesozoic stretching of West Europe.
Petrology and geochemistry of the lower continental crust: an overview
Authors: Kay R. W. , Kay S. M. 
Published: April 2008

Summary
Continental lower crust comes in a limited number of types that are best distinguished tectonically. Lower crust is formed primarily in oceanic or continental zones of lithospheric plate convergence and secondarily in regions of intracontinental rifting. Formation processes involve magmatic intrusion of mantle-derived basalt and structural burial of pre-existing upper crust by thrust or reverse faults. In both cases, metamorphism, crustal melting and ductile deformation result from the accompanying heating and release of volatiles. A compositional conundrum exists for both arcs and continental rifts since the new continental crust has a basaltic rather than an andesitic (mean crustal) composition. Possible solutions to this compositional disparity include formation of more silicic lower crust in the Archaean, and lower crustal delamination which could preferentially remove tectonically immature basaltic crust.
Petrogenesis of layered gabbros and ultramafic rocks from Val Sesia, the Ivrea Zone, NW Italy: trace element and isotope geochemistry
Authors: Pin C. , Sills J. D. 
Published: April 2008

Summary
Layered gabbros and ultramafics, well exposed in Val Sesia, have been interpreted as a layered complex. The lower part (LLG; up to 1 km thick) comprises well layered pyroxenites and gabbros with minor peridotite and harzburgite. The upper part consists of fairly homogeneous gabbros (MG), which grade into diorite (up to 5.5 km thick). This gabbro body intrudes already highly deformed metapelites, but is itself relatively undeformed.

These two groups (LLG and MG-diorite) are distinct on the basis of isotope, trace element and major element chemistry and cannot have been derived from the same liquid. The LLG has ɛ
Nd
ranging from +1.5 to +2.5 and ɛ
Sr
from +7 to −8 and was derived from a depleted source. The MG-diorite body has ɛ
Sr
ranging from +40 to +60 and a wide range of ɛ
Nd
from −2 to −6.

The LLG pyroxenites and gabbros are dominantly cumulates of clinopyroxene with lesser amounts of orthopyroxene. Cumulus plagioclase appears towards the top of the LLG. The LLG is strongly depleted in LREE and LIL elements and was derived from a basaltic liquid with relatively depleted trace element characteristics. It probably fractionated at moderate pressures and was emplaced into the Ivrea Zone along with the adjacent Balmuccia peridotite.

The MG comprises plagioclase ± olivine cumulates with minor cumulus apatite, ilmenite and pyroxene. The diorites additionally contain cumulus biotite. The whole body has strongly LREE-enriched patterns (Ce
N
4.5–20) and large positive Eu anomalies (Eu/Eu* from 2–12). The MG has calc-alkaline features with high Ba and low Nb. The parental magma was also LREE-enriched, with low Ni, Cr and MgO and high Ba. It was possibly an andesite.

The spread in ɛ
Nd
cannot be accounted for by contamination by any of the likely crustal contaminants. The spread in intial isotope ratios either results from a heterogeneous enriched mantle source or from a two stage process involving remelting of an intermediate mafic reservoir with moderate enrichment in Rb and LREE.

The MG-diorite body was emplaced into sediments already undergoing amphibolite-facies metamorphism at pressures of 5–7 kbar. It appears as if the development of magma chambers in the crust was an important process of crustal growth in the Ivrea Zone.
Geochemistry of granulite-facies lower crustal xenoliths: implications for the geological history of the lower continental crust below the Eifel, West Germany
Authors: Stosch H.-G. , Lugmair G. W. , Seck H.A. 
Published: April 2008

Summary

Mafic meta-igneous granulite facies xenoliths from Engeln/Eifel display petrographic, chemical and isotopic features which are not easily understood in terms of igneous fractionation or granulite-facies metamorphism. These features are best explained through a metasomatic modification of many of the xenoliths, characterized by the formation of amphibole and increasing Rb/Sr and Nd/Sm ratios as well as shifts in
143
Nd/
144
Nd towards values similar to those of enriched mantle under the Eifel. Granulites which essentially escaped metasomatism have a Sm-Nd depleted mantle model age of ∼1.6 Ga whereas metasomatically altered granulites have younger and highly variable model ages. A Sm-Nd isochron for minerals from one granulite resulted in an unexpectedly young age of 172 ± 5 Ma which can be regarded as the maximum age of metasomatism. This age may be indicative of a thermal event having affected the lower crust under the Eifel during the Mesozoic.
Mineral reactions in xenoliths from the Colorado Plateau; implications for lower crustal conditions and fluid composition
Authors: Broadhurst J. R. 
Published: April 2008

Summary

A study of lower crust and upper mantle xenoliths from Moses Rock Diatreme, Utah, has led to the discovery of evidence for low temperature/high pressure,
in situ
hydration of pyroxene and garnet granulites in isolated parts of the lower crust of the Colorado Plateau; one of the characteristic reactions being: Plagioclase→Zoisite+Paragonite+Quartz+Albite This was followed by a second hydration at lower temperature and pressure, under more oxidizing conditions, probably associated with the incorporation of the xenoliths into the diatreme. Under these conditions, pyroxenes were replaced by fibrous amphiboles and the plagioclases were rimmed by chlorite and epidote. Upper mantle xenoliths show similar histories of cooling and hydration. The origin of the cold hydrating fluid is linked to the presence of low T/high P group ‘C’ eclogites in the suite, xenoliths which may represent relics of a subducted/underplated fragment of the Farollan plate.
Relationships between major structures, salic volcanism and sedimentation in the Kenya Rift from the equator northwards to Lake Turkana
Authors: Williams L. A. J. , Chapman G. R. 
Published: April 2008

Summary
At the equator, the Kenya (Gregory) Rift Valley is a half-graben, faulted on the eastern side. It passes northwards into a deep graben with a double western margin, and then into what is essentially a downwarped depression. The deep graben sector (0°15′–1°00′N) is virtually devoid of late Miocene-Quaternary trachytic central volcanoes: their counterparts in areas of strong faulting are salic flood lavas. Moreover, the scarcity of pyroclastics in early-late Miocene ‘plateau’ phonolite sequences of the deep graben suggests that the thick tabular lava units are some distance from source. The phonolites exposed on the western side of the rift (Kamasia-Uasin Gishu) probably came from eruptive centres beyond the deep graben, whereas on the eastern side (Laikipia) a substantial part of the sequence could well belong to a lava shield on the plateau. In contrast to intra-volcanic pyroclastic sediments that occur predominantly N of latitude 1°N, the formations in the Kamasia region consist of waterlaid deposits intercalated with tabular lava flows. This spectacular development of waterlaid sediments is attributable to the absence of major eruptive centres and the existence of tectonic-geomorphic sediment traps in the deep graben sector of the rift.
Depth to metamorphic basement in the Koobi Fora region from seismic and gravity data
Authors: Swain C. J. , Skinner N. J. , Khan M. A. 
Published: April 2008

Summary
A detailed 2.3 km long seismic refraction line near Koobi Fora shows velocities increasing continuously with depth, apart from a 100 m thick low-velocity layer whose top lies at a depth varying from 100 to 250 m. This is thought to be a lacustrine sequence. Total thickness of rocks overlying basement is 1200–1300 m. Interpretations of four shorter profiles in this area are also presented, one of which indicates basement at only 40 m depth. These data are used to control the interpretation of part of the Bouguer gravity map of the region in terms of an upfaulted basement block partly coinciding with the Kokoi horst.