bluuebunny/crossref_metadata_2025 huggingface dataset:
Cenozoic palaeogeography and the rise of modern biodiversity patterns
Authors: Crame J. A. , Rosen B. R.
Published: April 2008

The steepest latitudinal and longitudinal gradients in taxonomic diversity at the present day are those associated with tropical high diversity foci. Although there has been a tendency in the past to regard these features as either evolutionary ‘cradles’ or ‘museums’ of considerable antiquity, this may not be the case. Within the marine realm, a uniform, pan-tropical fauna was progressively disrupted by a series of plate tectonic events, the most important of which were the Early Miocene (
c.
20 Ma) collisions of Africa/Arabia with Europe and Australia/New Guinea with Indonesia, and the Middle Miocene-latest Pliocene rise of the Central American Isthmus. This had the net effect of establishing two main tropical high diversity foci: the Indo-West Pacific and the Atlantic-Caribbean-East Pacific. Similar foci were also established at the same time in the terrestrial realm.

Together with the physical isolation of Antarctica, these same tectonic events contributed significantly to global cooling throughout the Cenozoic Era. This in turn led to the imposition of a series of thermally defined provinces, and thus a considerable degree of biotic differentiation on a regional scale. However, something else seems to have been involved in the creation of very steep tropical diversity peaks. This could in part be a coincidental radiation of a series of unrelated taxa, or some sort of evolutionary feedback mechanism between interacting clades. Alternatively, Late Cenozoic rates of origination may have been enhanced by an external forcing mechanism such as changes in Orbital Range Dynamics.
Palaeontological databases for palaeobiogeography, palaeoecology and biodiversity: a question of scale
Authors: Markwick Paul J. , Lupia Richard
Published: April 2008

Computerized databases provide an essential tool for investigating large-scale spatial and temporal palaeontological problems. Although advances in both software and hardware have made the logistics of building a database much easier, fundamental problems remain concerning the representation and qualification of the data. Data from the fossil record are highly heterogeneous. Databases must be designed to account for variations in scale (grain, resolution), inconsistency in the data, and potential errors (inaccuracy). These issues vary with the scope of the study (extent), the biological group, and the nature and scale-dependence of supplementary, non-biological datasets (e.g. climate and ocean parameters). With the application of desktop geographic information systems (GIS) to global Earth systems science, and the ability to efficiently integrate and query large, diverse datasets, the need to ensure robust qualification of data, especially scale, has become all the more essential. This chapter examines some of the issues involved, defines terminology and offers pragmatic solutions.
Neotectonics on the Arabian Sea coasts
Authors: Vita-Finzi Claudio
Published: April 2008

The Holocene record on the coasts of the Arabian Sea provides information on the nature and rate of deformation generated by the interaction between the Indian, Arabian and Eurasian Plates. Holocene marine terraces show that the southern Makran has been subject to the infrequent but vigorous coseismic uplift (≤2 m) that characterizes other subduction settings and they indicate landward rotation of the imbricate faults among which shortening is distributed. The lack of significant Holocene deformation on the SE coast of the Arabian peninsula is consistent with its position parallel to a transform, although there is evidence for large-scale buckling driven by convergence at the Strait of Hormuz in the NE. Geomorphological and tide-gauge evidence for localized uplift on the southwestern coast of India may represent compressional buckling here too in response to Himalayan collision. Bathymetric and geodetic data can help to bridge these sequences and thus enhance their value for quantifying plate rheology and dynamics, notably by linking variations in plate-margin displacement with major sea-floor strike-slip structures and by eventually confirming transitory as well as sustained compressive buckling on land.
Gas hydrates acting as cap rock to fluid discharge in the Makran accretionary prism?
Authors: Delisle G. , Berner U.
Published: April 2008

We present a numerical model of the geothermal field of the Makran accretionary prism and of the slab being subducted below it. Calculated heat flow density values for the sea floor of the abyssal plain and the shelf slope are compared with
in situ
measured and bottom simulating reflector (BSR)-derived heat flow density values. The result suggests a predominance of conductive heat transport within the accretionary complex. Little evidence is found to suggest that fluid flow or frictional heat modifies the observed geothermal field to any great extent. We also studied the geothermal field associated with the decay of the potential gas hydrate layers (indicated by the presence of BSRs), as gas hydrate layers are being tectonically uplifted out of the gas hydrate stability field into shallower and warmer sea water. Theoretical considerations suggest a complete disappearance of gas hydrates at a water depth of about 750 m. The observed presence of numerous gas seeps almost exclusively at water depths of less than 800 m suggests that gas hydrate layers in the Makran accretionary prism act as a very effective cap rock to upward-directed flow of fluids containing notable amounts of dissolved gas from within the prism to the sea floor.
The geometry of structures in the Zagros cover rocks and its neotectonic implications
Authors: Sattarzadeh Yosef , Cosgrove John W. , Vita-Finzi Claudio
Published: April 2008

The Zagros Mountains are situated along the NE margin of the Arabian plate and are the product of complex deformation which began in Late Cretaceous time as a result of the collision between the Arabian and Central Iranian plates. During Pliocene time, deformation increased when plate convergence was accelerated by the opening of the Red Sea. This stimulated the migration of a deformation front from the collision zone towards the SW into the undisturbed Zagros basin and led to the creation of the Zagros Mountain Belt. The type and distribution of the deformation in the Zagros are controlled mainly by plate velocity, which is linked to the anticlockwise rotation of the Arabian plate around a pole in Syria, and the regional stratigraphy. The sedimentary cover and the underlying metamorphic basement decouple along an important detachment horizon, the Hormuz Salt Formation, and the uneven thickness and distribution of this salt plays a key role in determining the geometry of the deformation belt. Analysis of the distribution and geometry of the folds provides evidence for the southwestwards migration of the deformation front into the Arabian plate. The analyses are consistent with field evidence for serial folding, which indicates that each fold takes
c.
600 ka to develop fully, and with the model of a southwestward advancing deformation front driven by the processes of serial folding and footwall collapse.
Calcareous cyst-producing dinoflagellates: ecology and aspects of cyst preservation in a highly productive oceanic region
Authors: Wendler Ines , Zonneveld Karin A. F. , Willems Helmut
Published: April 2008

Absolute and relative abundances of calcareous dinoflagellate cyst species in surface sediment samples from the Arabian Sea are compared with environmental parameters of the upper 100 m of the water column to gain information on their largely unknown autecology. Ten species or morphotypes were encountered of which four occurred only as accessories. On the basis of the distribution patterns of the six more abundant species or morphotypes, the studied area is subdivided into three provinces, demonstrating a clear relationship to monsoon-controlled upper-ocean conditions. The two dominant species,
Thoracosphaera heimii
and
Orthopithonella granifera
, show opposite trends in distribution of both their absolute and relative abundances. In the NE Arabian Sea, low absolute and relative abundances of
T. heimii
are mainly attributed to enhanced dissolution of the small tests in this region, whereas elevated concentrations of
O. granifera
seem to be related to higher water temperatures and the influence of the Indus River.
Sphaerodinella albatrosiana
and
Calciodinellum operosum
are most abundant in the open ocean, associated with lower nutrient levels, relatively high temperatures and low seasonality. Spiny cysts (mainly represented by
Scrippsiella trochoidea
), in contrast, exhibit a more shelf-ward distribution and are most abundant in regions that are influenced by coastal upwelling, characterized by eutrophic and rather unstable conditions with seasonally lower temperatures and a shallow thermocline. A generally negative correlation of calcareous dinoflagellate cysts with primary productivity or high nutrient concentrations, as proposed by other workers, cannot be confirmed. Cyst accumulation rates off Somalia show that strong turbulence and high current speeds are unfavourable for calcareous dinoflagellates, suggesting that these organisms are more successful under rather stratified conditions.
Periodical breakdown of the Arabian Sea oxygen minimum zone caused by deep convective mixing
Authors: Reichart Gert Jan , Nortier Juriaan , Versteegh Gerard , Zachariasse Willem Jan
Published: April 2008

The northern Arabian Sea is at present characterized by a pronounced oxygen minimum zone (OMZ) with oxygen concentrations reaching values as low as 2 µM between 150 and 1250 m. This intense mid-water OMZ results from high annual organic particle fluxes and a moderate rate of thermocline ventilation. Sediment studies have shown that the intensity of the northern Arabian Sea OMZ has fluctuated on Milankovitch and sub-Milankovitch time scales, in conjunction with changes in either surface water productivity or thermocline ventilation. Here we evaluate the role of convective mixing in the periodical breakdown of the OMZ by reconstructing the density gradient for periods showing a well-ventilated water column. For this reason we reconstructed sea surface temperatures and salinities for the last 70 ka based on alkenone thermometry and δ
18
O analyses on planktic and benthic foraminifers. For the studied time span thermocline ventilation by intermediate water formation in the northern Arabian Sea is a viable mechanism to explain observed fluctuations in the intensity of the OMZ. We postulate that the necessary decrease in the vertical density gradient during well-ventilated periods resulted from intensified winter monsoonal winds in combination with effects caused by glacio-eustacy.
On the evolution of the oxygen minimum zone in the Arabian Sea during Holocene time and its relation to the South Asian monsoon
Authors: Staubwasser Michael , Dulski Peter
Published: April 2008

The evolution of the oxygen minimum zone within the permanent thermocline of the Arabian Sea (AS) during early and mid-Holocene time was reconstructed from a laminated sediment core taken from the Pakistani continental margin (316 m water depth). A trace metal proxy for water column ventilation (authigenic U) was extracted by principal component analysis from a large dataset of inorganic and total organic carbon (TOC) measurements. This proxy is compared with preservation of lamination and paired benthic-planktonic
14
C data. The latter record the Δ
14
C depth gradient in the AS and may provide a sensitive indicator for ventilation by enhanced surface convection. Laminated sediments were preserved between 10 and 7.5 ka bp on the Pakistani continental margin and accumulated authigenic U independently from TOC accumulation. The inferred reducing conditions in the AS thermoline are in agreement with high palaeoproductivity in the western AS upwelling region. Century-scale variability in northern AS surface hydrography (recorded as δ
18
O in planktonic foraminifera) is reflected in the accumulation of authigenic U on the Pakistani margin. The agreement of AS surface conditions, which generally reflect the South Asian monsoon (SAM), with ventilation of the OMZ confirms a dominant influence of the SAM and summer monsoon upwelling in particular on AS thermocline ventilation during early Holocene time. However, the preservation of laminated sediments off Pakistan and palaeoproductivity in the western AS disagree before 10 ka cal. bp, and between 7.5 and 5.5 cal. ka bp. Here, the absence of lamination indicates better ventilation of the thermocline, whereas palaeoproductivity in the upwelling region was high. This suggests that other factors may also have contributed in variable proportions to AS thermocline ventilation. At present, these factors include lateral advection of oxygenated Central Indian Water and ventilation by winter surface convection in the northern AS.
Present and past influence of the Iceland Plume on sedimentation
Authors: Jones Stephen M. , White Nicky , Clarke Benjamin J. , Rowley Eleanor , Gallagher Kerry
Published: April 2008

The Cenozoic development of the North Atlantic province has been dramatically influenced by the behaviour of the Iceland Plume, whose striking dominance is manifest by long-wavelength free-air gravity anomalies and by oceanic bathymetric anomalies. Here, we use these anomalies to estimate the amplitude and wavelength of present-day dynamic uplift associated with this plume. Maximum dynamic support in the North Atlantic is 1.5–2 km at Iceland itself. Most of Greenland is currently experiencing dynamic support of 0.5–1 km, whereas the NW European shelf is generally supported by <0.5 km. The proto-Iceland Plume had an equally dramatic effect on the Early Cenozoic palaeogeography of the North Atlantic margins, as we illustrate with a study of plume-related uplift, denudation and sedimentation on the continental shelf encompassing Britain and Ireland. We infer that during Paleocene time a hot subvertical sheet of asthenosphere welled up beneath an axis running from the Faroes through the Irish Sea towards Lundy, generating a welt of magmatic underplating of the crust which is known to exist beneath this axis. Transient and permanent uplift associated with this magmatic injection caused regional denudation, and consequently large amounts of clastic sediment have been shed into surrounding basins during Cenozoic time. Mass balance calculations indicate agreement between the volume of denuded material and the volume of Cenozoic sediments deposited offshore in the northern North Sea Basin and the Rockall Trough. The volume of material denuded from Britain and Ireland is probably insufficient to account for the sediment in the Faroe-Shetland Basin and an excess of sediment has been supplied to the Porcupine Basin. We emphasize the value of combining observations from both oceanic and continental realms to elucidate the evolution of the Iceland Plume through space and time.
Timing and mechanisms of North Atlantic Cenozoic uplift: evidence for mantle upwelling
Authors: Rohrman Max , van der Beek Peter A. , Van Der Hilst Rob D. , Reemst Paul
Published: April 2008

Postrift domal uplift patterns are a distinct feature of northern North Atlantic margins. On the basis of apatite fission-track data, offshore seismic stratigraphy, geomorphology, gravity and seismic tomography, we argue that southern Norway is characterized by predominantly Neogene domal uplift. The uplift is tectonically driven and estimated at around 1.5 km. Low flexural rigidity (
c
. 10
22
N m) and corresponding equivalent elastic thickness
T
e
(
c
. 15 km) values for the southern Norwegian lithosphere indicate that the lithosphere is relatively weak. Additionally, high temperature estimates derived from low-velocity mantle P- and S-wave seismic tomography below the dome suggest a thermal anomaly at depth. Therefore, the observed topography is most plausibly explained by mantle upwelling. This would supercede other previously proposed primary mechanisms such as eustasy, isostatic readjustment to glacial erosion, magmatic underplating and intraplate compression. Currently available data suggest similar processes for other uplifted regions such as Spitsbergen, northern Norway, the British Isles and parts of East Greenland.
Cenozoic inversion and uplift of southern Britain
Authors: Blundell Derek J.
Published: April 2008

Whereas significant exhumation of northern Britain took place during Paleocene time, probably as a consequence of uplift caused by a mantle plume, Paleogene basin inversion and uplift in southern Britain appears to be a consequence of Alpine tectonism. Recent publications demonstrate that inversion of Mesozoic basins across southern Britain was accompanied by subsidence of flanking basins in areas that had previously remained stable. Structures observed on seismic sections across the Weald Basin in SE England reveal that inversion occurred locally by north-directed reverse movements on pre-existing normal faults that cut down at a low angle deep into the basement. The overall effect of inversion of the Weald Basin, however, is a bulk deformation that produced a domal uplift, flanked by subsidence of the London and Hampshire-Dieppe basins. A 2D finite element thermomechanical model of continental lithosphere containing a region of reduced strength in the crust simulates Jurassic-Early Cretaceous extension to form the Weald Basin, followed by compression during the Tertiary to produce its inversion and the flanking basins. The timing of tectonic events across southern Britain correlates with times when Alpine stresses were transmitted into the foreland to the north sufficiently well to link them. Through most of Tertiary time, the landscape of southern England was of relatively low elevation and low-energy surface processes. However, late Neogene uplift, generally greater in the west, appears to have been part of a larger-scale uplift of land areas with hard rock at surface, which has no obvious tectonic explanation.
Neogene uplift and erosion of southern Scandinavia induced by the rise of the South Swedish Dome
Authors: Japsen Peter , Bidstrup Torben , Lidmar-Bergström Karna
Published: April 2008

Basin modelling and compaction studies based on sonic data from the Mesozoic succession in 68 Danish wells were used to estimate the amount of section missing due to late Cenozoic erosion. The missing section increases gradually towards the coasts of Norway and Sweden from zero in the North Sea to
c.
500 m in most of the Danish Basin, but over a narrow zone it reaches
c.
1000 m on the Skagerrak-Kattegat Platform in northernmost Denmark. The increasing amount of erosion matches the increase in the hiatus at the base of the Quaternary, where Neogene and older strata are truncated, and the Mesozoic succession is thus found to have been more deeply buried by c. 500 Paleocene-Miocene sediments in large parts of the area. These observations suggest that the onset of erosion occurred during the Neogene, and that the Skagerrak-Kattegat Platform was affected by tectonic movements prior to glacial erosion. In southern Sweden just east of the Kattegat, the exposed basement of the South Swedish Dome attains altitudes of almost 400 m. The formation of the Dome started in the Late Palaeozoic, but geomorphological investigations have led to the conclusion that a rise of the Dome occurred during the Cenozoic. We find that the pattern of late Cenozoic erosion in Denmark agrees with a Neogene uplift of the South Swedish Dome and of the Southern Scandes in Norway. This suggestion is consistent with major shifts in sediment transport directions during the late Cenozoic observed in the eastern North Sea, and with formation of a new erosion surface as well as re-exposure of sub-Cambrian and sub-Cretaceous surfaces in southern Sweden. The Neogene uplift and erosion of southern Scandinavia appears to have been initiated in two phases, an early phase of ?Miocene age and a better-constrained later phase that began in the Pliocene. Neogene uplift of the South Swedish Dome with adjoining areas in Denmark fits into a pattern of late Cenozoic vertical movements around the North Atlantic.
Cenozoic evolution of the Faroe Platform: comparing denudation and deposition
Authors: Andersen Morten Sparre , Sørensen Aage Bach , Boldreel Lars Ole , Nielsen Tove
Published: April 2008

Throughout Paleocene and Eocene time the Faroe-Shetland Channel and the eastern part of the Faroe Platform was a subsiding marine basin. In Early Paleocene time, basin-floor fans of a British provenance were deposited in the eastern part of the basin. In Late Paleocene time,
c.
6 km of basalt entered the basin from the west and north, and the basin was constricted by the large volumes of basalt that entered the basin, creating the Faroe-Shetland Escarpment. In Eocene time subsidence continued in the basinal areas. Again, sediments of a dominantly eastern provenance were deposited. Throughout Eocene time, erosion products from the Faroe Platform were possibly deposited in the Faroe Bank Channel and the Norwegian Sea Basin, but only to a limited degree in the Faroe-Shetland Channel. The oldest sediments of documented western provenance on the eastern margin of the Faroe Platform are of Early Oligocene age. During a compressional phase commencing in Mid-Late Miocene time some basinal areas emerged and erosion took place on the top of emerged anticlines. However, denudation throughout Late Miocene and Early Pliocene time was apparently rather limited compared with a Late Pliocene phase of denudation. During this phase of denudation, a large progradational wedge was deposited on the eastern margin of the Faroe Platform. On the basis of a structural analysis of the Faroe Platform, the amount of basalt removed from it during Cenozoic time is estimated to be
c.
46 000 km
3
(131 100 × 10
12
kg). Using 2900 kg m
−3
as the density of basalt and 2300 kg m
−3
as sediment density the estimated amount of removed basalt is in fair agreement with the estimate of the volume of sediments derived from the platform (
c.
56 000 km
3
, 114 800 × 10
12
kg). The greatest deposition rates on the eastern Faroe Platform and in the Faroe-Shetland Channel apparently occurred after two distinct inversion or compression events in Mid-Eocene and Mid-Late Miocene time. However, uplift of the Faroe Platform could have been forced by denudation rather than endogenous processes.
The post-Variscan thermal and denudational history of Ireland
Authors: Allen Philip A. , Bennett Stuart D. , Cunningham Michael J. M. , Carter Andy , Gallagher Kerry , Lazzaretti Eric , Galewsky Joseph , Densmore Alex L. , Phillips W. E. Adrian , Naylor David , Hach Cristina Solla
Published: April 2008

The thermal and denudational history of Ireland is evaluated using an extensive new apatite fission-track (AFT) dataset derived from surface samples. Modelled thermal histories are used to construct maps of denudation for a number of time slices from Triassic time to 10 Ma using a time-dependent palaeogeotherm. The maps illustrate the spatial variability of denudation and subsidence within each time slice. The patterns of denudation are complex, showing considerable variability at the length scale of 10
1
–10
2
km, with especially high denudation rates found over known igneous centres such as the Mournes of County Down. Based on the onshore AFT data alone, there is no definitive signature of an Irish Sea Dome extending significantly across Ireland in Early Tertiary time. The cumulative amount of denudation during Tertiary time varies depending on the AFT annealing model used, but is generally in the region between 1 and 2 km and without clear spatial trends. High amounts of denudation have been mapped over the Tertiary intrusions in County Down, reflecting their unroofing since emplacement in Paleocene time. The cumulative denudation from Triassic time to 10 Ma shows relatively low amounts of denudation (<2 km) in the Irish Midlands and the extreme NE of the island, consistent with the observation that Mesozoic-Tertiary sediments and igneous products are preserved in the Ulster Basin. The western flank of Ireland and the region between Dublin and County Down show high cumulative amounts of denudation (<4 km), the latter being consistent with the high amounts of denudation interpreted for the Irish Sea region. This denudation pattern explains in part the outcrop of Precambrian and Lower Palaeozoic rocks in these areas. The spatial integration of the denudation over the entire landmass gives the average denudation rate and the sediment discharge from Ireland as a function of time. Average denudation rates are moderately high in Triassic time, falling to low values in Cretaceous time, and increasing substantially in Tertiary time. However, the total volumetric discharge of sediment in Tertiary time is an order of magnitude smaller than the preserved solid volume of Tertiary sediment in the basins offshore western Ireland.
Diagenesis and fluid flow in response to uplift and exhumation
Authors: Parnell John
Published: April 2008

Uplift of sedimentary rocks is accompanied by a wide range of physical and chemical changes that contribute to diagenesis and modify fluid flow regimes. Topography becomes a major driving force behind fluid flow patterns, and meteoric water may penetrate to several kilometres below the surface. Typical diagenetic processes include alteration and leaching of feldspars and other unstable minerals, precipitation of iron oxides and kaolin, and leaching of carbonate and sulphate cements. Reservoired oil may be degraded by near-surface waters, but reservoir rocks may become more oil-wet.

Brittle fracturing is enhanced near the surface, and fluid flow may become predominantly fracture-bound as fractures dilate. Uplift also causes tilting of fluid contacts and remigration of hydrocarbons. Exsolution and expansion of gas similarly causes remigration of oil to peripheral traps.

Although basin uplift is generally regarded as being detrimental to hydrocarbon prospectivity, especially as a result of breaching of traps, there is also an enhanced potential for hydrocarbon plays based on reserves of exsolved gas, condensate dropout, peripheral traps and fractured reservoirs.
Uplift-related hydrocarbon accumulations: the release of natural gas from groundwater
Authors: Cramer Bernhard , Schlömer Stefan , Poelchau Harald S.
Published: April 2008

Vertical tectonic movements often change the structural style and physicochemical habitat of sedimentary basins. Changes in pressure, temperature and salinity of the groundwater caused by tectonic uplift may result in the release of previously dissolved gas. This process of gas exsolution from groundwater is shown to be an important mechanism in the formation of gas accumulations in uplifted basins. Two principal types of gas release are discussed. A hydrodynamic type is active when groundwater flows into areas of lower pressure or mixes with water of different temperature or salinity. It is anticipated that this effect is more of local importance, but over long periods of groundwater flow large volumes of gas may be exsolved. The hydrostatic type of gas release can occur in any sequence of sedimentary rocks where uplift causes a drop in pressure and temperature. This phenomenon may act basin-wide. Mass balance calculations show that the largest gas accumulations on Earth, such as the Urengoy field in West Siberia, could have been formed by this process.
Depressurization of hydrocarbon-bearing reservoirs in exhumed basin settings: evidence from Atlantic margin and borderland basins
Authors: Corcoran D. V. , Doré A. G.
Published: April 2008

Depressurization of reservoirs in petroliferous basins commonly occurs through cap-rocks at structural crests where pore pressures are locally elevated because of either the presence of a hydrocarbon column or the redistribution of overpressures by water flow along laterally extensive inclined permeable aquifers. In exhumed petroliferous basins this deflation of excess pore pressures is enhanced by the denudation process, which results in the large-scale removal of overburden during regional uplift. Evidence from the exhumed basins of the Atlantic margin indicates that hydrocarbon accumulations in these basins are commonly characterized by underfilled traps and hydrostatically pressured or modestly overpressured reservoirs. These observations are reviewed in the context of the generic mechanisms by which top-seals leak, the properties of cap-rocks and the physical processes that occur during exhumation.

Water-wet shaly cap-rocks can form a capillary seal to a hydrocarbon column while simultaneously accommodating brine flow and equilibration of pressures between the reservoir and the top-seal. In contrast, thick, low-permeability shale or evaporite sequences may form pressure seals that restrict vertical brine and hydrocarbon flow and prevent the equilibration of aquifer pressures above and below the seal. In any sedimentary basin, the presence of regional pressure seals can result in a layered hydrogeological regime with hydrostatically pressured strata decoupled from over- or underpressured cells. Recently exhumed basins typically show limited overpressuring and in a number of these basins underpressured reservoirs have been described. Post-exhumation overpressure generation is primarily driven by tectonic compression, aquathermal pressuring and hydraulic head.

The fluid retention capacity of any cap-rock lithology during exhumation is dependent upon the physical and mechanical characteristics of the cap-rock at the time of exhumation and the timing and conditions of the associated deformation relative to the timing of hydrocarbon emplacement. The permeability and deformational characteristics of halite render it an excellent cap-rock with a high retention capacity, even under conditions of exhumation. However, mudrocks may also form effective cap-rocks in exhumed basins when the deformation associated with exhumation occurs before embrittlement and the shale cap-rock exhibits ductile behaviour.

Shale and evaporite cap-rocks form the main regional seals to hydrocarbon accumulations in exhumed basins of the Atlantic margin and borderlands.
Syn-exhumation
top-seal efficiency (fluid retention capacity) is a major exploration risk in these basins, although
post-exhumation
top-seal integrity in these basins may be relatively high under certain conditions. Consequently, a major exploration risk factor in exhumed basin settings pertains to the limited hydrocarbon budget available post-regional uplift and the efficiency of the remigration process.
Continental margin off Norway 62–75°N: Palaeogene tectono-magmatic segmentation and sedimentation
Authors: Eldholm O. , Tsikalas F. , Faleide J. I.
Published: April 2008

The development of rifted and sheared segments on the Norwegian continental margin between 62 and 75°N is spatially related to a distinct along-margin segmentation which is governed by transfer zones formed during the Late Jurassic-Early Cretaceous rift episode. In fact, these structures may represent a repeated structural inheritance going back to the Proterozoic. Complete lithospheric breakup near the Paleocene-Eocene transition was preceded by a rift episode which was probably initiated in the early to middle Campanian. It culminated with a massive, regional magmatic event during breakup characterized by eruption of thick lava sequences covering large areas along the continent-ocean transition. The Norwegian volcanic margin belongs to the North Atlantic Large Igneous Province formed by impingement of the Iceland plume on a lithosphere under extension. Offsets in the initial plate boundary, combined with late rift uplift and subsequent construction of emerged marginal highs during breakup, provide key constraints on the Palaeogene water mass circulation, basin evolution and sedimentation during a period of progressive environmental deterioration following early Eocene greenhouse conditions.
Volcanic stratigraphy of the southern Prinsen af Wales Bjerge region, East Greenland
Authors: Hansen H. , Pedersen A. K. , Duncan R. A. , Bird D. K. , Brooks C. K. , Fawcett J. J. , Gittins J. , Gorton M. , O’Day P.
Published: April 2008

The volcanic succession in the inland Prinsen af Wales Bjerge contains the oldest known onshore lava flows (61 Ma) of the Palaeogene East Greenland flood basalt province. These flows and interbedded sediments define the Urbjerget Formation and are found in the southernmost part of Prinsen af Wales Bjerge. Flows of the Urbjerget Formation are chemically similar to the coastal Vandfaldsdalen Formation flows and the two formations may be chronostratigraphical equivalents. The Urbjerget Formation is overlain by the < 57 Ma tholeiitic basalts of the Milne Land Formation. Four regional volcanic formations are found along the Blosseville Kyst, but the Milne Land Formation is the only one present in the southern Prinsen af Wales Bjerge. Flows of the absent formations (Geikie Plateau, Rømer Fjord and Skrænterne formations) may not have been able to enter the area due to local uplift, more distal located eruption sites or possibly topographic features. A high-Si (SiO
2
> 52 wt%) lave flow succession in the Milne Land Formation consists of crustally contaminated magmas which were arrested in crustal chambers as the magma supply rate from the mantle decreased, either due to a general lowering of potential mantle temperatures or a decrease in the rate of continental rifting. Tholeiitic high-Ti flows (MgO: 10–15 wt%, TiO
2
: 5–6 wt%) within the Milne Land Formation are unique to the Prinsen af Wales Bjerge region, and equivalents have not been reported from other flood basalt provinces. Local flow composition variations in the Milne Land Formation can be explained as the result of melting under lithosphere of variable thickness, small-scale variations in mantle composition and mixing in small magma chambers. Unconformably overlying the Milne Land Formation is a succession of
c.
53 Ma alkaline flows, known as the Prinsen af Wales Bjerge Formation. Several crater sites are known from this flow succession and this suggests that the Prinsen af Wales Formation was only covered locally by later volcanic or sedimentary units. The duration of alkaline volcanic activity in the Prinsen af Wales Bjerge is not well constrained but may have been less than 2.5 Ma. The hiatus between the Urbjerget and Milne Land formations is a regional feature in the North Atlantic as it occurs at a similar stratigraphic level at Nansen Fjord, the Faroe Islands and in the ODP Leg 152 volcanic succession off SE Greenland at
c.
63°N. It represents a 3–4 Ma long cessation of, or very low frequency of activity in East Greenland/Faroese volcanism and may be explained as the time interval between two pulses in the palaeo-Icelandic plume.
The stratigraphy, environment of eruption and age of the Faroes Lava Group, NE Atlantic Ocean
Authors: Ellis David , Bell Brian R. , Jolley David W. , O’Callaghan Michelle
Published: April 2008

Palaeogene volcanism on the NW margin of the Faroe-Shetland Basin is represented by the Faroes Lava Group, within an age range of 57.5–60.56 Ma. The volcanic sequence comprises >1000 m of basaltic volcaniclastic rocks deposited in estuarine or marginal lagoons, overlain by three laterally-extensive formations of subaerial facies basaltic lavas: Lower,
c.
3250 m; Middle,
c.
1400 m; Upper, at least 900 m (top not preserved). The Lower and Upper formations comprise high-volume sheet flows, commonly with ferrallitized tops, interbedded with reddened, thin, fluvial claystone and basaltic siltstone deposits. Laterally-impersistent coals occur within the Lower Lava Formation. The Coal-bearing Formation (
c.
20 m) was deposited in an overbank floodplain environment during an hiatus in the volcanism between the Lower and Middle formations. The Volcaniclastic Sandstone Sequence comprises hydroclastic and pyroclastic deposits which post-date the Coal-bearing Formation and represent a return to volcanism, prior to the eruption of the Middle Lava Formation which is mainly characterized by inflated pahoehoe flows. The onshore sequence of the Faroes Lava Group can be correlated with basaltic flows within the Faroe-Shetland Basin, where lavas in Well 205/9-1 are interpreted to be of Lower Lava Formation affinity, possibly erupted from a local vent system. Seismic and gravity mapping and modelling suggest that the offshore extension of the Lower Lava Formation, together with the oldest part of the Middle Lava Formation, comprise subaqueous hyaloclastites deposited in a prograding Gilbert-type lava delta system. The youngest part of the Middle Lava Formation and all of the Upper Lava Formation occur as subaerial facies lavas within the basin.
Coalfield closure and environmental consequence — the case in south Nottinghamshire
Authors: Robins N. S. , Dumpleton S. , Walker J.
Published: April 2008

The strata within and above the South Nottinghamshire Coalfield dip gently towards the east. There are many abandoned shallow workings in the western area where the coalfield is exposed, but to the east the coalfield is concealed beneath Permo-Triassic strata. The coalfield has yet to suffer closure, mine water rebound and the acid mine drainage (AMD) cycle. A very large area has been exploited with complicated internal drainage systems dependent on the maintenance of existing pumping regimes. An evaluation of the AMD threat has been carried out with particular regard to the risk posed to the Sherwood Sandstone aquifer, which overlies the concealed part of the South Nottinghamshire Coalfield. The evaluation has been assisted by three-dimensional (3-D) visualization that has enabled lumping of plentiful mine abandonment data, and predictive runs using the University of Newcastle GRAM model. These studies indicate that the critical spill-over elevation is 41 m above Ordnance datum (aOD), and that the aquifer will be at risk about 20 years after pumping ceases from the Coal Measures.
The hydrogeochemical dynamics of mine pit lakes
Authors: Bowell R. J.
Published: April 2008

On cessation of mining open pits or opencast workings that extend below the water table are likely to fill with water and thus develop a mine pit lake (MPL). This body of water remains as a permanent feature on the mine site and as such becomes a closure issue with respect to water quality and potential to degrade groundwater. Further, it may present a risk to the environment through the development of poor quality water with elevated concentrations of metals, metalloids, sulphate and depressed pH.

The prediction of future pit lake water quality within a MPL is, therefore, essential in considering environmental impact on a closed or abandoned mine facility. The controls on a MPL will vary over time, and will involve chemical, biological and physical processes. Localized and regional-scale processes affect these in turn. Consequently, in order to predict pit lake water quality it is essential to understand the hydrogeological, geochemical and limnological processes that influence water quality.
Secondary minerals in the abandoned mines of Nenthead, Cumbria as sinks for pollutant metals
Authors: Nuttall C. A. , Younger P. L.
Published: April 2008

Direct observations made during underground hydrogeochemical surveys of abandoned lead-zinc mines has highlighted the precipitation of secondary zinc minerals within abandoned lead-zinc mine workings in the north Pennines. Chemical analysis of mine waters has shown that molar concentrations of sulphate exceed those of zinc by two or three orders of magnitude, although they are released in equimolar proportions following the weathering of sphalerite. The excess of sulphate over zinc indicates that there must be significant sinks for zinc within the mine workings. Secondary zinc mineral sinks (principally hydrozincite and smithsonite) are the most likely explanation for the deficit in molar zinc concentrations and these minerals have been identified underground. In addition to the secondary zinc minerals, secondary calcite and aragonite from the workings have also been shown to provide sinks for zinc (by coprecipitation and solid-solution incorporation of zinc in these minerals). Calculation of the molar quantities of zinc and sulphate involved showed that as little as 5% of the zinc, weathered daily from the mineral deposits within the workings, is found to leave the mine dissolved in the mine water. However, this is sufficient to adversely impact the ecology of the receiving waters of the River Nent, which currently receives five circumneutral zinc-rich mine water discharges and drainage from a disused aqueduct.
Integrated hydraulic-hydrogeochemical assessment of flooded deep mine voids by test pumping at the Deerplay (Lancashire) and Frances (Fife) Collieries
Authors: Nuttall C. A. , Adams R. , Younger P. L.
Published: April 2008

To provide the basis for the design of two Coal Authority mine water management schemes, IMC Consulting Engineers (IMC) carried out step-drawdown pumping tests at the Deerplay (Lancashire) and Frances (Fife) abandoned collieries in the summer of 2000. Supplementary hydrochemical investigations were funded by NERC and undertaken by the University of Newcastle and Queen’s University Belfast (QUB).

The results of the step-drawdown tests can only be interpreted by invoking a substantial component of turbulent flow in large open voids. Overall, the Deerplay system behaves in a manner analogous to natural aquifers, lending itself to modelling (using VSS-NET) to obtain effective hydraulic parameters that may be applicable in similar systems of flooded bord-and-pillar workings elsewhere.

The hydrochemical results for both sites showed some similarities, for example there was evidence of depth stratification of water quality in both cases, but also contrasts. For instance, although the total iron in the mine water pumped from the Deerplay Colliery rose gradually to a plateau at around 30 mg 1
−1
, the water remained net-alkaline throughout the test. By contrast, not only did the total iron in the Frances waters rise in abrupt steps to as much as 600 mg 1
−1
, but the water also switched from being net-alkaline at the beginning of the test to become strongly net-acidic by the end.
The structure of the upper mantle beneath southern Africa
Authors: Priestley Keith , McKenzie Dan
Published: April 2008

A large number of velocity models derived from a variety of seismic data and using different seismic techniques have been published for the Archaean and Proterozoic shields. Here, we focus on the structure beneath southern Africa, where velocity models derived from most regional seismic data find the thickness of the seismic lithosphere to be less than 200 km. In contrast, velocity models derived from teleseismic body-wave and long-period surface-wave data determine the seismic lithosphere to be as much as 400 km thick. We believe that this disagreement is due to the ways in which the various datasets average the velocity structure. Our analysis of regional seismograms from propagation paths largely confined to the stable region shows that the average thickness of the seismic lithosphere beneath southern Africa does not exceed 160 km. We compare the vertical S-wave travel time of our velocity model derived from regional seismic data and those models derived from teleseismic data and find no significant difference. We determine the
in situ
velocities and densities from nodules from beneath southern Africa using a recently derived geobarometer and geothermometer; these are in excellent agreement with the velocity found in the high-velocity lid from the analysis of the regional seismic data. The lithospheric model that best fits the nodule data has a mechanical boundary layer thickness of 156 km and a lithosphere thickness of 176 km. However, the shear-wave velocity decrease at the base of the lid does not correspond to a change in mineralogy. Recent experimental studies of the shearwave velocity in olivine as a function of temperature and period of oscillation demonstrate that this decrease can result from grain boundary relaxation at high temperatures at the period of seismic waves. This decrease in velocity occurs where the mantle temperature is closest to the melting temperature.
Formation and early evolution of the atmosphere
Authors: Marty Bernard , Dauphas Nicolas
Published: April 2008

The tectonic activity of the Earth allowed exchange of volatile elements (H, C, N, rare gases) between the surface of the Earth (atmosphere, crust, sediments, oceans) and the mantle. However, some of these elements still present elemental and isotopic heterogeneities that allow us to reconstruct the volatile composition of the terrestrial mantle. The protosolar nebula supplied a significant fraction of helium and neon, which were presumably trapped during the major phase of the Earth’s accretion and were possibly hosted by accreting dust and/or small porous planetesimals. Surprisingly, volatile elements are in chondritic proportion despite their drastic (10
−3
) depletion in the mantle relative to chondrites, in a way that recalls the case of highly siderophile elements. From stable isotope systematics, we find that the contribution of comets to the volatile inventory of the Earth was very limited. The integrated flux of chondritic-like material necessary to provide water, carbon and nitrogen is consistent with that required for the formation of the lunar craters as well as that necessary to account for the inventory of siderophile elements in the mantle. A consequence of this scenario is that the Earth’s surface was oxidized very early. Alternatively, volatile and siderophile elements of the mantle could be the remnant of small patches of chondritic material that did not equilibrate with the core nor drastically degas.