bluuebunny/crossref_metadata_2025 huggingface dataset:
Monitoring sediment infilling at the Ship Creek Reservoir, Fort Richardson, Alaska, using GPR
Authors: Hunter Lewis E. , Ferrick Michael G. , Collins Charles M.
Published: April 2008

The Ship Creek Reservoir serves as the municipal water supply for Fort Richardson, Elmendorf Air Force Base, and Anchorage, the largest city in Alaska. The reservoir is located at the base of a ∼4.8 km-long canyon along the flanks of the Chugach Mountains, where it is fed by a 234 km
2
unglaciated drainage basin. High sediment production within the watershed results in rapid infilling of the reservoir and a need for periodic dredging. During March 2001, we conducted a ground penetrating radar (GPR) survey of the reservoir to document the current state of sedimentation and to evaluate sediment trap designs. These data are presented here as a case study in which the utility of GPR for evaluating sediment infilling in a shallow reservoir is evaluated

The survey was conducted from a 45 cm-thick ice cover in the lower reservoir that thinned to about 6 cm at a distance of 220 m above the dam. A total of 49 radar profiles were collected from the ice cover and an additional 10 profiles were collected on a gravel bar in the upper parts of the reservoir. Water depth near the dam was about 6 m and sediment in that reach forms a blanket deposit. More hummocky and asymmetric bed topography was found away from the dam, apparently controlled by palaeochannel geometry and bedrock sills. GPR profiles collected on the gravel bar document a sedimentary wedge that thickens downvalley and toward the southern edge of the reservoir, apparently the palaeothalweg of Ship Creek. Transverse profiles across the bar indicate that an average of about 2 m of sediment can be removed across this reach, with 3 m or more being available adjacent to the active channel. This survey indicates that infilling of the entire reservoir had reached a level approaching that of the pre-1995 dredging. Analysis of sediment-yield data and basin geometry showed that a weir built across the reservoir approximately 215 m from the dam would produce a trap capable of storing 60% to 70% of that currently held in the reservoir. Sediment trapped within this portion can be excavated using standard machinery, providing a more cost-effective alternative to periodic dredging.
Radar reflections from sedimentary structures in the vadose zone
Authors: Van Dam Remke L. , Van Den Berg Elmer H. , Schaap Marcel G. , Broekema Lucas H. , Schlager Wolfgang
Published: April 2008

Ground penetrating radar (GPR) is a suitable technique for imaging sedimentary structures in the vadose zone because small texture-related capillary-pressure variations lead to changes in water content and electromagnetic properties. To study exactly how GPR reflections are generated by sedimentary structures, GPR profiles of an aeolian sedimentary succession are combined with measurements of textural, electromagnetic and water-retention characteristics from a trench. Time domain reflectometry indicates that small variations in texture in the high-angle dune sediment are associated with changes in water content. Synthetic modelling shows that these changes cause clear GPR reflections. In an experimental approach to estimate the radar response of structures below the wave resolution, i.e. features smaller than λ/4, variations in grain-size distribution and porosity in a thin section were used to reconstruct water-retention curves and impedance models of the thinly layered sediment. Synthetic radar records calculated from the impedance models show that reflections from the studied subcentimetre-scale structures are composites of interfering signals. Although these low-amplitude interfering signals will commonly be overprinted by more prominent reflections, they may cause reflection patterns that change with frequency and do not represent primary bedding.
Influence of antenna configurations for GPR survey: information from polarization and amplitude versus offset measurements
Authors: Lutz P. , Garambois S. , Perroud H.
Published: April 2008

Ground penetrating radar (GPR) images depend strongly on the relative geometry between the transmitter, the receiver and the subsurface reflectors. This dependence results from the directional properties of the antennae and from the sensitivity of the reflector to the polarization of the incident electromagnetic wave. In the present study, GPR data sets have been recorded using several 100 MHz antennae configurations, including transverse electric (TE) or transverse magnetic (TM) modes that have been used both parallel and perpendicular to the recording line. The images obtained show a high complementarity that provides more detailed information of the studied geological reflectors compared to the image derived from a single conventional acquisition configuration. Consequently, we compute pseudoprofiles that gather information derived from all acquisition modes, thus improving the GPR images. These pseudo-profiles are characterized by either a low directional degree of the antennae or a neutral acquisition mode. In addition, we have conducted a polarization analysis by surveying the studied profile twice with parallel and perpendicular antennae, in both modes (TE and TM). The comparison of these data sets provided three-dimensional (3-D) information on reflectors, particularly their depolarization properties. These studies clearly emphasize how multiconfiguration antennae surveys have the potential to improve GPR imaging and interpretation. Furthermore, polarimetric surveys have been carried out in order to explore further whether depolarization phenomena could explain observations of phase inversion and amplitude decrease on TE common mid-point gathers that would induce perturbations of the GPR images in the stacking procedure for multi-offset surveys.
Process-based modelling of the climatic forcing of fluvial sediment flux: some examples and a discussion of optimal model complexity
Authors: Bogaart P. W. , Van Balen R. T. , Vandenberghe J. , Kasse C.
Published: April 2008

During the complex and highly dynamic climate of the Late Quaternary, precipitation and temperatures were highly variable and generally did not change synchronously. Reconstructed fluvial sedimentological response to this climatic forcing was previously shown to be complex. This response can be understood only by accounting for all the relevant catchment processes. This paper reviews a number of simple numerical models that aim to enhance our understanding of the role of different processes in this climate-sedimentology system. The applicability of these models depends on the scale of the models involved, the required input data and the way that parameters are estimated. Simple process-based models perform best on Quaternary timescales because their data needs are low and parameters can be interpreted in physical terms, which enables an
a priori
estimation. Process-based models of fluvial dynamics may provide a methodology for the understanding of the mechanisms responsible for the dynamics of sediment flux to basins.
Sediment fluxes and the evolution of a riverine-supplied tectonically-active coastal system: Kyparissiakos Gulf, Ionian Sea (eastern Mediterranean)
Authors: Poulos Serafim E. , Voulgaris George , Kapsimalis Vasilis , Collins Michael , Evans Graham
Published: April 2008

Kyparissiakos Gulf, located in the southwestern part of Greece (northeastern Ionian Sea), is a riverine-coastal system that has developed over the southern flank of the Alpine orogenic belt (Hellenides). Some 4 km in the vertical separates the heights of the mountain peaks to the depths of the adjacent offshore deep-water basin. This system extends horizontally over approximately 100 km. The area experiences intensive tectonism (e.g. seismicity), a Mediterranean type of climate and microtidal and moderate wave-energy oceanographic settings.

Large quantities of sediments (>2.5 × 10
6
t year
−1
), transferred principally by the River Alfios, are the product of denudation of the high relief (in excess of 2000 m), developed on erodible lithology (with siliciclastics and carbonates >90%) under moderate climatological conditions. The large amounts of sediments produced in the hinterland, in association with land-ocean process interaction, have led to the formation of a coastal zone that includes deltaic plains and coastal barriers with dune fields, which enclose lagoons. The shape and morphological characteristics of the shore zone indicate, clearly: (a) the dominance of the wave activity; (b) an overall northward longshore sediment movement; and (c) a major depocentre at the northern, naturally sheltered, end of the Gulf.

Seawards, the coastal zone includes a narrow continental shelf covered with a blanket of recent sediments, which are terrigenous in origin; these extend down a steep slope, where materials is transferred to the deep (approximately 1800 m) offshore basin (the northward component of the Hellenic Trench) primarily by gravitational mass movements; these are triggered often by earthquake activity. To a first approximation, some 50% of the riverine sediment fluxes accumulate over the shelf, whilst another 25% is transported over the slope to the deeper ocean waters.

The construction of (two) dams has led to a dramatic reduction in the sediment supply to the coast, having already caused the retreat of the River Alfios deltaic coastline, by >100 m. Similarly, artificial drainage of the lagoons (for the development of agricultural land) has affected the overall ecosystem (altering the the fauna and flora) of the coastal zone

Thus, the Upper Quaternary (mostly Holocene) evolution of this particular coastal system is attributed, primarily, to processes and balances between sediment fluxes (e.g. terrestrial transportation, seaward dispersion) and, recently, to human interference.
Palaeobiogeography and the Ordovician and Mesozoic-Cenozoic biotic radiations
Authors: Owen A. W. , Crame J. A.
Published: April 2008

Curves of taxonomic diversity through geological time consistently show major evolutionary radiations during the Ordovician Period and from the mid-Mesozoic to the present day. Both intervals were characterized by marked biotic provincialism, reflecting episodes of major continental break-up and global tectonism, and their later histories featured steep global climatic gradients. The Ordovician radiation can be recognized at a wide spectrum of taxonomic levels from species to class, and the biogeographical patterns associated with the radiation of individual clades reflect a complex combination of plate distribution, tectonic activity, sedimentary environment, sea-level rise and, ultimately, glaciation. The true scale of the mid-Mesozoic-Cenozoic biotic radiation is currently a topic of intense debate but there is no doubt that it affected plants and animals in both the marine and terrestrial realms. The role of land bridges and ocean gateways in controlling the formation of biodiversity patterns has been a persistent theme in Mesozoic-Cenozoic biogeography, and a complex set of Neogene tectonic events probably aided the development of both latitudinal and longitudinal provinces during the Cenozoic. The present volume highlights some of the successes across a spectrum of approaches to unravelling the Ordovician and Mesozoic-Cenozoic radiations within the context of palaeobiogeography.
The early evolution and palaeobiogeography of Mesozoic planktonic foraminifera
Authors: Hart Malcolm B. , Oxford Melissa J. , Hudson Wendy
Published: April 2008

The planktonic foraminifera almost certainly evolved from benthonic ancestors in the early Jurassic. The meroplanktonic genus
Conoglobigerina
, known from south-central and eastern Europe, appears in the Bajocian and is probably derived from the even more geographically restricted
Praegubkinella
. This genus was represented by a single taxon in the earliest Toarcian but diversified after the Toarcian anoxic event. At the same level
Oberhauserella quadrilobata
Fuchs, 1967 became more inflated and there is some evidence to suggest that the ‘anoxic event’ was the environmental perturbation that began the transition to a planktonic mode of life. In the Callovian-Oxfordian interval, the planktonic foraminifera are still restricted to a relatively limited area bounded by the North Atlantic Ocean, NW Europe and Eastern Europe and this remained the case even in the earliest Cretaceous. It was only in the Aptian-Albian that the palaeogeographical distribution changed dramatically, probably as a response to the elevated sea levels caused by the increased rate of ocean crust production which began in the Early Aptian. The principal diversification events in the Jurassic (Toarcian, Bajocian, Callovian-Oxfordian) also appear to be related to sea level highstands.
Cretaceous patterns of floristic change in the Antarctic Peninsula
Authors: Cantrill David J. , Poole Imogen
Published: April 2008

Cretaceous radiation of angiosperms from low to high palaeolatitudes, coupled with the break-up of Gondwana, played a major role in establishing and maintaining biogeographic patterns across the southern hemisphere. Uncertainties in details of plate reconstructions provide conflicting hypotheses about area relationships of Gondwana fragments. This has led to a number of competing proposals concerning angiosperm migration across Gondwana. Central to this debate is the role of the Antarctic Peninsula, a region that is often envisaged as providing the main connection between east and west Gondwana. The initial radiation of angiosperms into the Antarctic Peninsula region, however, postdates appearances elsewhere in east Gondwana (e.g. Australia), strongly suggesting that the Antarctic Peninsula was not the main gateway, at least in the early stages of Gondwana radiation. A steep climatic gradient in this part of the world probably acted as an effective barrier to angiosperm radiation. The peak of floristic replacement coincides with the peak of Cretaceous warmth (Turonian) which in turn suggests that climatic warming acted as a forcing mechanism by pushing latitudinal belts of vegetation southwards. Once into the southern high latitudes angiosperms diversified, and as climates cooled during the Late Cretaceous a number of important groups seem to have their origins here. Recent investigations of Antarctic macro- and microfloras indicate progressive floristic replacement through the Cretaceous. Bryophytes, hepatophytes, bennettites and other seed plants all show a rapid decline in diversity. In contrast, ferns initially decline then recover, while conifers remain relatively stable. The ecological preferences of the replaced groups imply that angiosperms initially occupied areas of disturbance and were understorey colonizers, only later replacing fern thickets and becoming important in the overstorey. This pattern is consistent with those observed elsewhere through the Cretaceous.
Tectonic geomorphology of the Gulf of Oman Basin
Authors: Uchupi Elazar , Swift S.A. , Ross D.A.
Published: April 2008

The margins of the Gulf of Oman Basin range from convergent at the north to translation at the west and east, and passive at the south. The basin’s northern margin has been a site of continuous subduction since Cretaceous time, which has led to the creation of an 800 km long and 650 km wide accretionary wedge, most of which is above sea level. Strata in the centre of the Gulf of Oman Basin display minor deformation resulting from the northward tilting of oceanic crust. A basin-wide unconformity dividing these strata in two was the result of erosion during Early Oligocene time when bottom water circulation was enhanced during a climatic deterioration. The morphology of the basin’s south margin is due to Early Triassic rifting, deposition during Jurassic-Early Cretaceous time, early Late Cretaceous ophiolite obduction and Late Cretaceous-Cenozoic deposition. The western side of the accretionary wedge, along the north side of the Gulf of Oman Basin, is in sharp contact with the western translation margin. Structures along this margin are the result of post-Eocene convergence of the Lut and Central Iran microplates. The eastern end of the accretionary wedge, however, is not in contact with the eastern transform margin, but is separated from it by a north-trending trough. The landward extension of this trough is defined by the north-trending Las Bela Valley. The eastern side of the accretionary wedge turns northward at 65°30′N along the west side of the trough and becomes aligned with the north-trending Ornach-Nal Fault along the west side of the Las Bela Valley. Similarly, the Murray Ridge complex turns northward at 25°N and becomes aligned with the north-trending Surjan Fault on the Las Bela Valley’s east side. The Ornach-Nal and Surjan faults merge at the apex of the Las Bela Valley with the north-trending Las Bela-Chaman Structural Axis. Differences between the eastern and western sides of the accretionary wedge may be due to the presence of the Ormara microplate on the eastern end of the wedge, a plate that is being pushed ahead of the Arabian plate. The morphology of the Murray Ridge complex is the result of transtension and secondary compression along the Indian-Arabian plate boundary. We infer that most of the relief of the Murray Ridge complex resulted from a change in plate geometry in Early Miocene time. Subsequent tectonic Pliocene-Quaternary events have enhanced this relief.
Constraints on India-Eurasia collision in the Arabian Sea region taken from the Indus Group, Ladakh Himalaya, India
Authors: Clift Peter D. , Carter Andrew , Krol Michael , Kirby Eric
Published: April 2008

The Indus Group is a Paleogene, syntectonic sequence from the Indus Suture Zone of the Ladakh Himalaya, India. Overlying several pre-collisional tectonic units, it constrains the timing and nature of India’s collision with Eurasia in the western Himalaya. Field and petrographic data now allow Mesozoic-Paleocene deep-water sediments underlying the Indus Group to be assigned to three pre-collisional units: the Jurutze Formation (the forearc basin to the Cretaceous-Paleocene Eurasian active margin), the Khalsi Flysch (a Eurasian forearc sequence recording collapse of the Indian continental margin and ophiolite obduction), and the Lamayuru Group (the Mesozoic passive margin of India). Cobbles of neritic limestone, deep-water radiolarian chert and mafic igneous rocks, derived from the south (i.e. from India), are recognized within the upper Khalsi Flysch and the unconformably overlying fluvial sandstones of the Chogdo Formation, the base of the Indus Group. The Chogdo Formation is the first unit to overlie all three pre-collisional units and constrains the age of India-Eurasia collision to being no younger than latest Ypresian time (>49 Ma), consistent with marine magnetic data suggesting initial collision in the Arabian Sea region at
c.
55 Ma. The cutting of equatorial Tethyan circulation north of India at that time may have been a trigger to the major changes in global palaeoceanography seen at the Paleocene-Eocene boundary. New
40
Ar/
39
Ar, apatite fission-track and illite crystallinity data from the Ladakh Batholith and Indus Group show that the batholith, representing the old active margin of Eurasia, experienced rapid Eocene cooling after collision, but was not significantly reheated when the Indus Group basin was inverted during north-directed Miocene thrusting (23–20 Ma). Subsequent erosion has preferentially removed 5–6 km (
c.
200°C) over much of the exposed Indus Group, but only
c.
2 km from the Ladakh Batholith. Reworking of this material into the Indus fan may complicate efforts to interpret palaeo-erosion patterns from the deep-sea sedimentary record.
Quaternary sedimentation on the Makran margin: turbidity current-hemipelagic interaction in an active slope-apron system
Authors: Stow Dorrik A. V. , Tabrez Ali R. , Prins Marteen A.
Published: April 2008

The Makran slope-apron system is a stepped convergent margin across an active subduction complex. Shallow penetration piston cores have been recovered from the upper-slope region, three mid-slope basins and the abyssal plain. At most sites the upper 5–14 m of cored section is dominated by fine-grained, thin- to medium-bedded turbidites, averaging 5–10 turbidite events per metre of section. Oxygen isotope stratigraphy yields mean sedimentation rates of 50–95 cm ka
−1
and a turbidite frequency of one event per 200–300 a. The upper-slope site has fewer turbidites and a greater proportion of hemipelagic mud. Fine-grained turbidite sequences are common, with top-cut-out and base-cut-out sequences most evident. Markov chain analysis of the transition between turbidite divisions confirms the normal T0–T8 order of sequence divisions. In some cases there is an upward gradation into a hemiturbidite facies. The range of turbidite bed thicknesses can be approximated by both power-law and log-normal distributions, typical of seismic triggering on an active margin, or of frequent river-flood sediment input. Small-scale vertical variations of turbidite bed thickness recognized by autocorrelation techniques can be interpreted as the result of bed-relief compensation effects (compensation cycles). The lateral distribution of both turbidites and hemipelagites is influenced by sediment focusing along pathways between slope basins. At a larger scale, climate, sea-level and tectonic effects have all played an important role in shaping margin sedimentation.
Centennial-millennial-scale monsoon variations off Somalia over the last 35 ka
Authors: Jung Simon J. A. , Ivanova Ekatarina , Reichart Gert Jan , Davies Gareth R. , Ganssen Gerald , Kroon Dick , Van Hinte Jan E.
Published: April 2008

We present a multi-proxy study of sediment Core 905 from the Arabian Sea offshore Somalia to assess the validity of a number of proxies for productivity, temperature and wind strength, to reconstruct the monsoon history in the western Arabian Sea. The present-day seasonal variation in productivity in the modern Arabian Sea off Somalia reflects the change from the high-productivity SW monsoon to the low-productivity NE monsoon seasons. Annual productivity is therefore largely controlled by SW monsoon driven upwelling. The geochemical records of Core 905 document millennial-scale variations, for example, in Ba/Al and C
org
content. The Younger Dryas and the time equivalent period to Heinrich event 1 show low annual productivity whereas the early Holocene and Bølling-Allerød periods are characterized by high productivity. The upwelling-productivity peaked during Early Holocene time and was followed by a decrease toward the modern values. The total flux of planktic foraminifera and the concentration of the planktic foraminifera
G. bulloides
are not always controlled by the total productivity. Variations in calcite dissolution, the advection of expatriate fauna or a seasonal decoupling of primary and secondary production appear to hamper straightforward interpretations of those foraminifera records. We conclude that at significantly changed climatic boundary conditions compared with the present day, bulk-sediment-related proxies of productivity more consistently record the local upwelling history than foraminifer-based productivity proxies.
Varves, turbidites and cycles in upper Holocene sediments (Makran slope, northern Arabian Sea)
Authors: von Rad U. , Khan A. Ali , Berger W. H. , Rammlmair D. , Treppke U.
Published: April 2008

We have analysed two Late Holocene records, each about 5 ka long, consisting of varved sediments deposited in the oxygen minimum zone off Pakistan (upper continental slope off Ormara and west of Karachi). Varve counting was checked by accelerator mass spectrometry (AMS)
14
C dating. Detailed lithofacies analysis, ultra-high-resolution X-ray fluorescence scanning, flux rates from sediment traps and the lamina-by-lamina-analysis of a 5 year record (1993–1998) support our interpretation of the annual character of the laminae. Although the pelagic material is deposited throughout the year, most of it is apparently laid down during the high-productivity period of the late summer monsoon. During the winter (mainly mid-December to February-March) mainly light-coloured detrital material (siliciclastic material and reworked carbonate flour) is deposited, probably by river flood events. Event deposits include turbid-plume or suspensate deposits (light grey homogeneous to graded silty clay layers), which are being laid down at decadal or shorter intervals; they are explained by episodically strong river floods after heavy rains transporting mud-charged waters to the narrow shelf and onto the steep continental slope. Medium grey or reddish grey, graded and laminated silt turbidites originated from less frequent, unchannelized, low-density turbidity currents. In general, periods with thin varves (generally correlated with rare turbidites) are correlated with minima of detrital element ratios (TiO
2
/Al
2
O
3
, Zr/Al
2
O
3
, K
2
O/Al
2
O
3
), especially in Period I (
c.
5600-4700 a bp), suggesting a climate with reduced precipitation and river runoff (possibly winter monsoon dominated). Period II (4700-2600 a bp) is characterized by comparatively thick varves documenting a generally wet period (with possibly summer monsoon domination). During Period III (2600-1000 a bp) a gradual thinning of varves and a decrease of turbidite abundance (thickness) per century is interpreted as a gradual decline of precipitation and river runoff leading finally to dry conditions from 1600 to 1000 a bp. The sequence of cycles detected by autocorrelation and standard Fourier analysis seems to contain a large proportion of multiples of the lunar perigee cycle (4.425 a, 8.85 a) and the lunar (half) nodal cycle (9.3 a, 18.6 a). Our test for cyclicity in the series of varve thickness (varve cycles) and of abundance of turbidites (turbidite cycles) detected prominent high-frequency cycles. Some cycles of varve thickness match the cyclicity of turbidite frequency. We also detected the presence of a 1470 a cycle, previously reported from the glacial-age Greenland ice record.
A structural transect between the central North Sea Dome and the South Swedish Dome: Middle Jurassic-Quaternary uplift-subsidence reversal and exhumation across the eastern North Sea Basin
Authors: Graversen Ole
Published: April 2008

The Jurassic-Cenozoic structural evolution of the eastern North Sea Basin is influenced by the central North Sea Dome, the Danish Megablock, the Tornquist Zone and the South Swedish Dome. The central North Sea Dome is a composite dome comprising the Triple Junction Dome, the Central Graben Dome and the Friesland Dome. The Danish Megablock, newly recognized here, is a first-order tectonic element between the Central Graben and the Tornquist Zone. In Jurassic-Cretaceous time it was tilted towards the east during uplift of the Central Graben Dome, whereas the movement was reversed during the Cenozoic post-rift subsidence. Contemporaneous with the westward tilting of the Danish Megablock, the South Swedish Dome was uplifted to the east. The uplift-subsidence reversal across the eastern North Sea Basin links the collapse of the Central Graben Dome and the tilt reversal of the Danish Megablock with the uplift of the South Swedish Dome. The uplift followed by subsidence probably involved mass flow in the asthenosphere to account for the observed balance between post-rift subsidence and marginal uplift. The model explains the uplift of both the South Swedish Dome and southern England as the result of Cenozoic post-rift subsidence of the Mesozoic Central Graben Dome.
Quantifying exhumation from apatite fission-track analysis and vitrinite reflectance data: precision, accuracy and latest results from the Atlantic margin of NW Europe
Authors: Green Paul F. , Duddy Ian R. , Hegarty Kerry A.
Published: April 2008

In areas where significant unconformities are present, palaeotemperatures derived from apatite fission-track analysis (AFTA) and vitrinite reflectance (VR) data through a vertical rock section can be used to estimate palaeogeothermal gradients and (by extrapolation to an assumed palaeo-surface temperature) amounts of exhumation (palaeoburial). AFTA also provides a direct estimate of the timing of exhumation. These parameters can be used to reconstruct more complete histories than those based purely on the preserved rock record.

Precision and accuracy of these estimates are controlled by a range of theoretical and practical factors, perhaps the most important being the use of appropriate kinetic models. In extracting thermal history information from fission tracks in apatite, it is essential to use models that can describe variation in response between apatite grains within a sample. It is also important to recognize the limitations of the methods. AFTA and VR are dominated by maximum temperatures, preserving no information on events prior to a palaeo-thermal maximum. Recognition of this allows definition of key aspects of the history with greater precision.

Results from NW Europe define a series of regionally synchronous palaeo-thermal episodes, with cooling beginning in Early Cretaceous, Early Tertiary and Late Tertiary times. Latest results show that Early Tertiary palaeo-thermal effects in NW England can be understood as being due to a combination of higher basal heat flow and deeper burial, and emphasize the importance of obtaining data from a vertical sequence of samples. Comparison with similar results from other parts of the world suggests that events at plate margins exert a key influence on the processes responsible for regional exhumation, as recognized through Mesozoic and Cenozoic times across NW Europe.
K/Ar and
39
Ar/
40
Ar whole-rock dating of zeolite facies metamorphosed flood basalts: the upper Paleocene basalts of the Faroe Islands, NE Atlantic
Authors: Waagstein Regin , Guise Philip , Rex David
Published: April 2008

The Paleocene flood basalts of the Faroe Islands form a central part of the North Atlantic Igneous Province, but have proven difficult to date because of very low-grade burial metamorphism in the chabazite-thomsonite to the laumontite zeolite zone. We present 17 replicated K/Ar and 8 Ar/Ar whole-rock analyses of basalts from the >3 km thick lower basalt formation, the age of which has been debated for years. Samples are from the massive core of thick, exposed flows, and two boreholes (Vestmanna-1 and Lopra-1). Six samples are drill cuttings. Extensive microprobe work and mass balance calculations show that roughly 60% of the potassium of the dated basalts resides in plagioclase, interstitial cryptocrystalline rhyolite and smectitic clay, the rest mainly forming thin rims of alkali feldspar on plagioclase. Six basalts fulfil the following criteria: (1) they are almost homogeneous in K and Ar (ages on different splits vary by <4 Ma); (2) the only low-temperature phase present is smectite (saponite±minor interstratified chlorite-smectite); and (3) max.
c.
6% of total K occurs in smectite. This smectite replaced metastable interstitial glass during early burial and has a trivial effect on measured ages. The six basalts give mean K/Ar whole-rock ages of 56.5 ± 1.3 to 58.9 ± 1.3 Ma (1σ), which are interpreted as igneous ages consistent with mapped palaeomagnetic reversals and unpublished Ar/Ar dates. They suggest that the oldest drilled lavas erupted at 58.8 ± 0.5 Ma (1σ) in the later part of magnetochron C26r accumulating at >2 km Ma
−1
, and that the volcanism came to a slow end at 56.4 ± 0.5 Ma in the beginning of chron C24r. The Lower Basalt Formation is overlain by 10m of coal-bearing sediments and 2 km syn-breakup lavas, deposited in early C24r (>55 Ma).

The remaining 11 basalts are either inhomogeneous, carry > 10% of the total K in clay, have C/S > saponite or contain traces of zeolites, secondary quartz, dioctahedral smectite or celadonite as probable indicators of prolonged alteration, and they give low or variable K/Ar ages. The Ar/Ar analyses include five of these poor samples plus three of the first group. They give a plateau age of 55.7 ± 0.9 Ma (1σ) for two exposed flows assigned to chron C25n, but of 60–63 Ma for six drilled lavas assigned to C26r. We argue that the later Ar/Ar ages are too high due to
39
Ar recoil loss out of the sample (0–25%) or relocation during irradiation and should be ignored.
About this title
Authors: Jolley D. W. , Bell B. R.
Published: April 2008

The North Atlantic Igneous Province has been the subject of extensive scientific investigation over the past thirty years, with a wide field of knowledge being accumulated. Recently, recognition of the potential role of Large Igneous Provinces in affecting ocean and atmosphere systems and biotic evolutionary pathways has lead to increased interest in this province. This has been further stimulated by the expansion in the search for oil and gas in Mesozoic and Tertiary sediments along the NE Atlantic Margin. An improved understanding of the interaction between igneous and sedimentary processes is vital for the identification of potential hydrocarbon resources.

The regions covered include continental margin Norway, east and west Greenland, the Faroe-Shetland Basin and the Faroe Islands themselves. The papers in this book contain new data and interpretations of North Atlantic Igneous Province magmatic processes, rift evolution, tectonics, stratigraphy (chemostratigraphy, biostratigraphy, seismic and isotope stratigraphy) and sediment dispersal. Many of the papers adopt a multidisciplinary approach to tha analysis and interpretation of complex volcanic and sedimentary sequences. These new data, and the reviews and compilations of existing data provide the reader with access to current research directions in North Atlantic Igneous Province geology.
Mine water tracing
Authors: Wolkersdorfer Christian
Published: April 2008

This paper describes how tracer tests can be used in flooded underground mines to evaluate the hydrodynamic conditions or reliability of dams. Mine water tracer tests are conducted in order to evaluate the flow paths of seepage water, connections from the surface to the mine, and to support remediation plans for abandoned and flooded underground mines. There are only a few descriptions of successful tracer tests in the literature, and experience with mine water tracing is limited. Potential tracers are restricted due to the complicated chemical composition or low pH mine waters. A new injection and sampling method (‘LydiA’-technique) overcomes some of the problems in mine water tracing. A successful tracer test from the Harz Mountains in Germany with
Lycopodium clavatum
, microspheres and sodium chloride is described, and the results of 29 mine water tracer tests indicate mean flow velocities of between 0.3 and 1.7 m min
−1
.
A physically based model of rebound in South Crofty tin mine, Cornwall
Authors: Adams Russell , Younger Paul L.
Published: April 2008

The recent closure of the South Crofty tin mine, the last working mine of this type in Europe, has raised questions over possible environmental consequences. During several centuries of operation, the mine was dewatered by a series of pumps located at different levels in the mine. Older workings near the ground surface were dewatered by a series of adits that discharge into nearby rivers and streams. The quality of water draining from these shallow workings is generally good and no treatment is required. However, because of bad experiences at the nearby Wheal Jane tin mine, the UK Environment Agency were concerned about the quality and quantity of water which was expected to discharge from the deeper workings when groundwater rebound was completed.

In order to address this problem and make predictions of the timing and volume of the discharge, computer simulations using the SHETRAN/VSS-NET model have been carried out. This model has already been applied to the simulation of groundwater rebound in several UK coalfields. However, the hydrogeological characteristics of coal mines differ considerably from the South Crofty mine. In this mine, the country rocks comprise granite and metamorphic slates, strata that have negligible transmissivity and very low storativity. Most of the groundwater flow is therefore in the ‘drives’ and stopes from which tin ore was extracted.

The inflows to the mine during its operation were mapped and quantified, and were found to be mainly head-dependent. These inflows usually originated from fault zones in the rock, and also from nearby disused and flooded workings, which surround the modern mine. Predictions of the water level during rebound are compared with the observed water levels in the main shaft which have been measured since the mine closed. The model was then used to predict the dates when surface discharges could be expected to commence. One of the main limitations of the predictions was a ‘blank’ depth interval in the mine plan records, which could be interpreted in two possible ways: (i) the zone was worked in the mid-nineteenth century but the plans were lost; or (ii) the zone was never worked.

Local professional opinion favoured interpretation (i), and the prediction scenarios considered most probable were based on the assumption that mining-related specific yield values would be similar in this ‘blank interval’ to those applicable in better-mapped intervals below. In the event, (ii) above appears to have been the true case, resulting in a marked steepening of the rebound curve during the later stages of rebound, with surface discharge commencing in November 2000, as much as a year in advance of most other predictions. A retrospective simulation assuming very low specific yield in the ‘blank interval’ confirms that the hydrodynamics were otherwise successfully simulated using the SHETRAN/VSS-NET code.
Modelling the oxidation of sulphides in an unsaturated soil
Authors: Saaltink Maarten W. , Domenech Cristina , Ayora Carlos , Carrera Jesus
Published: April 2008

Within the framework of a study on the impact of a mine-tailing spill at Aznalćollar, SW Spain, we investigated the oxidation of pyrite and other sulphides by means of two column experiments and reactive transport modelling. The columns were filled with pyritic sludge mixed up with a sandy and a clayey soil, respectively. The columns were located outdoors for 15 months and leached 10 times. Prior to simulating reactive transport, a flow model permitted a detailed description of the behaviour of the column at a daily time-scale. The most important parameter extracted was the hydraulic saturation. This parameter controlled the amount of O
2
that could diffuse into the soil, which, in its turn, affected the rate of pyrite oxidation. The sandy and clayey columns behaved very differently. In the sandy column, pH dropped due to the oxidation of pyrite. As a result, silicate minerals dissolved, providing Na and/or K that precipitate together with Fe and SO
4
as jarosite. The high concentration of Zn in the leachates was consistent with the concentrations predicted from sphalerite oxidation. The low As and Pb concentrations, however, were explained by their coprecipitation in the jarosite. In the clayey column, the dissolution of dolomite kept the pH high, impeding the dissolution of silicate minerals and precipitating amorphous Fe(OH)
3
in the place of jarosite. The model also permitted rate laws proposed in the literature for pyrite oxidation to be discussed. We found that the oxidation of pyrite by Fe
3+
was not faster than by O
2
, contrary reports in the literature. Finally, the model was used to predict the behaviour of other soil types and other sludge contents. According to the predictions the dissolution of jarosite was very important to maintaining the pH at a value of approximately 2, even for gravels or low reactive sand.
Laboratory and numerical modelling studies of iron release from a spoil heap in County Durham
Authors: Gandy Catherine J. , Evans Katy A.
Published: April 2008

At present there is no suitable method to predict either the longevity of contaminant sources within spoil heaps, or the evolution of their strength over the contaminating life time of the sites. Existing acid-base accounting techniques provide little information relevant to the prediction of field contaminant concentrations and time scales. For robust prediction, the relative rates of contaminant generation and attenuation must be evaluated then extrapolated to the physical scale and environmental conditions of real field sites. Laboratory unsaturated column experiments on colliery spoil from a well-documented site in County Durham have been set up to assess its contamination potential, and the results compared with results from a mathematical model for contaminant release and transport. The random walk method, a form of particle tracking, is used to transport iron and sulphate ‘particles’, released by oxidative weathering of pyrite minerals. The model also includes the oxidation of ferrous iron to ferric iron in an attempt to account for contaminant ‘sinks’, for example where ferric iron spontaneously precipitates as ferric oxyhydroxide and is effectively removed from the transport process. In general, the modelled results compare favourably with the laboratory results and any discrepancies can be accounted for.
Structural influence on plume migration from a tailings dam in the West Rand, Republic of South Africa
Authors: Neumann Ilka , Sami Karim , Neumann Ilka
Published: April 2008

Gold mining activity in South Africa is a potential cause of groundwater contamination. In particular, leachate infiltrating from tailings dams can affect surface water, as well as groundwater quality. This study was aimed at assisting an individual mine to investigate the groundwater flow system downstream of a tailings dam in order to predict contaminant plume migration emanating from the decommissioned dam. During the investigation, evidence was found that the contaminant plume emanating from the dam was affecting the groundwater quality in the area, predominantly by impacting on chloride and sulphate concentrations. It was suspected that structural features influenced plume migration rather than lithology, hence a strong emphasis was placed on the structural geology. The orientation of tensional and compressional couples were derived through tectonic analysis and verified through field observations. Incorporation of tensional structural features, acting as preferential groundwater flow paths, into a numerical model enabled the simulatation of the groundwater flow regime in the area to predict plume migration.
Influence of mine hydrogeology on mine water discharge chemistry
Authors: Rees S. B. , Bowell R. J. , Wiseman I.
Published: April 2008

Using data for 81 coal mine discharges in the UK, the influence of discharge hydrogeology on discharge chemistry is assessed and typical chemical parameters derived for five discharge types. A combination of modified and new classification schemes is used to differentiate between the various discharge sources. Drainage from spoil tips generally has a pH below 5 and net-alkalinity values as low as — 2500 mg l
−1
CaCO
3
. Drainage from flooded workings and pumped discharges are net-alkaline, while drainage from flooded and free draining workings are either moderately net-alkaline or net-acidic. Iron is the major contaminant of concern, although many mine waters contain less than 30 mg l
−1
and Fe/SO
4
ratios are less than unity. The classification schemes developed can be used to assess mine water treatment requirements and processes operating in passive treatment systems.
Strange partners: formation and survival of continental crust and lithospheric mantle
Authors: Arndt Nicholas T. , Lewin Éric , Albarède Francis
Published: April 2008

Continental lithosphere is a sandwich of two layers, each composed of materials that are rare in the upper parts of the Earth. Continental crust consists of low-temperature distillates produced during a succession of melting events; the underlying lithosphere is a remarkably pure concentrate of high-temperature, highly refractory minerals. Material with intermediate compositions, which should have been far more abundant, is missing. The two dominant components of Archaean lithospheric mantle, olivine with 92–94% forsterite and similarly magnesian orthopyroxene, form only a small proportion of the residue of large-scale mantle melting. Their accumulation to form the lithosphere requires efficient sorting, to separate them from the products of lower-degree melting. This sorting, which is driven by the buoyancy of these low-density phases and their high viscosity, takes place during: (1) plume ascent through the segregation of residues of high- and low-degree melting; (2) recycling of the residues through the mantle; (3) crystallization in the crust of a Hadean magma ocean. The higher-than-normal orthopyroxene content in the Kaapvaal and other cratons is due in part to density sorting and in part to exsolution of majorite, a residual phase during komatiite melting. Secular variation in lithosphere composition (a decrease in the proportion of magnesian olivine and orthopyroxene and an increase in clinopyroxene and spinel) reflects a progressive decline in high-degree melting, a consequence of falling mantle temperatures.
Key Lower Palaeozoic faunas from near the Trans-European Suture Zone
Authors: Cocks L. Robin M.
Published: April 2008

Following recognition of the Vendian to mid-Ordovician rotation of Baltica, with more than 55° of that rotation occurring in the Upper Cambrian and Lower Ordovician, the Tornquist Margin of Baltica must have faced northwards towards Laurentia and the Panthalassic Ocean, rather than, as now, southwestwards towards Gondwana (including Avalonia). Unequivocally Baltic endemic trilobite, brachiopod and other faunas are known from both the Cambrian and the Ordovician of the Holy Cross Mountains, Poland, and from both parts of them, i.e. the Małopolska Block and the Łysogóry Block. Whether or not these two blocks were united into a single terrane or were separate as two terranes is equivocal from the faunal evidence, and there is no faunal evidence of substantial strikeslip faulting of the blocks in relation to the main Baltic craton: they are perceived as having made up part of the margin of Baltica itself. However, both Holy Cross Mountain blocks were different and palaeogeographically separate from the Bruno-Silesian Block, whose continental origins are yet to be finally determined. The Ordovician clastic sediments at both Rügen, north Germany, and Pomerania, NW Poland, have yielded no macrofossils other than graptolites, but microfossils (acritarchs and chitinozoa) are interpreted as having been deposited at relatively high palaeolatitudes, i.e. at a higher palaeolatitude than Baltica, and may have been deposited in an ocean basin within the Tornquist Ocean between Baltica and Avalonia.