bluuebunny/crossref_metadata_2025 huggingface dataset:
Groundwater in the Celtic regions
Authors: Robins N. S. , Misstear B. D. R.
Published: April 2008

The Celtic regions of Britain and Ireland have a complex and diverse geology which supports a range of regionally and locally important bedrock aquifers and unconsolidated Quaternary aquifers. In bedrock, aquifer units are often small and groundwater flow paths short and largely reliant on fracture flow. Groundwater has fulfilled an important social role throughout history, and is now enjoying renewed interest. Groundwater quality is generally favourable and suitable for drinking with minimal treatment. However, many wells are vulnerable to microbiological and chemical pollutants from point sources such as farmyards and septic tank systems, and nitrate concentrations from diffuse agricultural sources are causing concern in certain areas. Contamination by rising minewaters in abandoned coalfields and in the vicinity of abandoned metal mines is also a problem in some of the Celtic lands.
Interdependence of groundwater and surface water in lowland karst areas of western Ireland: management issues arising from water and contaminant transfers
Authors: Coxon Catherine , Drew David
Published: April 2008

In lowland karsts, both surface and groundwater systems are often present. This is the case over large areas of limestone in the west of Ireland where gaining and losing streams and seasonal lakes (turloughs) are common and where much of the surface river system consists of artificial channels. A case study from County Clare illustrates the problems involved in delineating catchment areas for springs which have partially contributing surface stream sources. Case studies from counties Galway and Clare, with complex surface water-groundwater interactions, exemplify problems that may arise with water quality and quantity. Difficulties in defining realistic protection areas for groundwater resources and sources are discussed.
Shallow groundwater in drift and Lower Palaeozoic bedrock: the Afon Teifi valley in west Wales
Authors: Robins N. S. , Shand P. , Merrin P. D.
Published: April 2008

Detailed geological surveying in the Afon Teifi valley of west Wales has identified the distribution and geometry of a complex array of drift deposits over shales and greywackes of Silurian and Ordovician age. A well and borehole field inventory and groundwater sampling programme provides the basis for evaluating the groundwater flow patterns within these strata. Sustainable yields are mostly small with exceptional yields up to 345 m
3
d
−1
. Potential infiltration derived from an estimate of baseflow is 535 mm a
−1
; much of this discharges locally and only 9 Mla
−1
is estimated to flow longitudinally down the valley as groundwater throughflow. Total groundwater abstraction amounts to 760 Mla
−1
. Groundwater generally satisfies the EC maximum admissible concentration guideline levels and is Ca-HCO
3
to Ca-Cl type. Differences in bedrock groundwater chemistry between the western and the eastern parts of the study area are largely controlled by the drift type. By analogy, the groundwater potential demonstrated in the Afon Teifi valley is likely to be indicative of the potential in geologically similar valleys elsewhere in west and mid Wales.
Conceptual modelling of data-scarce aquifers in Scotland: the sandstone aquifers of Fife and Dumfries
Authors: Gaus I. , Dochartaigh B. É. Ó
Published: April 2008

Hydrogeological conceptual modelling is an essential tool in aquifer management, particularly in areas where groundwater abstraction is increasing. Conceptualization requires extensive (and expensive) amounts of data, for which resources are often lacking. This paper describes conceptual models of the Permo-Triassic sandstones in the Dumfries basin and the Upper Devonian sandstones in Fife. Data scarcity means that each aquifer requires an individually tailored approach to formulate the conceptual model and calculate the water balance. This approach can differ considerably from the standard techniques used when more data are available. The implications of data scarcity on the confidence in results are discussed and the conceptual models for both aquifers are compared.
The water resources of Bardsey, north Wales
Authors: Webb M. M.
Published: April 2008

Bardsey is a small island off the Welsh coast. Water supplies are drawn from spring sources but water shortages are experienced in summer. Sanitation depends on Elsan type toilets. There are limited groundwater resources in the Gwna Mélange, which is of Monian age, with groundwater transport controlled by fracture flow. There is evidence of some groundwater contamination.
Deposition of sedimentary organic matter in black shale facies indicated by the geochemistry and petrography of high-resolution samples, Blake Nose, western North Atlantic
Authors: Barker Charles E. , Pawlewicz Mark , Cobabe Emily A.
Published: April 2008

A transect of three holes drilled across the Blake Nose, western North Atlantic Ocean, retrieved cores of black shale facies related to the Albian Oceanic Anoxic Events (OAE) 1b and 1d. Sedimentary organic matter (SOM) recovered from Ocean Drilling Program Hole 1049A from the eastern end of the transect showed that before black shale facies deposition organic matter preservation was a Type III–IV SOM. Petrography reveals that this SOM is composed mostly of degraded algal debris, amorphous SOM and a minor component of Type III–IV terrestrial SOM, mostly detroinertinite. When black shale facies deposition commenced, the geochemical character of the SOM changed from a relatively oxygen-rich Type III–IV to relatively hydrogen-rich Type II. Petrography, biomarker and organic carbon isotopic data indicate marine and terrestrial SOM sources that do not appear to change during the transition from light-grey calcareous ooze to the black shale facies. Black shale subfacies layers alternate from laminated to homogeneous. Some of the laminated and the poorly laminated to homogeneous layers are organic carbon and hydrogen rich as well, suggesting that at least two SOM depositional processes are influencing the black shale facies. The laminated beds reflect deposition in a low sedimentation rate (6m Ma−1) environment with SOM derived mostly from gravity settling from the overlying water into sometimes dysoxic bottom water. The source of this high hydrogen content SOM is problematic because before black shale deposition, the marine SOM supplied to the site is geochemically a Type III–IV. A clue to the source of the H-rich SOM may be the interlayering of relatively homogeneous ooze layers that have a widely variable SOM content and quality. These relatively thick, sometimes subtly graded, sediment layers are thought to be deposited from a Type II SOM-enriched sediment suspension generated by turbidites or direct turbidite deposition.
Biostratigraphic subdivision and correlation of upper Maastrichtian sediments from the Atlantic Coastal Plain and Blake Nose, western Atlantic
Authors: Self-Trail Jean M.
Published: April 2008

Detailed biostratigraphic analyses of nine cores from the Atlantic Coastal Plain and two cores from the Blake Nose, western Atlantic Ocean, provide the basis for subdivision and correlation of upper Maastrichtian sediments along a shallow- to deep-water transect. The calcareous nannofossil record from these sites shows distinct differences between the middle to outer neritic Coastal Plain sediments and the lower to upper bathyal Blake Nose sediments.
Micula murus
, a reliable marker species for low- to mid-latitude sites, is shown herein to respond to differing palaeoenvironmental conditions of nearshore v. open-ocean sites. Its usefulness as a biostratigraphic marker for neritic sediments is called into question. The last appearance datum of
Ceratolithoides kamptneri
is documented as a reliable biozone marker for latest Maastrichtian time (within CC26b) in this region. The evolutionary radiation and resulting biostratigraphic utility of species of
Ceratolithoides, Lithraphidites
and
Micula
is discussed in detail, and their first and last occurrences are tied to magneto-stratigraphic chrons where possible.
Ceratolithoides amplector, Ceratolithoides indiensis
and
Ceratolithoides pricei
are shown to be useful, biostratigraphically, in sediments deposited under bathyal conditions. Several species of
Lithraphidites
(
Lithraphidites? charactozorro, Lithraphidites kennethii
and
Lithraphidites grossopectinatus
) can be used to further subdivide upper Maastrichtian sediments at both neritic and bathyal localities. The first and last occurrence of
Micula praemurus
in Zones CC25a and CC26a, respectively, are shown to be useful biostratigraphic datum points.
Biostratigraphic implications of mid-latitude Palaeocene-Eocene radiolarian faunas from Hole 1051A, ODP Leg 171B, Blake Nose, western North Atlantic
Authors: Sanfilippo Annika , Blome Charles D.
Published: April 2008

Abundant well-preserved radiolarians were recovered from Ocean Drilling Program Leg 171B Hole 1051A, western North Atlantic, and range from upper middle Eocene radiolarian Zone RP16 through lower Palaeocene Zone RP6. This mid-latitude fauna contrasts with tropical faunas in lacking many tropical zonal markers and in its high proportion of diachronous first and last occurrences. The sequence from Hole 1051A contains the lower Eocene-middle Eocene and Palaeocene-Eocene (P-E) boundaries, and the only known record of a well-preserved Late Palaeocene Thermal Maximum (LPTM) radiolarian assemblage. There is no gross change observed in the composition of the fauna, only a minor increase in the number of first and last occurrences across the LPTM interval and P-E boundary. Calcareous evidence indicates two hiatuses, each 1–2 Ma long, one in the lowermost middle Eocene sequence and a second in the upper Palaeocene sequence. Presence of the middle Eocene hiatus is corroborated by an abnormally large radiolarian turnover. Twenty-six events are documented and show that most of radiolarian Zone RP10 and a substantial part of Zone RP9 are missing. Seven new species are described:
Spongatractus klausi, Calocyclas aphradia, Lychnocanoma (?) parma, Sethocyrtis austellus, Sethocyrtis chrysallis, Thyrsocyrtis (Pentalacorys) krooni
and
Thyrsocyrtis (Thyrsocyrtis) norrisi
.
Carbon addition and removal during the Late Palaeocene Thermal Maximum: basic theory with a preliminary treatment of the isotope record at ODP Site 1051, Blake Nose
Authors: Dickens Gerald R.
Published: April 2008

The late Palaeocene Thermal Maximum (LPTM) was a brief interval at
c.
55 Ma characterized by a −2.5 to −3‰ shift in the δ
13
C of global carbon reservoirs. The geochemical perturbation probably represents a massive input of
12
C-rich carbon to the exogenic carbon cycle. Largely unresolved issues concerning this carbon injection during the LPTM are the rates of carbon input and removal. Simple expressions are developed here to describe a δ
13
C excursion in the exogenic carbon cycle after carbon input. A change in global δ
13
C (dδ
Ex
/d
t
) can be explained to a first approximation by a set of parameters: the initial mass and isotopic composition of the global carbon cycle (
M
Ex(o)
, δ
Ex(o)
), and the fluxes and isotopic compositions of external carbon inputs, outputs and injected carbon (
F
In
, δ
In
,
F
Out
, δ
Out
,
F
Add
, δ
Add
). In general, for a given exogenic carbon cycle, a large
F
Add
or low δ
Add
results in a larger δ
13
C excursion. Likewise, for a given negative δ
13
C excursion, a large M
Ex
or low δ
Ex
requires a greater input of
12
C. Differences in
F
In
, δ
In
,
F
Out
and δ
Out
cause changes in the response of δ
Ex
over time. For a negative δ
13
C excursion of given magnitude, a greater
F
In
requires a greater input of
12
C and lessens the time for δ
Ex
to return to initial conditions. A decrease in δ
Out
(caused by an increase in the relative output of organic matter and carbonate) has a similar effect. Variable d
M
Add
/d
t
produces transients in δ
Ex
that are related to the source function but modified by carbon removal. In theory, a well-dated and representative global δ
13
C excursion could be used to derive the carbon inputs and ouputs. Ocean Drilling Program (ODP) Site 1051 has an expanded early Palaeogene section, and recent work at this location has provided a well-dated δ
13
C record across the LPTM. This δ
13
C record contains transient variations of apparently global nature. These observed transients are best explained by a pulsed injection of CH
4
into an exogenic carbon cycle with a greater carbon throughput or enhanced burial of organic matter after carbon addition.
Palaeoenvironmental implications of palygorskite clays in Eocene deep-water sediments from the western Central Atlantic
Authors: Pletsch Thomas
Published: April 2008

Clay mineral analyses were performed on Eocene sediments from drill sites in the western Central Atlantic. The investigated sites cover the full range of early Palaeogene deep waters above and below the calcite compensation depth (CCD), but otherwise represent different depositional and hydrographic regimes. Palygorskite clays with authigenic microstructures were discovered in Lower Eocene hemipelagic sediments from the distal end of the Blake Nose depth transect and in pelagic clays of the same age from the distal Nares Abyssal Plain, where terrigenous input was reduced. Palygorskite clays were not detected in coeval sediments from a distal near-CCD setting on Bermuda Rise that received major terrigenous input. The distribution of palygorskite clays at these sites, the microstructures of the constituent minerals, their absence from contemporaneous deposits on the American margin, and the position of the northerly sites outside the range of a potential African aeolian supply strongly suggest an authigenic origin of these clays at the early Eocene sea floor. Palygorskite clays are widely distributed in lower Eocene sediments from about 50° N to 50° S palaeolatitude. The most widespread distributions and peak abundances in Atlantic oceanic sediments are reported from shelf to deep-water sites of the palaeo-tropical and -subtropical belt and correlate with the Early Eocene period of extreme warmth. Marine authigenic palygorskite clay may provide an indication of the localities and the time periods that were characterized by high bottom-water temperatures, by elevated alkalinity, silica and magnesium concentrations, and by reduced sediment accumulation rates.
When the Wilson Cycle breaks down: how orogens can produce strong lithosphere and inhibit their future reworking
Authors: Krabbendam Maarten
Published: April 2008

Although poly-cyclicity is common, many orogens show a remarkable lack of reworking. In this paper, a review of some factors that may either enhance or inhibit reworking of orogens is presented. As a general rule, orogens are unlikely to rift and rework if their lithospheric strength is higher than adjacent lithosphere. The strength of the lithosphere is strongly dependent on the geothermal gradient and the rheology of the rocks; both these factors can depend on the preceding orogenic evolution, even several hundred Ma after orogenesis. Strong orogenic lithosphere is expected if the crust is composed of material with a low radiogenic heat production capacity, such as island arcs, or if the underlying sub-continental lithosphere is still thickened, as in the Urals. Extensive dehydration metamorphism, a concentration of radiogenic heat production in the upper crust and erosional thinning of the orogenic crust can also strengthen the lithosphere and inhibit reworking. However, proximity of Archean cratons and anomalously high mantle heat flow appear to strongly enhance susceptibility to reworking.
From lithospheric thickening and divergent collapse to active continental rifting
Authors: Rey P.
Published: April 2008

The Aegean Sea, the Alboran Sea, and the Basin and Range Province suggest that continental lithosphere following gravitational collapse may end up being thinner than it was before convergence and thickening. In order to assess the condition leading to the development of finite lithosphere thinning following convergence and convective thinning, the strength of the continental lithosphere, the gravitational force, and the rate of gravity-driven flow (spreading rate) are calculated during and after continental collision. One-dimensional numerical experiments, presented here, assume that the deformation is homogeneous, that erosion is a function of strain rate and elevation, and that thermal relaxation involves no lateral conduction of heat. Results show that if 430f the lower lithospheric mantle is dragged into the convective mantle (convective thinning), gravitational collapse may lead to a lithosphere thinner than the initial lithosphere (pre-thickening lithosphere), provided that gravitational collapse is accommodated by the passive displacement of the surrounding lithosphere (free boundary collapse). When a slightly larger volume of lithospheric mantle is removed, a phase of extension leading to a necking instability and the formation of an active rift follows collapse. The presence of fixed boundaries and/or horizontal compressive stresses strongly reduces the spreading rate and opposes finite lithosphere thinning and therefore active rifting. It is suggested that back-arc extension occurring in continental settings could exemplify post-collapse active rifting.
Geodynamics of central Australia during the intraplate Alice Springs Orogeny: thin viscous sheet models
Authors: Roberts Emily A. , Houseman Gregory A.
Published: April 2008

This study investigates possible mechanisms that can account for the intraplate deformation in central Australia and the Canning Basin during the Devo-Carboniferous Alice Springs Orogeny. The intraplate orogeny in central Australia seems to have occurred without the association of a significant collisional orogenic event at the plate boundary. In contrast, the present-day Tian Shan may be viewed as a consequence of the plate boundary collision which has produced the Himalayas and the Tibetan Plateau. The experiments presented in this paper examine a mechanism that produces intraplate thickening and thinning of the crust but leaves the boundary relatively undeformed. A thin viscous sheet approximation of continental lithosphere is used to demonstrate that a clockwise rotational northern boundary acting on a lithospheric sheet with an internal weak zone may produce crustal thickening in the region representing central Australia, and thinning in the region representing the Canning Basin. In this model a clockwise rotation of the northern boundary may be induced either by an eastward shear traction or by a clockwise bending moment. The relation between rotation of the boundary and maximum crustal thickening factor is, to first order, independent of the way in which deformation is driven. It depends primarily on the relative dimensions of the intracratonic weak zone. For plausible estimates of thin viscous sheet geometry and variation of lithospheric strength within the sheet, it is inferred that clockwise rotation of the northern Australian block of order 20–25° is required to produce a maximum crustal thickening factor in central Australia of order 1.67. These calculations indicate that the depth-averaged strength of the lithosphere in central Australia prior to the Alice Springs Orogeny was of order
B
0
= 0.8 × 10
13
Pa s
1/3
, assuming plausible estimates of plate boundary force of 5 × 10
12
Nm
−1
and orogenic time span of 100 Ma. Based on a simplified approximate model for lithospheric strength this strength coefficient corresponds to a Moho temperature in central Australia of order 520°C. The concentration of deformation in this relatively narrow zone that stretches E-W across the continent, implies that the blocks to the N and S are much stronger, a difference which might be explained by a decrease in Moho temperature of order 60°C. If Moho temperatures prior to the Alice Springs orogeny were higher than those estimated above, the required deformation may have been compressed into a shorter period than 100 Ma, or may have been episodic rather than continuous.
A thin-plate model of Palaeozoic deformation of the Australian lithosphere: implications for understanding the dynamics of intracratonic deformation
Authors: Braun Jean , Shaw Russell
Published: April 2008

Presented here are the results of a thin-plate model of the continental lithosphere in which deformation is driven by velocities specified along the plate boundaries. The geometry of the model, the strength of each lithospheric block, and the boundary conditions have been chosen to reproduce the major tectonic episodes experienced by the Australian continent during a 200 Ma time period starting in the Ordovician (i.e. 470 Ma). The model’s focus is on the reactivation and/or reworking of zones of weakness within the continent that have either been set
a priori
or developed in response to previous tectonic regimes. Using the tectonic history of the Australian continent as a natural laboratory in which hypotheses on the nature and style of intracratonic deformation can be tested, the following conclusions can be made: (i) intracratonic deformation results from the concentration of strain into regions of decreased lithospheric strength; these weak zones are often caused by previous intracratonic deformation and/or develop at the interface between regions of contrasting strength; (ii) repeated deformation episodes lead to strain localization; (iii) localized deformation may also take place as the result of the constructive interaction between two tectonic regimes originating on separate margins; and (iv) there are mechanisms that operate within the lithosphere by which deformation leads to local strengthening.
Polyphase deformation and metamorphism at the Kalahari Craton — Mozambique Belt boundary
Authors: Manhica A. D. S. T. , Grantham G. H. , Armstrong R. A. , Guise P. G. , Kruger F. J.
Published: April 2008

The rocks of the Kalahari Craton in central western Mozambique have crystallization ages of between
c.
2300 and 3400 Ma and comprise dominantly granite-greenstones, peraluminous two-mica granites, subordinate younger mafic and granitic intrusions of uncertain age and cover sedimentary rocks. The rocks of the Mozambique Belt comprise
c.
1100 Ma intrusive granitoids as well as mafic intrusives and supracrustal migmatite gneisses of uncertain age. The boundary zone between and including these two crustal provinces is characterized by a strong N-S penetrative planar and migmatitic fabric. Sparse kinematic indicators suggest a sinistral sense of displacement along this shear zone. The metamorphic gradient increases from west to east from low grade on the Kalahari Craton to high-grade in the east, characterized by two generations of anatectic migmatization.
40
Ar/
39
Ar thermochronology on mica suggests that the Kalahari Craton lithologies have experienced heating above at least
c.
300°C during the
c.
1100 Ma Grenville age orogeny and again at
c.
530 Ma during the Pan-African Orogeny, possibly related to the collisional amalgamation of East and West Gondwana. The Mozambique Belt lithologies record a
c.
550 Ma thermal overprint with the lithologies in the vicinity of the N-S shear zone recording thermal reactivation at
c.
470 Ma. Comparisons of the new data with that from western Dronning Maud Land, which was adjacent to the study area prior to Gondwana fragmentation, yield many similarities.
Polymetamorphism of mafic granulites in the North China Craton: textural and thermobarometric evidence and tectonic implications
Authors: Zhao Guochun , Cawood Peter A. , Wilde Simon A. , Sun Min
Published: April 2008

The basement of the North China Craton can be divided into the Archaean Eastern and Western Blocks, separated by major Palaeoproterozoic terrane boundaries that roughly correspond with the limits of a 100–300 km wide zone, named the Trans-North China Orogen. Some mafic granulites from the orogen and adjoining areas in the Eastern and Western Blocks preserve textural evidence for two granulite facies events involving contrasting P-T paths. The first event is characterized by three distinct mineral assemblages, M
1a
to M
1c
. M
1a
is represented by fine-grained orthopyroxene + clinopyroxene + plagioclase ± quartz, which is surrounded by the M
1b
garnet + quartz symplectite, which itself is mantled by the M
1c
plagioclase + biotite symplectite. These assemblages and their P-T estimates define an anticlockwise P-T path, with peak metamorphism of 7.0–8.0 kbar and 800–850°C (M
1a
) followed by isobaric cooling to 700–750°C (M
1b
) and pressure-decreasing cooling to 630–700°C (M
1c
). The second event also includes three mineral assemblages, M
2a
to M
2c
. M
2a
represents growths of garnet porphyroblasts and matrix orthopyroxene + plagioclase + clinopyroxene + quartz; M
2b
consists of orthopyroxene + plagioclase ± clinopyroxene symplectites or coronas; and M
2c
is represented by plagioclase + hornblende symplectites. These assemblages and their P-T estimates define a clockwise P-T path, with peak metamorphism of 9.2–9.8 kbar and 820–850°C (M
2a
), followed by near-isothermal decompression (M
2b
) of 7.0–7.6 kbar and 760–810°C and cooling (M
2c
) to 690–760°C. The isobaric cooling, anticlockwise, P-T path of the first granulite facies event is similar to the P-T paths inferred for the
c.
2.5 Ga metamorphosed mafic granulites from the Eastern and Western Blocks, whereas the near-isothermal decompression, clockwise, P-T path of the second granulite facies event is similar to the P-T paths inferred for the
c.
1.8 Ga metamorphosed khondalite series in the Western Block and some mafic granulites in the Trans-North China Orogen. These relations suggest that the polymetamorphic granulites were derived from the reworking of the 2.5 Ga metamorphosed granulites during the 1.8 Ga collision between the Eastern and Western Blocks that resulted in the final amalgamation of the North China Craton.
A Quaternary geological perpective on geochemical exploration in glaciated terrain
Authors: Klassen Rodney A.
Published: April 2008

The application of Quaternary geology and glacial sedimentology is given as a broad guide for geochemical exploration in glaciated terrain. Predictive models of glacial dispersal provide an important basis for tailoring drift prospecting methods to suit regional variations in ice flow history and dynamics. The models relate compositional variations in glacial dispersal trains to ice flow direction, glacial history and subglacial processes. They are continually refined with reference to the geological and physical properties of the ice bed; new empirical field evidence constraining particle trajectories; and knowledge of subglacial processes affecting glacial erosion, transport and deposition. Transport at the ice bed leads to an exponential decrease in indicator concentrations with increasing distance of glacial transport, whereas linear decrease is associated with englacial transport, and may be characteristic of ice streams. The partitioning of rock and mineral fragments through subglacial comminution leads to compositional differences among size fractions that can reflect intensity of subglacial process, distance of transport, and provenance; hence, the choice of size fraction is important to drift prospecting by geochemical methods.
Till geochemistry and sampling techniques in glaciated shield terrain: a review
Authors: McMartin Isabelle , McClenaghan M. Beth
Published: April 2008

Till is a favoured sample medium for locating mineral deposits in glaciated shield terrains of Canada and Fennoscandia because it best reflects the primary composition of the bedrock source area. In the sampling phase, an important and costly component of till surveys, sample density, sample depth and sample method must be chosen according to the needs of the exploration program. Surface till sampling methods in forested areas differ from those used in permafrost terrain. However, in both areas, concentrations of labile ore minerals and their products of decomposition can be detected in the fine fraction (< 2 mm) of weakly oxidized till. In thin drift-covered areas, till samples are collected by hand excavation or trenching at < 5 m depth. In areas of thicker drift, more expensive methods such as reverse circulation rotary drills, rotasonic drills and portable drills are used to collect till samples at depth and to determine lateral and vertical variations in till geochemistry. Laboratory methods are an essential part of till geochemical surveys. The choices of the size fraction and analytical methods are determined by the nature and composition of the expected bedrock target, and by costs.
Indicator mineral and geochemical methods for diamond exploration in glaciated terrain in Canada
Authors: McClenaghan M. B. , Kjarsgaard B. A.
Published: April 2008

This paper provides a summary of selected diamond exploration techniques used in the glaciated terrain of Canada, focusing on indicator mineral methods and till geochemistry but also including geochemistry of lake sediments and vegetation. Diamond exploration in Canada focuses on kimberlite, the primary host rock for diamonds in this country. Kimberlite is a mineralogically and chemically distinct point source which may yield discrete dispersal trains in glacial sediments. Understanding the ice flow history and depositional history of glacial sediments and identifying multiple till sheets in areas covered by thick glacial sediments are essential for successful sampling, interpretation and follow-up of indicator mineral and geochemical anomalies related to these rocks. Orientation studies over known kimberlites provide important information on the mineralogical and geochemical signatures of kimberlite, and the size fractions of glacial sediments that are best suited to indicator mineral and geochemical analysis. Kimberlite indicator minerals survive glacial transport over long distances and the relative abundance of each mineral in till is a function of the primary mineralogy of individual kimberlites. Indicator mineral distributions observed at a regional scale define the net effect of glacial dispersal, often along different ice flow directions. Local scale distributions define individual dispersal trains. The finer (0.25 to 0.5 mm) fraction of heavy mineral concentrates prepared from till samples is best suited for indicator mineral surveys. Till geochemistry is gaining popularity in diamond exploration because it is significantly cheaper than indicator mineral analysis and it can be performed quickly. Important kimberlite pathfinder elements that provide good contrast in till geochemical surveys include Ni, Cr, Ba, Co, Sr, Rb, Nb, Mg, Ta, Ca, Fe, K, Ti and REE, the relative importance of which will depend on kimberlite composition as well as that of the surrounding bedrock. Biogeochemical studies over kimberlites in Canada reveal geochemical signatures in vegetation despite the glacially transported substrate.
Biogeochemical exploration methods in the Canadian Shield and Cordillera
Authors: Dunn Colin E.
Published: April 2008

This review article focuses on field methods in biogeochemical exploration and is based largely on the author’s experience. Consideration is given to reasons for applying biogeochemical methods as alternatives or supplements to other surficial sampling media that can be used in the exploration for mineral deposits in glaciated terrain. Extensive root systems can absorb metals from the substrate and integrate the geochemical signature of large volumes of sediment, groundwater and sometimes bedrock, thereby providing a more representative reflection of the chemical environment than that obtained from some other media. Sampling methods and precautions that should be taken are outlined. Variables that govern plant chemistry include the heterogeneity of composition among plant species and plant tissues, and the modifying effects of the seasons and contamination from external sources. Studies indicate that biogeochemical methods can provide a more proximal indication of concealed mineralization than the distal indications typical of till geochemistry programmes. Consequently, comparisons of till and biogeochemical data can help to define vectors toward mineralized sources such that the two methods are complementary.
Analysis of geochemical data for mineral exploration using a GIS — A case study from the Swayze greenstone belt, northern Ontario, Canada
Authors: Harris J. R. , Wilkinson L. , Bernier M.
Published: April 2008

Geographic Information Systems (GIS) provide the geologist with a powerful tool, when used in concert with statistical and geostatistical analysis, for archiving, manipulating, analysing and visualizing geochemical data. This paper uses geochemical (Zn, Cu) data obtained from various media (rock, lake sediments, till, soil and humus) over the Swayze greenstone belt in northern Ontario, to explore methods for analysing and visualizing geochemical data with a focus to mineral exploration applications.

The behaviour of Zn and Cu in both bedrock and the surficial environment is studied using statistical and geostatistical techniques. Interpretation and uses of traditional statistics and dot plots are contrasted with interpolated geochemical maps as well as red-green-blue (RGB) ternary maps. Techniques for multimedia comparison and geochemical anomaly detection and screening are presented. The processing methods presented in this paper can be utilized and adapted by other geologists for exploring their own geochemical data. Many of the algorithms presented here are available within standard GIS software packages, or can be written easily using a GIS macro language.
Application of composite glacial boulder geochemistry to exploration for unconformity-type uranium deposits in the Athabasca Basin, Saskatchewan, Canada
Authors: Earle Steven
Published: April 2008

Sampling glacially transported boulders is effective for mapping subcrop clay alteration patterns associated with deeply-buried unconformity-type uranium deposits in the Athabasca Basin of northern Saskatchewan, Canada. The technique works well because the subcrop alteration haloes show significant geochemical contrast with background, because the glacial deposits are consistently distributed and rich in boulders, and the altered boulders are typically well-represented in the boulder population. Boulder sampling is preferred over some other techniques because it is rapid and inexpensive, and the use of a lithological sampling medium provides a direct measure of subcrop clay-mineralogy, in an area where outcrop exposure is very restricted.

A large composite boulder sample data set, comprising
c.
20 000 samples from within the eastern part of the Athabasca Basin, has been compiled. Sampling and analytical techniques are descirbed, and results are presented at both regional and semi-regional scales. The distributions show clear correlations with both basin-scale features, such as stratigraphical variation and regional alteration patterns, and with deposit-related features, such as hydrothermal illite, dravite and chlorite alteration. Composite boulder lithogeochemistry may be equally effective for mineral exploration in other glaciated regions with restricted bedrock exposure.
Contrasting styles of glacial dispersal in Newfoundland and Labrador: methods and case studies
Authors: Batterson Martin J. , Liverman David G. E.
Published: April 2008

A review of practical approaches to drift exploration intended for use by exploration geologists working in drift covered areas is presented. The contrasting styles of glacial dispersal between Labrador, dominated by the effects of the Laurentide ice sheet, and the Island of Newfoundland, affected by small, coalescing ice caps at the glacial maximum and smaller topographically-controlled ice centres during deglaciation, are described. The effect has been to produce longer, ribbon-shaped dispersal trains in Labrador, except in the Labrador Trough near the centre of the Labrador sector of the Laurentide Ice Sheet, and shorter more diffuse dispersal patterns in Newfoundland.
Geochemical signatures around massive sulphide deposits in southern British Columbia, Canada
Authors: Lett Ray E.
Published: April 2008

This paper demonstrates the application of geochemical exploration for sulphide mineralization in glaciated areas by a case history illustrating the discovery of Cu-Pb-Zn-Ag-Au massive sulphide deposits in southern British Columbia, Canada. These deposits, hosted by Palaeozoic metasedimentary and metavolcanic rocks of the Kootenay Terrane, were first detected by weakly anomalous Cu and Au values in regional stream sediment samples and subsequently confirmed by more detailed stream and soil geochemical surveys, prospecting and diamond drilling.

Till geochemistry is a very effective exploration method because there is a well developed dispersal plume of mineralized bedrock down-ice from the massive sulphide deposits. Elevated Au, Pb, Cu and As levels in till samples collected up to 8 km down-ice from the deposits are direct indicators for sulphide mineralization. Barium, Cr and Ni are pathfinders for distinguishing different types of sulphide mineralization. The relationship between the bedrock, stream sediment, stream water and till geochemistry is shown more clearly in a conceptual model. This model has a practical application to future exploration for massive sulphides in southern British Columbia by establishing criteria such as geochemical anomaly size and contrast for different sample media.
Glacial transport and secondary hydromorphic metal mobilization: examples from the southern interior of British Columbia, Canada
Authors: Paulen Roger C.
Published: April 2008

Glacial transport of trace elements was studied at seven mineral occurrences in the southern interior of British Columbia; a region where mineral exploration is hampered by the scarcity of bedrock outcrop and by a variable sediment thickness associated with the Cordilleran Ice Sheet. The till deposited in the region was, for the most part, a product of the last glacial period. A review of previous geochemical studies conducted by the mineral exploration industry provides an indication to the variable configuration of the local dispersal patterns in the area. Dispersal trains in till are short, generally < 1–2 km, rarely exceeding 10 km in length and are usually proximal to bedrock source. They are commonly ribbon-shaped and rarely exceed 1 km in width. Observed dispersal patterns suggest that drastic changes in topography might have affected basal ice velocity which increased the distance of glacial transport. In addition, the distance that separates bedrock mineralization from its surficial geochemical expression in till varies with drift thickness and topography. Several glacial dispersal trains have been modified in shape by secondary hydromorphic dispersion.
Experimental constraints on the mechanical and hydraulic properties of deformation bands in porous sandstones: a review
Authors: Main Ian , Mair Karen , Kwon Ohmyoung , Elphick Stephen , Ngwenya Bryne
Published: April 2008

Deformation bands form in porous, clay-poor, sandstones in the top few kilometres of the Earth’s surface, involving the sequential growth of a set of discrete fault strands with minimal individual offset, ultimately culminating in the development of a slip surface with a large offset. We review some of our recent experimental results designed to reproduce the early stages of this sequence, obtained at room temperature and low confining pressure (
P
< 70 MPa) in a large-capacity (10 cm core diameter) deformation rig. We examine the physical weakening and strengthening mechanisms at work in the experiments, and discuss the implications for fault sealing. We describe laboratory experiments where deformation occurs by the progressive formation of new bands with a finite small offset and a relatively constant fault gouge grain-size distribution, at a relatively constant stress measured at the sample boundaries. The friction coefficient is 0.6, i.e. within the standard range. No large-offset slip surfaces were observed. Cross-fault permeability is transiently increased during dynamic stress drop, associated with the ‘suction pump’ provided by rapid near-fault dilatancy under conditions of constant flow rate. As the deformation band develops quasi-statically, permeability is then reduced further by up to two orders of magnitude as a result of shear-enhanced compaction and porosity loss of the poorly sorted gouge fragments. A simple microstructural model successfully predicts the physical sealing rates in the post-failure stage. Finally, we estimate the chemical sealing rates from mass balance calculations based on direct measurement of the pore fluid chemistry during constant flow experiments at temperatures up to 120°C. When extrapolated to longer timescales, these account quantitatively for the differences between permeability reductions measured in the laboratory and in the field.
Microfracturing associated with reactivated fault zones and shear zones: what can it tell us about deformation history?
Authors: Mitra Gautam , Ismat Zeshan
Published: April 2008

Deformation in fault zones is commonly characterized by grain-scale microfracturing, with microcrack density typically increasing toward the middle of the zone. The cracks can form under a wide variety of conditions and need to be used with great caution in making tectonic interpretations, particularly in areas with a complex history of fault reactivation. Microcracks may be intragranular (contained within single grains) or intergranular (with a length of several grain diameters). Intragranular cracks formed under dominantly plastic deformation conditions are crystallographically controlled and may not be directly related to regional stresses. Intragranular cracks formed during initial fracturing under cataclastic conditions develop only in grains that are optimally oriented to the deforming stresses. Intergranular cracks form during progressive cataclasis as intragranular cracks grow to join one another: they may develop as transgranular cracks that cut across several grains or as grain-boundary cracks. Once formed, microcracks may be preserved in a variety of ways (e.g. sintering, healing, cementation) depending on post-deformation conditions, and may be distinguished from one another on the basis of microstructural characteristics. Distinguishing between successive generations of microcracks in areas of fault reactivation is particularly important in determining the deformation history and obtaining deformation conditions. For example, Proterozoic quartzites collected from the central Utah Sevier belt have undergone multiple episodes of contractional deformation followed by Basin-and-Range extension. The use of polarized and dark-field optical microscopy and scanning electron microscopy allows microcracks related to the separate episodes of deformation to be distinguished on the basis of morphology, mode of preservation and consistent cross-cutting relationships. Variations in microcrack density and volume of cataclasized rock for the different generations of microcracks are used to establish the patterns of overprinting during fault reactivation. Anastomosing zones of intense deformation formed during successive episodes of faulting may not coincide with one another, as grain-size reduction and cementing during each episode hardens the zones, causing deformation to shift to adjoining weaker rock. However, the fault zone as a whole is a sufficiently large inhomogeneity that it is reactivated during successive faulting events.
Episodic weakening and strengthening during synmetamorphic deformation in a deep-crustal shear zone in the Alps
Authors: Steffen Kurt , Selverstone Jane , Brearley Adrian
Published: April 2008

The Greiner shear zone (western Tauern Window) deformed a variety of metasedimentary, metavolcanic, and plutonic lithologies at conditions of
c.
525–575 °C and 30–40 km depth. Microstructural relationships point to a succession of weakening and strengthening episodes. Stage I involved softening via a change in deformation mechanism. Grain-size reduction in plagioclase-rich horizons locally produced rocks with an average grain size of <30 μm microstructural features consistent with deformation via grain boundary diffusion creep (GBDC; a fluid-assisted deformation mechanism similar to pressure solution, which may result in superplastic behaviour). At constant stress, GBDC will result in a significant increase in strain rate relative to neighbouring layers. Stage II involved reaction-induced strengthening. Rapid bulk diffusion rates associated with GBDC allowed rapid growth of large (up to 20 cm) hornblende cystals. This growth of large cross-cutting crystals shut down grain-size-sensitive flow mechanisms in the plagioclase matrix and locally ‘locked’ the shear zone, shifting ductile deformation to weaker horizons. Stage III involved reaction-induced softening. Local variations in bulk composition and/or fluid availability caused large hornblende grains in some horizons to be partially replaced by biotite. These biotite-rich layers localized subsequent deformation, whereas adjacent layers with intact hornblende record minimal strain. Deformation and metamorphism together exert control on fluid availability, diffusion rates, and reaction kinetics, and these factors collectively control fabric development and rheology. The effects of interaction between small-scale deformational and metamorphic processes are difficult to predict, but can have an important influence on shear zone behaviour at depth. The resulting complexities need to be accounted for in models of crustal strength-depth relationships and shear zone rheologies.
Geometric controls on the evolution of normal fault systems
Authors: Walsh J. J. , Childs C. , Meyer V. , Manzocchi T. , Imber J. , Nicol A. , Tuckwell G. , Bailey W. R. , Bonson C. G. , Watterson J. , Nell P. A. , Strand J.
Published: April 2008

The growth of normal fault arrays is examined in basins where sedimentation rates were higher than fault displacement rates and where fault growth histories are recorded by thickness and displacement variations within syn-faulting sequences. Progressive strain localization is the principal feature of the growth history of normal faults for study areas from the Inner Moray Firth, a sub-basin of the North Sea, and from the Timor Sea, offshore Australia. The kinematics of faulting are similar in both study areas. Fault displacement rates correlate with fault size, where size is measured in terms of either displacement or length. Small faults have higher mortality rates than larger faults throughout the growth of the fault system. Displacement and strain are progressively localized onto the larger faults at the expense of smaller faults at progressively larger scales. Strain localization and the preferential growth of larger faults are attributed to geometric factors, such as size and location, rather than to the mechanical properties of fault rock in individual faults. This conclusion is supported by numerical models that reproduce the main characteristics of fault system growth established from both study areas.
The nature and origin of asymmetric arrays of shear surfaces in fault zones
Authors: Wojtal Steven F.
Published: April 2008

Mid- to upper-crustal fault zones often possess arrays of shear surfaces whose traces on sections perpendicular to the fault surface and parallel to the
ac
-plane conform with one or more of the ‘Riedel shear’ orientations. These shear surfaces often are oblique to the transport plane, however, so arrays exhibit monoclinic rather than orthorhombic symmetry. In a mudstone-dominated mélange in Humber Arm Supergroup strata in the Bay of Islands, Newfoundland, and in serpentinites from the base of the Bay of Islands complex, shear surfaces have orientations inclined to major fault-zone boundaries and an inferred
ac
-plane for macroscopic fault-related deformation. Deformation in these zones exhibits an overall monoclinic symmetry. The 3D, asymmetric character of shear surface fabrics suggests that a factor other than stress or the symmetric strain rate tensor controlled their formation. The velocity gradient tensor in a steady, non-coaxial shearing flow possesses a symmetry consistent with monoclinic fabrics. Shear surfaces in asymmetric arrays may initiate with predictable orientations relative to the velocity gradient tensor and then rotate toward flow apophyses, which identify stable positions in steady, 3D flows.