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A recent volcanic eruption occurred at Tseax volcano that formed a series of tephra cones in northwestern British Columbia, Canada. The explosive to effusive eruption also formed a 32 km long sequence of Fe-rich Mg-poor basanite–trachybasalt lavas covering ∼40 km2. Oral histories of the Nisg_a’a Nation report that the eruption may have caused as many as 2000 fatalities. The actual eruption date and question of whether there was one or multiple eruptive episodes in the 14th and 18th centuries are, as of yet, unresolved. New radiocarbon dating of wood charcoal from immediately beneath vent-proximal tephra deposits and complementary age information suggest an eruption in 1675–1778 CE (95.4% probability) was responsible for the formation of the tephra cone. New paleomagnetic and geochemical data from the tephra cone and lava flows suggest there is, in fact, no statistically significant difference in time between the explosive and effusive deposits and that they formed during a single eruptive episode.

As mineral exploration seeks deeper targets, there will be a greater reliance on geophysical data and a better understanding of the geological meaning of the responses will be required, and this must be achieved with less geological control from drilling. Also, exploring based on the mineral system concept requires particular understanding of geophysical responses associated with altered rocks. Where petrophysical datasets of adequate sample size and measurement quality are available, physical properties show complex variations, reflecting the combined effects of various geological processes. Large datasets, analysed as populations, are required to understand the variations. We recommend the display of petrophysical data as frequency histograms because the nature of the data distribution is easily seen with this form of display. A petrophysical dataset commonly contains a combination of overlapping sub‐populations, influenced by different geological factors. To understand the geological controls on physical properties in hard rock environments, it is necessary to analyse the petrophysical data not only in terms of the properties of different rock types. It is also necessary to consider the effects of processes such as alteration, weathering, metamorphism and strain, and variables such as porosity and stratigraphy. To address this complexity requires that much more supporting geological information be acquired than in current practice. The widespread availability of field portable instruments means quantitative geochemical and mineralogical data can now be readily acquired, making it unnecessary to rely primarily on categorical rock classification schemes. The petrophysical data can be combined with geochemical, petrological and mineralogical data to derive explanations for observed physical property variations based not only on rigorous rock classification methods, but also in combination with quantitative estimates of alteration and weathering. To understand how geological processes will affect different physical properties, it is useful to define three end‐member forms of behaviour. Bulk behaviour depends on the physical properties of the dominant mineral components. Density and, to a lesser extent, seismic velocity show such behaviour. Grain and texture behaviour occur when minor components of the rock are the dominate controls on its physical properties. Grain size and shape control grain properties, and for texture properties the relative positions of these grains are also important. Magnetic and electrical properties behave in this fashion. Thinking in terms of how geological processes change the key characteristics of the major and minor mineralogical components allows the resulting changes in physical properties to be understood and anticipated.

We evaluated imaging alteration associated with porphyry copper style mineralisation using aeromagnetic data in the Highland Valley Copper (HVC) district as part of the Natural Sciences and Enginee...

Wireline logs and vertical seismic profile data were acquired in two boreholes intersecting the main mineralized zone at the Cu–Au New Afton porphyry deposit, Canada, with the objectives of imaging lithological contacts, fault zones that may have acted as conduits that channelled the mineralization, and alteration zones. Log data provide physical rock properties for the main lithologies and alteration zones. Calliper logs reveal many faults and caved‐in zones generally indicating rocks with low integrity at the borehole wall. The preponderance of these zones, as indicated by the logs, suggests that their response may dominate the seismic‐reflection wavefield. Outside fault zones, compressional and shear‐wave velocities exhibit significant variability due to porosity, the heterogeneity of volcanic fragmental rocks and alteration. Distributed acoustic sensing was used to acquire vertical seismic profiling data in the two boreholes surveyed with wireline logs. Straight and helically wound fibre‐optic cables housed standard fibres and a fibre engineered to increase the intensity of backscattering at the distributed acoustic sensing interrogator. Standard and engineered optical fibres placed in the two boreholes were daisy‐chained together to form two 5‐km‐long continuous fibres that were interrogated at once with two interrogators. A new generation of interrogator connected to the engineered fibres provided field data with lower noise level and higher signal‐to‐noise ratio. These data with higher signal‐to‐noise ratio from straight fibre‐optic cable were processed and used for depth imaging. Depth images benefitted from new migration weights that account for the directional sensitivity of the straight fibre‐optic cable and limit the extent of migration artefacts. Migration results show several reflectors with shallow dips to the northwest, some explained by faults intersecting the surveyed boreholes. The main sub‐vertical lithological and alteration contacts at New Afton generated downgoing reflections that were not considered in the migration.

Magnetic and gravity inversions are used to create 2D or 3D models of the magnetic susceptibility and density, respectively, using potential field data. Unconstrained inversions generate an output based on mathematical constraints imposed by the inversion algorithm. Constrained inversions integrate lithological, structural, and petrophysical information in the inversion process to produce more geologically meaningful results. This study analyses the validity of this assertion in the context of the NSERC-CMIC Mineral Exploration Footprints project. Unconstrained and constrained geophysical inversions were computed for three mining sites: a gold site (Canadian Malartic, Québec), a copper site (Highland Valley, British Columbia), and a uranium site (Millennium – McArthur River, Saskatchewan). After initially computing unconstrained inversions, constrained inversions were developed using physical property measurements, which directly link geophysics to geology, and lithological boundaries extracted from an interpreted geological model. While each derived geological model is consistent with the geophysical data, each site exhibited some magnetic complexity that confounded the inversion. The gold site includes regions with a strong magnetic signature that masks the more weakly magnetic zone, thereby hiding the magnetic signature associated with the ore body. Initial unconstrained inversions for the copper site yielded solutions with invalid depth extent. A consistency between the constrained model and the geological model is reached with iterative changes to the depth extent of the model. At the uranium site, the observed magnetic signal is weak, but the inversion provided some insights that could be interpreted in terms of an already known complexly folded geological model.

Submarine turbidity currents are one of the most important processes for moving sediment across our planet; they are hazardous to offshore infrastructure, deposit petroleum reservoirs worldwide, and may record tsunamigenic landslides. However, there are few studies that have monitored these submarine flows in action, and even fewer studies that have combined direct monitoring with longer‐term records from core and seismic data of deposits. This article provides one of the most complete studies yet of a turbidity current system. The aim here is to understand what controls changes in flow frequency and character along the turbidite system. The study area is a 12 km long delta‐fed fjord (Howe Sound) in British Columbia, Canada. Over 100 often powerful (up to 2 to 3 m sec−1) events occur each year in the highly‐active proximal channels, which extend for 1 to 2 km from the delta lip. About half of these events reach the lobes at the channel mouths. However, flow frequency decreases rapidly once these initially sand‐rich flows become unconfined, and only one to five flows run out across the mid‐slope each year. Many of these sand‐rich, channelized, delta‐sourced flows therefore dissipated over a few hundred metres, once unconfined, rather than eroding and igniting. Upflow migrating bedforms indicate that supercritical flow dominated in the proximal channels and lobes, and also across the unconfined mid‐slope. These supercritical flows deposited thick sand beds in proximal channels and lobes, but thinner and finer beds on the unconfined mid‐slope. The distal flat basin records far larger volume and more hazardous events that have a recurrence interval of ca 100 years. This study shows how sand‐rich delta‐fed flows dissipate rapidly once they become unconfined, that supercritical flows dominate in both confined and unconfined settings, and how a second type of more hazardous, and much less frequent event is linked to a different scale of margin failure.

Ore-forming hydrothermal fluids react differently with different country rocks, but few studies have applied this knowledge with the specific goal of expanding the size of hydrothermal footprints in mineral exploration. To develop this concept, 122 metamorphosed mafic dykes from the world-class Canadian Malartic gold district (18.6 Moz Au) were sampled and analyzed for mineralogy, physical properties, and lithogeochemistry (partial and total digestion). The mafic dykes intrude mainly metasedimentary rocks, post-date D1 deformation, and cross-cut early-D2 quartz monzodiorite intrusions, but they were deformed and altered during D2 deformation, mineralization, and metamorphism. They can be subdivided into three groups: Group 1 dykes are least-altered, characterized by amphibole-rich regional metamorphic assemblages and distributed throughout the Pontiac Subprovince. Group 2 and 3 dykes underwent ore-related hydrothermal biotite–calcite–pyrite alteration and are associated with density- and volume-adjusted concentration gains of over 100% in Au–W–Te–C–S–Ag–Cs–Mo–Cu–K–Rb–Se–U–Pb–Ba–F–Bi–Sn. They define a metasomatic footprint up to 6 km away from the deposit toward the SE and up to 2 km away from the deposit toward the SW. Fifty-eight variables that define halos around the Canadian Malartic deposit have been identified and integrated using principal component analysis. PC1 explains 30% of the variance, separates least-mobile elements from ore-related elements, and is interpreted to reflect the ore-forming alteration process. PC2 and PC3 represent igneous processes. PC4 highlights the calcite–pyrite and biotite alteration. Spatial variations of the modal abundances of amphibole, biotite, calcite, and pyrite are the simplest expression of the metasomatic footprint, and they can easily be documented during exploration at the camp scale.

Repeat submarine landslides are challenging to study due to the tendency of subsequent slides to destroy previous deposits. Repeat slides are common in fjord head deltas where high amounts of sediment are focused in narrow valleys. This study examines a well-known slide deposit associated with the Kitimat Delta on Canada's west coast that has been linked to tsunamigenic landslides in 1974 and 1975. For the first time we incorporate multibeam bathymetry to a multifaceted dataset including new high resolution acoustic data and sediment cores to examine the history of submarine slides at the Kitimat Delta. Based on morphological analysis and age modelling using 210Pb and 14C data, we determine that the complex surface morphology of the slide lobe consists of at least two large slide deposits that reach 5 km from the delta: the known event that occurred in 1975 and an older event that occurred at 623 ± 83 cal BP (95% confidence interval). We demonstrate that slide deposits can be differentiated based on surface morphology and acoustic character. This is confirmed by age modelling. The 1975 slide resulted in a flow that ploughed through the seabed creating compression and translation along a basal shear plane, resulting in deep deformation and a surface characterized by pressure ridges. The 623 ± 83 cal BP event resulted in a large amount of blocky slide material that overran the former seafloor and was transported >5 km from the delta front. Several buried events are observed at depth, one of which occurred at 2592 ± 84 cal BP and appears to be on the same order of magnitude as the 1975 event and showing very similar acoustic characteristics. As for hazard implications, we show submarine landslides of varying sizes have naturally occurred on this delta throughout the past several thousand years.

The Canadian Malartic deposit is a world class intrusion-related Archean gold deposit hosted in the Pontiac Subprovince, Superior Province, in Quebec, Canada. Laboratory petrophysical properties measurements were performed on 824 rock samples collected from the various rock types observed within the ore body and peripheral host rocks. The various rock types present in the Malartic District, mainly meta-sedimentary rocks, felsic-intermediate intrusive rocks and mafic dykes have contrasting grain densities and magnetic susceptibilities. Using support vector machines, it is shown that these two physical properties can be used to predict the rock type of a sample with an average precision and recall rate of 89%. Within the meta-sedimentary rocks class, variations in magnetic susceptibility are due to the changes in mineralogy associated with hydrothermal alteration. These are caused by the destruction of iron-bearing silicate minerals and magnetite in unaltered rocks (10−4 to 10−3 SI) to form pyrite, carbonates, K-feldspar and Fe-depleted hydrothermal biotite in altered rocks (10−5 to 10−4 SI). Within the felsic-intermediate intrusive rocks, grain densities below 2.7 g/cm3 and magnetic susceptibilities in the 10−6 to 10−4 SI range yield the highest probabilities that a rock has been submitted to carbonate and pyrite alteration. However, magnetic susceptibility and grain density of these intrusive rocks are also dependent on their Fe2O3/Al2O3 and TiO2/Al2O3 ratios, which are not related to the hydrothermal alteration footprint, but are rather due to distinct protolith compositions. Within the mafic dykes, grain density is the best indicator of hydrothermal alteration. Unaltered mafic dykes (2.95 to 3.10 g/cm3) are mostly composed of amphibole, whereas altered mafic dykes (2.70 to 2.95 g/cm3) have reduced amphibole contents and higher abundances of carbonates, pyrite, quartz, and biotite alteration. The support vector machine classifier is extended to predict if meta-sedimentary rocks, felsic-intermediate intrusive rocks and mafic dykes have undergone hydrothermal alteration with average F1 scores of 73%, 69% and 93%, respectively. In altered meta-sedimentary rocks, the integration of grain density and magnetic susceptibility allows the identification of altered but unmineralized samples. The classifier is further extended to predict if the gold content of meta-sedimentary rocks is above or below threshold values of 0.01, 0.1 and 1 ppm with average F1 scores of 83%, 80%, and 76%, respectively. Using conceptual models of the rock physical properties at the Malartic District scale, it is shown that ground magnetic surveys are the most promising geophysical tool for early-stage greenfield exploration of this type of deposit. However, depending on the scale at which the surveys are conducted, magnetic susceptibility contrasts between the various investigated rock types can overshadow the specific signatures of hydrothermally altered rocks. This in part explains why past airborne geophysical exploration campaigns for this type of deposit in the Malartic District were inconclusive. Finally, the machine learning process used in this case study can be applied in advanced exploration stages, during which drilling and either subsequent laboratory petrophysical analyses of core samples or downhole geophysical surveys produce large amounts of data that can be used to train prediction models.

Spectral induced polarization (SIP) measurements are now widely used to infer mineralogical or hydrogeological properties from the low-frequency electrical properties of the subsurface in both mineral exploration and environmental sciences. We present an open-source program that performs fast multi-model inversion of laboratory complex resistivity measurements using Markov-chain Monte Carlo simulation. Using this stochastic method, SIP parameters and their uncertainties may be obtained from the Cole-Cole and Dias models, or from the Debye and Warburg decomposition approaches. The program is tested on synthetic and laboratory data to show that the posterior distribution of a multiple Cole-Cole model is multimodal in particular cases. The Warburg and Debye decomposition approaches yield unique solutions in all cases. It is shown that an adaptive Metropolis algorithm performs faster and is less dependent on the initial parameter values than the Metropolis-Hastings step method when inverting SIP data through the decomposition schemes. There are no advantages in using an adaptive step method for well-defined Cole-Cole inversion. Finally, the influence of measurement noise on the recovered relaxation time distribution is explored. We provide the geophysics community with a open-source platform that can serve as a base for further developments in stochastic SIP data inversion and that may be used to perform parameter analysis with various SIP models.

3D lithofacies and physical rock property models were generated to interpret 3D seismic data acquired over the Lalor volcanogenic massive sulphide deposit, Manitoba, Canada. The lithofacies model revealed that strong seismic reflectivity is associated with ore-host rock and mafic-felsic lithofacies contacts, including their hydrothermally-altered equivalents. Different physical rock property models were subjected to 3D seismic forward modelling using the SOFI3D finite difference code. Seismic synthetics from discrete and interpolated models in which kriging of P-wave velocity and density was conditioned by curvilinear grids conformable to the 3D-modelled geological structure, showed a much better match to the seismic data in comparison to those generated by kriging in Cartesian space. Synthetics from these curvilinear grid models corroborate the origin of seismic reflectors, as qualitatively inferred from the lithofacies model. Seismic synthetics generated from physical rock property models in which physical rock properties were augmented by densely-sampled secondary variables, such as FeO percentage, enhanced lateral continuity of seismic reflectivity, although these co-kriged petrophysical models were not more accurate than their kriged equivalents. The physical rock property modelling methodology was also useful for testing the utility of passive interferometric seismic surveys, as this highlighted the limitations of the discrete physical rock property model.

Models of the three-dimensional physical property variation of the NICO Au-Co-Bi-Cu deposit, Northwest Territories, and the Southern Breccia albitite-hosted uranium occurrences and their iron oxide-alkali alteration envelopes, were derived from inversion of high-resolution aeromagnetic, gravity, and magnetotelluric (MT) data at deposit to regional scales. In turn, integration of the geophysical results with physical property measurements and geologic observations leads to a new understanding of the geometry of the deposit, adjacent mineralized and altered zones, and potential cogenetic links within the host metasomatic system. NICO, which is a variant of the magnetite group iron oxide copper-gold (IOCG) class of deposit, is spatially associated with a discrete zone of lower electrical resistivity occurring within a broader, NE-dipping zone of higher density. The high-density zone overlaps a NE-dipping zone of higher magnetic susceptibility and is truncated to the southwest by a NW-striking geophysical discontinuity interpreted as a major fault zone. This inferred fault divides the magnetite-altered metasedimentary rocks hosting the NICO deposit from the albite-altered rocks within the Southern Breccia corridor to the southwest that host the uranium mineralization. Having been active during development of the metasomatic system, this fault influenced the formation of these distinct but complementary deposit types.

We present a high resolution sedimentary record of dinoflagellate cysts spanning the last ~ 900 years recovered from Effingham Inlet, a glacial fjord on the west coast of Vancouver Island, Canada. The combination of seasonal coastal upwelling supporting high levels of marine primary productivity in surface waters, together with restricted bottom water circulation in the silled fjord, fosters the preservation of laminated sediments in the inner basin of Effingham Inlet. Geochemical data are used to assess the sedimentary facies of the core, which is composed primarily of laminated units (50.2%) occasionally interrupted by “seismites” (39.5%) and homogenous units (10.2%). The chronology of the ~ 2 m-long core is based on varve counting and fifteen 14C dates, and is anchored by a seismite previously dated at AD 1946. The dinoflagellate cyst assemblages are diverse (total of 47 taxa), abundant (average concentrations of 102,900 cyst g− 1 of dry sediment), and characterized by a proportionally equal contribution of autotrophic and heterotrophic cyst taxa in most samples. Overall, cyst assemblages are characterized by Operculodinium centrocarpum (36.2%) accompanied by Brigantedinium spp. (18.0%) and Dubridinium spp. (6.6%). Multivariate analyses are used to extract the dominant patterns of variability in autotrophic and heterotrophic dinoflagellate cyst assemblages separately, and help in identifying the temperature and primary productivity gradients encoded in the cyst sedimentary record in this particular estuary. Specific intervals identified in the dinoflagellate cyst record are interpreted to represent the local expression of the “Medieval Climate Anomaly” (from the base of the record, ~ AD 1090 to 1230), the “Little Ice Age” (~ AD 1230 to late 19th century) and warming in the second half of the 20th century. The timing of these intervals are consistent with the regional paleoclimate and help constrain past climatic and oceanographic variability on the west coast of Vancouver Island. The origin of homogenous units in the sedimentary record of Effingham Inlet and paleoseismicity in the region are also discussed.

Slipstream Slump, a well-preserved 3 km wide sedimentary failure from the frontal ridge of the Cascadia accretionary wedge 85 km off Vancouver Island, Canada, was sampled during Canadian Coast Guard Ship (CCGS) John P. Tully cruise 2008007PGC along a transect of five piston cores. Shipboard sediment analysis and physical property logging revealed 12 turbidites interbedded with thick hemipelagic sediments overlying the slumped glacial diamict. Despite the different sedimentary setting, atop the abyssal plain fan, this record is similar in number and age to the sequence of turbidites sampled farther to the south from channel systems along the Cascadia Subduction Zone, with no extra turbidites present in this local record. Given the regional physiographic and tectonic setting, megathrust earthquake shaking is the most likely trigger for both the initial slumping and subsequent turbidity currents, with sediments sourced exclusively from the exposed slump face of the frontal ridge. Planktonic foraminifera picked from the resedimented diamict of the underlying main slump have a disordered cluster of 14C ages between 12.8 and 14.5 ka BP. For the post-slump stratigraphy, an event-free depth scale is defined by removing the turbidite sediment intervals and using the hemipelagic sediments. Nine 14C dates from the most foraminifera-rich intervals define a nearly constant hemipelagic sedimentation rate of 0.021 cm/year. The combined age model is defined using only planktonic foraminiferal dates and Bayesian analysis with a Poisson-process sedimentation model. The age model of ongoing hemipelagic sedimentation is strengthened by physical property correlations from Slipstream events to the turbidites for the Barkley Canyon site 40 km south. Additional modelling addressed the possibilities of seabed erosion or loss and basal erosion beneath turbidites. Neither of these approaches achieves a modern seabed age when applying the commonly used regional marine 14C reservoir age of 800 years (marine reservoir correction ΔR = 400 years). Rather, the top of the core appears to be 400 years in the future. A younger marine reservoir age of 400 years (ΔR = 0 years) brings the top to the present and produces better correlations with the nearby Effingham Inlet paleo-earthquake chronology based only on terrestrial carbon requiring no reservoir correction. The high-resolution dating and facies analysis of Slipstream Slump in this isolated slope basin setting demonstrates that this is also a useful type of sedimentary target for sampling the paleoseismic record in addition to the more studied turbidites from submarine canyon and channel systems. The first 10 turbidites at Slipstream Slump were deposited between 10.8 and 6.6 ka BP, after which the system became sediment starved and only two more turbidites were deposited. The recurrence interval for the inferred frequent early Holocene megathrust earthquakes is 460 ± 140 years, compatible with other estimates of paleoseismic megathrust earthquake occurrence rates along the subduction zone.

Repeated outburst flooding from glacial Lake Missoula, Montana, affected large areas of Washington during Marine Oxygen Isotope Stage 2 (29–14 ka). We present the first high-resolution rock magnetic results from two sites that are critical to interpreting these outburst floods and that provide evidence of sediment provenance: glacial Lake Missoula, the source of the floods; and glacial Lake Columbia, where floodwaters interrupted sedimentation. Magnetic carriers in glacial Lake Missoula varves are dominated by hematite, whereas those in outburst flood sediments and glacial Lake Columbia sediments are mainly magnetite and titano-magnetite. Stratigraphic variation of magnetic parameters is consistent with changes in lithology. Importantly, magnetic properties highlight depositional processes in the flood sediments that are not evident in the field. In glacial Lake Columbia, hematite is present in fine silt and clay deposited near the end of each flood as fine sediment settled out of the water column. This signal is only present at the end of the floods because the hematite is concentrated in the finer-grained sediment transported from the floor of glacial Lake Missoula, the only possible source of hematite, ~ 240 km away.

Rock physical properties provide the link between geophysical surveys and their geological interpretation. The British Columbia rock physical properties database, compiled by the Geological Survey of Canada, now comprises 3876 values of density, 930 values of electric resistivity, 12 356 values of magnetic susceptibility, and 2576 values of magnetic remanence and Koenigsberger ratio. The measurements are linked to sample locations, lithologies, and geological formation or unit. Maps, histograms, and biplots are used to demonstrate useful links between lithology and physical properties, and serve as a background for future rock physical properties studies. As expected, density and resistivity are controlled mostly by porosity and mineralogy. Magnetic susceptibility has a bimodal distribution (maxima at 4 × 10−4 and 2 × 10−2 SI) controlled by magnetite concentration. Magnetic remanence is shown to be more important than usually considered in magnetic survey analysis, with Koenigsberger ratios greater than unity in 42% of the samples. A case study of the Chilcotin Group basalts is highlighted, as they form a significant barrier to mineral exploration in central British Columbia. These rocks are magnetically distinct from other basalts in British Columbia, distinguished by magnetic susceptibilities having a range of values concentrated around 3 × 10−3 SI and falling in the valley between the two susceptibility modes. These basalts are also characterized by very high Koenigsberger ratios (96% above unity), probably caused by a preponderance of fine-grained single-domain magnetite. The database provides a wealth of petrophysical properties that can help constrain analysis of several types of geophysical surveys and, in particular, modelling of anomalies in the quest to determine the three-dimensional distribution of rock units.

Annually laminated sediments from the anoxic inner basin of Effingham Inlet, Pacific coast of Vancouver Island, British Columbia, Canada, yield a high-resolution 42 m paleoenvironmental record, from the present to about 14 ka 14C BP (17 ka cal BP). A new age model, based on 68 radiocarbon dates from twigs and small plant material, from the 40 m core MD02-2494 and 2 m freeze cores from the surface, is anchored by the Mazama Ash and varve counting. A Poisson-process sedimentation model is used, applying a new method to determine the Poisson k value, giving a realistic age model compatible with the multi-proxy core data. Twenty-one “seismites”, which are lithofacies in the Effingham cores that may be representative of seismically triggered mass-wasting events, are identified and dated precisely, then compared with the chronology of the deep-sea turbidite record farther south in the Cascadia Subduction Zone (CSZ), to determine if regional sediment disturbances can be identified. With 16 proposed correlations, Effingham seismite ages are 169 ± 206 years older than turbidite ages estimated largely by radiocarbon analysis of foraminifera in hemipelagic deposits.

New techniques for the integration of gravity and aeromagnetic data through rock physical property relationships are tested for the rapid location of potential iron oxide–copper–gold (IOCG) exploration targets across the Great Bear magmatic zone (GBMZ). These techniques are based on the recognition of coincident or near-offset magnetic and gravity anomalies associated with IOCG deposits, resulting from their intense and combined iron-oxide and alkali alteration. In the GBMZ, the NICO (Au–Co–Bi–Cu) deposit is an atypical magnetite-group IOCG hosted within an intensely hydrothermally-altered metasedimentary sequence. Prospectivity maps for the NICO area are derived from the integration of high-resolution aeromagnetic and surface gravity data with physical property measurements of magnetic susceptibility and density. Method 1 combines the pseudo-gravity (derived from the aeromagnetic data) and Bouguer gravity data to determine the locations of superimposed high anomalies. Method 2 estimates the apparent susceptibility and density subsurface distribution based on vertical prism models of the magnetic and gravity data. The apparent susceptibility data are transformed to apparent density using physical property relationships. The two apparent density datasets are then combined to determine the location of coincident magnetic and gravity derived anomalies. The results of these methods are supported by, and compared with, similar prospectivity maps generated through weights of evidence techniques. At NICO, the prospectivity maps accurately locate the deposit and nearby occurrences. Despite the lower resolution of the regional gravity data, application of the techniques across the GBMZ is successful at locating mineralised IOCG systems including the magnetite-group systems at Grouard, Fab, DeVries and Cole Lake, the magnetite to hematite-group systems of the Port Radium-Echo Bay district, and has highlighted possible targets for future exploration.

The Fraser River in British Columbia, Canada, is the longest non-dammed river on the west coast of North America and supplies 20 × 10 6 t/yr of sediment to the Pacific Ocean. Abundant geomorphological evidence indicates that the Fraser River reversed its course to southward flow in the recent geological past. Investigation of two volcanic dams at Dog Creek demonstrates northward flow of the Fraser until at least 1.06 Ma, before reversal and erosion of the 270-km-long Fraser Canyon. We propose that the submarine Nitinat Fan off the coast of British Columbia records the reversal and sudden input of coarse continental-derived sediment ca. 0.76 Ma. This study confirms reversal of the Fraser River and places a firm constraint on the maximum age of that reversal. Reversal likely followed stream capture in response to enhanced glaciofluvial erosion and uplift of the Coast Mountains.

Two new records of glacial stratigraphy obtained from borecores collected in southcentral Saskatchewan are compared to previously published records from Wellsch Valley and Swift Current Creek in southern Saskatchewan. The comparisons are based on magnetostratigraphy and tephrochronology, and describe preglacial, glacial, and interglacial deposits. The new stratigraphy is compared to the composite global marine oxygen isotope record. Although the ages and extents of late Pleistocene continental glaciations are relatively well constrained, they are less well defined for the middle and early Pleistocene. Data presented here highlight recent studies carried out from borecores and outcrops of extensive pre-Illinoian (pre-Saalian) glacial deposits. Based on this new data, at least seven Laurentide (continental) glaciations are recognized in Saskatchewan, and these records are the most extensive to date in the Northern Interior Plains of Canada. The magnetostratigraphic records from the Sutherland Overpass and Wascana Creek sites provide the first evidence of reversely magnetized glacial deposits in the Canadian Prairies. These deposits can be assigned to the latest Matuyama (MIS 20) and indicate that Laurentide (continental) glaciations did not impact southern Saskatchewan until the late Early Pleistocene.

Tunnicliffe, J., Church, M. & Enkin, R. J. 2012 (January): Postglacial sediment yield to Chilliwack Lake, British Columbia, Canada. Boreas, Vol. 41, pp. 84–101. 10.1111/j.1502-3885.2011.00219.x. ISSN 0300-9483. Seismic records and evidence from sediment cores at Chilliwack Lake provide the basis for a long-term (postglacial) sediment budget for a 324-km2 Cordilleran catchment. Chilliwack Lake (11.8 km2 surface area), situated in the North Cascade Mountains, near Chilliwack, British Columbia, was formed behind a valley-wide recessional moraine in the final phase of post-Fraser alpine glaciation. Seismic surveys highlight the postglacial lacustrine record, which is underlain by a thick layer of sediments related to deglacial sedimentation. Sediment cores provide details of grain-size fining from the delta to the distal lake basin. The cores also show a record of intermittent fire and debris flows. Magnetic measurements of lake sediments provide information on grain size, as well as a dating framework. The total postglacial lake-floor deposit volume is estimated to be 397 ± 27 × 106 m3. Including estimates of fan and delta deposition, the specific postglacial yield to the lake is calculated to be ∼86 ± 13 Mg km2 a−1. The sediment volume in the uppermost (Holocene) lacustrine layer is 128 ± 9 × 106 m3, representing ∼41 ± 4 Mg km2 a−1 in the Holocene. Compared with other Cordilleran lakes of similar size, particularly those with glacial cover in the watershed, Chilliwack Lake has experienced relatively modest rates of sediment accumulation. This study provides an important contribution to a growing database of long-term (postglacial) sediment yield data for major Cordilleran lakes, essential for advancing our understanding of the pace of landscape evolution in formerly glaciated mountainous regions.

The Tintina Trench in west-central Yukon has preserved an extensive record of late Cenozoic preglacial, glacial, and interglacial deposits. These deposits comprise multiple sequences of tills, outwash, loesses, and paleosols. The sediments that were laid down directly by ice (tills) are of both local (montane) and regional (Cordilleran) provenance. The Tintina Trench area was impacted repeatedly by montane ice from the southern Ogilvie Mountains to the northwest (2500 m above sea level (asl)), and also repeatedly along its southern extent by Cordilleran ice from the Selwyn Mountains to the east (2759 m asl), the latter forming the continental divide in this region. We report here the magnetostratigraphy of three sections: Rock Creek (64°13′N, 139°07′W), West Fifteenmile River (64°29′N, 139°55′W), and East Fifteenmile River (64°23′N, 139°48′W). The majority of the units identified at these sections record late Pliocene to mid-Pleistocene glaciations, although relatively thin surficial sequences of late middle Pleistocene to late Pleistocene loesses and tills are present as well. Of the 11 units described in the Tintina Trench, seven have normal polarity, three have reversed polarity, and one has an undefined polarity. These units span about 3.0 million years. It appears that most of the polarity chrons and subchrons of the late Cenozoic are present and that the sequence of six reversals record at least 10 glaciations (three in the Brunhes Chron and seven in the Matuyama Chron), and 11 interglaciations (four in the Brunhes Chron and seven in the Matuyama Chron). The interglacials are recorded as either paleosols or unconformities between glacial or loess units having opposite polarity. While not all Matuyama Chron glacial and interglacial cycles recorded in marine isotopic records are seen on land, the terrestrial records found in the Tintina Trench have thus far proven to be the most complete in terms of the polarity record. While no absolute ages were obtained from the sediments in the trench, the extensive polarity sequence constrains the timing of glaciations to a considerably greater degree than was previously possible for this region. The magnetostratigraphy of the trench sites are compared with the glacial, glaciofluvial, and loessic deposits at the nearby Klondike River valley and Fort Selkirk sites, central Yukon, where tephras and basalts provide absolute ages, and stratigraphic units contain an extensive late Cenozoic climate proxy for northwestern North America (eastern Beringia). In this study, we present new paleomagnetic polarity data and establish a magneto-lithostratigraphy describing preglacial, glacial, and interglacial deposits in the Tintina Trench. These deposits are referred to as the West Tintina Trench Allogroup and provide a broad framework for establishing a paleoclimate record for the northern Canadian Cordillera.

The sedimentary record in a 40.9 m giant (Calypso) piston core (MD02-2494) raised from the inner basin within Effingham Inlet, British Columbia, Canada, during the 2002 Marges Ouest Nord Américaines (MONA) campaign, spans from 14 360 14C years BP (17 300 calibrated calendar (cal.) years BP) to about nine centuries before present. The core archives changes in sedimentation and sea level immediately following deglaciation of the Late Wisconsin Fraser Glaciation, which peaked about 15 000 14C years BP. The presence of the Mazama Ash in the core anchors a detailed chronology based on 49 radiocarbon dates and seven Pleistocene paleomagnetic secular variation correlations. Diatom assemblages identify a marine–freshwater–marine transition in the basin, which occurred 11 630 14C years BP (13 500 cal. years BP). At this time, a bedrock sill, presently at 46 m depth, was briefly exposed as sea level fell and then rose again during isostatic crustal adjustments. These data constrain a new sea-level curve for the outer coast of Vancouver Island covering the past 12 000 14C years BP (14 000 cal. years BP), providing new information on the nature of deglaciation along the west coast of Canada and informing interpretations of regional paleoceanographic records and mantle viscosity models.

A 40.32 m piston core recovered from Effingham Inlet, on the west coast of Vancouver Island, provides the basis for a high-resolution geochemical study of the last deglaciation and the Holocene. Glacial retreat, basin isolation, sea-level rise, and productivity variations are determined using proxies for sediment composition (K/Al, Fe/Al, Mg/Al), grain size (Ti/Al, Zr/Al), sedimentary redox conditions (Mo/Al, U/Al), and productivity (wt.% organic carbon, wt.% opal). As local ice retreated and marine waters inundated the basin, coarse-grained glacimarine sediments were replaced by finer grained, laminated, opal-rich sediments. During meltwater pulse-1a, the dominance of local crustal rise over eustatic sea-level rise resulted in the progressive restriction of ocean circulation in Effingham Inlet and the formation of a temporary freshwater lake. The transition into stable Holocene conditions was initiated at ∼12 700 BP, which corresponds to the onset of the Younger Dryas, as identified by the Greenland Ice core Project (GRIP) ice core δ18O record and was completed by 10 700 BP, ∼800 years after the GRIP ice core record stabilized. Holocene Mo/Al and U/Al ratios range between 12–35 (×104) and 1–3.4 (×104), respectively, indicating that although large-amplitude, high-frequency fluctuations occur, the sediments of Effingham Inlet inner basin have remained organic rich and oxygen depleted for the entire Holocene period. The combination of anoxic bottom waters and a Holocene sedimentation rate of 217 cm/ka have preserved a high-resolution record of environmental change in the northeast Pacific over the last 11 000 years.

Paleomagnetic study of 46 sites in Bowser Basin in central British Columbia, Canada, gives evidence of a pervasive late tectonic hydrothermal event which remagnetized all rock types. Around Oweegee Dome (56.7°N, 129.5°W), samples from Permian through Jurassic strata hold a paleomagnetic component, which postdates most tilting (negative tilt test). The westerly direction (Dec=285.5°, Inc=60.8°, k=40.0, α95=4.2°, N=30 sites) is interpreted to have been acquired during Cretaceous or earliest Cenozoic time after the main stage of Skeena Fold Belt deformation in the western part of the foldbelt. The direction is anomalously shallow and counter-clockwise rotated, due to Late Cretaceous and later lateral displacements, rotations and tilting. The diagenetic event revealed by this study, its timing and its implications on subsequent tectonic motions contribute to the understanding of Bowser Basin development in support of petroleum assessment.

Rocks are often magnetically altered during burial, thus providing a useful method to study their thermo-chemical history. In order to improve the understanding of burial diagenetic magnetization, we experimentally synthesized magnetite in natural samples. Lower Jurassic argillites from the Paris Basin were heated to 150 °C, under a confined atmosphere of argon. When a magnetic field was applied during the heating, a chemical remanent magnetization was acquired. Rock magnetism studies reveal that most of the newly formed magnetic carriers were magnetite. Using anhysteretic remanent magnetization as a measure of the quantity of magnetite, an increase of up to 150% after heating was observed. Ferrimagnetic iron sulphide and hematite are observed to have formed in samples composed of less than 3% calcite, and new magnetite is sometimes completely absent in samples containing less than 0.5% calcite. Hysteresis measurements suggest that the new magnetite is in the pseudo-single domain state. Scanning electron microscope studies indicate that the new magnetic carriers are associated with pre-existing pyrite. The magnetic transformations during the experiments involved a fluid which reacted with iron-bearing and sulfur-bearing minerals in ways depending on local redox conditions. This study shows that magnetite can be produced in argillaceous sediments at the normal temperatures and pressures found in sedimentary basins, without any external supply from long-range fluid flow.

The tilt or fold test in paleomagnetism is used to infer whether paleomagnetic remanence was acquired before or after tectonic tilting. While several tilt test formulations have been proposed, none fully satisfies the requirements of statistical validity, applicability to all bedding geometries, and ease of use. This paper introduces the direction–correction (DC) test, which examines the relationship between the paleomagnetic site mean directions and their corresponding bedding tilt corrections. The DC test is similar to McFadden’s correlation test because both test whether or not the site directions contain information about the bedding tilts, however the DC test gives greater weight to sites with greater counter-bedding. The DC test is similar to Watson’s numerical tilt tests because they determine the degree of untilting which gives optimal concentration of site directions, however the DC test uses analytical rather than numerical methods. Graphical output aids the researcher in recognizing problem sites. Using both real and simulated data, the DC test is demonstrated to be more discriminating than other tilt test formulations for all bedding geometries. The simulations show that the power of the tilt test is inversely proportional to the 95% confidence interval (α95) of the overall mean. As a rule of thumb, paleomagnetists should attempt to sample sufficient sites to obtain an α95 less than 1/6 of the bedding attitude difference.

Recurring glacial outburst floods from the Yukon-Tanana Upland are inferred from sediments exposed along the Yukon River near the mouth of Charley River in east-central Alaska. Deposits range from imbricate gravel and granules indicating flow locally extending up the Yukon valley, to more distal sediments consisting of at least 10 couplets of planar sands, granules, and climbing ripples with up-valley paleocurrent indicators overlain by massive silt. An interglacial organic silt, occurring within the sequence, indicates at least two flood events are associated with an earlier glaciation, and at least three flood events are associated with a later glaciation which postdates the organic silt. A minimum age for the floods is provided by a glass fission track age of 560,000 ± 80,000 yr on the GI tephra, which occurs 8 m above the flood beds. A maximum age of 780,000 yr for the floods is based on normal magnetic polarity of the sediments. These age constraints allow us to correlate the flood events to the early-middle Pleistocene. And further, the outburst floods indicate extensive glaciation of the Yukon-Tanana Upland during the early-middle Pleistocene, likely representing the most extensive Pleistocene glaciation of the area.

The Belt-Purcell Supergroup crops out in Montana, Idaho, Washington, British Columbia, and Alberta. It is the largest and most intensively studied Middle Proterozoic succession in North America. A major paleomagnetic survey of the Belt-Purcell basin in Montana was carried out by the U.S. Geological Survey between 1975 and 1985, but only partial results have been published. We reanalyze these data and add new data from the Canadian part of the basin. Results come from >2700 samples (mostly red beds) from 93 localities, spanning 13 formations or members of formations. They typically exhibit stable magnetizations carried by hematite in detrital specularite grains and pigment. Coherent paleomagnetic directions have either southwest declinations and moderate positive inclinations (normal polarity) or northeast declinations and moderate negative inclinations (reverse polarity). These directions clearly pass fold and reversal tests. A stratigraphically coherent directional swing and a reproducible polarity zonation indicate that the stable magnetization is primary and was acquired during the course of deposition. U-Pb dates suggest an ∼50 m.y. duration of deposition of the upper part of the Belt-Purcell Supergroup. The limited amount of apparent polar wander and the few polarity reversals recorded in the Belt- Purcell deposits are similar to the rate of polar wander and a long interval of stable polarity observed for the middle Cretaceous. An apparent incompatibility between early Middle Proterozoic (Elsonian) paleomagnetic poles from different regions of North America is now resolved; the Belt- Purcell poles are middle Elsonian in age and form the southern extreme point on a hairpin loop of the 1500–1400 Ma part of a refined Elsonian apparent polar wander path.

The Baja B.C. model has the Insular Superterrane and related entities of the Canadian Cordillera subject to >3000 km of northward displacement with respect to cratonic North America from ~90 to ~50 Ma. The Upper Cretaceous Nanaimo Group (on and about Vancouver Island, British Columbia) is a prime target to test the model paleomagnetically because of its locality and age. We have widely sampled the basin (67 sites from seven islands spread over 150 km, Santonian to Maastrichtian age). Most samples have low unblocking temperatures (

New magnetic and paleomagnetic data for central British Columbia support and quantify the hypothesis that the area underwent significant Tertiary-age transtensional deformation. Paleomagnetically determined tilts in Eocene rocks indicate that four fault-bounded pits, which constitute the Endako molybdenum mine, were displaced on a series of normal (probably listric) faults that have separations of less than a kilometre. The interpretation also suggests there can be little vertical offset on the Denak West Fault, which separates the Denak East and Denak West pits. Regional paleomagnetic data indicate a predominance of easterly directed tilts to the east of the Casey Fault, but to the west a large variation in the orientation and magnitude of tilts is observed. Results at one site proximal to the Casey Fault indicate a component of dip-slip displacement on this dominantly dextral strike-slip fault. Mapped northeast- and northwest-trending faults commonly correspond to linear zones of steep magnetic gradient and near-surface magnetic sources. Several additional northwest- and northeast-trending lineaments are imaged in the magnetic data where no faults are mapped (particularly over massive and lithologically homogeneous phases of the Endako batholith). Euler deconvolution solutions confirm most such lineaments are also associated with shallow magnetic sources. In profile, they have either a fault or dyke character and are interpreted to be unmapped faults, some locally intruded by mafic dykes, which cut the region into a series of fault-bounded blocks.

A corollary of J. Chlachula's interpretation that chipped quartzite cobbles at the contact of Lake Calgary sediments and underlying till represent an “early Late Wisconsinan” lithics industry is the conclusion that Laurentide and Cordilleran ice did not coalesce in Late Wisconsinan time. Contrary to that conclusion are (1) NW–SE-oriented, streamlined landforms in the foothills area which could have been created only by coalescent ice flow, along with numerous radiocarbon dates which indicate that Laurentide ice did not advance to central and western Alberta before Late Wisconsinan time, (2) cosmogenic 36 Cl dates of 12–17 ka on the Foothills Erratics Train, indicating Late Wisconsinan coalescence, (3) an estimated thickness of 1000 m or more of Late Wisconsinan coalesced ice in western Calgary based on mapped Laurentide limits 100 km south of Calgary. Furthermore, recently discovered rare Shield clasts in the till at the Varsity Estates and Silver Springs sites suggest that the till was deposited by ice at least partly of Laurentide origin; as Laurentide ice retreated Lake Calgary would have immediately inundated the site, allowing no time or space for human cobble-chipping. Paleomagnetism indicates that the lake sediments at the Varsity Estates site rotated 25 degrees to the NW after deposition, presumably by rotational slumping. Slumping may have been syndepositional, or due to channel cutting during periods of lake drainage and refilling. Neither scenario either supports or contradicts the archeological interpretation. It is possible that the broken and chipped clasts interpreted to be artifacts were created by natural processes.

Paleomagnetic studies of carbonate rocks in mountain belts have been helpful to the understanding of orogenic mational origin. With only one exception, the A component has normal polarity in the Front Ranges and reverse processes, the timing of deformation, and the nature of fluid flow in actively deforming foreland basins. Most studies on shallow-water carbonates indicate that their remanence is not primary, but rather they record remagnetization events contemporaneous with orogeny. By considering the remanent directions, fold test results, and rock magnetic properties, and tying these results to complementary structural, geochronological and geochemical studies, we are able to interpret deformation history, hydrological environment, and orogenic diagenesis. We study the relationship between remagnetization and deformation of Paleozoic carbonates of the Front Ranges and Inner Foothills of the southern Canadian Rockies. The magnetic properties are remarkably constant along 500 km strike length, as sampled at 124 sites through 4 transects. Primary Paleozoic remanent directions which would have shallow inclination, are never observed. Rather, the paleomagnetic signal is dominated by geographically persistent remagnetizations, characterized by steep inclination. As well as a soft present field overprint, we observed two distinctive secondary magnetizations, named the A and B components, carried by fine-grained magnetite. Pervasive diagenesis induced the A component, a total chemical remanent remagnetization. Poles for the A component are better concentrated after bedding correction indicating a pre- or early syndefor-polarity in the Inner Foothills. Pole positions, polarity, and geological and thermal constraints indicate that the A component was acquired diachronously in advance of the eastward migrating Cordilleran tectonic wedge. Subsequently, an intermediate temperature partial thermo-remanent remagnetization, the B component, was superimposed on large regions of the Front Ranges and Inner Foothills. B component directions are brought into optimal concentration by differential untilting of 0% to 50%, indicating that the component was acquired after the rocks were incorporated into the orogenic wedge, but before the end of contractional deformation. The B component is strongest within a couple of kilometers of the frontal thrust of the Front Ranges. The relative magnitude of the B to A components and the maximum unblocking temperature of the B component decrease away from the frontal thrust over about 30 km, both to the west and to the east. The B component thermal overprint was attained by

The Late Pliocene - Early Pleistocene terraces of the Klondike area provide a conformal record of sedimentation which marks the transition from preglacial to glacial conditions, and is one of the most complete records of glaciation and interglaciation in the northern Cordillera. Preglacial sedimentation is recorded in the Lower White Channel gravel that contains a reverse-normal polarity sequence. A re-aggradation of the nonglaciated valleys of the goldfields in response to Late Pliocene cooling is recorded by the Upper White Channel gravel, which is characterized by a dominant normal polarity with a lower reversal likely associated with the first ice-wedge casts. Klondike gravel interfingers with Upper White Channel and is normally magnetized, indicating an equivalent magnetostratigraphic unit. This glaciofluvial gravel provides evidence of extra-basinal clasts, marking a major reorganization of drainage associated with the first advance of the Cordilleran Ice Sheet in western Yukon Territory correlated with the Gauss chron (>2.58 Ma). An intermediate terrace in Klondike valley is overlain by 8 m of fluvial and glaciofluvial gravel named the Midnight Dome gravel. This gravel is mantled by 15 m of loess and hillslope deposits, named the Midnight Dome loess, which preserve at least three interglacial pollen assemblages, and a reverse-normal-reverse-normal polarity sequence assigned to the late Matuyama chron, including Jaramillo subchron (1.07-0.99 Ma), and early Brunhes chron (2.58 Ma) making these among the oldest glacial sediments in North America.

The 70 Ma Carmacks Group, a subaerial volcanic succession which once covered much of central southwest Yukon, has a paleomagnetic remanent direction which passes the fold test and the reversal test. A new collection of 13 sites, combined with 13 sites from a previous study, renders a pole (088.6°E, 78.4°N, A95 = 7.8°) which is far-sided with respect to the pole for cratonic North America and implies a displacement from the south of 1900 ± 700 km. Late Triassic Mandanna Member red beds and Early Jurassic Nordenskiöld Formation tuffs, deformed in the Late Jurassic, fail the fold test and conglomerate test but pass a contact test with Eocene dykes. The postdeformational remanent direction is identical to that isolated from the Carmacks Group. The magnetic signature contained in these older formations is probably an overprint produced by an extensive hydrothermal system active during Carmacks extrusion. Geological work indicates that the Carmacks Group is plume related. Given its paleomagnetic latitude and geological nature, we hypothesize that the Carmacks Group is a displaced segment of the Yellowstone hot-spot track, and the hydrothermal system which remagnetized the older rocks was established by mantle upwelling below the region.

In the southern Canadian Cordillera, the paleomagnetic memory of Paleozoic carbonate strata in the Front Ranges and Inner Foothills of the Foreland thrust and fold belt retains no record of their known deposition at low latitudes. Instead, each folded structure exhibits a similar, but asynchronous, sequence of events including an eastwardly progressing, predeformational chemical remagnetization during the Cordilleran orogeny. The remagnetization of a "western Front Ranges" structure occurs during a period of normal polarity before 130 Ma. The paleomagnetic pole requires that the subsequent deformation of the western Front Ranges is Jurassic or younger. The remagnetization of a Front Ranges structure in the Lewis thrust sheet occurs during a period of normal polarity after 130 Ma but before deformation which, from other evidence, occurred around 75 Ma. The predeformational remagnetization of an "Inner Foothills" structure occurs during a reversed magnetic period that we interpret to be after 75 Ma. An Early Cretaceous sill in the Lewis thrust sheet was remagnetized during a reverse-polarity chron prior to the end of Lewis thrust deformation, when about 70% of the present dip of the sill was acquired. Remagnetization consistently predates deformation, whereas it occurs later at more easterly localities. There are also similarities in character and style of the remagnetizations among localities. When coupled with the eastward progression of the deformation, our observations suggest that an important and pervasive, but hitherto unrecognized and unappreciated, orogenic chemical process affected Paleozoic carbonate strata in the van of the deforming Cordilleran tectonic wedge.

SUMMARY Palaeomagnetic studies on bore core or on tectonically disturbed localities often lose declination information, but the inclination still offers important palaeogeographic information. While the arithmetic mean of inclinations, f, is a biased estimator, the bias is negligible with shallow data. Using co-inclination 6 = 90" - and precision K* = llvariance, we find that the arithmetic mean and associated 95 per cent confidence interval are acceptable estimates when 6fi > 400". When inclination is steep and /or precision low, numerical methods must be applied. We develop the likelihood function for f3 and K and offer an efficient method to find its maximum, (8, R), and to calculate the confidence interval. When O& < 200°, the confidence interval is asymmetric about the mean. When sites are collected from several rigid blocks, the relative declinations within each block can be useful. Using 'block-rotation Fisher analysis', better inclination estimates with tighter confidence intervals can be made, even on very steep data. We describe how to apply these methods to an inclination-only fold test. The techniques are illustrated on real data and are tested extensively using numerical simulations.

Appendices. -- 170 pages, 64 figures, 13 tables., Turbidite systems along the continental margin of Cascadia Basin from Vancouver Island, Canada, to Cape Mendocino, California, United States, have been investigated with swath bathymetry; newly collected and archive piston, gravity, kasten, and box cores; and accelerator mass spectrometry radiocarbon dates. The purpose of this study is to test the applicability of the Holocene turbidite record as a paleoseismic record for the Cascadia subduction zone. The Cascadia Basin is an ideal place to develop a turbidite paleoseismologic method and to record paleoearthquakes because (1) a single subduction-zone fault underlies the Cascadia submarine-canyon systems; (2) multiple tributary canyons and a variety of turbidite systems and sedimentary sources exist to use in tests of synchronous turbidite triggering; (3) the Cascadia trench is completely sediment filled, allowing channel systems to trend seaward across the abyssal plain, rather than merging in the trench; (4) the continental shelf is wide, favoring disconnection of Holocene river systems from their largely Pleistocene canyons; and (5) excellent stratigraphic datums, including the Mazama ash and distinguishable sedimentological and faunal changes near the Pleistocene-Holocene boundary, are present for correlating events and anchoring the temporal framework. (...)

Between the time of the India-Eurasia collision (50–45 Ma) [1] and the climax of crustal shortening and thrust stacking in the Himalaya when the Main Central Thrust (MCT) was active (21 Ma) [1,2] there is a ca. 30 My gap about which little is known. This paper aims to shed light on this period by dating the initiation of major erosion from the rising Himalaya and the probable start of uplift, a significant event in the orogen's history. This was achieved by accurately dating, for the first time, the Dagshai Formation sediments of northern India, which are interpreted as early Himalayan foreland basin deposits that record initial large-scale erosion of the orogen [3]. Oriented hand samples were collected from six sites and analysed, using palaeomagnetic techniques. Both polarities are represented and the remanence passes a fold test. Fitting the measured palaeolatitude to that expected for the Indian plate dates the Dagshai Formation at 35.5 Ma ± 6.7 Ma, and this is taken as the time when the embryonic Himalaya began to be strongly eroded and regionally uplifted.

Transdomain thermoremanent magnetization (TRM) is produced when thermally activated transitions between different domain structures become blocked during cooling. This paper investigates transdomain remanence in the pseudo-single-domain size range ( 6000kT for SD ↔ 2D transitions. Transdomain viscous remanent magnetization (VRM) will not occur, even on geological timescales, by a one-dimensional excitation such as edge nucleation of a domain wall. Transdomain blocking temperatures, at which energy barriers fall to 25kT–60kT, are ≥553°C for SD ↔ 2D and ≥574°C for 2D ↔ 3D transitions. There are two separate blocking temperatures, e.g. TB1 for SD ↔ 2D and TB2 for 2D ↔ SD transitions. Usually, only the higher of the two has practical significance because the favored (lower energy) state is already 100% populated at this temperature. Our theory is the first to make quantitative predictions of transition paths, relaxation times, and blocking temperatures for transdomain TRM. It is also quite robust. Relaxing the one-dimensional constraint and introducing crystal defects would make it easier to nucleate domains, but energy barriers and blocking temperatures would not be reduced greatly. Our principal conclusion, that only the lowest energy state at blocking is significantly populated, is a fundamental consequence of the Boltzmann statistics of equilibrium states and is unaffected by the details of transitions between states. Grain interactions may be responsible for the multiplicity of states observed in large titanomagnetite grains following replicate TRM experiments.

Natural gas hydrate reservoirs are hosted in heterogeneous sediments having variable pore fluid salinity. Questions concerning GH formation, detection and production are being addressed and measured in real time with simple laboratory apparatus. Our vessel is pressurized with methane and monitored with individually calibrated pressure transducers and thermistors. The silt or sand pack is assembled using uniform grain size layers containing ~20% by weight of pore fluids. This results in mixed wettability, with pendant water and initial partial gas saturation. Sand packs consisting of silica silts, sands, and charcoal were selected to emulate the dominant lithofacies observed in the Mallik gas hydrate reservoir. Fluids range from distilled-water to 37ppt salinity. A central needle probe permits the measurements of electromagnetic signals across the specimen. Formation of GH alters the bulk dielectric constant of the mixture, through the conversion of water to gas hydrate crystals and or ice. The infilling of primary porosity by gas hydrate or water ice tends to reduce permeability and increase electrical resistivity, while the expulsion of solutes by hydrate or ice formation decreases resistivity by building a salt bridge along alternate permeability paths. Four methods monitored GH formation and dissociation: 1) Deposition or evolution of gas derived from measurement of the ambient pressure and temperature; 2) Calorimetric measurements of latent heat production by exothermic crystallization and consumption by endothermic dissociation; 3) Time-Domain Reflectometry (TDR) measurement of the velocity of electromagnetic signal propagation and reflections at boundaries in the sand pack; 4) Electrical Impedance Spectroscopy (EIS), a frequency domain method permitting direct measurement of the resistance and capacitance spectra. Improvements in real time digital monitoring and data analysis have made possible the recognition of TDR reflections previously considered unattainable in the presence of conducting fluids. The independent monitoring methods, with their various temporal and spatial sensitivities, capture the intricate details of GH formation and dissociation as a time series. In more porous and permeable beds, GH formation as evidenced by a coherent pressure drop and thermal pulse precedes the increase in electrical conductivity and dielectric constant. These results are interpreted to be the result of a diffusive pulse of solute exclusion from the GH-bearing layer into neighbouring sediment. Measurable EM effects suggest that borehole EIS, with lower frequency and greater penetration than TDR, may be effective for monitoring the variable position of GH-Methane interfaces during GH production tests.

Understanding fluvial bedload transport and its geomorphic implications is hampered by the paucity and low accuracy of field-derived transport data. Tunnicliffe et al. (Hydrological Processes, 2000; 14: 2631–2643) described the Bedload Movement Detector (BMD), a magnetic induction system for measuring bedload movement in gravel-bed rivers based on a sensor that produces signals when its magnetic field is enhanced by a passing particle. We conducted two types of laboratory experiments to attempt to calibrate the BMD system: (1) rotating platter experiments were designed to relate sensor response curves to particle properties, and (2) flume experiments were designed to measure particle speed and permit computation of a calibrated model. Physically based relations were derived amongst particle volume, speed and magnetic content, and signal integral, amplitude and width. The calibrated relations demonstrate a basis to estimate sediment flux in gravel-bed rivers, but they require independent knowledge of particle magnetic susceptibility. Over the course of the experiments a number of weaknesses in the sensor design and performance were identified and suggestions are made to improve the system. The high spatial and temporal resolution of data that magnetic sensors of bedload movement are likely to offer makes them valuable to consider for sediment transport measurements in both the field and laboratory. Copyright © 2009 John Wiley & Sons, Ltd.

Upper Jurassic to lower Tertiary sites have been sampled from three localities, separated by up to 150 km, in the Sichuan Basin (∼30°N, 103°E) of the South China Block. Each locality has at least one stability test, but none alone gives a fully reliable result. When taken together, however, identical directions are found with a global average D=12.7°, I=34.2°, k=42.9°, α95=3.3° (N=44 sites) and corresponding pole 73.9°N, 234.4°E, dp=2.2°, dm=3.8°, paleolatitude λ=18.8°. There is no significant apparent polar wander (APW) with age, which is consistent with an acquisition of magnetization during the period of the stable tip of the Eurasian APW loop (∼130–70 Ma), as defined with poles from other continents transferred onto Eurasia. This age range is compatible with the available paleontological and magnetostratigraphic age constraints but is shorter than that suggested by the assigned formation ages. The paleolatitude of Sichuan is significantly lower (8.0°±4.0° at 90 Ma) than that predicted by the reference APW path, either because of northward shortening during the Tertiary or because of errors in the APW path. Cretaceous poles from other Chinese blocks are consistent with the Sichuan pole, but there is evidence that these blocks have suffered local rotations up to 10° during the Tertiary, probably as a result of the India-Eurasia collision.

To contribute to the apparent polar wander path (APWP) of the South China Block and Eurasia in general, we collected paleomagnetic samples from Mesozoic red beds around the city of Ya' an (30°N, 103°E) in the western tip of the Sichuan Basin. In this paper we present the results from 373 oriented cores taken from one section representing 3 km of sedimentary rocks. The section is dated with continental ostracods and with a magnetostratigraphic correlation between a densely sampled 272-m sequence and the polarity time scale, giving an upper Jurassic to Upper Cretaceous or Lower Tertiary age. The remanent direction is remarkably stable throughout the section (D=2.0°, I=34.2°, k=63.1,α95=3.6°, N=26/28 sites). While this fact might suggest that the section has been remagnetized, paleomagnetic and rock magnetic tests indicate that the remanence is primary. The pole position (78.6°N, 273.4°E, dp=2.4°, dm=4.1°) corresponds to a rather low paleolatitude (λ=18.8°±2.4°) but is consistent with other Cretaceous poles from China. If one accepts the Eurasian APWP of Irving and Irving (1982), this result would imply that more than 1000 km of shortening took place between South China and Eurasia, following the acquisition of the remanence. However, there is no geological evidence for this large shortening. We propose that the remanence was acquired within the time corresponding to the tip of the hairpin turn (∼150–50 Ma) in the revised APWP of Besse and Courtillot (this issue). The local geology suggests that the syncline from which the samples were taken has been rotated by 15°±5° counterclockwise, which is reflected in a similar discrepancy between the measured paleodeclination and that predicted by the Besse and Courtillot (this issue) Eurasian APWP. After correcting for this rotation, the pole position is 70.9°N, 225.2°E (dp=2.4°, dm=6.5°). We conclude that Eurasia was fully assembled by the end of the Jurassic and that the Mesozoic Eurasian hairpin turn is a real feature.

We use a one-dimensional micromagnetic model with temperature-dependent parameters for the mineral magnetite to calculate the critical sizes dSDmax, above which a single-domain (SD) state does not exist; d2Dmin, below which no two-domain state exists; and d0, at which the SD and two-domain states have equal energies, all as a function of temperature up to the Curie point TC. We also compute the structures, widths, and net moments of domain walls in two-domain particles from room temperature up to TC. In two-domain grains just above d2Dmin, the domain wall expands to fill an increasing fraction of the particle volume. In cubic SD grains just below dSDmax, magnetic moments are twisted symmetrically away from the easy axis at opposite ends of the crystal. The limits dSDmax and d2Dmin are determined with a precision of Domain walls in two-domain magnetites expand with rising temperature; however, the expansion is slow and the domain wall fills no more than 50% of the particle except within a few degrees of TC. The √(A/K) expansion predicted by Landau and Lifschitz and subsequent theories, in which there is no upper limit to the size of the walls, is a result of ignoring the demagnetizing energy of the domain wall. Domain walls have considerable structure, including ‘skirts’ of magnetic moments rotated beyond 0° and 180°. The skirts partly compensate the wall moment and expand as the temperature rises. As a result of the competing effects of expanding walls and expanding skirts flanking the walls, the net two-domain particle moment, normalized to the saturation magnetization MS, changes slowly as the temperature rises and may actually decrease. Remanence peaks observed at

[1] The J meter coercivity spectrometer is a machine capable of rapid and simple measurement of magnetic hysteresis, isothermal remanence acquisition and magnetic viscosity of rocks and sediments. The J meter was used to study a suite of samples collected from strata in the gas hydrate-bearing JAPEX/JNOC/GSC Mallik 5L-38 well (69.5°N, 134.6°W) in the Mackenzie Delta of the northwestern Canadian Arctic. The Day plot of magnetic hysteresis ratios for these samples is exotic in that the points do not plot along a hyperbola as is usually observed. Rather, they plot as a scatter which is shown to contour into vertical slices using coercivity field (HC) or saturation magnetization (JS), and horizontal slices using the relative quantity of superparamagnetism (JSPM/JS). Optical microscopy reveals that the magnetic minerals are detrital magnetite and authigenic greigite. Greigite is dominant in sands which in situ had >70% gas hydrate saturation and in silts in which gas hydrate growth was blocked by insufficient porosity. We infer that the silts were the accumulation sites for solutes which had been excluded from the pore waters in neighboring coarser-grained sediments during the course of gas hydrate formation. Consequently, we conclude that magnetic properties are related to gas hydrate-related processes, and as such, may have potential as a method of remote sensing for gas hydrate deposits.