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Parkinson, F.; Douglas, K.; Li, Z.; Meijer, A.; Stacey, C.D.; Kung, R., and Podhorodeski, A., 2024. A generalized semiautomated method for seabed geology classification using multibeam data and maximum likelihood classification. Journal of Coastal Research, 40(1), 1–16. Charlotte (North Carolina), ISSN 0749-0208. This paper presents a GIS-based model to perform semiautomated seabed classification that can act as a first-pass, pseudoclassified surficial geological map. The user can then edit the output into a finalized map in less time than by manual classification. The model uses maximum likelihood classification with unsupervised classification through iterative self-organizing clusters. This model is fully contained within the ArcGIS software suite as a ModelBuilder workflow composed of geoprocessing tools and Python script tools. Model inputs tested include different combinations of multibeam echosounder–derived data: slope, backscatter, and terrain ruggedness. Furthermore, to test the assumption of Gaussian distribution of input data required for maximum likelihood classification, Box–Cox power transformations were applied to slope and backscatter data and were used as model inputs. To illustrate the performance of the model, two locations are highlighted as case studies: Milbanke Sound and Spiller Channel, located on the central coast of British Columbia, Canada. Association between model outputs and ground-truth classes was generally weak to moderate when measured using Cramér's V association scores. Overall, the slope and backscatter parameter model had the highest scores of association. Results from an overlay analysis comparing model outputs with user-confirmed polygons show that the slope and backscatter model performs best in regions with distinct changes in the hardness of sediments but that in fjord regions dominated geologically by steeper bathymetric change, the slope parameter model may perform better. However, all model outputs had difficulty delineating bedrock units. The model has the flexibility to identify certain seabed habitat features as well, including glass sponge reefs—biologically active bioherms that have led to marine protected area designations in other areas of British Columbia. [ABSTRACT FROM AUTHOR]

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Infestation by the mountain pine beetle, Dendroctonus ponderosae, decimated the forests of central British Columbia from 1999 to 2012, severely impacting the forest industry of the Nechako-Chilcotin plateau. In response, all levels of government recognized the value in developing other areas of economic activity, such as hydrocarbon and mineral exploitation, to support local economies. Exploration for resources beneath the Nechako-Chilcotin plateau has historically been constrained by Tertiary volcanic sequences and Quaternary glacial deposits that obscure the underlying geology and limit geophysical imaging. Thus, a coordinated program comprising additional geological mapping, borehole data analysis, and modern geophysical surveys of the area was initiated in 2006, with the objective of better defining the subsurface geology, solving problems of imaging through the complex near-surface, and developing improved regional geological and tectonic models. An initial set of papers arising from this fieldwork, which focused on issues relevant to mineral and hydrocarbon exploration, was published in June 2011 in a Special Issue of the Canadian Journal of Earth Sciences. This Introduction to the second 'Mountain Pine Beetle' Special Issue summarizes a set of scientific papers that focus on topics more related to hydrocarbon exploration and the large-scale structure of the crust. The papers deal with the development, thickness, and present distribution of the most prospective Cretaceous sedimentary rocks, as well as characterizing the physical properties of the near-surface volcanic units. [ABSTRACT FROM AUTHOR]

Copyright of Canadian Journal of Earth Sciences is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Canadian Journal of Earth Sciences is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The geochemistry of produced fluids has been investigated in the Triassic Montney Formation in the Western Canadian Sedimentary Basin (WCSB). Understanding the geochemistry of produced fluids is a valuable tool in the exploration and development of a complex petroleum system such as the Montney Formation. The petroleum system changes from in situ unconventional reservoirs in the west to more conventional reservoirs that contain migrated hydrocarbons to the east. The workflow of basin modeling and mapping of isomer ratio calculations for butane and pentane as well as the mapping of excess methane percentage was used to highlight areas of gas compositional changes in the Montney Formation play area. This workflow shows the migration of hydrocarbons from deeper, more mature areas to less mature areas in the east through discrete pathways. Methane has migrated along structural elements such as the Fort St. John Graben as well as areas that have seen changes in higher permeability lithologies (i.e., well 14-23-74-8W6M). Excess methane percentage calculations highlight changes due to fluid mixing from hydrocarbon migration. The regional maturation polynomial regression line was used to determine the gas dryness percentage for each well on the basis of its maturation level determined by the butane isomer ratio. The deviation from the calculated gas dryness according to the regression was determined as an excess methane percentage. The British Columbia (BC) Montney play appears to have hydrocarbon compositions that reflect an in situ generation, while the Montney play in Alberta (AB) has a higher proportion of its hydrocarbon volumes from migrated hydrocarbons. The workflow provides a better understanding of the hydrocarbon system to optimize operations and increase production efficiency. Understanding the distribution of gas compositions within a play area will provide key information on the liquid and gas phases present and an understanding of how gas composition may change over the well life, as well as helping to maximize liquid recovery during well operations. [ABSTRACT FROM AUTHOR]

Copyright of Canadian Journal of Earth Sciences is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Canadian Journal of Earth Sciences is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Canadian Journal of Earth Sciences is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The character of the Paleozoic basement of Quesnel Terrane and the position of the terrane accretion surface that separates Quesnel and Kootenay terranes from rocks of the ancient North American margin are subjects of debate. To address these problems, detailed mapping and U–Pb geochronologic studies were carried out in the Christina Lake area to define the relationship of the Mollie Creek assemblage, Josh Creek diorite, and Fife diorite to similar lithologies in the Greenwood – Grand Forks and Rossland regions, and to place limits on the ages of regional deformation and local position of the terrane accretion surface. Deformed metasedimentary rocks of the Mollie Creek assemblage may correlate with sedimentary rocks of the Pennsylvanian to Early Triassic Mount Roberts Formation in the Rossland area. The Mollie Creek assemblage is intruded by the foliated Late Triassic Josh Creek diorite. The Josh Creek diorite and Mollie Creek assemblage have been deformed together as a result of phase two deformation, following the intrusion of the Josh Creek diorite in the Late Triassic and prior to the intrusion of the Fife diorite and deposition of the overlying Rossland Group in the Early Jurassic. Based on relative age, structural position, and lithological similarities to other units within Quesnel Terrane, the Mollie Creek assemblage, Josh Creek diorite, and Fife diorite are a part of Quesnel Terrane and lie above the terrane accretion surface in the Christina Lake area. Therefore, Quesnel Terrane does not unconformably overlie basement rocks of known North American affinity in this region.Le caractère du socle paléozoïque du terrane de Quesnel et la position de la surface d'accrétion du terrane qui sépare les terranes de Quesnel et de Kootenay des roches de l'ancienne marge nord-américaine sont sujets à discussion. Afin d'aborder ces problèmes, de la cartographie de détail et des études géochronologiques U–Pb ont été entreprises dans la région du lac Christina afin de définir la relation entre l'assemblage de Mollie Creek, la diorite de Josh Creek, la diorite de Fife et des lithologies similaires dans les régions de Greenwood–Grand Forks et de Rossland et de circonscrire les âges de la déformation régionale ainsi que la position locale de la surface d'accrétion du terrane. Des roches métasédimentaires déformées de l'assemblage de Mollie Creek correspondent peut-être à des roches sédimentaires de la Formation de Mount Roberts (Pennsylvanien à Trias précoce) dans la région de Rossland. La diorite foliée de Josh Creek (Trias tardif) pénètre dans l'assemblage de Mollie Creek. La diorite de Josh Creek et l'assemblage de Mollie Creek ont été déformés ensemble à la suite d'une déformation de phase deux, après l'intrusion de la diorite de Josh Creek au Trias tardif et avant l'intrusion de la diorite de Fife et la déposition du Groupe de Rossland sus-jacent, au Jurassique précoce. Selon les âges relatifs, la position structurale et les similitudes lithologiques aux autres unités à l'intérieur du terrane de Quesnel, l'assemblage de Mollie Creek, la diorite de Josh Creek et la diorite de Fife font partie du terrane de Quesnel et reposent au-dessus de la surface d'accrétion du terrane dans la région du lac Christina. Le terrane de Quesnel ne repose donc pas en discordance sur les roches du socle d'affinité nord-américaine connue dans cette région.[Traduit par la Rédaction] [ABSTRACT FROM AUTHOR]

New U–Pb ages and K–Ar dates, primarily for rocks proximal to mineral occurrences in the Fawnie Range of central British Columbia, document latest Cretaceous (ca. 74–66 Ma) continental-arc igneous activity and date associated base and precious metal mineralization. U–Pb ages of ca. 73–69 Ma for the Capoose pluton and hypabyssal to extrusive garnet rhyolites at the Capoose prospect demonstrate a latest Cretaceous age for mineralization and a likely plutonic source for mineralizing fluids. A U–Pb age of ca. 67 Ma for a late mineralized felsic dyke and two K–Ar dates (ca. 70 and 68 Ma) for hornfelsed Jurassic volcanic rocks at the Blackwater–Davidson prospect constrain a latest Cretaceous age for mineralization. A U–Pb age of ca. 74 Ma for a fine grained diorite sill that cuts a significant epithermal gold vein at the Tsacha prospect places a minimum age on mineralization at this probable Jura-Cretaceous deposit and documents latest Cretaceous magmatism. Latest Cretaceous K–Ar dates are reported for an andesite flow adjacent to the Eocene Holy Cross deposit (ca. 66 Ma), about 35 km north of the Fawnie Range, and a Kasalka Group rhyolite (ca. 68 Ma) exposed near the western margin of the Nechako Plateau. Latest Cretaceous magmatism and mineralization in the Fawnie Range represent the waning stages of Bulkley suite magmatism and porphyry-style mineralization, which was concentrated along the western margin of the Nechako Plateau at circa 88–70 Ma. The distribution of latest Cretaceous arc igneous rocks along the North American Cordilleran is reviewed and tectonic implications discussed.De nouveaux âges U–Pb et de nouvelles datations K–Ar, surtout pour des roches à proximité d'occurrences minérales dans la chaîne Fawnie du centre de la Colombie-Britannique documentent la plus récente activité ignée d'arc continental au Crétacé (ca. 74–66 Ma) et datent la minéralisation associée de métaux précieux et de métaux de base. Des âges U–Pb d'environ 73–69 Ma pour le pluton de Capoose et les rhyolites grenatifères hypabyssales à extrusives dans la zone d'intérêt Capoose démontrent un âge Crétacé terminal pour la minéralisation et une source plutonique probable pour les fluides minéralisateurs. Un âge U–Pb d'environ 67 Ma pour un dyke felsique à minéralisation tardive et deux datations K–Ar (ca. 70 et 68 Ma) pour des roches volcaniques au faciès des cornéennes, datant du Jurassique, à la zone d'intérêt Blackwater–Davidson limitent l'âge de la minéralisation au Crétacé terminal. Un âge U–Pb d'environ 74 Ma pour un filon-couche de diorite à grains fins qui recoupe une importante veine d'or épithermale à la zone d'intérêt Tsacha donne un âge minimum pour la minéralisation de ce dépôt, probablement au Jurassique–Crétacé, et documente le magmatisme au Crétacé terminal. Des datations K–Ar de Crétacé terminal sont rapportées pour un écoulement d'andésite adjacent au gisement de Holy Cross, datant de l'Éocène (ca. 66 MA), situé à environ 35 km au nord de la chaîne Fawnie et pour une rhyolite du Groupe de Kasalka (ca. 68 Ma) affleurant près de la bordure ouest du plateau Nechako. Du magmatisme et de la minéralisation dans la chaîne Fawnie, au Crétacé terminal, représentent les dernières phases du magmatisme de la suite Bulkley et de la minéralisation de type porphyrique, qui a été concentrée le long de la bordure ouest du plateau Nechako il y a environ 88–70 Ma. On passe en revue la distribution des roches ignées d'arc au Crétacé terminal le long de la Cordillère nord-américaine et on discute des implications tectoniques.[Traduit par la Rédaction] [ABSTRACT FROM AUTHOR]

The Quaternary stratigraphy of the Nechako River – Cheslatta Lake area of central British Columbia is described and interpreted to reconstruct the late Quaternary history of the region. Exposures of glacial and nonglacial sediments deposited prior to the last glaciation (Fraser) are limited to three sites. Pollen assemblages from pre-Fraser nonglacial sediments at two of these sites reveal forested conditions around 39 000 BP. During the advance phase of the Fraser Glaciation, glacial lakes were ponded when trunk glaciers blocked some tributary valleys. Early in the glaciation, the drainage was free in easterly draining valleys. Subsequently, the easterly drainage was blocked either locally by sediments and ice or as a result of impoundment of the Fraser River and its tributaries east of the study area. Ice generally moved east and northeast from accumulation zones in the Coast Mountains. Ice flow was influenced by topography. Major late-glacial lakes developed in the Nechako River valley and the Knewstubb Lake region because potential drainage routes were blocked by ice.La stratigraphie du Quaternaire de la région de la rivière Nechako et du lac Cheslatta sise au centre de la Colombie Britannique est décrite et interprétée dans le but de reconstruire l'histoire du Quaternaire tardif de cette région. Seul trois coupes stratigraphiques mettent en évidence des sédiments glaciaires et non-glaciaires mis en place avant la dernière glaciation (Fraser). À deux sites, l'assemblage pollinique des sédiments non-glaciaires prédatant la Glaciation de Fraser reflète un environnement forestier aux environs de 39 000 BP. Lors de l'avancée des glaciers au début de la Glaciation de Fraser, des lacs glaciaires furent retenus dans les vallées secondaires par les glaciers qui occupaient les vallées primaires. Au début de cette glaciation, le drainage vers l'est fut tout d'abord ouvert mais subséquemment, il fut bloqué soit localement par des sédiments et de la glace ou en raison du blocage du fleuve Fraser et ses tributaires à l'est de la région d'étude. Les glaciers se sont écoulés vers l'est et le nord-est à partir de zones d'accumulation centrées sur la Chaîne Côtière. Les écoulements glaciaires furent influencés par la topographie. Des lacs post-glaciaires se sont formés dans la vallée de la rivière Nechako et dans la région du lac Knewstubb suite au blocage du drainage potentiel par la glace.[Traduit par la Rédaction] [ABSTRACT FROM AUTHOR]

In this paper we present the framework and open-source software code to train and apply Deep Learning Convolutional Neural Networks (CNNs) to the prediction of geological lineaments using topographic, magnetic, and gravity raster data. Many important applications relate to the recognition of linear geological structures from remote sensing data, such as thrust faults, bedrock fault and shear zones, lithological contacts, fractures and fold structures. The digitization of fault lineaments is conventionally performed by geologists or geophysicists with working knowledge of the relevant data, e.g., topographic Digital Elevation Model, magnetic data, and gravity data. Visual inspection and extraction is simple but subjective; the process is also time-expensive with efficiency and accuracy depending on the individual's knowledge, experience, and skill. For decades there has been interest in ways to automate this process. Our CNN approach is trained using publicly available lineament GIS data from the Quest BC project in British Columbia, Canada, and the Loch Lilly-Kars area of New South Wales, Australia. The datasets used to train the prediction models resulted in interesting predictions proximal to the training areas: some major lineaments are indicated, some are missed, and potential new (valid) lineaments are indicated. The results indicate potential for use as a semi-automated lineament detection solution. In contrast, but as anticipated, application of the model to the blind-test area of the Swayze greenstone belt, Ontario, produced poor lineament prediction results (as compared to publicly available interpretations). We interpret this result as related to insufficiently large training data inputs. However, it is inferred that results could be improved through feature engineering (e.g., use of topographic slope, rather than simply elevation) without the need to simply create larger training datasets. We hope that, by making the code open-source, the geoscience community will use this platform to gradually improve an open source fault prediction model. [Display omitted] • CNNs used to predict fault lineaments with remote sensing data. • Terrain models, magnetic and gravity data are used as input features. • Clustering and post-processing are the key elements for post-prediction processing. • We infer that improved feature engineering can improve future model generalization. [ABSTRACT FROM AUTHOR]

Although alkalic porphyry Au--Cu deposits are much less common than their calc-alkalic counterparts, they represent attractive exploration targets both due to their occurrence as, locally concealed, clusters and their high Au contents. In this paper, the geology of the Mt. Milligan Au--Cu deposit, Canada, and its geophysical footprint on magnetic and AEM data is used as a case-study for the exploration and discovery of concealed alkalic porphyry Au--Cu deposits. The Cole-Cole parameters in the AEM data are extracted using an improved Airborne Induced Polarization (AIP) mapping algorithm. We propose that the subtle electromagnetic signatures of disseminated sulfides around the intrusive porphyry stocks at Mt. Milligan could be mapped by the m τ product, where m is AIP apparent chargeability, and τ the Cole-Cole time-constant, provided that the depths of the alteration zone does not exceed 75 m. The product is called Tau-Scaled Chargeability or TSC. In order to improve the exploration success in the search for concealed alkalic porphyry Au--Cu deposits, we propose to: (1) concentrate the exploration on known and well-endowed mineral districts; and (2) apply innovative digital data-processing techniques capable of extracting weak and subtle signatures from airborne geophysical data and, subsequently, to utilize DCIP ground surveys in the follow-up of anomalies, ideally in combination with enzyme-leach soil sampling. • Alkalic porphyry Au-Cu deposits are attractive exploration targets due to their high Au contents. • They occur in clusters, typically above fractionating magma chambers in the upper crust. • AIP mapping can define pyrite halos around concealed intrusive stocks at Mt. Milligan. • AIP mapping can be used as a vectoring tool. [ABSTRACT FROM AUTHOR]

In geo-engineering projects dealing with rock formations, and especially with rocky outcrops, discontinuity orientation is one of the most important parameters that should be carefully estimated. Slope stability is significantly dependent on discontinuity geometry, and even slight changes in orientation may affect the factor of safety. For this reason, joint orientation measurement is the main component of the preliminary site investigation for slopes. The use of three dimensional models derived from LiDAR scans or photogrammetric models has seen substantial growth in the field of geosciences in the last decade, with many examples of useful application and analysis. Several authors have developed techniques and methodologies (Jaboyedoff et al. 2010; Kemeny et al. 2006; Lato at al. 2007; Riquelme et al. 2014) to semi-automatically extract geometric features including joint orientation by using LiDAR data. In this study, the Discontinuity Set Extractor (DSE) (Riquelme et al. 2014) methodology for plane detection and joint orientation extraction is examined.DSE provides a powerful toolset for plane detection and plane orientation assessment, and has been tested in several cases (Riquelme et al. 2017; Buyer, AA & Schubert, W. 2017; Farmakis, I. 2018). However, when evaluating the stability of complex rock masses, some difficulties and uncertainties may arise. The current study demonstrates an application of the DSE methodology on a complex rocky slope in British Columbia, comprising four different lithologies and complex tectonics. In this case, The methodology was found to be problematic, in part due to the available LiDAR data set, and in part due to the complexity of the surface exposure of the joint surfaces. The method was modified as are discussed in this paper so that realistic outputs can be extracted. All of the tests, together with the different approaches, are presented in detail, and the results are compared with manually measured orientations along the point cloud for the verification of their validity. [ABSTRACT FROM AUTHOR]

Copyright of Canadian Journal of Earth Sciences is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

When used in a comprehensive risk assessment framework, aquifer vulnerability maps are a tool to identify the relative susceptibility of the groundwater from sources of contamination at the land surface. The DRASTIC method was designed for use over large areas with a wide variety of geological and hydrogeologic settings as a screening tool in groundwater protection and management. In this study, a series of vulnerability maps were made for the Greater Oliver area, in south central Okanagan, British Columbia, Canada, to test the sensitivity of the methodology to changes in input data type, interpretation, and mapping approaches. The study also illustrates how DRASTIC can be modified for use in areas of limited geological variability, where it may be important for smaller-scale changes in vulnerability to be recognized. Maps were produced using the original DRASTIC rating tables, a set of expanded tables using the original properties but modified ranges to accommodate the variability of data in the valley bottom region, and alternate tables, with modified properties and ranges. Differences in vulnerability rating for the maps using selected combinations and data interpretations are compared to the map using original DRASTIC rating tables using visual and statistical methods. One map was generated using expert hydrological knowledge. The modified tables allowed a greater amount of variability to be expressed in the valley bottom area compared to using the original tables and methods, and could provide a reasonable approach for assessing local scale variability for source water protection planning. [ABSTRACT FROM AUTHOR]

The physical significance of a negative correlation between a varve record from Mud Lake, British Columbia, and temperature is discussed in the context of a process-network. The process-network is defined as the system of temporally and spatially connected processes involved in the transfer of a signal from climate to varved glaciolacustrine sediment. The six systems defining the network include climate, glacier, fluvial, geomorphic, terrestrial biologic and lacustrine systems to which each process belongs. A literature review outlines significant variation in the strength and character of correlations between components of the process-network and highlights that more comprehensive interpretations of varves as a hydroclimatic proxy require an improved understanding of the process-network. Documenting each process in the network is integral to informing a more complete model of this system, identifying processes that constitute signal transfer and assessing hydroclimatic proxies based on linear correlation. Such documentation is of growing importance as varved lacustrine sediments are increasingly used as a hydroclimatic proxy. The complex nature of the process-network requires greater emphasis on interdisciplinary cooperation and alternative methods to the linear statistical model. [ABSTRACT FROM AUTHOR]

The Holocene sedimentary infill of proglacial Mud Lake, British Columbia, Canada, was investigated using 3.5 kHz acoustic sub-bottom profiling and sediment samples. The sediment infill is a mixture of silt and clay and is divided into five stratigraphic units: massive silt (Unit 1), weakly laminated silt with very fine sand beds (Unit 2), weakly laminated silt with rippled beds of fine sand (Unit 3), weakly laminated clay with very fine sand laminations (Unit 4) and silt–clay varves (Unit 5). Acoustic reflectors correlate with stratigraphic unit boundaries. Annual accumulation rates were estimated for six age/depth intervals: prior to 9.6 kyr cal. BP, accumulation rates were very high – on the order of several centimetres per year. Early to middle Holocene sediment inputs (9.6–3.6 kyr cal. BP) were variable but low, ranging from 0.3 mm/yr to 1.2 mm/yr. The late Holocene (most recent 3.6 kyr) shows annual accumulation rates that generally exceed 2 mm/yr. Surface sediment reveals a mean of 4.3 mm/yr over the last 20 years. These results are consistent with regional Holocene chronologies and long-term paraglacial succession: (1) maximum sediment and meltwater availability and minimum stabilization by vegetation following Fraser deglaciation replaced by (2) less meltwater and sediment availability during the Hypsithermal, and (3) more stabilized sediment during the early and mid Holocene. Renewal of glacial activity, particularly in the late Neoglacial, has led to increased rates of accumulation in Mud Lake. Despite the contrasting geologic setting of Mud Lake in the Omineca belt, contemporary sediment yield is consistent with the trend of sediment yield with glacier cover in lakes of the adjacent Foreland belt. [ABSTRACT FROM AUTHOR]

Bracketing ages on marine-freshwater transitions in isolation basins extending from sea level to 100 m elevation on Lasqueti Island, and data from shallow marine cores and outcrops on eastern Vancouver Island, constrain late Pleistocene and Holocene sea-level change in the central Strait of Georgia. Relative sea level fell from 150 m elevation to about -15 m from 14 000 cal. yr BP to 11 500 cal. yr BP. Basins at higher elevations exhibit abrupt changes in diatom assemblages at the marine-freshwater transition. At lower elevations an intervening brackish phase suggests slower rates of uplift. Relative sea level rose to about +1 m about 9000 cal. yr BP to 8500 cal. yr BP, and then slowly fell to the modern datum. The mean rate of glacio-isostatic rebound in the first millennium after deglaciation was about 0.11 m a -1 , similar to the peak rate at the centres of the former Laurentide and Fennoscandian ice complexes. The latter feature smooth, exponential-style declines in sea level up to the present day, whereas in the study area the uplift rate dropped to less than one-tenth of its initial value in only about 2500 years. Slower, more deeply seated isostatic recovery generated residual uplift rates of <0.01 m a -1 in the early Holocene after the late-Pleistocene wasting of the Cordilleran ice sheet. [ABSTRACT FROM AUTHOR]

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Copyright of Canadian Journal of Earth Sciences is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Anyox Pendant contains complexly deformed greenschist-facies volcanic strata overlain by a thick succession of turbidite sedimentary rocks. At the contact between the two are well-studied copper-rich volcanogenic massive sulphide deposits; however the age and correlation of the volcanic strata, including the ore horizon, are poorly known. New stratigraphic, structural, and geochronology studies elucidate the regional stratigraphic, tectonic, and metallogenic settings and significance of these strata. The thick turbidite succession is correlated with Bowser Lake Group and conformably overlies the volcanic succession. Volcanogenic units include pillowed basalt, volcaniclastic rocks, chlorite phyllite, tuffaceous siltstone, and abundant gabbroic sills and dykes. Strained leucocratic intrusions yielded U–Pb zircon crystallization ages of 176.9 ± 0.2 Ma and 185.6 ± 0.3 Ma. Volcaniclastic rocks yielded detrital zircons that constrain the maximum ages of the volcanic succession. The youngest zircon grains from four samples in different structural segments limit strata to younger than ca. 186 Ma, ca. 178 Ma, ca. 183 Ma, and ca. 186 Ma. The results, combined with the regional oldest age limit of Bowser Lake Group, constrain the volcanic succession to late Early Jurassic(?) and early Middle Jurassic age, and support correlation with Hazelton Group of Stikinia. Furthermore, they enable comparisons with the coeval Au-Ag-rich stratiform Eskay Creek deposit, expanding southward the zone of extension in western Stikinia, which tapped primitive mafic magmas and accompanied the last vestiges of Stikinian volcanism in the early Middle Jurassic.Le pendant Anyox contient des strates volcaniques au faciès des schistes verts, déformées de façon complexe et recouvertes d'une épaisse succession de roches turbidites sédimentaires. Au contact entre les deux, on retrouve des gisements d'origine volcanique de sulfures massifs, riches en cuivre, qui ont été étudiés en détail; toutefois, l'âge et la corrélation des strates volcaniques, incluant l'horizon contenant le minerai, sont mal connus. De nouvelles études stratigraphiques, structurales et géochronologiques définissent les contextes régionaux stratigraphiques, tectoniques et métallogéniques ainsi que l'importance de ces strates. L'épaisse succession de turbidites est corrélée au Groupe de Bowser Lake et repose en concordance sur la succession volcanique. Les unités d'origine volcanique comprennent des basaltes en coussins, des roches volcanoclastiques, de la phyllite chloriteuse, une siltite tufacée et un grand nombre de filons-couches et de dykes gabbroïques. Des intrusions leucocratiques sous contraintes ont donné des âges de cristallisation U–Pb sur zircon de 176,9 ± 0,2 Ma et 185,6 ± 0,3 Ma. Des roches volcanoclastiques ont fourni des zircons détritiques qui restreignent les âges maximums de la succession volcanique. Les grains de zircon les plus jeunes provenant de quatre échantillons dans des segments structuraux différents limitent les strates à plus jeunes que ~186 Ma, ~178 Ma, ~183 Ma et ~186 Ma. Les résultats, combinés à la limite d'âge régionale la plus vieille du Groupe de Bowser Lake, restreignent la succession volcanique au Jurassique précoce (?) et au Jurassique moyen précoce et appuient la corrélation avec le Groupe de Hazelton de Stikinia. De plus, ils permettent des comparaisons avec le gisement contemporain de Eskay Creek, riche en Au-Ag, qui étend vers le sud la zone d'extension dans le Stikinia occidental, laquelle a pénétré les magmas mafiques primitifs et a accompagné les derniers vestiges du volcanisme stikinien au Jurassique moyen précoce.[Traduit par la Rédaction] [ABSTRACT FROM AUTHOR]

The lithospheric structure of the transition from the craton to the Cordillera in northeastern British Columbia is interpreted from inversion of seismic refraction – wide-angle reflection data along a 460-km profile, and from 3-d (3-dimensional) inversion and 2.5-d forward modelling of Bouguer gravity data. The seismic profile extends westward from the sediment-covered edge of cratonic North America across the Foreland and Omineca morphogeological belts to the eastern boundary of accreted terranes, beyond the Tintina Fault. Across the ancient cratonic margin, the resultant models reveal a westward-thickening package of low upper crustal velocities (6.2 km/s and less) and low densities to almost 20 km depth below the Western Canada Sedimentary Basin, overlying a west-facing ramp of higher velocities and densities in the middle and lower crust. These features are inferred to represent passive-margin sediments deposited on the ancient rifted margin during the mid-to-late Proterozoic and early Paleozoic. A wedge-shaped high-velocity (7.3 km/s) crustal layer at the base of the crust beneath the edge of cratonic North America is interpreted to be the result of magmatic underplating during rifting. In the Cordilleran Foreland Belt, high velocities (6.4 km/s) in the upper 5 km of the crust indicate rocks upthrust from the middle crust. A narrow trench of low velocities in the near-surface, which is imaged ~20 km to the west of the inferred location of the Tintina Fault, is interpreted to represent the actual location of the fault or a major splay. From east to west, the Moho decreases in depth from ~40 km to ~34 km below the rifted margin of ancestral North America, then defines a small root at ~38 km depth below the high topography and upper crustal velocities of the eastern Foreland Belt, and gradually shallows to ~34 km beneath the Omineca belt. An enigmatic laterally heterogeneous upper mantle has anomalously high velocities (up to 8.3 km/s) beneath the Foreland Belt, flanked by regions of low velocities (7.7–7.8 km/s). Results indicate that the location of the Cordilleran deformation front west of the ramped cratonic margin directly affected the tectonic evolution of the region.La structure lithosphérique associée à la transition du craton à la Cordillère, dans le nord-est de la Colombie-Britannique, est interprétée à l'aide d'une inversion de données de sismique réfraction–réflexion grand-angle enregistrées sur un profil de 460 km de longueur, jumelée à une inversion tridimensionnelle de données gravimétriques et avec la construction itérative de modèles de densités 2,5-d correspondant aux anomalies gravimétriques de Bouguer mesurées le long du profile sismique. Le profil sismique s'étend à l'ouest de l'ancienne marge du craton nord-américain, maintenant couverte de dépôts sédimentaires, puis traverse le Domaine de l'avant-pays et le Domaine d'Omineca jusqu'à la bordure est de l'ensemble des terranes accrétés, à l'ouest de la faille Tintina. Le long de l'ancienne marge du craton nord-américain, les modèles résultants présentent une région de basses vitesses (< 6,2 km/s) et de basses densités s'épaississant vers l'ouest jusqu'à 20 km de profondeur sous le Bassin Sédimentaire de l'Ouest Canadien. Cette région recouvre une rampe d'échelle crustale inclinée vers l'ouest et caractérisée par de hautes vitesses et de hautes densités dans la croûte médiane et inférieure. Ces traits sont interprétés comme représentant les sédiments d'une marge passive déposés durant le Protérozoïque moyen jusqu'au Phanérozoïque sur l'ancienne marge continentale. Une couche tronquée de hautes vitesses (7,3 km/s) située à la base de la croûte, sous l'ancienne marge du craton nord-américain, est interprétée comme le résultat de plaçage sous la croûte de matériel magmatique durant la période de rifting. Dans le Domaine de l'avant-pays, des vitesses élevées (6,4 km/s) à 5 km de la surface de la croûte indiquent des roches soulevées de la croûte médiane. Un fossé étroit, caractérisé par de basses vitesses et situé près de la surface, est observé 20 km à l'ouest de la localisation actuelle de la faille. Nous déduisons de nos résultats que le fossé représente la position exacte de la faille Tintina ou d'une faille associée avec une large zone de failles. D'est en ouest, la profondeur du Moho diminue d'environ 40 km à 34 km sous l'ancienne marge du craton nord-américain, définie ensuite une racine crustale à environ 38 km de profondeur sous la haute topographie et les hautes vitesses dans la croûte supérieure de la partie orientale du Domaine de l'avant-pays, pour ensuite remonter graduellement jusqu'à environ 34 km sous le Domaine d'Omineca. Un manteau supérieur énigmatique et hétérogène est caractérisé par des vitesses anormalement élevées (jusqu'à 8,3 km/s) sous le Domaine de l'avant-pays flanquées par des régions de basses vitesses (7,7–7,8 km/s). Les résultats indiquent que la position du front de déformation de la Cordillère à l'ouest de la rampe de la marge cratonique a affecté directement l'évolution tectonique de la région. [ABSTRACT FROM AUTHOR]

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.De nouvelles données magnétiques et paléomagnétiques pour le centre de la Colombie-Britannique supportent et quantifient l'hypothèse que la région a subi d'importantes déformations de tension transversale au Tertiaire. Des inclinaisons déterminées par paléomagnétisme dans des roches datant de l'Éocène indiquent que les quatre fosses, limitées par des failles, qui constituent la mine de molybdène Endako ont été déplacées selon une série de failles normales (probablement listriques) séparées par moins d'un kilomètre. L'interprétation suggère également qu'il ne peut y avoir eu qu'un léger déplacement vertical le long de la faille Denak Ouest qui sépare les fosses Denak Est et Denak Ouest. Les données paléomagnétiques régionales indiquent une prédominance d'inclinaisons à direction est à l'est de la faille Casey mais, à l'ouest, on observe une grande variation dans l'orientation et la magnitude des inclinaisons. À une site près de la faille Casey, les résultats indiquent une composante de déplacement normal le long de cette faille à décrochement surtout horizontal dextre. Les failles cartographiées à tendance nord-est et nord-ouest correspondent fréquemment à des zones linéaires de gradient magnétique abrupte et à des sources magnétiques près de la surface. Plusieurs linéaments additionnels à tendance nord-ouest et nord-est sont imagés dans les données magnétiques où aucune faille n'est cartographiée (surtout au-dessus de phases massives et à lithologie homogène du batholite Endako). Des solutions de déconvolution eulériennes confirment que la plupart de tels linéaments sont également associés à des sources magnétiques à faible profondeur. En profil, ils ont le caractère d'une faille ou d'un dyke et on les interprète comme des failles non cartographiées, quelques-unes ayant subi une intrusion locale par des dykes mafiques qui découpent la région en une série de blocs délimités par des failles.[Traduit par la Rédaction] [ABSTRACT FROM AUTHOR]

Twenty-three new, precise, Eocene U–Pb and [sup 40] Ar/[sup 39] Ar age determinations for calc-alkaline volcanic rocks of the Ootsa Lake Group and associated intrusive rocks, widespread in the Nechako Plateau in central British Columbia, constrain the timing of the Eocene magmatism to 53.2–47.6 Ma, with a local duration of as little as 2–3 million years. The new dates show that magmatism in the study area is partly coeval with that responsible for the Babine Igneous Suite – Newman Volcanic Suite (53–50 Ma) to the north, and for the Endako Group (51–45 Ma), which overlies the Ootsa Lake Group; however, locally the three magmatic suites are distinct in age and (or) the strata record a magmatic hiatus of as much as 7.5 million years. The ages generally young from north to south (52–47 Ma) along the western portion of the study area. The Babine Igneous Suite – Newman Volcanic Suite represents the oldest member of this series. However, in the east, the Ootsa Lake Group volcanic rocks are generally older (53–51 Ma). The anomalously older ages may be related to the interaction of magmatism and formation of a nearby and coeval core complex, which ongoing studies show was uplifted at about the same time during the Eocene. Felsic plutonism associated with the Ootsa Lake Group occurred between 50.5 and 47.3 Ma. These plutons were emplaced in an extensional setting along north-northeast-trending faults. The new dates, stratigraphic relationships, and suggested correlations of Eocene strata in the study area with that to the west and north require a revision of the stratigraphic nomenclature for the Ootsa Lake and Endako groups.Vingt-trois nouvelles déterminations d'âge, précises, U–Pb et [sup 40] Ar/[sup 39] Ar sur des roches volcaniques calco-alcalines du Groupe d'Ootsa Lake et des roches intrusives associées, datant de l'Éocène, largement répandues dans le plateau de Nechako au centre de la Colombie-Britannique, limitent le magmatisme à l'Éocène à 53,2–47,6 Ma et à une durée aussi courte que 2 à 3 millions d'années. Les nouvelles dates montrent que le magmatisme dans la région étudiée est en partie contemporain avec celui qui est responsable de la suite ignée Babine – suite volcanique Newman (53–50 Ma) vers le nord et du Groupe Endako (51–45 Ma) qui repose sur le Groupe d'Ootsa Lake; localement, les trois suites magmatiques sont toutefois distinctes en âge et (ou) les strates enregistrent un hiatus magmatique allant jusqu'à 7,5 Ma. Les âges sont généralement plus jeunes du nord vers le sud (52–47 Ma) le long de la partie occidentale de la région à l'étude. La suite ignée Babine – suite volcanique Newman représente le membre le plus âgé de cette série. Toutefois, vers l'est, les roches volcaniques du Groupe d'Ootsa Lake sont généralement plus âgées (53–51 Ma). Les âges anormalement plus vieux peuvent être reliés à l'interaction du magmatisme et à la formation, à proximité, d'un complexe noyau contemporain, lequel, selon des études en cours, s'est soulevé à peu près à la même époque, à l'Éocène. Le plutonisme felsique associé au Groupe d'Ootsa Lake aurait eu lieu il y a environ 50,5 à 47,3 Ma. Ces plutons ont été mis en place dans un environnement extensionnel le long de failles de direction nord-nord-est. Les nouvelles dates, les relations stratigraphiques et les corrélations suggérées pour les strates de l'Éocène dans la région à l'étude et celles vers l'ouest et le nord demandent une révision de la nomenclature stratigraphique pour les groupes d'Ootsa Lake et d'Endako.[Traduit par la Rédaction] [ABSTRACT FROM AUTHOR]

Presents a study which explored the interplay of plutonism and regional deformation in an obliquely convergent arc in Southern Coast Belt, British Columbia. Regional geologic setting of the Harrison Lake Area; Description of the plutons in the study area; Structural data; Summary of the orogenic history.

Presents a study which describes the Tatshenshini shear zone in Yukon, Canada and compares it to the Coast shear zone in British Columbia. Implications of this comparison with regards to the sense of movement on the Coast shear zone and the formation of the Shakwak suture; Description of the study area; Conclusions.

Landsat Thematic Mapper (TM) data have been used to detect the presence of altered rocks associated with ore mineral deposition. In arid environments, the spectral signatures of diagnostic minerals are often not masked by water, vegetation, or surficial materials. There are many studies in which TM data have been used to locate hydrothermallyaltered rocks in near desert regions, but few successful examples can be found that relate to glaciated, vegetated terrain at high latitudes. In this paper, TM data, in concert with lithogeochemical data and field observations, are used to detect and map altered rocks in theSulphurets-Brucejack Lake district of northwestern British Columbia.Areas of iron-pyrite and phyllic (sericitic) alteration as well as areas of intense silicification have been located using band ratioing techniques. The chemical nature of these alteration zones has been established through comparison with lithogeochemical data. These alteration styles reflect the underlying rock type, as would be expected, but also appear to reflect two different styles of alteration, perhapsreflecting different mineralizing systems. The western half of the study area, characterized by iron-pyritic alteration, reflects a base metal (Cu porphyry and minor Au) system while the eastern half, characterized by areas of silicification and clay alteration, may represent a precious metal (Au, As, Sb) system. [ABSTRACT FROM AUTHOR]

Studies Nd isotopic data for rocks of the terrane assembly that lies inboard of the Stikine terrane in the Canadian Cordillera of British Columbia and Yukon, with focus on geology. Methodology used in the study; Indication that sedimentary rocks are indicators of tectonic position of the crustal fragments; Implications of the findings.