摘要:

Several Au–Ag gossans occur over massive sulphide deposits in the Ordovician Tetagouche Group near Bathurst, New Brunswick. The Murray Brook and Heath Steele B zone goethite gossans were about 45 and 15 m thick, respectively, prior to mining. They contain no minerals suitable for radiometric age dating. Geologically they must be younger than the Devonian Acadian orogeny and older than the last glaciation. Paleomagnetic methods were used to analyse specimens from 29 sites, mostly from ore on the pit walls. Host rocks and sulphide mineralization retain characteristic remanent magnetization directions in magnetite and pyrrhotite with a variety of directions that include possible Devonian overprints. Fertile and barren gossan specimens at 21 sites retain antiparallel normal and reversed A characteristic remanence components in goethite and (or) hematite. The A direction isD = 357.7°,I = 61.7 °(α95 = 4.5°,k = 31). Its pole of 134.2°E, 85.2°N (dp = 5.4°, dm = 7.0°) falls on the North American apparent polar wander path and circumscribes the Earth's present rotational axis, indicating that the gossans formed during the Pliocene–Pleistocene. Examination of the site locations in the pits, along with the remanence polarity of their goethite and hematite A components, suggests the gossans formed during Chrons 1 and 2 only, or in the past 2.3 ± 0.3 Ma.

ISSN:0008-4077    

DOI:10.1139/e96-001

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

The reliability of the long-wavelength portion (> 300 km) of the magnetic field over Canada, as represented by the national aeromagnetic anomaly database compiled by the Geological Survey of Canada (GSC), is assessed by comparison with two independent data sets: a high-altitude country-wide survey carried out by the former Earth Physics Branch (EPB) and data from the MAGSAT and POGO satellite missions. The different altitudes at which each data set was measured (300 m, ~4 km, and ~400 km), and their different resolution and time span of observations allow a determination of the integrity of selected wavelength bands in each data set. The (upward-continued) EPB and MAGSAT–POGO fields compare well for wavelengths of 300–2500 km. The GSC data show significant differences to the former, indicating that the levelling and merging of several hundred individual surveys has degraded the longer wavelength components of the magnetic field. Replacing the GSC wavelength components >300 km with those from the EPB field produces a magnetic data set containing more dependable information within the largest possible waveband.

ISSN:0008-4077    

DOI:10.1139/e96-002

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

A new ichthyosaur species is described from the Upper Triassic (middle Norian) of Williston Lake, northeastern British Columbia. Aside from the foramen enclosed between the radius and ulna–a characteristic of Triassic ichthyosaurs–the new specimen is typical of Lower Jurassic forms. Indeed, if the specimen had been collected from the English lower Liassic, there would have been no hesitation in referring it to the common English genusIchthyosaurus, a taxonomic course I follow here. Referring the new species toIchthyosaurusextends the geological range of the genus by approximately 9 Ma, to the middle Norian.Ichthyosaurus janicepssp. nov. has an abbreviated snout, like that ofIchthyosaurus breviceps, but it is a much larger species, and has a distinctly different forefin.

ISSN:0008-4077    

DOI:10.1139/e96-003

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

Studies of Coleoptera remains from two late-glacial sites on Cape Breton Island, Nova Scotia, Canada, present a picture of the paleoenvironment and paleoclimate during the Allerød–Younger Dryas transition in the Maritimes region. They provide evidence for the Younger Dryas event in northeastern North America. Between 11 300 and 10 800 BP, the beetle assemblages at the Campbell site are typical of faunas of the modern middle to northern boreal forest. The West Mabou site contains beetle fossils younger than 10 900 BP, possibly as young as 10 500 BP, extending into the time period of the Younger Dryas, dated from 10 800 to 10 000 BP in the Maritimes. A "cold climate" indicator recognizable in the beetle fauna,Olophrum boreale, occurs in relative abundance and provides an interesting comparison with sites in Europe where the same northern boreo-montane species is evident at the beginning of the Younger Dryas.

ISSN:0008-4077    

DOI:10.1139/e96-004

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

For this study, 84 samples of glacial and juxtaglacial sediments were collected in valleys of the Ruby Range and Aishihik Basin (southwestern Yukon). Analyses were conducted to quantify the heavy minerals in the sand fraction and to assess the petrography of the gravel fraction. A cluster analysis performed on the heavy mineral results showed five groups of deposits, three of which are related to local glaciers inside the Ruby Range, the other two being related to regional ice lobes of Kluane and Aishihik, respectively. The three groups of local sediments correspond to the three lithologies of the Ruby Range, i.e., the granitic batholith, the schists, and the alaskite. The sediments from the regional ice lobes are characterized by highly diversified mineralogy and petrography and the relative abundance of minerals from the Saint Elias Mountains, the main source of the ice lobes. A correspondance factor analysis performed on the heavy mineral results organizes samples and minerals into a triangular cloud, the three vertices corresponding to biotite, carbonate, and titanite–garnet. These are the key elements of local glaciers, Kluane ice lobe, and Aishihik ice lobe, respectively. Finally, the study shows the extension of Kluane lobe in one valley of the Ruby Range, the ice flow pattern in another valley, as well as a transfluence from Kluane lobe inside the Range.

ISSN:0008-4077    

DOI:10.1139/e96-005

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

Five offshore drill holes northeast of Richards Island reveal permafrost conditions, which are interpreted in terms of the sea-level and paleoenvironmental history of the Canadian Beaufort Shelf. The top of ice-bonded permafrost lies 76–88 m below the seabed within 12 km of the shore, 11 m below the seabed 20 km offshore, and at 60 m some 50 km offshore. The base of permafrost is 500 m to over 700 m deep. Temperature–depth gradients are negative or nearly isothermal, and permafrost is degrading. Geothermal modelling of the temperatures and permafrost observations indicates that the sites were subaerially exposed throughout most of the Wisconsinan, and during the early Holocene. Three sites 2–10 km from the present shoreline experienced inundation at 3.5–4.0 ka. These times support dates of marine transgression predicted by the sea-level curve, but the sites may have been occupied by thermokarst lakes prior to transgression. In contrast, the site 20 km offshore with shallow ice bonding was inundated about 0.4 ka; this area may have persisted as an island until recently. Shoals observed nearby may be analogues of this process, being outliers that are now being eroded below sea level. Marine transgression occurred about 6 ka some 50 km offshore.

ISSN:0008-4077    

DOI:10.1139/e96-006

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

In the Mackenzie–Beaufort region, maximum permafrost thickness is 750 m in the Pleistocene Tuktoyaktuk Coastlands, less than 100 m in the Holocene Mackenzie Delta, and 500 m and anomalously warm in the Big Lake Delta Plain between the two areas. Numerical modelling has been used to derive surface temperature histories that fit ground temperatures and permafrost conditions at 12 wells in the Unipkat, Kumak, and Taglu hydrocarbon fields. The models indicate that the present Holocene Mackenzie Delta was built by fluvial processes into a submarine trough. The delta front passed a site presently some 20 km from the coast about 4.5 ka, and subsequently 58 m of ice-bonded permafrost has aggraded. In contrast, the Big Lake Delta Plain was a subaerial platform for much of the Wisconsinan. It experienced several thousand years of inundation in the Holocene, probably due to widespread development of thermokarst lakes. At sites 8–12 km from the coast, the present subaerial conditions were established 0.5–1.5 ka through lake drainage and fluvial–deltaic deposition.

ISSN:0008-4077    

DOI:10.1139/e96-007

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

Hot and boiling springs in Kenya and New Zealand that are emitting water with temperatures more than 90 °C are commonly characterized by a complex array of CaCO3and SiO2precipitates that have been formed through abiogenic and biogenic processes. Thermophilic bacteria are the only microbes that can survive in the boiling water that is discharged into pools around the spring orifice. Analysis of modern substrates from various springs in the Kenya Rift Valley and the Taupo Volcanic Zone in New Zealand shows that they are inhabited by a diverse array of coccoid and filamentous bacteria. In some areas these bacteria produce copious amounts of mucus that coat the substrates. Although the coccoid and filamentous bacteria provide substrates for CaCO3and SiO2precipitation, the microbes do not seem to have any direct influence on the morphology of the precipitates that are produced. Conversely, the mucus found in these hot spring pools selectively takes up elements such as Si, Mg, Al, and Fe, but is not calcified. In many cases the elements that are selectively fixed by the mucus are only present in very low concentrations in the spring water. In one of the Waikite springs in New Zealand, the mucus plays an active role in the formation of the calcite deposits by providing a template for crystal nucleation and binding the small calcite crystals to the substrate. The latter process is especially important because the flowing waters of the spring could easily transport the grains if they were not bound to the substrate.

ISSN:0008-4077    

DOI:10.1139/e96-008

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

A field structural analysis has been carried out in the High Atlas Mountains of Morocco. Paleostress solutions provide information on the successive orientations of major stress patterns during Mesozoic and Cenozoic time. An initial rift stage in the Early Jurassic is characterized by normal–oblique faults bounding tilted blocks, which are associated with tensional paleostress patterns whose minimum component trends west-northwest–east-southeast. Faults parallel to this direction are interpreted as paleotransfer faults. We assume that the divergent motion responsible for the opening of the rift system in the Early Jurassic was oriented west-northwest–east-southeast, subparallel to the paleotransfer faults and the trend of the minimum component (σ3) of the paleostress field. The east–west-trending Jurassic central–eastern High Atlas rift opened obliquely, and not in a pure strike-slip stress regime along east–west-striking faults as previously proposed. A later stage of rifting (Middle Jurassic) is characterized by large normal faults and is supposed to accompany local movements, probably due to gravity. The uplift of the High Atlas belt occurred mainly during the Cenozoic period as a consequence of a north–south- to northwest–southeast-directed compression related to collision between Europe and Africa.

ISSN:0008-4077    

DOI:10.1139/e96-009

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

The Pliocene Cirotan gold deposit provides an exceptional example of mineralized breccias, and in particular cockade breccias. Analysis of these breccias, approached through both field observation and image analysis on photographs, made it possible to determine their method of graded formation. The mineralized structure, as much a 25 m thick in places, is a right-lateral strike-slip fault that evolved to a normal fault at the end of the system's development. It consists of juxtaposed breccia bodies separated by major slip, or "septa," which formed at a major inflection of the host fault. The breccia bodies all show a similar internal organization. From footwall to hanging wall, one passes from a siliceous breccia with angular clasts to a thick infill of cockade breccia showing a reverse grading with small centimetre-size cockades (aspect ratios of 1:10) passing to larger (up to 1 m) more equant cockades (aspect ratios 1:3) in contact with the hanging wall. The different stages of cockade formation demonstrate genesis in an open milieu through rolling-accretion and collapse of the clasts, which show signs of mechanical attrition. The large cockades are formed of an agglomeration of several small cockades. Ore deposition occurred during a pulsating process that was active throughout the complex evolution of the structure. The final ore stage, filling the intercockade spaces, marked the end of the structure's evolution. High fluid pressures and the local structural context combined to maintain open the hydrothermal channelways, enabling cockade growth and collapse. The process of breccia formation at Cirotan was therefore exclusively of hydrothermal origin in an active tectonic context. It represents a self-organizing system within a fault zone.

ISSN:0008-4077    

DOI:10.1139/e96-010

出版商:NRC Research Press    

年代:1996

数据来源: NRC