摘要:

Shatter cones, an unusual type of fracturing produced by intense shock, are found widespread on the Slate Islands in northern Lake Superior. The islands have been interpreted as the central uplift of an eroded meteorite impact crater about 30 km in diameter. The cones are best developed in certain rock types: Keweenawan basalt flows and chilled margins of associated feeder dikes, and Archean diorite and foliated feldspar porphyry. At certain sites cones show an elongate cross section and anomalous orientation caused by foliation-induced elastic anisotropy in the host rock.In general the cones point upward and inward toward the centre of the Slate Islands group. After structural correction of some sites according to paleomagnetic data, there is increased convergence of cone axes to a central focus (the inferred impact point) that occurs at a height of about 1 km above the present land surface.

ISSN:0008-4077    

DOI:10.1139/e83-001

出版商:NRC Research Press    

年代:1983

数据来源: NRC

摘要:

A specimen of the palaeoryctidPararyctes(Mammalia: Eutheria), from Paleocene strata of Alberta, shows nearly the complete replacement pattern of the dentition. Unexpectedly, premolars at two positions are seen replacing dP4, whereas the premolars at the anteriormost three positions seem not replaced or shed. The resulting total of concurrently functional teeth at five premolar and three molar positions, while mimicking that in certain ancestral eutherians, is clearly a derived character state, achieved independently. Furthermore, this pattern is inconsistent with the assumptions that deciduous and permanent teeth need belong to the same tooth families and that identical adult dental formulae are secure guides to homology.

ISSN:0008-4077    

DOI:10.1139/e83-002

出版商:NRC Research Press    

年代:1983

数据来源: NRC

摘要:

The present study deals with the geochemical stratigraphic evolution of the recent sediments of 26 lakes located throughout the Province of Quebec, Canada. Although there is no major anthropogenic activity within the watersheds of many of these lakes, it is shown that Pb, Zn, Hg, and Cu levels in the most recent sediments of all lakes increased significantly from 1940 onwards. It is suggested that these increases are due to the increased burning of fossil fuels (particularly coal). The heavy-metal increases tend to be relatively high, especially for Pb, Hg, and Zn, in the sediments of lakes from areas close to the U.S.A.–Quebec boundary, while lakes in more remote areas show smaller increases in the strata laid down in the same time periods. Pb contents in the sediments show a sustained increase in all of the upper strata. However, the subsequent reduction in the stratigraphic concentration of Zn and Hg since 1960 in both an acidified system (Lake Tantare) and a non-acidified lake (Lake Laflamme) might be the result of the important decrease of the total particulate emissions to the atmosphere associated with new technology for coal-fired power plants and the use of cleaner energy sources.The increase in Al in the sediments of Lake Tantare since 1950 is attributed to the processes of surface water acidification of this watershed induced by the long-range atmospheric transport of SOxand NOx.Based on the sedimentary anthropogenic enrichment factor (SAEF) values for the remote sites there is no evidence in the present study for associating the origin of certain heavy metals in these lake sediments with alternative anthropogenic sources such as the Ni and Cu smelting complexes located in Sudbury (Ontario) and Rouyn–Noranda (Quebec). The major sources of heavy-metal deposition and acid precipitation are thus associated with the long-range transport of emissions from fossil fuel combustion originating in the heavily industrialized American Midwest region.

ISSN:0008-4077    

DOI:10.1139/e83-003

出版商:NRC Research Press    

年代:1983

数据来源: NRC

摘要:

Brownish yellow saprolite derived from granite gneiss is exposed beneath 1–2 m of reddish brown till along a roadcut in the Cape Breton Highlands. The strongly acid soil is similar to other Podzolic soils of the region except for the presence of gibbsite in the silt and clay fractions. In the saprolite, feldspar and biotite have weathered to poorly crystalline kaolinite, gibbsite, and a minor component of iron oxide. The poorly crystalline kaolinite does not occur in the overlying till.The evidence presented is consistent with the view that the area was covered either by "cold-based" or by stagnant "warm-based" glaciers that eroded the pre-Quaternary surface only slightly and deposited a thin, discontinuous veneer of till derived mainly from local bedrock and saprolite. Weathering products from the saprolite are probably incorporated commonly in tills of the area. During the formation of soils in these tills the poorly crystalline kaolinite and most of the gibbsite are either transformed to other minerals or dissolved and removed in solution.

ISSN:0008-4077    

DOI:10.1139/e83-004

出版商:NRC Research Press    

年代:1983

数据来源: NRC

摘要:

The Dollyberry Lake volcanics occur at the base of the Huronian Supergroup and outcrop ~15 km north of Elliot Lake, Ontario. Ten specimens were collected from each of 36 sites in the volcanics and from a further five sites in stratigraphically equivalent volcanics ~9 km east of Elliot Lake. Alternating field (AF) and thermal step demagnetizations were done on two specimens from each site up to 100 mT and 650 °C, respectively. AF demagnetization led to the isolation of an A component in 33 sites, a B component in three sites, and both components in two sites. Fold tests demonstrate that both the A and B components are postfolding in origin at the >97 and >80% confidence level, respectively. It is argued that the A component (pole 154°W, 56°N, δp = 8°, δm = 10°) was acquired during the Penokean Orogeny at ~2215 ± 40 Ma, and that the B component (pole 60°W, 20°S, δp = 8°, δm = 13°) was acquired probably at ~ 1900 ± 100 Ma in response to some geographically restricted thermal or chemical event. The results indicate that the coeval Thessalon volcanics studied by Symons and O'Leary retain the Penokean A component. This leads to the retraction of their conclusion that the superadjacent uranium ores were formed at an ~35° paleolatitude and to the conclusion by analogy that the Penokean Orogeny was the only significant orogenic event in the evolution of the ore deposits.

ISSN:0008-4077    

DOI:10.1139/e83-005

出版商:NRC Research Press    

年代:1983

数据来源: NRC

摘要:

Materials from two glacial intervals and one nonglacial interval have been identified on northern Vancouver Island, British Columbia. The oldest Pleistocene unit, termed "older drift," consists of glaciomarine silt and clay >38 000 years BP in age that overlie a till that has only been recorded in well logs. "Older drift" is tentatively correlated with Dashwood drift of the Semiahmoo Glaciation (early Wisconsin or older). No sediments of the succeeding Olympia nonglacial interval (mid-Wisconsin) have been found in the area. It is thought that this interval was characterized by a period of degradation in which Olympia-age sediments were deposited in transient sedimentary environments and subsequently eroded, in part during the Fraser Glaciation (late Wisconsin). The youngest Pleistocene unit, termed Port McNeill drift, includes advance deposits, till, and deglacial sediments, all deposited during Fraser Glaciation. Ice of this glaciation did not cover most of northern Vancouver Island until after 20 600 ± 330 years BP. At the maximum, which probably occurred about 15 000 years ago, Coast Mountain ice coalesced with and overrode Vancouver Island ice, and flowed in a westerly to northwesterly direction across northern Vancouver Island. Deglaciation commenced prior to 12 930 ± 160 years BP and possibly as early as 13 630 years ago on the eastern coast. Maximum sea level during and immediately following deglaciation was about 92 and 20 m elevation on the east and west coasts, respectively. This suggests that ice thickness at the Fraser maximum decreased westward across the study area. Deposits of Recent time include colluvial sediments formed by weathering and mass movement processes, alluvial fan and floodplain deposits, eolian sands associated with active beaches on the west coast, and organic deposits.

ISSN:0008-4077    

DOI:10.1139/e83-006

出版商:NRC Research Press    

年代:1983

数据来源: NRC

摘要:

Typical sections of the Ordovician carbonate platform sequence in the St. Lawrence Lowlands (Beekmantown, Chazy, Black River, Trenton, and Utica Groups) were sampled at Neuville, Joliette, and Montreal, in the Province of Quebec. The purpose of this work was to determine the level of thermal maturation of the carbonates using organic matter and clay studies, and to correlate it with the crystal characteristics of the microcrystalline calcite.The studied formations are supermature in the Joliette and Montreal areas, whereas they are only mature at Neuville.The numerical analysis of the petrographic data shows that some microstructures observed in the rock samples and the size and morphology of the microcrystalline calcite crystals are partly related to the thermal maturation as determined by other methods.

ISSN:0008-4077    

DOI:10.1139/e83-007

出版商:NRC Research Press    

年代:1983

数据来源: NRC

摘要:

Uptonia?dayiceroidesMouterde is placed in the genusDayicerasand its age established as latest Jamesoni Zone to possibly earliest Domerian. The species is abundant and associated with faunas of Tethyan aspect along the northeastern Pacific margin. First occurrences in Oregon and Nevada and new occurrences in British Columbia are reported. Localities at apparently high paleolatitudes are attributed to post-early Pliensbachian transcurrent fault displacements. Genetic continuity with a disjunct population in Portugal is postulated via a central Atlantic seaway, here named the Hispanic Corridor, connecting the eastern Pacific and western Tethys Oceans. The existence of this corridor during the Pliensbachian is supported by several lines of independent paleobiogeographic evidence.

ISSN:0008-4077    

DOI:10.1139/e83-008

出版商:NRC Research Press    

年代:1983

数据来源: NRC

摘要:

Uranium mineralization in pegmatites and granites occurs widely in the Grenville Province but is especially important near Bancroft, Ontario and north of Mont Laurier and Johan Beetz in Quebec. Most investigators have concluded that these rocks were produced by anatexis of a uranium-enriched sedimentary protolith. We have used Rb–Sr isotopic methods to test this and other hypotheses and have reexamined the petrologic and structural features that led to these hypotheses.Rb–Sr whole-rock isochron ages from all three areas range from 937 to 980 Ma, some 150 Ma younger than the age of the peak of Grenville metamorphism as inferred from numerous ages from syntectonic intrusive rocks and high-grade metasediments. The ages of the pegmatites are similar to or just slightly greater than K–Ar ages from this region. The initial87Sr/86Sr ratios range from 0.7028 to 0.7054, plus one poorly defined value of 0.709. Excluding this last one, these values are only slightly greater than mantle ratios, and calculations show that these rocks could not have been derived from the quartzofeldspafhic gneisses of these areas and certainly not from Grenville Supergroup sediments.The late timing of the emplacement of these rocks and the popularity of a continental collision model for the Grenville Province producing a very thick crust lead us to suggest an origin by deep melting due to isothermal decompression during rapid uplift. This suggestion is supported by the location of all the occurrences near zones interpreted to be paleorift systems.

ISSN:0008-4077    

DOI:10.1139/e83-009

出版商:NRC Research Press    

年代:1983

数据来源: NRC

摘要:

Two components of magnetization have been isolated from Chequamegon Sandstone samples using chemical demagnetization. A characteristic magnetization resides in magnetite of detrital origin. The pole calculated from this magnetization is 12.3°S, 177.7°E (K = 111.5, A95 = 4.6°). This pole lies with other poles of late Keweenawan age and is very close to the Jacobsville Sandstone poles. A secondary magnetization resides in authigenic hematite and yields a pole close to the present north pole. This high-latitude pole is known from an earlier study of the Chequamegon and has been used as evidence for the Hadrynian APW track. However, most if not all of the high-latitude poles that define the Hadrynian track are secondary and undated. Our preferred alternative to the Hadrynian track is that the high-latitude poles are recent remagnetizations and that the antipodal equatorial poles that mark its end points represent field reversals.

ISSN:0008-4077    

DOI:10.1139/e83-010

出版商:NRC Research Press    

年代:1983

数据来源: NRC