摘要:

Paleomagnetic investigations have been carried out on about 250 oriented block samples collected from Early Tertiary lava flows representing an altitude span of about 1200 m on the Disko Island and 600 m on the Nûgssuaq Peninsula of West Greenland. The results reveal a record of two polarity transitions on the Disko Island and the existence of normal (N) and reverse (R) groups of lava flows on the Nûgssuaq Peninsula. A tentative correlation of the lava sequences from the two areas, on the basis of polarity of magnetization, has been suggested. Subject to the assumption of relatively uniform extrusion rates in northern Disko, a correlation of the comparatively thick sequence of reverse (R) polarity flows with the relatively long reverse epoch between the anomaly no. 25 (ca. 63 m.y.) and anomaly no. 24 (ca. 60.5 m.y.B.P.), has been attempted and an age estimate of the lava flows has been obtained.The Early Tertiary paleomagnetic pole for Greenland, computed from stable remanent magnetic directions of the Disko lavas is located at 67.5 °N and 165 °W. This pole position and the one for contemporaneous lava flows on the Baffin Island of Canada have been used in testing the models proposed by various workers for a paleogeographic reconstruction of Greenland and Canada, involving a closure of the Baffin Bay – Labrador Sea. The results of this paleomagnetic test suggest the existence of an ocean basin in the area, prior to the eruption of Early Tertiary lava sequences on Baffin Island and West Greenland, and also that this ocean basin had a much wider extent in Pre-Tertiary times.A model for the evolution of Baffin Bay – Labrador Sea has been suggested in the light of available geological/geophysical information about the region. It involves the opening of this sea in the Mesozoic and its partial closure during the Cenozoic as a consequence of the drift of Greenland in the northwesterly direction.

ISSN:0008-4077    

DOI:10.1139/e75-001

出版商:NRC Research Press    

年代:1975

数据来源: NRC

摘要:

A detailed study of the Tafraoute area granites points out the existence of a Cambrian granitization (with the present geochronological scale) in the Moroccan Anti-Atlas and allows to define in that granitic massif, up to now considered as an unique one, at least three types of granites with different ages and/or origin (Tafraoute: 530 m.y., Tahala: 1920 m.y., Tarsouat: undetermined).

ISSN:0008-4077    

DOI:10.1139/e75-002

出版商:NRC Research Press    

年代:1975

数据来源: NRC

摘要:

The distribution of peatland as a percentage of land area and the distribution of open and treed peatlands as percentages of peatland area have been determined for the Province of New Brunswick, For this work, aerial photographs, a dot planimeter, a mirror stereoscope and a computerized mapping procedure, SYMAP, in conjunction with the University of New Brunswick IBM system/360 computer were used. The results have been displayed in the form of symbolized computer printout maps (SYMAP) showing the distribution of peatland in New Brunswick. About 10% (about 700 000 ha) of the land area of New Brunswick is covered by peatland.

ISSN:0008-4077    

DOI:10.1139/e75-003

出版商:NRC Research Press    

年代:1975

数据来源: NRC

摘要:

Perennially frozen peatlands were divided into five morphological types: peat plateaus, polygonal peat plateaus, palsas, fen ridges and lowland polygons. One hundred and eight different peatlands were cored, measured and sampled. The internal structure of all but the lowland polygons suggests that the peat was deposited in wet fens unaffected by permafrost, and that permafrost developed only after a thin layer of Sphagnum covered them. The lowland polygons evolved in a permafrost environment. The study area was divided into four regions oh the basis of predominance of different peatlands forms.

ISSN:0008-4077    

DOI:10.1139/e75-004

出版商:NRC Research Press    

年代:1975

数据来源: NRC

摘要:

A unique occurrence of Mesozoic breccia cut by lamprophyric-carbonatite dikelets, near Makkovik, Labrador is interpreted to relate to the opening of the Labrador Sea. The breccia has been dated by nannofossils; vitrinite reflectance studies show that some time during or after deposition the rock was heated to at least 170 °C. It is suggested that shallow seas extended westward beyond the present Labrador Marginal Trough during early Jurassic time and that the period of late alkaline igneous activity is related to the rifting between Greenland and Labrador that commenced about the middle of the Mesozoic Era.

ISSN:0008-4077    

DOI:10.1139/e75-005

出版商:NRC Research Press    

年代:1975

数据来源: NRC

摘要:

Stable remanent directions have been obtained from fifteen sites located in the Purcell, Shepard and Kintla Formations of the upper Belt – Purcell Supergroup. The geomagnetic polarity sequence revealed by these and other studies suggests that the frequency of reversals was probably an order of magnitude lower than that observed over the last few million years. The polarity transitions have considerable potential as regional, and possibly, global, time lines for geological correlation.The paleomagnetic pole obtained (142 °W, 17 °S, dp = 4°, dm = 7°) agrees well with other results from the Belt Supergroup. It falls in a cluster of poles derived from various geological provinces of the Canadian Shield, which may imply that the shield was an integral unit as early as 1400 m.y. ago. However, the constancy of the pole position obtained from Belt rocks thought by some workers to be as young as 1100 m.y. conflicts with the large northward polar excursion (the Logan Loop) derived from other provinces. Possible explanations of this apparent conflict are discussed.

ISSN:0008-4077    

DOI:10.1139/e75-006

出版商:NRC Research Press    

年代:1975

数据来源: NRC

摘要:

Twenty specimens, from lavas in Oregon and Mull, have been used to test Irving's (1968) suggested method for determination of the polarity of unoriented dredged basalt samples. Polarity measurements were first made by independent workers, and the samples were provided following removal of orientation and identification marks. The natural remanent magnetism (NRM) of each specimen was first measured, demagnetized at 10 Oe intervals between 40 and 180 Oe (remeasuring being made after each treatment), and the operation was then repeated following the superimposition of anhysteritic remanent magnetism (ARM), by demagnetization in a peak field of 1400 Oe in the presence of a field of 0.5 G. Analyses of the resulting two coercivity spectra for each specimen produced the polarity predictions which were then compared to the independent polarity measurements. The results clearly show that the method is unsuccessful or doubtful as many times as it is successful, and therefore, cannot be considered reliable unless further research can isolate specimen characteristics which can be used to select material. In this experiment, however, no correlation exists between success or failure of the method and titanomagnetite sizes, and/or deuteric titanomagnetic oxidation index.

ISSN:0008-4077    

DOI:10.1139/e75-007

出版商:NRC Research Press    

年代:1975

数据来源: NRC

摘要:

Bison occidentals(extinct western bison),Ovis canadensis(mountain sheep), andEquus conversidens(extinct Mexican ass) are represented by new specimens recovered since 1968. The bison is represented by four additional horn-cores, a third lower molar and other elements; the sheep by a manual proximal phalanx, and the horse by four lower cheek-teeth and postcranial material.

ISSN:0008-4077    

DOI:10.1139/e75-008

出版商:NRC Research Press    

年代:1975

数据来源: NRC

摘要:

Eight species of graptolites not recognized in a previous study (Lenz 1972) are described from the Gaspé region. These compriseMonograptus bouceki, of Late Pridolian age from the Roncel-les Formation;M. cf.M.galaensisandM.communis rostratusof mid-Llandoverian age from the Burnt Jam Brook and White Head Formations respectively;Pristiograptus auctusof latest Wenlockian or earliest Ludlovian age, andP.tumescensandSaetograptus chimaera semispinosusof early Ludlovian age, from the St. Léon Formation;P.dubius dubiusof Wenlockian or early Ludlovian age from the Laforce and St. Léon Formations; andP.ludensisof latest Wenlockian age from the Gascons Formation.To date thirty species of graptolites have been recognized from the stratigraphic units studied.The low diversity of the Wenlockian-Ludlovian faunas is considered indicative of a shallow water community setting. It is tentatively suggested that the latest WenlockianP.ludensiszones fauna might be the shallow water equivalent of the deep waterM.testiszone.

ISSN:0008-4077    

DOI:10.1139/e75-009

出版商:NRC Research Press    

年代:1975

数据来源: NRC

摘要:

The first Precambrian ages from the Northern Ellesmere Fold Belt are reported. Six rocks from the largest gneiss terrain in northern Ellesmere Island yield a Late Precambrian age (minimum 742 ± 12 m.y.) of regional metamorphism. Relatively high initial87Sr/86Sr suggests that the rocks were derived from crustal materials.

ISSN:0008-4077    

DOI:10.1139/e75-010

出版商:NRC Research Press    

年代:1975

数据来源: NRC