摘要:

Cored drill hole on a high electromagnetic conductivity anomaly near the Onakawana lignite field penetrated 50.3 m of Pleistocene, Cretaceous, and Devonian strata. Spore–pollen floras from the Cretaceous interval indicate an early middle Albian age and a correlation with the lower part of the Mattagami Formation. Spores, acritarchs, and tasmanitids from the Devonian interval indicate that the upper part of the Long Rapids Formation is marine and is Frasnian–Famennian in age. Multiple recycling events are documented between the Devonian and Cretaceous and between the Cretaceous and Pleistocene, provenances being local near the margins of the basin.

ISSN:0008-4077    

DOI:10.1139/e82-001

出版商:NRC Research Press    

年代:1982

数据来源: NRC

摘要:

The central Pelly Mountains in southeastern Yukon Territory consist of imbricate thrust sheets, which have undergone syn- and post-thrusting deformation and metamorphism. The local geology is further complicated by the intrusion of Late Cretaceous batholiths, and by strike-slip faulting related to the Tintina Fault, a major northwest-trending transcurrent fault of latest Cretaceous or early Tertiary age. This faulting disrupts the northeast edge of the study area.Upper Devonian and Mississippian strata are present in at least two of the structural packages, but the Mississippian metavolcanic rocks occur only in the lowermost package. Rb–Sr geochronology indicates a mid-Mississippian age for the igneous suite. The volcanic rocks consist of volcaniclastic material with minor interbedded flows, and were deposited in a submarine environment. Several coeval and cogenetic syenite and trachyte domes and small stocks are the remains of vent areas. Although the volcanic rocks are all highly altered and show evidence of widespread chemical mobility, trace element data indicate that the rocks are metaluminous trachytes, most closely resembling peralkaline volcanics generated in extensional environments. This suggestion of a predominantly extensional tectonic setting in mid-Mississippian time in the Pelly Mountains is consistent with recent tectonic syntheses for the area.

ISSN:0008-4077    

DOI:10.1139/e82-002

出版商:NRC Research Press    

年代:1982

数据来源: NRC

摘要:

A 3.1 m section of limnic sediment and peat from a bog on the Morley Flats and a 2.8 m section of limnic sediment from Wedge Lake in the Kananaskis Valley have yielded the first comprehensive late Quaternary biostratigraphic record from south-western Alberta. Both sections were analyzed for subfossil pollen, molluscs, and several sedimentary indices. Two distinct pollen zones were recognised. The basal zone, characterized by high relative abundancy ofArtemisia–Salix–Juniperus, suggests that the Morley Flats were dominated by a sparse vegetation composed of aggressive pioneer species following deglaciation until prior to approximately 10 000 BP. Similarly, the mollusc fauna from this zone is dominated by northern ranging species. The second zone is typified by a predominance ofPinusandPicea. This reflects the expansion of coniferous forest into the region. Both the relative abundance of southern ranging mollusc species and the total carbonate concentration in the sediment increase in this zone. The vegetation of the region has remained generally stable since at least 9395 BP. However, increases in the abundance ofPinusrelative toPiceaandAbiesin the mid-Holocene suggest that this period experienced an increase in fire frequency, possibly generated by climatic amelioration.

ISSN:0008-4077    

DOI:10.1139/e82-003

出版商:NRC Research Press    

年代:1982

数据来源: NRC

摘要:

There is a systematic relationship between anisotropy in the fabric of rocks and anisotropy in their dielectric properties, although the relationship is difficult to express in any quantitative sense. In general, the dielectric constantK′, the dielectric lossK″, and the real conductivity σ′ are a maximum when measured along the lineation axis (L) of rock, and a minimum when measured along the foliation normal (F). In this study, rocks were measured both vacuum dried and with varying degrees of water present; the anisotropy of wet rocks is greater than when vacuum dried, due presumably to anisotropic distribution of water parallel to the petrofabric. The effects of water, however, can be eliminated by means of measurements in vacuum or, more simply, by heat drying the sample, and subsequent impregnation of the rock with a hydrophobic low-loss dielectric material (paraffin wax). This is particularly significant since it greatly reduces the cost and time involved in this type of study.Dielectric anisotropy is frequency dependent. It was largest at the lowest measurement frequencies (30 Hz) and diminished with increasing frequency. For this and other reasons, dielectric anisotropy in rock is attributed to Maxwell–Wagner effects, which are low frequency relaxation phenomena related to the shape, size, and dielectric anisotropy in rock, reflecting primarily the grain-shape and grain-aggregate-shape fabric.

ISSN:0008-4077    

DOI:10.1139/e82-004

出版商:NRC Research Press    

年代:1982

数据来源: NRC

摘要:

Volcanic rocks of the Archean Oxford Lake Group are characterized by a stratigraphic progression from mafic to felsic compositions, accompanied by a systematic decrease in incompatible element abundances. This, coupled with high abundances of Sr, Rb, K2O, and La, high (La/Yb)n, and unfractionated (flat to concave) heavy-REE (rare earth element) profiles, distinguishes these rocks as an Archean shoshonite to high-K andesite – dacite–rhyolite series, directly comparable to modern analogues formed in convergent tectonic settings. The trace-element data support a model of petrogenesis in which an Archean mantle source region was modified by volatiles rich in large-ion-lithophile elements, the modified mantle was subjected to partial melting forming a parental liquid of shoshonitic character, and this liquid principally underwent amphibole fractionation to form the evolved rock compositions. This process is envisaged as terminal magmatism during the final (senile) stage of activity in an arc setting. The Rb–Sr age (2650 ± 80 Ma) and initial-Sr ratio (0.70145 ± 38) of the Oxford Lake Group are in accord with this model; when coupled with the 2.7 Ga age for the underlying Hayes River Group volcanics, these data indicate a short interval (<50 Ma?) for Archean crustal development in the area.

ISSN:0008-4077    

DOI:10.1139/e82-005

出版商:NRC Research Press    

年代:1982

数据来源: NRC

摘要:

In eastern Yunnan the Upper Permian Lungtan and Changhsing Formations and the Lower Triassic Kayitou Formation each contain a characteristic assemblage of spores and pollen.TheTorispora gigantea–Patellisporites meishanensisassemblage in the Lungtan Formation contains abundant pteridophyte and pteridosperm spores and few gymnosperm pollen. Some genera are known from the Carboniferous and Lower Permian of Europe but most are Cathaysian. TheYunnanospora radiata–Gardenasporitesassemblage in the Changhsing Formation has a Paleozoic aspect but characteristic Mesozoic genera and species occur. TheLundbladispora–Aratrisporites–Pteruchipollenitesassemblage in the Kayitou Formation contains numerous pteridophyte and pteriodosperm spores and gymnosperm pollen; some Paleozoic genera occur (Crassispora,Lycospora?,Stellisporites,Thymospora,Torispora,Triparites,Triquitrites, andWaltzispora), but Mesozoic genera predominate. Thirty metres above the base of the Kayitou Formation gymnosperm pollen, especially that of conifers, becomes dominant.It is suggested that the Carboniferous and Lower Permian species in the Changhsing Formation and the Paleozoic genera in the Kayitou Formation are not reworked but are indigenous and that the composition of the resulting microflora reflects the parent flora. The presence of this microflora in Lower Triassic rocks suggests that, at least locally, sedimentation was essentially continuous across the Permian–Triassic boundary.

ISSN:0008-4077    

DOI:10.1139/e82-006

出版商:NRC Research Press    

年代:1982

数据来源: NRC

摘要:

The clastic metasedimentary rocks that form the Flinton Group occur as arcuate belts within the Grenville Structural Province, southeastern Ontario. Metamorphic isotherms transect these rocks and allow comparison of deformation over an approximate temperature range of 550–650 °C. Two geometrically discrete but temporally continuous deformation phases contribute significantly to pebble deformation within the conglomeratic units. There is a general increase in both finite strain, over which there is a strong compositional control, and the frequency of D2minor structures with increasing metamorphic temperature. D1is characterized by the creation of a subgrain structure and progressive misorientation of the subgrains as strain accumulates. Ultimately this leads to formation of high-angle boundaries defining recrystallized grains of a size similar to that of the precursor subgrains. D2produces a new, finer subgrain structure, elongated grains, grain boundary migration (bulging), and small recrystallized grains. Empirical relationships between stress and subgrain diameter suggest that D1is a low stress (5–6 MPa) deformation and D2is a higher stress (12–80 MPa) deformation. This emphasizes that rotation recrystallization defines a low-temperature, low-stress regime, whereas migration recrystallization is typical of higher temperatures and stresses. Although dislocation creep predominates in most pebble types, evaluation of the deformation in terms of non-uniform flow laws can explain the compositional control of strain in the quartzite pebbles and suggests that significant grain boundary sliding occurred.

ISSN:0008-4077    

DOI:10.1139/e82-007

出版商:NRC Research Press    

年代:1982

数据来源: NRC

摘要:

Lowell Glacier, a large valley glacier in the St. Elias Mountains of southwestern Yukon Territory, advanced across Alsek Valley and blocked south-flowing Alsek River many times during the Neoglacial interval. The resulting lake, termed Neoglacial Lake Alsek, extended east of the front of the St. Elias Mountains and inundated parts of Dezadeash Valley that presently are populated. Lake Alsek, at its maximum, was about 200 m deep at the glacier dam and over 100 km long. Staircase flights of beaches, wave-cut benches, layers of driftwood, and thin lacustrine sediments provide evidence of the former lake. Giant dunes and flood terraces on the floor of Alsek Valley indicate that the lake emptied catastrophically when the Lowell Glacier dam failed.Several phases of Lake Alsek have been identified. Each was preceded and followed by intervals during which the lake was empty and the present southward drainage pattern in Alsek Valley prevailed. Historical records, radiocarbon and tree-ring dates on driftwood, and radiocarbon dates on buried soils separating lacustrine units indicate that Lake Alsek extended into Dezadeash Valley sometime betweenA.D. 1848 and 1891, betweenA.D. 1736 and 1832, twice between 250 and 500 years ago, and at least once between 800 and 2900 years ago. In addition, a small lake may have existed in Alsek Valley after 1891, but before 1917, although the evidence for this is equivocal. During each ponding phase, Lake Alsek may have emptied and filled repeatedly, perhaps on a regular cycle, as is common for some existing glacier-dammed lakes.Lowell Glacier, during a future surge, might again block Alsek River and form a new lake. However, populated areas in Dezadeash Valley probably would not be inundated because Lowell Glacier has thinned and receded somewhat since Lake Alsek last extended beyond the St. Elias Mountains in the nineteenth century.

ISSN:0008-4077    

DOI:10.1139/e82-008

出版商:NRC Research Press    

年代:1982

数据来源: NRC

摘要:

Previously thought to be a salamander (Prosirenidae),AlbanerpetonEstes and Hoffstetter (Jurassic to Miocene) possesses no known features otherwise restricted to salamanders. Its salamander-like features are only those held in common with small, limbed, non-saltatorial amphibians in general. In still other aspects (including feeding apparatus, dermal bones of the skull, and anterior cervical vertebrae),Albanerpetonappears unique. Already well isolated from salamanders,Albanerpetonseems no nearer phyletically to any other known amphibians, from Devonian to Recent. The relationships ofAlbanerpetonare most consistently indicated by classification in its own family (Albanerpetontidae, new) and order (Allocaudata, new), perhaps referrable to the Lissamphibia.

ISSN:0008-4077    

DOI:10.1139/e82-009

出版商:NRC Research Press    

年代:1982

数据来源: NRC

摘要:

Detailed petrography across a metapelitic sequence in the eastern axial zone of the Montagne Noire, France, is the basis for a sequence of isograds marking the first appearance of biotite–cordierite, staurolite, andalusite, and sillimanite. The juxtaposition of low-grade biotite-free rocks against medium-grade rocks at the gently dipping biotite–cordierite isograd is attributed to tectonic telescoping of the metamorphic sequence. Study of mineral assemblages with respect to an AFM reaction sequence indicates the staurolite isograd is related to changes in rock composition, and complex assemblages in the sillimanite zone may be the result of unstable persistence of minerals formed when metamorphic grade was lower. These assemblages are interpreted to contain a record of part of theP–Thistory during which pressure decreased as temperature increased.P–Tprofiles show that temperature gradients of 200–300 °C/km suggested by previous workers are not required to explain the isograd pattern; gradients of 37 °C/km or less are sufficient.

ISSN:0008-4077    

DOI:10.1139/e82-010

出版商:NRC Research Press    

年代:1982

数据来源: NRC