摘要:

Materials from two glacial and two nonglacial intervals are identified on north-central Vancouver Island, British Columbia. The oldest Pleistocene unit, Muchalat River drift, consists of till and overlying glaciolacustrine silt. It has been tentatively correlated with Dashwood drift of the Semiahmoo Glaciation. An overlying single exposure of mudflow sediment in the Gold River valley contains wood dated at 40 900 ± 2000 years BP within the time span of the Olympia nonglacial interval. The Olympia nonglacial interval was characterized by a period of degradation in which Olympia-age sediments were deposited in transient sedimentary environments and subsequently eroded. Gold River drift includes Gold River advance deposits, Gold River till, and Gold River late glacial deposits, and was deposited during the Fraser Glaciation. The Fraser Glaciation was well underway on north-central Vancouver Island by 25 200 ± 330 years BP. During the Fraser Glaciation maximum, which occurred after 20 600 ± 330 years BP, Coast Mountain ice flowed in a southwesterly direction across north-central Vancouver Island overtopping all but the highest peaks of the Vancouver Island Mountains. Deglaciation commenced prior to 12 930 ± 160 years BP and the ice had probably disappeared before 9500 years ago. During postglacial times rivers have dissected older Quaternary sediments and bedrock up to at least 40 m. Macroflora data recorded in postglacial lacustrine sediments suggest that the Hypsithermal Interval commenced before 8300 ± 70 years BP.

ISSN:0008-4077    

DOI:10.1139/e81-001

出版商:NRC Research Press    

年代:1981

数据来源: NRC

摘要:

Approximately 11 km of four-fold common reflection point data have been recorded across a region that spans the contact fault zone between the Thompson nickel belt and the Churchill Tectonic Province. From these data it is shown that the upper crust in this region and, to a lesser extent, the lower crust are characterized by numerous scattered events that originate from relatively small-scale features. Within the Thompson nickel belt two extensive and particularly high-amplitude reflection zones, at two-way travel times oft = 5.0–5.5 s andt = 6.0–6.5 s, are recorded with apparent northwesterly dips of 0–20 °C. These reflection zones, which have a laminated character, are truncated close to the faulted contact with the Churchill Province. Both the contact fault zone and the Churchill Province in this region have crustal sections that are relatively devoid of significant reflectors. The evidence presented here confirms that the crustal section of the Thompson nickel belt is fundamentally different from that of the Churchill Tectonic Province.

ISSN:0008-4077    

DOI:10.1139/e81-002

出版商:NRC Research Press    

年代:1981

数据来源: NRC

摘要:

Helikian anorthositic rocks in the Puttuaaluk Lake area, Labrador are in contact with granitic rocks of similar age and basement granulites of Archean (?) age. Internal variation within the anorthositic rocks has led to their subdivision into anorthosite, leuconorite, and oxide-rich anorthosite, which suggests three separate intrusive events and at least three magma types. The major differences among the anorthositic rocks are that anorthosite typically carries augite, leuconorite carries orthopyroxene ± augite, and oxide-rich anorthosite carries ilmenite ± magnetite with minor orthopyroxene. Plagioclase compositions plotted in the system Ab–An–Or lie within 3 mol% Or of the Ab–An join, and regression analyses for anorthosite and leuconorite show a slight decrease of K with decreasing An. Hence a distribution coefficient DKplag–liq ≥ 1.0 is implied for the anorthositic parent magmas.The average modal composition of the leuconorite, assuming 1% ilmenite, is 23% orthopyroxene and 76% plagioclase (volume percent). This approaches the cotectic composition (25% Opx, 75% Plag) for leuconorite estimated for the system OI–Plag–SiO2after correction for the effects of Ab, Fe2+, and pressure. It is concluded that the leuconorite unit represents on the average a cotectic composition or a composition slightly more plagioclase-rich than the cotectic. It is likely that the leuconorite magma composition lay in the plagioclase field near the Plag–Opx join and the average rock composition. The low color index of the anorthosite unit, with an average modal composition, assuming 1% ilmenite, of 6% pyroxene and 93% plagioclase, suggests that crystallization from a magma equivalent to the rock composition is highly unlikely. Flotation of plagioclase from a leucogabbroic magma could account for the extreme plagioclase richness of the anorthosite unit. The oxide-rich anorthosite with its calcic plagioclase and abundant ilmenite cannot be the logical daughter product of either the anorthosite or the leuconorite and is more likely a product of a magma enriched in Fe-Ti oxide components relative to the other two units.

ISSN:0008-4077    

DOI:10.1139/e81-003

出版商:NRC Research Press    

年代:1981

数据来源: NRC

摘要:

Bryozoan mounds, dominated byBatostoma chazyensisfrom the Laval formation of the Chazy Group (early Middle Ordovician) near Montreal, Quebec contain framework cavities that house a coelobiontic (cavity-dwelling) biota. Reports of coelobionts of Ordovician age are rare, and this is the first report of Chazy Group mounds containing coelobionts.Algae, sponges, and bryozoa (Batostoma) dominate the cavity biota, and are found encrusting cavity walls and roofs. The algae are represented by mammillary encrustations (now micrite), andSolenporasp. on the roofs. The sponges are not identified, but occur both as isolated monaxial, triaxial, and six-rayed spicules, and as body fossils within the cavities. Coccoid cells, of unknown affinities, are also found. These cavities provide the first evidence of coelobiontic biological erosion.Trypanites, a compound morphogenus, is the only macroborer and is found in cavity walls; endolithic (boring) algae are present, and indicate that as early as the Middle Ordovician bio-erosion of reef and mound interior cavities was active and that micro- and macroendoliths had invaded the cavity habitat.

ISSN:0008-4077    

DOI:10.1139/e81-004

出版商:NRC Research Press    

年代:1981

数据来源: NRC

摘要:

The olistostromal Carmanville ophiolitic mélange of northeastern Newfoundland contains two extensive mafic volcanic and volcaniclastic rafts (4 km × 1 km, 11 km × 7 km), which were previously interpreted as an assemblage of lavas and pyroclastics. These rafts are ? Upper Cambrian – Arenigian in age and, prior to tectonic transport and subsequent resedimentation and incorporation into the submarine slides (olistostromes) of the Carmanville ophiolitic mélange, were originally deposited on the slopes of a volcanic edifice (volcanic islands). The primary sedimentation history and depositional environment of the volcanic and volcaniclastic rocks are examined in detail. Four volcaniclastic facies are now recognized (facies 1–4), each differentiated on the basis of megascopic descriptive and genetic criteria. The essential characteristics of each facies are described in detail. These facies essentially represent shallow-water mafic volcanic material resedimented into a deeper water submarine slope or fan valley system by mass-emplacement depositional mechanisms, which included debris, turbidity, and possibly fluidized sediment flows. Normal contour-following bottom currents could possibly have been responsible for depositing or at least reworking some of the volcaniclastic siltstones of facies 3. Facies 1–4 were introduced into a deeper water environment itself characterized by the formation of massive and pillowed lavas and their hyaloclastic equivalents (facies 5) envisaged as the end product of deposition from submarine seamounts and guyots.

ISSN:0008-4077    

DOI:10.1139/e81-005

出版商:NRC Research Press    

年代:1981

数据来源: NRC

摘要:

Sea cliffs at Victoria expose submarine flow tills within an ice-contact complex of flow till – outwash proglacial cones interbedded with dinoflagellate-bearing glaciomarine fine sediments. Glacial debris flow lobes (mainly flow tills) were formed by supraglacially, englacially, and basally transported sediment slumping off an ice margin grounded in the Strait of Juan de Fuca. The structures and textures reveal that lobes formed by a conveyor mechanism. In some lobes a double sorting phenomenon apparently developed involving an outer, winnowed, layer of pseudo-plastic flow around an inner core of till that was sorted by dewatering and expulsion of fines outward from the centre during flow. Structures and fabric data indicate lobe travel was gravitationally controlled down cone flanks and independent of ice movement.A depositional model for the complex proposes the ice margin produced a proglacial apron of interdigitating cones, which accumulated on the sea floor. Sediment facies variations were probably controlled by shifts in cone development along the margin: cones formed where glacial and glaciofluvial debris discharged from the ice into the sea and glaciomarine deposits accumulated from glacial flour suspended in the seawater between the cones.Although this is the first reported example of submarine flow tills, casual observations elsewhere suggest that they are common in coastal areas.

ISSN:0008-4077    

DOI:10.1139/e81-006

出版商:NRC Research Press    

年代:1981

数据来源: NRC

摘要:

The hydrologic and limnologic conditions of Sunwapta Lake, a small proglacial lake in the Canadian Rocky Mountains, were investigated with special reference to the sedimentology of this lake. Discharge and suspended sediment concentrations of the inflowing streams were measured to give estimates of sediment input. Distribution of large loads of fine glacial sediment is largely by an inflow- and wind-controlled circulation, which commonly fluctuates diurnally. The spatial distribution of sedimentation was determined by use of sediment-collecting pans placed on the lake bed. Turbidity currents are rare with only one event monitored in 2 years. This event was caused by a burst of highly sediment-charged inflow water. The rarity of turbidity currents is attributed to the high sediment concentration in the lake water, which results from the small size of the lake in relation to the inflow. Wind-generated water movement at the lake floor ranges from 0.0–0.03 m/s while the maximum recorded velocity of the turbidity currents was 0.32 m/s.Sedimentation rates are calculated and six cores from the lake bed, each containing sediment deposited over several years, are described. Although bedding and lamination are found in all cores, correlation between cores was not possible. Sedimentary characteristics are related to inflow and lake conditions: laminated and massive beds of medium to fine sand and silt are related to turbidity events, graded laminae in coarse and fine silt to diurnal variations in lake currents, and massive beds in silt to periods of continuous sedimentation without diurnal variation. Deformed beds result from subaqueous slumps.

ISSN:0008-4077    

DOI:10.1139/e81-007

出版商:NRC Research Press    

年代:1981

数据来源: NRC

摘要:

Deformed and recrystallized, amphibolite facies, trondhjemitic to granodioritic orthogneiss along the north margin of the Archean Lake of the Woods greenstone belt has an Rb–Sr isochron age of 2950 ± 150 Ma and an initial87Sr/86Sr ratio of 0.7028 ± 0.0014. Preserved primary textures and complex internal intrusive relationships document the original plutonic nature of the orthogneiss. Based on isotopic age and degree of deformation and recrystallization, the orthogneiss is interpreted to be basement to the adjacent metavolcanic sequence of the greenstone belt. The contact between the orthogneiss and greenstone belt is the locus of deformation, but may be an unconformity. It is also the boundary between the English River subprovince on the north and the Wabigoon subprovince on the south.Similar orthogneiss ranging in age from 2800 to 3800 Ma is widespread in the Canadian Shield. It is basement to the 2650–2750 Ma Archean volcanism, at least in some areas, but is not necessarily basement to the older (2800–3000 Ma) volcanism. The orthogneisses are remnants of a once much more extensive sialic terrain, but the contemporaneity and extent of this sialic terrain are uncertain.

ISSN:0008-4077    

DOI:10.1139/e81-008

出版商:NRC Research Press    

年代:1981

数据来源: NRC

摘要:

A comparison of geological data shows that most of the earthquakes of western Quebec lie within or near the eastern and western boundaries of a Grenville (ca. 1000 Ma) central metasedimentary belt and in the area of the younger fault zone along the Ottawa River. Although most of the earthquakes have occurred within terrain of Grenville age or older, the younger rift zone is characterized by the larger earthquakes (Temiskaming, M6.2, 1935; Cornwall–Massena, M5.7, 1944). The earthquakes also correlate with gradient zones around two prominent anomalies in the smoothed Bouguer gravity field.The pattern of aeromagnetic anomalies and drainage channels reflects Preeambrian structural trends and indicates the central metasedimentary belt continues beneath Paleozoic sediments to Lake Ontario. The strikes of magnetic, gravity, and drainage features north of Lake Ontario are parallel to features mapped to the south of the lake. Geological data and geophysical trends suggest that a cataclastic zone is continuous along most of the eastern border of the metasedimentary belt. A prominent, positive regional aeromagnetic trend and some cataclastic evidence characterize the western border.Although the seismicity may reflect the adjustment of existing structures to stresses from regional density variations, continental deglaciation, and interplate forces, the reason for the greater seismic activity in the Grenville age terrain than along the younger fault zones remains unclear.

ISSN:0008-4077    

DOI:10.1139/e81-009

出版商:NRC Research Press    

年代:1981

数据来源: NRC

摘要:

Penetrative deformation and granite intrusion in the northeastern Gander Zone, Newfoundland, represent a progressive Acadian event. Interference between ductile, strike–slip shearing along the southeastern margin of the Appalachian orogen and the emplacement of syntectonic granite diapirs results in the formation of a vertical, northeast–southwest strike–slip ductile shear zone where granites come to outcrop and a ductile strike–slip thrust zone where granites are absent at the surface. Sinistral movement along the vertical shear zone is compatible with recent palaeomagnetic models for the Appalachians and the British Caledonides. The constraints that the geologic model places on the symmetry of the Appalachian orogen in Newfoundland and the definition and extrapolation of the Gander tectonostratigraphic zone are discussed.

ISSN:0008-4077    

DOI:10.1139/e81-010

出版商:NRC Research Press    

年代:1981

数据来源: NRC