Canadian Journal of Earth Sciences
1480-3313
0008-4077
Canada
Cơ quản chủ quản: Canadian Science Publishing , National Research Council of Canada
Lĩnh vực:
Earth and Planetary Sciences (miscellaneous)
Các bài báo tiêu biểu
The Mid-Atlantic Ridge Near 45 °N. XVI. Serpentinized Ultramafic Intrusions Detailed descriptions of the mineralogy, petrography, geochemistry, and physical properties of serpentinized ultramafic rocks dredged from the Mid-Atlantic Ridge at 45° N support an interpretation of the events which affected these rocks after their original crystallization. Crystallization apparently took place in lopoliths emplaced at the Crust/Upper Mantle interface beneath the axis of the ridge under conditions quiet enough to permit gravity crystal differentiation and layering. The rocks were then fractured without hydration under high hydrostatic pressure, with a feeble directional component, possibly under conditions favoring solid-state recrystallization of interstitial minerals. Hydration (amphibolization) began during the last phases of intimate mechanical deformation and the commencement of rodingitic metasomatism. Further hydration resulted in multiple overlapping periods of serpentinization dependent on varying physical conditions. Hydrating fluids may have been derived both from juvenile waters and from sea water.
Tập 8 Số 6 - Trang 631-663 - 1971
Sedimentary record of Harrison Lake: implications for deglaciation in southwestern British Columbia A sedimentary record from 60 km long Harrison Lake was constructed by using 3.5 kHz subbottom acoustic profiles and gravity cores of surface sediments. In places, the glaciolacustrine sediments exceed 70 m in thickness and represent the entire deglacial and postglacial accumulation record. An upper, acoustically transparent layer decreases in thickness from 12 to 4 m. southward from the upper lake. Cores from the upper metre of this layer demonstrate that deposition is dominated by settling of suspended sediment transported in a laterally mixed, wind-driven surface plume from the north. Depositional rates, inferred from 14 C dating of organic macrofossils and counting of probable annual laminated couplets in the cores, are almost 2 mm/a in the north and decline to less than 0.1 mm/a in the south. Hence, the upper acoustic layer accounts for all postglacial (last 10 500 years BP) lacustrine deposition, with most of the sediment derived from Lillooet River. A lower, thicker (12–22 m), acoustically stratified layer is interpreted as high-energy glaciolacustrine deposits. This large volume of deglaciation sediment is derived from two sources: (i) ice retreating rapidly northwest up the Lillooet valley, which may have existed for no more than 400 years in the lower valley prior to opening of Lillooet Lake (which now traps most sediment derived from the upper basin); and (ii) inflow from the south as the late-glacial Fraser River rapidly built a delta north from the sill at Harrison Hot Springs. Despite known higher sea levels during deglaciation of the eastern Fraser Lowland, we have no evidence for a marine incursion.
Tập 28 Số 5 - Trang 800-815 - 1991
Neoglacial history of the Coast Mountains near Bella Coola, British Columbia The maximum Holocene extent of glaciers in the study area is marked by late Neoglacial (Little Ice Age) terminal moraines. Moraine stratigraphy and 14 C dates from a small number of sites suggest that glacier advance, almost as extensive as that of the late Neoglacial, occurred about 2500 14 C years BP, and that late Neoglacial advance began well before 770 14 C years BP (or the thirteenth century A.D.); glacier termini then stood close to the position of the climax moraines for several centuries. Dates of stabilization of end moraines at 16 glaciers were determined by dendrochronology, with tree-ring counts corrected for sampling errors and ecesis. Most terminal moraines date from 1860 to 1900. Many recessional moraines were formed between 1900 and 1940, coincident with a regionally documented phase of cooler and wetter climate. The proposed chronology is similar to results from elsewhere in the Canadian Cordillera.
Tập 27 Số 2 - Trang 281-290 - 1990
Sediments of ice-dammed, self-draining Ape Lake, British Columbia The glacier damming Ape Lake has withdrawn from its Neoglacial terminal moraines in the lake since early in this century at an average rate of 15 m/a. As a result, the first known drainings of Ape Lake occurred in October 1984 and August 1986. In each event, about 54% of the volume of the lake was lost through a tunnel in the damming glacier. Most of the remaining water was held in the deep basin of the lake behind partially breached Neoglacial terminal moraines. As the glaciers have withdrawn, the character of the sediments has changed. Sediments in the deep basin of the lake are varved, but the grain size, especially of the summer deposits, has decreased and rates of sedimentation have decreased from about 4 mm/a to less than 2 mm/a. In shallow water, deposition of varved sediments has given way to the deposition of massive sediments at rates of less than 1 mm/a. Ice-rafted debris is rare in deep water, despite the presence of calving bergs.During and following the first draining, significant subaerial erosion occurred as a result of the event itself, the drawdown and steepened gradients, and the action of waves on the exposed sediments as the lake refilled. In proximal areas, distinct deposits within the normal winter deposits are recognised. In deep water, deposition of massive, highly underconsolidated, fine-grained sediments occurred. Organic debris released from shallow deposits by erosion has become concentrated in both shallow- and deep-water sediments. Within a year of the first draining, sediment loads in the lake water were returning to normal.
Tập 24 Số 9 - Trang 1735-1747 - 1987
BRIDGE RIVER ASH AND SOME OTHER RECENT ASH BEDS IN BRITISH COLUMBIA The character, distribution, and age of the Bridge River ash from postglacial sites in British Columbia and Alberta are discussed. The ash consists of dust-sized shards with ellipsoidal fragments of pumice. With a source in the region of the upper Lillooet River, the ash both, thins and fans out east-northeasterly as far as westernmost Alberta in the vicinity of the North Saskatchewan River. Peat immediately below the ash in a bog near Jesmond, British Columbia, was dated by radiocarbon at 2 440 ± 140 years before present (B.P.). The track of the Bridge River ash overlaps that of the Mazama ash of about 6 600 years, but lies north of the presently known distribution of St. Helens Y ash of approximately 3 200 years B.P. It is suggested that with a distinctive character and limited distribution, the Bridge River ash is potentially valuable as a postglacial marker horizon in southcentral British Columbia.
Tập 4 Số 1 - Trang 163-170 - 1967
Sedimentation in Lillooet Lake, British Columbia Sediment from Lillooet River Basin, 3580 sq km of alpine and subalpine landscape, 7% of which is glacier-covered, is deposited in Lillooet Lake. During the summer when the lake is stratified by temperature and suspended sediment content, processes of interflow and underflow distribute sediment throughout the lake and give rise to a distinctive sedimentary sequence of varved silts and clays interspaced irregularly with massive beds of coarser grained sediments up to 120 mm thick. Coarse sediment deposited on the proximal delta slope is redistributed by infrequent slumps; mounds of slumped material cover the foreset slopes to their base at 120 m depth. Thickness of varves is related to the annual inflow to the lake, and continuous records of water temperature near the lake bottom indicate that the numerous laminae within varves are due to intermittent underflow events.
Tập 12 Số 10 - Trang 1697-1711 - 1975
The late Quaternary sedimentary record of Stave Lake, southwestern British Columbia The postglacial sedimentary record of 59 km2 Stave Lake was investigated using 3.5 kHz subbottom profiles and cores from the sediment surface. The acoustic data show a thin cover of acoustically transparent sediment (unit 1) overlying bedrock or glacial sediment on the floor of the lake. Overlying acoustically stratified sediment is divided into unit 2, which thins from 28 m in the south of the lake to less than 12 m in the north, and unit 3, which thins from 20 m in the north to about 12 m in the south. Unit 1 is interpreted as resulting from deposition in a relatively quiet lacustrine or marine environment following retreat of Vashon glaciers about 13 ka ago. Unit 2 is ascribed to deposits of sediment in runoff to Stave Lake from the Sumas ice sheet in the Fraser Valley and connecting valleys to the Stave Basin. Following the retreat of the Sumas ice about 11 ka ago, deposition of unit 3 resulted almost entirely from sediment input from Stave River entering at the north end of the lake. Raising the lake in 1912 by damming for hydroelectric generation resulted in deposition of a thin but distinct marker horizon in the sediment, from which modern rates of accumulation averaging 3 mm/a are estimated. These are more than twice the average rates for the Holocene estimated from the total thickness of unit 3. The rates of sediment yield calculated from accumulation in Stave Lake are 4.5 × 105 kg∙km−2 ∙a−1 (modern) and less than 2 × 105 kg∙km−2 ∙a−1 (averaged over the Holocene).
Tập 29 Số 9 - Trang 1997-2006 - 1992
Normal Modes of the Bay of Fundy and Gulf of Maine Platzman's (1972) numerical scheme has been used to study the inviscid normal modes of the Bay of Fundy and Gulf of Maine for a variety of boundary conditions. The results support the contention that the resonant period associated with the lowest mode is greater than the M2 tidal period. Calculation of a damping rate from the inviscid solution gives a dissipative Q of 3.3 for the system, though this is probably an underestimate. Changes of period and normal mode shape due to changes in geometry at the head of the Bay of Fundy are investigated and some rather uncertain implications for tidal power development are discussed.
Tập 11 Số 4 - Trang 549-556 - 1974
What are glacier surges? A total of 204 surging glaciers has been identified in western North America. These glaciers surge repeatedly and probably with uniform periods (from about 15 to greater than 100 years). Ice flow rates during the active phase may range from about 150 m/year to > 6 km/year, and horizontal displacements may range from < 1 to > 11 km. Ice reservoir and ice receiving areas can be defined for surging glaciers, and the reservoir area does not necessarily coincide with the accumulation area. Glaciers of all shapes, sizes, and longitudinal profiles can surge, and no unusual "ice dams" or bedrock constrictions are evident. Surges occur in many different climatic, tectonic, and geologic environments, but only in certain limited areas (mainly in the Alaska, eastern Wrangell, and St. Elias mountains). Three types of surging glaciers are defined: (I) large to moderate-sized glaciers with large displacements and very fast flow, (II) large to moderate glaciers with moderate displacements and flow rates, and (III) small glaciers with small displacements and moderate to fast flow rates. All three types involve an inherent instability which is self-triggered at regular intervals, but with Type I surges an additional (unknown) mechanism produces the very high flow rates.
Tập 6 Số 4 - Trang 807-817 - 1969
Geochemistry of metasedimentary rocks of the Proterozoic Xingxingxia complex: implications for provenance and tectonic setting of the eastern segment of the Central Tianshan Tectonic Zone, northwestern China The eastern segment of the Central Tianshan Tectonic Zone in northwestern China includes the Proterozoic metasedimentary Xingxingxia complex. Because these rocks have been extensively deformed and metamorphosed to greenschist or amphibolite facies, a geochemical and Nd isotopic study was undertaken to constrain their provenance and tectonic setting, as well as to evaluate the effects of weathering and sedimentary processes on the source rock signature. Major- and trace-element data indicate that these samples are characterized by negative Eu anomalies, low chemical index of alteration values, and high index of compositional variability values. Chemical index of alteration values and the plot of molecular proportions Al2 O3 (CaO* + Na2 O)K2 O suggest low degrees of weathering of the source. They are compositionally immature and poorly sorted. Geochemical data and immobile elemental ratios, for example Al2 O3 /TiO2 , Cr/Th, Eu/Eu* and (La/Yb)n , indicate that the clastic materials were derived predominantly from felsic sources. Sedimentary tectonic discrimination diagrams demonstrate that most of the samples of the Xingxingxia complex were deposited on an active continental margin or continental island-arc setting. Rare-earth element distributions, εNd (t) values (calculated at 1.20 Ga, varying from 3.00 to +6.1), TDM model ages (ranging from 1.30 to 2.30), and t εNd (t) plot, indicate that sediments of the Proterozoic Xingxingxia complex were derived from varying degrees of mixing between Paleoproterozoic crust and juvenile materials with the former predominating. There is an increased flux of juvenile materials from Weiya in the east through Dikar to Kumishi. The secondary juvenile source may be 1.2 Ga arc-magma materials.
Tập 42 Số 3 - Trang 287-306 - 2005