A Middle pleistocene (isotope stage 10) glacial sequence in the Stikine River valley, British Columbia

In the Stikine River valley, northwestern British Columbia, glacial and nonglacial sediments are preserved beneath Middle Pleistocene basalt-flow remnants that originated from Mount Edziza. The magnetic polarity is consistently normal, indicating that the sediment and the basalts were probably deposited within the Bruhnes normal polarity chron (<780 ka). The sediments record a regional glacial advance. Initial ice advance in the Coast Mountains blocked the westward drainage of the Stikine River and formed an advance-phase glacial lake. Sediments deposited in this lake form a coarsening-upwards sequence; debris-flow diamicton units that originated from the valley sides are common. The lacustrine sequence culminates in a poorly sorted ice-marginal gravel deposited as ice encroached upon the study area. There is little record of ice retreat. The basalts are deposited on fluvial and (or) glaciofluvial gravels, indicating that postglacial reincision was taking place at the time of eruption. Hence, the sediments were deposited in the glacial period immediately prior to the emplacement of the basalt. Evidence is presented that indicates that glacial conditions occurred between 341 and 352 ka, which corresponds to pre-Illinoian isotope stage 10.

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III.—Recent Observations on the Glaciation of British Columbia and Adjacent Regions

Geological Magazine ◽

10.1017/s0016756800182159 ◽

1888 ◽

Vol 5 (8) ◽

pp. 347-350 ◽

Cited By ~ 8

Author(s):

Geo. M. Dawson

Keyword(s):

British Columbia ◽

Glacial Period ◽

Coast Range ◽

Coast Mountains ◽

One Stage ◽

Queen Charlotte Islands ◽

Glacier Ice ◽

Inland Ice ◽

Great Valley ◽

The U.S

Previous observations in British Columbia have shown that at one stage in the Glacial period—that of maximum glaciation—a great confluent ice-mass has occupied the region which may be named the Interior Plateau, between the Coast Mountains and Gold and Eocky Mountain Kanges. From the 55th to the 49th parallel this great glacier has left traces of its general southward or southeastward movement, which are distinct from those of subsequent local glaciers. The southern extensions or terminations of this confluent glacier, in Washington and Idaho Territories, have quite recently been examined by Mr. Bailley Willis and Prof. T. C. Chamberlin, of the U.S. Geological Survey. There is, further, evidence to show that this inland-ice flowed also, by transverse valleys and gaps, across the Coast Range, and that the fiords of the coast were thus deeply filled with glacier-ice which, supplemented by that originating on the Coast Range itself, buried the entire great valley which separates Vancouver Island from the mainland and discharged seaward round both ends of the island. Further north, the glacier extending from the mainland coast touched the northern shores of the Queen Charlotte Islands.

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New advances on the magnetic chronostratigraphy of cave sediments in Atapuerca Gran Dolina, Spain

10.5194/egusphere-egu21-9682 ◽

2021 ◽

Author(s):

Josep M Pares ◽

Mathieu Duval ◽

Isidoro Campaña ◽

José M. Bermúdez de Castro ◽

Eudald Carbonell

Keyword(s):

Magnetic Polarity ◽

Age Dating ◽

Middle Pleistocene ◽

Geologic History ◽

Cave Sediments ◽

Normal Polarity ◽

Gran Dolina ◽

Geomagnetic Polarity ◽

Quartz Grains ◽

Numerical Dating

<p>Magnetostratigraphy has proven to be a powerful and versatile method as well the first line of defence for dating sediments. When properly anchored to the Geomagnetic Polarity Time Scale (GPTS), chron boundaries provide a basis for numerical dating by correlating the local magnetostratigraphy to the GPTS. A caveat and intrinsic limitation when anchoring magnetic stratigraphy to the GPTS is that we deal with essentially a binary code, a sequence of normal and reverse polarity zones. To overcome such limitation biostratigraphy or (ideally) numerical (absolute) age dating is required. Unfortunately, numerical dating of sediments is typically hampered by the lack of amenable minerals for the application of standard methods such as Ar-Ar, requiring thus the use of less conventional methods. Burial dating is possible using methods such as Electron Spin Resonance (ESR) on optically bleached quartz grains. Similar to luminescence, ESR is a paleodosimetric method that provides the time elapsed since the last exposure of quartz grains to natural sun light. Cave sediments are particularly amenable for paleodosimetric methods, as sediments are preserved in the dark and the ESR signal should survive over the geologic history of the deposits. On the down side, we date the moment when the quartz grain enters the karst system, not its deposition. If the transit time is too long, this might be an issue and we would be significantly overestimating the true burial age. Caves at Atapuerca (N Spain) hold the richest Quaternary paleontological record in Eurasia, including fossils and lithic tools. Sediments in these caves have been traditionally dated via magnetostratigraphy by identifying the Matuyama-Brunhes reversal (0.78 Ma) thus providing the Lower to Middle Pleistocene boundary. Nevertheless, the appearance of older sediments in the caves required the combination of paleomagnetism with methods such as ESR to interpret older intra-Matuyama Subchrons. In the deepest levels of the Gran Dolina cave, close to the floor of the cavity, a number of short intervals of normal polarity have been identified in the fluviatile sediments belonging to TD1 unit, which we interpret in terms of Subchrons using ESR ages of quartz grains. We will discuss both paleomagnetic data and interpret the magnetic polarity stratigraphy in the view of the ESR ages obtained from the Multiple Centre (MC) approach.&#160;</p>

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Eocene paleo-physiography and drainage directions, southern Interior Plateau, British Columbia

Canadian Journal of Earth Sciences ◽

10.1139/e04-062 ◽

2005 ◽

Vol 42 (2) ◽

pp. 215-230 ◽

Cited By ~ 28

Author(s):

Selina Tribe

Keyword(s):

British Columbia ◽

Middle Eocene ◽

Regional Scale ◽

River Valley ◽

Coast Mountains ◽

Base Level ◽

The North ◽

Bedrock Geology ◽

River Valleys ◽

Early Cenozoic

A map of reconstructed Eocene physiography and drainage directions is presented for the southern Interior Plateau region, British Columbia south of 53°N. Eocene landforms are inferred from the distribution and depositional paleoenvironment of Eocene rocks and from crosscutting relationships between regional-scale geomorphology and bedrock geology of known age. Eocene drainage directions are inferred from physiography, relief, and base level elevations of the sub-Eocene unconformity and the documented distribution, provenance, and paleocurrents of early Cenozoic fluvial sediments. The Eocene landscape of the southern Interior Plateau resembled its modern counterpart, with highlands, plains, and deeply incised drainages, except regional drainage was to the north. An anabranching valley system trending west and northwest from Quesnel and Shuswap Highlands, across the Cariboo Plateau to the Fraser River valley, contained north-flowing streams from Eocene to early Quaternary time. Other valleys dating back at least to Middle Eocene time include the North Thompson valley south of Clearwater, Thompson valley from Kamloops to Spences Bridge, the valley containing Nicola Lake, Bridge River valley, and Okanagan Lake valley. During the early Cenozoic, highlands existed where the Coast Mountains are today. Southward drainage along the modern Fraser, Chilcotin, and Thompson River valleys was established after the Late Miocene.

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Late Pleistocene stratigraphy and chronology of lower Chehalis River valley, southwestern British Columbia: evidence for a restricted Coquitlam Stade

Canadian Journal of Earth Sciences ◽

10.1139/e04-037 ◽

2004 ◽

Vol 41 (7) ◽

pp. 881-895 ◽

Cited By ~ 8

Author(s):

Brent C Ward ◽

Bruce Thomson

Keyword(s):

British Columbia ◽

Late Pleistocene ◽

River Valley ◽

Glacial Lakes ◽

Coast Mountains ◽

Source Areas ◽

Definitive Evidence

Sediments in lower Chehalis valley span middle Wisconsin (Olympia nonglacial interval) to Holocene time. Sediments are divided into six units with chronological control provided by 14 new radiocarbon ages. Fluvial gravel spans the transition from the late Olympia nonglacial interval to the early Fraser Glaciation. Glaciolacustrine sedimentation represents the first definitive glacial activity in the valley and indicates that Vashon ice in the Fraser Lowland blocked the mouth of the Chehalis valley at ca. 1817 ka BP. Ice then flowed down the Chehalis valley. The Chehalis valley deglaciated while ice persisted in the Fraser Lowland, forming another lake. After this lake drained, terraces and fans formed. This style of glaciationdeglaciation is typical of many watersheds peripheral to the Fraser Lowland in that local valley ice was slightly out of phase with ice in the lowland. This resulted in glacial lakes forming during both advance and retreat phases. However, in contrast to watersheds in the northwestern Fraser Lowland, no definitive evidence of a Coquitlam ice advance was found within the Chehalis valley. Although glaciers in the area were likely active and advancing, data from the Chehalis valley indicates that they were not as extensive as previously thought. Since ice source areas in the northeastern Fraser Lowland are in the leeward area of the Coast Mountains, it is suggested that lower precipitation resulted in limited glacier activity there during the Coquitlam Stade.

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Magnetic Polarity Stratigraphy of the Middle Pleistocene (Ensenadan) Tarija Formation of Southern Bolivia

Quaternary Research ◽

10.1016/0033-5894(83)90003-0 ◽

1983 ◽

Vol 19 (2) ◽

pp. 172-187 ◽

Cited By ~ 42

Author(s):

Bruce J. MacFadden ◽

Oscar Siles ◽

Peter Zeitler ◽

Noye M. Johnson ◽

Kenneth E. Campbell

Keyword(s):

Fission Track ◽

Magnetic Polarity ◽

Middle Pleistocene ◽

Time Interval ◽

Zircon Age ◽

Matuyama Chron ◽

Composite Section ◽

Normal Polarity ◽

Reversed Polarity ◽

Land Mammal

AbstractThe Tarija Formation of southern Bolivia, which is well known for its classic vertebrate faunas, is of prime importance in understanding of the chronology of the Ensenadan Land Mammal Age. This formation consists of well-exposed and relatively fossiliferous sections of clays, clayey silts, sands, gravels, and tuffs which were deposited in a predominately fluviatile regime in a Pleistocene structural basin. Four stratigraphic sections, each measuring 110 m or less, were studied to establish a magnetic polarity stratigraphy. Paleomagnetic samples were collected from the finer-grained sediments at 100 sites spaced at stratigraphic intervals of 5 m or less. All paleomagnetic specimens were demagnetized in alternating fields of least 250 oersteds (oe). Some specimens were also thermally demagnetized at 200°C or more. Of the 100 sites, 77 were ultimately used to determine the magnetic polarity zonation. Based on the four sections sampled, the Tarija Formation spans a time interval from about 1 my to about 0.7 my B.P. or perhaps younger. The lower half of the composite section is of reversed polarity punctuated by a short normal event. This sequence probably represents the late Matuyama chron with the Jaramillo subchron. The upper part of the section is of normal polarity and represents early Brunhes time. A tuffaceous unit 43 m above the Brunhes-Matuyama boundary yielded a fission track (zircon) age of 0.7 ± 0.2 by B.P. These data indicate that the classic Tarija fauna is middle Pleistocene Ensendan in age.

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A record of Early Pleistocene glaciation on the Mount Edziza Plateau, northwestern British Columbia

Canadian Journal of Earth Sciences ◽

10.1139/e95-158 ◽

1995 ◽

Vol 32 (12) ◽

pp. 2046-2056 ◽

Cited By ~ 14

Author(s):

I. S. Spooner ◽

G. D. Osborn ◽

R. W. Barendregt ◽

E. Irving

Keyword(s):

British Columbia ◽

Lacustrine Sediments ◽

Early Pleistocene ◽

Volcanic Complex ◽

Pleistocene Glaciation ◽

Sedimentary Record ◽

Basalt Flow ◽

Glacial Ice ◽

Normal Polarity

Mount Edziza is a Plio-Pleistocene volcanic complex that is located in the Stikine Terrane in northwestern British Columbia. A sequence of diamictites preserved between Ice Peak Formation basalts on the northwestern blank of Mount Edziza records an Early Pleistocene regional glaciation. The lowest Ice Peak Formation basalt flow (IP1; about 1 Ma) was probably extruded onto glacial ice because it is deformed and brecciated, it is pillowed at the base, it lies directly on hyaloclastite deposits, and there is a lack of fluvial and lacustrine sediments at the base. Fabric measurements from the underlying diamictites are consistent with lodgement processes and indicate northwest and southwest transport directions. These data, and an abundance of striated exotic cobbles, indicate that the sediment was deposited by Coast Mountain ice. Radiometric, paleomagnetic, and stratigraphic data all support the interpretation that diamictites at the section are the sedimentary record of an Early Pleistocene (about 1.1 Ma, isotope stage 32–34) regional glaciation(s). The normal paleomagnetic polarity of one of the Ice Peak Formation basalts (IP2) records extrusion during the Jaramillo normal polarity subchron (1.07–0.99 Ma) and further constrains the age of the underlying diamictites.

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