Sheep Track Member

Sheep Track Member
Sheep Track Member
Stratigraphic range: Holocene ; 0.0118–0 Ma PreꞒ Ꞓ O S D C P T J K Pg N ↓
Type	Geological member
Unit of	Big Raven Formation
Overlies	Snowshoe Lava Field, Ice Peak Formation, Kakiddi Formation
Area	About 40 square kilometres (15 square miles)
Thickness	Up to 2 metres (6.6 feet)
Lithology
Primary	Comenditic trachyte
Location
Coordinates	57°38′N130°40′W / 57.64°N 130.67°W
Region	British Columbia
Country	Canada
Type section
Named by	Souther, 1988
	; Location in Mount Edziza Provincial Park

Last updated July 20, 2024

The Sheep Track Member is a stratigraphic unit of the Big Raven Formation, part of the Mount Edziza volcanic complex in northwestern British Columbia, Canada. It consists of pumice from an explosive eruption that fell over an area about 40 square kilometres (15 square miles). The pumice is of comenditic trachyte composition and reaches a thickness of up to 2 metres (6.6 feet) along the western edge of Tencho Glacier.

The Sheep Track Member was originally defined as the Sheep Track Formation in 1984 and was one of many geological formations comprising the Mount Edziza volcanic complex. However, it was lowered to member rank in 1988 when it became a unit of the Big Raven Formation. The Sheep Track Member has also been called the Sheep Track Pumice due to the member consisting primarily of pumice.

History

The Sheep Track Member was initially ranked as a geological formation by Jack Souther, Richard Lee Armstrong and J. Harakal in 1984 who grouped it together with the Big Raven Formation in their descriptions and mapping.^[6]^[7] Formerly called the Sheep Track Formation, it was reassigned as a member of the Big Raven Formation by Jack Souther in 1988; its recognition as a geological formation has since been abandoned.^[1]^[6] Sheep Track Pumice has been used as an alternative name for the Sheep Track Member by Natural Resources Canada and the Geological Association of Canada.^[5]^[8]

During its time as a geological formation in 1984, it was one of 15 geological formations comprising the Mount Edziza volcanic complex in northwestern British Columbia, Canada.^[7]^[9] In 1988, the number of geological formations comprising the Mount Edziza volcanic complex dropped to 13 when the Sheep Track and Kounugu formations were reassigned as members of the Big Raven and Nido formations, respectively.^[1]^[3]^[10]

Stratigraphy

Stratigraphically, the Sheep Track Member is a minor unit of the Big Raven Formation, covering area of about 40 square kilometres (15 square miles) with a total volume of less than 1 cubic kilometre (0.24 cubic miles).^[11] It was deposited on nearly all Snowshoe Lava Field flows and cinder cones of the Big Raven Formation, as well as on sediment of the surrounding Big Raven Plateau.^[3]^[12] The Sheep Track Member was also deposited on Koosick Bluff of the Ice Peak Formation and on Kakiddi Formation trachyte from Punch Cone on the western flank of Ice Peak.^[3]^[13] Both the Ice Peak and Kakiddi formations are older units of the Mount Edziza volcanic complex that were deposited about one million and 0.3 million years ago, respectively.^[14] Erosion has largely removed the Sheep Track Member from drainage channels of small intermittent streams on the upper Big Raven Plateau, but deposits as much as 2 metres (6.6 feet) thick occur in interfluvial areas.^[4]

Lithology

The Sheep Track Member is lithologically distinct from the rest of the Big Raven Formation, consisting mainly of comenditic trachyte that straddles near the alkaline–peralkaline boundary.^[15] It is in the form of air-fall pumice which reaches a thickness of up to 2 metres (6.6 feet) along the western edge of Tencho Glacier where snowball-sized pumice fragments up to 10 centimetres (3.9 inches) wide are distributed over an area of several square kilometres.^[16] The pumice rapidly decreases to pea-sized fragments around the margins of the pile, covering a circular area at least 10 kilometres (6.2 miles) in diameter.^[17] Thin drifts of wind-blown pumice cover The Saucer in the Snowshoe Lava Field which likely postdates the deposition of the Sheep Track Member.^[4]

Pumice of the Sheep Track Member comprises clear trachytic glass with tubular, open vesicles; alkali feldspar is in the form of rare microphenocrysts.^[18] It is compositionally distinct from the Finlay tephras which may have originated from Level Mountain, Hoodoo Mountain, Heart Peaks or the Mount Edziza volcanic complex.^[19]

Source

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Location of the Sheep Track Member in British Columbia, Canada

The Sheep Track Member was deposited by a small but violent VEI-3 eruption from the southwestern flank of Ice Peak near the end of the Big Raven eruptive period.^[20]^[21] The vent location for this eruption remains unknown but it is probably hidden under Tencho Glacier, the largest glacier of the Mount Edziza volcanic complex.^[18]^[22] An artifact of the Sheep Track eruption may lie north of Coffee Crater where a deep, circular depression is present on the surface of the glacier.^[23] This depression may be caused by subglacial melting brought on by fumaroles, hot springs or heightened ground temperatures adjacent to the vent.^[18]

Age

The Sheep Track Member is absent within the trim lines of Mount Edziza's alpine glaciers, indicating that it was deposited by the Sheep Track eruption during the last glacial advance starting about 2,600 years ago.^[24] However, Sheep Track pumice is present on the subglacial volcano of Tennena Cone which suggests that glaciers of the last glacial advance had already begun to retreat before deposition.^[18] Fission track dating of pumice on the southwestern flank of Ice Peak has yielded an age of 950 CE ± 6000 years.^[21]

Related Research Articles

Mount Edziza, sometimes called Edziza Mountain or Edziza Peak, is a stratovolcano in Cassiar Land District of northwestern British Columbia, Canada. It is located on the Big Raven Plateau of the Tahltan Highland which extends along the western side of the Stikine Plateau. The mountain has an elevation of 2,786 metres, making it the highest volcano of the Mount Edziza volcanic complex. However, it had an elevation of at least 3,396 metres before its original summit was likely destroyed by a violent, climactic eruption in the geologic past; its current flat summit contains an ice-filled, 2-kilometre (1.2-mile) in diameter crater. Mount Edziza contains several lava domes, cinder cones and lava fields on its flanks, as well as an ice cap that is characterized by several outlet glaciers stretching out to lower altitudes. All sides of the mountain are drained by tributaries of Mess Creek and Kakiddi Creek which are situated within the Stikine River watershed.

Tennena Cone, alternatively Icebridge Cone, is a small volcanic cone in Cassiar Land District of northwestern British Columbia, Canada. It has an elevation of 2,390 metres and lies on the western flank of Ice Peak, the prominent south peak of Mount Edziza. The cone is almost completely surrounded by glacial ice of Mount Edziza's ice cap which covers an area of around 70 square kilometres. Tennena Cone is 200 metres high, 1,200 metres long and up to 600 metres wide, its symmetrical structure resembling a black pyramid. The cone and the surrounding area are in Mount Edziza Provincial Park which also includes the Spectrum Range to the south.

The Mount Edziza volcanic complex is a group of volcanoes and associated lava flows in northwestern British Columbia, Canada. Located on the Tahltan Highland, it is 40 kilometres southeast of Telegraph Creek and 85 kilometres southwest of Dease Lake. The complex encompasses a broad, steep-sided lava plateau that extends over 1,000 square kilometres. Its highest summit is 2,786 metres in elevation, making the MEVC the highest of four large complexes in an extensive north–south trending volcanic region. It is obscured by an ice cap characterized by several outlet glaciers that stretch out to lower altitudes.

Cartoona Ridge is a mountain ridge extending east from the eastern side of the Mount Edziza volcanic complex in northwestern British Columbia, Canada. It is bounded on the north by Shaman Creek valley, on the south by Chakima Creek valley, on the east by Kakiddi Creek valley and on the west by the Big Raven Plateau. Its highest point and only named peak is Cartoona Peak at the westernmost end of the ridge with an elevation of 2,300 metres. Carttona Ridge is one of three ridges east of the Big Raven Plateau named by Canadian volcanologist Jack Souther, the other two being Idiji Ridge and Sorcery Ridge to the north.

The volcanic history of the Northern Cordilleran Volcanic Province presents a record of volcanic activity in northwestern British Columbia, central Yukon and the U.S. state of easternmost Alaska. The volcanic activity lies in the northern part of the Western Cordillera of the Pacific Northwest region of North America. Extensional cracking of the North American Plate in this part of North America has existed for millions of years. Continuation of this continental rifting has fed scores of volcanoes throughout the Northern Cordilleran Volcanic Province over at least the past 20 million years and occasionally continued into geologically recent times.

The Armadillo Formation is a stratigraphic unit of Miocene age in northwestern British Columbia, Canada.

The Nido Formation is a stratigraphic unit of Neogene age in northwestern British Columbia, Canada.

The Pyramid Formation is a stratigraphic unit of Pleistocene age in northwestern British Columbia, Canada.

The Big Raven Formation is a stratigraphic unit of Quaternary age in northwestern British Columbia, Canada. It is the youngest and least voluminous geological formation of the Mount Edziza volcanic complex (MEVC); it overlies at least six older formations of this volcanic complex. The main volcanic rocks of the Big Raven Formation are alkali basalts and hawaiites, although a small volume of trachyte comprises the Sheep Track Member. These rocks were deposited by volcanic eruptions in the last 20,000 years during the latest magmatic cycle of the MEVC. Alkali basalt and hawaiite are in the form of lava flows and small volcanic cones while trachyte of the Sheep Track Member is mainly in the form of volcanic ejecta which covers an area of about 40 square kilometres.

Kakiddi Creek is a tributary of the Klastline River in northwest part of the province of British Columbia, Canada. It flows north about 35 km (22 mi) through two lakes in a broad hummocky lowland to join the Klastline River, which in turn is a tributary of the Stikine River. Kakiddi Creek forms the northeastern boundary of Mount Edziza Provincial Park which lies within the traditional territory of the Tahltan people.

Tenchen Creek is a tributary of Kakiddi Creek, which in turn is a tributary of the Klastline River, part of the Stikine River watershed in northwest part of the province of British Columbia, Canada. It flows generally flows northeast for about 8 km (5.0 mi) to join Kakiddi Creek about 13 km (8.1 mi) south of Kakiddi Creek's confluence with the Klastline River. Tenchen is a combination of the Tahltan words "ten" and "chen", which mean "ice" and "dirty" respectively.

The Mount Edziza volcanic complex (MEVC) in British Columbia, Canada, has a long history of volcanism that spans more than 7 million years. It occurred during five cycles of magmatic activity, each having produced less volcanic material than the previous one. Volcanism during these cycles has created several types of volcanoes, including cinder cones, stratovolcanoes, subglacial volcanoes, shield volcanoes and lava domes. The approximately 1,000-square-kilometre (400-square-mile) volcanic plateau forming the base of the MEVC owes its origin to successive eruptions of highly mobile lava flows. Volcanic rocks such as basalt, trachybasalt, benmoreite, tristanite, mugearite, trachyte and rhyolite were deposited by multiple eruptions of the MEVC; the latter seven rock types are products of varying degrees of magmatic differentiation in underground magma reservoirs. At least 10 distinct flows of obsidian were produced by volcanism of the MEVC, some of which were exploited by indigenous peoples in prehistoric times to make tools and weaponry. Renewed volcanism could produce explosive eruptions and block local streams with lava flows.

Tencho Glacier is a mountain glacier in northwestern British Columbia, Canada. It is located inside Mount Edziza Provincial Park on the Tahltan Highland, an upland area of the Stikine Plateau. Tencho Glacier is the source of several small streams that flow from the Mount Edziza volcanic complex.

Tenchen Glacier is located on the eastern flank of Mount Edziza in northwestern British Columbia, Canada. It lies within an immense cirque whose headwall has breached the eastern side of Mount Edziza's summit crater. At the head of Tenchen Glacier are icefalls that drape down shear, 300-metre-high (980-foot) cliffs from the breached eastern crater rim; permanent ice fills the summit crater. Meltwater from Tenchen Glacier feeds Tenchen Creek which eventually merges with Kakiddi Creek.

Tennaya Glacier is one of several glaciers draining the eastern side of the Mount Edziza ice cap in northwestern British Columbia, Canada. It is located southeast of the summit of Mount Edziza and northwest of Ice Peak at the head of Tennaya Creek. Meltwater from Tennaya Glacier feeds Tennaya Creek which eventually flows into Nuttlude Lake, an expansion of Kakiddi Creek.

Idiji Glacier is one of several glaciers draining the eastern side of the Mount Edziza ice cap in northwestern British Columbia, Canada. It is located south of the summit of Mount Edziza in a cirque just southeast of Ice Peak. Idiji Glacier is separated from the much larger Tencho Glacier by a ridge that extends south of Ice Peak above the Idiji cirque headwall. Idiji Glacier is the namesake of Idiji Ridge which is just to the southeast.

The Edziza Formation is a stratigraphic unit of Pleistocene age in northwestern British Columbia, Canada. First described in 1984, the Edziza Formation was mapped as one of several geological formations of the Mount Edziza volcanic complex. It overlies at least four other geological formations of this volcanic complex that differ in age and composition. The main volcanic rock comprising the Edziza Formation is trachyte which was deposited by volcanic eruptions at the end of the third magmatic cycle of the Mount Edziza volcanic complex 0.9 million years ago.

Yagi Ridge is a mountain ridge extending northwest from the middle of the Spectrum Range at the southern end of the Mount Edziza volcanic complex in northwestern British Columbia, Canada. It is bounded on the north by Nagha Glacier and Nagha Creek valley, on the south by Yeda Creek on the Arctic Lake Plateau and on the west by Mess Creek valley. Yagi Ridge reaches an elevation of 2,243 metres at the head of Nagha Glacier where its eastern end adjoins to the Spectrum Range just northwest of Yeda Peak.

Sorcery Ridge is a mountain ridge extending east of Tencho Glacier on the southern flank of Mount Edziza in northwestern British Columbia, Canada. It is bounded on the north and south by valleys containing unnamed streams while to the east and northeast it is bounded by Tennaya Creek valley. Sorcery Ridge is the namesake of Sorcery Creek which flows adjacent to Tennaya Creek from another ridge just to the south.

Idiji Ridge is a mountain ridge extending east of Tencho Glacier on the southern flank of Mount Edziza in northwestern British Columbia, Canada. It is bounded on the south by a valley containing an unnamed valley, on the east by Tennaya Creek valley and on the north by cirques extending east of Ice Peak. Idiji Ridge takes its name from the adjacent Idiji Glacier; Idiji means "it thunders" in the Tahltan language.

References

1 2 3 4 "Sheep Track Member". Lexicon of Canadian Geologic Units . Government of Canada. Archived from the original on 2023-12-15. Retrieved 2024-03-10.
1 2 Souther 1992, p. 213.
1 2 3 4 Souther, J. G. (1988). "1623A" (Geologic map). Geology, Mount Edziza Volcanic Complex, British Columbia. 1:50,000. Cartography by M. Sigouin, Geological Survey of Canada. Energy, Mines and Resources Canada. doi: 10.4095/133498 .
1 2 3 4 Souther 1992, p. 236.
1 2 "Sheep Track Pumice". Catalogue of Canadian volcanoes. Natural Resources Canada. Archived from the original on 2010-12-11. Retrieved 2024-03-10.
1 2 "Sheep Track Formation". Lexicon of Canadian Geologic Units . Government of Canada. Archived from the original on 2023-12-15. Retrieved 2024-03-06.
1 2 Souther, J. G.; Armstrong, R. L.; Harakal, J. (1984). "Chronology of the peralkaline, late Cenozoic Mount Edziza Volcanic Complex, northern British Columbia, Canada". Geological Society of America Bulletin . 95 (3). Geological Society of America: 339. doi:10.1130/0016-7606(1984)95<337:COTPLC>2.0.CO;2. ISSN 0016-7606.
↑ "Fieldwork at Mount Edziza" (PDF). Ash Fall. Geological Association of Canada. 2007. p. 6. Archived from the original (PDF) on 2024-01-12.
↑ Souther, J. G.; Symons, D. T. A. (1974). Stratigraphy and paleomagnetism of Mount Edziza volcanic complex, northwestern British Columbia (Report). Paper 73-32. Geological Survey of Canada. doi: 10.4095/102538 .
↑ "Kounugu Member". Lexicon of Canadian Geologic Units . Government of Canada. Archived from the original on 2023-12-15. Retrieved 2024-03-10.
↑ Souther 1992, pp. 236, 267.
↑ Souther 1992, pp. 214, 236.
↑ Souther 1992, pp. 24, 25, 155.
↑ Souther 1992, p. 267.
↑ Souther 1992, pp. 213, 238.
↑ Souther 1992, pp. 27, 28, 228, 236.
↑ Souther 1992, pp. 28, 236.
1 2 3 4 Souther 1992, p. 237.
↑ Lakeman, Thomas R.; Clague, John J.; Menounos, Brian; Osborn, Gerald D.; Jensen, Britta J. L.; Froese, Duane G. (2008). "Holocene tephras in lake cores from northern British Columbia, Canada". Canadian Journal of Earth Sciences . 45 (8). NRC Research Press: 939, 940. Bibcode:2008CaJES..45..935L. doi:10.1139/E08-035. ISSN 1480-3313.
↑ Souther 1992, p. 27.
1 2 "Edziza: Eruptive History". Global Volcanism Program . Smithsonian Institution. Archived from the original on 2023-05-20. Retrieved 2024-03-11.
↑ "Tencho Glacier". BC Geographical Names . Archived from the original on 2024-06-07. Retrieved 2024-07-12.
↑ Souther 1992, pp. 214, 237.
↑ Souther 1992, pp. 25, 237.

Sources

Souther, J. G. (1992). The Late Cenozoic Mount Edziza Volcanic Complex, British Columbia. Geological Survey of Canada (Report). Memoir 420. Canada Communication Group. doi: 10.4095/133497 . ISBN 0-660-14407-7.