The Little Iskut Formation is a

stratigraphic unit A stratigraphic unit is a volume of rock of identifiable origin and relative age range that is defined by the distinctive and dominant, easily mapped and recognizable petrographic, lithologic or paleontologic features ( facies) that characteriz ...

Miocene The Miocene ( ) is the first epoch (geology), geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and mea ...

age in northwestern

British Columbia British Columbia is the westernmost Provinces and territories of Canada, province of Canada. Situated in the Pacific Northwest between the Pacific Ocean and the Rocky Mountains, the province has a diverse geography, with rugged landscapes that ...

, Canada.

Naming

The Little Iskut Formation takes its name from the Little Iskut River, a

tributary A tributary, or an ''affluent'', is a stream or river that flows into a larger stream (''main stem'' or ''"parent"''), river, or a lake. A tributary does not flow directly into a sea or ocean. Tributaries, and the main stem river into which they ...

of the

Iskut River The Iskut River, located in the northwest part of the Provinces and territories of Canada, province of British Columbia, is the largest tributary of the Stikine River, entering it about above its entry into Alaska. From its source at Kluachon Lak ...

which flows southeast from the southern end of the

Mount Edziza volcanic complex The Mount Edziza volcanic complex ( ; abbreviated MEVC) is a group of volcanoes and associated lava flows in northwestern British Columbia, Canada. Located on the Tahltan Highland, it is southeast of Telegraph Creek and southwest of Dease Lak ...

Geology

The Little Iskut Formation has a volume of , making it the seventh most voluminous

geological formation A geological formation, or simply formation, is a body of rock having a consistent set of physical characteristics (lithology) that distinguishes it from adjacent bodies of rock, and which occupies a particular position in the layers of rock expo ...

comprising the Mount Edziza volcanic complex. It occurs at the northeastern end of the

Spectrum Range The Spectrum Range, formerly gazetted as the Spectrum Mountains and the Rainbow Mountains, is a small mountain range in Cassiar Land District of northwestern British Columbia, Canada. Located at the southern end of the Tahltan Highland, it bord ...

where it covers a roughly area. A small portion of the Little Iskut Formation is exposed in the Mess Creek Escarpment to the west. The Little Iskut Formation consists of

trachybasalt Trachybasalt is a volcanic rock with a composition between trachyte and basalt. It resembles basalt but has a high content of alkali metal oxides. Minerals in trachybasalt include alkali feldspar, calcic plagioclase, olivine, clinopyroxene and l ...

flows and

breccia Breccia ( , ; ) is a rock composed of large angular broken fragments of minerals or Rock (geology), rocks cementation (geology), cemented together by a fine-grained matrix (geology), matrix. The word has its origins in the Italian language ...

. It ranges in thickness from on Stewpot Ridge to about near the middle of Artifact Ridge. The Little Iskut Formation originally formed a small symmetrical

shield volcano A shield volcano is a type of volcano named for its low profile, resembling a shield lying on the ground. It is formed by the eruption of highly fluid (low viscosity) lava, which travels farther and forms thinner flows than the more viscous lava ...

during the Miocene. The Little Iskut Formation conformably overlies the Raspberry Formation south of Bourgeaux Creek. Little Iskut trachybasalt is overlain by

rhyolite Rhyolite ( ) is the most silica-rich of volcanic rocks. It is generally glassy or fine-grained (aphanitic) in texture (geology), texture, but may be porphyritic, containing larger mineral crystals (phenocrysts) in an otherwise fine-grained matri ...

of the Armadillo Formation and

basalt Basalt (; ) is an aphanite, aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the planetary surface, surface of a terrestrial ...

of the Nido Formation. Two subunits comprise the Little Iskut Formation; the upper unit consists entirely of trachybasalt lava flows while the lower unit consists of abundant breccia.

K–Ar dating Potassium–argon dating, abbreviated K–Ar dating, is a radiometric dating method used in geochronology and archaeology. It is based on the measurement of the product of the radioactive decay of an isotope of potassium (K) into argon (Ar). Potas ...

has yielded an age of 7.2 ± 0.3 million years for Little Iskut trachybasalt.

References

{{Mount Edziza volcanic complex Geologic formations of the Mount Edziza volcanic complex Miocene Canada Miocene shield volcanoes Shield volcanoes of Canada

Naming

Geology

See also

References