The Little Iskut Formation is a stratigraphic unit of

Miocene The Miocene ( ) is the first 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 means "less recen ...

age in northwestern

British Columbia British Columbia (commonly abbreviated as BC) is the westernmost province of Canada, situated between the Pacific Ocean and the Rocky Mountains. It has a diverse geography, with rugged landscapes that include rocky coastlines, sandy beaches, ...

, Canada.

Naming

The Little Iskut Formation takes its name from the

Little Iskut River The Little Iskut River is a tributary of the Iskut River in the northwest part of the Provinces and territories of Canada, province of British Columbia, Canada, in Cassiar Land District. From its source at Little Ball Lake in Mount Edziza Provincia ...

, a

tributary A tributary, or affluent, is a stream or river that flows into a larger stream or 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 drain the surrounding drainage ...

of the Iskut River which flows southeast from the southern end of the Mount Edziza volcanic complex.

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 exp ...

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

Spectrum Range The Spectrum Range, formerly called the Spectrum Mountains and the Rainbow Mountains, is a subrange of the Tahltan Highland in the Stikine Country of northwestern British Columbia, 20 km west of the Stewart-Cassiar Highway, south of Mount ...

where it covers a roughly wide area. A small portion of the Little Iskut Formation is exposed in the

Mess Creek Escarpment The Mess Creek Escarpment is an escarpment in northwestern British Columbia, Canada, located on the east side of Mess Creek below Mess Lake and southeast of Telegraph Creek. It forms the central-western flank of the Mount Edziza volcanic complex, ex ...

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 li ...

flows and

breccia Breccia () is a rock composed of large angular broken fragments of minerals or rocks cemented together by a fine-grained matrix. The word has its origins in the Italian language, in which it means "rubble". A breccia may have a variety of di ...

. 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 warrior's 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 v ...

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, but may be porphyritic, containing larger mineral crystals (phenocrysts) in an otherwise fine-grained groundmass. The mineral ...

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

References

{{Northern Cordilleran volcanoes Geologic formations of British Columbia Mount Edziza volcanic complex Miocene Canada Miocene shield volcanoes Shield volcanoes of Canada

Naming

Geology

See also

References