The Husky Formation is a fossiliferous stratigraphic

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 ...

located in the Aklavik Range, in the District of Mackenzie,

Yukon Yukon () is a Provinces and territories of Canada, territory of Canada, bordering British Columbia to the south, the Northwest Territories to the east, the Beaufort Sea to the north, and the U.S. state of Alaska to the west. It is Canada’s we ...

. Regional Geology The Husky formation is a part of a larger,

Jurassic The Jurassic ( ) is a Geological period, geologic period and System (stratigraphy), stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately 143.1 Mya. ...

aged sedimentary package that spans from Northern Yukon to the Northwest Territories. This package is a regional wedge concentrated in the

Richardson Mountains The Richardson Mountains are a mountain range located west of the mouth of the Mackenzie River in northern Yukon, Canada. They parallel the northernmost part of the boundary between Yukon and Northwest Territories. Although some sources consider ...

, that sits atop

North American Cordillera The North American Cordillera, sometimes also called the Western Cordillera of North America, the Western Cordillera, or the Pacific Cordillera, is the North American portion of the American Cordillera, the mountain chain system along the Pacifi ...

basement rocks. The wedge demonstrates classic basin-ward thickening. Associated with this thickening is a stratigraphic range from coarser, lower to middle-Jurassic sedimentary units to upper-Jurassic

shale Shale is a fine-grained, clastic sedimentary rock formed from mud that is a mix of flakes of Clay mineral, clay minerals (hydrous aluminium phyllosilicates, e.g., Kaolinite, kaolin, aluminium, Al2Silicon, Si2Oxygen, O5(hydroxide, OH)4) and tiny f ...

, which marks the Husky formation. The Husky formation is one of the two shale units in the Aklavik range, and is characterized by its fossil assemblages. The “Husky shale” lies immediately above the bivalve rich, heavily bioturbated Aklavik sandstone. The “Husky shale” is one of the youngest units (second youngest to the Porcupine River formation) in this wedge-succession and marks an

unconformity An unconformity is a buried erosional or non-depositional surface separating two rock masses or strata of different ages, indicating that sediment deposition was not continuous. In general, the older layer was exposed to erosion for an interval ...

with the Aklavic sandstone units below. Fossils in The Husky Formation The Husky succession preserves fossils dating back to the Upper Jurassic (Oxfordian-Volgian) period including

foraminifera Foraminifera ( ; Latin for "hole bearers"; informally called "forams") are unicellular organism, single-celled organisms, members of a phylum or class (biology), class of Rhizarian protists characterized by streaming granular Ectoplasm (cell bio ...

bivalves Bivalvia () or bivalves, in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class of aquatic molluscs (marine and freshwater) that have laterally compressed soft bodies enclosed by a calcified exoskeleton consis ...

ostracod Ostracods, or ostracodes, are a Class (biology), class of the crustacean, Crustacea (class Ostracoda), sometimes known as seed shrimp. Some 33,000 species (only 13,000 of which are extant taxon, extant) have been identified,Brandão, S.N.; Antoni ...

s and

ammonite Ammonoids are extinct, (typically) coiled-shelled cephalopods comprising the subclass Ammonoidea. They are more closely related to living octopuses, squid, and cuttlefish (which comprise the clade Coleoidea) than they are to nautiluses (family N ...

s. provide environmental proxies related to paleoclimatic reconstructions during the deposition of The Husky Formation. Placement of stratigraphic markers between Upper and Middle Jurassic sections along The Husky Succession have been debated.

Biostratigraphic Biostratigraphy is the branch of stratigraphy which focuses on correlating and assigning relative ages of rock strata by using the fossil assemblages contained within them.Hine, Robert. "Biostratigraphy." ''Oxford Reference: Dictionary of Biology ...

analysis of foraminifers as

index fossils Biostratigraphy is the branch of stratigraphy which focuses on correlating and assigning relative ages of rock strata by using the fossil assemblages contained within them.Hine, Robert. "Biostratigraphy." ''Oxford Reference: Dictionary of Biology ...

and

lithostratigraphic Lithostratigraphy is a sub-discipline of stratigraphy, the geological science associated with the study of strata or rock layers. Major focuses include geochronology, comparative geology, and petrology. In general, strata are primarily igneous ...

analysis of sedimentary layers indicated suitable placement of a GGSP between The Porcupine River Formation and the Aklavik Formation in the upper Oxfordian Jurassic period. Foraminifera are

protist A protist ( ) or protoctist is any eukaryotic organism that is not an animal, land plant, or fungus. Protists do not form a natural group, or clade, but are a paraphyletic grouping of all descendants of the last eukaryotic common ancest ...

s classified as a sub-phylum of Domain Eukarya and have been preserved in The Husky Formation. Foraminifera are free-living

heterotroph A heterotroph (; ) is an organism that cannot produce its own food, instead taking nutrition from other sources of organic carbon, mainly plant or animal matter. In the food chain, heterotrophs are primary, secondary and tertiary consumers, but ...

ic marine organisms suggesting the Aklavik Range was a marine environment during the Jurassic. Bivalves including clams, scallops and mussels were discovered in The Husky Formation. Bivalves are a sub-category of Class Bivalvia and Phylum Mollusca. Marine, freshwater and terrestrial specimens are common. Characteristics of Mollusca include

bilateral symmetry Symmetry in biology refers to the symmetry observed in organisms, including plants, animals, fungi, and bacteria. External symmetry can be easily seen by just looking at an organism. For example, the face of a human being has a plane of symme ...

, non-segmented

cephalization Cephalization is an evolutionary trend in animals that, over a sufficient number of generations, concentrates the special sense organ (biology), organs and nerve ganglia towards the front of the body where the mouth is located, often producing a ...

, complete digestive tract, triploblastic and a reduced coelom. Distinguishing characteristics of Class Bivalvia include a greatly reduced head, laterally compressed foot and a laterally compressed body and shell forcing the mantle to overhang the body. These defining characteristics represent adaptions for burrowing in a soft substrate, which explains the presence of bivalves in soft sediment along the Husky Formation. Not all modern day bivalves are soft bottom dwellers, as much diversity has occurred within the class due to adaptions necessary for survival suggesting depositional environment has changed in the Northern Yukon since the Jurassic. Ammonites are also a part of Phylum Mollusca as Class Cephalopoda, Order Nautilida. Ammonites have well-developed shells that have been preserved as fossils that provide further evidence of a marine environment during deposition of The Husky Formation. A marine environment was essential for cephalopods as their characteristics represented adaptations for a swimming, predatory mode of existence. Contraction of the mantle pushes out water from the

mantle cavity The mantle (also known by the Latin word pallium meaning mantle, robe or cloak, adjective pallial) is a significant part of the anatomy of molluscs: it is the dorsal body wall which covers the visceral mass and usually protrudes in the form of ...

causing propulsion for swimming. Ostracods are a part of Phylum Arthropoda as Class Crustacea. Ostracods are limited to damp environments due to gas exchange using gills, but primarily inhabit aquatic environments which is further evidence supporting a marine environment during the Jurassic in Northern Yukon.

References

{{reflist • Israel, S., Colpron, M., Roots, C., Fraser, T. 2015. “Overview of Yukon Geology”. Yukon Geological Survey. • Poulton, T.P., 1991. “Hettangian through Aalenian (Jurassic) guide fossils and biostratigraphy, northern Yukon and adjacent Northwest Territories”. Geological Survey of Canada, bulletin 410. • Poulton, T.P. 1982. “Paleogeographic and tectonic implications of lower and middle Jurassic facies patterns in northern Yukon Territory and adjacent Northwest Territories”. Canadian Society of Petroleum Geologists, Memoir 8, pg 13-27. • Various Contributors to the Paleobiology Database. "Fossilworks: Gateway to the Paleobiology Database". Archived from the original on 31 July 2014. Retrieved 8 July 2014. Jurassic Yukon

See also

References