Watrous Formation

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Watrous Formation
Stratigraphic range: Triassic to Jurassic
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Type Geological formation
Sub-units Upper Watrous
Lower Watrous
Thickness up to 110 metres (360 ft) [1]
Lithology
Primary Shale, anhydrite
Location
Coordinates 51°16′57″N105°52′48″W / 51.2826°N 105.8801°W / 51.2826; -105.8801 (Watrous Formation) Coordinates: 51°16′57″N105°52′48″W / 51.2826°N 105.8801°W / 51.2826; -105.8801 (Watrous Formation)
Region WCSB
CountryFlag of Canada.svg  Canada
Type section
Named for Watrous, Saskatchewan
Named by R.L. Milner and G E. Thomas, 1954

The Watrous Formation is a stratigraphical unit of Triassic to Jurassic age in the Western Canadian Sedimentary Basin.

Stratigraphy The study of rock layers and their formation

Stratigraphy is a branch of geology concerned with the study of rock layers (strata) and layering (stratification). It is primarily used in the study of sedimentary and layered volcanic rocks. Stratigraphy has two related subfields: lithostratigraphy and biostratigraphy.

The Triassic is a geologic period and system which spans 50.6 million years from the end of the Permian Period 251.9 million years ago (Mya), to the beginning of the Jurassic Period 201.3 Mya. The Triassic is the first and shortest period of the Mesozoic Era. Both the start and end of the period are marked by major extinction events.

The Jurassic period was a geologic period and system that spanned 56 million years from the end of the Triassic Period 201.3 million years ago (Mya) to the beginning of the Cretaceous Period 145 Mya. The Jurassic constitutes the middle period of the Mesozoic Era, also known as the Age of Reptiles. The start of the period was marked by the major Triassic–Jurassic extinction event. Two other extinction events occurred during the period: the Pliensbachian-Toarcian extinction in the Early Jurassic, and the Tithonian event at the end; however, neither event ranks among the "Big Five" mass extinctions.

Contents

It takes the name from the town of Watrous, and was first described in well Tidewater Davidson Crown No. 1, located south-west from the settlement, by R.L. Milner and G E. Thomas in 1954. [2]

Watrous, Saskatchewan Town in Saskatchewan, Canada

Watrous is a small town in Saskatchewan, Canada. It is 106.9 km east of Saskatoon and has an economy is based on agriculture and tourism because of its proximity to Manitou Beach, home of the Mineral Spa and Danceland dance hall. Watrous was named after Frank Watrous Morse. The town has many restaurants, a hospital, medical clinic, two schools, community college, bowling alley, RCMP detachment, banks, grocery stores, co-operatives, tea store and motels.

Lithology

Subdivisions

The Watrous Formation is divided into a lower and an upper member. The Lower Watrous is composed of red shale and mudstones with laminated anhydrite interbeds and sandstone and conglomerate in the base. The Upper Watrous is composed of massive anhydrite and only occurs at the rims of the depositional pool. [1]

Shale A fine-grained, clastic sedimentary rock

Shale is a fine-grained, clastic sedimentary rock composed of mud that is a mix of flakes of clay minerals and tiny fragments of other minerals, especially quartz and calcite. Shale is characterized by breaks along thin laminae or parallel layering or bedding less than one centimeter in thickness, called fissility. It is the most common sedimentary rock.

Anhydrite mineral, anhydrous calcium sulfate

Anhydrite, or anhydrous calcium sulfate, is a mineral with the chemical formula CaSO4. It is in the orthorhombic crystal system, with three directions of perfect cleavage parallel to the three planes of symmetry. It is not isomorphous with the orthorhombic barium (baryte) and strontium (celestine) sulfates, as might be expected from the chemical formulas. Distinctly developed crystals are somewhat rare, the mineral usually presenting the form of cleavage masses. The Mohs hardness is 3.5, and the specific gravity is 2.9. The color is white, sometimes greyish, bluish, or purple. On the best developed of the three cleavages, the lustre is pearly; on other surfaces it is glassy. When exposed to water, anhydrite readily transforms to the more commonly occurring gypsum, (CaSO4·2H2O) by the absorption of water. This transformation is reversible, with gypsum or calcium sulfate hemihydrate forming anhydrite by heating to around 200 °C (400 °F) under normal atmospheric conditions. Anhydrite is commonly associated with calcite, halite, and sulfides such as galena, chalcopyrite, molybdenite, and pyrite in vein deposits.

Sandstone A clastic sedimentary rock composed mostly of sand-sized particles

Sandstone is a clastic sedimentary rock composed mainly of sand-sized mineral particles or rock fragments.

Distribution

The Watrous Formation occurs in southern Saskatchewan to the border with Manitoba and stretches south into North Dakota. It reaches a maximum thickness of 110 metres (360 ft) on the North Dakota border, and thins out to zero at the margins of the depositional pool. [1]

Saskatchewan Province of Canada

Saskatchewan is a prairie and boreal province in western Canada, the only province without a natural border. It has an area of 651,900 square kilometres (251,700 sq mi), nearly 10 percent of which is fresh water, composed mostly of rivers, reservoirs, and the province's 100,000 lakes.

Manitoba Province of Canada

Manitoba is a province at the longitudinal centre of Canada. It is often considered one of the three prairie provinces and is Canada's fifth-most populous province with its estimated 1.3 million people. Manitoba covers 649,950 square kilometres (250,900 sq mi) with a widely varied landscape, stretching from the northern oceanic coastline to the southern border with the United States. The province is bordered by the provinces of Ontario to the east and Saskatchewan to the west, the territories of Nunavut to the north, and Northwest Territories to the northwest, and the U.S. states of North Dakota and Minnesota to the south.

North Dakota State of the United States of America

North Dakota is a U.S. state in the midwestern and northern regions of the United States. It is the nineteenth largest in area, the fourth smallest by population, and the fourth most sparsely populated of the 50 states. North Dakota was admitted to the Union on November 3, 1889, along with its neighboring state, South Dakota. Its capital is Bismarck, and its largest city is Fargo.

Relationship to other units

The Watrous Formation fills in the Paleozoic erosional surface, resting disconformably on older strata. It is equivalent to Amaranth Formation in Manitoba and represents a northern extension of the Spearfish Formation in North Dakota. The Upper Watrous can be correlated with the Nesson Formation.

The PaleozoicEra is the earliest of three geologic eras of the Phanerozoic Eon. It is the longest of the Phanerozoic eras, lasting from 541 to 251.902 million years ago, and is subdivided into six geologic periods : the Cambrian, Ordovician, Silurian, Devonian, Carboniferous, and Permian. The Paleozoic comes after the Neoproterozoic Era of the Proterozoic Eon and is followed by the Mesozoic Era.

Unconformity distorted sediment deposition

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 of time before deposition of the younger, but the term is used to describe any break in the sedimentary geologic record. The significance of angular unconformity was shown by James Hutton, who found examples of Hutton's Unconformity at Jedburgh in 1787 and at Siccar Point in 1788.

Spearfish Formation

The Spearfish Formation is a geologic formation, originally described from the Black Hills region of South Dakota, United States, but also recognised in North Dakota, Wyoming, Montana and Nebraska. It is a heterogeneous red bed formation, commonly with siltstone and gypsum low in the formation and sandstone and shale higher up. Other rock types include claystone, conglomerate, dolomite, and oil shale. It is typically regarded as Permian–Triassic in age, although its original description included Jurassic rocks.

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References

  1. 1 2 3 Lexicon of Canadian Geologic Units. "Watrous Formation" . Retrieved 2010-02-01.
  2. Milner, R.L. and Thomas, G E., 1954. Jurassic System in Saskatchewan. In: Western Canada Sedimentary Basin. American Association of Petroleum Geologists, p. 250-267