Unit Name: Ostracod Beds
Unit Type: Lithostratigraphic
Rank: Member
Status: Formal
Usage: Currently in use
Age Interval: Early Cretaceous (145.5 - 99.6 ma)
Age Justification: The sediments are richly fossiliferous, particularly in the Ostracod Limestone (Unit B). Fossils include Ostracods, charophytes, gastropods, pelecypods and fish teeth. The ostracods Bisulcocypris (Metacypris) albertensis (Pinto and Sanguenette) and Candona sterlingensis (Loranger), charophyta: Stellatochara mundular (Peck) and Charaxis sp. A and B, and gastropods: Viviparus murrainensis (Russell) and Zaptychius off. (Walcott) and Rubeyella carbonarius (Yen) are typical of the unit.
Province/Territory: Alberta
Originator: Farshori, 1983.
Type Locality:
Southern Alberta. Loranger described a type section in the Imperial Leduc No. 1 well (5-22-50-26W4M) between about 1,284 and 1,291.7 m (4,210 and 4,235 ft).
Distribution:
The Ostracod Beds range in thickness from zero to 40 m (131 ft) and thin over Mississippian highs. The Ostracod Beds are widely distributed throughout south-central Alberta.
Lithology:
The Ostracod Beds are divided into four distinct lithostratigraphic units which are, in ascending order: Unit A: Light grey, carbonaceous and bentonitic shale interbedded with light grey, creamy, fossiliferous limestone. Unit B: Light grey to buff argillaceous, fossiliferous (ostracods) limestone. This unit may be used as a regional marker. Unit C: Dark grey to black shales interbedded with light grey siltstones and sandstones which coarsen upwards The thin-bedded Unit C is finely laminated, lightly bioturbated and contains flaser beds, lenticular bedding and syneresis cracks Unit D: Light grey, fine- to medium-grained, well sorted, feldspathic, calcareous, kaolinitic, cherty litharenite.
Relationship:
The Ostracod Beds are Albian in age (McLean and Wall, 1981). They are thin or absent over paleotopographic highs on the pre-Cretaceous surface in southeastern Alberta. The upper contact with the upper Mannville Sediments is disconformable and the lower contact with the underlying Sunburst Sandstone Member is unconformable. The Ostracod Beds of the southern Alberta Plains have many lithological and palaeontological similarities to the Calcareous Member of the foothills in central and southern Alberta (Glaister, 1959). The Calcareous Member of the Kootenai Formation in Montana can be correlated with the Ostracod Beds of the southern Alberta Plains.
History:
The Ostracod Limestone of the Mannville Group in southern Alberta, generally referred to as the Ostracod Zone (Loranger, 1951) and Calcareous Member (Glaister, 1959), includes the Bantry Shale and overlying fossiliferous limestone. Farshori (1983) re-defined the Calcareous Member of Glaister, renaming it the Ostracod Beds, and subdivided it into four members (A, B, C, and D units). A and B units include the Bantry Shale, the Ostracod Limestone of the Ostracod Zone and Calcareous Member, which forms a regional marker. Unit C is composed of interbedded siltstones and shales and is conformably overlain by unit D.
Other Citations:
Farshori, 1983; Finger, 1983; Glaister, 1959; Hunt 1950; Loranger, 1951; McLean and Wall, 1981.
Source: CSPG Lexicon of Canadian Stratigraphy, Volume 4, western Canada, including eastern British Columbia, Alberta, Saskatchewan and southern Manitoba; D.J. Glass (editor)
Contributor: Z. Farshori
Entry Reviewed: Yes
Name Set: Lithostratigraphic Lexicon
LastChange: 28 May 2008