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Soft-bodied biota from the Middle Cambrian (Drumian) Rockslide Formation, Mackenzie Mountains, northwestern Canada

Julien Kimmig and Brian R. Pratt
Soft-bodied biota from the Middle Cambrian (Drumian) Rockslide Formation, Mackenzie Mountains, northwestern Canada
Journal of Paleontology (January 2015) 89 (1): 51-71


A new Burgess Shale-type Lagerstatte is described from the middle Cambrian (Series 3, Drumian) Rockslide Formation of the Mackenzie Mountains, Northwest Territories, Canada. The Rockslide Formation is a unit of deeper water ramp to slope, mixed carbonate, and siliciclastic facies deposited on the northwestern margin of Laurentia. At the fossil-bearing locality, the unit onlaps a fault scarp cutting lower Cambrian sandstones. There it consists of a succession of shale and thick-laminated to thin-bedded lime mudstone, calcareous sandstone, and greenish-colored calcareous mudstone, overlain by shallower water dolostones of the Avalanche Formation, which is indicative of an overall progradational sequence. The Rockslide Formation is of similar age to the Wheeler and Marjum formations of Utah, belonging to the Bolaspidella Biozone. Only two 1 m thick units of greenish mudstone exhibit soft-bodied preservation, with most specimens coming from the lower interval. However, the biota is common but not as diverse as that of other Lagerstatten such as the Burgess Shale in its type area. The shelly fauna is dominated by the hyolith Haplophrentis carinatus Matthew, 1899 along with sparse linguliformean brachiopods, agnostoid arthropods, and ptychoparioid trilobites. The nonmineralized biota includes the macrophytic alga Margaretia dorus Walcott, 1911, priapulid worms, and the carapaces of a number of arthropods. The arthropods belong to Isoxys mackenziensis n. sp., Tuzoia cf. T. guntheri Robison and Richards, 1981; Branchiocaris? sp., Perspicaris? dilatus Robison and Richards, 1981; and bradoriids, along with fragments of arthropods of indeterminate affinities. The style of preservation indicates that most soft parts underwent complete biodegradation, leaving just the more resistant materials such as chitinous arthropod cuticles. The range of preservation and similarity to the coeval biotas preserved in Utah suggests that the composition of this Lagerstatte is probably representative of the community living on the relatively deep-water ramp or slope during middle Cambrian time in Laurentia. This would argue that the extraordinary diversity of the Burgess Shale at Mount Field is anomalous.

ISSN: 0022-3360
EISSN: 1937-2337
Serial Title: Journal of Paleontology
Serial Volume: 89
Serial Issue: 1
Title: Soft-bodied biota from the Middle Cambrian (Drumian) Rockslide Formation, Mackenzie Mountains, northwestern Canada
Affiliation: University of Saskatchewan, Department of Geological Sciences, Saskatoon, SK, Canada
Pages: 51-71
Published: 201501
Text Language: English
Publisher: Paleontological Society, Lawrence, KS, United States
References: 107
Accession Number: 2016-003446
Categories: Invertebrate paleontology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. sect., strat. col., 1 table, sketch map
N63°10'00" - N63°10'00", W127°55'00" - W127°55'00"
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Abstract, Copyright, The Paleontological Society. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 201602
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