Mount Cap formation

The Mount Cap formation is a geological unit exposed in the Mackenzie Mountains, northern Canada. It was deposited in a shallow shelf setting in the late Early Cambrian,^[1] and contains an array of Burgess Shale-type microfossils that have ben recovered by acid maceration.^[2]

The formation is one to three hundred metres thick, and comprises shales, silt- and sand-stones with a high glauconite content.^[1] It has been exposed to remarkably little metamorphic activity given its great age; it is dated to the Bonnia–Olenellus Trilobite Zone.^[1] This zone lies within the Lower Cambrian Waucoban stage in North America, which is equivalent to the Caerfai in Wales, and thus the Comley of England^[3], and has yet to be formally ratified. Nevertheless, this makes it just younger than the earliest trilobites, and thus the earliest known Burgess Shale-type deposit. Its organic-walled fauna, known as the "Little Bear biota", includes both non-mineralized and originally-mineralized taxa, including hyolith and trilobite fragments, anomalocaridid claws, arthropod carapaces and brachiopods.^[4]

References

1. ^ ^{a b c} Butterfield, N. J. (1994). "Burgess Shale-type fossils from a Lower Cambrian shallow-shelf sequence in northwestern Canada". Nature 369 (6480): 477–479. Bibcode 1994Natur.369..477B. doi:10.1038/369477a0.  edit
2. ^ Harvey, T.; Butterfield, N. (2008). "Sophisticated particle-feeding in a large Early Cambrian crustacean". Nature 452 (7189): 868–871. Bibcode 2008Natur.452..868H. doi:10.1038/nature06724. PMID 18337723.  edit
3. ^ Siveter, D. J.; Williams, M. (1995). "An early Cambrian assignment for the Caerfai Group of South Wales". Journal of the Geological Society 152: 221. doi:10.1144/gsjgs.152.2.0221.  edit
4. ^ Butterfield, N. J.; Nicholas, C. J. (1996). "Burgess Shale-Type Preservation of Both Non-Mineralizing and 'Shelly' Cambrian Organisms from the Mackenzie Mountains, Northwestern Canada". Journal of Paleontology 70 (6): 893–899. JSTOR 1306492.  edit