The Phyllopod bed, designated by
USNM locality number 35k,
[ is the most famous fossil-bearing member of the ]Burgess Shale
The Burgess Shale is a fossil-bearing deposit exposed in the Canadian Rockies of British Columbia, Canada. It is famous for the exceptional preservation of the soft parts of its fossils. At old (middle Cambrian), it is one of the earliest foss ...
fossil ''Lagerstätte
A Lagerstätte (, from ''Lager'' 'storage, lair' '' Stätte'' 'place'; plural ''Lagerstätten'') is a sedimentary deposit that exhibits extraordinary fossils with exceptional preservation—sometimes including preserved soft tissues. These for ...
''. It was quarried by Charles Walcott from 1911–1917 (and later named Walcott Quarry
The Walcott Quarry is the most famous quarry of the Middle Cambrian Burgess Shale, located in the Canadian Rockies of British Columbia, bearing the Phyllopod bed
The Phyllopod bed, designated by USNM locality number 35k, is the most famous foss ...
), and was the source of 95% of the fossils he collected during this time;
tens of thousands of soft-bodied fossils representing over 150 genera have been recovered from the Phyllopod bed alone.
Stratigraphy and location
The phyllopod bed is a 2.31 m thick layer of the 7 m thick Greater Phyllopod Bed,[ found in the Walcott Quarry on Fossil Ridge, between Wapta Mountain and Mount Field, at an elevation of around , around north of the ]railway town
A railway town, or railroad town, is a settlement that originated or was greatly developed because of a railway station or junction at its site.
North America
During the construction of the First transcontinental railroad in the 1860s, temporar ...
of Field, British Columbia
Field is an unincorporated community of approximately 169 people located in the Kicking Horse River valley of southeastern British Columbia,
Canada, within the confines of Yoho National Park. At an elevation of , it is west of Lake Louise along ...
, in the Canadian Rocky Mountains. It is adjacent to Mount Burgess
Mount Burgess, , is a mountain in Yoho National Park and is part of the Canadian Rockies. It is located in the southwest buttress of Burgess Pass in the Emerald River and Kicking Horse River Valleys.
History
It was named in 1886 by astronomer ...
, where Walcott first discovered the Burgess Shale formation.
Walcott divided the bed into twelve units based on the rock type and fossil content. Certain fossil beds provide reference levels and can be recognized by the superabundance of a particular type of fossil: for instance, the ''Great Marrella
''Marrella'' is an extinct genus of marrellomorph arthropod known from the middle Cambrian Burgess Shale of British Columbia. It is the most common animal represented in the Burgess Shale, with tens of thousands of specimens collected. Much rar ...
layer'' and ''Great Eldonia layer''.
History
After locating soft-bodied fossils in loose fragments of rock in 1907, the Phyllopod bed was located in a source for the fragments' origins by the Walcotts in 1910. Extensive quarrying was performed in field seasons until 1913, and Walcott considered the ton of shale he collected in his next visit, in 1917, to have practically exhausted the productive potential of the bed.[
]
Taphonomy
Most of the organisms within the Phyllopod bed had been transported minimal distances before they were buried, and decayed in place until they were buried (at which time decay and disarticulation was halted).[ Mineralization of tissues occurred shortly afterwards.][ The community of organisms preserved is a good representation of the (preservable) community; the biasing effects of time-averaging and preferential decay seem to be minimal.][ A great deal of compaction occurred after the deposition of the fossils.][
]
Sedimentation
The unit consists of mudstones that intergrade into coarser shelly sandstones that sometimes form small nodules.[ There are (very rare) turbidite layers, but on the whole the unit was deposited in large events that dumped tens of centimetres of sediment at a time as a slurry of mud was washed over the site by a density current, sweeping up and entombing any organisms in its path.]
Preservation
The preservation of the fossils – and their pre-burial livelihoods – was likely facilitated by mats of the cyanobacterium
Cyanobacteria (), also known as Cyanophyta, are a phylum of gram-negative bacteria that obtain energy via photosynthesis. The name ''cyanobacteria'' refers to their color (), which similarly forms the basis of cyanobacteria's common name, blue ...
'' Morania'', which served to bind the sediment and allow anoxic conditions to quickly form.[
]
Community structure
The phyllopod bed preserves a range of organisms from both a rich benthic community (organisms living on and in the sediment) and representatives of the nekton
Nekton or necton (from the ) refers to the actively swimming aquatic organisms in a body of water. The term was proposed by German biologist Ernst Haeckel to differentiate between the active swimmers in a body of water, and the passive organisms t ...
. Many feeding modes are present and a complex food web can be inferred.[
Whilst some shelly fossils are present (and seem to be typical of any Cambrian shelly fossil assemblage), the majority of fossils – probably 98% of what was alive at the time of burial – do not derive from biomineralized components.][
]
Ichnofauna
Whilst trace fossils
A trace fossil, also known as an ichnofossil (; from el, ἴχνος ''ikhnos'' "trace, track"), is a fossil record of biological activity but not the preserved remains of the plant or animal itself. Trace fossils contrast with body fossils, ...
or ichnofauna are locally abundant in other areas of the Burgess Shale, they are almost completely absent in the Phyllopod bed, perhaps as a result of the presence of ''Morania''.
References
{{DEFAULTSORT:Phyllopod Bed
Burgess Shale