Phyllopod bed
Encyclopedia
The Phyllopod bed, designated by USNM locality number 35k, is the most famous fossil-bearing member of the Burgess shale
fossil lagerstatte
. It was quarried by Charles Walcott from 1911–1917, 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.
, at an elevation of around 2300 metres (7,545.9 ft), around 5 kilometres (3.1 mi) north of the railway town of Field.
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 layer and Great Eldonia
layer.
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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.
, which served to bind the sediment and allow anoxic conditions to quickly form.
. 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 have biomineralized components.
Burgess Shale
The Burgess Shale Formation, located in the Canadian Rockies of British Columbia, is one of the world's most celebrated fossil fields, and the best of its kind. It is famous for the exceptional preservation of the soft parts of its fossils...
fossil lagerstatte
Lagerstätte
A Lagerstätte is a sedimentary deposit that exhibits extraordinary fossil richness or completeness.Palaeontologists distinguish two kinds....
. It was quarried by Charles Walcott from 1911–1917, 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 Mount Wapta and Mount FieldMount Field (British Columbia)
Mount Field is a mountain located about east of the town of Field in Yoho National Park, Canada. The mountain was named in 1883 after Cyrus West Field, a guest of the CPR who were building the national railway....
, at an elevation of around 2300 metres (7,545.9 ft), around 5 kilometres (3.1 mi) north of the railway town of Field.
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 layer and Great Eldonia
Eldonia
Eldonia is a soft-bodied animal of unknown affinity, best known from the Fossil Ridge outcrops of the Burgess Shale, particularly in the 'Great Eldonia layer' in the Walcott Quarry...
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) turbitite 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 MoraniaMorania
Morania is a genus of cyanobacterium preserved as carbonaceous films in the Middle Cambrian Burgess Shale. it is present throughout the shale; 2580 specimens of Morania are known from the Greater Phyllopod bed, where they comprise 4.90% of the community. It is filamentous, forms sheets, and...
, 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 nektonNekton
Nekton refers to the aggregate of actively swimming aquatic organisms in a body of water able to move independently of water currents....
. 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 have biomineralized components.