Middle Cambrian stromatolites high in the Canadian Rockies

August 9th, 2009

FIELD, BRITISH COLUMBIA, CANADA–Our study group was fortunate to meet Whitey Hagadorn (Amherst College and Denver Museum of Natural History) and Sally Walker (University of Georgia) for a hike to an exposure of stromatolites in the Pika Formation (Middle Cambrian) near Lake Helen and Lake Katherine in Banff National Park. A stromatolite is a finely-laminated sedimentary rock produced by mats of cyanobacteria in a shallow sea collecting and trapping thin layers of sediment. They are relatively common features in Precambrian sediments (the oldest of fossils, in fact) and become significantly more rare in younger rocks (although they are still around today). These Cambrian stromatolites are interesting because of what they can tell us about Cambrian marine conditions, including tidal dynamics, bioturbation, and grazing herbivore pressures.

stromatoliteoutcrop080809

Stromatolites exposed as domal structures in this eroding outcrop of the Pika Formation (Middle Cambrian) above Helen Lake in Banff National Park.

A natural cross-section of the Pika Formation stromatolites showing their laminated nature and sediment which has accumulated around their heads.

A natural cross-section of the Pika Formation stromatolites showing their laminated nature and sediment which has accumulated around their heads.

A hardground (light unit) exposed in cross-section in the sediment between stromatolite heads.  This is a layer of carbonate sediment which was cemented on the seafloor and then eroded by currents.  The dark sediment was deposited later on top of the scoured surface.  The hardground layer had been previously burrowed when still soft.

A hardground (light unit) exposed in cross-section in the sediment between stromatolite heads. This is a layer of carbonate sediment which was cemented on the seafloor and then eroded by currents. The dark sediment was deposited later on top of the scoured surface. The hardground layer had been previously burrowed when still soft.

Beautiful folds in the rocks above the Pika Formation stromatolites.  They are nearly recumbent in some parts.  I'll leave their interpretation to my structural geologist colleagues Sam Root and Shelley Judge!

Beautiful folds in the rocks above the Pika Formation stromatolites. They are nearly recumbent in some parts. I'll leave their interpretation to my structural geology colleagues Sam Root and Shelley Judge!

A marmot on the banks of Helen Lake.  Not at all camera shy, this little guy.

A marmot on the banks of Helen Lake. Not at all camera shy, this little guy.

Mt. Stephen Trilobite Beds (Middle Cambrian)

August 8th, 2009

FIELD, BRITISH COLUMBIA, CANADA–After a very steep and long climb, our little field party visited another restricted quarry of famous Middle Cambrian fossils: the Mt. Stephens Trilobite Beds. Charles Walcott also collected from this site when he was working on the Burgess Shale. The fossiliferous unit is about a million years old (more or less) than the Burgess Shale itself, and it has a rather different fauna dominated by large trilobites. One of the most exciting new ideas is that these fossils may represent an ancient cold seep community associated with methane degassing from the sediments.

Our Canadian guide (and paleontologist) Paul McNeil and our trip leader Matthew James in the Mt. Stephen Trilobite Beds Quarry.

Our Canadian guide (and paleontologist) Paul McNeil and our trip leader Matthew James in the Mt. Stephen Trilobite Beds Quarry.

A view from the Mt. Stephen Trilobite Beds down the mountain to Field and the Trans-Canada Highway. Note the steepness.  Nearly did me in!

A view from the Mt. Stephen Trilobite Beds down the mountain to Field and the Trans-Canada Highway. Note the steepness. Nearly did me in!

Trilobites in the Mt. Stephen Trilobite Beds. (I know -- I should have had a Canadian quarter for scale!)

Trilobites in the Mt. Stephen Trilobite Beds. (I know -- I should have had a Canadian quarter for scale!)

A beautiful complete trilobite. Very common here.

A beautiful complete trilobite. Very common here.

An appendage of one of the most famous Middle Cambrian fossils: Anomalocaris. The Mt. Stephen Trilobite Beds also have soft-bodied preservation.

An appendage of one of the most famous Middle Cambrian fossils: Anomalocaris. The Mt. Stephen Trilobite Beds also have soft-bodied preservation.

The wondrous Burgess Shale

August 7th, 2009

FIELD, BRITISH COLUMBIA, CANADA–I stepped on Paleontological Holy Ground when I visited the Burgess Shale earlier this week. It is often cited as the most important fossil locality ever. I felt the historical as well as the scientific vibrations in the Walcott Quarry, the site where the extraordinary Charles Walcott began his explorations of the unit in 1909.

The Walcott Quarry of the Burgess Shale.

The Walcott Quarry of the Burgess Shale.

There are numerous websites illustrating the famous Burgess Shale Fauna. I’ll just share some of the favorite fossils I found. (We could pick up and examine any fossil, but collecting, of course, is strictly forbidden.)

The humble sponge Vauxia. I like the less charismatic taxa in the Burgess Shale. The fancy arthropods get plenty of love!

The humble sponge Vauxia. I like the less charismatic taxa in the Burgess Shale. The fancy arthropods get plenty of love!

The primitive mollusc Scenella on the left and a trilobite on the right. The Burgess Shale fauna has plenty of skeletonized fauna along with the soft-bodied forms.

The primitive mollusc Scenella on the left and a trilobite on the right. The Burgess Shale fauna has plenty of skeletonized fauna along with the soft-bodied forms.

This is an odd breccia at the base of the Burgess Shale. The white parts are limestone fragments and the black is calcite. This may be an indication of carbonate hardgrounds -- features I study.

This is an odd breccia at the base of the Burgess Shale. The white parts are limestone fragments and the black is calcite. This may be an indication of carbonate hardgrounds -- features I study.

It is a tradition among paleontologists to pose with Charles Walcott at his famous quarry! I lack the knickers, though.

It is a tradition among paleontologists to formally pose with Charles Walcott at his famous quarry. I lack the knickers, though, and that certain set of jaw.

The Walcott Quarry of the Burgess Shale on a beautiful day

August 6th, 2009

FIELD, BRITISH COLUMBIA, CANADA–We have a small group of seven people for this expedition organized by Matthew James of Sonoma State University in California. Everyone is from California except me (although I was invited through my California roots). Our guide to the Walcott Quarry didn’t show up yesterday morning, so we joined a much larger group from Chevron — an interesting and productive mix of industry professionals and academics. Here is a movie of our exploration in the quarry:

Our Burgess Shale group.  Clockwise starting with the guy in the orange shirt: Matthew James, Howard Adams, Rebecca Perlroth, Mark Wilson, Bob Rubin, Bob Davies, Kurt Burmeister.

Our Burgess Shale group. Clockwise starting with the guy in the orange shirt: Matthew James, Howard Adams, Rebecca Perlroth, Mark Wilson, Bob Rubin, Bob Davies, Kurt Burmeister.

Wooster geologist at the Burgess Shale

August 6th, 2009

FIELD, BRITISH COLUMBIA, CANADA–I’ve been waiting to write those words! More later when I get better wireless access. The summary: my colleagues and I successfully made the long hike to the Walcott Quarry of the famous Middle Cambrian Burgess Shale today (5.5 hours to get there); it rained all morning, and then the sun appeared in time to dry out the outcrop before we arrived; we saw many wonderful fossils on this iconic outcrop.

walcottquarry01

Walcott Quarry of the Burgess Shale in the lower right, with Emerald Glacier and Mount Wapta in the background. Stunning in all respects!

« Prev