Trace fossils of the Grand Canyon
When critters interact with their environment, sometimes they leave behind traces of that interaction. If we're lucky, these traces fossilize and can be preserved through time to tell us interesting things about the past. This past summer, when I rafted down the Grand Canyon with my father and two brothers, I saw some cool trace fossils. In chronostratigraphic order (earliest first), here they are:
The Bright Angel Shale can be found atop the Tapeats Sandstone, and below the Muav Limestone along the river in much of the canyon. The Bright Angel is middle Cambrian in age. For my money, it's one of the most spectacular sedimentary layers there, because it's so varied. The colors of the individual strata range from purple to green to brown to tan, and they are in many places chock full of horizontally-oriented feeding traces. Here's some of those wormy shapes along the trail to a waterfall we hiked to... (sorry, don't remember the name or exact location... I think it was day 4 or so of the overall trip... Hmmm, I guess I should have blogged this in early July when I photographed it...)
Nearby, we saw a spectacular trilobite crawling trace (Cruziana?):
Earlier in the trip (day 1, at lunchtime), and higher in the stratigraphic stack (the Permian Coconino Sandstone, which is a sand dune deposit), we saw these reptile (synapsid?) footprints:
This is a trackway left by an ancient reptile as it was walking up and down the dunes, preserved on the slip-face (which defines the feature we recognize from a side-view as "cross bedding"), and now, 260 million years later, I'm viewing those same tracks from underneath, as the older slip-faces of the dune have peeled off, and only the overlying (younger) ones are preserved in this particular alcove. Pretty spectacular stuff. And it offers some nice lunchtime shade, too... Can't complain about that. Here's another shot, with a sense of scale in it:
You can see the individual toes! Wild!
The Bright Angel Shale can be found atop the Tapeats Sandstone, and below the Muav Limestone along the river in much of the canyon. The Bright Angel is middle Cambrian in age. For my money, it's one of the most spectacular sedimentary layers there, because it's so varied. The colors of the individual strata range from purple to green to brown to tan, and they are in many places chock full of horizontally-oriented feeding traces. Here's some of those wormy shapes along the trail to a waterfall we hiked to... (sorry, don't remember the name or exact location... I think it was day 4 or so of the overall trip... Hmmm, I guess I should have blogged this in early July when I photographed it...)
Nearby, we saw a spectacular trilobite crawling trace (Cruziana?):
Earlier in the trip (day 1, at lunchtime), and higher in the stratigraphic stack (the Permian Coconino Sandstone, which is a sand dune deposit), we saw these reptile (synapsid?) footprints:
This is a trackway left by an ancient reptile as it was walking up and down the dunes, preserved on the slip-face (which defines the feature we recognize from a side-view as "cross bedding"), and now, 260 million years later, I'm viewing those same tracks from underneath, as the older slip-faces of the dune have peeled off, and only the overlying (younger) ones are preserved in this particular alcove. Pretty spectacular stuff. And it offers some nice lunchtime shade, too... Can't complain about that. Here's another shot, with a sense of scale in it:
You can see the individual toes! Wild!
Labels: arizona, cambrian, fossils, grand canyon, permian, primary structures, travel
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