![]() |
![]() |
||
![]() ![]() ![]() ![]() ![]() ![]() |
|||
![]() |
|||
|
Willow Creek: Hoodoos, Fossil Oysters, and Petrified Tree Stumps
Hoodoos form where there is a hard
"caprock" which shelters the Hoodoos at this site show three layers -- base, pillar, and caprock -- that were all deposited during the Upper Cretaceous Period, between 75 and 70 million years ago. The base is red-brown marine shale of the Bearpaw Formation, which was laid down in the inland Bearpaw Sea. The pillar and caprock are sand and clay of the Horseshoe Canyon Formation. They were deposited along the shoreline in deltas and tidal-flats and by rivers that flowed across this area as the sea shallowed. The caprock contains nearly 40 per cent calcite cement and is therefore more resistant to erosion than the pillar. This hoodoo group consists of 8 to 10 columns ranging in height from one to three metres. Across
Willow Creek from the hoodoos is another section of the Horseshoe Canyon
Formation. A scramble across the creek and a 100-metre climb up
the slope will bring you to these rocks. Exposed here is a
two-metre thick bed of fossilized oyster shells. These shells were
broken by storms and washed on to the shore as the Bearpaw Sea deepened
briefly and spilled over the delta and tidal-flats. Going farther
up the slope, you will see that the oysters are covered by layers of sandstone,
shale, and coal. These represent another lowering of the sea level
and the resulting influx of river sediments and decaying swamp
vegetation that slowly engulfed and buried the oyster shell
fragments. The shale and coal contain large, petrified tree
stumps, some still in the same position that they grew, some 70 million
years ago. Many geologists believe that these trees were drowned
by a quick rise in the sea and were preserved in place. Reprinted with permission from A Traveller's Guide to Geological Wonders in Alberta by Ron Mussieux and Marilyn Nelson, with permission by the authors and the Provincial Museum of Alberta. |
||
Updated October 16, 2001 by DM |