Unconformity at Blacktail Canyon

February 11, 2011

Photographer: Nel Graham 
Summary Author: Nel Graham

This photo showing a geologic feature known as an unconformity was taken in Blacktail Canyon, Arizona; one of the many small slot canyons that adjoin the Grand Canyon at the level of the Colorado River. Sarah, our river raft guide, is pointing out the "Great Unconformity," where Tapeats Sandstone rests upon the Grand Canyon supergroup of layered sedimentary rocks. The span of her fingers represents a gap in the geologic record of at least 250 million years. This sandstone slab is estimated to be about 550 million years old; whereas the supergroup ranges from 1.2 billion to 800 million years old. Photo taken in July of 2008.

Photo details: Camera Maker: OLYMPUS OPTICAL CO., LTD; Camera Model: C3100Z,C3020Z; Focal Length: 6.6mm; Aperture: f/2.8; Exposure Time: 0.025 s (1/40); ISO equiv: 100; Exposure Bias: none; Metering Mode: Matrix; Exposure: program (Auto); Flash Fired: No; Orientation: Normal; Color Space: sRGB.