Phantom Ranch Tour - interbedded sandstone & shale beds

This view shows interbedded sandstone and shale beds in the upper Bright Angel Shale along South Kaibab Shale. The Cambrian Bright Angel Shale gradationally overlies the Cambrian Tapeats Sandstone. These rocks preserve a record of the gradual transgression of a shallow sea during the Cambrian, about 515 to 525 million years ago. Sediments eroding from the coastline or carried by rivers were deposited in the sea. Currents moved, reworked and sorted the sediments into sandy offshore shoals and bars (which later became sandstone beds). Mud and silt accumulated in lower energy areas, (later becoming shale). Beds of sandstone, siltstone, mudstone, shale, and limestone pinch out, transition to other lithologies, or interfinger with other beds across the region. The Cambrian-age sedimentary rocks yield fossils of extinct marine species (trilobites), and preserve tracks and trails of burrowing and crawling organisms (Beus, 1987; Beus and Morales, 1990; Mathis and Bowman, 2005).