| Sixtymile Formation | Kwagunt Formation | Galeros Formation | Nankoweap Formation |
| Cardenas Lava
| Dox Formation
| Shinumo Quartzite
| Hakatai Shale
| Bass Limestone |
The Hakatai Shale
The Hakatai Shale is a member of the Unkar Group formations and is the second oldest Supergroup formation. The Hakatai Shale was conformably deposited atop the Bass Limestone towards the end of the Middle Proterozoic Eon. The regressing sea which deposited the upper members of the Bass Limestone produced deltaic conditions as it retreated, and their predominance marks the beginning of Hakatai time.
The Hakatai formation can be lithologically divided into two lower members which are composed of mudstones and shales that erode to form gentle to moderate slopes, and an upper member composed of cliff forming beds of medium-grained quartz sandstone. The Hakatai is generally regarded to be the most colorful formation in the Grand Canyon, varying from purple to red to brilliant orange on outcrop due to oxidation of iron bearing minerals contained in its rocks.
The sedimentary nature of the Hakatai is pronounced and clearly revealed by high frequency and sometimes paper thin laminations of shales in its lower members that alternate in color from a somewhat nondescript, light brown to outrageous reddish purples. At right is a photo illustrating a characteristic structure. The variegation was caused by and records changing conditions along the margins of the ancient sea as it transgressed and regressed in sub-cycles following a generally regressive trend during the deposition of the Hakatai.
Fossilized mud cracks, ripple marks and cross bedded sedimentary structures provide evidence the beds of the Hakatai were deposited in marginal marine environments, the mudstones and shales recording a low energy mud flat environment and the overlying sandstones recording a shallower, higher energy environment of deposition.
The images above left and right were photographed from the Shinumo cliffs on the southwest edge of the Utah Flats area atop a mesa immediately west of Phantom Ranch. They record the spectacular exposures the Bass Limestone, Hakatai Shale and Shinumo Quartzite across a side canyon at the base of Cheops Pyramid, named after the pharaoh who built the Great Pyramid in ancient Egypt. In the image above left the Bass Limestone tops the folded crystalline core of the Vishnu as a ribbon of pinkish, vertical cliffs. Atop the Bass are purplish, softer shale and mudstone members of the Hakatai Shale which have eroded to form receding, stair stepped mounds. Above right, further towards the north and further up the base of Cheops Pyramid are brilliant orange outcrops of the Hakatai, which are striking and highly visible features viewed by millions annually from miles away on the South Rim in the general vicinity of Grand Canyon Village and nearby outlooks. A purplish band of vertical cliffs formed by the Shinumo Quartzite lies disconformably atop the Hakatai.
The mesa surface in the Utah Flats vicinity is extensively eroded in several areas, with curious and dramatically shaped outcrops of the Hakatai Shale exposed in these drainages, some of which bear a marked resemblance to stacks of pancakes. Note the tilt that is characteristic of Grand Canyon Supergroup formations revealed in the photo at right, where the stalk of a blooming century plant at the end of its life cycle forms the indicator of a natural 'tilt meter'.
Detailed above are fossilized, cross bedded ripple marks in an eroding sandstone member of the Hakatai exposed along the southern flank of the erosion channel at approximately UTM 12S 0400588, 3996208, elevation 3829 feet. A 55 mm lens cap provides scale. These ripple structures and the relatively coarse sand clasts suggest these sediments were deposited by a higher energy environment than the finely stratified mudstone and shale members. The overall lithologic sequence beginning with the underlying Bass Limestone, overlain by mudstone and shale and finally sandstone members of the Hakatai, indicate a chronological progression of increasingly shallower and higher energy environments of deposition.
Stromatolite fossils are preserved and weathering out of the Hakatai sandstones in the Utah Flats vicinity.
The outcrop of fossils pictured above left preserves some nice three dimensional detail of the structures created by these Proterozoic stromatolites. The image above right provides an overhead perspective of detail from an outcrop. A 55 mm lens cap provides scale.
This stromatolite "biscuit" had weathered completely out and separated from one of the outcrops.
Tectonic activity along a series of northwest trending, high angle reverse faults marks the end of Hakatai time in the Phantom Ranch / Bright Angel Creek vicinity. The Hakatai emerged above sea level and eroded prior to the deposition of the sediments composing the overlying Shinumo Quartzite. The contact between the Hakatai and the Shinumo Quartzite is unconformable and truncates channel deposits and cross bedded structures in the Hakatai.