The Kaibab Formation was named after the flat Kaibab Plateau. Kaibab is
a Southern Paiute Indian word meaning “mountain lying down.” The formation
is composed of sedimentary rocks: limestone, sandstone and chert formed
under a shallow inland sea. Although some Grand Canyon layers were terrestrial,
all were deposited on a flat landscape either near or beneath sea level.
Much later, geological processes raised the Grand Canyon area to its present
altitude, averaging 7000 feet at the South Rim and 8200 feet on the North
Rim.
Limestone and dolomite are composed mostly of the shells of sea creatures
such as clams and snails. A few of these may be preserved as fossils, but
most shells become crushed or dissolved and are no longer recognizable.
The Kaibab Formation is sandy because at maximum the sandy beach was only
about 50 miles east of Grand Canyon. In fact, toward the east the Kaibab
is mostly sandstone.
Chert is a major constituent
of the Kaibab Formation. It is a hard, brittle rock made of silica that
forms as lumps or “nodules” within limestone beds under the sea. Chert
is the chief tool and arrowhead material of ancient people world wide.
The brown lumps of chert in the Kaibab are mostly made from the silica
skeletons of ancient sponges called Actinocoelia.
Chert is very hard, so the
sturdy Kaibab Formation resists erosion. Thus, in a sense the lowly sponge
protects the Grand Canyon. This is a photo of Actinocoelia.
Every
rock formation at Grand Canyon formed long before there were people--even
long before dinosaurs! But I enjoy pretending that people were alive during
the formation of each layer. This is my fantasy of how we, the "tribe,"
may have lived under the prevailing circumstances.
Our Tribe in Kaibab time
The shoreline is in the east and we are diving in 100 feet of sea water.
There are sharks and bony fish in the water, shellfish and seaweed on the
bottom. Everything has that salt-slimy smell. The sea floor is also thick
with sponges: we collect them for trade in Pangaea, our world continent.
From our human perspective the sea will be here “forever.” We have always
lived like this.