GRAND CANYON SUPERGROUP
The sedimentary units of the Grand Canyon begins with the Grand Canyon
Supergroup. This in turn is divided into the Unkar Group, the Nankoweap
Formation, the Chuar Group, and Sixtymile Formation. Within the Unkar
Group there is the Bass Limestone, Hakatai Shale, Shinumo Quartzite, Dox
Formation, and Cardenas Lava. These all have their own members too.
Within the Bass Limestone biscut-form and biohermal stromatolites can be
found. Stromatolitic dolomite layers can be found within the Dox
Formation. The Unkar Group records a major west to east trangression of
the sea. Minor fluctuations of sea level or sediment surface elevation
is recorded by features suggesting both subaerial and marine deposition
throughout the sequence. Apparently the Unkar Group was deposited in a
basin in which the rate of subsidence was approximately equal to the
rate of deposition.