nazSTUFF - Grand Canyon Ancient Environments 01

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Grand Canyon Geology

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The Grand Canyon in Arizona is known as a living laboratory displaying the oldest rock formations on earth. Science, art and adventure come together in this magnificant place. This page presents some elementary information about Grand Canyon geology. JVroom

Learn names of the major depositional layers that are visible in the Grand Canyon.

Here's a review of the geological layers as they appear today.

Here's a conceptual illustration of the prehistoric worlds of the past.

There is a lot one could say about this illustration for it contains some simple symbolism for many facts about the canyon geology. For example, the large brown block on top represents just how much southwest geology is missing at the Grand Canyon. To find and verify that this material was probably once here you must travel north into Utah where it is exposed in other national parks like Bryce Canyon and Canyonlands National Parks.

This is also why there are no dinosaur fossils at the Grand Canyon! All the geological layers from the time periods in which dinosaurs existed are gone. Here, we are dealing with development of life on earth FAR earlier than the time of dinosaurs.

It is evident from this illustration that evolution exists in large chunks or chapters, each composing huge periods of time. Also in the area of the earth that is now the Grand Canyon several distinctly different environments have occurred in our past.

In the lower region of this illustration you can see displaced blocks of rock layers. These are remnants of the Grand Canyon Supergroup dealt with on a previous page of this album. Here's a clue: We know that these layers are tilted toward the northeast about 12 degrees. From this we can deduce that this drawing represents a chunk of the north rim and we are looking east. Once you know this you will find a lot of reference books that have it wrong. Now you know!

The Grand Canyon is often referred to as a time machine since so much prehistory is on display. Feel free to investigate the major layers and the prehistoric environment that created it in the illustrations below:

The Kaibab & Toroweap Formations - 250 to 260 million years old

The Kaibab Limestone forms the rim of the Grand Canyon and is easily recognized as the irregular gray cliff which stretches from the rim to the vegetated slope of the Toroweap Formation below. It varies between 250 and 500 feet thick. This is the youngest of the rock layers exposed in the Grand Canyon. Deposited in a shallow marine (salt water) environment in warm tropical seas which covered the Grand Canyon region during the late Paleozoic Era, the Kaibab Limestone is rich in invertebrate fossils, including sponges, brachiopods and crinoids.

The scene above includes a shark, sponges, brachiopods, crinoids, bryozoa, rugose corals and a coiled cephalopod

The Toroweap Formation, about 250 feet thick, occupies the tree-covered interval between the overlying Kaibab Limestone and the underlying Coconino Sandstone, which forms the sheer, cream colored cliff below. Similar to Kaibab Limestone the Toroweap Formation is limestone with interbedded sandy layers, typical of shallow water marine sediments which accumulated here at the end of Paleozoic Era. The presence of thin, interbedded sandstones indicates changing environments (shifting shorelines) at the time of deposition.

The Coconino Sandstone - 270 million years old

One of the most conspicuous layers at Grand Canyon, the Coconino Sandstone forms a sheer, light-colored cliff near the rim, just above the predominantly red beds of the Hermit Shale and the Supai Group. The high angle cross-beds which are characteristic of this formation are visible from some distance and are indicative of its eolian (or windblown) origin. The thickness of Coconino Sandstone varies a great deal from east to west in the canyon, between 600 feet thick to areas where it is eroded away completely. Composed almost entirely of sand, the Coconino Sandstone represents remnants of an extensive Sahara-like dune field present here in the early Permian Period. The high angle cross-beds as well as the random reptile tracks (trace fossils) found throughout the formation are all important clues to its windblown, terrestrial origin. This scene indicates the sparsity of animal and plant life. Unknown species of large and small reptiles and invertebrates (like scorpions) have left footprints and trails. Vegetation was minimal.

The Hermit Shale - 280 million years old

The Hermit Shale is the uppermost of a series of brilliant red cliffs and slopes which comprise much of the exposed depositional layers at Grand Canyon. The iron-rich red beds of the Hermit Shale provide much of the red color characteristics of Grand Canyon. In the central portion of the canyon the Hermit Shale forms a soft, deep red slope immediately below the sheer, light-colored cliff of Coconino Sandstone. It is about 300 feet thick along the Bright Angel Trail and extends to the top of the Supai Group. In places the wide slope of the Hermit Shale broadens into a shelf known as the Esplanade (primarily in the western portion of the Grand Canyon). The deep red and maroon siltstones and mudstones of the Hermit Shale represent a coastal lowland environment (lagoon) on the edge of a sea, with occasional swampy conditions. This layer is rich with plant fossils in areas.

The animal in this scene is a Dimetridon. There is also a giant dragonfly. The trees are conifers (Araucarian Pines) which are similar to the trees responsible for the petrified wood today at the Petrified Forest southwest of the Grand Canyon. Giant Horsetails and ferns fill out the scene.

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