Navajo Sandstone Wood Specimens

Different regions have different chemical characteristics

The three sites described below are separated by a distance of 150 miles.   Each one of these sites is located near the top of the Navajo Sandstone formation.  

Site 1 showed evidence of a shallow lake.  Site 2 is in a general area that shows evidence of deeper and more permanent lakes.  Site 3 was a much drier environment and seems to have affected more by groundwater perhaps in an area of deflation in between dune field.

The fossils at each site have unique chemical characteristics which may provide additional clues relating to the depositional environment.

Site 1

This Moab, Utah site has good quality, fine-grained silica permineralized wood.  Specimens are mostly black but occasionally gray or brown in color.  Some of the samples show fine texture and detail.

Site Description: There is evidence of a shallow lake directly on top of a dune field.  Flood cut channels are evident in lower horizons.

Site 2:   The specimens at Lake Powell have a more coarse texture and contain more iron and carbonate. 

Site description:  The host horizon at this location has been exposed a long time.  The specimens exist in random scattered locations and have been transported from there original burial locations.   A second younger horizon contains some small embedded features and paleosols.

Site 3 located at Page, Arizona reflects a different type of depositional environment.  The specimens in many cases are still intact with the host horizon and are much larger in size than those found at the other two sites.  The largest specimens range from 10-15 feet in length and have a diameter of 12" in some instances.

The fossilized material is not strikingly different from the host sandstone and consists of little more than cemented sand grains and some trace iron.  There is no evidence of a fresh water lake like the other two sites.  Instead, it appears that the moisture was provided by high water table in an area subject to deflation. 

The sand grained texture of the specimens are similar to that found in concretions but the orientation and shape of the specimens provide a strong argument that these were not random formed deposits.    The orientation of each specimen is consistent with dune encroachment from the NW-N which was the prevailing wind direction and the size and shape of the specimens are unmistakable tree-like with small branches.

The exact details of how the Navajo fresh water oasis and playas formed and the role that groundwater played in this sandstone formation are still a matter of geologic debate.  The three sites discussed above provide a cross section of the moist environments that existed in the Navajo erg.   These watered sites were obviously important to the existence of life forms as the presence of dinosaur trackways can attest to.  Perhaps further investigation will lead to the identification of some of the flora that existed at these oases locations.

Send comments to  pmostapu@srpnet.com

Click here to read more about the Navajo Sandstone and the unique depositional environment that creates fossils in this sandstone formation.

Click here to see more pictures of the Page fossil site.

Paul Ostapuk

September 1999