Navajo Sandstone

“One of the largest wind-deposited formations in

the geologic record."

Picture: http://www.agiweb.org/geotimes/nov03/NN_navajo.html

What you need to know:

• Navajo Sandstone is a sedimentary rock formation located in Utah, Arizona and Colorado.

• Being sedimentary rock it is very difficult to date because it has multiple sources and never underwent metamorphism, which can be dated radiometrically.

Stages

• “The ages of strata deposited in succession within a given age of time. They are often defined by a consistency found within the rock, such as index fossils or the polarity. In other words, stages are "groups" of strata containing the same major fossil assemblages.”

• Navajo Sandstone is its own stage???*Boggs Jr., S., 2006, Principles of Sedimentology and Stratigraphy: Upper Saddle River, NJ,

Prentice Hall, p. 481.

Need help here, is the stage what we’re trying to narrow it down to or is NS its own stage???

Problem

• Here in lies the problem, how can we date the Navajo Sandstone and how can we assume the environment of deposition?

• The sediments comprising this formation are from multiple sources so how did they reach this area and organize into a wide-spread rock structure?

Deposition

• Ripples show that the sediment was deposited by wind.

• Deposited by consistent Northeast winds.

Both Pictures: http://www.thetravelen.com/the-wave-arizona/

DepositionAeolian deposited sand dunes.

Previously believed to be from Ancestral Rockies, now believed to mainly be from Appalachians.

Photo: http://www.digital-images.net/Gallery/Scenic/Southwest/So_Utah/body_so_utah.html

Radioisotope-dating

• Jeffrey Rahl and Peter Reiners used two forms of radiometric dating to find when grains were formed and cooled.

• “Using uranium-lead dating, the researchers found that most of the grains were formed between 1.2 billion and 950 million years ago. And using helium dating, they found that the grains cooled, and therefore eroded, between 500 million and 250 million years ago. Rahl and Reiners say there is only one place in North America with zircons like these — the Appalachians.”

*Pratt, Sara. Geotimes. November 2003.

Coast to Coast

• Must prove sediment traveled most of the way by ancient river system.

Biostratigraphy

• Many fossilized remains in the Navajo Sandstone.

• Dinosaur remains and tracks lead scientists to believe the formation dates to the late Jurassic.

Picture: http://www.geosciences.unl.edu/~dloope/NavajoTracks&BurrowsWeb/NavajoTracks&Burrows.html

Add 1 or 2 slides on specific fossils

Semi-Aquatic EcosystemStromatolites!!-found in marine environments!Protosuchus-first crocodileNavajo Sandstone must have at least been semi-aquatic with seasonally saturated ground and lakes.Photo: http://www.geosciences.unl.edu/~dloope/NavajoTracks&BurrowsWeb/NavajoTracks&Burrows.html

Not as arid as believedSeasonal monsoons and rainfall lead to slumping in sand dunes.

Same seasonal slumps are found in Navajo Sandstone.

Both Photos: http://www.geosciences.unl.edu/~dloope/NavajoSlumpsWeb/NavajoSlumps.html

Should relate to other places

• Newark Basin?

Setting

• With an approximate age, good idea of how sediments arrived, and significant fossil evidence we can claim the Navajo Sandstone as…

• An aeolian sand dune, composed of sediments from the distant Appalachians, near a significant source of water, and dating back to the Jurassic. MORE PRECISE.

Unsolved:

• Our research only brings us so far, so as for a more specific age of the Navajo Sandstone we will have to continue to wait for more breakthroughs in the future.

Photo: http://www.sunsetcities.com/Valley-of-Fire/mesozoic-era.html

Better chart? Too small?

The End.