THE CHINLE GROUP

OF

NORTH EASTERN ARIZONA

 

      
General
      Overview

      
The late Triassic
      Chinle Group represents lacustrine and fluvial terrestrial deposits
      some 225 million years in age. Sediments contained primarily
      in North Eastern Arizona include sandstones, mudstones, claystones
      and shale. Beds of conglomerates and gypsums complete the formation
      which extends up into the Four Corners Area. The Chinle is famous
      for its collection of unique fossil fauna and flora, which incudes
      the earliest dinosaurs, metopasaurs, phytosaurs and mammal like
      reptiles. We also find the remains of freshwater lungfish, sharks
      and horseshoe crabs, and a rich floral assemblage of cycads,
      tree ferns, giant neocalamites herbs, and of course, Araucarioxylon,
      the giant petrified conifers which made famous the Petrified
      Forest near Holbrook.

      
The Chinle Group
      consists of in ascending order, the Shinarump, Mesa Redondo,
      Monitor Butte, and Petrified Forest formation which includes
      the Blue Mesa Member, Sonsela Sandstone, and Painted Desert Members,
      then the Petrified Forest Formation is overlain by the Owl Rock
      and Rock Point Formations.

      
In the southernmost
      extensions of the Chinle it is underlain by the Triassic Moenkopi
      Formation which is primarily a series of redbeds, but on the
      northern boundary of the state, is underlain by the Permian Kaibab
      formation. We found a great many beds in the Chinle with reworked
      Kaibab cherts containing Paleozoic fossils.

      

        

          
 
          
 
        
        

          

            
Left: Generalized stratigraphic
            column of the

            
Chinle Group in
            North Eastern Arizona and in adjoining states.

            
Above: Topographical coverage
            of the Chinle in Arizona.