AbstractsEarth & Environmental Science

"Conodonts were discovered in the limestones of the Marathon region in the Big Bend country, Brewster County, Texas, as a result of field work during the summer of 1939. This was not the first known occurrence of these fossils from this region, however, as King earlier mentioned the occurrence of conodonts in siliceous shales of Devonian age. The discovery of conodonts in the Ordovician and Pennsylvanian limestones of the area had its inception in the attempt to determine whether the Dimple limestone (lower Pennsylvanian) or Maravillas limestone (upper Ordovician) was involved in a fault that was being mapped. These limestones are similar lithologically and the nature of the outcrop along the fault trace was such that the age relations of the limestone involved could not be determined...The stratigraphic distribution, systematic descriptions, and illustrations of conodonts of Ordovician and Pennsylvanian age from the Marathon region form the basis of this thesis. In some instances, such as the occurrence in the dimple formation, conodonts are the only positively identifiable fossils found in the rocks and, for this reason, have special significance in determining the age of these beds. The Ordovician conodont faunas are of importance because the occurrence in this region extends their known geographic and geologic range" – Introduction, pages [1]-3.