Abstract

The average fold axis trend of the Marathon facies in the Marathon Basin is north 45 degrees east plunging 10 degrees northeast. The Solitario, located 36 mi southwest of the Marathon Basin, is a laccolith formed by late Eocene granite (Corry, et al., 1990). The inner ring, four mi in diameter, consists of folded Marathon facies, Tertiary intrusives and extrusives, and a downdropped block related to the intrusion. Cretaceous rocks are domed upward around the inner ring. These later rotations were removed from the attitudes of the Marathon facies by means of a stereonet, resulting in an average fold axis direction of north 40 degrees east plunging 9 degrees northeast, which agrees closely with the fold axis direction in the Marathon Basin. The similarity of stratigraphy and structural trend is suggestive that the Solitario and the Marathon Basin are on the same regional tectonic block, or that they have undergone the very similar Marathon age deformation. Persimmon Gap, 13 mi south of the Marathon Basin, is an area in which folded and thrusted Marathon facies are cut by Laramide thrusts and Tertiary normal and strike-slip faults. The attitude of the overlying Cretaceous Glen Rose was removed from the bedding direction of the Marathon facies. The resulting average fold axis direction of the Marathon facies is south 83 degrees east with east plunge of 14 degrees. This may match a previously observed trend in the eastern part of the Marathon Basin where the Marathon structures appear to be oriented in a more easterly direction.