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The El Paso Group and at least the upper part of the underlying Bliss Sandstone at their type sections in the southeastern Franklin Mountains probably is the most complete Canadian section exposed in northern Chihuahua, New Mexico, and west Texas.
The El Paso Group represents deposits of a general, but complex, west-to-east transgression of the Cambrian and Early Ordovician seas across Arizona, New Mexico, and west Texas. The group thins to a feather-edge in central New Mexico as a result of post-Canadian erosion of the upper part of the sequence.
Flower (1964) has given 10 formational names for the El Paso Group that represent not only rock-stratigraphic units, but also distinct sequential biostratigraphic units.
Seven of these El Paso Group units are regional in extent and recognizable in the southern Franklin Mountains. They are (in order from oldest to youngest): the early Canadian Sierrite Formation; the middle Canadian Cooks, Victorio Hills, and Jose Formations; and the late Canadian McKelligon Canyon, Scenic Drive, and Florida Mountains Formations. The basal middle Canadian Big Hatchet Formation may be present and unrecognized because of facies changes in the southern Franklin Mountains area. The uppermost middle Canadian Mud Springs Mountain and Snake Hills Formations are believed to be absent because of nondeposition or erosion.
The El Paso Group overlies the Bliss Sandstone disconformably. The Late Ordovician Montoya Group overlies the El Paso Group with a regional angular unconformity in the west Texas-New Mexico area. The
Middle Ordovician Simpson equivalents are not present because of nondeposition or erosion.
The nearshore to supratidal El Paso Group section faunal zones have been correlated tentatively with the deeper water, miogeosynclinal, western standard section (Ibex and Garden City, Utah composite sections) of Hintze (1951, 1952) and Ross (1951).
Paleoecological studies of the sabkhas to nearshore sediments of the El Paso Group strata show excellent examples of digitate algae, stromatolithic algae, and cyclic reefoid mound structures. Recent sedimentation in the Khor al Bozam (Persian Gulf) and Shark's Bay (Australia) probably are modern analogues.
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