Remnants of the late Eocene erosion surface in the region between the Kaibab uplift and the Rio Grande rift

Conference · Thu Apr 01 04:00:00 EST 1993 · Geological Society of America, Abstracts with Programs; (United States)

OSTI ID:5290202

Ely, R W ^[1]

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1. Woodward-Clyde Consultants, Oakland, CA (United States)

A widespread low-relief erosion surface is thought to have formed in the Colorado Plateau region during the late Eocene between the end of the Laramide orogeny and the beginning of widespread Oligocene volcanism. The present configuration of the late-Eocene surface (LES) is depicted on east-west cross sections that extend from the Kaibab uplift to the Rio Grande rift. The LES is best preserved underneath the Oligocene Chuska Sandstone on the Defiance uplift at about 8,000 ft. MSL. The Chuska is an aeolian arkose that contains rhyolitic ash beds, and was eroded to hilly surface by 30 my ago prior to eruption of the Navajo volcanic field. To the north, the Paleocene Carrizo Mtns. intrusive appear to have been an isolated upland that stood above surrounding plains during the late Eocene. To the west, the north rim of Black Mesa is close to the elevation of the LES on the Defiance Plateau. Siliceous lag-gravels on the rim of Black Mesa may have been derived from sediments originally deposited on the LES. Farther west the Kaibab uplift rises above 9,000 ft. MSL for 14 miles along its crest. The Kaibab uplift probably was a karst plateau that stood above alluviated late Eocene lowlands to the east, north and west. East of the Defiance Plateau, the early Eocene San Jose Formation of the San Juan basin is preserved at elevations as high as 7,500 ft. under the eastern part of the basin, and as high as 8,450 ft. along the deformed eastern flank of the basin. Several thousand feet of middle Eocene deposits probably were once present in the basin. Several thousand feet of middle Eocene deposits probably were once present in the basin, putting the LES at about 9,000--10,000 ft MSL along the eastern side.

• OSTI ID: 5290202
• Report Number(s): CONF-9305259--
• Conference Information: Journal Name: Geological Society of America, Abstracts with Programs; (United States) Journal Volume: 25:5
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580000* -- Geosciences
COLORADO PLATEAU
DEPOSITION
EROSION
GEOLOGIC FORMATIONS
GEOLOGIC HISTORY
GEOLOGIC STRATA
GEOLOGIC STRUCTURES
GEOLOGY
MOUNTAINS
RIFT ZONES
STRATIGRAPHY