ABSTRACT: Integrated Geologic History of the San Juan Basin, New Mexico

Dag Nummedal, Ming Pang, Mark A. Pasley, Greg W. Riley, Paul L. Templet, Donald E. Owen

The San Juan basin, located at the eastern margin of the Colorado Plateau tectonic province, contains a sedimentary record of all major Phanerozoic orogenies affecting the western United States (Pennsylvanian, Jurassic, Late Cretaceous, and early Tertiary). The Phanerozoic section ranges from Cambrian to Eocene and attains a maximum thickness of about 4500 m.

Of the six Sloss sequences, the San Juan basin contains all but the Tippecanoe. Eastward marine onlap of basal clastic sands (Ignacio Quartzite) characterizes the Sauk sequence, whereas the Kaskaskia sequence records deposition of passive margin platform carbonates (Elbert, Ouray, and Leadville limestones). Total pre-Pennsylvanian basin subsidence was less than 200 m. The Absaroka sequence (Hermosa, Abo, and Chinle formations) consists of clastics derived from the Uncompahgre highlands to the north and (in Triassic time) the rising orogenic belt along the southwestern margin of North America. Pennsylvanian subsidence locally exceeded 1500 m (compaction corrected) and was probably driven by transtension along major northwest-southeast-trending wrench faults related to suturing of North America and Gondwanaland. The Zuni sequence contains thick clastic units of Middle Jurassic through Late Cretaceous age. Gradual subsidence, related to back-arc(?) spreading resulted in deposition of thick continental strata (Entrada, Wanakah, and Morrison Formations). In Late Cretaceous time the San Juan basin became part of a foreland basin

east of the Sevier thrust belt, resulting in deposition of a series of continental and marine clastic wedges (Dakota Sandstone, Gallup Sandstone, Mesaverde Group, and Mancos Shale). Cumulative basin subsidence (compaction corrected) of 2000 m occurred during deposition of the Zuni sequence. The Tejas sequence consists entirely of continental clastics (Ojo Alamo, Nacimiento, and San Jose formations) derived from basement-cored uplifts of the Laramide orogeny. Basin subsidence in these entirely continental deposits is difficult to determine, but maximum preserved thickness locally exceeds 1000 m.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990