HEMMERICH, MARTA J., and SHARI A. KELLEY, Dept. of Earth and Environmental Sciences, New Mexico Institute of Mining and Technology, Socorro, NM 87801

ABSTRACT: Patterns of Cenozoic Denudation on the Southern High Plains

Spatial and temporal patterns of denudation on the southern High Plains of northeastern New Mexico, southeastern Colorado, the Texas panhandle, and western Oklahoma are constrained using apatite fission-track (AFT) thermochronology, heat flow, and sonic well-log velocity studies. AFT and modern temperature data are combined to estimate the timing and the magnitude of cooling due to denudation on the High Plains. AFT analysis of core samples from five deep oil wells in the area indicate that the base of the apatite partial annealing zone (PAZ) is preserved in the subsurface and it can be precisely located in two of the wells. The depth of the base of the PAZ below the ground surface and the amount of denudation recorded in the Logan and Payne wells are tabulated below:

1. <1230 m, east-central New Mexico (1 Latigo Ranch C)
2. ~825 m, northeastern New Mexico (Logan), ~2-3 km
3. <1800 m, Oklahoma panhandle (Stonebraker 1-AP)
4. <3390 m, Texas panhandle (Hobart Ranch 1-21)
5. ~3074 m, Anadarko basin, Oklahoma (Payne 1), ~1-1.5 km

The AFT cooling age just beneath the break-in-slope on the age-depth plot is -27 Ma in northeastern New Mexico and -38 Ma in the Anadarko basin.

The interval transit time digitized from sonic logs can be used as an independent measure of the amount of denudation in an area. The interval transit time decreases with increasing burial depth according to a compaction curve that has to be calibrated for each unit examined. Rock units that are at a depth shallower than their maximum burial depth will have a lower-than-expected interval travel time. Approximately 50 sonic logs from SE Colorado and NE New Mexico have been digitized and estimates of the amount of erosion have been determined. The amount of erosion in southeastern Colorado predicted from this analysis ranges from ~3 km along the Sangre de Cristo Mountain front to 0.8 km near the Colorado-Kansas state line.

AAPG Search and Discovery Article #90915©2000 AAPG Rocky Mountain Section, Albuquerque, New Mexico