New Mexico Geological Society Annual Spring Meeting — Abstracts

Tension joints in flat-lying sediments are produced during uplift by thf' release of strain energy imposed on the rocks during burial and compression. Theoretical studies show that the joint frequency is dependent on the bed thickness, the physical properties of both the rock bed and its surroundings, and the degree of tectonic deformation.

An integrated investigation into the relationship between strain energy and jointing involving field work, theory and experiments in rock mechanics was conducted on three coal-bearing sedimentary sequences in New Mexico and Virginia. Data on the frequency, spacing, orientation and surface characteristics of jointing in coals and adjacent sediments of the Cretaceous Fruitland and Crevasse Canyon Formations (New Mexico) and the Pennsylvanian Lee Formation (Virginia) were collected. Samples of the rocks were tested by a variety of experimental techniques to determine their physical properties. These quantities were used to calculate joint densities, which were compared with observed values. Comparison with the jointing data obtained in the field has shown good-to-fair agreement with theory. Estimates of extensional strain at these localities have been calculated from the data.