PREPARATION OF A GEOLOGIC TRANSECT OF THE NORTHERN SIERRA MADRE OCCIDENTAL

Graduate student mapping projects completed at the University of Texas at Austin during the 1970’s and 1980’s are being compiled to produce a 325-km-long transect across the Sierra Madre Occidental (SMO) between Chihuahua City and Yécora at approximately 28.5° N. Each project was focussed upon rocks of the mid-Tertiary SMO volcanic field, and each used informal map units of local convenience. Hence, a major necessity is to develop an informative set of map units that convey sufficient detail and that can be used consistently for the entire transect. Other challenges are posed by the variety of original mapping scales and by the fact that several of the projects were completed before suitable topographic base maps became available.

An initial version of the transect will be displayed for comment, along with examples of related information (e.g. time-correlation diagrams, geochronology, etc.) that could be published along with it. The map units used in the present version are time slices based upon clustering of K-Ar ages. This scheme works well for individual and adjacent areas but is less satisfactory at regional scale. Suggestions regarding a more effective approach to map units, availability of digital base maps, and the nature and format of supplementary information will be especially welcome.