New Mexico Geological Society Annual Spring Meeting — Abstracts

The database for the new state geologic map consists for the most part of maps produced since 1965. These maps number approximately 80, range in scale from 1:24,000 to 1:250,000, and include formal publications, open file reports, and thesis and dissertation maps. Many of these have been digitized and the digital data is stored on Bernoulli cartridges. However, little new work (post-1965) has been done in the southeast quadrant of the state, and thus our compilation work has to a large degree been confined to the other three-fourths of the state.

Selection of map units has produceeded on a statewide basis nonetheless, and all 164 units on the "active list" are presented as a correlation diagram. This format requires the compiler to face squarely the task of establishing relative ages of map units and recognizing the importance of regional correlations. Some units have new names, especially within the Mesozoic. A somewhat different approach to the complex Tertiary volcanic and volcaniclastic sequence in southwest N.M. has been implemented; few formal names are used and the units are based on age, lithology, and genesis. We have suggested rank changes in some instances; other suggested rank changes are too poorly supported for implementation at this time. All rank or name changes are being made for the purpose of clarification and to facilitate regional correlation. Basinal, regional, and even worldwide correlation is the ultimate purpose of describing and mapping local geologic units; that plus utility with respect to economic and environmental geology.

Thus the following changes and expanded format are proposed: (1) divide the Precambrian rocks into ten units (instead of lumped as one); (2) include correlation charts of certain Paleozoic units, (e.g., Mississippian carbonates) to illustrate in-state relationships as well as interstate correlation problems (e.g. The Permian at the N.M. -AZ state line); (3) acknowledge the recent work on the upper Triassic Chinle Formation and elevate it to a group-rank unit, recognizable in eight western states: (4) re-evaluate the U. S. Geological Survey proposal to downgrade the Todilto from a formation to a member; (5) include a longitudinal profile of the Rio Grande rift basin-fill illustrating how the Upper Cenozoic Santa Fe Group may be regarded as a Supergroup; and (6) relate all other Upper Cenozoic units (e.g. Gila Group, Fence Lake Fm, Bidahochi Fm., Ogallala Fm.) to show transitions from the Rio Grande rift to both the Colorado Plateau and the High Plains.