ABSTRACT: New Insight and Hypothesis on Zuni Basin Fold Structures, New Mexico: Exploration Significance

Orin J. Anderson, Richard M. Chamberlin

Recent interest in the petroleum potential of asymmetric anticlines and monoclines of the southern Zuni basin has led to several attempts to test the San Andres Limestone (Permian) and to renewed interest in the details and origins of these structures.

The northwest-trending monoclines have been related to crustal shortening resulting from northeast-directed Laramide compression. Moreover, the segmented or truncated nature of these folds, the alignment of their endpoints, an isolated Tertiary intrusive along one of these alignments, and the apparent juxtaposition of marine and nonmarine Upper Cretaceous rocks, all point to the presence of northeast-trending zones of lateral shear; the marine-nonmarine facies offset indicates as much as 2 to 4 mi of left slip along a N56°E trend. The resulting pattern was likened to the compartmental deformation of some authors.

An alternative hypothesis calls upon indentation-extrusion tectonics to produce the Zuni basin folding, a mechanism that has been used to explain the adjacent Zuni uplift. In this model lateral extrusion at the leading edge of a NNE-trending rigid indenter (a mafic Precambrian intrusive) is postulated as the primary mechanism responsible for transmitting compressive stress into the Colorado Plateau. Movement was primarily to the west and west-southwest of the Mt. Sedgewick area, the direction of least confinement. Extruded crustal blocks were rotated counter-clockwise as they were pushed aside in this nonuniform stress field and developed leading edges that were strongly convergent. Most responsible for the Zuni basin deformation was the southwest-vergent Atarque block, which produced the Atarque and Galestina monoclines. These two N40°W-trending, 15 mi long structures relate better to local, southwest-vergent blocks than to a northeast-directed regional stress field.

The Galestina monocline, site of some recent tests, loses expression where the competent, locally 500 ft thick, Zuni Sandstone (Jurassic) thins to less than 20 ft on a paleohigh in Plumasano basin. This should correspond to an area of maximum structural closure on the San Andres; however, the structure has not been tested. Of even greater exploration significance may be an analysis of the nonuniform Laramide stress fields around the hypothesized indenter; local zones of tensile stress should have been sites of fluid accumulation.

AAPG Search and Discovery Article #91002©1990 AAPG Rocky Mountain Section Meeting, Denver, Colorado, September 16-19, 1990