New Mexico Geological Society Annual Spring Meeting — Abstracts

The type section of the Yeso Formation was first designated by W. T. Lee in 1909. His section was located along the east edge of the Socorro 15' quadrangle. structural problems at Lee's original section forced Needham and Bates in their redefinition of Permian type sections to move its location east two miles to a "relatively" undeformed series of exposures in 1943. They subsequently redescribed all of the strata in the upper three members of the Yeso Formation (Torres, Canas and Joyita Members).

Recent detailed structural mapping in the area containing this type section has revealed previously unrecognized structural complexity which affects the upper two-thirds of the Yeso Formation. First, the Yeso Formation at this location contains at least three low-angle faults which reduce its apparent true thickness by several hundred feet. Second, the entire section is allochthonous; Permian strata in and north of the type section are separated from underlying Triassic strata by a low-angle fault. Third, an effort to reconstruct the Yeso sequence from stratigraphic section measured on nearby Sierra de la Cruz has met with limited success; the total section is still thin when compared to stratigraphic data from Chupadera Mesa and oil tests drilled in the Jornada del Muerto immediately to the east.

Because ·of this structural complexity, I recommend that the Yeso type section designated by Needham and Bates be abandoned as a type section for the formation, that it be retained as a reference location for study, and that a new reference section be established for the formation based on outcrop and well-log data from adjacent, less deformed area.