PERMIAN AGE ARAGONITE CEMENTS IN THE TEPEES OF THE GUADALUPE MOUNTAINS, WEST TEXAS & NEW MEXICO

Permian age aragonite still exists in the botryoidal fibrous cements comprising the tepee structures in the lower Yates and lower/middle Tansill formations of the Guadalupe Mountains of West Texas and New Mexico.

Botryoidal cements composed of radiating fans make upwards of 50% of the carbonate comprising the tepees. The cements occur in layers that extend for several meters laterally and are up to tens of centimeters thick between beds of the original pisolitic strata. Sedimentary relationships unequivocally indicate that the botryoidal cements formed contemporaneously with the tepee structures. The great majority of the botryoidal fibrous cements are predominantly composed of an equant mosaic of weakly cathodoluminescent diagenetic low magnesium calcite (dLMC). Observed through this diagenetic overprint, the dLMC comprising the botryoids most commonly display a relict structure composed of fibrous, straight-sided crystals with flat-ended terminations, and contain as much as 2000 ppm Sr. As previously recognized by other geologists, the botryoidal cements in the tepees were originally composed of aragonite. Centimeter-sized, irregularly shaped dark brownish patches are present within the dLMC of the botryoids. Some of these darker patches display: well preserved aragonitic fibers, are non-cathodoluminescent, have Sr concentrations that range up to 3700 ppm, and X-ray diffraction patterns indicate that they are composed of as much as 25% aragonite within a mosaic of dLMC. All these attributes indicate that the original aragonite cements altered in a relatively closed system, i.e., very low water to rock ratio, and that some of the original aragonite cements have survived essentially unaltered within the predominantly dLMC.