New Mexico Geology

On Glorieta Mesa in San Miguel County, northern New Mexico, the lower Permian Glorieta Sandstone contains numerous sandstone cylinders from two areas and two stratigraphic intervals of interdunal sedimentary deposits in the lower part of the formation. Most of these cylinders are perpendicular to bedding, although some are slightly oblique to the layers of enclosing sediment. They range in diameter from 2.6 to 43 cm and are as much as 58 cm long. Most of the cylinders have smooth exteriors and, in cross section, have a structureless core surrounded by thin, concentric laminae. Some cylinders taper toward one end, which in situ specimens indicate is the lower end, and some are slightly curved. Some have one or more external grooves that demarcate a helical trajectory of flat to very slightly concave, slightly imbricated surfaces around the circumference of the exterior, sometimes with grooves spiraling in opposite directions. The lack of deformation of the sediment in and around the cylinders and the preservation of the external markings on some of the cylinders preclude their identification as inorganic dewatering structures or other forms of water conduits. Nevertheless, the concentric laminae of the cylinders are likely a diagenetic feature. The sandstone cylinders do not resemble any known cylindrical or plug-shaped trace fossils, and the lack of ornamentation (bioglyphs) on the cylinder walls is one of several reasons that preclude their identification as animal burrows. The most likely origin of these cylinders is as the fill of molds left by plant stems that were buried upright. However, the botanical affinity of these molds and casts is uncertain because they do not contain diagnostic features of anatomy or external morphology. By a process of elimination, the Glorieta sandstone cylinders are most likely to have been produced by woody calamitaleans.