Water Table Controlled Syndepositional Alteration Textures and Fabrics in Salt Pan Halite: Modern Analogues and Ancient Examples

HOLT, ROBERT M., IT Corporation, Albuquerque, NM, and DENNIS W. POWERS, Consulting Geologist, El Paso, TX

At the Devil's Golf Course, Death Valley, CA, vadose zone and phreatic zone alteration of subaqueously accumulated halite produces characteristic textures and fabrics that are recognizable in ancient salt pan halite (Late Permian Salado Formation) exposed in a shaft at the Waste Isolation Pilot Plant. Water table depth and duration

control fabric type. The crystal size of surficial halite is reduced by hygroscopic alteration. Efflorescent crusts extend the capillary fringe to the surface along vertical permeability pathways. When the water table is shallow, planar dissolution in the vadose zone removes all or most halite from successive thin depositional sequences and progressively disrupts strata consisting of clay or sulfate into irregular strata, stringers, isolated blebs, and, ultimately, "blebby" laminae. With a deeper water table, point dissolution occurs along vertically oriented permeability pathways (e.g., polygonal margins) producing characteristic textures. Vertical pits, pipes, and macropores form first. Then the surface becomes slightly hummocky as point solution pathways to the water table widen an coalesce. A complex terrain of spires, hummocks, and columns develops and exhibits characteristic pods and lenses of fine halite surrounded by and containing solution lags of insoluble material. Relief is reduced by solution, and lenses and pods of fine halite become smaller and less common. Ultimately, halite is entirely removed leaving only insoluble material. Halite cements grow in the phreatic zone. Halite passively fills voids in more mechanically competent halite. Displacive halite cements dilate fabrics within less competent bedded halite. These textures can be integrated into an idealized lithologic sequence for ancient salt pan halite.

AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)