DIAGENETIC COLORATION FACIES AND ALTERATION HISTORY OF THE JURASSIC NAVAJO SANDSTONE, ZION NATIONAL PARK AND VICINITY, SOUTHWESTERN UTAH Gregory B. Nielsen, Marjorie A. Chan, and Erich U. Petersen Department of Geology and Geophysics University of Utah 115 S. 1460 E., Rm. 383 FASB Salt Lake City, Utah 84112-0102
[email protected] [email protected] [email protected] ABSTRACT Coloration patterns in the Jurassic Navajo Sandstone of Zion National Park and vicinity are examined using a broad variety of geochemical, geospatial, petrographic, and bedform analysis techniques. Six diagenetic coloration facies (including 12 subfacies) are defined and characterized. Results indicate a prolonged and complex diagenetic history with variations in color resulting largely from changes in the concentration and distri- bution of iron oxides. In the northern Kolob Plateau, the Navajo Sandstone has a uniform red pigmentation (red primary facies) that formed during early diagenesis to produce the “primary” sandstone color. In contrast, Navajo Sandstone of main Zion Canyon displays “secondary” alteration features occurring in three distinct vertical coloration facies: brown (lower), pink (middle), and white (upper). The white and pink facies in Zion Canyon are characterized by a combination of prevalent bleaching, areas of remnant “primary” sandstone, and small concretionary iron-enriched lenses. Bleaching is concentrated in the upper Navajo Sandstone where alteration occurred during middle diagenesis (deep burial). Widespread bleaching and alteration in Zion Canyon terminates abruptly in the central park but narrow, well-defined, white bleached bands locally follow high-permeability beds northward for several kilometers into the red-colored Kolob Plateau (red/white facies). The brown facies is characterized by widespread dark iron oxide cement concentrations precipitated beneath a well-defined subhorizontal boundary.