2015 GSA Annual Meeting in Baltimore, Maryland, USA (1-4 November 2015)

Paper No. 222-15
Presentation Time: 9:00 AM-6:30 PM


HASIOTIS, Stephen T., Department of Geology, University of Kansas, 1475 Jayhawk Blvd, Lindley Hall, rm 120, Lawrence, KS 66045, PARRISH, Judith Totman, Dept. of Geological Sciences, Univ of Idaho, P.O. Box 443022, Moscow, ID 83844 and CHAN, Marjorie A., Department of Geology and Geophysics, University of Utah, 115 S 1460 E, Room 383 FASB, Salt Lake City, UT 84112, hasiotis@ku.edu

The Lower Jurassic Navajo Sandstone (Ss) eolianite near Moab, Utah, has a remarkable amount of rhizoliths, rhizocretions, and rhizohaloes representing herb, shrub, and tree roots. Four types of rhizoliths occur in the Navajo Ss to date. Rhizoliths are root casts or molds formed by infilling with sediment after plant death, and weather in positive relief or as voids. Rhizoliths also include carbonaceous and mineral-replaced root remains. Rhizocretions are concretionary or nodular bodies of calcium carbonate, siderite, silica, or Fe and/or Mn oxide that form in and around the roots. Rhizohaloes are the Fe- and Mn-depleted (bleached) areas formed around roots due to fluctuating soil moisture and root decay. Rhizomats are horizontal surfaces densely covered in preserved records of thin, fibrous root hairs.

Preliminary research indicates that rhizofacies can be constructed based on lithofacies association and type of rhizolith preservation, distribution, density, and penetration depth. These associations record the stability of the landscape based on sedimentation rate, depositional energy, groundwater profile, and speed of dune movement. Rhizofacies I is the association of rhizoliths in grain flow and wind ripple laminations in the toe-of-slope slipface of dunes. The rhizoliths are vertical to subhorizontal and < 2 cm deep, comprising < 3% of visible surface area. Rhizofacies II is the association of rhizohaloes in wet interdune deposits of red massive, planar, and/or wrinkled bedding. The rhizohaloes are predominantly subhorizontal and < 1 m deep, comprising < 15% of visible surface area. Associated traces include Naktodemasis, and Planolites that represent arthropod-plant interactions. Rhizofacies III is the association of rhizocretions and rhizoliths along supersurfaces and 1st order bounding surfaces where bedding is mostly massive. The structures are predominantly vertical to subhorizontal and < 2 m deep, comprising < 25% of visible surface area. Associated traces include Maconopsis, Beaconites, Scoyenia, Entradaichnus, and large-diameter vertebrate burrows. Rhizofacies IV is the association of rhizomats in lacustrine limestone with biolaminates and stromatolites. They are horizontal with little to no penetration, comprising up to 100% of the visible surface area.