INTERDUNE FACIES OF THE LOWER JURASSIC GLEN CANYON GROUP SANDSTONE AND THEIR PALEONTOLOGIC POTENTIAL IN AND AROUND DINOSAUR NATIONAL MONUMENT, NORTHEASTERN UTAH

The Glen Canyon Group is well exposed within Dinosaur National Monument and in the surrounding area in northeastern Utah. It consists of hundreds of meters of massive sandstones dominated by eolian dune sequences. Interdune facies up to a few meters in thickness occur sporadically throughout the Glen Canyon but are more common and best developed in the upper third and the lower third of the section. These deposits vary somewhat with respect to grain size, bedding and other sedimentary structures. All appear to indicate deposition by water or under conditions in which the availability of water played a role. They have limited exposure and are traceable only for short distances.

Most of the interdune deposits are horizontally bedded sandstones, stained red by iron oxide, usually to a greater degree than the surrounding eolian dune sands. Often the horizontal bedding is disturbed or disrupted, possibly by some degree of trampling. Some interdune sands are heavily carbonate cemented, up to two meters thick, and can be traced more than 100 meters in the canyon walls. In places, the carbonate is finely laminated, suggesting algal structures, and some cross sectional geometries resemble spring seeps described elsewhere in Glen Canyon carbonates.

Most interdune deposits are unfossiliferous, but all fossils found in the Glen Canyon in this area have been within the interdune facies. The most abundant and widespread fossils are vertebrate tracks and trackways, preserved as undertracks, sometimes in the hundreds, at several localities, near the top and near the bottom of the section. At one locality numerous more or less tubular structures, up to 30 cm in diameter, subparallel to and cutting across bedding may represent termite nests. A few small, high-spired, freshwater gastropods have been found in the carbonate at one locality. Sphenophyte plant compression fossils have been collected from one site. Another locality is a bone bed with at least several dozen disarticulated, theropod dinosaur bones. This is the northernmost reported occurrence of vertebrate body fossils in the Glen Canyon.