BIOFABRICS OF THE LATE DEVONIAN GUILMETTE FORMATION, GREAT BASIN REGION OF THE WESTERN UNITED STATES

The Late Devonian Guilmette Formation is a Frasnian aged unit that crops out in the Great Basin region of central and eastern Nevada and western Utah. The Guilmette limestones reflect deposition in a carbonate ramp setting, and include material deposited in the fore-reef, reef, and back-reef environments. While the sedimentology and stratigraphy of this formation has been described previously in detail, the biofabrics have not been examined. Biofabric studies offer an opportunity to gather ecologic, paleontologic, sedimentologic, and stratigraphic data that is not readily available through other means and can be utilized to determine community structure, provide a proxy for community dominants and gross abundance, and indicate taphonomic factors.

Guilmette limestones include all three types of biofabrics: constructional, depositional, and post-depositional. Constructional fabrics are formed in-situ by the members of a community, and are represented in the Devonian limestones by massive reef systems dominated by a large variety of stromatoporoid forms, with subordinate colonial rugose and tabulate corals. These fabrics are laterally continuous on a kilometer scale, and may exceed 20 meters in thickness. Depositional fabrics are created by the accumulation of skeletal or shell material, and are represented by several types of beds, including brachiopod, gastropod, and solitary rugose coral beds. These are generally polytaxic in composition, but are usually dominated by one group. These fabrics range from centimeters to a few meters in thickness, and are laterally continuous at the outcrop scale. Post-depositional biofabrics are created through animal sediment interactions and are represented in the Devonian by a variety of ichnofabrics, both simple and complex. These fabrics are laterally continuous at the outcrop scale, and range from a few centimeters to a few meters in thickness.

Analysis of the Guilmette biofabrics provides an excellent opportunity to examine the complex structure and relationships of shallow marine communities just prior to one of the greatest mass extinctions in the Phanerozoic history of life.