PRELIMINARY STUDY ON THE ICHNOPEDOFACIES OF THE MIXED CARBONATE-SILICICLASTIC, LOWER PERMIAN HALGAITO FORMATION, GOOSENECKS, SOUTHEASTERN UTAH

This study focuses on the Lower Permian Halgaito Formation that contains a succession of thinly interbedded, siliciclastic and carbonate deposits, and is time-equivalent with the Lower Cutler Group. Mixed carbonate-siliciclastic systems are common in the geologic record, but few studies have focused on them. Trace fossils of the Halgaito Formation are poorly studied and this research provides new data on the diversity, distribution, abundance, and ichnofossil-pedofacies-facies relationships. This study tests whether trace-fossil assemblages vary predictably with environmental conditions through a combined ichnopedologic approach, which looks at both trace-fossil assemblages and paleosol features to accurately interpret depositional, eustatic sea-level, and paleoclimatic histories of the formation. In general, marine trace fossils are well studied. Marine organisms react to a variety of marine conditions (i.e. medium, nutrients content, salinity, turbidity, temperature, and oxygen content) and suites of trace fossils can be used to interpret depositional environment. Trace fossils are also common in continental settings, and are created by organisms that are reacting to a suite of environmental factors different from marine organisms, including soil moisture and saturation, temperature, seasonality, and precipitation. Fieldwork consisted of measuring three stratigraphic sections for vertical and lateral correlations, which were logged spatially with GPS. Beds were described sedimentologically and lithologically and assigned to lithofacies. Photographic mosaics were be used to illustrate stratal architecture. Paleosols were trenched to examine morphology, remnant sedimentary structures, and ichnofossil assemblages, and classified using the U.S. Soil Taxonomic System. Grain-size fractionation was estimated in the field. The depositional history has been subdivided into three distinct successions. This study aims to better understand these complex systems through spatial and temporal changes in organism behavior. Understanding the depositional history of mixed carbonate and siliciclastic systems will help predict vertical and lateral facies changes and creation of models for larger scale regional architecture, and for identifying targets for oil and gas production.