Determining Sedimentary Sources and Environments: Applications in a Secondary Science Classroom

Sandstones record conditions under which sediment was deposited in the past. These conditions reveal the environment of ancient landscapes. Key indicators of these conditions include size, shape, and degree of sorting of the sediment. Sediment composition (i.e., the chemical makeup of the sand grains) can reveal sediment sources, and bedforms (i.e., the structures of sedimentary layers) provide additional clues about environment. We collected data on bedform structure and grain size from exposures of Sego Sandstone in western Colorado. In the lab, we quantified degree of sorting and mineral composition of sediment via microscopy of samples collected in the field. As expected, based on previous studies, our analysis shows that the Sego was deposited in a tidally influenced environment. Our study indicates that the source of the sand was quartz-rich. This suggests the Sego was derived from the Sevier Orogeny, a mountain range that was being uplifted nearby during the time of deposition. We developed an inquiry-based study of sedimentary environments for 8th-9th grade students. In the classroom, students learned how sediments and bedforms indicate depositional environments. In the field, they measured characteristics of a Laramie-area sedimentary outcrop. Students analyzed data and synthesized results in the context of classroom exercises.