MAKING SEDIMENTARY STRUCTURES IN THE LAB: A DISCOVERY-BASED EXERCISE FOR UNDERGRADUATE SEDIMENTARY GEOLOGY COURSES

Most undergraduate courses in sedimentary geology include lecture and laboratory sections on sedimentary structures. Traditional lab exercises focus on identifying structures in rocks and interpreting the conditions under which they formed. Some well-equipped geology departments also call for students to observe the formation of bedforms in a flume. An alternate approach is a simple and inexpensive laboratory exercise in which students attempt to make a variety of sedimentary structures in various sediments. First, students are briefly introduced to sedimentary structures with photographs and an explanation of how some common ones form. Then, a visit to our biology department's herpetology lab allows students to see how some organic sedimentary structures are made. Then, students, in teams of two or three, visit six stations set up in the sed./strat. lab room. The first three stations are focused on inorganic sedimentary structures. For example, one station includes three aquarium tanks, each with shallow water and mud, sand, or gravel. Students are asked to try to make ripple marks in each tank and note their techniques and observations. The last three stations involve organic sedimentary structures. One station contains small trays of dry and wet mud, sand, and gravel and gastropods. Students experiment to see in which sediment the gastropods leave the best trails. This lab shows students how factors such as sediment size, presence of water, and other conditions play a role in the formation of various sedimentary structures. In addition, students enjoy the hands-on approach, freedom to experiment, and critical thinking involved. A follow-up lab exercise follows the traditional format, asking students to identify and interpret sedimentary structures in photographs and in ancient rocks. Students seem to better identify sedimentary structures and interpret past depositional conditions after performing this exercise in making sedimentary structures.