TEACHING SEDIMENTOLOGICAL AND STRATIGRAPHIC CONCEPTS USING OUTCROPS FROM THE HARTFORD BASIN, CONNECTICUT

Outcrops are traditionally used to illustrate concepts that are first taught in the classroom. However, certain outcrops can be successfully used as the primary tool for teaching many sedimentological and stratigraphic topics that are difficult to illustrate in the classroom. For example, outcrops of clastic sedimentary rocks from the Portland Formation (Lower Jurassic) in the Hartford Basin are ideal for teaching the concepts of lateral facies change, vertical trends in facies, and tectonic/climatic controls on sedimentation.

Lateral facies changes typically occur over distances that exceed the length of most outcrops in northeastern U.S., making this concept difficult for introductory students to comprehend. To illustrate lateral facies changes, we use an outcrop of the Portland Formation that contains a dramatic lateral change from sandstone to conglomerate over a distance of about 50 meters, as a major syndepositional normal fault is approached. By measuring and correlating several short, closely-spaced stratigraphic sections, students easily recognize gradual lateral changes in lithology. A nearby outcrop of gneiss in the footwall of the fault can be used to link the facies change to tectonic depositional controls. We use a second outcrop to illustrate vertical stacking of facies and interpretation of depositional controls. This outcrop, which is located adjacent to the same normal fault as the first outcrop, contains lacustrine siltstone and sandstone that is interbedded with very coarse alluvial fan conglomerate. These dramatically contrasting facies are ideal for teaching introductory students how to identify cyclicity in sedimentary rock successions, and how to interpret climatic (humid versus arid climate) and tectonic (changes in sediment supply) controls on sedimentation. Furthermore, erosional features in an adjacent sand pit pond provide a scaled-down analog for illustrating the concepts of fluvial base level, erosion, and deposition.

Exercises are used at each outcrop to integrate stratigraphic section measurement, lithological description, and stratigraphic correlation. These exercises can be written at different levels to introduce high school through advanced undergraduate students to many concepts that are difficult to illustrate in classroom settings.