RECONSTRUCTING THE “SLUG” MODEL OF SEQUENCE STRATIGRAPHY USING THE “DELTA BOX” PHYSICAL MODEL OF SEDIMENTATION

Following the instructions developed by the National Center for Earth surface Dynamics (NCED) and available at http://www.nced.edu/SERC.html, we built the “Delta Box” and used it to reconstruct the classic “slug” model of sequence stratigraphy for teaching purposes. Constructing the model is relatively simple and inexpensive (under $300 without a water recirculation pump). The model is small and does not take up much lab space: the tank made of clear Plexiglas is only about 1.15 m long, 0.4 m high, and 5 cm wide. The model is also fairly easy to operate. It uses a mixture of quartz sand and coal to demonstrate sedimentation patterns from a point source into a standing body of water whose depth can be easily changed.

We ran the model during one complete cycle of water-level change to demonstrate processes of sedimentary sequence development. The model successfully reproduced the “slug” model of sequence stratigraphy and all of its main components were visually easily recognized: two sequence bounding surfaces (or sequence boundaries SB1 and SB2), and the lowstand (LST), transgresive (TST) and higstand (HST) system tracts separated by the transgresive (TS) and maximum flooding (MFS) surfaces. Even though the model also works very well in producing parasequences, we were not able to discern all details of parasequence stacking patterns directly comparable to those of the theoretical “slug” model. It is possible that this aspect of the physical modeling might be improved by further experimenting with variable conditions (e.g., rates of sedimentation or water-level change). Alternatively, a longer channel might be needed to enhance sediment sorting during transport.

Overall, the delta model is an effective teaching tool, which is easy to build and fun to operate. Even though many sedimentology and stratigraphy instructors have already built their versions of the NCED's delta box, we would like to encourage others to consider constructing and using such physical models for exploring various sedimentary processes and products with their students.