General Program Description

Sedimentology, the study of sediment and ancient sediments preserved as rock, is a significant discipline in geology. In Geology 260 (Sedimentology and Stratigraphy), students study local sedimentary rocks (limestones and sandstones) and discover that there are patterns in these rocks that were caused by tidal currents hundreds of millions of years ago when the sedimentary precursors to these rocks were deposited on the shores of an ancient tropical ocean that covered North America. When students learn about the processes that create sandstones, they can observe the Cannon River or use a water-sediment flume to create ripples in quartz sand grains under the influence of moving water. Unlike sandstones however, limestones are created by the deposition of lime (i.e., "carbonate" CaCO₃) sediment derived from the shelly remains of aquatic organisms such as clams and corals (but also including less familiar types of organisms like algae and plankton). Limestones constitute a large proportion of the sedimentary record on earth, and host much of the marine fossil record. These carbonate rocks, however, are usually non-intuitive for the sedimentology student. Many of these students have never felt the heave and pull of the daily tides or experienced a wave-swept shore. Field research in modern marine coastal environments can provide a visceral understanding of the physical processes that move and shape sediments, and can fundamentally change the learning experience for students of sedimentary geology.

San Salvador is one of the outermost (Atlantic-wards) islands in the Bahamian archipelago, and was recently battered by Hurricane Floyd. In 1492 Christopher Columbus made his landfall in the New World at San Salvador. Today the island is unusual among the Bahamian chain because of its relative lack of resort or harbor development; San Salvador retains a largely rural culture that is both safe and slow-paced.

Geologically, San Salvador has a variety of marine shoreline and shallow subtidal settings in which carbonate sediments are being created and deposited. Among these are: living and dead coral-algae reefs, active carbonate sand shoals, a muddy tidal estuary, and shallow, wave-swept inshore areas that host a variety of bottom-dwelling carbonate-secreting organisms. Importantly, San Salvador also has extensive outcrops of Pleistocene limestone, including fossil reefs and lithified carbonate sand dunes that were deposited 120 thousand years ago when sea-level was higher than it is today. This juxtaposition of the ancient and the modern provides students with the rare opportunity to study living settings in which sediments are being created and distributed by waves and currents, and then to compare those to what is preserved in the rock record. There is often a one-to-one correspondence between the modern and the ancient here, because many (but not all!) of the organisms that created the sediment in the Pleistocene are still alive and abundant in today's oceans.

San Salvador is unique among Caribbean islands in that it also has a network of undeveloped ponds whose waters range from fresh to hypersaline. These ponds host numerous species of carbonate-secreting organisms, and provide a superb natural laboratory to study the effects of habitat on lacustrine to salt-basin carbonate benthos (some of these environments may be analogous to those of Cambrian Minnesota). In short, San Salvador provides a wealth of opportunity for Carleton undergraduates to conduct field investigations in sedimentology.

The course of study for the Bahamas Program begins fall term with GEOL 361, Carbonate Sedimentology, in which students learn background on carbonate sediments and do preliminary research for projects that will be continued on San Salvador. About a week after the end of the term, students gather in Ft. Lauderdale, Florida and take a flight to San Salvador Island. While on the island they stay at the Gerace Research Center, a facility with classroom, laboratory, and living accomodations.

Field instruction will cover a variety of topics, most of which will require extensive snorkeling and water-based activities. Topics will include:
     • Common marine flora and fauna that generate carbonate sediments
     • Infaunal and epifaunal benthos
     • Ecological structure of modern marine communities
     • Shoreline and beach processes, including bedforms
     • Pleistocene eolianites and karst

Most of the field days will be spent on student research projects. Four teams of three students eeach will execute research projects designed during fall term in GEOL 361. Projects can focus on Caribbean oceanography and climatology, beach dynamics, carbonate diagenesis, or tide and estuary dynamics. On San Salvador December days are short, so most evenings (as well as foul-weather days) are spent in the laboratory and classroom. At the end of the two week stay on San Salvador students will present interim results of their projects and outling how they plan to continue their research back on campus in GEOL 362. Most projects include extensive laboratory work and/or computational or statistical analyses.