By Tom Rothfus

The 2005 Spring Break field course, which was led by Professors Susan Kidwell and Michael LaBarbera, focused on modern carbonate environments—although the surrounding geology facilitated some minor excursions into the world of volcanics. Following a quarter of student-led presentations covering the geologic history and physical setting of the Gulf of California, the production of carbonate sediments, and some core concepts in sedimentology, a group of 28 students, faculty, and family headed to the Sonoran Desert and the Gulf of California.

The field portion of the course began with a short drive from Tucson, AZ to Organ Pipe Cactus National Monument (OPCNM) located along the Arizona-Mexico border. The group spent two days examining the very interesting though understudied volcanic flow deposits of the area combined with some complicating structural geology. While at OPCNM, student-led presentations on the biology of large cacti and the environmental concerns associated with resource management in an international border zone served to guide some discussion. The beautiful colors of the wildflowers in full bloom complemented the wonderful geology of OPCNM, thanks to recent rains in the area.

From OPCNM the group headed south to the Intercultural Center for the Study of Deserts and Oceans (CEDO), located in Puerto Peñasco, Mexico on the northeastern portion of the Gulf of California. While at CEDO the group visited the extensive tidal flats of Cholla Bay, a cooperative aquaculture farm located in a local estuary, and the rocky tide pools on the shore just outside CEDO’s back door. Students conducted two separate projects, either solo or as pairs, examining aspects of the interaction of sedimentology and biology over space and time. These projects (a list of titles appears below) were developed independently by the students with consultation from Professors Kidwell and LaBarbera, and TA Tom Rothfus. Topics ranged from a sediment grain size analysis spanning the inner-, middle-, and outer-flat, to examination of the relationship between bivalve species abundance and biomass in death assemblages, to current orientation of gastropods and ripple formation. Each project was performed over two days, culminating in project presentations on the evening of the second day. Interspersed in the group’s time at CEDO were additional student-led presentations, covering topics such as negative estuarine environments and the effectiveness of marine reserves. There was also a one-day excursion to visit more volcanic rocks at the Pinacate Biosphere Reserve, including numerous cinder cones and the impressive Crater Elegante.

Project Titles from Cholla Bay excursion (order of authorship is alphabetical)

Session 1

• Is the Orientation of Bivalve Shells Indicative of Current Direction on Tidal Flats? Steve Brusatte and Nicole Lunning
• Changes in Ripple Dimensions Across the Tidal Flat, Lindsey Oliver and Heather Rosenfeld
• Horizontal and Vertical Variations in Shell Assemblages from the Tidal Flats of Bahia de Cholla, Nick Heavens
• Characterization of a Vegetative Gradient in the Littoral Zone at Cholla Bay, Andrew Leslie
• Ray Disturbance as a Driver of Sediment Mixing in Cholla Bay, Ole Shelton
• Encrusting Patterns on Hermit Crab Shells, Carl Simpson
• Destruction of Shells, Shannon Loomis and Alison Wendlandt
• Relative Abundance of Foraminifera and Ostracodes in Recent Death Assemblages, Erin Atkinson and Ayla Pamukcu
• Foraminifera Species Abundance: Onshore to Offshore Zonation, Leif Appanaitis and Roger Simon
• Relationships Bivalve Species Abundance and Biomass in Recent Death Assemblages, Erin Grey and Paul Harnik
• Live/Dead Fidelity of the Scaling Relationship Between Body Size and Density, Mark Novak and Becca Terry
• Microbial Mats in the Mid Flat and their Effect on Sediment Cementation, Thomas Bauska and Gwen Williams
• Bill and Bob Excellent Journey: Sedimentology in the Intertitle, but not in the Subtitle, Guilherme Gualda and Bjarte Hannisdal

Session 2

• Bird Feeding as a Contributor to Bioturbation, Lindsey Oliver and Alison Wendlandt
• Vertebrate Taphonomy of Tidal Flats, Steve Brusatte, Katie LaBarbera, and Gwen Williams
• Transportation of Hermitted Versus Empty Gastropod Shells in the Intertidal, Leif Appanaitis
• Turnover of Ocypode Occidentalis Burrows in Cholla Bay and its Implications for Sediment Re-Working, Erin Grey
• Physical Controls on the Oxygenation of Sediments on the Tidal Flats of Bahia de Cholla, Nick Heavens and Roger Simon
• Survey of Redox Layer Depth in an Estuarine Environment, Andrew Leslie and Ole Shelton
• Stratigraphy of Wash over Fans, Nicole Lunning and Heather Rosenfeld
• Rates of Sediment Removal in Rocky Tide Pools: Assessing the Role of Tide Pool Geometry, Paul Harnik and Mark Novak
• Shell Transport in the Mid Flat as a Function of Channel Influence over a Tidal Cycle, Thomas Bauska and Shannon Loomis
• Longshore Drift as a Mechanism for Transporting Sediment Grains, Erin Atkinson and Ayla Pamukcu
• The Concordance of Current Indicators: Snails Versus Ripples, Carl Simpson and Becca Terry
• The Talented Mr. Ripple: Analysis of Empirical Dot-a, Guilherme Gualda and Bjarte Hannisdal