FUNCTIONAL ECOLOGY COMPARISONS BETWEEN CRETACEOUS BLACK HILLS AND MODERN GULF OF MEXICO COLD-SEEP COMMUNITIES

Tepee buttes are fossil hydrocarbon cold-seeps from the Cretaceous Western Interior Seaway (WIS) which supported chemosynthetic-based communities. Modern cold-seeps are viewed as analogs for tepee buttes despite significant taxonomic differences. In the Black Hills tepee buttes, lucinids are the most common and dominant taxon present, however lucinids are not always present and rarely the dominant taxon in Gulf of Mexico (GM) cold-seep communities. In addition, the diversification of fish species and extinction of taxa such as ammonites makes these systems taxonomically distinct.

I assign modern seep taxa with hardparts likely to preserve in the fossil record to ecological guilds and compare to WIS seep guilds to test the hypothesis that the communities are similar in their ecology despite taxonomic differences. This study includes 20+ tepee buttes near Newell, SD from the Campanian, 15 tepee collections from the SDSM&T Museum of Geology spanning the Black Hills area, and 26 modern GM cold-seeps from Bush Hill and Green Canyon. If modern seeps are analogous in their functional ecology and community structure to WIS tepees it would be expected that these two seep systems have similar spatial heterogeneity at multiple geographic scales and similar guild diversity and evenness at individual seeps.

Preliminary data suggest that the spatial heterogeneity of GM cold-seeps are greater than those of WIS tepee buttes at the local (less than 10 km) scale and at the regional (170 km) scale. These results suggest that hydrocarbon seep communities of the WIS had a less diverse metacommunity to recruit from. WIS tepees also have less even assemblages than GM cold-seep communities, indicating Cretaceous seeps were more often occupied by a few dominants than modern seeps. Thus, these seep communities are distinct in their community structures and modern seeps may not be precise ecological analogs for Cretaceous communities.