PALEOCOMMUNITY STRUCTURE IN CRETACEOUS METHANE SEEPS: COMPARING NORTH AMERICAN EPEIRIC SEA COMMUNITIES TO THOSE BORDERING THE GLOBAL OCEAN

Methane seeps in the Cretaceous Western Interior Seaway (WIS) occurred in relatively shallow and low circulation oceanographic conditions not typical for modern or other fossil methane seeps. This project compares methane seep paleocommunities within the WIS to contemporaneous methane seeps at continental shelf depths in the eastern Pacific based on the ecological roles represented in fossil assemblages. WIS seeps occur at estimated paleobathymetric depths of less than 200 meters and are most abundant in the upper Cretaceous, whereas eastern Pacific seeps are found at estimated depths of 200 to 500 meters and are most abundant in the lower and middle Cretaceous. Faunal composition is classified using a 3D ecospace matrix to identify modes of life present in seep paleocommunities and test for significant differences between regions. Preliminary results using a MANOVA test show a statistically significant difference in ecospace composition between WIS and eastern Pacific seeps. In addition, there is an observable difference in the most abundant modes of life found at WIS seeps and eastern Pacific seeps. The most abundant modes of life in WIS seeps are shallow infaunal suspension feeding or chemosymbiotic, represented by bivalves such as Nymphalucina, and free-swimming ammonites which are either suspension feeding or predatory. The most abundant modes of life for eastern Pacific seeps are epifaunal grazers and suspension feeders, represented by gastropods such as Hokkaidoconcha. Further analysis will use the fossil food web model Cascading Extinctions on Graphs (CEG) to integrate seep faunas within the wider ecosystem of their biogeographic region and compare vulnerability to secondary extinction. The results of this study will indicate whether WIS seep paleocommunities are distinct from broadly contemporaneous oceanic seeps in the adjacent region of the global ocean.