LOOKING OVER THE LATE CRETACEOUS CORDILLERA: A COMPARISON OF STABLE ISOTOPE RECORDS AND CLIMATE MODEL SIMULATIONS FROM UTAH AND NEW MEXICO WITH THOSE FROM BAJA CALIFORNIA, MEXICO

Western North America had two coastlines during the Late Cretaceous, one to the east associated with the Western Interior Seaway (WIS), and one to the west other associated with the Pacific Ocean. Between them was an area of high elevation that formed in response to subduction-related tectonics. Fluvial sediments flowing from the central highlands to the WIS extend from northern Mexico to Alaska, and preserve exceptional records of plant and animal fossils from a relatively short time interval (the late Campanian). Paleoclimatic studies based on paleobotanical and stable isotope proxies provide evidence for higher than modern temperatures and a reduced latitudinal temperature gradient along the coast of the WIS, while climate model simulations suggest highly seasonal precipitation associated with monsoonal atmospheric circulation.

What has been absent is any paleoenvironmental information for sites along the Pacific coast, to the west of the Cordillera. As a result, important question regarding the nature of temperature and precipitation patterns to the west of the highlands, and how these conditions may have influenced sedimentation patterns and local ecological patterns remain unanswered. In an effort to answer these questions, we we present carbon and oxygen isotope data from authigenic and biogenic carbonates collected from the Campanian El Gallo Formation of Baja California, Mexico. Initial results indicate that Baja was isotopically distinct from sites to the east of the Cordillera at similar latitudes (in Utah and New Mexico), and was thus characterized by different climatic conditions and perhaps vegetation. Climate model simulations also suggest differences in precipitation patterns, which may in turn relate to different styles of sedimentation between regions.

Overall the paleoenvironmental study of Baja provides an excellent point of contrast to the better-known localities along the WIS, and isotopic data and climate model simulations from both areas can ultimately be compared to records from East Asia at similar latitudes.