STRATIGRAPHIC RECORD OF MIDDLE CAMPANIAN SEVIER-LARAMIDE TECTONIC AND CLIMATIC TRANSITION, SOUTHERN CORDILLERAN FORELAND BASIN AND SOUTHWESTERN LARAMIDE PROVINCE
Lithic sandstones of the overlying Kaiparowits Formation (~76-74 Ma) containing Mesoproterozoic and Mesozoic zircons were derived from the Mogollon highlands and arc terranes to the south and deposited in a Laramide basin formed during early partitioning of the foreland. Contemporary intermontane basins near the US-Mexico border in SE Arizona and SW New Mexico accumulated thick lacustrine deposits (Fort Crittenden and Ringbone formations) and attest to onset of significant topographic relief by late middle Campanian time.
Stratigraphic patterns indicate not only a shift from foreland basin to broken foreland but also waning influence of monsoonal precipitation in the Western Interior. We postulate that regional precipitation patterns which developed upon connection of the Gulf of Mexico and interior seaway near the end of Early Cretaceous time were altered by newly-formed southwestern Laramide uplifts, such that monsoonal moisture, previously delivered to Utah by north-flowing summertime air masses and backstopped by eastward-advancing thrust-belt topography, was instead partially captured in Laramide intermontane basins of the Southwest.