ALBIAN-TURONIAN FLOODING PROCESSES, TIMING AND RATES IN THE U.S. WESTERN INTERIOR CRETACEOUS SEAWAY

A high-resolution geologic time scale for the U.S. Western Interior (WI) was constructed by graphic correlation of nearly 200 global sections and more than 3400 taxa, bentonites and geologic event markers. This Cretaceous chronostratigraphic database calibrates the nine major transgressive-regressive (T-R) cycles to standard stage definitions and precise numerical ages. Paleogeographic maps of nine time intervals from Middle Albian to Late Turonian document the distance of shoreline transgression associated with flooding events. The ages of transgressive deposits above these flooding contacts are measured by graphic correlation of key sections from Fort Worth to Kansas and to southwestern Colorado-northwestern New Mexico. Early Late Albian and Albian-Cenomanian floodings were faster than intervening Late Albian floodings. Flooding rates decreased from 2.75 km/kyr to 0.46 km/kyr as distances increased from 200 to 2200 km.

Possible processes that drove repeated flooding of the Western Interior Seaway were Cordilleran tectonics, epeirogenic flexure, increased seafloor spreading rates producing younger Cretaceous seafloor, and large pulses of oceanic crustal production resulting in longer mid-ocean ridges. Long-term transgressive-regressive cycles (T-R) in the Western Interior correlate partly with sea floor spreading rates. Major Middle to early Late Albian, Cenomanian-Turonian, and Campanian Sea floor spreading events correlate with marine encroachment T-R cycles 5, 6, and 9 into the U.S. Western Interior. However T-R cycles 7 and 8 match younger slower spreading rates. Seaway expansion was driven by sea floor processes and sediment accumulation rates were modulated by Cordilleran tectonics and Cretaceous climate change.