| Abstract: | In any comparison between the changes of sea-level in two regions, one has to distinguish two different aspects: (1) the dates of the highest and lowest sea-levels, i,e., the peaks of transgression and the troughs of regression; in EXXON terms, the time of eustatic stillstand in the highstand systems tract and the lowstand wedge in the lowstand systems tract; and (2) the extent of transgressions and regressions. The first is largely or entirely controlled by eustasy; the second commonly has a strong local tectonic factor.
Aspect 1. Eustatic control means that one can recognize quite modest sea-level lows in both North America and Europe, e.g., Rouen no. 1 Hardground in the Middle Cenomanian of Normandy is represented by the erosion surface beneath the Thatcher Limestone in Colorado. Similarly, the Campanian-Maastrichtian boundary in the Western Interior can be fixed by its distance above the eustatic high in the Bearpaw Shale in Montana.
Aspect 2. The general fall in sea-level in Wyoming-Montana-Alberta during the Late Campanian-Early Maastrichtian was caused by Laramide uplift. The fall in sea-level in this region of North America coincides with some of the highest Cretaceous sea-levels in northwest Europe when the sea transgressed on to older rocks in Ireland, Belgium and Sweden. At the same time the deepest water Cretaceous facies were being deposited in northern Mississippi and Tennessee against the south-western flank of the Appalachians. |