Strontium isotope stratigraphy of samples from Holes 1183A and 1186A combined with biostratigraphic data provide a good stratigraphic framework for the mid- to Late Cretaceous sections recovered during Leg 192. Sr isotope stratigraphy suggests that the section recovered in Hole 1183A consists of an upper lower Aptian to lower Albian interval separated by an unconformity from a Santonian interval that unconformably underlies a thick upper Campanian to upper Maastrichtian interval. The section recovered at the top of Hole 1186A also consists of a relatively expanded upper Campanian to upper Maastrichtian interval.