Original paper

The age of the Cayo Formation, Ecuador

Bristow, C. Roger

Abstract

The age of the Cayo Formation has generally been regarded as ranging from Cenomanian to upper Senonian. The Cenomanian date has been given to the Calentura Member, which, at its type locality is of unknown stratigraphic position. The faunal evidence for the age of this member is reviewed and it is shown that its affinities are more with the Senonian. This is confirmed by radiometric dates. The Calentura Member, not being a diagnostic lithostratigraphic or faunal unit, is dropped from the Ecuadorian nomenclature. The Maastrichtian silicified argillites at the top of the Cretaceous sequence, generally known as the Guayaquil Formation, are regarded as the product of secondary silicification affecting differing levels and are relegated to member status at the top of the Cayo Formation.