Glauconite dates from the Upper Jurassic and Lower Cretaceous

Abstract

Summary Few dates are available from stratigraphically well-documented igneous materials of late Jurassic and early Cretaceous age. Glauconite dates therefore have a special interest despite the geochronological limitations of the mineral. Evidence from the Albian and Cenomanian, moreover, shows that some Mesozoic glauconites give results only slightly lower than the probable correct dates. New glauconite determinations from sedimentary rocks near the Jurassic–Cretaceous boundary include four English dates close to 130 m.y. Those from Greenland and Russia are lower, ranging between 107 and 117 m.y. Published information concerning comparable stratigraphical horizons also includes low values and several near 130 m.y. Our results suggest that the Jurassic–Cretaceous boundary (sensu borealis) is a little older than 130 m.y. They are thus consistent with the figure of 135 m.y. assigned to the boundary by Holmes and Kulp.