Carbon-Isotope Stratigraphy and Paleoceanographic Significance of the Lower Cretaceous Shallow-Water Carbonates of Resolution Guyot, Mid-Pacific Mountains

Abstract

Matching of Lower Cretaceous carbon-isotope curves derived from pelagic sediments of the Tethyan-Atlantic sector with that obtained from peritidal carbonates of Resolution Guyot (Site 866, Mid-Pacific Mountains) provides constraints in positioning the Hauterivian/Barremian, Barremian/Aptian, and Aptian/Albian stage boundaries. A negative excursion in the earliest Barremian of the reference sections suggests that the Hauterivian/Barremian boundary on Resolution Guyot should lie in the interval 1425 to 1500 mbsf. A major positive isotopic excursion, whose onset is positioned just below the base of a major oolitic sand package, is ascribed to the blowi Zone (late early Aptian), a time of regional deep-marine organic-carbon burial (Selli Level) in the Pacific, Atlantic, and European regions. A finely laminated organic-carbon-rich level (14.2% total organic carbon) in the shallow-water packstone-wackestones is exactly coincident with the beginning of the isotopic excursion and can be considered an equivalent to the Selli Level deposited in water of very modest depth. The Barremian/Aptian stage boundary must be located below strata attributed to the blowi Zone, and should lie close to 900 mbsf. Decay of the excursion is complete by about 500 mbsf, a level which should be near to the Aptian/Albian boundary.