Variations in Trace Element Contents and Isotopic Compositions of Lower Cretaceous Carbonates from the Galicia Margin (ODP Leg 103): Reconstruction of the Paleochemistry of the Early Cretaceous Ocean

Abstract

Trace element contents (Sr, Mg, Mn, and Fe) and the composition of oxygen and carbon isotopes show that late bur­ ial diagenesis did not play an important role in pelagic carbonate chemistry in the bulk carbonates recovered from Holes 638B, 638C, and 641C (except for anoxic pore-water diagenesis in Valanginian sediments). The evolution of these differ­ ent geochemical markers documents the importance and global extent of the Barremian ocean chemistry crisis. A recon­ struction of paleoceanographic and climatic conditions during the Early Cretaceous is proposed. Sea level rose eustatically from the early Hauterivian to early Albian, but a rapid down and up fluctuation occurred during the Barremian. Soluble supply from the continent decreased during the Valanginian-early Hauterivian while oceanic hydrothermal sup­ ply increased. The climate cooled slightly during the Hauterivian, rapidly warmed during the Barremian, and cooled again during the Aptian.