Oxygen and carbon isotope stratigraphy of the Middle Miocene, Holes 805B and 806B

Abstract

Bulk carbon isotope records are an effective chemostratigraphic tool for the middle Miocene because of the large and systematic variation in first-order δ13C signals. Bulk δ13C measurements support the presence of a hiatus at 305 mbsf in Hole 805B (latest middle Miocene), provisionally located while on board ship using biostratigraphic and magnetostratigraphic events. Records at Holes 805B and 806B show the middle Miocene Monterey carbon isotope excursion although the record at Hole 806B is apparently more stratigraphically continuous. Detailed analysis of multispecies foraminiferal carbon isotope records during the middle Miocene ("Monterey excursion') segment at Hole 806B support the assertion that this carbon isotope excursion comprises mainly between-reservoir effects. The benthic δ18O data increase after 15.3 Ma, which may correspond to the mid-Miocene cooling step/ice volume increase of other authors. -from Authors