HIATUSES ON VORING PLATEAU - SEDIMENTARY GAPS OR PRESERVATION ARTIFACTS

The sediments recovered on ODP Leg 104 have been reported to be charac terized by hiatuses. The hiatuses were defined by biostratigraphy and were believed to be caused by erosion related to temporary changes of bottom current composition and velocity. They have been associated wit h major paleoenvironmental changes, reorganization of global deep wate r production, and increased bottom water flows. Because of the importa nce of hiatuses for ongoing research, we decided to closely investigat e the sedimentation history for the most significant Pliocene and Mioc ene biostratigraphic hiatuses by sedimentologic and geochemical means. The sedimentologic studies include clay mineral distributions, grain size data, and organic carbon concentrations. The geochemical studies include determination of Sr-87/86 ratios, Be-10 and Ir concentrations. The results of the sedimentologic studies suggest either that paleoen vironmental changes associated with hiatuses are not represented in th e preserved sediments, or that the hiatuses are an artifact of interpr etation of the biostratigraphic data. Strontium isotopes indicate cont inuous sedimentation for the interval investigated at Site 642, an int erpretation confirmed by the steady decline in Be-10. Sr-87/86 ratios in the interval from above and below proposed hiatuses H 2.2/2.3 and H 2.1/2.2 at Site 643 display stronger changes with depth than expected by steady sedimentation. Ir data for this same interval indicate reduc ed sedimentation rates. Combining both, sedimentologic and geochemical evidence, the proposed hiatuses could not be confirmed and may repres ent preservation artifacts. (C) 1998 Elsevier Science B.V.