Strontium-isotope stratigraphy from Sites 918 and 919

Abstract

A detailed Sr-isotope stratigraphy has been established for the Cenozoic sediments drilled during Leg 152. The Sr-isotope record is distributed in several intervals due to reworking of foraminifers and reaction between pore waters and carbonate. A Sr-isotope chronology based on well-preserved samples has been established for the Neogene sediments drilled, while diagenesis and low abundance of carbonate fossils hindered age determination in older sediments. Ages have been calculated by comparing our results with previously published, well-dated 87Sr/86Sr records. At Site 918, which contains one of the most complete records of glaciation in the North Atlantic, more or less continuous Sr-isotope dating was possible back to 22.6 ± 0.8 Ma (early Miocene). Site 919 was found to contain Pleistocene sediment no older than 1.0 Ma. The sedimentation rate at the two studied sites is about 11.0 cm/k.y. in the Pliocene-Pleiostocene part of the sequence (2.9 Ma until today). In the older sediment deposited between 22.5 and 10.4 Ma, the sedimentation rate has been calculated to 2.4 cm/ky. The higher sedimentation rate in the Pliocene-Pleistocene sediment probably reflects the buildup of glaciers in southern Greenland followed by increasing amounts of ice-rafted detritus into the Greenland Sea sediments.