MAGNETOSTRATIGRAPHY AND TEPHROCHRONOLOGY OF THE UPPER QUATERNARY SEDIMENTS IN THE OKHOTSK SEA: IMPLICATION OF TERRIGENOUS, VOLCANOGENIC AND BIOGENIC MATTER SUPPLY

Abstract

Seven lithological units, alternating between horizons enriched in biogenic opal (diatoms) and carbonate (foraminifera) and units composed largely of terrigenous sediment with very low biogenic admixture, were distinguished in a series of Late Quaternary sediment cores from the Sea of Okhotsk. Sediments were characterised using on-board visual description, smear-slides analyses, grain-size composition and magnetic susceptibility (MS) records. Five tephra marker layers, identified as Ko, TR, K2, K3 and K4, were distinguished using petrological, mineralogical and geochemical analyses. Age models were developed by comparing lithological units, tephra stratigraphy and MS records with oxygen isotope curves and with records of biogenic CaCO3, opal content, and sediment grain-size composition in three AMS radiocarbon dated Okhotsk cores. This chronological framework allowed us to investigate climate control over the sedimentation regime and productivity, and to clarify the formation times of the lithological and tephra units.