MINERALOGICAL ASSOCIATION AND PHYSICAL-PROPERTIES OF SEDIMENTS WITH PALEOCLIMATIC IMPLICATIONS (ODP SITE 798B, JAPAN SEA) - A COMPARATIVE-STUDY FROM CORE AND DOWNHOLE MEASUREMENTS

The aim of our approach is to provide a reliable and continuous minera logical description derived from downhole logs and constrained by core measurements. This study focuses on a series of 742,000 year drilled during Ocean Drilling Program (ODP) Leg 128 at Site 798 on Oki Ridge ( Japan Sea). A linear matrix algebraic procedure has been applied to ei ght logs (bulk density, neutron porosity, natural gamma-ray, uranium, thorium and potassium concentrations, photoelectric effect and electri cal resistivity) to compute the proportions of opal, quartz, clay mine rals (illite, chlorite, kaolinite, smectite) and water in the sediment . Similarly, a continuous cation exchange capacity (CEC) log is derive d from the natural gamma-ray (CGR). A continuous intrinsic formation f actor (FF), which depends on the structure of the pore space, is then computed from the CEC. The log-derived mineralogy and CEC are compared to laboratory analysis on samples. High-resolution mineralogy derived from the logs allows recognition of well-known episodes of climate ev olution (development of glaciation and of aeolian processes at 2.5-2.3 Ma), as well as new insights into climate dynamics (occurrences of sh ort, warm excursions and of unstable periods). Periodic oscillations i n relation to orbital parameters are also deduced from log-derived min eralogy. (C) 1998 Elsevier Science B.V. All rights reserved.