Mineralogical association and physical properties of sediments with palaeoclimatic implications (ODP Site 798B, Japan Sea): a comparative study from core and downhole measurements

• Published in: Marine geology 1998-09, Vol.150 (1), p.73-98
• Main Authors: Lauer-Leredde, Christine, Pezard, Philippe A., Robert, Christian, Dekeyser, Ivan
• Format: Article
• Language: English
• Subjects: clay mineralogy; downhole logs; Earth Sciences; palaeoclimates; physical properties; Sciences of the Universe; sedimentology
• ISSN: 0025-3227; 1872-6151
• DOI: 10.1016/S0025-3227(98)00035-8

The aim of our approach is to provide a reliable and continuous mineralogical 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 eight logs (bulk density, neutron porosity, natural gamma-ray, uranium, thorium and potassium concentrations, photoelectric effect and electrical resistivity) to compute the proportions of opal, quartz, clay minerals (illite, chlorite, kaolinite, smectite) and water in the sediment. Similarly, a continuous cation exchange capacity (CEC) log is derived from the natural gamma-ray (CGR). A continuous intrinsic formation factor (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 evolution (development of glaciation and of aeolian processes at 2.5–2.3 Ma), as well as new insights into climate dynamics (occurrences of short, warm excursions and of unstable periods). Periodic oscillations in relation to orbital parameters are also deduced from log-derived mineralogy.