TERRAPUB Journal of Oceanography

Journal of Oceanography, Vol. 53 (No. 1), pp. 1-7, 1997

Age Determination of Marine Sediments in the Western North Pacific by Aspartic Acid Chronology

Naomi Harada1, Nobuhiko Handa2, Tadamichi Oba3, Hiromi Matsuoka4, Katsunori Kimoto5 and Masashi Kusakabe1

1Japan Marine Science and Technology Center, 2-15 Natsushima-cho, Yokosuka 237, Japan
2Institute for Hydrospheric-Atmospheric Sciences, Nagoya Univ., Furo-cho, Chikusa-ku, Nagoya 464-01, Japan
3Graduate School of Environmental Earth Science, Hokkaido Univ., Kita 10, Nishi 5, Kita-ku, Sapporo 060, Japan
4Department of Geology, Faculty of Science, Kochi Univ., 2-5-1 Akebono-cho, Kouchi 950-21, Japan
5Ocean Research Institute, Univ. of Tokyo, 1-15-1 Minamidai, Nakano-ku, Tokyo 164, Japan

(Received 10 November 1995; in revised form 11 April 1996; accepted 1 May 1996)

Abstract: The ages of fossil planktonic foraminifera, Pulleniatina obliquiloculata, in sediments (core 3bPC) from the western North Pacific were determined by aspartic acid chronology, which uses the racemization reaction rate constant of aspartic acid (kAsp). Aspartic acid racemization-based ages (Asp ages) ranged from 7,600 yrBP at the surface, to 307,000 yrBP at a depth of 352.9 cm in the sediments. This sediment core was also dated by the glacial-interglacial fluctuation of d18O chronology, and the ages determined by both chronologies were compared. The ages derived from aspartic acid chronology and d18O stratigraphy were more or less consistent, but there appeared to be some differences in age estimates between these two dating methods at some depths within the core. In the core top sediments, the likely cause for the age discrepancy could be the loss of the surface sediment during sampling of the core. At depths of 66.3 and 139 cm within the core, Asp ages indicated reduced sedimentation rates during ca. 60,000-80,000 yrBP and ca. 140,000-190,000 yrBP. The maximum age differences in both chronologies are 33,000 yr and 46,600 yr during each of these periods. These anomalous reductions in sedimentation rates occurring during these periods could possibly be related to some geological events, such as an increased dissolution effect of the calcium carbonate in the western North Pacific. Another possible reason for these age differences could be the unreliability in d18O ages of core 3bPC as they were estimated by d18O ages of another core, 3aPC.

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