Sedimentation Rates in the Western Philippine Sea

Sedimentation rates in the western Philippine Sea have been determined on three piston cores using the excess (superscript 230)Th method. In the deep basin, the sedimentation rates as determined from two cores are 5.3 and 6.8 mm ka^(-1) at least for the past 70,000 years. Immediately before that time, a disturbed zone which is recognized at one station appears to have coincided with the onset of the last glaciation. Dating back further, the data suggest a higher sedimentation rate of 17.4mm ka^(-1). However, the data are by no means unambiguous; another interpretation suggests a slower rate (10.6mm ka(-1)) between yet another disturbed zone at greater depth and the one just mentioned. In the southwestern end of the Ryukyu Trench, the excess (superscript 230)Th activities are too low to allow a meaningful treatment with this method. The sedimentation rate is expected to be high due to the geologic environment of the trench. A value of about 13mm ka(-1) with a large uncertainty is obtained when the method is attempted. These sedimentation rates are quite consistent with those obtained in the Philippine Sea by earlier workers.