Nannofossil Biochronology of Tephra Layers in Core MD972143, Benham Rise, Western Philippine Sea


During the IMAGES III-IPHIS-Leg II Cruise in June 1997, a long piston core, MD972143 (15 degree 52.62°N, 124 degree 38.96°E, water depth 2989m), was raised from Benham Rise, east of Luzon in the western Philippine Sea. The core measures 38 m in length, consisting mainly of calcareous ooze are 21 volcanic layers. Four major age-diagnostic nannofossil datum levels were recognized: the first appearance datum (FAD) of Emiliania huxleyi (0.27 Ma) at 365 cm, the last appearance datum (LAD) of Pseudoemiliania lacunose (0.46 Ma) at 1105 cm, the LAD of Calcidisus macintyrei (1.59 Ma) at 2510 cm and the LAD of Discoaster broweri (1.95 Ma) at 2970 cm. A turbidity layer at 33 to 34 m, consisting mainly of foraminiferal sands, appears to truncate the sequence and result in a hiatus. The age of the lowermost part of the core (34-38 m) was constrained as being older than 2.59 Ma (the last appearance of D. surculus) and younger than 2.78 Ma (the last appearance of D. tamalis). Based upon our preliminary nannofossil biochronology, these tephra layers were deposited at 2.65 Ma 9 (?), 2.1 Ma, 1.9 Ma, 1.7 ¡V 1.8 Ma, 1.5 Ma, 1.35 Ma, 0.9 Ma, 0.8 Ma and 0.5 ¡V 0.3 Ma, respectively.

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