Middle and Late Pliocene Diatom Datum Levels from the Central Pacific

Abstract

Sixteen diatom datum levels from the Middle and Late Pliocene of the central Pacific are ranked and related to the paleomagnetic reversal record and the oxygen isotope record. The datum levels and their positions relative to the paleomagnetic record are as follows: (1) first appearance of Thalassiosira convexa in the upper part of the Gilbert; (2) disappearance of T. convexa in the lower part of the Gauss; (3) recurrence of T. convexa in the Mammoth Event of the Gauss; (4) first appearance of Rhizosolenia praebergonii in the normal event between the Mammoth and Kaena Events; (5) last appearance of Nitzschia jouseae in the upper part of the Gauss; (6) first appearance of R. praebergonii var. robusta in the lower part of the Matuyama; (7) recurrence of Coscinodiscus nodulifer var. cyclopus in the lower part of the Matuyama; (8 and 9) last appearance of T. convexa and T. convexa var. aspinosa in the lower part of the Matuyama; (10) last appearance of C. nodulifer var. cyclopus; (11 ) change in dominance between R. praebergonii and R. praebergonii var. robusta below the Olduvai Event; (1 2) recurrence of C. nodulifer var. cyclopus just below the Olduvai Event; (13) final occurrence of C. nodulifer var. cyclopus just below the Olduvai Event; (14) final occurrence of R. praebergonii in the lower part of the Olduvai; (15) first occurrence of Pseudoeunotia doliolus in the mid-part of the Olduvai Event; (16) final occurrence of R. praebergonii var. robusta just above the Olduvai Event. When these data are related to the oxygen isotope record it becomes apparent that climatic fluctuations are an important arbiter of diatom first and last appearances. A new variety, Rhizosolenia praebergonii var. robusta, is named. Middle and Late Pliocene diatom datum levels from the central Pacific