26. PLIOCENE DISCOASTER ABUNDANCE VARIATIONS, DEEP SEA DRILLING PROJECT

• Main Authors: Site Biochronology, Paleoenvironmental Implications, Jan Backman
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Subjects: Pacific; North Atlantic
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.605.5204; http://www.deepseadrilling.org/94/volume/dsdp94pt2_26.pdf

Abundance variations of six Pliocene species of the calcareous nannofossil genus Discoaster have been determined for the time interval between 1.9 and 3.6 Ma at DSDP Site 606, using a sample interval of 30 cm (<9 kyr.). These quan-titative data contain information which can be interpreted in terms of both biochronology and paleoclimatic develop-ment. The following datums have been examined: D. brouweri (extinction at 1.89 Ma), D. triradiatus (extinction at 1.89 Ma), D. triradiatus (peak abundance begins at 2.07 Ma), D. pentaradiatus (extinction between 2.33 and 2.43 Ma), D. surcu-lus (extinction between 2.42 and 2.46 Ma), D. asymmetricus (sharp decline in abundance at 2.65 Ma), and D. tamalis (extinction at 2.65 Ma). The age of the peak abundance of D. triradiatus is accurately determined for the first time. The remaining estimates agree with those previously obtained from the northern North Atlantic and Pacific oceans. Plots of changes in total Discoaster accumulation rate indicate a long-term trend of progressive cooling of sea-sur-face temperatures during preglacial times in the area of Site 606. This trend is overprinted by short-term abundance os-cillations. The orbital forcing of paleoclimatic change is strongly imprinted on these short-term variations, as indicated by spectral analysis. The 413-kyr. eccentricity period, the 41-kyr. obliquity period, and the 23- and 19-kyr. precessional periods (not separated in our record) are identified, and the eccentricity period is dominant. The eccentricity period co-incides with sharp changes in the Discoaster record at 2.3-2.4 Ma, 2.7-2.8 Ma, 3.1-3.2 Ma, and 3.5-3.6 Ma. Only the youngest of these cycles can be linked with major glacial buildup.