Stratigraphic and paleoenvironmental interpretation of coccoliths from ocean drilling program site 647, Labrador Sea

Yi, Ul-Sung (1989) Stratigraphic and paleoenvironmental interpretation of coccoliths from ocean drilling program site 647, Labrador Sea. Masters thesis, Memorial University of Newfoundland.

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Abstract

A total of 18 coccolith species was identified in the upper ca. 55 m of Ocean Drilling Program Site 647 Hole B (cores 1H to 6H) and the upper 1.1 m of gravity core Hudson 84-030-003. E. huxleyi Zone (NN 21), G. oceanica Zone (NN 20) and the upper part of P. lacunosa Zone (NN 19) were recognized at 0 to 11.1 m, 11.1 to 21.8 m and 21.8 to 56 m, respectively. The biostratigraphic zones were identified primarily based on the FAD of E. huxleyi and the LAD of P. lacunosa which are found to occur at the lowermost part of oxygen isotopic stage 7 and at the lowermost part of oxygen isotopic stage 12. -- Total floral record indicated that i) glacial and interglacial stages are characterized by minimum and maximum coccolith abundances, respectively; ii) early phases of several glacial stages are characterized by relatively high coccolith abundances; and iii) a few glacial to interglacial stage transitions are barren of coccoliths. These barren zones may be the result of dilution by terrigenous sediments or/and the result of suppressed biogenic carbonate productivity by the input of low-salinity and low-nutrient melt waters during deglaciation. The floral assemblages indicated that the study area was dominated by subpolar and transitional water-masses from 0 to ca. 0.472 Ma (oxygen isotopic stages 1 to 12/13) and by transitional water-masses from ca. 0.472 to ca. l.076 Ma (isotopic stages 12/13 to 35/36). The floral assemblage data also showed that early phases of several glacial stages are characterized by the presence of transitional or subpolar water-masses, indicating possible northward advection of warm North Atlantic water during the initial period of Northern Hemisphere ice sheet growth. -- R-mode cluster and factor analyses recognized an environmentally significant floral group consisting of C. pelagicus, E. huxleyi and G. oceanica. The floral group may reflect possible interactions between the cold Labrador Current and the warm North Atlantic Drift or coexistence of the two currents in the southern Labrador Sea during the interval studied. Q-mode cluster analysis recognized the most significant floral change slightly above the top of Jaramillo magnetic event, ca. 0.91 Ma when the dominant species, C. doronicoides was replaced by G. caribbeanica. It is interesting to note that the stratigraphic level marked by this floral change approximately coincides with the mid-Pleistocene interval ca. 0.9 to 0.6 Ma marked by the shift in climatic response of the North Atlantic from 41,000 years to 100,000 years periodicities (Ruddiman, Backman et al., 1987).

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