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Nancy
Price
Research Training Program, 2003
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Planktonic Foraminiferal Turnover and Paleoceanographic Change Across the Aptian-Albian Boundary in the Subtropical North Atlantic It
has been long recognized that the Aptian-Albian boundary marks an evolutionarily
significant turnover in planktonic foraminiferal assemblages. This turnover,
which precedes the deposit of black shales during the Ocean Anoxic Event
1b of the Albian, is best seen in the unrecrystalized and pristinely
preserved samples of Ocean Drilling Program Site 1049. In an effort
to better understand this turnover, stable isotope analysis, abundance
counts, stratigraphic distribution of species, and SEM images were used
to make conclusions about depth ecology, and morphological and paleoceanographic
change across the boundary.
Processed ODP samples: Isolated foraminifera from matrix of pelagic clay and chalk using a 45µm sieve and water. Picked for Stable Isotope Analysis: Picked 10-50 individuals of at least two planktic and one benthic species of closely spaced intervals for analysis. Made Abundance Counts: Used microsplitter to obtain unbiased sections of the selected samples. Separated and counted the number of planktics vs.benthics and the number planktic specimens per species per sample. Obtained SEM Photographs: Obtained photos of selected specimens & documented changes in surface texture Direct Observation of Samples: Observed samples under microscope to determine distribution of species across the Aptian-Albian boundary.
Larger forms displaying
pore mound wall texture, including T. bejaouaensis, H. trocoidea,
and H. infracretacea, disappear at the Aptian-Albian boundary.
Surviving assemblage
is comprised of a less diverse assemblage of smaller forms that is dominated
by H. rischi and P. tunisiensis. The foraminiferal turnover event appears to be abrupt with the change in forms occurring over a small stratigraphic interval.
The simultaneous and abrupt changes of both the planktonic foraminiferal assemblages and the stable isotope values in conjunction with the onset of Ocean Anoxic Event 1b at the Aptian-Albian boundary indicate that changes associated with that event had a profound effect on the climate, oceanography, and biota of North American oceans. Further study of this interval is required, however, to make any conclusions about a definable cause for the faunal turnover at the Aptian-Albian boundary.
We would like to thank the National Science Foundation for their generous support of The National Museum of Natural History’s 2003 Research Training Program; the Ocean Drilling Program for the core samples and photos; and My Le Ducharme, Scott Whittaker, RTP coordinator Mary Sangrey and her assistant Elisa Maldonado, Nina Butler, and the 2003 RTP class for all their help and support. Want to ask a question? Visit the Message Board Virtual
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