--> Abstract: Evolutionary Trends in Paleocene and Eocene Calcareous Nannofossil Species from the Gulf and Atlantic Coastal Plains, by L. M. Bybell and J. M. Self-Trail; #90987 (1993).

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BYBELL, LAUREL M., and JEAN M. SELF-TRAIL, U. S. Geological Survey, Reston, VA

ABSTRACT: Evolutionary Trends in Paleocene and Eocene Calcareous Nannofossil Species from the Gulf and Atlantic Coastal Plains

Calcareous nannofossils from upper Paleocene and lower Eocene marine sediments of the Gulf (Alabama) and Atlantic (New Jersey, Maryland, and Virginia) Coastal Plains were examined with the scanning electron microscope. Detailed morphologic studies of these microfossils document evolution within individual species, as well as evolution of one calcareous nannofossil species into another. Several types of morphological trends that occur from older into younger sediments were observed in this study, and they include increase in size, change in the axial ratio, broadening of the crossbar, lowering of the central perforate region, change in the number and shape of pores in the central region, and increase in the height and width of the rim. Some of these evolutionary changes occurred gradua ly over a period of several million years, whereas others happened within a much shorter period of time (100,000 years or less).

The number of observed evolutionary changes noticeably increases in sediments that were deposited during a period of significant climatic and oceanographic changes that began near the end of the Paleocene within the upper part of calcareous nannofossil Zone NP 9 (approximately 55.5

Ma) and that continued into the early Eocene. If, as expected, calcareous nannofossil evolutionary events are consistent worldwide, then other marked increases in the evolutionary rate may indicate major global climatic events.In addition, once the stratigraphic positions of these evolutionary shifts are confirmed at other geographic locations, they can he used to increase the precision with which marine sediments can be dated worldwide.

AAPG Search and Discovery Article #90987©1993 AAPG Annual Convention, New Orleans, Louisiana, April 25-28, 1993.