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Science 8 July 1983:
Vol. 221. no. 4606, pp. 150 - 152
DOI: 10.1126/science.221.4606.150
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Articles

Multiple Microtektite Horizons in Upper Eocene Marine Sediments: No Evidence for Mass Extinctions

GERTA KELLER 1, STEVEN D'HONDT 2, and TRACY L. VALLIER 3

1 U.S. Geological Survey, Menlo Park, California 94025, and Department of Geology, Stanford University, Stanford, California 94305
2 Department of Geology, Stanford University
3 U.S. Geological Survey

Microtektites have been recovered from three horizons in eight middle Eocene to middle Oligocene marine sediment sequences. Five of these occurrences are coeval and of latest Eocene age (37.5 to 38.0 million years ago); three are coeval and of early late Eocene age (38.5 to 39.5 million years ago); and three are of middle Oligocene age (31 to 32 million years ago). In addition, rare probable microtektites have been found in sediments with ages of about 36.0 to 36.5 million years. The microtektite horizon at 37.5 to 38.0 million years can be correlated with the North American tektite-strewn field, which has a fission track age (minimum) of 34 to 35 million years and a paleomagnetic age of 37.5 to 38.0 million years. There is no evidence for mass faunal extinctions at any of the microtektite horizons. Many of the distinct faunal changes that occurred in the middle Eocene to middle Oligocene can be related to the formation of the Antarctic ice sheet and the associated cooling phenomena and intensification of bottom currents that led to large-scale dissolution of calcium carbonate and erosion, which created areally extensive hiatuses in the deep-sea sediment records. The occurrence of microtektite horizons of several ages and the lack of evidence for faunal extinctions suggest that the effects of extraterrestrial bolide impacts may be unimportant in the biologic realm during middle Eocene to middle Oligocene time.

Submitted on December 22, 1982
Revised on May 16, 1983


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