Multiple microtektite horizons in upper Eocene marine sediments; no evidence for mass extinctions

Author(s): Keller, Gerta; D'Hondt, Steven; Vallier, Tracy L.
Author Affiliation(s): Primary:
U. S. Geol. Surv., Menlo Park, CA, United States
Other:
Stanford Univ., United States
U. S. Geol. Surv., United States
Volume Title: Science
Source: Science, 221(4606), p.150-152. Publisher: American Association for the Advancement of Science, Washington, DC, United States. ISSN: 0036-8075 CODEN: SCIEAS
Note: In English. 19 refs.; illus. incl. 1 table, chart
Summary: Microtektites have been recovered from three horizons in eight Middle Eocene to Middle Oligocene marine sedimentary sequences. Five of these occurrences are coeval and of latest Eocene age (37.5- 38.0 m.y. ago); three are coeval and of early late Eocene age (38.5- 39.5 m.y. ago); and three are of Middle Oligocene age (31-32 m.y. ago). In addition, rare probable microtektites have been found in sediments with ages of approx 36.0-36.5 m.y. The microtektite horizon at 37.5-38.0 m.y. can be correlated with the North American tektite-strewn field, which has a fission track age of 34-35 m.y. and a palaeomagnetic age of 37.5-38.0 m.y. The microtektites are most abundant in the radiolarian ooze of sites 149 and RC9-58 where the Ir anomalies were found. However, most of the CaCO3 in these sediments has been dissolved, which suggests that the microtektites, and perhaps Ir, are selectively concentrated at dissolution intervals. 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 attributed to the formation of the Antarctic ice sheet. It is concluded that: 1) not all Middle Eocene to Middle Oligocene horizons are coeval, and 2) no faunal extinctions can be correlated with any of the microtektite horizons, or with the late Eocene bolide impact at 37.5-38.0 m.y. ago. (Authors' abstract)
Year of Publication: 1983
Research Program: DSDP Deep Sea Drilling Project
Key Words: 12 Stratigraphy, Historical Geology and Paleoecology; Age; Algae; Cenozoic; Concepts; Correlation; Deep Sea Drilling Project; Eocene; Erosional unconformities; Extinction; Foraminifera; Global; Invertebrata; Magnetostratigraphy; Marine environment; Marine sediments; Microfossils; Microtektites; Middle Oligocene; Nannofossils; Oligocene; Paleoclimatology; Paleoecology; Paleogene; Paleomagnetism; Paleontology; Plantae; Protista; Radiolaria; SEM data; Sediments; Stratigraphy; Tektites; Tertiary; Thallophytes; Unconformities; Upper Eocene
Record ID: 1983057383
Copyright Information: GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom

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