Glass, B. P. and Koeberl, C. (1999): Ocean Drilling Project Hole 689B spherules and upper Eocene microtektite and clinopyroxene-bearing spherule strewn fields

Leg/Site/Hole:
ODP 113
ODP 113 689
Identifier:
1999-043284
georefid

Creator:
Glass, B. P.
University of Delaware, Geology Department, Newark, DE, United States
author

Koeberl, C.
University of Vienna, Austria
author

Identification:
Ocean Drilling Project Hole 689B spherules and upper Eocene microtektite and clinopyroxene-bearing spherule strewn fields
1999
Meteoritics & Planetary Science
Meteoritical Society, Fayetteville, AR, United States
34
2
197-208
Montanari et al. (1993) reported a positive Ir anomaly in the upper Eocene sediments from Ocean Drilling Program Hole 689B on the Maud Rise, Southern Ocean. Vonhof (1998) described microtektites and clinopyroxene-bearing (cpx) spherules associated with the Ir anomaly in Hole 689B and suggested that they belong to the North American and equatorial Pacific cpx strewn fields, respectively. We searched a suite of 27 samples taken through the spherule layer from Hole 689B, and we recovered 386 microtektites and 667 cpx spherules. We studied the petrography of the microtektites and cpx spherules and determined the major element compositions of 31 microtektites and 14 cpx spherules using energy dispersive x-ray analysis. We also determined the minor element compositions of eight microtektites using instrumental neutron activation analysis. We found that the peak abundance of cpx spherules is approximately 2 cm below the peak abundance of the microtektites ( approximately 128.7 m below sea floor), which suggests that the cpx spherule layer may be slightly older ( approximately 3-5 ka). The microtektites are mostly spherical and are generally transparent and colorless. They are similar to the North American microtektites in composition, the biggest differences being their generally lower Na (sub 2) O and generally higher Zr, Ba, and Ir (up to 0.3 ppb) contents. We agree with Vonhof (1998) that the Hole 689B microtektites probably belong to the North American tektite strewn field. We calculate that the number of microtektites (>125 mu m)/cm (super 2) at Hole 689B is 52. This number is close to the concentration predicted by extrapolation of the trend of concentration vs. distance from the Chesapeake Bay structure, based on data from other North American microtektite-bearing sites. Thus, the North American strewn field may be at least four times larger than previously mapped. The Hole 689B cpx spherules range from translucent yellow to opaque black, but most are opaque tan to dark brown. They are generally spherical in shape and all are <125 mu m in diameter. Some contain Ni-rich spinels in addition to clinopyroxene microlites. The cpx spherules are petrographically and compositionally similar to cpx spherules previously found in the northwestern Atlantic Ocean, Caribbean Sea, Gulf of Mexico, equatorial Pacific, and eastern Indian Ocean. The abundance and widespread geographic occurrence of these spherules suggest that the strewn field may be global in geographic extent. Assuming a global extent, we estimate that there may be at least 25 billion metric tons of cpx spherules in the strewn field. Based on age, size, and geographic location, we speculate that the 100 km diameter Popigai crater in northern Siberia may be the source of the cpx spherule layer.
English
Serial
Coverage:Geographic coordinates:
North:-64.3100
West:3.0559East: 3.0600
South:-64.3101

Petrology of meteorites and tektites; Geochemistry of rocks, soils, and sediments; alkaline earth metals; Antarctic Ocean; barium; Cenozoic; chain silicates; clinopyroxene; Eocene; geochemical anomalies; iridium; Leg 113; Maud Rise; metals; microtektites; minor elements; Ocean Drilling Program; ODP Site 689; Paleogene; platinum group; pyroxene group; SEM data; silicates; Southern Ocean; spherules; strewn fields; tektites; Tertiary; upper Eocene; Weddell Sea; zirconium;

.