The late Eocene clinopyroxene-bearing spherule layer; new sites, nature of the strewn field, Ir data, and discovery of coesite and shocked quartz

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doi: 10.1130/2009.2452(04)
Author(s): Liu, Shaobin; Glass, B. P.; Kyte, Frank T.; Bohaty, Steven M.
Author Affiliation(s): Primary:
University of Delaware, Department of Geological Sciences, Newark, DE, United States
Osservatorio Geologico di Coldigioco, Italy
University of California Los Angeles, United States
University of Southampton, United Kingdom
Volume Title: Late Eocene Earth; hothouse, icehouse, and impacts
Volume Author(s): Koeberl, Christian, editor; Montanari, Alessandro
Source: Special Paper - Geological Society of America, Vol.452, p.37-70; Geological Sociaty of America (GSA) Penrose conference, Ancona, Italy, Oct. 3-6, 2007, edited by Christian Koeberl and Alessandro Montanari. Publisher: Geological Society of America (GSA), Boulder, CO, United States. ISSN: 0072-1077. ISBN: 978-0-8137-2452-2 CODEN: GSAPAZ
Note: In English. NSF Grant EAR-9903811. 140 refs.; illus., incl. 11 tables, sketch maps
Summary: In order to better define the late Eocene clinopyroxene-bearing (cpx) spherule layer and to determine how the ejecta vary with distance from the presumed source crater (Popigai), we searched for the layer at 23 additional sites. We identified the layer at six (maybe seven) of these sites: Deep Sea Drilling Project (DSDP) and Ocean Drilling Program (ODP) Holes 592, 699A, 703A, 709C, 786A, 1090B, and probably 738B. The cpx spherule layer occurs in magnetochron 16n.1n, which indicates an age of ca. 35.4±0.1 Ma for the layer. We found the highest abundance of cpx spherules and associated microtektites in Hole 709C in the northwest Indian Ocean, and we found coesite and shocked quartz in the cpx spherule layer at this site. We also found coesite in the cpx spherule layer at Site 216 in the northeast Indian Ocean. This is the first time that coesite has been found in the cpx spherule layer, and it provides additional support for the impact origin of this layer. In addition, the discovery of coesite and shocked quartz grains (with planar deformation features [PDFs]) supports the conclusion that the pancake-shaped clay spherules associated with quartz grains exhibiting PDFs are diagenetically altered cpx spherules. An Ir anomaly was found associated with the cpx spherule layer at all four of the new sites (699A, 709C, 738B, 1090B) for which we obtained Ir data. The geometric mean of the Ir fluence for the 12 sites with Ir data is 5.7 ng/cm2, which is -10% of the fluence estimated for the Cretaceous-Tertiary boundary. Based on the geographic distribution of the 23 sites now known to contain the cpx spherule layer, and 12 sites where we have good chronostratigraphy but the cpx spherule layer is apparently absent, we propose that the cpx spherule strewn field may have a ray-like distribution pattern. Within one of the rays, the abundance of spherules decreases and the percent microtektites increases with distance from Popigai. Shocked quartz and coesite have been found only in this ray at the two sites that are closest to Popigai. At several sites in the Southern Ocean, an increase in δ18O in the bulk carbonate occurs immediately above the cpx spherule layer. This increase may indicate a drop in temperature coincident with the impact that produced the cpx spherule layer.
Year of Publication: 2009
Research Program: DSDP Deep Sea Drilling Project
IPOD International Phase of Ocean Drilling
ODP Ocean Drilling Program
Key Words: 02 Geochemistry; 12 Stratigraphy, Historical Geology and Paleoecology; Algae; Angola Basin; Asia; Atlantic Ocean; Biostratigraphy; Blake Nose; Blake Plateau; Cenozoic; Chain silicates; Clinopyroxene; Coesite; Commonwealth of Independent States; DSDP Site 111; DSDP Site 522; DSDP Site 543; DSDP Site 592; Deep Sea Drilling Project; Emperor Seamounts; Eocene; Exmouth Plateau; Foraminifera; Framework silicates; IPOD; Iberian abyssal plain; Impacts; Indian Ocean; Invertebrata; Iridium; Isotope ratios; Isotopes; Kerguelen Plateau; Labrador Sea; Leg 105; Leg 110; Leg 113; Leg 114; Leg 115; Leg 119; Leg 12; Leg 121; Leg 122; Leg 125; Leg 145; Leg 149; Leg 171B; Leg 174A; Leg 177; Leg 73; Leg 78A; Leg 90; Lord Howe Rise; Magnetostratigraphy; Maud Rise; Metals; Metamorphism; Microfossils; Microtektites; Nannofossils; Ninetyeast Ridge; North Atlantic; North Pacific; Northeast Atlantic; Northwest Pacific; O-18/O-16; ODP Site 1053; ODP Site 1073; ODP Site 1090; ODP Site 647; ODP Site 672; ODP Site 674; ODP Site 689; ODP Site 699; ODP Site 703; ODP Site 709; ODP Site 738; ODP Site 744; ODP Site 757; ODP Site 762; ODP Site 763; ODP Site 782; ODP Site 786; ODP Site 884; ODP Site 900; Ocean Drilling Program; Oxygen; Pacific Ocean; Paleogene; Plantae; Platinum group; Popigay Structure; Protista; Pyroxene group; Quartz; Russian Federation; Shock metamorphism; Silica minerals; Silicates; South Atlantic; South Pacific; Southern Ocean; Southwest Pacific; Spherules; Stable isotopes; Tektites; Tertiary; Upper Eocene; Weddell Sea; West Pacific
Coordinates: S362825 S362823 E1652632 E1652631
N315227 N315229 E1411336 E1411334
S425449 S425449 E0085359 E0085359
S035454 S035454 E0603306 E0603306
Record ID: 2009074330
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