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

Shaobin Liu, B. P. Glass, Frank T. Kyte and Steven M. Bohaty
The late Eocene clinopyroxene-bearing spherule layer; new sites, nature of the strewn field, Ir data, and discovery of coesite and shocked quartz (in The late Eocene Earth; hothouse, icehouse, and impacts, Christian Koeberl (editor) and Alessandro Montanari (editor))
Special Paper - Geological Society of America (2009) 452: 37-70

Abstract

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+ or -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/cm (super 2) , 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 delta (super 18) O 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.


ISSN: 0072-1077
EISSN: 2331-219X
Coden: GSAPAZ
Serial Title: Special Paper - Geological Society of America
Serial Volume: 452
Title: The late Eocene clinopyroxene-bearing spherule layer; new sites, nature of the strewn field, Ir data, and discovery of coesite and shocked quartz
Title: The late Eocene Earth; hothouse, icehouse, and impacts
Author(s): Liu, ShaobinGlass, B. P.Kyte, Frank T.Bohaty, Steven M.
Author(s): Koeberl, Christianeditor
Author(s): Montanari, Alessandroeditor
Affiliation: University of Delaware, Department of Geological Sciences, Newark, DE, United States
Affiliation: University of Vienna, Department of Lithospheric Research, Vienna, Austria
Pages: 37-70
Published: 2009
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
ISBN: 978-0-8137-2452-2
Meeting name: Geological Sociaty of America (GSA) Penrose conference
Meeting location: Ancona, ITA, Italy
Meeting date: 20071003Oct. 3-6, 2007
References: 140
Accession Number: 2009-074330
Categories: StratigraphyIsotope geochemistry
Document Type: Serial Conference document
Bibliographic Level: Analytic
Annotation: NSF Grant EAR-9903811
Illustration Description: illus. incl. 11 tables, sketch maps
S36°28'25" - S36°28'23", E165°26'31" - E165°26'32"
N31°52'27" - N31°52'29", E141°13'34" - E141°13'36"
S42°54'49" - S42°54'49", E08°53'59" - E08°53'59"
S03°54'54" - S03°54'54", E60°33'06" - E60°33'06"
Secondary Affiliation: Osservatorio Geologico di Coldigioco, ITA, ItalyUniversity of California Los Angeles, USA, United StatesUniversity of Southampton, GBR, United Kingdom
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute.
Update Code: 200940
Program Name: ODPOcean Drilling Program
Program Name: DSDPDeep Sea Drilling Project
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