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| Titel |
Hydrocarbon Maturation and Os Mixing on Bolide Impact at the Frasnian-Famennian Boundary |
| VerfasserIn |
H. Stein, A. Zimmerman, G. Yang, J. Hannah, S. Egenhoff |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250029024
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| Zusammenfassung |
| An intractable problem in the application of Re-Os geochemistry has been knowledge of the
distribution of Re and Os between source rock and generated hydrocarbon. Solutions lie in
combined experimental work with controlled and induced maturation, and field studies
optimized by known source rock and time of hydrocarbon generation. The Siljan impact
site with its variably tilted but largely intact Ordovician-Silurian sections provides
an unsurpassed opportunity to examine the Re-Os systematics of source rock and
generated crude oil, and the Re-Os imprint of the bolide. This three-component
system contains (1) a time pin for maturation (377 ± 2 Ma; laser argon dating of
impact melt, Reimold et al. 2005) arguably at the Frasnian-Famennian boundary,
(2) known source rocks with kerogens still intact, and (3) crude oils generated on
impact. Modeling takes into consideration the possibility of pre-impact maturation as
well.
At Siljan, numerous quarries expose the Upper Ordovician Boda and Kullsberg limestone
mounds, and locally, the underlying and laterally equivalent Tretaspis (Fjäcka) shale. We
obtained a sample of crude oil seeping from a drill hole in the quarry floor at Solberga.
Preliminary Re-Os analyses on four aliquots of this oil form an excellent linear array in
187Re/188Os versus 187Os/188Os space. The associated age, however, is impossibly old
(Neoproterozoic), and the initial 187Os/188Os unreasonably low (0.2). Rather, this
linear array fits a mixing line between a meteoritic component and a hydrocarbon
generated from the Tretaspis shale. We are presently performing further tests to
isolate the two end-members. Filtering suggests that the extraterrestrial component
consists of small physical particles which can be largely removed from the petroleum
fraction. The extreme contrast in Re-Os composition between meteorite (known) and
black shale (in progress) end-members maximizes the sensitivity of the isotopic
study.
Reimold, W.U., Kelley, S.P., Sherlock, S.C., Henkel, H., and Koeberl, C. (2005) Laser
argon dating of melt breccias from the Siljan impact structure, Sweden: implications for a
possible relationship to Late Devonian extinction events: Meteoritics & Planetary Science, v.
40, no. 4, p. 591-607. |
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