The sedimentary record of extraterrestrial impacts in deep-shelf environments: Evidence from the early Precambrian

Title:
The sedimentary record of extraterrestrial impacts in deep-shelf environments: Evidence from the early Precambrian
Authors:
Hassler, Scott W.; Simonson, Bruce M.
Abstract:
Impact ejecta layers in four formations in the Hamersley Basin (Western Australia) and in one formation from the Transvaal Supergroup (South Africa) show striking evidence for impact-related reworking. Each layer contains sand-sized spherules of a former silicate melt that resemble those found in well-documented impact layers. Given available isotopic age dates of associated strata and uncertainties in stratigraphic correlation, these layers represent a minimum of three and a maximum of five impacts between ca. 2.49 and 2.63 Ga. All of these layers were deposited below wave base in deep-shelf environments, yet they show a common suite of sedimentary features indicating deposition and reworking under high-energy conditions. These features occur in a consistent order: (1) extensive erosion, including the transport of meter-scale rip-up clasts, (2) reworking by waves, (3) synwave to postwave offshore-directed bottom return flow, and (4) later reworking by sediment gravity flows. We interpret the consistent association of erosion, wave reworking, and bottom return flow as a result of tsunami triggered by the impact. The sediment gravity flows may have been triggered by impact or may occur much later. The wave features in these layers indicate they are the result of oceanic impacts, and their sedimentological similarities suggest a consistent set of depositional processes that can be used to recognize the distal ejecta layers of marine impacts, particularly those deposited in deep-shelf settings. Given the relatively rapid tectonic recycling of oceanic crust, such layers probably constitute our best source of information on the frequency and effects of large impacts in open-ocean basins.
Citation:
Hassler, Scott W., and Bruce M. Simonson. 2001. "The sedimentary record of extraterrestrial impacts in deep-shelf environments: Evidence from the early Precambrian." Journal of Geology 109(1): 1-19.
Publisher:
University of Chicago Press
DATE ISSUED:
2001-01
Department:
Geology
Type:
article
PUBLISHED VERSION:
10.1086/317958
PERMANENT LINK:
http://hdl.handle.net/11282/309558

Full metadata record

DC FieldValue Language
dc.contributor.authorHassler, Scott W.en_US
dc.contributor.authorSimonson, Bruce M.en_US
dc.date.accessioned2013-12-23T16:12:11Z-
dc.date.available2013-12-23T16:12:11Z-
dc.date.issued2001-01en
dc.identifier.citationHassler, Scott W., and Bruce M. Simonson. 2001. "The sedimentary record of extraterrestrial impacts in deep-shelf environments: Evidence from the early Precambrian." Journal of Geology 109(1): 1-19.en_US
dc.identifier.issn0022-1376en_US
dc.identifier.urihttp://hdl.handle.net/11282/309558-
dc.description.abstractImpact ejecta layers in four formations in the Hamersley Basin (Western Australia) and in one formation from the Transvaal Supergroup (South Africa) show striking evidence for impact-related reworking. Each layer contains sand-sized spherules of a former silicate melt that resemble those found in well-documented impact layers. Given available isotopic age dates of associated strata and uncertainties in stratigraphic correlation, these layers represent a minimum of three and a maximum of five impacts between ca. 2.49 and 2.63 Ga. All of these layers were deposited below wave base in deep-shelf environments, yet they show a common suite of sedimentary features indicating deposition and reworking under high-energy conditions. These features occur in a consistent order: (1) extensive erosion, including the transport of meter-scale rip-up clasts, (2) reworking by waves, (3) synwave to postwave offshore-directed bottom return flow, and (4) later reworking by sediment gravity flows. We interpret the consistent association of erosion, wave reworking, and bottom return flow as a result of tsunami triggered by the impact. The sediment gravity flows may have been triggered by impact or may occur much later. The wave features in these layers indicate they are the result of oceanic impacts, and their sedimentological similarities suggest a consistent set of depositional processes that can be used to recognize the distal ejecta layers of marine impacts, particularly those deposited in deep-shelf settings. Given the relatively rapid tectonic recycling of oceanic crust, such layers probably constitute our best source of information on the frequency and effects of large impacts in open-ocean basins.en_US
dc.language.isoen_USen_US
dc.publisherUniversity of Chicago Pressen_US
dc.identifier.doi10.1086/317958-
dc.subject.departmentGeologyen_US
dc.titleThe sedimentary record of extraterrestrial impacts in deep-shelf environments: Evidence from the early Precambrianen_US
dc.typearticleen_US
dc.identifier.journalJournal of Geologyen_US
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