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TitleEvidence of a regional paleoearthquake during deglaciation interpreted from mass transport deposits, Ontario-Quebec, Canada
AuthorBrooks, G RORCID logo
Source34th International Association of Sedimentologists Meeting of Sedimentology, program; 2019 p. 1
Alt SeriesNatural Resources Canada, Contribution Series 20200394
PublisherInternational Association of Sedimentologists
Meeting34th International Association of Sedimentologists Meeting of Sedimentology; Rome; IT; September 10-13, 2019
File formatdocx
ProvinceOntario; Quebec
NTS31F; 31G; 32D
Lat/Long WENS -78.0000 -74.0000 46.0000 45.0000
Lat/Long WENS -80.0000 -78.0000 49.0000 48.0000
Subjectssurficial geology/geomorphology; stratigraphy; geochronology; Nature and Environment; Science and Technology; landslides; mass wasting; earthquakes; sediment transport; glacial history; deglaciation; glacial deposits; paleogeography; earthquake magnitudes; lake sediments; varved deposits; Laurentide Ice Sheet; Glacial Lake Ojibway; glaciolacustrine sediments; Phanerozoic; Cenozoic; Quaternary
ProgramPublic Safety Geoscience Assessing Earthquake Geohazards
Released2019 09 10
AbstractNumerous stratigraphic occurrences of subaqueous mass transport deposits (MTDs) are preserved in lakes in the northeastern Ontario and western Quebec region, Canada. The MTDs are interbedded within glaciolacustrine deposits that accumulated within glacial Lake Ojibway, a major lake impounded against the Laurentide Ice Sheet (LIS) between 10,570 and 8470 cal BP. Three-dimensional mapping used dense grids of sub-bottom acoustic profiles to produce a series of two-dimensional event horizon maps of MTDs buried within study areas at Dasserat, Dufresnoy and Duparquet lakes, Quebec. The event horizon maps depict the distribution and thickness of the MTDs at different stratigraphic levels within the upper half of the lake deposits. Coring collected varve deposits that are interbedded between or overlying the mapped MTDs. The cored varve sequences were correlated to the regional Timiskaming varve series using distinctive varves and distinctive varve thickness patterns. The varves provide precise relative chronological control for the MTD event horizons between the three lakes. The event horizon with the greatest number and most laterally extensive MTDs in all three lakes occurred in the identical varve year (vyr) 1483 within the Timiskaming varve series (equivalent to 9087 ± 200 cal BP). A high certainty of varve age correlation between the locations is provided by the nearby stratigraphic presence of varve (v) 1528, which is an easily-identifiable, regionally-distinctive, marker layer. The vyr 1483 event horizons are interpreted to be a regional MTD signature as the lakes are located 24 to 38 km apart. To estimate the broader extent of the signature, sediment cores were collected at sites from Chassignolle and Malartic lakes located east of Rouyn-Noranda, Quebec. MTDs with interpreted ages of vyr 1485 are present in both lakes. These deposits are interpreted to correlate to the vyr 1483 signature with the slight difference in varve age probably reflecting missing varves between the MTDs and the overlying v1528 within the relatively thin Chassignolle and Malartic varve sequences. At 12 locations to the north and west of Dasserat, Dufresnoy and Duparquet lakes, published logs of varve exposures mention disrupted or contorted varves with inferred varve ages of 1483-1489. These disturbed varves are considered to be part of the same MTD signature. The presence of the vyr 1483 MTD signature was verified in varve exposures along the Abitibi and Frederick House rivers in northeastern Ontario. Overall, the vyr 1483 MTD signature can be traced over an approximately east-west distance of 220 km. The best explanation for the widespread, synchronous signature is that the MTDs were triggered by a strong paleoearthquake occurring during deglaciation at 9087 ± 200 cal BP. The magnitude is estimated to be about Mw 7.2, based upon a published empirical plot relating the area of landsliding to earthquake magnitude. There are no equivalent widespread MTDs deposits in the post v1483 glaciolacustrine deposits or apparent in the deposits of the modern residual lake basins suggesting that this region has not experienced a younger earthquake of this magnitude.
Summary(Plain Language Summary, not published)
Landslide deposits buried within the sediments of a now-drained, large glacial lake have a common age and can be traced over a distance of 220 km in northeastern Ontario and western Quebec. The landslides are interpreted to have been triggered by a strong ancient earthquake about 9100 years ago.

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