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TitleThe Jurassic succession at Lisadele Lake (Tulsequah map area, British Columbia, Canada) and its bearing on the tectonic evolution of the Stikine terrane
AuthorShirmohammad, F; Smith, P L; Anderson, R G; McNicoll, V J
SourceVolumina Jurassica vol. 9, no. 1, 2011 p. 43-59 Open Access logo Open Access
Alt SeriesEarth Sciences Sector, Contribution Series 20080497
PublisherNRC Research Press
Mediapaper; on-line; digital
File formatpdf
Subjectsgeochronology; general geology; conglomerates; clasts; clastic facies; cherts; mudstones; zircon dates; radiometric dating; Bowser Lake Group; Jurassic
ProgramTargeted Geoscience Initiative (TGI-3), 2005-2010
Released2011 01 01
AbstractJurassic rocks in the central Tulsequah map area include conglomerates and interbedded fossiliferous finer clastics of the Takwahoni Formation (Laberge Group) which unconformably overlie Triassic rocks. Ammonite collections document the Pliensbachian, Toarcian and Bajocian stages. We refine the age and provenance of episodes of coarse clastic input and confirm the progressive change of dominant clast lithology from reworked sedimentary rocks above the Triassic-Jurassic unconformity to volcanic, plutonic and then metamorphic clasts in the Upper Toarcian. The uppermost coarse clastic unit is a Bajocian chert-pebble conglomerate which, along with the immediately underlying black mudstone, we include in the Bowser Lake Group. Together with regional correlations, this confirms that the age of the basal part of the Bowser Lake Group is diachronous, younging southwards into Stikinia.
Sandstone petrofacies trends and changes in conglomerate clast composition indicate arc uplift and dissection followed by Middle Jurassic orogen recycling. The isotopic ages of detrital zircons and granite clasts compared with the biochronologically constrained ages of the enclosing strata suggests that processes of intrusion, arc uplift, unroofing, and clastic deposition during the Early Jurassic occurred over intervals of significantly less than five million years.

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