Dinoflagellate cysts from the Upper Jurassic and Lower Cretaceous sedimentary rocks of Grassy Island, British Columbia, Canada

Date

2011-10-18

Authors

Bonnett, Clio J. M.

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Abstract

This is the first study of the Upper Jurassic and Lower Cretaceous dinoflagellate cysts of the Kyuquot Group on Grassy Island, British Columbia. Thirty nine dinoflagellate cyst taxa were identified in 85 samples collected from the Upper Tithonian Kapoose and Berriasian to Middle Valanginian One Tree formations. Cyst recovery, concentrations and diversity are relatively high in the samples from of the Kapoose Formation, whereas samples from One Tree Formation had poor dinoflagellate cyst recovery. Four dinoflagellate cyst zones were identified. Three cyst zones (Cometodinium habibii-Endoscrinium campanula-Oligosphaeridium sp.-Pareodinia spp.- Gonyaulacysta jurassica zone; Cyst Type P zone; and Circulodinium spp.-Cyst Type P zone) correspond to the Buchia columbiana zone from of the Kapoose Formation and the fourth cyst zone (Cyst Type D-Cyst Type Q-Circulodinium spp.-Gonyaulacysta spp. zone) is identified from the One Tree Formation, where four Buchia zones are recognised. The change in the ratio of marine to terrestrial palynomorphs indicates that the basin went through progressive shallowing and/or the shore came closer to the site of deposition beginning in the Upper Tithonian and continuous through to the Valanginian. The zones resemble established Siberian dinoflagellate cyst zones of the same age. This correlation suggests that the two regions were a part of the Boreal Realm during the interval.

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Keywords

Kyuquot Group, Kapoose Formation, dinoflagellate cyst

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