Date of Award

1994

Degree Type

Thesis

Degree Name

Doctor of Philosophy (PhD)

Department

Geology

Supervisor

R.G. Walker

Abstract

The Late Jurassic to Late Cretaceous stratigraphy and sedimentology of the Queen Charlotte Islands (QCI) was studied on the outcrop scale in order to reconstruct the Late Mesozoic depositional history of the Queen Charlotte Basin. The newly defined Late Oxfordian to Tithonian White Point Formation consists of three gravelly fan delta successions up to 180 m thick. Each was deposited within a small fault bounded basin during a period of regional block faulting. The overlying Late Valanginian to Early Turonian Longarm, Haida, and Skidegate Formations were deposited within an expanded northwest-southeast trending, southwest-deepening basin. Eight depositional sequences 150 to 600 m thick and 1 to 17 Ma in duration are recognized within the three formations. The sequences consist of shallow shoreface, muddy offshore, slope and submarine fan deposits. Each sequence was deposited during a period of sea level fall and rise, and all progressively onlapped the northeastern margin of the basin over time.

The Late Turonian to Coniacian Honna Formation consists of up to 2500 m of gravelly submarine deposits. Two distinct submarine systems are recognized: a longitudinal northwest - southeast trending braided channel complex, and transverse radial fans sourced from an uplifted and dissected magmatic arc to the east. Turbidity currents and debris flows within the channel complex flowed primarily from southeast to northwest, and were probably derived from the radial fans, one of which is preserved in the Skidegate Inlet region. The Honna is overlain by unnamed Late Coniacian to Maastrichtian volcanic and mudstone strata deposited within subaerial and muddy shelf environments respectively.

The Late Mesozoic succession exposed on the QCI accumulated within a continental forearc basin setting situated between an active magmatic arc to the northeast and a subduction zone to the southwest. Different tectonic mechanisms controlled deposition on both the small and large scale. Deposition of both the fan delta successions within the White Point Formation and the progradational shoreface successions within the Longarm and Haida Formations was influenced by local block faulting. The northwest-southeast paleocoastline trend also reflects an underlying structural control. The progressive eastward onlap of Late Oxfordian to Early Turonian strata exposed on the QCI tracked the progressive eastward migration of active magmatism within the Coast Plutonic Complex. Deposition of the Honna Formation was influenced by crustal thickening along the northeast margin of the basin during a period of Late Cretaceous compression.

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