ABSTRACT: A Marine Transgressive Sequence--The Late Early to Early Late Cretaceous Haida and Skidegate Formations, Queen Charlotte Islands, British Columbia, Canada

GAMBA, CHARLES A., McMaster University, Hamilton, Ontario, Canada

Thick transgressive marine sequences are uncommon within the geological record. The Albian to Turonian Haida and Skidegate formations form a 2100 m thick transgressive sequence deposited along the eastern margin of the Queen Charlotte forearc basin, one of Canada's foremost west coast hydrocarbon frontiers. Three facies assemblages are recognized: a basal sandy shelf assemblage, a middle muddy offshore assemblage, and an upper submarine fan assemblage.

The 1046 m thick sandy shelf assemblage comprises four stacked transgressive successions, each exhibiting a sharp-based sequence of swaley cross-stratified sandstones up to 7 m thick gradationally overlain by massive bioturbated silty sandstones up to 537 m thick. Deposition of each succession is attributed to a rapid drop in relative sea level followed by slow marine transgression. The deposits of the sandy shelf assemblage grade westward into those of the 428 m thick muddy offshore assemblage that comprise bioturbated mudstones, tempestites, and spectacular slump deposits. The abundance of wave-formed sedimentary structures and the occurrence of a diverse offshore ichnofauna indicate deposition above storm wave base. The 630 m thick submarine fan assemblage comprises classical turbi ites and channel-levee complexes deposited basinwards of the muddy offshore assemblage.

Prolonged thermal subsidence of the arc massif to the east throughout Albian and Turonian time resulted in the progressive eastward onlap of the three assemblages, producing an overall transgressive sequence. The small-scale transgressive successions of the sandy shelf assemblage reflect small relative sea level fluctuations superimposed upon large-scale basin subsidence.

AAPG Search and Discovery Article #91012©1992 AAPG Annual Meeting, Calgary, Alberta, Canada, June 22-25, 1992 (2009)