Biostratigraphy and depositional environment of the Escalante and Hesquiat formations (Early Tertiary) of the Nootka Sound area, Vancouver Island, British Columbia

Abstract

The best exposures of early Tertiary rocks on the west coast of Canada occur in the Nootka Sound area of Vancouver Island. A detailed study of these rocks was undertaken to understand the depositional and tectonic framework of readily accessible parts of the Tofino Basin. An exhaustive study of the microfaunas of the Escalante and Hesquiat formations of the Nootka Sound area led to the recognition of five foraminiferal assemblage zones within the succession. On the basis of the foraminifers, molluscs, and crustaceans, the ages assigned to the rocks range from Late Eocene to Early or Middle Oligocene. Local correlation with other west coast exposures are with rocks assigned to the Lincoln and Blakeley molluscan "stages" (Galvinian, Matlockian) and the Refugian and Zemorrian foraminiferal stages. The Escalante Formation is a diachronous basal sandstone unit of Late Eocene age whose depositional environment is interpreted to vary from lower neritic to upper bathyal water depths in the type area to exclusively bathyal water depths elsewhere. The Hesquiat Formation of Late Eocene to Early or Middle Oligocene age is represented by proximal turbidites, including partly fluxoturbidites, in the type area and distal facies elsewhere. Sediments, sedimentary structures, and fossil collections indicate deposition ·of the Hesquiat Formation occurred in bathyal water depths as a submarine fan complex. Previous estimates of the total thickness of the Hesquiat Formation in the Nootka Sound area are found to be far in excess of their true stratigraphie thickness. This is explained by a highly complex network of faults and the concomitant difficulty in recognizing lithologie equivalents due to rapid facies changes.

Cenozoic ichthyolith biostratigraphy: Tofino Basin, British Columbia

“…Well samples are studied from the top down to interpret possible contamination from well sloughing. The age of an ichthyolith zone is determined by correlation through co-occurrence with foraminifers and zones established by Cameron (1980) and Narayan et al (2005) and correlated with zones of McNeil (1997) and Rau and Johnson (1999) (Fig. 3).…”

“…Apollo J-14 strata indicate complex deformation in this part of the Tofino Basin, which is also evident in the Hesquiat Peninsula area (Fig. 6) (e.g., Cameron 1980).…”

“…4. Carmanah Group stratigraphy in the Nootka Sound area, Vancouver Island, British Columbia (modified from Cameron 1980), showing indigenous Cenozoic and transported-reworked Cretaceous ichthyoliths and associated lithologies. however, to consider the possible influences of ecological, geochemical, and sedimentological factors on the temporal and spatial distribution of ichthyoliths in sedimentary deposits.…”

“…For example, transportedreworked intervals correlate with the Oligocene Turrilina alsatica and Bulimina cf. alsatica foraminifer zones by Cameron (1980). These intervals correspond to tectonic events in the region involving emplacement of the Pacific Rim Terrane (e.g., Brandon 1989;Hyndman et al 1990) followed by thrusting and accretion (in part) of the Crescent Terrane (e.g., MacLeod et al 1977;Fairchild and Cowan 1982;Hyndman et al 1990).…”

“…At Matlahaw Point and Estevan Point, Cretaceous ichthyoliths occur within units and sedimentary structures described by Jeletzky (1973Jeletzky ( , 1975 and Cameron (1980) as faulted, disturbed, containing angular fragments, and finer grained at the top. The ichthyoliths in these samples may have been transported by gravity flows and ultimately incorporated into Oligocene strata.…”