Jurassic foraminifera from the Queen Charlotte Islands, British Columbia: Biostratigraphy, paleoenvironments and paleogeographic implication

Lower and Middle Jurassic (Sinemurian to Callovian) foraminifera were examined from 66 sections of the Queen Charlotte Islands, British Columbia, Canada. Over 200 species of well preserved benthic calcareous and agglutinated taxa belonging to 50 genera were identified. Foraminifera from the Lower Jurassic are represented by a predominantly abundant and diverse, Tethyan-derived calcareous assemblage with Boreally-derived agglutinated taxa becoming gradually more dominant in the late Lower Jurassic to early Middle Jurassic. Sedimentary strata and their faunal components and position of hiatuses correlate approximately with the Jurassic eustatic sea-level curve. Sea-level changes have resulted in a variety of depositional environments ranging from deep-water euxinic shales with abundant tuff beds, characterized by small pyritized foraminifera, to a well oxygenated outer shelf setting, characterized by a major faunal increase, to shoreface sandstones and conglomerates with absent to rare benthic foraminifera. A gradual shallowing from a slope- to a shelf-dominated deposition, with a magmatic arc provenance is suggested for the Lower Jurassic and a nearshore environment (i.e. inner shelf to upper shoreface) dominated by sedimentary strata of volcaniclastic origin is suggested for the Middle Jurassic. A marked faunal turnover is observed for the Lower Jurassic Whiteaves Formation (middle Toarcian) with the extinction of several earlier species and the appearance of a new diverse assemblage equating to 225 species. This turnover is also observed for the ammonite and radiolarian assemblages of the Queen Charlotte Islands. In comparison to the dominantly Tethyan-derived taxa of pre-middle Toarcian age, many of the species from the middle Toarcian are found in northern latitudes such as Alaska, Arctic Islands and the Northwest Territories. Hence, foraminifera, in conjunction with existing radiolarian and ammonite data, suggest a northward displacement of the Queen Charlotte Islands from low to mid-paleolatitudes by late Lower Jurassic (Toarcian) to early Middle Jurassic (Bajocian) time.*.;*This dissertation includes a CD that is multimedia (contains text and other applications that are not available in a printed format). The CD requires the following applications: Windows 95/98, Microsoft Office.