Sedimentology and tectonic implications of Cretaceous fan‐delta conglomerates, Queen Charlotte Islands, Canada

Abstract

The Honna Formation, of Coniacian age, consists of several hundred metres of polymictic clast‐supported conglomerate associated with sandstone and mudstone. Five conglomerate facies are recognized: ungraded beds; inverse graded beds; normal graded beds; inverse‐to‐normal graded beds; and parallel‐stratified beds. These facies are interpreted as the deposits of subaqueous cohesionless debris flows and/or high‐density turbidity currents. The depositional environment was a deep‐water, gravelly fan that draped a fault‐controlled, basin‐margin slope. The fan is inferred to have passed upslope directly into an alluvial fan (unpreserved); hence, the name fan delta can be applied to the overall depositional system. This type of fan delta, of which the Brae oilfield in the North Sea is an example, is defined here as a deep‐water fan delta. The lack of a shelf is in marked contrast to other types of fan delta. Three facies associations are recognized in the Honna Formation: subaqueous proximal‐fan conglomerates, distal‐fan turbiditic sandstones, and pro‐fan/interfan mudstones with thin sandy turbidites. The proximal fan is envisaged as an unchannelled gravel belt with a downslope length of at least 20 km; such a long subaqueous gravel belt lacks a known modern analogue. The distal fan was an unchannelled sandy extension of the proximal gravel belt. It is postulated that the Honna Formation accumulated in a foreland basin which migrated westwards from the Coast Mountains where the Wrangellia‐Alexander terrane was colliding with North America. In this model, the Honna fan delta was sourced by a (west‐verging) thrust sheet whose sole‐thrust was the Sandspit Fault immediately to the east. Deep‐water fan deltas appear to develop preferentially when eustatic sea‐level is relatively high, so that the‘feeder’ alluvial fan is small, and gravelly throughout. In petroleum exploration and field development, care should be taken to distinguish deep‐water fan deltas from base‐of‐slope (canyon‐fed) submarine fans, because the two systems differ significantly in terms of coarse‐sediment distribution.

Palaeoproterozoic, rift-related, 13C-rich, lacustrine carbonates, NW Russia. Part I: Sedimentology and major element geochemistry

“…8a), are most consistent with the influx of fluvial sediment to the shoreline (Hyne et al 1979;Miall 1984;Elliott 1986), i.e. Lowe 1982;Chough et al 1990;Higgs 1990) from turbulent suspension with insufficient time for bedform development (e.g. Massive sandstone is attributed to rapid deposition by subaqueous, high-density turbidity currents (e.g.…”

Tertiary extension and tilting in the Queen Charlotte Islands, evidence from dyke swarms and their paleomagnetism

“…No possible rotation will bring near-sided paleopoles into agreement with those from mainland North America (Fig. 16), a result which does not support the rotations invoked by Hicken and Irving (1977) and Higgs (1990Higgs ( , 1991. The former authors based their speculations on paleomagnetic data from lavas of Masset Inlet (Fig.…”

“…Souther and Jessop (1991) proposed that the islands comprise a complex of small tectonic domains separated by major faults, each domain having a different stress field. In contrast, Higgs (1990Higgs ( , 1991, to explain widely varying paleocurrent measurements in sandstones of the Cretaceous Honna Formation, speculated that small blocks with dimensions of the order of 10 km have undergone relative rotation about vertical axes. Hicken and Irving (1977), on the basis of paleomagnetic data, also invoked rotation of central Graham Island.…”

Distribution of Albian-Cenomanian Foraminifera From Queen Charlotte Islands, British Columbia, Canada: Constraints on the Timing of the Northward Migration of the Wrangellia Terrane

“…Subsequently, in the Turonian and Coniacian, coarse-grained fan-delta and submarine-fan complexes of the Honna Formation prograded into the basin from the east (Higgs, 1990(Higgs, , 1991. Latest Cretaceous deposition is represented by upper Santonian to upper Campanian shelf mudstones of the informally named Tarundl formation (Haggart, 2004;Haggart and others, in press).…”