Textural and mineralogical variations in the surficial sediments of Chagvan Bay, Alaska: Some stratigraphic implications of a subarctic bay

Abstract

The surficial sediments of Chagvan Bay consist of: (1) coarse-grained (−3 Φ to −2 Φ) lithic fragments of dunites, diorites and sandstones; (2) fine sands (2—3 Φ) composed of quartz and feldspar; and (3) coarse silts (4—5 Φ) composed mostly of quartz. The lithic fragments primarily result from wave erosion of the coastal bluffs, while the fine sands are transported into the bay by tidal currents and the coarse silts by fluvial currents. During successive ebb tides tidal currents remove most or all of the newly deposited material and tend to maintain a balance between erosion and deposition. The texture and mineralogy of the bay deposits are primarily controlled by provenance. Inasmuch as most of the sedimentary particles are being supplied at present and the dispersal of the surficial sediments reflects the present configuration of distributor processes, the sediments are classified as “neoteric”. Benthic epifauna are present only in relatively low-energy depositional areas, although other parts of the bay offer a similar environment. For this reason, it is postulated that the distribution of benthic organisms is influenced by the scouring activity of currents. Although there is seasonal ice-cover, the sediments rapidly acquire characteristics which reflect the energy regime during the ice-free period and form a hydraulically graded profile. It is concluded from this that the sediments are always at or near an equilibrium state, and that this situation should lead to a diastem or unconformity in the stratigraphic record.