Marine Fossils of the Gastineau Channel Formation
BIVALVIA
Astarte alaskensis Dall
Astarte montagul (Dillwyn)
Chlamys rubida (Hinds)
Clinocardium ciliata (Fabricius)
Cyclocardita ventricosa (Gould)
Hiatella arctica (Linnaeus)
Macoma brota Dall
Macoma calcarea(Gmelin)
Macoma obliqua (Sowerby)
Mya truncata Linnaeus
Mytilus edulis
Nucula tenuis (Montagu)
Nuculana fossa (Baird)
Nuculana minuta (Fabricius)
Nuculana pernula (Muller)
Parvamussium alaskensis (Dall)
Protothaca staminea (Conrad)
Saxidomus gigantea (Deshayes)
Serripes groenlandicus (Bruguiere)
Tresus capax (Gould)
GASTROPODA
Acmaea mitra Rathke
Admete couthouyi (Jay)
Boreotrophon beringi (Dall)
Buccinum kadiakense Dall
Colus halli Dall
Cryptobranchia concentrica(Middendorff)
Cylichna alba (Carpenter)
Fusitriton oregonense (Redfield)
Natica clausa Broderip & Sowerby
Neptunea lyrata Gmelin
Nucella canaliculata (Duclos)
Nucella lamellosa (Gmelin)
Ocenebra lurida (Mlddendorff)
Oenopta harpularia (Couthouy)
Puncturella galeata (Gould)
Tectura persona (Rathke)
Trichotropis borealis Broderip & Sowerby
Trichotropis cancellata Hinds
CRUSTACEA
Balanus nubilis Darwin
Balanus spp.
Ostracoda
BRACHIOPODA
Laqueus californianus (Koch)
POLYCHAETA
Serpula vermicularis Linnaeus
Sinistrella sp.
Spirorbissp.
BRYOZOA
Heteropora alaskensis (Borg
Bryozoa spp
ECHINODERMATA.
Urchin fragments
PORIFERA
Spicules
Spicula matrix
Station Location/
Sites
The fossils in the Gastineau Channel Formation were deposited in water that was shallow (less than 150 feet), saline to brackish (35 to 27 %) and cold (0° C to 10° C). Miller (1973), Smith (1961) and Todd & Low (1967) came to this conclusion based on the tolerances of the species commonly present. Elphidium clavatum was the most abundant and wide spread foraminiferan. It tolerates variations in temperature and salinity but not greater depth. Other commonly occurring forams, while tolerant of greater depth, were less tolerant of greater temperature and salinity variations.
Isostatic rebound has lifted Gastineau Channel Formation deposits above sea level, in some places as much as 750 feet. The highest sample taken in this study was at 300 feet above current sea level. The radiocarbon age of shell material reported by Miller (1975) was 9,500 yr BP to 12,000 yr BP.
Sampling this formation was of necessity opportunistic. The material ranged from muddy gravel to muddy sand to sandy clay. Much of it was readily eroded. Banks exposed by road construction were later stabilized by rocks and vegetation. Material dug up to set power poles was often rich in fossils but soon vegetated. Some very solid clay samples were in streams and only available at low water. Ditch cleaning by the road department exposed some sites that would have been missed otherwise.
Macro fossils were picked from the surface when exposed and from the screens used to process the foraminifera samples. Approximately a cup (200— 300 g. dry weight) of blue—gray sandy mud was dried then rewetted to soften the clods. The material was washed through four screens with sizes and mesh openings of #18 (1.0 mm), #35 (0.5 mm), #70 (0.212. mm) and #140 (0.106 mm).
The material from each screen was examined under a dissecting microscope. Forams and other micro— fossils were picked and identified. A sample size of over 200 forams was considered adequate to characterize the site. Some samples had fewer than 200 and many had more.
The sample sites in this study showed a range of habitats from a high energy site with strong currents to moderate energy sites and low energy sites with deposition instill water. Diversity was greatest in the low energy sites and moderate to low in the moderate energy sites. The single high energy site had species adapted to live in stronger currents.
Following are sections on the macrofossils, foraminifera and descriptions of the sample sites. The bibliography includes references on the Gastineau Channel Formation and keys used to identify the fossils.
Station Location/
Sites
Foraminifera |