Graduate Thesis Or Dissertation
 

Foraminiferal trends of the central Oregon shelf

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  • Sediments of a portion of the central Oregon shelf between 17 and 339 m have been examined for modern foraminifera. Eighty-three samples were collected from 33 stations along three traverses located between 43° 16'N and 43° 50'N. One hundred fifty-five benthic and nine planktonic species are recognized. Fifty-six benthic species occur with a frequency of more than two percent in at least one sample. Benthic species are grouped into four distinct bathymetric faunas. Elphidiella hannai and Buccella spp. are indicative of Fauna A (17-50 m). Fauna B (50-100 m) is characterized by Buliminella elegantissima and Elphidium magellanicum. In the rocky area off Cape Arago Cassidulina californica, C. limbata, Cibicides fletcheri, and C. lobatulus become dominant. Spiroplectammina biformis, Textularia earlandi, and Trifarina angulosa are important species of Fauna C (100-175 m). Abundant species of Fauna D (175-339 m) include Eggerella advena, Epistominella exigua, and Uvigerina juncea. Species diversity increases offshore to a maximum of about 35 benthic species near 100 m and then decreases slightly with depth. Standing crop is low nearshore, rises to a maximum of approximately 300 specimens per 20 cm³ between 125 and 150 m, and then declines. Total benthic population reaches a maximum of approximately 6000 specimens per sample between 150 and 175 m. Values then decrease to about 2000 specimens at 339 m. A maximum of 15 to 20 percent live benthic specimens occurs near 50 m. Planktonic foraminifera constitute less than ten percent of the total population. Maximum percentages generally occur shoaler than 100 m, while maximum specimens per sample occur at the deepest stations. Porcelaneous specimens do not exceed six percent of the benthic population. Agglutinated foraminifera are more abundant than calcareous specimens deeper than 100 m. The frequency of occurrence of a species may vary by as much as 25 percentage points from samples collected approximately 15 cm apart. Statistical analysis of selected species indicates that sampling density was not too close along any one traverse, although the traverses possibly could have been spaced farther apart. Miscellaneous biofacies trends indicate that: thecamoebians are most abundant between 50 and 125 m; statoliths and otoliths occur most frequently between 75 and 2OO m; highest ostracod values are found between 25 and 150 m; and radiolarians generally exceed foraminifera deeper than 250 m.
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