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Along the eastern margin of the North Pacific agglutinated forams generally increase in number from very few in the innermost sublittoral region to maxima in the middle sublittoral to upper bathyal regions. South of 30°N lat., the maxima range upward to approximately 20% of the total benthic fauna; north of 40°N lat. values range from 80 to 100%. The transition between these two realms occurs over only a few degrees of latitude. Off Oregon, the frequency of agglutinated forams decreases seaward of the maxima to values around 30% between 600 m and 1,800 m, then increases again into the abyssal region. Maxima in the latter region, however, do not reach values as high as those found in the sublittoral.
The sublittoral agglutinated populations between 37 and 43°N lat. are dominated by Textularia earlandi and Spiroplectammina biformis. These are replaced northward by Recurvoides turbinatus and Eggerella advena. There is an orderly progression of agglutinated species into the abyssal region off Oregon.
It is suggested that calcium carbonate availability may not be the only or even the principal factor controlling the ratio of agglutinated to calcareous benthic forams in the area under discussion. The amount and character of suspended detritus may be more important.
Trends of modern agglutinated forams may not be directly applicable to an interpretation of the geologic record. Many agglutinated tests are more easily destroyed than are calcareous tests. The frequency and quality of preservation of agglutinated tests drop off noticeably below the sediment surface.
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