About This Item
- Full text of this item is not available.
- Abstract PDFAbstract PDF(no subscription required)
Share This Item
The AAPG/Datapages Combined Publications Database
AAPG Bulletin
Abstract
Volume:
Issue:
First Page:
Last Page:
Title:
Author(s):
Article Type:
Abstract:
Deep-sea channel and interchannel deposits from the southern part of the Cascadia abyssal plain have been studied through textural and coarse fraction analyses, fauna, radiocarbon dating, and stratigraphic sequence. Piston cores were taken along a line from the base of the continental slope off central Oregon to the western edge of the abyssal plain.
Faunal and color changes between the upper and lower sections of several cores take place abruptly in the cores. The horizon separating the upper and lower sections is a significant one (a change from glacial to post-glacial conditions). The ratio of planktonic foraminifers to radiolarians is less than one above the horizon and greater than one below. The radiocarbon age of the deposits just below the horizon is 15,200 B.P.
Both channel and interchannel sediments show a marked increase in the number and thickness of sand layers deposited during glacial time, whereas post-glacial deposits show a decrease in sand. Only post-glacial deposits have been observed in Cascadia and Astoria channels and in the interchannel area east of the latter. The coarsest layers in these channels consist of coarse silt and very fine sand, respectively. Two unnamed channels on the western side of the plain display a largely glacial section consisting chiefly of very fine sand and coarse silt. Interchannel deposits on the western edge of the plain are significantly finer-grained than those on the east.
The highest sedimentation rates in the area apparently occurred during glacial time. Radiocarbon dates indicate a rate of accumulation during glacial time of about 170 centimeters per 1,000 years for an interchannel area on the western edge of the plain. Post-glacial rates of deposition are highest on the eastern side of the plain, particularly in the area adjacent to the continental slope, and in Astoria and Cascadia channels.
End_of_Article - Last_Page 472------------