Geology Reference
In-Depth Information
Sand bars were deposited in shallow waters
ancient submarine setting, the huge blocks or "olisto-
high on the continental shelf and slope in the southern
liths" are found imbedded in chaotic masses of rock
basin. Deep water currents spread sediments in a broad
indicating they slid down steep submerged oceanic
alluvial pattern across the middle of the basin, while
slopes after breaking off an escarpment.
fine-grained sediments were carried farthest from the
After Flournoy time, the end of Coast Range
source and into the deepest region of the seaway to the
collision and renewed subsidance of the forearc basin
north. In the Roseburg Formation, there is evidence
marked a new phase of deposition. White mica, potas-
that large cohesive blocks of mud and rocks slumped
sium feldspar, and quartz, carried into the basin during
from a steep upper shelf onto the deep sea fan. In this
the Tyee interval, reflect a major change in the source
