| Summary: | In July 1964 three seismic refraction profiles were recorded
over Stonewall Bank (44°32'N, 124°24'W) to determine gross sub-bottom
geological structure to depths of thousands of feet. In August
1964 a continuous seismic reflection profiler was used to document
shallow geological structure within the rocks forming the Bank.
Stonewall Bank is composed of eastward dipping Pliocene siltstones
which emerge westward from beneath unconsolidated Quaternary
sediments. These siltstones form gentle dip slopes on the
Bank's ea-stern flank but rougher topography is found on the top and
western flank where the bedding planes intersect the sea floor at
greater angles. Refraction data from this study indicate the siltstones
thicken southward by 5000 feet over a six mile distance which
accounts for almost all of the thickness change in the measured section.
A deeper layer, 5000 feet thick, which appears to be Miocene
may be exposed west of the Bank beneath the sediments. The base
of this deeper layer has a southerly dip component of about six degrees
and lies 12, 000 feet below the southern end of the Bank.
Although this was the deepest interface encountered, the underlying
material is not believed to be basement. === Graduation date: 1967
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