Natural radionuclides may be indicators for dense mineral
placers along marine shorelines. Relict beach and river deposits
occur in continental shelf sediments. These deposits result from the
reworking of beach sands by wave action during the Holocene Transgression.
Some dense, resistant minerals associated with placer
deposits are known to contain ²³⁸U and ²³²Th activities. Shelf sediments,
enriched in heavy minerals, might be expected to be high in
these natural radioactivities. The usefulness of natural radioactivity
to locate and to map dense mineral deposits was therefore explored
and relations between natural radioactivity in marine sediments and
dense mineral content were established.
High ⁴⁰K activity in sediments was positively correlated significantly
with high mud content. High ²³⁰Th and ²³²Th activities were
associated with fine, well-sorted sands and correlated very highly
with the weight percent total heavy mineral sands in the sediment.
These relations distinguish depositional environments as high in
⁴⁰K content and erosional environments as high in ²³⁰Th and ²³²Th
content.
Two areas of enrichment were found by radiometric mapping and
by mineral analyses. Off Destruction Island, Washington, maximum
²³⁰Th and ²³²Th activities were found in 30 m water depth. Activity
distribution and mineral enrichment were consistent with general
northward transport of nearshore sediment. In 33 m water depth off
Clatsop Spit, Oregon, the second enrichment area was found. The
²³²Th/²³⁰Th activity ratios are different for these two areas.
Probably the heavy minerals in these two areas are from different
sources. / Graduation date: 1975
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/28506 |
| Date | 30 August 1974 |
| Creators | Scheidt, Ronald Carl |
| Contributors | Cutshall, Norman H. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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