In this thesis anomalous downcore shallowing of paleomagnetic
inclinations is interpreted to be caused by sediment compaction. Thus,
compaction-induced inclination shallowing may influence tectonic
reconstructions that are based on inclinations from deep-sea sediment
cores.
Progressive downcore shallowing of the remanent inclination was
observed in a 120-m section of Plio- Pleistocene sediments at Deep Sea
Drilling Project (DSDP) site 578 in the northwest Pacific. Near the top
of the section the average inclination corresponds to the expected
geocentric axial dipole value of 53° but shallows downcore by about 6°
to 8°. In sediments spanning the same time interval of neighboring site
576, no inclination shallowing was observed. This second site has
considerably lower sedimentation rates, and the Plio- Pleistocene is
represented by a 26-m sedimentary section. The inclination shallowing
at site 578 was correlated to a downhole decrease in porosity, and these
results are interpreted to suggest that both the downhole inclination
shallowing and decrease of porosity in site 578 were caused by sediment
compaction.
Microscopic models demonstrate that sediment compaction may lead
to inclination shallowing of the magnetic remanence. Furthermore, it is
shown that inherent initial within-sample dispersion of the magnetic
moments will transform any form of microscopic mechanism to an
equation of a standardized form: tan (I-ΔI) = (1-a ΔV) tan I,
where I is the inclination of the ambient field, ΔI is the inclination
shallowing, a is a constant and ΔV the compaction.
Paleomagnetic inclinations of Cretaceous DSDP sediments from the
Pacific plate are known to be systematically shallower than predicted
from paleolatitudes of hot spot reconstructions. Published paleomagnetic
data were reexamined and the shallow Cretaceous inclinations explained
as a result of sediment compaction. The Cretaceous data are used to
estimate the parameter a. The resulting a values are comparable to those
of previous studies of compaction-induced inclination shallowing, both
from laboratory experiments and the considerably younger deep-sea
sediments at site 578. Values of the parameter a suggest that it might be
controlled by sediment lithology with greater shallowing for clayey than
calcareous sediments. / Graduation date: 1991
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/29238 |
| Date | 18 April 1991 |
| Creators | Arason, Pórdur |
| Contributors | Levi, Shaul |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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