The Effects of Compaction on the Paleomagnetic Record from IODP Expedition 333, Nankai Trough and Shikoku Basin
Abstract
Deposition and compaction of sediments causes shallowed magnetic inclinations, but this relationship is poorly defined. Sediments from Integrated Ocean Drilling Program (IODP) Expedition 333 were studied in order to better understand the effects of compaction on the paleomagnetic record. Cores were collected off the coast of the Kii Peninsula Japan from one site within the Nankai Trough accretionary prism and two sites seaward of the Nankai Trough trench. At Site C0018, 314 m of a Pleistocene to Holocene sedimentary succession were sampled. Coring at Sites C0011 and C0012 resulted in 380 m and 530 m respectively of a Miocene to Holocene succession. Analysis of the paleomagnetic record with depth will be used to determine the effects of compaction and slumping on the paleomagnetic signal as well as to create revised magneto-stratigraphy for all three sites. Preliminary paleomagnetic data from Sites C0018, C0011, and C0012 indicate normal and reverse polarity chrons with inclination values near expected (52° or -52°). Random scatter away from the expected inclination may indicate disturbance within the sediments (drilling disturbance, slumps, etc.) Shallowing of the magnetic inclination with increasing depth may indicate a direct relationship between compaction and the paleomagnetic record. Correlations with physical properties data (porosity and strength measurements from IODP Exp 333) provide a reference for the amount of compaction at varying depths at each site. Paleomagnetic results from this expedition indicated scattering of the inclination directions at C0018. These results in combination with magnetic fabric data collected using anisotropy of magnetic susceptibility (AMS) indicate disturbed sediments, making it difficult to see a link between compaction and inclination. The role of compaction in the magnetic record is best illustrated at Sites C0011 and C0012 where the sediments are less disturbed. Overconsolidated sediments found at Site C0012 may record a sudden shallowing of the magnetic inclination if compaction plays a significant role in the paleomagnetic record. Site C0011 is the most complete non-slumped stratigraphic section of the three sites and may provide the best record of the compaction/inclination relationship.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2011
- Bibcode:
- 2011AGUFMGP51A1150N
- Keywords:
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- 1500 GEOMAGNETISM AND PALEOMAGNETISM;
- 1520 GEOMAGNETISM AND PALEOMAGNETISM / Magnetostratigraphy;
- 3005 MARINE GEOLOGY AND GEOPHYSICS / Marine magnetics and paleomagnetics;
- 3036 MARINE GEOLOGY AND GEOPHYSICS / Ocean drilling