12. AN EXAMINATION OF THE PALEOINTENSITY RECORD AND GEOMAGNETIC EXCURSIONS RECORDED IN LEG 155 CORES1Stanley M. Cisowski2 and Frank R. Hall3 |
ABSTRACTThe normalization of the natural remanent magnetism to laboratory-induced remanence for discrete samples from the top 54 m of Hole 932A produces a pattern similar to the apparent variation of the geomagnetic dipole intensity for the period 10-80 ka. Similar patterns in the shipboard archive-half intensity measurements for several other holes suggest that a paleointensity stratigraphy can be employed to date Leg 155 fan sediments. Two short intervals of anomalous field directions, or excursions of the geomagnetic field, have been identified in Hole 932A, at ages of ~32 ka and ~43 ka, as determined from their positions within the intensity pattern. The younger excursion, which has been identified in nine Leg 155 holes, is best defined by discrete samples from Hole 930B. This excursion, which may correspond to the Lake Mungo Excursion, as recorded in aboriginal firepits in Australia, and sediment cores from the Gulf of Mexico, is characterized by short-lived (~40 yr) synchronous peaks in inclination and intensity. The older Hole 932A excursion probably represents the Laschamp Excursion. Discrete sample analyses for Holes 942C and 946A revealed two other anomalous polarity intervals within interglacial Stage 5. The younger excursion is associated with an interglacial carbonate layer representing Substage 5c. The older interval includes several short periods during which the field was nearly reversed, and may represent the Blake polarity event within Substage 5e. |
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