The Australasian microtektite layer: Implications concerning its source area and its relationship to the Brunhes/Matuyama Geomagnetic Reversal

Microtektites are widely believed to be the product of the surficial melting of terrestrial materials from the impact of an extraterrestrial body. However, the impact source area for the youngest and one of the largest tektite groups (the Australasian tektites) has not been identified. One objective of this investigation is to use concentration, size, and major element compositional data for microtektites obtained from deep-sea sediment cores to predict the location of the source area.; The same Australasian microtektites are found stratigraphically close to the Brunhes/Matuyama geomagnetic reversal in deep-sea sediments. This observation has prompted some workers to speculate that a large terrestrial impact may have triggered the geomagnetic reversal. A second objective of this investigation is to determine the precise age relationship between the microtektite layer and the geomagnetic reversal boundary in deep-sea sediments in order to determine whether this speculation has any merit.; In order to determine the precise age relationship between the microtektite layer and the reversal boundary, it was also necessary to determine the depth of acquisition of post-depositional remanent magnetization (PDRM) in deep-sea sediments. PDRM is a process that acts to displace the original position of the reversal boundary downward in the sediment column.; Results from the first part of the investigation indicate that microtektite concentration and size data, when used separately, are not effective in predicting a source area. However, when combined in the form of microtektite mass per unit area, a statistically significant location can be derived. The source area indicated is located in the vicinity of 8-15{dollar}spcirc{dollar} N and 98-102{dollar}spcirc{dollar} E; in general consistent with the predictions made by other workers. Major element compositional data were not helpful in predicting a source area.; Results from the second part of the investigation indicate that the microtektites were deposited approximately 12,000 yrs prior to the midpoint of the geomagnetic reversal. The potential therefore exists, based only on sequence, that the impact that produced the Australasian microtektites may have triggered the geomagnetic reversal. The age relationship was determined from a model in which the depth of acquisition of PDRM varies in a nonlinear manner with sediment accumulation rate. Over the range in sediment accumulation rates used in the study, depth of acquisition of PDRM ranges from 7 to 28 cm. This is consistent with the few other published estimates available.