A Possible Lacustrian Record of the Blake Episode from La Pine Oregon

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A high-resolution record of a geomagnetic polarity episode has been recovered from a 20-meter section of diatomaceous lacustrine sediments from near La Pine, Oregon. The age of this record is constrained between 18,000 years and 0.6 m.y. based upon a pollen date from the older part of the lakebed sequence and the age of the younger glacial deposits that overlie the lakebeds. The record provides a VGP path that identifies a well- defined clockwise NE to SW loop with a radius of 60o, followed a second feature (younger) that traces out a counterclockwise which is 30 degrees in diameter residing in the NE quadrant and characterized by shallow inclinations. These two characteristic features are similar to the two features present in the Blake event (105,000 years and 114,000 years B.P.). The PI will study this phenomenon by sampling nearby parallel sections to the 20- meter profile. In addition, he will do field work to identify and correlate the marker horizons present in the section to date more accurately the possible excursion in the field. Thermoluminescence experiments are planned to verify the tephrachronology work.