Batchawana Bay, Lake Superior: late Quaternary sedimentary fill and paleomagnetic record

Abstract

The lake-bottom sediments of the shelf area of Batchawana Bay are composed of sands, and the basinal sediments grade from silts to coarse-grained clay basin ward. There is a significant relationship of decreasing mean grain size to increasing water depth for the sediments of the basinal areas. Although the sediments of Batchawana Bay would appear to be formed by the variable mixing of sand and clay, hydraulic action probably removed the clay end member and ultimately deposited it in the lake proper.Grains of magnetic minerals deposited on a lake bottom tend to align in the direction of the Earth's magnetic field at the time of deposition, imparting a remanent magnetic direction to the sediments. The late Holocene sedimentary sequence of Batchawana Bay provides a record of the secular changes of the Earth's magnetic field. "Type" paleodeclination and paleoinclination logs plotted against time can be utilized to date the sedimentary sequence of Batchawana Bay. This paleomagnetic time scale indicates that glacial outwash and varve deposition continued for approximately 600 years after glacial retreat from the lake basin to about 8700 years BP.