Macrofabric Analysis of Glacial Till

Abstract

Previous studies on till fabrics of glacial tills indicate that the fabric elements are oriented in preferred directions. The long axes of elongated fabric elements are statistically oriented parallel or transverse to the directions of ice flow. Published studies on the mechanisms by which stones in till become oriented reveal that there is no one set mechanism by which a fabric element obtains a preferred orientation. A study of the till fabrics of the Twig, Independence, and Alborn quadrangles of northeastern Minnesota shows that the glacial tills usually have two preferred orientations, a major and minor orientation. The directions of the two preferred orientations of the till fabric are approximately at right angles to each other. In most cases the major preferred orientation is parallel to the direction of the known ice flow, but in some till fabrics the major preferred orientation is transverse to the direction of known ice movement. The long axes of elongated stones usually plunged up-glacier in the drumlin till, but there was no consistency to the pattern of plunge in the ground moraine till. It is advisable to limit as many variables of the till fabric element such as size, shape, and axial-ratio to obtain accurate results. The positive correlation obtained between the results of the author's till fabric analysis and Wright's and Watt's (1969) interpretation of the studied area support the use of preferred orientation of till fabric as a meaningful indicator of ice movement.