ABSTRACT

Long-axis clast fabrics from the diamictites of the Squantum "Tillite" in Massachusetts and the Gowganda Formation of Ontario are dissimilar in their general features. The Squantum fabrics have well-developed girdles which dip steeply down the paleoslope. The fabrics are most like those of mudflows in their general features but dip considerably more steeply than expected. Modes occur parallel to the strike of the paleoslope, a feature not previously observed in mudflow fabrics. Each of two fabric diagrams from the Gowganda Formation has two subhorizontal modes, one parallel and the other transverse to the paleoslope. The modes are contained in broad horizontal girdles. A third fabric diagram from the Gowganda has a single well-developed subhorizontal mode parallel to the strike of the paleoslope. The Gowganda fabrics are most similar to known till fabrics. Thus the fabrics tend to support a mudflow origin for the Squantum "Tillite" and a glacial origin for the Gowganda Formation. This comparison demonstrates the usefulness of long-axis clast fabric as a criterion for the determination of the origin of diamictite deposits.