Variations in clay mineralogy across facies boundaries in the Middle Devonian (Ludlowville) New York

Abstract

A series of essentially time-equivalent shales and sandstones from the Middle Devonian Hamilton Group in New York State was traced and collected from those rocks representing the offshore marine environment through the nearshore and brackish water deposits into the nonmarine red bed facies to the E. The samples were studied by means of X-ray diffraction, X-ray fluorescence, and electron microscopy. The results of these analyses were treated statistically for reproducibility and significance of trend. The data indicate that the clay mineralogy of the shales and sandstones consists of dominant illite and subordinate chlorite. The chlorite is more susceptible to diagenetic change than is the illite. In the transition from the nonmarine to the marine environment, the evidence indicates that detrital chlorite is being supplemented by a diagenetic chlorite that seems to form more readily in the shales than in their associated sandstones. Subtle lateral variations in the clay mineralogy are discussed. Both illite and chlorite show a decrease in c-axis and an increase in a-b axis dimensions with distance from the source. Total Fe content decreases with distance.