Milankovitch cycles. Lacustrine strata in the Newark basin show multiple types of cyclical changes in color and depth rank. The basic cycle of lake-level rise, highstand, and lake-level fall--the Van Houten cycle (produced by precession with a period of ~20,000 years)--is grouped into a series of longer compound cycles. There are about 5 Van Houten cycles in the short-modulating cycle (~100,000-year eccentricity cycle), and 20 Van Houten cycles in the McLaughlin cycle (~400,000-year eccentricity cycle). Note that the character of the Van Houten cycle changes within the compound cycle. In the short modulating cycle, the lowest Van Houten cycle has a thick black shale, whereas the second cycle has a much thinner black shale. The third cycle lacks black and gray shale, and the fourth and fifth cycles do not show any appreciable color changes (although the rock typically becomes less massive). These cycles of lake-level changes are caused by changes in evaporation-precipitation rates driven by changes in climate caused by changes in the Earth's orbit. Modified from Olsen et al. (1989).