These cycles of
sea level change have been divided into at least six magnitudes of order. Each order is a span of years that become smaller. The smallest unit is described as a punctuated aggradational cycle (PAC) and represents between 225,000 and 100,000 years of sediment accumulation. In the field, these units are usually one to five meters thick and contain several different rock units. These units show quick changes in sea level that were controlled by climate change due to glaciers. The fifth order is often called a
cyclothem and may contain several PAC sequences and generally represent about 500,000 years. Again, glaciation seems to be the cause of the cyclic nature of the strata. ==References==