 What about the number of these banding patterns? Can we account for that? The key is the post-flood ice age. These diatoms use silica to construct their skeletons. And there are factors that can cause you to have more than one period of diatom growth per year, where these diatoms can grow very rapidly. Anything that tends to increase the amount of silica in the lake water is going to tend to spur diatom growth.