The Quaternary in Iowa, US

Paleontology and geology

Quaternary deposits in Iowa are primarily glacial and alluvial in origin. Glacial sediments occur over most of the state, and the extensive glacial record preserved in Iowa provided the basis for the original subdivisions of the Pleistocene Epoch. During this time, coniferous forests of spruce, larch, hemlock, and fir extended over the state in areas out of reach of the continental glaciers. Tundra also existed in the state during a particularly cold interval between 16,500–21,000 years ago. The wide variety of environments hosted a great diversity of mammals. Mastodon, mammoth, musk ox, bison, caribou, camel, deer, horse, moose, giant sloth, giant beaver, and wolf fossils all have been found in the state. As the glaciers retreated from Iowa for the last time (between about 12,500 and 14,000 years old), wind-blown silt (loess) was deposited across much of the state. It is thick enough in part of western Iowa to have its own hilly topography: the Loess Hills. During this interval, the coniferous forests yielded to deciduous forests, which in turn yielded to the prairie grassland present today.