Paleontology and geology
During much of the Carboniferous, rivers drained the eroding remnants of the Acadian Mountains and deposited large amounts of sand in expansive deltas and periodically, further out to sea. Fossil communities were composed of crinoids, bryozoans, brachiopods, gastropods, and bivalves. Trace fossils are also common in these rocks. By the Late Carboniferous, Indiana lay close to the equator, making the climate humid and warm. Swamps and wetlands were prominent in much of the state. Plant material accumulated in these areas and became the source of Indiana’s abundant coal deposits. Dominant fossil plants from this time include lycopods, Cordaites (conifer relatives), and seed ferns (extinct gymnosperms). The most southwestern part of the state remained under water, and brachiopods, bivalves, and gastropods were able to flourish in the shallow sea.
This map shows extensive exposures of Carboniferous rocks across the north and in the southwestern sections of the state.