During 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. dominant fossil plants from this time include lycopods, conifers, and seed ferns (extinct gymnosperms). plant material accumulated in these areas of indiana and eventually became the source of indiana’s abundant a) coal deposits. b) granite outcrops. c) limestone deposits. d) layers of sandstone.