CARBON ISOTOPE STRATIGRAPHY OF THE LITTLE CEDAR FORMATION IN EASTERN IOWA

The Devonian Period (~419.2-358.9 million years ago) was marked by a rapid radiation of plants into continental environments, and associated global cooling lead to the development of continental ice sheets. During the Devonian, Iowa was located at low latitudes south of the equator and submerged in a shallow epicontinental sea that experienced multiple marine transgressions and regressions. The limestones deposited in this environment are widespread in the eastern portion of the state and are well exposed in the Cedar Valley. Limestone samples were collected from the Eagle Center and Hinkle members of the Little Cedar Formation from the Waterloo South Quarry and Raymond Quarry. Samples from the Eagle Center Member are brecciated, mottled, and contain banded chert and chert nodules. The Eagle Center is largely unfossiliferous, though heavily burrowed, and contains stromatolites. The fine grained limestone of the Hinkle Member conformably overlies the Eagle Center. Twenty samples were analyzed for δ¹³C carbonate at NASA Goddard Spaceflight Center using a Costech Elemental Analyzer coupled to a Thermo Scientific Delta Plus. The negative δ¹³C shift (from -0.2‰ to -3.5‰) through this section shown by the samples is consistent with reports of a long-term negative shift spanning from the early Givetian to the mid-upper Frasnian.