GSA Annual Meeting in Denver, Colorado, USA - 2016

Paper No. 52-11
Presentation Time: 4:40 PM


KISSOCK, John Kyle, University of Iowa, 208 Lonsdale Ave, Dayton, OH 45419, FINZEL, Emily S., Earth & Environmental Science Department, University of Iowa, Trowbridge Hall, North Capitol Street, Iowa City, IA 52242, MALONE, David, Geography-Geology, Illinois State University, Campus Box 4400, Normal, IL 61790-4400 and CRADDOCK, John P., Geology Department, Macalester College, 1600 Grand Avenue, St. Paul, MN 55105,

In the Forest City and Illinois midcontinent basins, Morrowan, Atokan, and Desmoinesian (Lower-Middle Pennsylvanian) clastic strata unconformably overlie Mississippian and Devonian strata. This relationship is interpreted to reflect a renewed influx of detritus after a significant middle Paleozoic depositional hiatus. We analyzed detrital zircons from Lower-Middle Pennsylvanian strata collected from seven localities in the Forest City Basin and seven localities in the Illinois Basin. In the total combined dataset (n=3,106), U-Pb ages of approximately 66% of the zircons match ages interpreted to be derived from the Appalachian region, including Grenville (1.3-1.0 Ga), Pan-African (530-620 Ma and 750 Ma), Taconic (440-490 Ma), Acadian (350-420 Ma), and Alleghenian (330-270 Ma) ages. Subordinate populations of grains consist of Granite-Rhyolite (1300 -1500 Ma), Yavapai and Mazatzal Terrane (1653- 1750 Ma), Penokean and Trans-Hudson orogens (1800-1900 Ma), and Superior Province (>2.5 Ga) ages. Overall, our detrital zircon signatures from Morrowan-early Desmoinesian strata in the Illinois basin are interpreted to reflect a change from regional drainages that reworked local sedimentary strata to extensive extra-basinal fluvial systems that supplied detritus shed from the northern Appalachians. By middle Desmoinesian time, detrital zircon signatures in the Illinois basin are more similar to those from coeval units in the central Appalachian Basin, indicating a southward shift in the headwaters of these fluvial systems. In the Forest City basin, Morrowan strata are absent and our detrital zircon data indicate that Atokan-early Desmoinesian sedimentation was dominated by local fluvial systems. The introduction of extra-basinal fluvial systems with northern Appalachian headwaters in the middle Desmoinesian coincided with the overtopping of the Mississippi River Arch and depositional linking of the Forest City and Illinois basins. The Forest City and Illinois basins collectively contain an Early-Middle Pennsylvanian sedimentary record in the backbulge depozone of the Alleghenian foreland basin system that records overtopping of the forebulge located along the Cincinnati Arch.