DETRITAL ZIRCON GEOCHRONOLOGY OF THE DEVONIAN DUTCH CREEK SANDSTONE IN THE SOUTHERN ILLINOIS BASIN

The Dutch Creek Sandstone (basal member of the Grand Tower Formation) accumulated in a shallow subtropical marine shelf between the Ozark Uplift and Cincinnati Arch in the Illinois Basin. In Union and Jackson counties, the Dutch Creek consists of Early Devonian fossiliferous cross-bedded quartz arenites deposited on the Sparta-Wabash platform of the southern Illinois Basin. Conodonts document an upper Emsian age for the Dutch Creek at the Grand Tower Formation type section in Jackson County. For this investigation, detrital zircon (DZ) U-Pb geochronology was used to determine ages and assess the likely provenance of source rocks of Dutch Creek Member sandstones sampled near Alto Pass, Union County, Illinois. 209 zircons were recovered and analyzed at the Laserchron Center at the University of Arizona. Detrital zircon U-Pb dates of the Dutch Creek sands have major peak ages at 1082 Ma, 1858 Ma, and 2702 Ma; indicating that the DZs were contributed from the Grenville orogen (16%), the Penokean orogen (10%), and Archean basement (67%) respectively. Other minor peaks indicate DZs were also derived from the Paleozoic (404-462 Ma), Midcontinent Granite-Rhyolite (1319- 1481 Ma), and Yavapai-Mazatzal (1610-1754) terrane sources; however, most of the DZ ages are ~2460 Ma to 3030 Ma, indicating that the majority of DZs in the Dutch Creek Sandstone were derived from Archean sources. Paleogeographic reconstructions place the Sparta-Wabash platform in the South-East Trade Winds belt favoring eolian and surface current transport of sands from Archean-Cambrian sources presently located to the north of the study area. This is significant as DZs in samples from the Cambrian and Ordovician (see Konstantinou) have peak ages around ~2700 Ma. Early Paleozoic (Cambrian-Ordovician) DZ populations which have similar morphology and grain sizes to the Dutch Creek sands have been interpreted as reworked from a St. Peter Sandstone (Ordovician) source eroded from the Ozark Dome during a sea level low-stand event (Sub-Kaskaskia unconformity). However, our DZ data suggests that the Ozark Dome is not the primary DZ source for the Dutch Creek sands. Our data is most consistent with Paleozoic quartz arenites exposed on the Wisconsin Arch as the most likely source for the dominant DZ populations in the Dutch Creek Sandstone.