143-21 Basal Cambrian Sediment Sourcing and Routing in the Western Laurentian Midcontinent, Iowa, USA

Abstract:

The Cambrian Mt. Simon Sandstone records the initial Paleozoic transgression of the Laurentian midcontinent. Here we evaluate detrital zircon U-Pb data from six drill core samples in Iowa in order to constrain sediment sourcing and routing in the western Laurentian midcontinent. Zircons were analyzed by LA-ICPMS at the University of Arizona Laserchron Center.  In southeast Iowa, the FrissU core is dominated by a ~2700 Ma age peak, indicating a distal, northerly sediment source in the Archean Superior Provence. The FrissL core has a broad, age distribution dominated by ~1350–1450 Ma zircons, with secondary Paleoproterozoic (~1700–1850 Ma) and Archean (~2700 Ma) populations, recording a well-mixed transgressive fluvial system traversing Iowa. In southcentral Iowa, The KeithU core exhibits a broad age distribution from 1100–1400 Ma and a lesser Paleoproterozoic contribution (1780-1840 Ma), indicating mixed localized erosion of underlying Iowa basement rocks such as the Midcontinent Rift or Granite-Rhyolite Province and western sources from the Transcontinental Arch. The KeithL core has a prominent age peak of ~1400 Ma, indicating erosion of Iowa Granite-Rhyolite basement rocks. In northcentral Iowa, the MN6 core exhibits a bimodal signature with peaks at ~1850 Ma and ~2700 Ma, where the older population indicates sourcing from Paleoproterozoic and Archean basement along the Transcontinental Arch. The A1-2 NJ core contains a Mesoproterozoic cluster (~1100–1450 Ma) paired with a lesser ~2700 Ma peak indicating a mix of local basement and distal northerly sediment sourcing. Overall, the Mt. Simon in Iowa contains mostly zircons sourced from local basement rocks, with the Transcontinental Arch sourcing sediment. An interesting finding of this research is that most of these samples contain sparse late Neoproterozoic and early Cambrian zircons. The zircons occur only in core east and south of the southern boundary fault of the Midcontinent rift, indicating the presence of juvenile crust of this age in Iowa, such as the late Neoproterozoic to Early Cambrian (~540–500 Ma) Elk Creek Carbonatite. Alternatively, a younger shallower arm of the Illinois Aulacogen may occur in the Iowa subsurface.

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