143-18 Detrital Zircon Geochronology of the Middle Ordovician St. Peter Sandstone in the Western Midcontinent Basin

Abstract:

Quartz arenites are a distinctive feature of the early Paleozoic stratigraphic record in the Laurentian midcontinent.  The St. Peter Sandstone was deposited during the Middle Ordovician Tippecanoe transgression.  The provenance of the St. Peter Sandstone was studied in the central and eastern midcontinent and new data from five cores in Iowa and Missouri refine sediment sourcing in the western midcontinent basin.  We test the hypotheses that the Transcontinental Arch and Ozark Dome were sediment barriers and source areas.

Samples were collected from the Camp Quest, WPF, Arthur Brown, Wisnom, and Roy Lewis cores archived by the Iowa Geologic Survey.  Zircons were analyzed by LA-ICPMS at the University of Arizona Laserchron Center (Zn=836).  Previous work on the St. Peter Sandstone in the eastern Laurentian midcontinent revealed three principal sources area that variably supplied sediment, the Superior Province (distal to the north), the Grenville Orogen (distal to the east) and recycling of the Neoproterozoic Jacobsville sandstone (proximal to the north).  Our goal was to determine whether the Ozark Dome and Transcontinental Arch were supplying sediment to the western midcontinent basin.  The Camp Quest (westernmost sample) has prominent 1830 and 2700 Ma age peaks, which were likely derived from Trans-Hudson/Penokean and Superior Province rocks exposed along the Transcontinental Arch to the west.   The other four samples have a mix of Grenville (1000-1300 Ma) and Superior (2700 Ma) age peaks.  The Arthur Brown and Wisnom cores cluster with the regional Superior Province chronofacies, whereas the WPF and Roy Lewis cores cluster with the Grenville chronofacies.  None of the samples have 1300-1500 Ma age peaks, which indicates that no Ozark Dome sediment source area existed during St. Peter deposition.  Our hypothesis that the Transcontinental Arch supplied sediment to the western midcontinent depositional basin is supported by our data, and a fourth St. Peter chronofacies is herein established.

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