107-9 Detrital Zircon Geochronology of the Prairie du Chien Group in northeast Iowa, USA

Session: Sedimentary Geology Division/SEPM Student Research Poster Competition: Dynamics of Stratigraphy and Sedimentation

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Abstract:

The lower Ordovician (upper Sauk Sequence) Prairie du Chien Group of northeast Iowa is a mixed carbonate-siliciclastic succession that includes the lower Oneota Dolomite middle New Richmond Sandstone and upper Shakopee Formation.  Shallow marine and terrestrial conditions prevailed during deposition of these units.  Here we present a provenance analysis of compositionally and texturally mature quartz arenites sampled from each of the three units from Lycurgas Quarry (Oneota, n=135), Dorchester (New Richmond, n=135), and McGregor, n=135).  The abundance of garnet in the heavy mineral spits is notable.  The zircons were analyzed by ICP-MS at the University of Arizona Laserchron Center.  Each sample contains a prominent 2700 Ma age peak, which is interpreted to have been derived from the Superior Province.  Each sample also have secondary age peaks of ~1100 and ~1450 Ma, which indicates distal sediment sourcing from the Grenville and Picuris-Baraboo-Pinware orogens, respectively.  The prominence of the two Proterozoic peaks increases higher in the section.  The Dorchester sample also has a secondary ~1850 Ma peak, indicating sourcing from the proximal Penokean orogeny to the north.  These detrital zircon age spectra are consistent with the patterns of other Cambro-Ordovician arenites in the Laurentian midcontinent, which reflect distal sediment sourcing that is dominated by Mesoproterozoic and Archean source areas.  Subtle variations can be attributed to shoreline position, wind patterns, and far-field tectonics.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-9225

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