Abstract

Up to 2 km of siliciclastic and chemical sedimentary rocks, metamorphosed to greenschist facies, are preserved in the Baraboo Hills of southern Wisconsin. The strata compose two sedimentary successions separated by an angular unconformity. The lower succession includes the Baraboo quartzite, Seeley slate, and Freedom Formation, and the upper includes the Dake quartzite and Rowley Creek slate. Despite being studied for more than 100 y, the exposed section is only recently subdivided into informal members based on identification of sedimentary lithofacies and geologic mapping. This study integrates detrital zircon and paleocurrent analyses with sedimentologic and stratigraphic observations derived from detailed field mapping of the Baraboo and Dake quartzites. Our purpose is twofold: (1) characterize lithofacies of the Baraboo quartzite to interpret the environments of deposition for this unit and (2) evaluate sediment provenance and constrain depositional age. Lithofacies, paleocurrent, and detrital zircon U-Pb analyses of the Baraboo quartzite record fluvial braid plain, eolian, and fluvial-, tide- and wave-influenced deltaic depositional environments with sediments sourced from the north and deposited after 1714 ± 17 Ma. Lithofacies compose two backstepping alluvial to marine successions separated by a thick, laterally continuous coastal dune deposit. North-directed paleocurrents and detrital zircon ages confirm the Dake quartzite is a distinct unit with maximum depositional age of less than 1630.1 ± 8.6 Ma. Deposition of the Dake quartzite reflects basement uplift that postdates deposition of the Baraboo quartzite. The hiatus represented by the unconformity beneath the Dake quartzite is unconstrained and may represent more than 100 My.

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