Precambrian tidalites from the Baraboo Quartzite Wisconsin, U.S.A.

The Baraboo Quartzite is a 1.7 billion year old, almost pure meta-quartzarenite unit that is 1500 m thick and that crops out in a doubly-plunging syncline in south-central Wisconsin, U.S.A. It is one of several similar quartzites that are exposed throughout the upper part of the Midwestern United States.Two general depositional environments are represented by this well-sorted, quartzarenite: a lower braided stream complex characterized by wedge sets of cross-strata with pebble conglomerate at the base and small cut and fill structures, and an upper, tidally-influenced environment characterized by small-scale planar–tabular cross-strata separated by reactivation surfaces and scattered tidal bedding sequences. The Baraboo Quartzite represents one of the oldest tidally influenced rock units known but has no direct modern analog.