Geologic units in Wood county, Wisconsin

Additional scientific data in this geographic area

Cambrian, undivided (Cambrian) at surface, covers 54 % of this area

Sandstone with some dolomite and shale, undivided; includes Trempealeau, Tunnel City, and Elk Mound Formations

Milladore Volcanic Complex (Early Proterozoic) at surface, covers 18 % of this area

Succession of poorly exposed interlayered metavolcanic and metasedimentary rocks. Lithic units described in Sims (1990)

Alkali feldspar granite of 1835 Ma age group (Early Proterozoic) at surface, covers 11 % of this area

Red to pink, medium-grained leucocratic alkali feldspar granite; contains miarolitic cavities; biotite is altered to opaque oxide minerals; contains fluorite locally. Called red granite previously (Sims, 1990). Exposed in both Pembine-Wausau and Marshfield terranes.

Gneiss, migmatite, and amphibolite (Late Archean) at surface, covers 10 % of this area

Quartzofeldspathic gneiss and less abundant amphibolite and migmatite. Includes granitoid rocks. Granitic gneiss at Port Edwards, WI on Wisconsin River has a U-Pb zircon age of 2870 +/- 13 Ma, and gneiss at Jim Falls in Chippewa River valley has a U-Pb zircon age of 2522 +/- 22 Ma (Sims and others, 1989)

Granitic rocks, undivided (Early Proterozoic) at surface, covers 5 % of this area

Gray, weakly foliated to massive granite in poorly exposed areas.

Prairie du Chien Group (Ordovician) at surface, covers 2 % of this area

Dolomite with some sandstone and shale; includes Shakopee and Oneota Formations

Foliated tonalite (Early Proterozoic) at surface, covers 0.7 % of this area

Medium-gray, mottled, medium-grained, equigranular tonalite and granodiorite. Intrudes rocks of the Milladore Volcanic Complex.