A Gravity Investigation of the Baraboo Syncline Region

A gravity investigation is presented of the Baraboo syncline, which is an inlier of folded pre-Cambrian igneous and metasedimentary rocks in the flat-lying Paleozoic sedimentary rocks of south-central Wisconsin. This investigation shows that gravity measurements can be useful in depicting the surface geology (lithology and structure) of a limited structural feature-the Baraboo syncline. The regional gravity anomaly consists of the southern terminus of a gravity minimum that is centered over Wisconsin. This minimum is interpreted in the light of seismic crustal studies as originating from a thickening of both the "granitic" layer and the earth's crust. A distinct gravity minimum which cannot be explained by surface geology is found associated with the Baraboo syncline. It is interpreted as originating from a local increase in thickness of the "granitic" layer. This minimum, which is quantitatively investigated, provides the clue which suggests that the Baraboo syncline does not terminate at its western end, as generally believed, but rather extends to the southwest for an additional 5 miles. Other structural and lithologic relations of the syncline are studied with the aid of the gravity data. An analysis of the complementary magnetic study of the Baraboo syncline substantiates the conclusions reached from the gravity investigation.