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Magnetic Susceptibility Stratigraphy of the Cambrian Lone Rock Formation, Wisconsin, U.S.A.

Session: 37th Annual Undergraduate Research Exhibition Sponsored by Sigma Gamma Epsilon (Posters)

Presenting Author:

Daniyar Henry Herkstroeter Ali

Authors:

Ali, Daniyar Henry Herkstroeter¹, Weissman, Zoe², Rougvie, James R.³, Zambito, James Joseph⁴

(1) Colgate University, Hamilton, NY, USA, (2) Hamilton College, Geosciences, Clinton, NY, USA, (3) Beloit College, Beloit, WI, USA, (4) Beloit College, Beloit, WI, USA,

Abstract:

This study uses magnetic susceptibility (MS), geochemical, and mineralogical data from two cores to better understand the utility of MS stratigraphy in the Lone Rock Formation of western Wisconsin. In the study area, the Lone Rock Formation consists of three members. From oldest to youngest these are the: dolomitic, coarse-grained, glauconitic sandstone of the Birkmose Member; medium-grained, glauconitic quartz sandstone of the Tomah Member; and medium- to coarse-grained, glauconitic quartz sandstone of the Reno Member. Herein, MS is established as a useful tool for determining the rate of allogenic sediment input to the study area when combined with mineralogical and geochemical data.

In the WGNHS Arcadia Quarry Core, MS has consistently low values both above and below the Lone Rock Formation, and three MS peaks within the Lone Rock Formation: at the top of the Birkmose Member; in the middle of the Tomah Member (the largest of these peaks), and at the top of the Reno Member near the contact with the overlying St. Lawrence Formation. Similarly, the WGNHS Weltzien Quarry Core, located 18.15 km to the southeast, also displays three MS peaks at similar levels in the Lone Rock Formation. The relationship between MS values with mineralogy and geochemistry in the Tomah Member peak of the Arcadia Quarry Core shows that MS values correspond with the presence of glauconite and to a lesser degree dolomite, have a strong correlation with iron, and follow a similar pattern to magnesium and calcium. Furthermore, a gamma log for the Arcadia Quarry Core is similar to that of potassium and corresponds to the presence of potassium feldspars.

A preliminary interpretation of the patterns observed is that variation in MS values is due to changes in detrital flux: at times with more allogenic sediment (quartz and feldspar) input, dilution of the authigenic minerals glauconite and dolomite leads to lower MS values, whereas at times with less allogenic sediment input, authigenic minerals are more concentrated, leading to higher MS values. In this model, iron is predominantly present in glauconite and is the overarching control on MS values in the strata studied. Additionally, potassium in glauconite is subordinate to the potassium present in allogenic feldspar, as suggested by a lack of correlation between MS and gamma.