Origin of illite in the lower Paleozoic of the Illinois basin: Evidence for brine migrations

摘要

In the lower Paleozoic of the Illinois Basin, three illite polytypes are found: 2M₁ of detrital origin, and 1M_d and 1M of diagenetic origin. Illite polytype quantification of detrital 2M₁ illite and diagenetic 1M_d and 1M illite, combined with K-Ar age dating, allows extrapolation to apparent detrital and diagenetic illite ages. Kinetic modeling of smectite illitization, combined with the calculated age of illitization, can evaluate different origins of illite. The diagenetic illite in the lower Paleozoic of the Illinois Basin is interpreted not to have formed solely by burial diagenesis but mainly during multiple brine events.