Uysal and three co-authors reported in 2003 that clay mineral fractions from one of the largest Phanerozoic impact structures, the Woodleigh impact structure were investigated by XRD, electron microscopy and K-Ar and stable isotopic studies. Samples were collected from the central uplifted Precambrian basement granitoid, conglomeratic rocks derived from reworked impact rocks, and from the Ordovician-Devonian sandstones located ~30 km west of the central uplift.
There are remarkable lateral and vertical variations in authigenic clay mineral compositions and illite crystallinity (IC) values (Kubler index). Clay minerals from shocked granitoid basement rocks are mainly smectite-rich (> 75%) mixed-layer illite-smectite with some discrete illite formed as an alteration-product (replacement) of biotite. Clay minerals in the conglomeratic rocks consist of mainly illite and Fe-rich chlorite, and in the lower part of the section, chlorite-rich (>50%) mixed-layer chlorite-smectite. Smectite in the oxidized upper part of the conglomeratic section is probably a weathering-product.
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