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Mount Simon Sandstone

The Mount Simon formation is the equivalent of the La Motte Sandstone formation in the St. Francois Mountains of Missouri.^[1] It was deposited in a nearshore environment, unconformably overlying Precambrian basement, and underlying the Eau Claire Formation in Wisconsin.^[2]

The Mount Simon sandstone is named after an escarpment of sandstone in Eau Claire, Wisconsin, called Mount Simon by E.O. Ulrich.^[1]

Geology[edit]

The Mount Simon sandstone is composed of three main lithofacies. First, the lower Mount Simon is composed of a medium to coarse gained sandstone, which is interpreted to have a diagenesis of a high-energy river system.^[3]

The middle Mount Simon is a fine to medium grained sandstone with shale beds in it, which is interpreted to be in a high-energy delta.^[4]

Finally, the upper Mount Simon is a sandstone that is interpreted to be deposited in a sand shoal or a tidal flat deposits. The upper Mount Simon also has fossil content such as brachiopod shells that are broken up.^[4]

There are also different lithofacies within the Mount Simon, which include siltstones, mudstones, and conglomerates. The mudstone and siltstone range from 8cm to 1m and is gray to green-gray; however, it is predominantly red. There are also some interbedded layers of small sand grains. The mudstone and siltstone layer is interpreted to be deposited in a distal braid plain (braided river).^[5]

The conglomerate layer consists of quartz pebble (1-2cm with a maximum of 3-4cm) conglomerates that are well to poorly sorted. The conglomerate layer is at the basal scour of the bed and is 2.5-13cm thick. This layer is interpreted to be deposited in a medial braid plain and the conglomerate is a result of fluctuations in the energy of the river.^[5]

Accessory Minerals[edit]

Minerals other than quartz grains are included in the Mount Simon. Zircon is the most abundant non-opaque mineral in the sandstone, ranging in length, with the average being .1-.2mm. The color of the zircons was colorless to pink, and some were oxidized, leaving a reddish-orange to yellow color. The next most abundant mineral is tourmaline, which ranges between .15 to .3mm. The vast majority of the grains are green to yellow-brown, and the minority are blue, pink, green, and violet colors. Rutile is the next most abundant mineral, ranging between .1-.2mm in size, and is a yellow-brown or red color. Garnet is the next most abundant and is colorless to pinkish-brown, and ranges in size between .1-.3mm. Apatite, Amphibole, Pyroxene, Epidote, Diaspore, Staurolite, and Anatase are all minerals that occur in the sandstone; however, they are not very abundant and only take up a small percent of the grains in the rock. ^[6]

References[edit]

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