On Saturday, November the 21st, I visited the Gypsum mine with my lab group: Luke Petro, Liz Morehead, and Kylie Hoef, along with several other groups. After procuring the necessary tools from the geology lab like a meter stick, rock hammer, flashlight, bottle of acid, and helmet, we set off to the mine. Located roughly 100 feet below the surface near Grand Rapids, the mine is now a storage facility owned by Michigan Natural Storage. In the mine, we measured the various rock columns to find how large the different sections of gypsum, shale and dolomite were. In addition to measuring the rock types, we took samples using the hammer. After the trip in lab the next week, we looked at the different rock types under the microscope and discovered
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They were instead formed by a large body of salty water, over a very long time. Shale is at the bottom of our stratigraphic column, and since the ages of rocks follow the principle of superposition, shale is the oldest, Figure 1. The shale was formed in water with a low energy level, which is why there are ripple marks and quite a bit of clay found in this section. The salinity content steadily rose for there to create gypsum, a rock that needs a high salinity content to form. In the gypsum we find fossils, evidence of life forms that inhabited the water by creatures. In the gypsum layer we also know that the water was around for a long time, due to the layer being about 130 cm thick, and looking very similar all throughout, Figure 1. Lastly we find the dolomite layer. This layer, while it is not very thick at 10 cm, occurs twice, both after a thick column of gypsum. This can be attributed to the water becoming less and less salty, as more and more gypsum is formed, getting to the point were dolomite can be formed, and then suddenly rising in the salinity level. I would propose that the bay that covered the Grand Rapids area must have been closed off, forcing the evaporation of the water creating large amounts of gypsum. Later the bay was opened up, letting new water in and lowering the salinity content. This happen several times as the dolomite and gypsum layers repeat in the ceiling and in
They were instead formed by a large body of salty water, over a very long time. Shale is at the bottom of our stratigraphic column, and since the ages of rocks follow the principle of superposition, shale is the oldest, Figure 1. The shale was formed in water with a low energy level, which is why there are ripple marks and quite a bit of clay found in this section. The salinity content steadily rose for there to create gypsum, a rock that needs a high salinity content to form. In the gypsum we find fossils, evidence of life forms that inhabited the water by creatures. In the gypsum layer we also know that the water was around for a long time, due to the layer being about 130 cm thick, and looking very similar all throughout, Figure 1. Lastly we find the dolomite layer. This layer, while it is not very thick at 10 cm, occurs twice, both after a thick column of gypsum. This can be attributed to the water becoming less and less salty, as more and more gypsum is formed, getting to the point were dolomite can be formed, and then suddenly rising in the salinity level. I would propose that the bay that covered the Grand Rapids area must have been closed off, forcing the evaporation of the water creating large amounts of gypsum. Later the bay was opened up, letting new water in and lowering the salinity content. This happen several times as the dolomite and gypsum layers repeat in the ceiling and in