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How Wyoming Bentonite was formed
How Bentonite Was Formed (Wyoming Bentonite)
During the Late Cretaceous period (120,000,000 years ago), the North American plate drifted westward, forcing the eastern edge of the Pacific plate deep into the earth’s mantle. This caused numerous volcanic eruptions in present-day western Wyoming and Idaho. Volcanic Ash ejected from these eruptions was blown by the prevailing westerly winds, eastward and deposited it in a large inland sea (which occupied much of the central United States). As the Ash fall subsided, the ash deposits were covered with sediment from the eroding nearby landforms. The above listed scenario happened time and time again resulting in over fifty, recorded distinct layers/deposits within the Cretaceous formations. Over the next millions of years, the situ alteration of the ash took place and formed bentonite.
Several million years ago the Black Hills of Wyoming/South Dakota and the Big Horn Mountains of Wyoming were formed and the bentonite bearing formations were raised. The sea drained away and thousands and thousands of feet eroded away to re-expose the bentonite deposits.
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