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Why does coarse sand reduce the organic richness of oil shale?
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oil shale
Kuskerite (oil shale) outcrop that dates to the Ordovician Period, northern Estonia.
Coarse sediment, such as sand, is generally incompatible with the preservation of organic material required to form oil shale. Because oil shale deposits are typically fine-grained sedimentary rocks, the presence of coarse-grained sandstone—such as that found in parts of the Green River Formation—significantly reduces the organic richness of the deposit.1