Wednesday, January 20, 2021


Thin-section photomicrograph of limestone, a small patch of grainstone filling a shelter void within a microbial reef. "Q" = quartz sand particle, "E" = echinoderm ossicle, "O" = upper part of an ooid, two black arrows = microcrystalline meniscus cement. This kind of cement forms where menisci of water dry up at the points where particles touch. These are diagnostic of cementation above the water table. Crossed-polarized light, image 1 mm wide. Mississippian, North Alabama.

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