Eroded edge of microbial reef (T=thrombolite). Upper arrow points to a geopetal structure, which indicates original way up. The lower part of a void was filled with medium-gray fine sediment, later capped by white calcite cement. The lower arrow points to a fossil fragment; part of the fossil was planed off when the reef was eroded by fast-moving water. Dark blob in lower left is a chunk of the reef (tu=tuberoid). What's left of the reef was buried by poorly sorted fine sediment. Image area is 2.5 millimeters high, Mississippian, North Alabama.
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