English: Mudcracks in limestone in the Ordovician of South Korea.

Mudcracks are diagnostic sedimentary structures indicating subaerial exposure of sediment surfaces, with alternating wet & dry conditions. They are much more common that raindrop imprints, which indicate the same environmental setting. Mudcracks are most likely to occur in fine-grained siliciclastic rocks, fine-grained carbonate sediments, and in some evaporitic successions.

Mudcracks are distinctive and easy to identify, but they do vary in appearance. The cracks themselves vary in width, depth, and areal density. Mudcrack polygons also vary in size & shape.

The outcrop shown above has structurally-tilted Ordovician limestones representing tidal and peritidal facies. Mudcracks are present here; the rest of the outcrop has stromatolites, mudmounds, symmetrical ripples, gypsum needles, and birdseye structures.

Stratigraphy: lower Makgol Formation, ~Lower Ordovician to ~Middle Ordovician

Locality: riverbank exposure next to waterfalls in the Yonchi River, immediately north of river tunnel, eastern side of Rt. 35, ~1.5 kilometers north of Dongjeom railway station, far-southeastern Gangwon South Province, eastern South Korea (37° 05' 36.52" North latitude, 129° 02' 29.70" East longitude) (= stop 9 of Choi et al., 2004)

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Reference cited:

Choi et al. (2004) - Cambrian in the land of morning calm, IX International Conference of the Cambrian Stage Subdivision Working Group. Paleontological Society of Korea Special Publication 8: 36, 46-47.