Abstract

Large numbers of circular mound structures, c.2 mm wide and 1 mm high, occur in carbon-rich laminated shales and siltstones of lacustrine origin in the Middle Devonian Caithness Flagstones. A central pit, characteristic of pit and mound structures, is absent. Experiments indicate that the mound structures could have formed when sediment fell from the surfaces of gas bubbles rising from the lake bottom.

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