ABSTRACT

In the Cretaceous lacustrine deposits of the Yucheon Group of Korea, lenticular cracks are commonly found in the interlaminated to thinly interbedded sandstone/mudstone facies. The general shape of the cracks is variable, many having lenticular shape, incomplete development, and random distribution. In places cracks are orthogonally intersected, or polygonally interlinked. Elongate rhombic to subrhombic, hemipyramidal, bladed, prismatic, or swallow-tail twin-shaped cracks and square, cuboid or rectangular sand patches are associated with the lenticular cracks, which suggests the former presence of soluble evaporite minerals. In the unit layers of the crack-bearing deposits, sandstones have sharp bases and grade upward into mudstones. Planar lamination, low-angle cross-lamination, and small-scale ripples are present. Mudstone chips, some of which preserve the cracks, are present in the sandstones. These crack-bearing layers are interpreted as sheetflood deposits. On the basis of these characteristics, the lenticular cracks of the Yucheon lacustrine deposits in Korea are interpreted as subaerial desiccation cracks formed on dried mudflats. The similarity between the Yucheon lenticular cracks and those described from the Devonian lacustrine deposits in Scotland (Astin and Rogers 1991) suggests that subaerial lenticular cracks associated with evaporite minerals are not rare in geologic time and space.