Diplocraterion luniforme (Blanckenhorn, 1916)

Diagnosis: Small sized, vertical U-shaped burrows with parallel marginal tubes, protrusive spreite and distinctive luniform basal cross-section (after Pollard, 1981). Description: Preserved in endorelief in typically ripple drift cross-laminated or parallel-laminated shale. Burrows are nearly straight and vertical and can be observed as straight bars or dumbbells on the bedding plane. U-shaped morphology only rarely observed in the field, but is clearly seen in vertical section of blocks. The width of Uburrows varies from 5 to 18 mm (mode 10-12 mm); the depth from 4 to 20 mm (usually <15 mm), and the marginal tube diameter is 1-2 mm. Width of burrows generally constant along burrow depth. The spreiten are generally well developed, predominantly protrusive and regular or irregular. The passive fill of coarse sediment, generally variably sized, up to 2 mm long, is occasionally oriented nearly parallel to the spreite in the upper part of the U-burrows. The spreiten, however, cannot be clearly observed in some specimens which consist mostly of massive, unoriented shale fragments and pyrite crystals in the burrows. The observed interval between adjacent menisci is up to 2 mm. In U-plane section, the burrows generally show an evenly rounded lower termination.