Macaronichnus segregatis Clifton et Thompson, 1978

The ichnofabric consists of a c. 5 cm thick, totally bioturbated dark grey sandstone layer with a sharp erosive surface at the top, and another 5.5 cm thick clean and light grey sandstone horizon above, which exhibits only a few individual burrows near its top. The size of M. segregatis is variable and ranges from 2 to 4mm in diameter, although smaller burrows were also observed. Under the microscope, the structure of M. segregatis can be recognized by a pale core comprising essentially quartz and feldspar grains, whereas the dark particles such as heavy minerals and mica are concentrated in the thin mantle. A laminated backfill structure occurs sporadically. Due to compaction, some burrows are flattened and a slickensided appearance results from tectonic shearing.The crowded occurrence and the internal structure of the mantled burrows with an active fill are typical for M. segregatis (Clifton and Thompson 1978; Keighley and Pickerill 1995; Bromley 1996)