Plate 99

Groove casts and fluid drag casts


More details of groove morphology can be detected in these partial views of the previous outcrop. Beside the compresence of smooth and striated groove casts, produced by rounded and jagged objects, respectively, you can see the occurrence of lobate marks, partly similar to the frondescent forms shown in plate 97 (fluid  impact and/or fluid drag structures, also called by someone flowage casts ). Their down flow divergence enables the determination of the paleocurrent direction, which grooves alone do not indicate.

Along the intrastratal surface exhumed by peeling off the basal "crust," mudstone pebbles occur, isolated or grouped (see upper right-hand corner). These are the "tools" that made most of the marks.

Marnoso-arenacea Formation, northern Apennines.


Sedimentographica