The Marl Slate (finely laminated shales) signifies rapid drowning of the Yellow Sands (aolian dunes) as the sea flooded in at the start of Zechstein Cycle 1 (Z1).
Conditions in the lower water column were anoxic leading to amazing fossil preservation of offshore, nearshore and terrestrial fauna and flora.
Platysomus (shallow seas)
Source:
Tim Pettigrew