Experimental modelling of Carboniferous <i>Cordaites</i> and <i>Calamites</i> casts

ABSTRACT Observations of Carboniferous pith casts preserved in a channel deposit of the Mary Lee Coal zone, Black Warrior Basin, Alabama, led to an experimental study in a Recent fluvial channel to model the physical conditions under which these fossils formed. We describe the sedimentology of a cordaitean pith cast from this Pennsylvanian‐age log jam preserved in a split of the Mary Lee Coal, Alabama, and the results of sediment fill and casting in a natural stream channel of the Alabama Coastal Plain using glass tubes as ‘hollow stem’ analogue of the same diameter. These analogue fills modelled at the sediment–water interface and oriented sub‐perpendicular to flow develop the same sedimentological features recorded in the cordaitean cast. We document the presence of the same features in a larger diameter horsetail ( Calamites ) cast from the same log‐jam accumulation, demonstrating that the diameter of the void doesn't alter the pattern of internal sedimentation, which depends on the orientation of the axis relative to current flow and sediment transport. Actualistic experiments under natural conditions, as opposed to modelling under the constraints of a small flume, provide a more realistic means to assess the taphonomic factors and resultant fossil that influenced preservation of prostrate plant casts.