Load Casts

Load casts, unlike flute casts, are deformational structures, rather than erosional structures.  They occur commonly along the bases of sandstone beds that overlie mudstone or shale beds.  While they may sometimes resemble flute casts, load casts can be differentiated from flute casts by their greater irregularity of shape and the lack of any indication of paleoflow direction.  Load casts range in size, and may be associated with other deformational structures like flame structures and/or ball-and-pillow structures.  Load casts form in settings where water-saturated muddy sediments are buried rapidly by coarser (sandy) sediments, creating a situation where dewatering of the mud cannot take place.  The weight of the overlying sand causes it to sink unevenly into the muddy substrate, creating these features.

	These are relatively large load casts, seen in cross-sectional view.   The weightof the overlying sand was sufficient to cause the darker muddy layer to rupture, such that deformation became more intense, making it difficult to distinguish boundaries between beds.
	This photo shows the relationship between load structures and flame structures.  The weight of the overlying beige sandy layer created the load structures and caused concurrent injection of the darker mud into the sand, creating flame structures.