Way-Up Structures

These structures may be either primary or secondary in origin.  The significant feature of these structures is that they give information about the direction of stratigraphic top.   This is a critical field tool, because it is usually critical to know whether the section is upright or has been overturned.

	Mudcracks.   The pencil points upward.  Notice the "V" shape of the cracks is wider at the top of the bed and narrower (pointier) at the bottom of the crack (which points to the base of the bed).
	Flame Structures.  The trick with flame structures is to understand how these form.  Flames form when more dense sediment (usually sand) is deposited on top of less dense sediment (usually mud) that is still wet and fluid.  The mud cannot support the weight of the overlying sand, and some of the mud is "injected" upward into the sand.  Thus, the "flame" points to the top of the bed.
	Flame and Load Structures.  Here the dark, finer-grained muddy sediment is producing "flames" into the overlying coarser sand.  The beige sand is, in turn, producing "load" structures into the mud, as the weight of the sand locally "loads" and depresses the mud.
	Flame and Load Structures.  Similar to above: dark mud, and light sand.
	Flute Casts.  These structures form on the base of the bed.  They, they indicate stratigraphic top by forming on the bottom of the bed.  Flutes are asymmetric depressions, usually filled by sand and formed in mud.  The steeper side of the asymmetry faces in the upstream direction, so these structures also indicate paleocurrent direction.
	Dish Structures.  Dish structures form as a result of sediment de-watering.  The original sediment is typically laminated, and the dewatering process breaks the laminae at irregular intervals as the fluids escape upward through the bed.  The upward movement of fluid creates the structure, which looks like small convex-up dishes throughout the outcrop.  These are not very well developed dish structures.
	This is a tricky one!  This is a normally graded sandstone bed.  When the photograph was taken, stratigraphic up was determined by other means (perhaps by indicators above).  Once stratigraphic top is known, graded beds can be used to give additional information about depositional conditions.  In the case of "normally graded beds", as in this photo, the coarsest grains are found at the base of the bed, and the grain size fines upward.   Note that the base of this normally graded bed is at approximately the location of the base of the pen.