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Lenticular Shale Fabrics Resulting from Intermittent Erosion of Water-Rich Muds—Interpreting the Rock Record in the Light of Recent Flume Experiments

¹ Department of Geological Sciences, Indiana University, Bloomington, Indiana 47405, U.S.A.
² Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, U.S.A.
³ Department of Geological Sciences, Indiana University, Bloomington, Indiana 47405, U.S.A.

Lenticular lamination is a fabric that is known from shales of all ages, but its origin and paleoenvironmental significance is poorly understood. We have successfully reproduced this fabric in flume experiments. Beds of water-rich mud were eroded in a flume and yielded sub-millimeter to centimeter-size fragments that can be transported in bedload for distances of ten kilometers or more. Upon redeposition and compaction, these deposits have the same textural qualities as lenticular laminated shales from the rock record. Although accumulation of fecal pellets or abundant burrow tubes in a shale may produce comparable fabrics upon compaction, these can be distinguished from erosion-produced lenticular lamination via petrographic criteria. Lenticular lamination in shales that is due to deposition of water-rich mud fragments most likely records intermittent erosion and transport of surficial muds by currents.