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Biogenic Cross-Lamination Produced by the Pistol-Shrimp Alpheus bellulus in Microcosm Experiments

¹ Department of Earth Sciences, Memorial University, St. John's, Newfoundland, NL A1B 3X5, Canada

Study of aquaria containing the shrimp Alpheus bellulus and poorly sorted, coarse-grained sand has revealed the potential for macroorganisms to create structures closely resembling ripple cross-lamination, including climbing-ripple cross-lamination. A. bellulus excavates decimeter-scale craters in the sediment, carrying sediment grains up the steep inner (stoss-equivalent) slope of the crater and depositing them on the outside (lee-equivalent side). The fabrics produced resemble hydrodynamically produced ripple cross-lamination, particularly when observed in the limited cross sections available in core. This biogenic cross-lamination can be distinguished from hydrodynamic cross-lamination in that the biogenic cross-lamination is steeper than is typical for current-generated ripple cross-lamination, the tabular foresets are close to angle of repose, and the structure has a circular ripple crest.