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The AAPG/Datapages Combined Publications Database
Flank beds adjacent to the Rich Valley bioherm, Wabash County, Indiana, display unusual structures suggesting catastrophic slumping during and shortly after deposition. Lithotopes representative of reef core, reef flank, and interreef environments are mixed randomly within the deformed sedimentary rocks. Deformation appears to have involved processes of both brittle and semiplastic materials.
Displaced boulders, 1 to 2 m in diameter, are imbedded in laminated calcilutite. Uniformly inclined stratification typical of reef flanks is here locally reversed in dip, faulted, and contorted into minor folds within the sequence. A dike of fine-grained limestone, about 0.5 m thick, perpendicularly transects an inclined sequence of flank beds. Masses of mature quartz sandstone also are present, apparently as isolated blocks, displaced from some formerly higher location.
Observed features tentatively are attributed to multiple failures resulting from unstable oversteepening of normal flank sediments, storm ripping of semilithified core materials, and plastic flowage of poorly lithified flank-margin materials. Individual events could have been triggered by storms, earth shocks, or other catastrophic events.
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