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Abstract

A remarkable range of syndepositional deformation structures are present in eolian and sabkha strata across the Colorado Plateau. In a classification based on scale and style of deformation, these structures include (1) millimeter- to centimeter-scale crinkly and contorted laminae and liquefaction structures; (2) meter- scale folded, contorted cross-strata and liquefied zones; (3) decameter-scale rotated blocks, slumps, and mass-flow deposits; and (4) bed-scale to multiformation-scale clastic pipes. These syndepositional structures record a range of brittle, hydroplastic, liquefaction, and fluidization properties of the sediment at the time of deformation. The pipes are the most enigmatic structures, and these can range from simple forms with structureless fill to complex forms with structureless fill, breccia blocks, and warping or faulting of surrounding and encasing host strata. A disproportionate abundance of syndepositional deformation structures in Jurassic strata of the Colorado Plateau is attributed to (1) the deposition and dissolution of evaporites associated with interdunes, sabkhas, and adjacent shallow seas; (2) a high water table, especially in response to adjacent marine transgressions; (3) dune progradation and loading over saturated, poorly consolidated, marine, and sabkha substrates; and (4) the interbedding of mobile sabkha deposits with bedded and laminated eolian sands capable of recording the overpressurization and deformation of sabkha and eolian deposits. External triggering events may have included catastrophic flooding events, bolide impacts, and seismicity. The range of deformation structures has important implications for understanding syndepositional processes. Furthermore, these studies have applications to interpreting the interconnections of high-permeable injectite conduits across multibed to multi- formational scales.

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