Clastic-injection Pipes and Syndepositional Deformation Structures in Jurassic Eolian Deposits: Examples from the Colorado Plateau
Published:January 01, 2007
Marjorie Chan, Dennis Netoff, Ronald Blakey, Gary Kocurek, Walter Alvarez, 2007. "Clastic-injection Pipes and Syndepositional Deformation Structures in Jurassic Eolian Deposits: Examples from the Colorado Plateau", Sand Injectites: Implications for Hydrocarbon Exploration and Production, Andrew Hurst, Joseph Cartwright
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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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Sand Injectites: Implications for Hydrocarbon Exploration and Production
Sand injectites are described in scientific literature as an increasingly common occurrence in hydrocarbon reservoirs, in particular in deep-water clastic systems, where they are known to influence reserves distribution and recovery. Seismically-detectable injected sand bodies constitute targets for exploration and development wells and, subseismic sand bodies provide excellent intra-reservoir flow units that create field-wide vertical communication through depositionally extensive, low-permeability units. As sand injectites form permeable conduits in otherwise low-permeability units they facilitate the expulsion of basinal fluids; hence they act both as a seal risk and mitigate timing and rate of hydrocarbon migration. Injected sand bodies form intrusive traps, which are distinct from structural or stratigraphic traps. Included in this publication are 10 chapters on subsurface examination of sand injectites, 1 chapter on theoretical considerations, and 13 outcrop analogs in reservoirs across the world. Captured in this volume is at least a taste of the global and stratigraphic distribution of sand injectites, and an attempt to introduce readers to sand injectites and their significance in the context of hydrocarbon exploration and production. The book is not intended as a complete review of the field-based literature, but emphasizes high quality case studies from the surface and subsurface. The geographic scope of the book is large, and illustrates the diversity of geological settings in which these fascinating and economically significant features are found.