Draft:White Pocket
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White Pocket is located geographically in the Grand Staircase Escalante Monuments, Arizona and geologically on the Colorado Plateau. The Navajo Sandstone is exposed on the plateau as mounds and ridges. These are mostly reddish erosional remnants, but those remnants in White Pocket are blanketed with a white layer appearing as “Cauliflower Rock” (see figure). This white layer makes this area unique and thus being called the White Pocket.
Genesis
[edit]On the surface exposure, the “Cauliflower Rock”, which appears to be intertwined with the underlying formation (see figure), has been interpreted as contorted formation and thus prompted two schools of thought for the extraordinary geological processes at White Pocket. Some geologists proclaim that White Pocket results from soft-sediment deformation [1], and others suggest that large-scaled slumping and landslides generated by earthquakes were responsible [2]. Both have attributed to structural deformation involved in the formation of the apparent “contorted formation”.
Small scale soft-sediment deformation in outcrops is quite common and has been reported locally in the Glen Canyon region [3], and in Zion National Park [4]. Regional soft-sediment deformation, such as those interpreted in White Pocket, is rare and requires geological mechanisms to induce such deformation. Marc Deshowitz (2011) [2] interpreted that earthquake created a sand mass, which is the present day featureless bleached-white sandstone or “Cauliflower Rock” on the surface. He attributed the apparent “contorted” features to fluid escape structures as sand volcano.
Compelling evidence provided in a recent study by Chen (2024) [5] has, however, indicated that the “Cauliflower Rock” is a depositional feature, representing an excessive thick weathering crust, which is formed in arid region by deposition of minerals, derived from uprising ground water. The rock is cored or underlain by undisturbed stratification (see figures), demonstrating little structural disturbance in the formation of the white mass. The appearance of “contorted formation” in the rock is, in fact, generated by exposure of undisturbed cross-bedding sets on landscape surfaces with different curvatures and orientations. Varying degrees of the weathering crust development have been also noted, a clear evidence of depositional process (see figures).
References
[edit]- ^ Chan, M. A. and R. L. Bruhn, 2014, Dynamic liquefaction of Jurassic sand dunes: processes, Origins, and implications, Earth Surface Processes and Landforms, 39, pages 1478– 1491, doi: 10.1002/esp.3539.
- ^ a b Deshowitz, Marc, 2011, An Earthquake-Induced Flash Flood Event within the Early Jurassic Navajo Sandstone, White Pocket, Vermillion Cliffs National Monument, Arizona, AAPG Search and Discovery #90126, AAPG Rocky Mountain Section, Cheyene, Wyoming June 25-29 2011. (https://www.searchanddiscovery.com/pdfz/abstracts/pdf/2011/rocky/abstracts/ndx_deshowitz.pdf.html)
- ^ Bryant, Gerald, Giovanni Monegato, and Andrew Miall, 2013, An example of liquefaction-induced interdune sedimentation from the early Jurassic Navajo Sandstone, USA,Sedimentary Geology,Volume 297, Pages 50-62,ISSN 0037-0738, https://doi.org/10.1016/j.sedgeo.2013.09.001. (https://www.sciencedirect.com/science/article/pii/S0037073813001668)
- ^ Ford, Colby, Kevin Nick and Gerald Bryant, 2015, 3D visualization of liquefaction-induced dune collapse in the Navajo Sandstone, Utah, USA. EGU General Assembly 2015, held 12-17 April, 2015 in Vienna, Austria. id.8561 (https://ui.adsabs.harvard.edu/abs/2015EGUGA..17.8561F/abstract)
- ^ Percy PH Chen. Formation of “White Pocket” in The Surface Exposure of Jurassic Navajo Sandstone in Arizona. ESS Open Archive . August 19, 2024. DOI:10.22541/essoar.172405821.11678903/v1