白袋地区

白袋地区（英语：White Pocket）位于亚利桑那州大楼梯埃斯卡兰特纪念碑(Grand Staircase Escalante Monuments)，地质上位于科罗拉多高原(Colorado Plateau)。纳瓦霍砂岩 (Navajo Sandstone)以土丘和山脊的形式暴露在高原上。这些大多是淡红色的侵蚀遗迹，但在白袋地区中的那些侵蚀遗迹却被一层白色的岩石层覆盖，看起来像花椰菜岩（CauliflowerRock）（见图）。这白色层使该区域独一无二，因此被称为“白袋地区”。

成因

从表面上看，花椰菜岩似乎与底下地层交织在一起（见图），因此被解释为扭曲的地层，从而导致有关于白袋地区非凡地质过程的两种思流派。一些地质学家宣称，白袋地区的成因是由于软沉积物变形(soft-sediment deformation) ^[1]，而另一派认为，成因是地震引起的大规模塌陷和山体滑坡^[2]。两派都归因扭曲地层于结构变形。小规模的软沉积物变形在露头中常见，并已在局部格伦峡谷（Glen Canyon)及锡安国家公园(Zion National Park)地区有报道^[3]^[4]. 但区域性的软沉积物变形，例如在白袋地区中，却很少有报道。因此需要一种地质机制来引发这种区域性变形。 Marc Deshowitz (2011) ^[2] 解释说，地震形成了流动沙体，而构成现今地表上的毫无特色白色砂岩或“花椰菜岩”。他认为扭曲地层是一种流体逃逸结构(fluid escape structure)，如同沙火山(sand volcano)。

Chen (2024)^[谁？]^[5]的最近的一项研究中提供了具信服力的证据，指出在亚利桑那州白色口袋地区出露的花椰菜岩是一种沉积构造，代表在干旱地区形成的过度厚风化壳。它是由地下水上升所系带的的矿物质在地表沉积而形成的。花椰菜岩石的核心或下方都是未受干扰的地层层理（见图），显示白色地层形成过程中几乎没有构结干扰。事实上，岩石表面出现的扭曲结构，是由于常规未受干扰的交错层理, 出露在不同曲率和方向的露头表面上而产生的。岩石表面也具有不同发育程度的风化壳（见图）。这都是沉积过程的明显证据（见图）。

参考

^ 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.
^ ^2.0 ^2.1 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

[”Chan”-1] 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.

[”Deshowitz”-2] 2.0 ^2.1 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”-3] 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”-4] 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)

[”Chen”-5] 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

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