Sugarloaf Mountain Tephra — A Pleistocene Rhyolitic Deposit of Base-Surge Origin in Northern Arizona
Sugarloaf Mountain Tephra — A Pleistocene Rhyolitic Deposit of Base-Surge Origin in Northern Arizona
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舒格洛夫山火山灰岩 — 亚利桑那州北部更新世基涌起源的流纹岩矿床
DOI：
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发表时间：
1975
期刊：
影响因子：
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通讯作者：
R. Updike
中科院分区：
文献类型：
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作者：
M. Sheridan;R. Updike
甜面包山是亚利桑那州旧金山山顶东北部的一个流纹状圆顶，在糖面包山周围形成了一个围裙。凝灰岩沉积沿内生穹隆北侧出露180°，最大厚度为75m。凝灰岩环中可识别出三种层理(或沉积)单元：平面层、块状层和沙波层。相关的3到10米厚的空降沉积物延伸到凝灰岩环的东北方向。圆顶形成于21.2万年前，与之相关的冰盖沉积早于邻近的伊利诺斯时代冰川沉积。
紧贴地面的流态化密度流与无粘性底板的相互作用是用于底流输送的模式。颗粒大小数据表明，凝灰质地类型代表离散的亚群体。通过对尺度数据的因子分析提取的两个主根被分配给涌流底部的粘性剪切和惯性剪切。砂波床是在具有薄牵引力的稀相流态化系统中，在粘性剪切作用下形成的。在几米厚的稀相流态化涌浪云下，1-10厘米厚的推移质层中，平面床层通过惯性剪切发展。巨大的床层是粘性和惯性力共同作用的结果，这些力在稀密相流态化的泄气云中运行。流云含固率和推移质层厚度是凝灰岩沉积结构形成的关键因素。
Sugarloaf tephra forms an apron surrounding Sugarloaf Mountain, a rhyolitic dome northeast of the San Francisco Peaks, Arizona. Tuffring deposits, exposed for 180° around the north side of the endogenous dome, have a maximum thickness of 75 m. Three types of bedding (or depositional) units are recognized in the tuff ring: plane beds, massive beds, and sand-wave beds. A related 3- to 10-m-thick air-fall deposit extends northeast of the tuff ring. The dome, dated at 212,000 yr B.P., and its associated tephra deposits predate the adjacent Illinoian-age glacial deposits.
Interaction of a ground-hugging fluidized density flow with a cohesionless substrate is the model used for base-surge transport of the tephra deposits. Particle-size data show that the tuffring textural types represent discrete subpopulations. The two principal roots extracted by factor analysis of the size data are assigned to viscous and inertial shear at the base of the surge flow. Sandwave beds form under the influence of viscous shear in a dilute-phase fluidized system with a thin traction layer. Plane beds develop through inertial shear in a 1- to 10-cm-thick bed-load layer beneath a dilute-phase fluidized surge cloud several meters thick. Massive beds result from a combination of viscous and inertial forces operating in a deflating, dilute- to dense-phase fluidized cloud. Solid fraction of the flowing cloud and thickness of the bed-load layer are the critical factors in developing the textures of the tuffring deposits.