The Quaternary Campo de la Piedra Pomez ignimbrite (CPPI) is a superbly exposed, partially indurated, rhyolitic ignimbrite emplaced on the southern Puna of Argentina. It is characterized by a variety of facies that record in unprecedented detail the flow dynamics of the parent pyroclastic density currents (PDCs). Detailed facies analysis and internal architecture defined using a sequential stratigraphy approach reveal that CPPI was formed by sustained PDCs, generated from a low fountain eruptive style (boiling over). The PDCs had overall flow conditions characterized by high particle concentration and limited capability to surmount topographic obstacles. The mobility of the PDCs was largely controlled by high pore pressure and the continuous supply at the source (sustained forced convection-dominated PDCs). The successive forestepping-backstepping stacking patterns identified in the CPPI reflect a marked unsteadiness of its parent PDCs due to a pulsating discharge rate at the source. The lateral facies variations in the CPPI record the non-uniform character of its parent PDCs as they flowed outward from the base of the collapsing fountain. Proximal-medial areas characterized by steady aggradation rates pass through to distal braided thalwegs with highly variable aggradation rates, to frontal edges characterized by the step aggradations of secondary decoupled pumice-rich lobes. Collectively, the facies variations in the CPPI record the complex dynamics of sustained PDCs that include pulsating discharge rate at the source, progressive modification of the original topography, and lateral flow transformations.

中文翻译：

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持续的、强迫的火山碎屑密度流的脉动流动动力学：来自阿根廷普纳南部 Campo de la Piedra Pómez ignimbrite 的相分析的见解

Quaternary Campo de la Piedra Pomez ignimbrite (CPPI) 是位于阿根廷南部普纳的流纹质凝灰岩，出露极好，部分硬化。它的特点是各种相以前所未有的细节记录母体火山碎屑密度流 (PDC) 的流动动力学。使用连续地层学方法定义的详细相分析和内部结构表明，CPPI 是由持续的 PDC 形成的，由低喷泉喷发方式（沸腾）产生。PDC 具有整体流动条件，其特点是粒子浓度高，克服地形障碍的能力有限。PDC 的流动性在很大程度上受高孔隙压力和源头的连续供应（持续强制对流主导的 PDC）控制。在 CPPI 中确定的连续的前步 - 后步堆叠模式反映了由于源处的脉动放电率，其母 PDC 的显着不稳定。CPPI 中的横向相变化记录了其母 PDC 从坍塌喷泉底部向外流动时的非均匀特征。以稳定加成速率为特征的近端-中间区域通过具有高度可变的加成速率的远端编织 thalwegs，到以二级去耦富浮石叶的阶梯加成为特征的前缘。总的来说，CPPI 中的相变化记录了持续 PDC 的复杂动态，包括源处的脉动放电率、原始地形的逐步修改和侧向流转换。