Collaborative Research: Hydrogeologic Analysis of Oriented Carbonate Concretions, Sierra Ladrones Formation, New Mexico

9725194 Davis地质非均质性对流体流动的影响是处理污染物运移问题时最困难的问题之一。渗透率的空间变化导致速度的空间变化，进而导致频散。重要的理论进展为理解地质非均质性和分散性之间的关系提供了定量框架。然而，关于地质非均质性的本质以及流体如何在具有多尺度非均质性的介质中流动，仍然存在许多问题。传统上，有两种类型的实地研究被用来补充理论模型。大规模的地下示踪实验侧重于水力导率的空间变化和由此产生的羽流行为。露头研究提供了对地质非均质性的本质及其与随机模型的关系的认识。然而，这两种方法在一定程度上是孤立的，因为大规模的示踪实验研究了羽流的演化，但在记录地质非均质性和速度相关结构方面的能力有限。相反，露头研究提供了地质非均质性的高分辨率信息，但从历史上看，并没有量化明确的流动成分。我们已经发现证据表明，成岩结构的元素保存了新墨西哥州Sierra Ladrones组古地下水流动的定量信息。长度从厘米到几十米不等的碳酸盐结核取向被解释为古地下水流动方向的指示。拟议的研究将获得重要的额外数据，并采用最先进的定量方法来进一步验证固结取向记录当地地下水流动方向的假设。我们将通过以下方法来验证这一假设：1)获得水文地质和固结方向的额外数据；2)获得固结化学和生长历史的高分辨率图像；3)进行流动和化学反应的数值实验，以测试固结生长的概念模型。我们的测绘工作将包括对原始沉积构造、凝块取向和渗透率的米尺度研究，以及对100米尺度的凝块取向和相组合的测绘。我们将通过表征地球化学分带（ICP-MS和离子探针）和残余微生物种群（SEM）的存在来测试其他凝块起源模型。流动、输运和反应的数值模拟将为综合我们的水文地质、岩石学和地球化学结果提供定量手段。在Davis （EAR 9725194）和Mozley （EAR 9726416）的合作安排下，研究将侧重于水文地质制图（结核方向和水文地质性质）和表征结核生长特征（岩石学和地球化学）。反应性输运建模将在EAR-9734404下与H. Rajaram博士合作进行。如果这些定向固结物确实记录了古地下水的流动方向，它们可能会进一步深入了解流体如何在大空间尺度上通过多孔介质流动，表现出多尺度的非均质性。

9725194 Davis The effect of geological heterogeneity on fluid flow is one of the most difficult issues when dealing with problems of contaminant transport. Spatial variations in permeability result in spatial variations in velocity which in turn result in dispersion. Significant theoretical advances have provided a quantitative framework for understanding the relationship between geologic heterogeneity and dispersion. However, many questions remain regarding the nature of geologic heterogeneity and how fluids flow through media exhibiting multiple scales of heterogeneity. Two types of field studies have traditionally been used to complement the theoretical models. Large-scale subsurface tracer experiments focus on the spatial variation in hydraulic conductivity and the resulting plume behavior. Outcrop studies have provided insight into the nature of geologic heterogeneity and its relation to stochastic models. However, these two approaches are somewhat isolated in that the large scale tracer experiments have studied the evolution of plumes but are limited in their ability to document geologic heterogeneity and velocity correlation structure. Conversely, outcrop studies provide high-resolution information on the geologic heterogeneity, but historically, have not quantified an explicit flow component. We have found evidence that elements of diagenetic fabrics preserve quantitative information about the paleogroundwater flow in the Sierra Ladrones Formation, New Mexico. The orientations of elongate carbonate concretions ranging in size from centimeters to 10s of meters are interpreted as indicators of paleogroundwater flow direction. The proposed research will obtain important additional data and employ state-of-the-art quantitative methods to further test the hypothesis that concretion orientations record local groundwater flow directions. We will test this hypothesis by 1) obtaining additional data on the hydrogeology and concretion orientations, 2) obtaining high-resolution i mages of concretion chemistry and growth history, and 3) conducting numerical experiments of flow and chemical reactions to test conceptual models of concretion growth. Our mapping will include both meter-scale studies of primary sedimentary structures, concretion orientations, and permeability as well as mapping concretion orientations and facies assemblages at the scale of 100s of meters. We will test alternative models of concretion origin by characterizing geochemical zonation (ICP-MS and Ion Microprobe) and presence of relict microbial populations (SEM). Numerical modeling of flow, transport, and reactions will provide the quantitative means of synthesizing our hydrogeologic, petrographic, and geochemcial results. The research under this collaborative arrangement between Davis (EAR 9725194) and Mozley (EAR 9726416) will focus on hydrogeologic mapping (concretion orientations and hydrogeologic properties) and characterizing concretion growth characteristics (petrography and geochemistry). The reactive transport modeling will be conducted in a cooperative arrangement with Dr. H. Rajaram under EAR-9734404. If these oriented concretions do record paleogroundwater flow directions, they may provide further insight into how fluids flow through porous media over large spatial scale exhibiting multiple scales of heterogeneity.