The mineralogical and geochemical composition of carbonatized tephras of the Vaca Muerta Formation (Tithonian-Berriasian) in the Neuquén Basin (Argentina), allows retracing the diagenetic history and the origin of clay minerals in order to establish the sequence of diagenetic transformations and to explain the presence of chlorite in the felsic/intermediate ash beds. The carbonatized ash beds were studied in three sections located in the central part of the Neuquén Basin: El Trapial (ET), Puerta Curaco (PC) and Chacay Melehue (CM). Rock-Eval analyses performed in the enclosing marls revealed that ET section belongs to the oil window, whereas PC and CM to the dry gas window. The clay mineralogy of ET section is mostly constituted by R1/R3 mixed-layer illite/smectite (I/S) type, whereas in PC and CM sections, by highly-crystalline, aluminum-, magnesium-rich chlorite (sudoite) and R1/R3 I/S type. The high-ordered I/S (80–90% illite layers) in the oil window stage indicates that the central part of the Neuquén Basin was characterized by a geothermal gradient higher than previously reported, with an estimated value of 57 °C/km. The absence of any sudoite precursors in ET section and the pervasive distribution of sudoite aggregates in the matrix, suggests that sudoite have precipitated in situ from pore waters. The overmaturation of organic matter in PC and CM sections suggests that precipitation of sudoite occurred during late diagenetic stages, between 150 and 200 °C. The aluminum, magnesium and silicon, essential to sudoite's precipitation were available in the pore waters after the dissolution/recrystallization of minerals and volcanic glass shards present in the tephra. The formation of sudoite was related to the development of the Chos Malal Fold and Thrust Belt, which generated overpressure, deformation and fracturing of the rocks, thus facilitating the circulation of hot waters.

内乌肯盆地（阿根廷）Vaca Muerta 组（Tithonian-Berriaasian）碳化火山灰的矿物学和地球化学组成，可以追溯成岩历史和粘土矿物的起源，以建立成岩转变的序列并解释长英质/中间灰层中存在绿泥石。在内乌肯盆地中部的三个部分研究了碳化灰床：El Trapial (ET)、Puerta Curaco (PC) 和 Chacay Melehue (CM)。在封闭泥灰岩中进行的 Rock-Eval 分析表明，ET 剖面属于油窗，而 PC 和 CM 属于干气窗。ET剖面粘土矿物主要由R1/R3混合层伊利石/蒙脱石(I/S)型构成，而PC和CM剖面则由高结晶、铝、富镁绿泥石（sudoite）和R1/R3 I/S型。油窗阶段的高阶 I/S（80-90% 伊利石层）表明内乌肯盆地中部的地温梯度高于先前报道的地温梯度，估计值为 57°C/km . ET 剖面中不存在任何sudoite 前体和sudoite 聚集体在基质中的普遍分布，表明sudoite 已经沉淀原位来自孔隙水。PC 和 CM 剖面中有机质的过度成熟表明，sudoite 沉淀发生在晚成岩阶段，在 150 到 200 °C 之间。在火山灰中存在的矿物质和火山玻璃碎片溶解/重结晶后，孔隙水中可以获得对苏云石沉淀必不可少的铝、镁和硅。Sudoite的形成与Chos Malal褶皱逆冲带的发育有关，使岩石产生超压、变形和破裂，从而促进了热水的循环。