The Vaca Muerta is a marine source rock with excellent petroleum potential containing a large range of heterogeneities such as natural fractures filled with fibrous calcite (“beef”), concretions and ash beds. An exhaustive diagenetic study of ash beds samples was carried out, based on petrographic, mineralogical and geochemical investigations on five wells from the Neuquén Basin with different burial (1.1–1.6% VRo Eq). Ash beds usually display two facies, the clay-rich and the calcite-cemented one, both with complex alterations. The clay-rich ash beds are characterized by predominance of illite/smectite assemblage, added mainly to albite, pyrite and Fe–Ti oxides. They are interpreted to correspond to the first, denser and less porous ash emitted by the volcanoes, with a high amount of micro-crystals transported over relatively short distances. The calcite-cemented ash beds consist mostly of argillitized glass shards and pumice fragments cemented by calcite. They may represent late eruptive stage, wind-blown tephra deposited at greater distance from the volcanic source, with higher initial porosity and lower crystal content favoring early calcite cementation. Diagenetic alteration has completely modified the initial minerals of both facies, which makes it difficult to establish the precursor mineral composition. However, geochemical analyses demonstrate that both facies display well marked calc-alkaline magmatic signature (andesite, dacite/rhyodacite), and similar conditions of alteration during burial.

Vaca Muerta 是一种海相烃源岩，具有极好的石油潜力，包含大量非均质性，例如充满纤维方解石（“牛肉”）、结核和灰层的天然裂缝。基于对内乌肯盆地不同埋藏度（1.1-1.6% VRo Eq）的五口井的岩相学、矿物学和地球化学调查，对灰层样品进行了详尽的成岩研究。灰层通常呈现两种相，富粘土相和方解石胶结相，两者都具有复杂的蚀变。富含粘土的灰层的特点是伊利石/蒙脱石组合占优势，主要添加到钠长石、黄铁矿和 Fe-Ti 氧化物中。它们被解释为对应于火山喷出的第一个密度更大、孔隙更少的火山灰，大量的微晶在相对较短的距离内传输。方解石胶结的灰床主要由泥化玻璃碎片和方解石胶结的浮石碎片组成。它们可能代表喷发晚期，风吹的火山灰沉积在距火山源更远的地方，具有较高的初始孔隙度和较低的晶体含量，有利于早期方解石胶结。成岩蚀变已经完全改变了两相的初始矿物，这使得很难确定前体矿物组成。然而，地球化学分析表明，这两种相都显示出明显的钙碱性岩浆特征（安山岩、英安岩/流纹英安岩），以及埋藏期间类似的蚀变条件。风吹的火山灰沉积在距火山源较远的地方，具有较高的初始孔隙度和较低的晶体含量，有利于早期方解石胶结。成岩蚀变已经完全改变了两相的初始矿物，这使得很难确定前体矿物组成。然而，地球化学分析表明，这两种相都显示出明显的钙碱性岩浆特征（安山岩、英安岩/流纹英安岩），以及埋藏期间类似的蚀变条件。风吹的火山灰沉积在距火山源较远的地方，具有较高的初始孔隙度和较低的晶体含量，有利于早期方解石胶结。成岩蚀变已经完全改变了两相的初始矿物，这使得很难确定前体矿物组成。然而，地球化学分析表明，这两种相都显示出明显的钙碱性岩浆特征（安山岩、英安岩/流纹英安岩），并且埋藏期间的蚀变条件相似。