The Lower Cretaceous Agrio Formation is a source rock considered to be a possible unconventional reservoir. However, no detailed microstructure characterization of this hydrocarbon play has been performed. An exceptional oil-prone level is determined through outcrop information, petrography, x-ray diffraction, geochemical analysis, and x-ray micro–computed tomography (µCT). Microscopic studies reveal a lenticular fabric and calcareous nannofossils suggesting high carbonate productivity in the water column and algal-derived organic matter. The high organic matter content points to anoxic–euxinic conditions consistent with pyrite framboids, authigenic fluorapatite, and an elevated concentration of redox-sensitive elements. However, burrows reveal the activity of infaunal organisms, thus rejecting the idea of persistent bottom-water anoxia. The bioturbated, calcareous plankton and carbonate-rich mudstone represents accumulation in a distal outer ramp setting with calcareous plankton blooms and the co-occurrence of benthic microbial mats. Bottom currents, probably as a consequence of storm-related processes, were involved in detrital transport and oxygenation pulses. A three-dimensional (3-D)–microstructure reconstruction reveals three main µCT density-dependent phases: (1) a low-density phase composed of organic matter and calcite, (2) an intermediate-density phase dominated by calcite and minor organic matter, and (3) a high-density phase composed of authigenic minerals (pyrite, marcasite, and fluorapatite) and silt-sized detrital quartz and plagioclase. This analysis showed that burial diagenesis did not create enough pore space to be evaluated through µCT and that besides mineralogy, particle-size distribution, particle arrangement (sorting), and the local compaction degree affect the 3-D reconstructed structure. The analyzed sample is located toward the carbonaceous end member of the shale spectrum and exemplifies new approaches for the characterization of carbonate oil shales in the unit and similar deposits. From the perspective of unconventional exploration, the evaluation of depositional and postdepositional controls on the resultant microstructure might contribute to a better understanding of potential target intervals within the Agrio Formation.

中文翻译：

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微结构规模油页岩类似物的沉积和沉积后过程：巴塔哥尼亚北部内乌肯盆地下白垩统阿格里奥组

下白垩统阿格里奥组是被认为是可能的非常规储集层的烃源岩。然而，尚未对该烃的开采进行详细的微观结构表征。通过露头信息，岩石学，X射线衍射，地球化学分析和X射线微计算机断层扫描（µCT）可以确定异常多发油的水平。显微镜研究表明，一种柱状纤维和钙质纳米化石表明水柱和藻类衍生的有机物具有较高的碳酸盐产率。高有机物含量表明与黄铁矿黄铁矿，自生氟磷灰石和氧化还原敏感元素浓度升高相一致的缺氧-富余条件。然而，洞穴揭示了不孕生物的活性，因此拒绝了持续的底部水缺氧的想法。经过生物扰动的钙质浮游生物和富含碳酸盐的泥岩代表了在远端外部斜坡环境中的沉积，并伴有钙质浮游生物水华和底栖微生物垫的共同存在。可能由于风暴相关过程而导致的底流参与了碎屑运输和充氧脉冲。三维（3-D）-微观结构重建揭示了三个主要的μCT密度相关相：（1）由有机物和方解石组成的低密度相，（2）由方解石和少量有机物为主的中等密度相（3）由自生矿物（黄铁矿，镁铁矿和氟磷灰石）和粉砂大小的碎屑石英和斜长石组成的高密度相。该分析表明，埋藏成岩作用不能产生足够的孔隙空间，无法通过µCT进行评估，并且除了矿物学，粒径分布，颗粒排列（排序）和局部压实度还会影响3-D重建结构。被分析的样品位于页岩光谱的碳质末端，并举例说明了表征单元和类似矿床中碳酸盐油页岩的新方法。从非常规勘探的角度来看，对最终微结构的沉积和沉积后控制的评价可能有助于更好地了解阿格里奥组内潜在的目标层段。被分析的样品位于页岩光谱的碳质末端，并举例说明了表征单元和类似矿床中碳酸盐油页岩的新方法。从非常规勘探的角度来看，对最终微结构的沉积和沉积后控制的评价可能有助于更好地了解阿格里奥组内潜在的目标层段。被分析的样品位于页岩光谱的碳质末端，并举例说明了表征单元和类似矿床中碳酸盐油页岩的新方法。从非常规勘探的角度来看，对最终微结构的沉积和沉积后控制的评价可能有助于更好地了解阿格里奥组内潜在的目标层段。