The Carboniferous was a period of intense environmental perturbations, climate changes between greenhouse and icehouse, eustatic sea level change, and accumulation of organic carbon-rich sediments. At this time, the Tyler Formation was deposited in the midcontinent USA. A detailed palynological analysis of the Tyler Formation revealed a highly diverse assemblage of spores with minor pollen content, represented by 100 species belonging to 51 genera. Stratigraphically constrained spores and pollen grains were used to construct three interval zones of middle-late Chesterian (late Viséan-Serpukhovian) to early Morrowan (middle Bashkirian) ages. The stratigraphic position of the Mississippian-Pennsylvanian boundary was determined in the lower Tyler Formation based on the last appearance of typical forms of the late Chesterian, including , , , , and , compared to the first appearance of early Morrowan , , , and . Palynofacies analysis and statistical clustering of the Tyler Formation showed three palynofacies assemblages. PFA-1 showed moderate relative abundances of phytoclasts and AOM, suggesting deposition close to fluvio-deltaic and shallow marine environments, while PFA-2 exhibited high abundances of phytoclasts, mostly of opaque wood, reflecting deposition in active river-dominated delta plains. PFA-3 showed the highest abundances of AOM, suggesting deposition in a shallow marine environment. Organic petrography and geochemistry data indicate that the Tyler Formation is one of the best source rock intervals throughout the midcontinent USA. Based on organic matter richness, the Tyler Formation is subdivided into three groups. The first group has TOC contents higher than 10 wt% of kerogen Types III, mixed II/III, and II with excellent hydrocarbon generation potential. The second group has TOC content in the range of 2–10 wt% of kerogen Types III, mixed II/III, and II, and fair to excellent hydrocarbon generation potential. The third group shows organic matter richness with TOC content below 2 wt% with good organic matter richness and kerogen Types III to IV, and poor to fair hydrocarbon generation potential. The organic matter thermal maturity is evaluated based on T and VRo% values, suggesting that all samples of Tyler Formation are in the early to late stages of the oil window. However, care should be considered when assessing a mature source rock because the kerogen typing and generation is based on present-day TOC, S, and HI rather than their original values.

中文翻译：

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美国威利斯顿盆地泰勒组密西西比-宾夕法尼亚边界孢粉地层学：对富含有机质烃源岩和古环境重建的启示


石炭纪是一个环境剧烈扰动、温室和冰库之间气候变化、海平面变化以及富含有机碳沉积物积累的时期。此时，泰勒组沉积在美国大陆中部。对泰勒组的详细孢粉学分析揭示了具有少量花粉含量的高度多样化的孢子组合，包括属于 51 属的 100 种。地层限制的孢子和花粉粒被用来构建中晚期切斯特阶（晚维塞恩-塞尔普霍夫阶）到早期莫罗万（中巴什基尔阶）时代的三个区间带。密西西比-宾夕法尼亚边界的地层位置是根据晚切斯特阶典型形态的最后出现（包括 、 、 、 和 ）与早期 Morrowan 、 、 和 的首次出现相比较，确定在泰勒组下部。泰勒组的孢粉相分析和统计聚类显示了三个孢粉相组合。 PFA-1 显示出植物碎屑和 AOM 的相对丰度中等，表明沉积物靠近河流三角洲和浅海环境，而 PFA-2 显示出高丰度的植物碎屑，主要是不透明的木材，反映了沉积在活跃的河流主导的三角洲平原。 PFA-3 显示 AOM 丰度最高，表明沉积在浅海环境中。有机岩相学和地球化学数据表明，泰勒组是美国中部大陆最好的烃源岩层段之一。根据有机质丰富度，泰勒地层分为三组。第一组的 TOC 含量高于 10 wt% 的干酪根类型 III、混合 II/III 和具有优异生烃潜力的 II。 第二组干酪根类型 III、混合 II/III 和 II 的 TOC 含量在 2–10 wt% 范围内，具有中等至优异的生烃潜力。第三组显示有机质丰富度，TOC 含量低于 2 wt%，具有良好的有机质丰富度和干酪根类型 III 至 IV，但生烃潜力较差至一般。根据T和VRo%值对有机质热成熟度进行评价，表明泰勒组所有样品均处于含油窗口的早期至晚期。然而，在评估成熟烃源岩时应小心谨慎，因为干酪根分型和生成是基于当前的 TOC、S 和 HI，而不是其原始值。