Ahmed Mansour , Thomas Gentzis , Timothy O. Nesheim , Jian Wang , Xiugen Fu , Mohamed S. Ahmed , Humberto Carvajal-Ortiz
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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 <em>Tripartites vetustus</em>, <em>Knoxisporites triradiatus</em>, <em>Knoxisporites stephanephorus</em>, <em>Densosporites diatretus</em>, and <em>Schopfipollenites acadiensis</em>, compared to the first appearance of early Morrowan <em>Crassispora kosankei</em>, <em>Cirratriradites saturnii</em>, <em>Radiizonates aligerens</em>, and <em>Raistrickia saetosa</em>. 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<sub>max</sub> 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<sub>2</sub>, and HI rather than their original values.</p></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":null,"pages":null},"PeriodicalIF":5.6000,"publicationDate":"2024-05-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":"{\"title\":\"Palynostratigraphy of the Mississippian-Pennsylvanian boundary in the Tyler Formation, Williston Basin, USA: Implications for organic matter-rich source rocks and paleoenvironmental reconstruction\",\"authors\":\"Ahmed Mansour , Thomas Gentzis , Timothy O. Nesheim , Jian Wang , Xiugen Fu , Mohamed S. Ahmed , Humberto Carvajal-Ortiz\",\"doi\":\"10.1016/j.coal.2024.104533\",\"DOIUrl\":null,\"url\":null,\"abstract\":\"<div><p>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 <em>Tripartites vetustus</em>, <em>Knoxisporites triradiatus</em>, <em>Knoxisporites stephanephorus</em>, <em>Densosporites diatretus</em>, and <em>Schopfipollenites acadiensis</em>, compared to the first appearance of early Morrowan <em>Crassispora kosankei</em>, <em>Cirratriradites saturnii</em>, <em>Radiizonates aligerens</em>, and <em>Raistrickia saetosa</em>. 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<sub>max</sub> and VRo% values, suggesting that all samples of Tyler Formation are in the early to late stages of the oil window. 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引用次数: 0
摘要
石炭纪是一个环境剧烈扰动的时期,气候在温室和冰室之间变化,海平面发生震荡性变化,富含有机碳的沉积物不断积累。此时,泰勒地层沉积于美国中部大陆。对泰勒地层进行的详细古生物学分析表明,这里的孢子种类繁多,花粉含量较少,共有 51 个属 100 个种。根据地层制约的孢子和花粉粒,构建了从切斯特期中晚期(Viséan-Serpukhovian 晚期)到莫罗期早期(Bashkirian 中期)的三个区间带。根据晚期切斯特期典型形态的最后出现时间,包括、、、和,与早期摩罗期的首次出现时间、、、和,确定了密西西比期-彭斯瓦尼期界线在泰勒地层下部的地层位置。泰勒地层的古生界分析和统计聚类显示出三种古生界组合。PFA-1显示出中等相对丰度的植物蜕皮器和AOM,表明沉积在靠近氟三角洲和浅海环境的地方;PFA-2显示出较高丰度的植物蜕皮器,主要为不透明木质,反映出沉积在以河流为主的活跃三角洲平原。PFA-3 显示出最高的 AOM 丰度,表明沉积在浅海环境中。有机岩石学和地球化学数据表明,泰勒地层是整个美国中部大陆最好的源岩层段之一。根据有机质的丰富程度,泰勒地层被细分为三组。第一组的总有机碳(TOC)含量高于 10 wt%,属于角质三类、混合二/三类和二类,具有极佳的碳氢化合物生成潜力。第二组的 TOC 含量在 2-10 wt%之间,包括 III 型角质、II/III 混合型和 II 型角质,碳氢化合物生成潜力从一般到优秀。第三组显示有机质丰富度,TOC 含量低于 2 wt%,有机质丰富度较好,角质类型 III 至 IV,碳氢化合物生成潜力较差至一般。根据 T 和 VRo%值评估有机质热成熟度,表明泰勒地层的所有样本都处于石油窗口的早期至晚期阶段。不过,在评估成熟源岩时应注意,因为角质层的分类和生成是基于目前的 TOC、S 和 HI 值,而不是其原始值。
Palynostratigraphy of the Mississippian-Pennsylvanian boundary in the Tyler Formation, Williston Basin, USA: Implications for organic matter-rich source rocks and paleoenvironmental reconstruction
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 Tripartites vetustus, Knoxisporites triradiatus, Knoxisporites stephanephorus, Densosporites diatretus, and Schopfipollenites acadiensis, compared to the first appearance of early Morrowan Crassispora kosankei, Cirratriradites saturnii, Radiizonates aligerens, and Raistrickia saetosa. 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 Tmax 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, S2, and HI rather than their original values.
期刊介绍:
The International Journal of Coal Geology deals with fundamental and applied aspects of the geology and petrology of coal, oil/gas source rocks and shale gas resources. The journal aims to advance the exploration, exploitation and utilization of these resources, and to stimulate environmental awareness as well as advancement of engineering for effective resource management.