This study investigates the geochemical and petrological characteristics of solid bitumen in the DBH15/73 core from the Furongian (upper Cambrian) and Miaolingian (middle Cambrian) Alum Shale in Billingen, south central Sweden. At Billingen a > 30 m thick Permian diabase (dolerite sill) intruded approximately 100 m above the Alum Shale that promoting the formation of solid bitumen in the uppermost half of the Alum Shale due to enhanced heat flow. The bitumen has been classified into bituminite/diagenetic solid bitumen (DSB), initial-oil solid bitumen (IOSB), and primary-oil solid bitumen (POSB) based on their genesis, morphology and random solid bitumen reflectance (BR). The Miaolingian shale, constituting the lower part of the Alum Shale, is immature and contains solely bituminite and DSB, with measured BR ranging from 0.40% to 0.48%. In contrast, the Furongian shale exhibits enrichment in IOSB and POSB and range from marginally mature to peak oil generation with towards the top of the section. Characteristics of uneven heating is seen in the IOSB (BR: 0.97–1.08%) including oxidation rims and abnormally high maturity surrounding fractures. The POSB (BR: 0.63–2.01%) is present not only in the Alum Shale but also in the overlying Ordovician Latorp limestone and the underlying Kakeled Limestone Bed, and shows flow structures which is further evidence for migration. The abundance of POSB and IOSB is determined through maceral point counting, revealing POSB as the dominant bitumen type (1.54–7.13 vol%), while IOSB constitutes the minority (0.05–0.31 vol%) within the Furongian shale. This distribution suggests rapid thermal evolution of organic matter within the oil generation window. Additionally, a reduction in free hydrocarbons (Rock-Eval S1), potential hydrocarbons (Rock-Eval S2), and unexpectedly low T was observed in the Furongian shale. Results indicate that hydrocarbon generation resulting from thermal intrusion contributes to the relatively low S2. Migration of POSB and generated oil to adjacent layers leads to the loss of S1, while the reduced Tmax may be attributed to high uranium content which weakens carbon chain bond energy. These anomalies result in an underestimation when evaluating thermal maturity and kerogen type conversion based on Rock Eval data alone.

中文翻译：

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热侵入对瑞典中南部明矾页岩的影响


本研究调查了瑞典中南部比林根芙蓉系（上寒武统）和苗岭系（中寒武统）明矾页岩 DBH15/73 岩心中固体沥青的地球化学和岩石学特征。在比林根，超过 30 m 厚的二叠纪辉绿岩（辉绿岩基）侵入明矾页岩上方约 100 m，由于热流增强，促进了明矾页岩上半部分固体沥青的形成。根据其成因、形态和随机固体沥青反射率（BR），沥青被分为沥青/成岩固体沥青（DSB）、初始油固体沥青（IOSB）和原生油固体沥青（POSB）。苗岭期页岩属于明矾页岩下部，未成熟，仅含烟煤和 DSB，测得的 BR 范围为 0.40% 至 0.48%。相比之下，芙蓉系页岩表现出 IOSB 和 POSB 富集，范围从边缘成熟到产油峰值，并接近该部分的顶部。在IOSB（BR：0.97-1.08%）中可以看到加热不均匀的特征，包括氧化边缘和异常高成熟度的周围裂缝。 POSB（BR：0.63-2.01%）不仅存在于明矾页岩中，而且还存在于上覆奥陶纪 Latorp 石灰岩和下伏 Kakeled 石灰岩层中，并显示出流动结构，这是迁移的进一步证据。 POSB 和 IOSB 的丰度通过显微点计数确定，显示 POSB 是芙蓉系页岩中主要的沥青类型（1.54–7.13 vol%），而 IOSB 构成少数（0.05–0.31 vol%）。这种分布表明有机质在生油窗口内快速热演化。 此外，在芙蓉系页岩中还观察到游离碳氢化合物 (Rock-Eval S1)、潜在碳氢化合物 (Rock-Eval S2) 减少以及 T 值出乎意料地低。结果表明，热侵入引起的碳氢化合物生成导致了相对较低的 S2。 POSB和生成的石油向邻近层的迁移导致S1的损失，而Tmax降低可能归因于高铀含量削弱了碳链键能。仅根据岩石评估数据评估热成熟度和干酪根类型转换时，这些异常会导致低估。