摘要: 鄂西-黔南地区下寒武统富有机质页岩层系是页岩气勘探的重要目标，查明不同地区富有机质页岩层段的等时地层关系及其成因已成为页岩气勘探的关键问题。通过对鄂西聂地1井及黔南黄页1井下寒武统测井自然伽马数据的旋回地层学分析，识别出下寒武统主要的天文周期，以文献已报道的锆石年龄作为锚点建立了两口井的天文年代标尺。研究表明，鄂西聂地1井牛蹄塘组36 m和9 m的沉积旋回及黄页1井16.6 m和4 m的沉积旋回代表了轨道周期405 kyr和100 kyr偏心率；聂地1井牛蹄塘组和黄页1井九门冲组持续时间分别为3.3 Myr和2.6 Myr，其年龄区间分别处于535.4±1.7 Ma~536.82±1.7 Ma和535.2±1.7 Ma~537.84±1.7 Ma。基于沉积噪音模型恢复了两口井下寒武统时期的相对海平面变化，经过对比分析，两口井海平面变化对应于1.2 Myr旋回和两个三级层序（SQ1和SQ2）。将下寒武统富有机质页岩有机碳含量（TOC）和405 kyr旋回滤波及海平面变化曲线对比，结果显示TOC高值段对应于405 kyr旋回最大值，而TOC低值段正好对应了聂地1井两个405 kyr旋回之间的低值。由于太阳系的混沌行为，无法准确预测早寒武纪理论轨道偏心率对富有机质页岩驱动的机制。假设偏心率最大值和有机碳含量最大值对应，则在更长的时间里强季节性变化在某种程度上触发了黑色页岩的富集。此外，相对海平面变化和有机碳含量对比表明海平面变化和有机质富集不具有因果关系。
Cyclostratigraphic analysis of the Lower Cambrian shales in western Hubei and southern Guizhou
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Abstract: The Lower Cambrian organic-rich shale is important marine shale exploration target in western Hubei and southern Guizhou. Understanding the chronostratigraphic relationships and their underlying causes of organic-rich shale intervals in different areas is crucial for shale gas exploration. In this study, we conducted cyclostratigraphic analyses using natural gamma-ray logging data from the Lower Cambrian Niedi-1 well in western Hubei and the Huangye-1 well in southern Guizhou, and determined the primary astronomical periods. Using previously reported zircon age as anchoring points, we constructed an astronomical time scale for the Lower Cambrian. Our results reveal that wavelengths of 36 m and 9 m in the Niedi-1 well, and 16.6 m and 4 m in the Huangye-1 well, correspond to orbital 405 kyr and 100 kyr cycles, respectively. Furthermore, we calculated the durations of the Niutitang Formaion in the Niedi-1 well and Jiumengchong Formation in the Huangye-1 well to be 3.3 Myr and 2.6 Myr, respectively, with age intervals falling within the range of 535.4±1.7 Ma to 536.82±1.7 Ma and 535.2±1.7 Ma to 537.84±1.7 Ma. Using a sedimentary noise model, relative sea-level changes in the Lower Cambrian were reconstructed. Through correlation between sea-level change curves (DYNOT and ρ1), eccentricity cycles and sedimentary cycles, our results indicate that sea-level changes correspond to 1.2 Myr obliquity modulation cycles and two sedimentary sequences (SQ1 and SQ2). In addition, comparing the total organic carbon content (TOC) of the Lower Cambrian organic-rich shale with orbital eccentricity, sedimentation rates and sea-level changes, our findings reveal that the intervals with high TOC value correlate with the maximum eccentricity of 405 kyr, while low TOC value correspond to minimum value in Niedi-1 well. Because of the chaotic behavior of the solar system, accurately predicting the mechanism driving organic-rich shale during the early Cambrian is impossible. Assuming that the maximum eccentricity corresponds to the maximum organic carbon content at that time, strong seasonal variation will, to some extent, trigger the enrichment of black shale over a more extended period. Furthermore, the comparison between relative sea-level changes and organic carbon content reveals no causal relationship between sea-level fluctuations and the enrichment of organic matter.