Astronomically forced cycles in Lower Carboniferous Luzhai Formation shales, Guizhong Depression, South China
Astronomically forced cycles in Lower Carboniferous Luzhai Formation shales, Guizhong Depression, South China
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DOI：
10.1016/j.marpetgeo.2023.106427
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发表时间：
2023-07
影响因子：
4.2
通讯作者：
Siding Jin;Sibing Liu;Xiangfeng Wei;Chao Ma;Yicai Chen;Jingyu Hao;Kaijun Ni;Daojun Zhou
中科院分区：
文献类型：
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作者：
Siding Jin;Sibing Liu;Xiangfeng Wei;Chao Ma;Yicai Chen;Jingyu Hao;Kaijun Ni;Daojun Zhou
早石炭世鹿寨组发育连续厚层页岩，是中国南方油气勘探和开发的重要层序。然而，没有高分辨率的地层层序格架或旋回地层学研究早石炭世（图尔奈阶）的有机质丰富的页岩地层。在桂中坳陷鹿寨组的两个钻孔中发现了米兰科维奇旋回的证据。自然伽马测井资料允许建立一个5.9亿年浮动天文时标（FATS）的基础上稳定的长偏心率（405-kyr）周期的鹿寨组。我们将FATS定年为泥盆纪和石炭纪的界线年龄（359.3 ± 0.4Ma），并建立了359.3 ~ 353.4Ma的绝对时间尺度。采用相关系数法、演化COCO法和演化TimeOpt法对观测到的地层旋回与天文旋回进行定量拟合，给出沉积速率的可能范围。采用沉积噪声模型探测了与120万年周期振幅调制（AM）周期相关的轨道强迫控制的高分辨率海平面变化。沉积噪声模型（自相关系数分析ρ1和轨道调谐分析后的动态噪声DYNOT）揭示了早石炭世鹿寨组的高分辨率AM旋回（120万年-120万年）与海平面变化的相关性。120万年前的振幅调制（AM）是三级层序发育的主要驱动力，三级层序界面与DYNOT中值曲线的最大值和120万年前振幅调制（AM）曲线的最小值有关。
Early Carboniferous Luzhai Formation developed continuous and thick shales, which is a critical succession for hydrocarbon exploration and production in southern China. However, no high-resolution stratigraphic sequence framework or cyclostratigraphic studies on early Carboniferous (Tournaisian Stage) are available for this organic-rich shale formation. In this research, Milankovitch cycle evidence has been reported in two boreholes of Luzhai Formation in Guizhong Depression. Natural gamma-ray logging data allowed the establishment of a ∼5.9-Myr floating astronomical timescale (FATS) based on stable long eccentricity (405-kyr) cycles in Luzhai Formation. We anchored FATS to Devonian and Carboniferous boundary age (359.3 ± 0.4 Ma), and an absolute timescale for intervals of 359.3 to 353.4 Ma was developed. Correlation coefficient (COCO), evolutionary COCO, and evolutionary TimeOpt method (eTimeOpt) were employed for quantitatively fit observed stratigraphic cycles to astronomical cycles for providing possible range of sedimentation rates. Sedimentary noise model was adopted for detecting orbital forcing-controlled high-resolution sea-level changes which were correlated to ∼1.2-Myr obliquity amplitude modulation (AM) cycles. Sedimentary noise models (autocorrelation coefficient analysis, ρ1, and dynamic noise after orbital tuning analysis, DYNOT) revealed a correlation between obliquity AM cycle (∼1.2-Myr) and sea level changes in early Carboniferous Luzhai Formation. The ∼1.2-Myr obliquity AM was the main driver of third-order sequence development, the 3rd-order sequence boundaries were related to maximum values of DYNOT median curve and minima values of ∼1.2-Myr amplitude modulation (AM) curve.