Inorganic geochemical characteristics and evaluation of Sinian-Cambrian post-mature source rocks in Sichuan Basin
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摘要: 高演化烃源岩评价因有机质的损耗而使得传统有机地球化学参数逐渐失效,而烃源岩中的无机元素不易受成熟度的影响。为探索无机地球化学方法在高演化烃源岩评价中的应用,以四川盆地震旦—寒武系为例,基于无机(主量、微量和稀土元素)地球化学方法,从烃源岩发育的三大控制因素(古生产力、沉积环境和沉积速率)分析入手,开展了烃源岩无机地球化学研究。结果表明,综合运用Ba和Ni元素丰度确定烃源岩古生产力,MoEF、UEF、Ce异常特征确定沉积水体氧化—还原条件,TiO2/Al2O3比值确定沉积速率,揭示研究区烃源岩有机质富集主要受控于沉积环境与古生产力,而受沉积速率的影响相对较小;川中与威远—资阳地区下寒武统筇竹寺组烃源岩古生产力高、沉积环境最为还原,烃源岩质量最好,属于高生产力和好保存模式。无机地球化学方法是高演化烃源岩评价的一种有效途径。Abstract: The evaluation of post-mature source rocks gradually invalidates by traditional organic geochemical parameters due to the decreasing of organic matter abundance. However, the inorganic elements in source rocks are not easily affected by thermal evolution. In order to explore the application of inorganic geochemical methods in the evaluation of post-mature source rocks, this paper takes the Sinian-Cambrian source rocks in the Sichuan Basin as an example to conduct an evaluation based on the inorganic (major, trace and rare earth elements) geochemistry method with three controlling factors of source rock development (paleoproductivity, sedimentary environment and sedimentary rate). The concentration of Ba and Ni, MoEF and UEF and Ce anomaly, and TiO2/Al2O3 ratio could be correlated with paleoproducitvity, sedimentary environment and sedimentary rate, respectively. The results showed that the enrichment of organic matter was mainly controlled by sedimentary environment and paleoproductivity, but are barely effected by sedimentary rate. Source rocks in the Lower Cambrian Qiongzhusi Formation in the central Sichuan and Weiyuan-Ziyang areas have high paleoproductivity and the most reduced environment and thus are one of the best quality source rocks. Therefore, inorganic geochemistry method is an effective way to evaluate postmature source rocks.
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图 2 四川盆地震旦—寒武系高演化烃源岩无机地球化学参数特征
a.Babio和Nibio特征;b.U-Mo协变关系(图版据TRIBOVILLARD等[4]);c.TiO2/Al2O3比值特征
Figure 2. Inorganic geochemical parameters of Sinian-Cambrian post-mature source rocks in Sichuan Basin
表 1 四川盆地震旦—寒武系高演化烃源岩研究样品基本信息及元素地球化学分析结果
Table 1. Sample information and element geochemical data of Sinian-Cambrian post-mature source rocks in Sichuan Basin
层位(岩性) 地区 井号 样品号 深度/m ω(TOC)/% Al2O3/% Ba/10-6 Ni/10-6 Eu/Eu* Al/(Al+Fe+Mn) Ti/Zr Babio/10-6 Nibio/10-6 (P2O5)bio/% MoEF UEF Ce/Ce* TiO2/Al2O3 筇竹寺组(泥页岩) 川中 安平1 1 5 030.0 1.93 11.0 727 64 0.93 0.71 21 329 50 0.10 55 10.3 - 0.076 2 5 031.1 2.24 11.1 926 76 0.90 0.70 20 524 61 0.10 37 10.5 - 0.071 3 5 033.2 1.84 13.8 863 70 0.88 0.68 22 364 52 0.06 24 7.1 - 0.058 4 5 035.1 1.46 14.2 799 71 0.83 0.71 20 285 52 0.04 25 6.9 - 0.057 威远—资阳 资4 5 4 224.5 1.91 12.9 1 050 140 0.97 0.68 19 583 123 0.07 24 7.1 - 0.056 6 4 238.1 2.36 14.4 1 140 93 0.92 0.66 19 619 74 0.06 30 7.8 - 0.055 7 4 265.4 1.15 9.4 723 34 0.94 0.85 21 383 22 0.00 12 9.0 - 0.049 川西南 汉深1 8 5 103.5 0.40 14.4 918 47 0.97 0.68 27 397 28 0.08 5.3 2.0 - 0.054 9 5 106.2 0.33 14.3 937 48 0.98 0.69 27 420 29 0.06 3.8 1.8 - 0.052 10 5 106.9 0.42 14.2 1 060 47 0.94 0.66 25 546 28 0.05 4.5 1.7 - 0.052 11 5 109.1 0.33 13.6 1 090 46 0.96 0.72 22 598 28 0.04 4.4 1.8 - 0.051 12 5 110.5 0.52 14.6 978 47 0.91 0.72 24 450 28 0.06 7.4 2.3 - 0.055 麦地坪组(泥质白云岩) 威远—资阳 资4 13 4 296.1 0.86 0.50 416 27.3 0.95 0.45 24 398 27 6.59 - - - 0.086 14 4 341.3 1.21 0.65 131 39 0.95 0.66 19 107 38 0.53 - - - 0.044 资7 15 3 930.9 1.40 1.81 659 27.9 0.94 0.64 20 594 26 7.68 - - - 0.051 川西南 汉深1 16 5 128.5 0.42 8.2 689 26.4 0.90 0.64 24 392 16 7.19 1.8 5.4 - 0.054 17 5 130.2 0.40 5.4 380 25.4 0.93 0.61 24 185 18 2.66 7.7 3.8 - 0.044 18 5 131.3 0.52 0.49 33 21.1 0.95 0.25 33 15 20 0.56 - - - 0.050 灯影组三段(泥岩) 川中 高科1 19 5 351.9 1.49 9.9 772 57 0.89 0.62 23 414 44 2.62 4.8 4.1 - 0.054 20 5 353.3 0.68 12.1 762 74 0.88 0.64 23 324 58 2.35 5.8 4.0 - 0.053 21 5 355.7 0.56 5.3 435 38 0.95 0.64 23 243 31 1.28 6.2 4.8 - 0.055 22 5 356.2 1.40 13.1 997 56 0.86 0.66 20 523 39 2.28 3.7 3.2 - 0.051 23 5 357.0 0.58 3.4 317 27.8 0.97 0.63 16 194 23 1.73 4.7 4.3 - 0.054 24 5 357.6 1.37 8.7 676 42 0.93 0.64 22 361 31 1.67 4.8 3.1 - 0.057 灯影组(藻云岩) 川中 高石1 25 4 976.6 0.03 0.052 81 15.3 1.41 0.09 22 79 15 0.04 - - 0.77 - 高科1 26 5 150.5 0.74 0.031 128 15.9 1.11 0.11 25 127 16 0.15 - - 0.59 - 安平1 27 5 062.9 0.96 0.023 11.1 14.0 2.01 0.08 23 10 14 0.02 - - 0.80 - 盘1 28 5 620.4 1.53 0.38 163 16.1 1.22 0.46 15 149 16 0.17 - - 0.36 - 威远—资阳 资6 29 3 678.6 0.99 0.072 36 19.7 1.38 0.11 14 33 20 0.10 - - 0.66 - 威113 30 3 118.9 0.36 0.054 29.5 16.9 2.05 0.17 7 28 17 0.05 - - 0.84 - 川西南 自深1 31 5 428.1 0.05 0.065 33 15.8 1.48 0.21 9 31 16 0.03 - - 0.85 - 陡山沱组(泥岩) 川西南 先锋 32 露头样 1.71 13.0 1 070 47 1.02 0.62 28 600 30 0.42 4.9 2.8 - 0.058 注:有机碳含量数据引用自SHI等[10];“-“表示未计算该值。 -
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