西藏尼玛地区古近系牛堡组古湖平面变化的沉积地球化学记录

发布时间：2018-05-30 17:14

本文选题：尼玛盆地 + 牛堡组　；参考：《成都理工大学》2017年博士论文

【摘要】：根据岩相类型和地球物理探测手段所重建的古湖平面变化易受制于地表露头条件、取芯连续程度及地震分辨率等的影响。为此,本论文尝试着从沉积地球化学角度重建古湖平面变化。以西藏尼玛地区古近系牛堡组湖相地层为研究材料,通过野外地质调查和室内测试分析,应用沉积学、稳定同位素地球化学、有机地球化学及古湖泊学等方法和理论,针对沉积相及沉积环境演化、古湖泊水文特征、盐度特征及温度特征、有机质类型、丰度及成熟度进行了分析,探讨了西藏尼玛地区古近系牛堡组湖相地层古湖平面变化的沉积地球化学记录。通过剖面实测观察和岩石薄片鉴定,查昂巴剖面古近系牛堡组湖相地层顶、底发育扇三角洲相沉积,湖相地层自下而上发育半深湖-深湖亚相—滨浅湖亚相—半深湖-深湖亚相—滨浅湖亚相的旋回沉积。在此过程中,剖面有五次水体深度较大时期,分别对应着五层烃源岩——灰黑色钙质泥页岩。碳酸盐碳、氧稳定同位素测试结果显示,δ~(13)C值介于-4.40‰~2.20‰之间,δ~(18)O值介于-10.60‰~-4.10‰之间,分布范围同现代和古代世界上其他地区湖相碳酸盐基本一致。δ~(13)C值和δ~(18)O值呈正相关关系,Z值介于114.50~126.53之间,古温度介于8.94~39.16℃之间。综合分析确定古湖泊为封闭型咸化湖泊,古温度分布与现代湖泊水温相一致,更多地反映温暖季节湖泊水温状态。有机质类型以Ⅱ1型和Ⅱ2型为主,含有少量Ⅰ型和Ⅲ型,反映有机质来源以内源为主,随着保存条件变弱和陆源有机质输入量增大,有机质类型向Ⅲ型转化。TOC介于0.10%~2.97%之间,生烃潜力(S_0+S_1+S_2)介于39.34mg/g~630.22mg/g之间,显示湖泊初级生产力较高。无定形有机质含量介于35.00%~97.00%之间,其中有93.33%的大于50.00%,结合HI-TOC相关变化分析,较强的还原性沉积环境是控制有机质类型和丰度的主导因素,较高的湖泊初级生产力是重要的辅助因素。Tmax介于434~494℃之间,H/C原子比介于1.09~1.77之间,腐泥组颜色为棕色和棕黄色,反映有机质成熟度处于未成熟到成熟阶段,意味着干酪根结构和组成破坏程度偏低。论证了湖水δ~(18)O值和δ~(13)C_(DIC)值、有机质HI值、δ~(13)C_(org)值及TOC值与湖平面变化的关系。受入流量与蒸发量之比的影响,湖平面上升,湖水δ~(18)O值减小,而湖平面下降,湖水δ~(18)O值增大。当湖泊初级生产力较低,湖水δ~(13)C_(DIC)值和δ~(18)O值呈正相关变化,湖平面上升,湖水δ~(13)C_(DIC)值减小,而湖平面下降,湖水δ~(13)C_(DIC)值增大;当湖泊初级生产力较高,使得湖泊水生植物光合作用成为控制古湖水δ~(13)C_(DIC)值组成的主导因素时,湖水δ~(13)C_(DIC)值和δ~(18)O值呈反相关变化,湖平面上升,湖水δ~(13)C_(DIC)值增大,而湖平面下降,湖水δ~(13)C_(DIC)值减小。受有机质来源的影响,湖平面上升,陆源有机质贡献相对减小,HI值和δ~(13)C_(org)值增大,而湖平面下降,陆源有机质贡献相对增多,HI值和δ~(13)C_(org)值减小。受湖泊初始生产力和沉积环境的影响,湖平面上升,TOC值增大,而湖平面下降,TOC值减小。利用这些指标恢复了查昂巴剖面古近系牛堡组湖相地层古湖平面变化历史,表现为局部对称性突发上升与回落、总体阶步式升高与下降的波动特征。各记录均能反映古湖平面升降过程,HI值和δ~(13)C_(org)值的记录更为细致,仅能反映古湖平面变化的波动过程,而无法记录变化幅度与趋势。但δ~(13)C_(org)值的记录在半深湖-深湖沉积地层较为有效,而在滨浅湖沉积地层效果欠佳。古湖水δ~(18)O值、δ~(13)C_(DIC)值及TOC值的记录还能反映古湖平面升降过程、变化趋势及幅度,前两者反映的是半深湖-深湖沉积地层的古湖平面变化,而无法记录滨浅湖沉积地层的古湖平面变化,但TOC值的记录没有这一限制。同时,指出应用这些指标重建古湖平面变化的条件:封闭型咸化湖泊,有机质来源以内源为主,有机质类型以Ⅱ型为主,有机质保存受沉积环境控制,水体分层,有机质成熟度不能过高,越低越好。古湖水δ~(18)O值和δ~(13)C_(DIC)值主要记录的是半深湖-深湖沉积古湖平面变化历史,而HI值、δ~(13)C_(org)值和TOC值则基本不受这一限制,但δ~(13)C_(org)值记录的滨浅湖沉积古湖平面变化需谨慎对待。最后,预测出尼玛盆地查昂巴剖面最佳烃源岩层位处于150m附近。
[Abstract]:The changes in the paleo Lake plane, which are based on the lithofacies type and geophysical exploration means, are easily affected by the surface outcrop conditions, the continuity of the core and the seismic resolution. Therefore, this paper attempts to reconstruct the paleo Lake plane change from the sedimentary geochemistry angle. The study materials are the lacustrine facies of the nimpu group in the nimma region of Tibet. Through field geological survey and indoor test analysis, the methods and theories of sedimentology, stable isotope geochemistry, organic geochemistry and paleolakes are used to analyze the evolution of sedimentary facies and sedimentary environment, the characteristics of paleolake hydrology, Salinity Characteristics and temperature characteristics, organic matter type, abundance and maturity, and discuss the Tibet Nepal The sedimentary geochemistry records of the paleo lake level changes in the Paleogene Niu Bao formation of the Paleogene of the Ma area. Through the observation of the profile and the identification of the rock slices, the Chaoba section of the Paleogene Niu Bao formation is the top of the lacustrine stratum, the bottom of the fan delta facies, the lower part of the lacustrine strata from the bottom to the bottom of the lake, the subfacies of the shallow lake, the half deep lake and the deep lake. In this process, there are five depths of water depth in the section, which correspond to five layers of source rocks, gray and black calcium shale. Carbonate carbon and oxygen stable isotopes show that the value of delta ~ (13) C is between -4.40 and ~2.20 per thousand, and the value of delta ~ (18) O is between -10.60 and ~-4.10 per thousand. The range is basically the same as the lacustrine carbonate in the modern and ancient world. The value of delta ~ (13) C and delta ~ (18) O is positively correlated, the Z value is between 114.50~126.53, and the paleotemperature is between 8.94~39.16 C. The comprehensive analysis determines that the ancient lake berth is a closed salty lake, the distribution of the paleotemperature is in accordance with the modern lake water temperature, and more reflect the temperature. The main types of organic matter in the warm season are type II 1 and type II 2, containing a small amount of type I and type III, reflecting the source of organic matter in the internal source. With the weakening of the preservation conditions and the increase of the input of the organic matter in the land source, the transformation of organic matter to type III is between the.TOC and the 0.10%~2.97%, and the hydrocarbon potential (S_0+S_1+S_2) is between 39.34mg/g~630.22m. G/g shows that the primary productivity of lakes is higher. The content of amorphous organic matter is between 35.00%~97.00% and 93.33%, which is more than 50%. Combining with the correlation analysis of HI-TOC, the strong reductive sedimentary environment is the dominant factor to control the types and abundance of organic matter. The higher primary productivity of the lake is an important auxiliary factor,.Tmax Between 434~494 and 1.09~1.77, the ratio of H/C atom is between 1.09~1.77 and brown and brown, reflecting the maturity of organic matter in immature to mature stage, which means that the structure and composition of the kerogen are low. The value of delta ~ (18) O and delta ~ (13) C_ (DIC), HI value of organic matter, delta ~ (13) C_ (ORG) value and TOC value and the lake level are demonstrated. The change is influenced by the ratio of flow and evaporation. The lake level rises, the lake delta ~ (18) O value decreases, the lake level decreases and the lake water delta ~ (18) O values increase. When the lake primary productivity is low, the lake water delta ~ (13) C_ (DIC) values and delta ~ (18) O values are positively correlated, the lake level rises, the lake water delta ~ (13) C_ (DIC) values decrease, while lake level drops, lake water delta The value of ~ (13) C_ (DIC) increases; when lake primary productivity is high, when the photosynthesis of lake aquatic plants is the dominant factor controlling the value of the delta ~ (13) C_ (DIC) value of the lake water, the delta ~ (13) C_ (DIC) value and Delta ~ (18) O value of lake water are inverse correlation, the lake level rises, the lake delta ~ (13) C_ (DIC) value increases, the lake level drops, and the lake water delta ~ (13) C_ (DIC) values decrease. Influenced by the organic matter, the lake level rises, the contribution of the land source organic matter is relatively reduced, the value of HI and delta ~ (13) C_ (ORG) increases, while the lake level decreases, the contribution of the land source organic matter is relatively increased, the HI value and the delta ~ (13) C_ (ORG) value decrease. The lake level rises, the TOC value increases, and the lake level drops, the lake level drops, TOC is affected by the lake initial productivity and the sedimentary environment. The history of the lake level changes in the lake facies stratum of the Paleogene niupburg formation of the section of the Charles Ba section was restored by these indexes, which showed the sudden rise and fall of the local symmetry and the fluctuation characteristics of the overall step type and descent. All records could reflect the ascending and descending process of the ancient lake plane, and the record of HI value and delta ~ (13) C_ (ORG) value is more meticulous and only can be recorded. It reflects the fluctuation process of the change of the ancient lake plane, but can not record the change amplitude and trend. But the record of the delta ~ (13) C_ (ORG) value is more effective in the semi deep lake deep lake sedimentary strata, but the effect of the sedimentary strata in the shallow lake is not good. The record of the delta ~ (18) O value, the delta ~ (13) C_ (DIC) value and the TOC value of the ancient lake water can also reflect the ascending and lowering process of the ancient lake plane, and the trend of the change and the change trend. The amplitude and the former two reflect the paleo lake level changes in the semi deep lake deep lake sedimentary strata, but can not record the ancient lake level changes in the shallow lake sedimentary strata, but the record of the TOC value is not limited. At the same time, it is pointed out that the conditions for the application of these indexes to reconstruct the changes of the ancient lake level: the closed salty lake, the organic matter from the internal source, and the organic matter. The mass type is dominated by type II, the preservation of organic matter is controlled by the sedimentary environment, the water layer is stratified and the maturity of organic matter can not be too high, the lower the better. The value of delta ~ (18) O and ~ (13) C_ (DIC) of the ancient lake water is mainly recorded in the history of the paleo lake level change in the semi deep lake deep lake, while the HI value, delta ~ (13) C_ (ORG) value and TOC value are basically not restricted by this limit, but delta ~ (13) C_ (ORG) the shallow lake sediments should be treated with caution. Finally, it is predicted that the best source rocks in the 150m section near the upper part of the basin are in the vicinity.
【学位授予单位】：成都理工大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：P618.13;P534.611

【参考文献】