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引用本文:张天福,张云,金若时,俞礽安,孙立新,程银行,奥琮,马海林. 鄂尔多斯盆地东北缘侏罗系层序界面特征对砂岩型铀矿成矿环境的制约[J]. 中国地质, 2020, 47(2): 278-299.
ZHANG Tianfu,ZHANG Yun,JIN Ruoshi,YU Reng'an,SUN Lixin,CHENG Yinhang,AO Cong,MA Hailin. Characteristics of Jurassic sequence boundary surfaces on the northeastern margin of Ordos basin and their constraints on the spatial-temporal properties of sandstone uranium mineralization[J]. Geology in China, 2020, 47(2): 278-299(in Chinese with English abstract).
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鄂尔多斯盆地东北缘侏罗系层序界面特征对砂岩型铀矿成矿环境的制约
张天福1, 张云1, 金若时1, 俞礽安1, 孙立新1, 程银行1, 奥琮1, 马海林2
1.中国地质调查局天津地质调查中心, 天津 300170;2.内蒙古地质调查院, 内蒙古 呼和浩特 010000
摘要:
依据野外露头、钻井岩芯、地震、测井及地球化学等资料,对鄂尔多斯盆地东北缘侏罗系延安组(J1-2y)和含铀岩系——直罗组(J2z)关键层序界面进行了系统研究。延安组—直罗组层序界面在露头剖面和钻井岩芯上表现为铁质风化壳、削截侵蚀面或岩性岩相转化面等特征;地震剖面上表现为上超、下超、削截等反射特征;测井曲线岩电关系和微量元素地球化学均表现为不同类型的突变特征。由此识别出10个不同级次层序界面,其中包括3个Ⅰ型层序界面(TSB1~TSB3)和7个Ⅱ型层序界面(SB1~SB7)。Ⅰ型层序界面主要包括:侏罗系延安组(J1-2y)与上三叠统延长组(T3y)之间的界面TSB1—对应地震剖面上的Ty;延安组(J1-2y)与直罗组(J2z)界面TSB2—对应地震剖面上的Tz-1;侏罗系与白垩系层序界面TSB3—对应地震剖面上的Tk。TSB1、TSB2和TSB3Ⅰ型层序界面主要为区域性质的不整合面,反映了中生代构造活动在盆地中的响应; Ⅱ型层序界面主要为气候转化面,反映了层序地层单元形成过程中古气候因素引起的旋回变化。微量元素Sr、Cu、Sr/Cu、FeO/MnO、Al2O3/MgO等比值垂向变化总体上反映延安期至直罗期古气候环境经历了温暖潮湿—干湿交替—干旱—半干旱的转变过程,直罗组底部不整合界面TSB2及上段红层广泛发育的起始界面SB6为古气候环境突变的关键界面。此外,本区三维地层结构显示,侏罗系延安组至直罗组具有明显的“垂相分带”特征,铀矿层在三维空间中主要呈板状赋存于TSB2界面之上的“泛连通厚”辫状河道砂体中,其产出明显受侏罗系垂相分带结构和古气候环境变迁因素的共同制约。本文建立的综合识别层序界面方法减少了层序地层研究中依靠人为经验识别的随意性,为本区侏罗系层序划分和等时地层格架建立提供重要依据。关键层序界面的时空属性及其所指示的地质意义对揭示燕山幕式构造活动发生、发展过程对古气候条件变迁和砂岩型铀大规模成矿作用的影响具有重要意义。
关键词:  砂岩型铀矿  侏罗系  延安组  直罗组  层序界面  三维建模  矿产勘查工程  鄂尔多斯盆地
DOI:10.12029/gc20200202
分类号:P612
基金项目:国家重点研发计划(2018YFC0604200)、中国地质调查局项目(DD20190813)和国家973项目(2015CB4530006)联合资助。
Characteristics of Jurassic sequence boundary surfaces on the northeastern margin of Ordos basin and their constraints on the spatial-temporal properties of sandstone uranium mineralization
ZHANG Tianfu1, ZHANG Yun1, JIN Ruoshi1, YU Reng'an1, SUN Lixin1, CHENG Yinhang1, AO Cong1, MA Hailin2
1.Tianjin Geological Survey Center of China Geological Survey, Tianjin 300170, China;2.Inner Mongolia Institute of Geological Survey, Hohhot 010010, Inner Mongolia, China
Abstract:
On the basis of outcrop, drilling cores seismic, logging and geochemical data, the main sequence boundary surfaces of the Yan'an and Zhiluo Formation of Jurassic on the northeast margin of Ordos basin were systematically studied. On outcrop profiles and drilling cores, the sequence boundary surfaces show characteristics of iron weathering crust, truncation and lithologiclithofacies transformation. On seismic profiles, the boundaries are featured by onlap, downlap and truncation. The rock-electricity relation indicates different types of mutations. The trace elements also show mutation characteristics. Ten different orders of sequence boundaries were identified, including three I-type(TSB1-TSB3)and seven Ⅱ-type(SB1-SB7)sequence boundary surfaces. Ⅰ-type boundaries include TSB1 sequence boundary surface between Yan'an(J1-2y)and Yanchang Formation(T3y), corresponding to Ty in seismic profiles; TSB2 sequence boundary surface between Yan'an(1-2y)and Zhiluo Formation(J2z), corresponding to Tz-1 in seismic profiles; TSB3 sequence boundary surface between Jurassic and Lower Cretaceous, corresponding to Tk in seismic profiles. As regional unconformities,Ⅰ-type sequence boundaries including TSB1, TSB2, TSB3 reflected tectonic activity during Mesozoic period. The Ⅱ-type sequence boundaries were main climate transformation surfaces and showed the cyclic changes in climate factors. The vertical variations of values of Sr, Cu, Sr/Cu, FeO/MnO and Al2O3/MgO indicate that the paleoclimate and paleoenvironment experienced a changing process from warm-humid climate to dry-wet alternation, arid and semi-arid climate; TSB2 and SB6 were main climate transformation surfaces. Vertical zonation of stratigraphic structure is obvious between Yan'an and Zhiluo Formation on the 3D models of the study area. The uranium bodies mainly lie in the large sandstone overlying TSB2 sequence boundary surface, in the form of plate on the 3D models of sandstone and uranium mineralization bed. The uranium bed was obviously influenced by the vertical zonation of stratigraphic structure and paleoclimate transformation. The integrated identification of sequence boundaries will not only reduce the casualty of artificial empirical recognition but also provide a basis for the division of Jurassic sequences and the establishment of isochronous sequence stratigraphic framework. The research on space-time attributes and the indicated geological meanings of the main sequence boundary surfaces will be helpful to revealing the process of "Yanshan movement" and its influence on the paleoclimate transformation and sandstone-type uranium mineralization.
Key words:  sandstone-type uranium ore  Jurassic  Yan’an Formation  Zhiluo Formation  sequence boundary surfaces  3D model  mineral explotation engineering  Ordos basin