“干化蒸发”与“回灌重溶”——对鄂尔多斯盆地东部奥陶系蒸发岩成因的新认识

鄂尔多斯盆地东部奥陶系发育巨厚的蒸发岩地层,已有不少学者对其成因提出了不同的假设。本文通过对该区蒸发岩微相分布规律、剖面结构及地球化学等特征的分析,提出该区蒸发岩形成于成盐盆地与外海周期性隔绝的“干化蒸发”条件下的新认识。首次提出用“回灌重溶”机制来解释厚层石盐岩中的泥质薄夹层的成因、各种石盐岩颜色的成因及蒸发岩剖面中缺乏干化蒸发晚期阶段的钾镁盐层的原因,并由此提出 “溶积层”的概念。微相分析表明,在形成蒸发岩的盐坳盆地东部的水下古地形隆起上,发育有堤坝状的礁或生物丘等生物建隆,其在地形上的隆起构成了盐坳盆地与外海的障壁,在海平面下降期间可使盐坳与外海完全隔绝而进入干化蒸发阶段,从而形成了石盐沉积;由海平面上升所造成的突发性海水回灌事件又使先成的石盐层部分溶解（回灌重溶）,并由于不溶残余物的富集成层（溶积层）而阻止了下伏石盐层的进一步溶解。这是该区蒸发岩地层中缺少典型干化证据的主要原因。本区奥陶系马家沟组碳酸盐岩与蒸发岩间互分布的地层层序结构特征,主要受控于区域海平面变化旋回,碳酸盐岩主要形成于海侵期和高水位期,蒸发岩则主要形成于低水位期。     

Palynology of Yanchang Formation of Middle and Late Triassic in Eastern Gansu Province and Its Paleoclimatic Significance

INTRODUCTION The Ordos basin belongs to the marginal terraceof North China ancient land,extendingtothe QinlingSea before the Mesozoic . The basin was formed dur-ing the Middle Triassic because of the extrusionfromwest to east onthe western margin of the North Chi-na plate .It was gradually depressedinto a lake basinphase in the Middle and Late Triassic ,to form thedeeper southwestern part and shallower northeasternpart lacustrine-delta clastic sedi ments of over 1 000m,known as the Y…     

Precursors Revealed by the Multifractal Dimension Around Ordos Block,North China

Seismicity around the Ordos Block in the northern part of China has been studied by the multifractal dimensions with the help of complete data set of earthquakes with M≥2.5 since 1977.Seven regions around this block have been examined whiere the eight large earthquakes with M≥6.0 for the complete data occurred.In oirder to display the temporal distribution of the correlation dimension D2,a moving window of fixed number of events is used in every of the seven regions.Except for two regions with less seismic activity,all other five regions have obviously been found to display sudden changes of the correlation dimension for the events with M≥4.5.     

鄂尔多斯盆地北缘地球化学大数据样本优选分析

众所周知,地球化学数据携带有众多地质噪音,这些噪音严重影响地球化学数据信息的客观性与可靠性;对于地球化学大数据融合分析而言,确定样品的有效性及变量优选是滤除地质噪音、建立最优样本集合的必要性工作,因而在地球化学大数据处理分析前需首先进行大样本优选,从而更加客观、真实的揭示地球化学大数据信息及相关地质意义。本文以鄂尔多斯盆地北缘1∶20万地球化学土壤测量数据为例,考虑元素之间的地球化学亲和力与组合匹配关系,建立非线性大样本优选模型。具体做法是基于优选后的样品矩阵,将39个元素变量分解成若干独立因子向量,将最优独立因子向量作为元素组合,其向量各分量作为元素变量的权重,依权重大小进行变量优选;优选后的样本集合可以作为该区地球化学数据分析与信息识别的有效地学信息集合,运用这种集合可以有效开展鄂尔多斯盆地外围铀地球化学分析,并为盆地铀资源预测奠定基础。     

核磁共振技术在苏里格致密气层识别中的应用

鄂尔多斯盆地苏里格气田储集层为一致密砂岩储层.低阻气层与高阻气层共存,气水关系复杂,气层评价是现场工作面临的主要问题.为快速准确储层评价,将核磁共振录井技术方法应用于现场分析,通过综合分析与参数优选组合,建立研究区含气、含水评价参数及解释模版,有效量化了储集空间流体,现场气藏评价应用效果较好.此技术的成功应用,为致密天然气储层识别与评价提供了新的思路和技术手段.     

Characteristics of horizontal crustal move-ment in Weihe basin and adjacent zones by GPS observation

Introduction GPS observation results provide high-accuracy and large-range crustal movement data with real time, which makes it possible to obtain the velocity field of current crustal movement in Chi-nese mainland within a short time and check the previous tectonic deformation model. Geoscien-tists at home and abroad have made a great number of researches on the crustal movement in Chi-nese mainland and have obtained many results in this field (JIANG, et al, 2001; WANG, et al, 2001; ZHA…     

Analysis of Vertical Sedimentary Successions in the Lower Part of Kelimoli Formation,Middle Ordovician,Zhuozishan Area

There is significance to study high-frequency cyclicity thin-bedded limestone which deposited in carbonate ramp and deep-water basin for its well record of astronomic cycles. And there is an ideal section for these studies in the lower part of Kelimoli Formation, in Darriwilian Stage, Middle Ordovician of western Ordos Basin(Zhuozishan area in Inner Mongolia) for its well rhythmic alternations of thin-bedded limestones and mudstones. This work focused on detailed vertical sedimentary successions analysis of these thin-bedded limestones based on detailed field work, as well as the data of rare earth elements and other related trace elements in limestones. The results show as follows: ① there are four types of sedimentary successions(bundles) in thin-bedded limestones, including thinning-upward succession, thickening-upward succession, bidirectional succession(thickening- and thinning-upward) and waving-upward succession; ② the section consists of 145 limestone-mudstone rhythmics, 33 bundles and 7 superbundles; ③ the variation in(La/Nd)_N and Mn/Fe molar ratios of limestones along with depth have a similar trend which decreases from bottom to top in general, but have some anomalies distribution; ④ the variation in REE concentrations and Eu anomalies along with depth have a perfect enantiomorphous relationship as well as coupling with the molar ratios of(La/Nd)_N; ⑤ the variation of crystal size, V/Cr and V/(V+Ni) molar ratios also have a similar trend which is increasing and then decreasing from bottom to top, and have some local enantiomorphous relationship with the molar ratios of(La/Nd)_N in the overall similar distribution patterns. Some conclusion can be drawn according to the types of sedimentary successions and its distribution in profile as well as the ratios of some geochemical parameter along depth based on previous works. These include: ① thickening-upward and bidirectional successions maybe reflect the intensity of tectonism and contour current which is controlled by Milankovitch cycle respectively, and the rising of sea level may be was responsible both for the thinning-upward and waving-upward successions; ② the intensity of contour current which is controlled by Milankovitch cycle was acted throughout the depositions, and the range of deposition time is not less than 2.9 Ma; ③ the vertical sedimentary evolution is perhaps controlled by the alternating of tectonism and rising sea levels, and the section suggests two tectonic stages.     

Tectonic Evolution of the Tianhuan Depression and the Western Margin of the Late Triassic Ordos

Abstract: The Ordos Basin is one of the most important oil and gas basins in China. Based on surface outcrop, key exploratory wells and seismic reflection data and by using the technology of “prototype basin recovery”, seismic profile “layer flattening” and “restoration of balanced section”,and other methods, the sedimentary boundary, structure and the evolution history of the Tianhuan depression on the western margin of the Ordos Basin are reestablished. The following results have been obtained. (1) The west boundary of the Late Triassic Ordos Basin was far beyond the scope of the current basin. The basin is connected with the Late Triassic Hexi Corridor Basin, and its western margin did not have tectonic characteristics of a foreland basin. (2) The Tianhuan depression was first formed in the Late Jurassic. At the late stage it was impacted by the late Yanshanian and Himalayan tectonic movement and the depression axis gradually moved eastwards to the present location with a cumulative migration distance of ~30 km. (3) Eastward migration of the depression axis caused adjustment and even destruction of the originally formed oil and gas reservoirs, so that oil and gas remigrated and aggregated, resulting in secondary structural reservoirs formed at high positions on the western flank of the depression.     

鄂尔多斯盆地纳岭沟铀矿床板状矿体形成机制:来自含矿层黏土矿物研究的制约

纳岭沟铀矿床是近年来在鄂尔多斯盆地北部发现的一个大型铀矿床。与典型层间氧化带砂岩型铀矿不同,纳岭沟铀矿床具有矿体呈板状、似层状产出与铀矿物以铀石为主等特点。文章通过扫描电镜与X衍射等方法对含矿层不同地球化学分带砂岩黏土矿物组合类型、相对含量的变化开展了系统的研究,为该区铀成矿模式与板状矿体的形成机制提供依据。研究结果表明,含矿层砂岩中黏土矿物以呈蜂窝状、片絮状产出的蒙脱石为主,其次为呈片状、书页状及蠕虫状产出的高岭石与呈叶片状、花朵状集合体产出的绿泥石,局部可见伊利石与蒙脱石向绿泥石转化而成的绿蒙混层;从二次还原绿色带→矿带与原生带,呈现蒙脱石、绿泥石明显减少,高岭石含量与w(TOC)、CH_4明显增加的趋势,说明二次还原绿色带与矿带之间存在E_h-pH突变界面;含矿层经历了弱碱性大气降水(含铀含氧)、酸性流体(有机酸与煤成气)、中-低温碱性热液油气与富Na~+、Ca~(2+)的弱碱性流体(盆地卤水)的共同作用,其中弱碱性大气降水与中-低温碱性热液混合而成的碱性-氧化成矿热液与下伏延安组煤系地层演化产生的酸性-还原流体(有机酸与煤成气)在相互接触面上因Eh-pH突变而造成铀石的沉淀,并在E_h-pH突变界面上形成板状矿体。     

鄂尔多斯盆地南缘晚奥陶世钾质斑脱岩——SHRIMP测年及其成因环境

鄂尔多斯盆地南缘上奥陶统金粟山组以深水碳酸盐岩沉积为特征,含多层桔黄色凝灰质粘土岩。矿物和化学成分分析表明,其主要由伊利石和伊蒙混层粘土矿物组成,含少量石英、长石和锆石等中酸性岩浆矿物,富K2O,属钾质斑脱岩;微量元素分析显示本区斑脱岩的源岩为中酸性岩浆成因,源于同碰撞火山弧构造环境。应用SHRIMP技术对其中的锆石进行了U-Pb测年,取得了(451.5±4.9)～(452.1±5.1)Ma、(457.5±5.1)Ma和(465.8±8.3)Ma 3组谐合年龄,前两者分别与欧美广布的Millbrig-Kinnekulle和Deicke斑脱岩同时,但15种化学组分的多元统计分析显示,金粟山组的斑脱岩与欧美同期著名的斑脱岩可能并不同源。形成本区斑脱岩的火山凝灰质可能源自沿商丹洋盆北缘展布的火山弧喷发,而鄂尔多斯盆地南缘晚奥陶世发生的强烈沉降和沉积转换可能与北秦岭弧后盆地的拉伸与扩张密切相关。