Dolomite characteristics and diagenetic model of the Calcari Grigi Group (Asiago Plateau,Southern Alps – Italy): an example of multiphase dolomitization

A multidisciplinary study, conducted over the carbonate platform deposits of the Liassic Calcari Grigi Group (Southern Alps), highlighted how the use of outcrop analogues can contribute to better define the distribution of dolomitic bodies related to fault networks, to characterize the petrophysical properties of the dolomitic sequence and unravel a complex diagenetic history. This study was carried out in the Asiago Plateau (southernmost part of the eastern Southern Alps, northern Italy) which provides excellent outcrops of the Jurassic Calcari Grigi Group. The dolomitization of the Jurassic sequence is variable in terms of stratigraphic extension and geographic distribution. In the studied localities the dolomitization is generally limited to the Mount Zugna Formation and is characterized by an undulatory front, with ‘sub‐vertical dolomitic chimneys’ along the major faults. Within this unit, and often associated with faults, stacked high‐porosity and permeability bed‐parallel dolomitic bodies are developed that show excellent petrophysical properties. The dolomitic intervals are characterized by pervasive unimodal and patchy polymodal dolomite crystals. Thin section, cathodoluminescence, isotopic and fluid inclusion analyses were used to constrain the paragenetic evolution of the sequence which is similar in all the studied localities. The first dolomitization stage is marked by zoned dolomite crystals with a dull luminescent core. The porosity is thought to have increased after this stage, with dark blue luminescent dolomite accompanied by the corrosion of older crystals. The appearance of saddle dolomite marks the onset of the porosity reduction stage, ending with the infilling of vugs and the remaining open pores with calcite cement. The diagenetic evolution locally stopped at the saddle dolomite stage with the complete occlusion of the remaining pores. Paragenetic and fluid‐inclusion data suggest an evolutionary trend of increasing temperatures and decreasing salinity toward brackish fluids responsible for dolomite and calcite precipitation. The integration of the available data seem to indicate that the diagenetic evolution of the study area is related to: (i) the interplay between evolving fluids (from marine to brackish); (ii) the burial of the sequence (increasing temperature); and (iii) the evolution of the hydrogeological system (fault and fracture network, fluid mixing). This complex paragenetic evolution is strongly linked to the evolution of the porosity framework that evolved from a good, widespread network in the early stages of the burial history to a confined system in the later stages due to reduction of porosity by the deposition of late calcite and dolomite cements.     

A Reconstruction for the Late Paleozoic Tectonic Evolution of the Tekes Daban Area, Western Tianshan Mountains: Evidence from Unconformities

The identification of unconformities is the key to reconstructing tectonic evolution, revealing crust movement and establishing tectonic cycle. For a long time, there were some controversial issues on the episodes of Variscan cycle (especially on the period of Carboniferous-Permian stages) of the Tianshan area. The essential questions fall on the numbers and property of unconformities in this area, for example, in the western Tianshan area. Previous research only recognized three or four fold movements. Detailed regional geological mapping of 1:50000 in the Tekes Daban area, western Tianshan have allowed us to characterize the seven unconformities within the Carboniferous-Permian strata and understand its implications for tectonic reconstruction of the Tianshan orogen. Seven angular unconformities, which indicate that seven tectonic episodes occurred in the Late Paleozoic Period, were identified in this area. Therein, the newly discovered unconformities based on the angle-unconformity between the Dongtujinhe and Keguqinshan Formations, and angle-unconformity between the Wulansayi and Wulang Formations, respectively indicates the Tekes episode and Gongliu episode. The unconformity between the Dongtujinhe and Yishijilike Formations is angle-unconformity instead of parallel unconformity indentified by previous research, so the former Bogda ascending can be revised as Bogda movement. Therefore, these newly identified seven episodes, including the Tekes episode, suggest that there are seven tectonic movements in the Tianshan area at least. This has significant implications for reconstruction of the Late Paleozoic tectonics in the Tianshan Area, NW China     

格尔木－额济纳旗地学断面走廊域地壳－上地幔岩石学结构与深部过程

基于岩石学研究与地球物理场的结合，提出了祁连山、柴达木与北山３个地区的壳幔岩石学结构．认为造山带加厚的下地壳与山根带分别由高压麻粒岩相与榴辉岩相岩石构成，对断面走廊域进行了岩石学填图．探讨了山根的形成与不对称、陆壳物质的分异与新莫霍界面的形成、造山岩石圈增厚机制、岩石围拆沉与玄武岩岩浆底侵作用等．讨论了青藏高原南、北缘岩石图增厚机制的差异及其岩石学标志．     

A Study on Hydrocarbon—Generating Potential and Kinetics of Source—Rock Pyrolysis

A study on the potential and kinetics of hydrocarborn(HC) generation of 30 source-rock samples from a certain depression has been made by means of ROCK-EVAL technique .In the pyrolysis experiment, the source material types, maturation and hydrocarbon-generating potential of source rocks from three Upper Jurassic horizons of that area have been evaluated in terms of such indicators as the type-index, hydrocarbon-generating potential and maximum pyrolysis temperaturw(Tmax) .The results show that the pyrolysis HC yield of immature source rocks is much higher than that of mature rocks in case that the source mateuial is of high quantity and organic matter is abundant, which suggests that it is important for evaluating the HC-generating potential to use immature samples for pyrolysis.In the pyrolytic simulation experiments on other two immature samples,it was found that the hydrocarbon yield is temperature-dependent, and thereafter the kinetical parameters for source rocks, such as reactional grade, appearant activation energy and frequency factor were calculated.     

积分法三维电阻率成像

二维或是三维电阻率反演成像研究,最关键的环节是在反演系数矩阵即敏感矩阵(或雅可比矩阵)的求取上.本文从微分方程的积分解出发,推导了表达式极为简单的三维雅可比系数矩阵,构造了成像方程.根据反演方程系数的稀疏特征,采用改进的降维高斯赛德尔迭代法来求解该反演方程,并通过内外迭代的结合,对大型稀疏欠定方程能很快收敛,得到可靠的解答.合成数据模型结果及实际资料的成像结果表明积分法不但实现起来极容易,成像结果的精度也相当高.     

中国霞石正长岩的地质特征

介绍了中国霞石正长岩的分布，产出的大地构造环境，岩体的岩石组合，岩石的地球化学和造岩矿物组合特征，论述了主要造岩矿物的矿物学特征及产出母岩的关系，以及工业岩石对霞石正长岩的一些指标要求。     

衍射波地震勘探方法

本文提出了衍射波勘探方法资料处理流程的构思框架,并给出了以复杂结构为目标所做的物性结构成像、几何结构成像及迭代开关识别等研究结果.     

生油岩热解生烃潜力及生烃动力学研究

利用岩石评价仪(R0cK EVAL I)对某凹陷30块生油岩进行了热解生烃和生烃动力学研究。在热解实验中，用类型指数、生烃潜量、最大热解峰温Tmax、等指标对上侏罗统3个层位的生油岩进行了母质类型、成熟度和生烃能力评价，结果表明，母质类型好、有机质丰富的未成熟生油岩的热解生烃量要比相同的已成熟生油岩高得多，说明选择未成熟生油岩热解对评价其生油能力的重要性。在对另2个未成熟生油岩的热解模拟实验中，得到了生烃率与温度之间的关系，并由此计算了生油岩的表观活化能、频率因子等动力学参数。     

X射线荧光光谱－点滴麦勒膜制片法测定金标准样品中金银铜锌

酸分解试样，点滴麦勒膜制片，Ｎｉ元素作内标，使用Ｘ射线荧光光谱法同时测定金银标准样品中Ａｕ、Ａｇ、Ｃｕ和Ｚｎ，分析范围为０．２％～１００％。对于Ａｕ、Ａｇ、Ｃｕ和Ｚｎ含量为８３％、８．Ｏ％、６．２％、３．０％的试样，其Ｒ８Ｄ（ｎ＝６）分别为０．１％、１．１％、０．９％和１．１％。