Occurrence and biomarker potential of 23-methyl steroids in diatoms and sediments     

Sebastiaan W. Rampen  Stefan Schouten  Ellen C. Hopmans  Ben Abbas  Anna A.M. Noordeloos  Jan A.J. Geenevasen  J. Michael Moldowan  Peter Denisevich  Jaap S. Sinninghe Damsté 《Organic Geochemistry》2009,40(2):219-228

23-Methyl sterols have been reported to be synthesized by a few marine algae, but unambiguous identification of 23-methyl steroids in sediments and petroleum is lacking. We report the presence of 23-methylcholesta-5,22E-dien-3β-ol in 14 out of 106 diatom cultures, thereby showing that diatoms, together with dinoflagellates, may be an important environmental source for such steroids. Synthesis of authentic 23-methylcholestanes showed that their mass spectra are identical to those of 24-methylcholestanes, but that they elute earlier on apolar stationary phases during gas chromatography (GC) analysis. Co-injection of the authentic standards with sediment extracts revealed the presence of these compounds in the Skole unit of the Oligocene Menelite Formation, the Miocene Monterey Formation and the Messinian Vena del Gesso Formation. In addition, we tentatively identified 23,24-dimethyl-27-norcholestanes in some of these sediments. Molecular clock calculations suggest that diatoms are a possible source for 23-methyl steroids in sediments and petroleum from the late Jurassic onwards.  相似文献   

Identification of sinkhole development mechanism based on a combined geophysical study in Nahal Hever South area (Dead Sea coast of Israel)   总被引：2，自引：0，他引：2  

Michael Ezersky  Anatoly Legchenko  Christian Camerlynck  Abdallah Al-Zoubi 《Environmental Geology》2009,58(5):1123-1141

Seismic refraction, magnetic resonance sounding (MRS), and the transient electromagnetic (TEM) method were applied to investigate the geological and hydrogeological conditions in the Nahal Hever South sinkhole development area at the Dead Sea (DS) coast of Israel. Microgravity and MRS results reliably reveal large karst cavity in the central part of investigated area. The map of the seismic velocity shows that sinkholes in Nahal Hever can be divided into two major groups: sinkholes close to the salt edge and sinkholes over compact salt formations between a few tens to a hundred meters from the major cavern. The present study shows that the formation of sinkholes of the first group is caused by soil collapsing into the cavern. In the area occupied by sinkholes of the second group, karst was not detected either by MRS or by seismic diffraction methods. TEM results reveal shallow clay layer saturated with DS brine underlain sinkholes of this group. It allows suggestion that the water drainage and intensive water circulation during rain events wash out fine rock particles from the unsaturated zone into the pre-existing cavern, initiating the formation of sinkholes of the second group. Karst development takes place at a very low bulk resistivity (<1 Ω m) of the DS aquifer, attesting to the fact that pores are filled with a highly saline solution. Refilling of the karstic cavities with collapsing and flushed soil slows down sinkhole development in the area. The sinkhole formation cycle at the site is estimated at 10 years. Sinkhole development throughout the studied area is triggered by a drop in the level of the DS, which reduces the head of the confined aquifer and the strength of the overlain sediments.

Abdallah Al-ZoubiEmail:

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Results from the European Deep Ocean Margins Research Training Network     

Miquel Canals  Ben De Mol 《International Journal of Earth Sciences》2009,98(4):715-720

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Discovery and Analysis of Shale Gas in a Carboniferous Reservoir and its Enrichment Characteristics in the Northern Nanpanjiang Depression,Guizhou Province,China     

LU Shufan  LUO Xiangjian  DU Shengjiang  HE Ben  FU Hongbin  LIU Kuiyong 《《地质学报》英文版》2019,93(3):561-572

Shale gas resources are considered to be extremely abundant in southern China, which has dedicated considerable attention to shale gas exploration in recent years. Exploration of shale gas has considerably progressed and several breakthroughs have been made in China. However, shale gas explorations are still scarce. Summary and detailed analysis studies on black shale reservoirs are still to be performed for many areas. This lack of information slows the progress of shale gas explorations and results in low quantities of stored black shale. The Carboniferous Dawuba Formation, which is widely distributed and considerably thick, is one of the black shale formations targeted for shale gas exploration in southern China in the recent years. The acquisition and analysis of total organic carbon, vitrinite reflectance,types of organic matter, mineral composition, porosity, and permeability are basic but important processes. In addition, we analyzed the microscopic pores present in the shale. This study also showesd the good gas content of the Dawuba Formation, as well as the geological factors affecting its gas content and other characteristics. To understand the prospect of exploration, we compared this with other shale reservoirs which have been already successfully explored for gas. Our comparison showesd that those shale reservoirs have similar but not identical geological characteristics.  相似文献   

黔西南郭家湾新发现幻龙化石的埋藏特征及时代     

向坤鹏  贺永忠  赵磊  安亚运  刘奎勇  何犇  盘应娟 《地质通报》2019,38(8):1266-1273

1∶5万区域地质调查在黔西南郭家湾新发现了一处幻龙化石点。通过剖面测制,详细解剖了化石的异地埋藏特征,并依据区域地质填图和化石资料确定其时代为中三叠世安尼期。在此基础上,根据黔西南及邻区安尼期化石群的分布,结合岩相古地理分布特征,浅析了幻龙化石可能的物源,结果显示郭家湾一带为幻龙活动范围的可能性较大。该幻龙化石的发现及其时代的限定,为研究三叠纪海生爬行动物的演化和迁移提供了新的素材,具有重要的科学意义。  相似文献   

论核工程选址中的弥散地震   总被引：2，自引：1，他引：1       下载免费PDF全文

张裕明  时振梁  常向东  周本刚  环文林  董瑞树  冉洪流 《地震地质》2004,26(4):727-732

弥散地震评价是核工程选址中地震安全性评价的重要内容之一。文中在分析弥散地震涵义的基础上,论述了弥散地震评价中地震构造区划分的原则和依据、弥散地震确定的方法和技术途径等关键性技术内容  相似文献   

论发震构造特性在潜在震源区参数确定中的应用   总被引：6，自引：0，他引：6       下载免费PDF全文

周本刚 《地震地质》2004,26(4):750-760

发震构造特性是潜在震源区划分及其地震年发生率确定的重要依据。潜在震源区除了反映“未来具有发生破坏性地震的地区”的内涵外,还应反映高震级档地震具有相似复发特征的涵义。由于在地震活动性参数统计单元内,有一些具有不同本底地震的活动构造块体,为更好地反映地震活动的空间不均匀性,考虑潜在震源区的三级划分是有必要的。通过分析潜在震源区内高震级档地震的复发特征,计算预测时段内潜在震源区的高震级档地震的发震概率,采用预测时段内概率等效转换获得地震年平均发生率的方法,有助于在中国地震危险性分析框架内考虑潜在震源区的强震复发特性。另外,文中还对潜在震源区内特征地震次级震级档频度不足的特性和发震构造上强震非均匀性在地震危险性分析中的应用问题进行了探讨  相似文献   

Incision of alluvial channels in response to a continuous base level fall: Field characterization, modeling, and validation along the Dead Sea   总被引：5，自引：1，他引：4  

L. Ben Moshe  I. Haviv  Y. Enzel  E. Zilberman  A. Matmon 《Geomorphology》2008,93(3-4):524-536

The dramatic lake level drop of the Dead Sea during the twentieth century ( 30 m) provides a field-scale experiment in transport-limited incision of gravel-bed channels in response to quasi-continuous base level fall at approximately constant rate. We apply a one-dimensional numerical incision model based on a linear diffusion equation to seven ephemeral channels draining into the Dead Sea. The model inputs include the measured twentieth century lake level curve, annual shoreline location (i.e., annual channel lengthening following the lake level drop), reconstructed longitudinal profiles of each of the channels based on mapped and surveyed terraces, and the current profiles of the active channels. The model parameters included the diffusion coefficient and the upstream-derived sediment flux. Both were first calibrated using a set of longitudinal profiles of known ages and then validated using additional sets of longitudinal profiles.The maximum at-station total incision observed at each of the studied channels was significantly less then the total lake level drop and varied in response to both drainage area and lake bathymetry. The model applied predicted degradation rates and the pattern of degradation with high accuracy. This suggests that sediment flux in the modeled channels is indeed linearly dependent on slope. Further support for this linear dependency is provided by a linear correlation between the diffusion coefficient and the mean annual rain volume over each basin (a proxy for discharge). The model presented could be a valuable tool for planning in rapid base level fall environments where incision may risk infrastructure.  相似文献   

海洋可控源电磁法空气波研究现状及展望   总被引：2，自引：0，他引：2  

殷长春  刘云鹤  翁爱华  贾定宇  贲放 《吉林大学学报(地球科学版)》2012,42(5):1506-1520

海洋可控源电磁法是钻前储层评价的有效手段,它可作为海洋地震重要辅助手段识别海底构造的储油/储水特征,从而减少盲钻率和勘探成本。然而,当使用水平电偶极作为发射源在浅水区测量时,沿空气-海水分界面传播的空气波会完全掩盖从高阻储油层返回的有用信号。由于空气波不含海底储油层的任何信息,空气波的存在严重影响海洋电磁的应用。因此,如何在浅水区观测数据中去除空气波影响以取得好的反演结果成为当前海洋电磁法的研究热点之一。首先基于Weidelt的空气波理论并采用对TE谱核直接求导的方法推导出空气波的主导项,然后根据空气波的物理成因及影响特征阐述了海洋电磁数据解释之前必须去除空气波的原因,最后将目前处理空气波问题的方法分成3类：1)根据空气波在频率域和时间域的特性去除或压制空气波,2)采用无空气波的测量方式,3)直接对含空气波的电磁数据进行反演解释。通过比较各种方法的效果,发现所有方法都有自己的应用条件和局限性。为有效地压制和去除空气波,各种方法的组合也许有更好的应用效果。  相似文献   

Clinoform quantification for assessing the effects of external forcing on continental margin development     

Vanessa Kertznus  Ben Kneller 《Basin Research》2009,21(5):738-758

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