Yucatán karst features and the size of Chicxulub crater     

Martin Connors  Alan R. Hildebrand  Mark Pilkington  Carlos Ortiz-Aleman  Rene E. Chavez  Jaime Urrutia-Fucugauchi  Eduardo Graniel-Castro  Alfredo Camara-Zi  Juan Vasquez  John F. Halpenny 《Geophysical Journal International》1996,127(3):F11-F14

The buried Chicxulub impact structure is marked by a dramatic ring of sinkholes (called cenotes if containing water), and adjacent less prominent partial rings, which have been shown to coincide with maxima in horizontal gravity gradients and a topographic depression. These observations, along with the discreteness and spacing of the features, suggest a formation mechanism involving faulting in the outer slump zone of the crater, which would thus have a diameter of approximately 180 km.
An opposing view, based primarily on the interpretation of gravity data, is that (he crater is much larger than the cenote ring implies. Given the association of the known cenote ring with faults, we here examine northern Yucatan for similar rings in gravity, surface features and elevation, which we might expect to be associated with outer concentric faults in the case of a larger, possibly multiring, structure.
No such outer rings have been found, although definite patterns are seen in the distribution of karst features outside the crater rim. We explain these patterns as resulting mainly from deformation related to the block fault zone that parallels tbe shelf edge of eastern Yucatan.  相似文献   

频率域位场快速正则化反演界面和物性分布     

张贵宾  申宁华 《吉林大学学报(地球科学版)》1996,(4)

从理论与模型算例两方面对一种以Ｐａｒｋｅｒ公式为基础的频率域位场反演方法做了进一步深入研究。表明它是一种能够更有效地引入低通滤波因子的迭代方法。与改进的正则化稳定因子相结合，提出新的快速正则化反演方法。除了将其用于反演求解均质界面以外，它也被推广至变物性的界面反演以及物性反演  相似文献   

南天山北缘麻粒岩残迹与辉石相韧性变形研究   总被引：9，自引：4，他引：9       下载免费PDF全文

舒良树  王赐银 《地质科学》1996,31(4):375-383

对新疆北部南天山北缘蛇绿混杂岩带中麻粒岩的岩石学、矿物学、岩石化学、矿物化学、稀土元素地球化学特征及辉石相韧性变形构造的研究表明,榆树沟麻粒岩的共生矿物组合为透辉石-次透辉石-紫苏辉石-石榴石-斜长石,属基性岩类暗色麻粒岩,以低硅高钙为特征,稀土总量低,轻稀土与铕弱亏损,反映高温高压熔融环境和岩浆分异差的特点。麻粒岩及超镁铁岩中的辉石经历了强烈的韧性剪切变形作用,不对称辉石残斑系、动态重结晶辉石亚颗粒集合体、辉石变形双晶纹、鱼尾构造、核幔构造等显微韧变构造广泛发育。宏观和微观运动学分析揭示了一期从南向北的推覆构造。麻粒岩的形成与早古生代大陆地壳拉伸作用有关,辉石相韧性变形则与早古生代末南天山边缘海的挤压关闭和推覆逆冲有关。  相似文献   

测氡法快速确定油气田边界及深度   总被引：5，自引：0，他引：5  

叶树林 《华东地质学院学报》1996,19(2):150-156

本介绍了运用测氡法快速确定大庆××油气田边界，估算其埋藏深度试验，结果表明，该方法具有可行性和实用性。由于所做工作有限，尚属经验性探讨，还必须从理论和实践上进一步地工作，进而充实、完善它。  相似文献   

河北唐山—卢龙地区寒武－奥陶系界线地层的牙形刺及其重要属种的演化   总被引：1，自引：0，他引：1  

王志浩  方一亭 《高校地质学报》1996,(4)

本文对唐山和卢龙地区寒武－奥陶系界线地层中的牙形刺再次进行研究，厘定了过去报道的一些重要属种，并对最具地层意义的Ｃｏｒｄｙｌｏｄｕｓ的几个种的演化进行了分析。指出了该属的两个进化系列，第一支进化系列是Ｅｏｃｏｎｏｄｏｎｔｕｓｎｏｔｃｈｐｅａｋｅｎｓｉｓ－Ｃｏｒｄｙｌｏｄｕｓｐｒｉｍｉｔｉｖｕｓ－Ｃ．ｐｒｏａｖｕｓ－Ｃ．ｃａｂｏｔｉ－Ｃ．ｉｎｔｅｒｍｅｄｉｕｓ－Ｃ．ａｎｇｕｌａｔｕｓ；而另一支则是Ｅｏｃｏｎｏｄｏｎｔｕｓｎｏｔｃｈｐｅａｋｅｎｓｉｓ－Ｃ．ｃａｂｏｔｉ－Ｃ．ｐｒｏｌｉｎｄｓｔｒｏｍｉ－Ｃ．ｌｉｎｄｓｔｒｏｍｉ－Ｃ．ｐｒｉｏｎ。本文对寒武－奥陶系界线的几个划分方案也进行了简单的讨论  相似文献   

The Best Natural Boundary:a New Concept Developed by Combining the Sequence Boundary with the GSSP     

Mei Shilong China U niversity of Geosciences  Beijing 《《地质学报》英文版》1996,70(1):98-107

Through a detailed study of sequence boundaries, it is concluded that sequence stratigraphy is an independent regional and transitional stratigraphic system between local lithostratigraphy and global chronostratigraphy. Therefore, a new tripartite stratigraphic classification scheme has been proposed. By combining organically the concept of sequence boundaries with the GSSP, it is suggested that the GSSP should be chosen in a conformale portion of a related sequence boundary, and the boundary established in light of this concept is defined as the Best Natural Boundary (BNB). The definition of the BNB points out the working area and stratigraphic level for the GSSP. By referring to a case study of the Permian Guadalupian/Lopingian boundary, the concept of the BNB has been elaborated in detail, and it is proposed that the BNB of the Guadalupian and the Lopingian lies between the Mesogondolella granti Zone and the Ctarkina postbitteri Zone, which is also the sequence chronostratigraphic boundary between th  相似文献   

The mean and turbulence structure simulation of the monsoon trough boundary layer using a one-dimensional model withe-l ande-ε closures     

Kusuma G. Rao  V. N. Lykossov  A. Prabhu  S. Sridhar  E. Tonkacheyev 《Journal of Earth System Science》1996,105(3):227-260

An attempt has been made here to study the sensitivity of the mean and the turbulence structure of the monsoon trough boundary layer to the choice of the constants in the dissipation equation for two stations Delhi and Calcutta, using one-dimensional atmospheric boundary layer model withe-ε turbulence closure. An analytical discussion of the problems associated with the constants of the dissipation equation is presented. It is shown here that the choice of the constants in the dissipation equation is quite crucial and the turbulence structure is very sensitive to these constants. The modification of the dissipation equation adopted by earlier studies, that is, approximating the Tke generation (due to shear and buoyancy production) in theε-equation by max (shear production, shear + buoyancy production), can be avoided by a suitable choice of the constants suggested here. The observed turbulence structure is better simulated with these constants. The turbulence structure simulation with the constants recommended by Aupoixet al (1989) (which are interactive in time) for the monsoon region is shown to be qualitatively similar to the simulation obtained with the constants suggested here, thus implying that no universal constants exist to regulate dissipation rate. Simulations of the mean structure show little sensitivity to the type of the closure parameterization betweene-l ande-ε closures. However the turbulence structure simulation withe-ε. closure is far better compared to thee-l model simulations. The model simulations of temperature profiles compare quite well with the observations whenever the boundary layer is well mixed (neutral) or unstable. However the models are not able to simulate the nocturnal boundary layer (stable) temperature profiles. Moisture profiles are simulated reasonably better. With one-dimensional models, capturing observed wind variations is not up to the mark.  相似文献   

吉林大阳岔寒武系-奥陶系界线层型候选剖面再描述   总被引：1，自引：2，他引：1  

张俊明  王海峰 《地层学杂志》1996,20(2):81-103

吉林大阳岔剖面是目前国际寒武系-奥陶系界线工作组(ICOBWG)所确认的全球唯一的寒武系-奥陶系界线层型候选剖面。运用坐标系统对大阳岔界线剖面进行重新测量、详细描述Cambrooistodus 带至 Cordylodus lindstromi 带45.9m 厚的地层序列,将不同学者在大阳岔剖面所采用的样品采集系统相应地标在新的坐标剖面上,以统一它们在新坐标剖面上的坐标位,置点。新的坐标剖面将为国际寒武系-奥陶系界线工作组在确定全球界线层型剖面和点位(GSSP)时提供一个共同的参照标准。  相似文献   

垂直断层附近三维不均匀体点源电场的边界单元法     

李予国  徐世浙 《物探化探计算技术》1996,18(2):147-151

本文将给出垂直断层附近三维不均匀体电阻率法的数值解，所用方法是边界单元法，但基本解的选择与以往的边界单元法不同。  相似文献   

洞庭湖地区重力资料精细反演解释     

朱自强  程真 《物探与化探》1996,20(5):393-396

用快速准确重力三维正演算法计算白垩系顶面及以上各密度界面的重力异常,采用“剥皮法”从实测重力异常中减去自垩系顶面及以上各密度界面的重力效应后得到剩余异常,由此反演研究区内白垩系底面深度。由于采用快速三维反演算法并顾及地质及航磁异常信息,求得了白垩系厚度,计算出的底板埋深等更为合理、精细,为洞庭地区油气资源基础性研究及评价提供了重要的信息。  相似文献