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101.
Various microbialite lithofacies were common in the shallow-water environments which flourished under highly saline and arid climate conditions in the Polish part of the Zechstein (Upper Permian) Main Dolomite (Ca2) carbonates. Data came from detailed analysis of 78 cores from wells located at the southern and northern margins of the Main Dolomite basin in west Poland. Microbialite lithofacies are represented by columnar, planar and domal stromatolites, clotted thrombolites and biolaminites developed in high-to-low energy environments within the upper slope, lower parts of oolitic barrier/shoal, restricted lagoon, and tidal flat and tidal channel zones. In barrier environments ooids were predominant whereas in lagoonal settings microbial oncoids and peloids were common. In basinal settings laminated dolomudstones formed which are regarded as hemipelagic and are partly pelagic microbial in origin. Microbial communities coexisted with algae and developed mainly within shallow marine environments. Microbialites are built of cyanobacterial filaments and organo-mineral coccoidal forms possibly of bacterial origin. Organic geochemistry data confirm that organic matter was transformed by cyanobacteria and bacteria which may have played a main role in hydrocarbon generation. This is confirmed by C29 to C35 hopanes, Pr/Ph ratio below 1.0, and the presence of gammacerane as typical for Ca2 profiles. The role and occurrence of algae, as confirmed by C29-steranes, in hydrocarbon generation was possibly minor. Thus it is concluded that the Main Dolomite microbialites could be the likely source rocks for hydrocarbons, with calculated original TOC values from 0.8 to ca 2.0 wt. %. These units also form the reservoir rocks, with porosities reaching 20%. 相似文献
102.
103.
Sebastián Ferrer Juan Félix San-Juan Alberto Abad 《Celestial Mechanics and Dynamical Astronomy》2007,99(1):69-83
In the analytical approach to the main problem in satellite theory, the consideration of the physical parameters imposes a
lower bound for normalized Hamiltonian. We show that there is no elliptic frozen orbits, at critical inclination, when we
consider small values of H, the third component of the angular momentum. The argument used suggests that it might be applied also to more realistic
zonal and tesseral models. Moreover, for almost polar orbits, when H may be taken as another small parameter, a different approach that will simplify the ephemerides generators is proposed. 相似文献
104.
有限差分法广泛应用于地震波数值模拟、成像和波形反演中,差分数值解的精度直接影响着地震成像和反演的效果.因为有限差分算子可以通过截断伪谱法的空间褶积序列得到,而截断窗函数的属性影响有限差分算子逼近微分算子的精度.具体地讲,窗函数的幅值响应的主瓣和旁瓣决定了有限差分算子逼近的精度,主瓣越窄,旁瓣衰减越大,则有限差分算子逼近微分算子的精度越高,更好地压制数值频散.基于此认识,本文提出了一种基于Chebyshev自褶积组合窗截断逼近的有限差分算子优化方法.Chebyshev自褶积组合窗的主瓣较窄,且旁瓣衰减大,其可通过只调节三个参数,更直观和可视化地控制主瓣和旁瓣的形状,改变有限差分算子逼近微分算子的精度;该窗函数截断逼近的有限差分算子不仅有较大的谱覆盖范围,而且精度误差波动较小,这表明低阶的差分算子可以达到高阶算子的精度,且逼近误差更稳定;从经济上来讲,将有效地减少模拟计算花费,提高计算效率. 相似文献
105.
本文用中国地磁场复测点和地磁台站资料,建立了2000年代中国参考地磁场长期变化模型CGRF-SV2000.模型显示,中国地区地磁场变化比较平缓,X、Y、Z、H、D、I、F七个地磁要素的“无符号平均年变率”分别为122 nT/a、82 nT/a、438 nT/a、118 nT/a、096(′)/a、299(′)/a、224 nT/a,比国际参考地磁场IGRF给出的全球年变率约小1/3到1/2.各地磁要素的变化显示,地磁北极正在向中国移近,或者说,中国正在向高地磁纬度方向移动,平均移动速度约为3(′)/a.磁偏角变化还显示,中国地区东西部偏角差异继续扩大.作为检验和对比研究,本文利用第8代国际参考地磁场(IGRF)模型,分析了全球地磁场长期变化的时空特征,讨论了全球长期变模型IGRF_SV与中国长期变模型CGRF_SV的异同点.对比分析表明,中国地区地磁场的长期变化与全球长期变化总趋势基本符合,但是,CGRF_SV也表现出一些特有的局部异常特征. 相似文献
106.
东亚季风环流演变的主要模态及其与中国东部降水异常的联系 总被引:2,自引:0,他引:2
利用美国国家环境预报中心和国家大气研究中心(NCEP/NCAR)再分析环流资料、美国国家海洋和大气管理局(NOAA)重构的海温资料和中国国家气象信息中心(NMIC)整理的752个测站降水资料,对东亚地区季风环流季节演变主要模态及其与中国东部降水异常的关系进行了分析。结果表明,东亚地区850hPa季风环流季节演变存在两个主要模态,第一模态主要受热带印度洋海温和赤道东太平洋海温偏低背景下印度洋偶极(IOD)演变过程控制;第二模态主要受赤道东太平洋ENSO循环和IOD演变控制。对应第一模态,夏季华北多雨,长江流域少雨;对应第二模态,夏季华北、长江流域多雨,淮河、华南少雨。近50年两模态发生了明显改变,与降水变化有很好的对应关系。 相似文献
107.
Hydrogeochemical study in the Main Ethiopian Rift: new insights to the source and enrichment mechanism of fluoride 总被引:2,自引:0,他引:2
Tewodros Rango Gianluca Bianchini Luigi Beccaluva Tenalem Ayenew Nicolò Colombani 《Environmental Geology》2009,58(1):109-118
The central Main Ethiopian Rift suffers a severe water quality problem, characterized by an anomalously high fluoride (F)
content that causes an endemic fluorosis disease. The current study, conducted in the Ziway–Shala lakes basin, indicates that
the F content exceeds the permissible limit for drinking prescribed by the World Health Organization (WHO; 1.5 mg/l) in many
important wells (up to 20 mg/l), with even more extreme F concentration in hot springs and alkaline lakes (up to 97 and 384 mg/l
respectively). The groundwater and surface water from the highlands, typically characterized by low total dissolved solids
(TDS) and Ca (Mg)–HCO3 hydrochemical facies, do not show high F content. The subsequent interaction of these waters with the various rocks of the
rift valley induces a general increase of the TDS, and a variation of the chemical signature towards Na–HCO3 compositions, with a parallel enrichment of F. The interacting matrixes are mainly rhyolites consisting of volcanic glass
and only rare F-bearing accessory minerals (such as alkali amphibole). Comparing the abundance and the composition of the
glassy groundmass with other mineral phases, it appears that the former stores most of the total F budget. This glassy material
is extremely reactive, and its weathering products (i.e. fluvio/volcano-lacustrine sediments) further concentrate the fluoride.
The interaction of these “weathered/reworked” volcanic products with water and carbon dioxide at high pH causes the release
of fluoride into the interacting water. This mainly occurs by a process of base-exchange softening with the neo-formed clay
minerals (i.e. Ca–Mg uptake by the aquifer matrix, with release of Na into the groundwater). This is plausibly the main enrichment
mechanism that explains the high F content of the local groundwater, as evidenced by positive correlation between F, pH, and
Na, and inverse correlation between F and Ca (Mg). Saturation indices (SI) have been calculated (using PHREEQC-2) for the
different water groups, highlighting that the studied waters are undersaturated in fluorite. In these conditions, fluoride
cannot precipitate as CaF2, and so mobilizes freely without forming other complexes. These results have important implications for the development of
new exploitation strategies and accurate planning of new drilling sites.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
108.
109.
西藏班公湖-怒江成矿带主碰撞期成矿作用:荣嘎钼矿岩石地球化学及同位素年龄的证据 总被引:2,自引:1,他引:1
荣嘎钼矿是新近在班公湖-怒江成矿带发现并证实的首例斑岩型钼矿床。为了查明班公湖-怒江成矿带主碰撞期的成岩成矿作用,探讨荣嘎钼矿的富Mo机制,对该矿床进行岩石地球化学以及同位素年代学的研究。本次研究获得荣嘎含矿二长花岗斑岩的锆石SHRIMP206Pb/238U加权平均年龄为99. 8±1. 9Ma (MSWD=2. 0),属晚白垩世早期。7件辉钼矿样品的模式年龄较为一致,介于98. 0±1. 6Ma~101. 8±1. 7Ma之间,加权平均年龄为99. 7±1. 1Ma。荣嘎含矿二长花岗斑岩样品主量元素表现为富硅(SiO_2=72. 83%~75. 49%)、富碱(Na_2O+K_2O=8. 12%~8. 55%)、过铝质(A/CNK=1. 08~1. 13)的高钾钙碱性系列岩石。样品明显富集Rb、K、Th、U等元素,中等亏损Nb、Ta,强烈亏损Ba、Sr、P、Ti等元素,具中等程度的负Eu异常(δEu=0. 53~0. 63),稀土元素配分曲线呈轻稀土相对较陡,重稀土较为平坦的右倾型。荣嘎含矿二长花岗斑岩样品的(~(87)Sr/~(86)Sr)i值为0. 7042~0. 7055,ε_(Nd)(t)值介于0. 03~0. 68之间,锆石ε_(Hf)(t)值介于+12. 4~+17. 9之间,两阶段模式年龄t_(DM2)较为年轻(31~314Ma)。基于以上同位素以及岩石地球化学特征研究,荣嘎含矿二长花岗斑岩很可能是幔源岩浆诱发了富Mo洋底沉积物的熔融并与壳源熔体混合形成母岩浆,再经历结晶分异作用而形成。结合本文以及区域上的研究资料,荣嘎钼矿可能形成于拉萨地块与南羌塘地块碰撞的大地构造背景,富Mo大洋沉积物熔体的加入及随后的结晶分异是荣嘎含矿岩浆中金属Mo富集的主要原因。班公湖-怒江成矿带南缘侏罗-白垩纪海相地层分布的地区,可能为勘查钼矿床的有利靶区,应重点评价晚白垩世早期高分异中酸性岩体的含矿性。 相似文献
110.
藏南帕里至达吉地带的上地壳结构特征──REFTEK顺带广角地震观测结果分析 总被引:3,自引:1,他引:3
本文主要介绍1992年中美喜马拉雅和青藏高原深剖面与综合研究项目第一阶段(INDEPTHI-1)广角地震观测资料利用Seis81程序(Cerveny,1981)进行二维解释所获得的帕里一达吉地带的上地壳结构特征。主要成果为:(1)前寒武结晶基底之顶界表现为R1界面。据本项目地质调查,藏南拆离系(STDS)在帕里以北约10km处出露,向北缓倾并向地下延伸。认为R1界面不仅是结晶基底之顶界的反映,而且STD可能沿着R1界面展布,也即R1界面同时是一条沉积盖层和基底之间的拆离层。R1界面埋深3±0.6—11±0.6km。(2)上述拆离层在萨马达一达吉之间,以R1界面之上的负速度梯度楔状体(LVL)为特征。LVL可能是STDS活动时拖带下沉的中生代特提斯沉积,或可能是含水破碎带。(3)在结晶基底内部存在第二条拆离带(LVZ),表现为T2反射波组。LVZ在帕里埋深8.5±0.6km,向北陡倾,至萨马达为22.5±0.6km深;再向北,倾角变缓,至达吉之下,达27±0.6km深。LVZ在帕里─萨马达之间,厚仅0.5km;至达吉,增厚至5km;也具楔形负速度梯度带性质;它可能是花岗岩局部融熔体之反映...更多。(4)在萨马达─达吉。 相似文献