Paleomagnetism of the Cu�CZn�CPb-bearing Kupferschiefer black shale (Upper Permian) at Sangerhausen, Germany     

David T. A. Symons  Kazuo Kawasaki  Sabine Walther  Gregor Borg 《Mineralium Deposita》2011,46(2):137-152

Syngenetic, diagenetic and epigenetic models have been proposed for the Cu?CZn?CPb Kupferschiefer mineralization at Sangerhausen, Germany. Paleomagnetic and rock magnetic measurements have been made on 205 specimens from mine workings on the margin of the Sangerhausen Syncline. The mineralization is richest in the ??0.5-m-thick Upper Permian (258?±?2?Ma) Kupferschiefer black marly shale (nine sites) and dies out over ??0.2?m in the underlying Weisliegend sandstones (three sites) and overlying Zechstein carbonates (two sites). Except for one site of fault zone gypsum, characteristic remanent magnetization directions were isolated for all 14 sites using alternating field and thermal step demagnetization. These directions provide a negative fold test, indicating that the remanence postdates Jurassic fault block tilting. Rock magnetic measurements show that the Kupferschiefer shale marks a redox front between the oxidized Weissliegend sandstones and non-oxidized Zechstein carbonates. The 14 site directions give a Late Jurassic paleopole at 149?±?3?Ma. It is significantly different from the paleopole reported by E.C. Jowett and others for primary or early diagenetic Rote F?ule alteration that gives an age of 254?±?6?Ma on the current apparent polar wander path and is associated with Kupferschiefer mineralization. We suggest that the Late Jurassic extensional tectonic event that formed the nearby North German Basin also reactivated Variscan basement faults and extended them up through the overlying strata, thereby allowing hydrothermal basement fluids to ascend and epigenetically mineralize the Kupferschiefer shale. The possibility of a 53?±?3?Ma mineralization age is also considered.  相似文献   

Microstructural evolution during experimental albitization of K-rich alkali feldspar   总被引：1，自引：1，他引：0  

Nicholas Norberg  Gregor Neusser  Richard Wirth  Daniel Harlov 《Contributions to Mineralogy and Petrology》2011,162(3):531-546

Crystals of K-feldspar (C2/m), in contact with highly concentrated aqueous NaCl solutions at 500°C and 200 MPa, are pseudomorphically replaced by high albite (C[`1]) (C\bar{1}) as a result of an interface-coupled dissolution/reprecipitation process. The reaction occurs at an extremely sharp reaction front (<10 nm) and involves the complete breakdown of the initial framework structure. This results in the release of tetrahedrally incorporated elements such as Fe³⁺ and Ti⁴⁺ and a significant increase in Si/Al disorder across the reaction interface. The evolving microstructure is controlled by crystallographic relations between the phases. This leads to highly anisotropic, sawtooth-shaped intergrowths of albite and initial K-feldspar, resulting in the least structural misfit between the two framework structures. As a result, the newly formed interfaces appear to be semicoherent, and cracks across the reaction fronts even indicate elastic strain. The reaction produces 2 distinctive albite types (albite-1 and albite-2). Both are polycrystalline, with albite-2 showing significantly larger subgrain sizes. This indicates a secondary coarsening step driven by the reduction in interfacial energy within the polycrystalline replacement product. The reaction also produces a highly porous rim. However, the porosity is not evenly distributed resulting in a porous albite-1 and a non-porous albite-2 that mostly surrounds large, euhedral pores. Despite the substantial volume fraction of porosity in albite-1, no significant 3D interconnectivity could be detected, making the presence of a pervasive porosity unlikely. However, the result of coarsening is the continuous modification of the 3D porosity distribution. This could potentially provide a mechanism for fluid transport through the replacement rim until textural and chemical equilibration is achieved.  相似文献   

Consequences of anthropogenic activity for two remote alpine lakes in NW Slovenia as tracked by sediment geochemistry     

Gregor Muri  Branko Čermelj  Radojko Jaćimović  Dragomir Skaberne  Andrej Šmuc  Martina Burnik Šturm  Janja Turšič  Polona Vreča 《Journal of Paleolimnology》2013,50(4):457-470

Several geological and geochemical parameters were determined in the sediments of the 5th (5 J) and 6th (6 J) Triglav Lakes, Julian Alps (NW Slovenia), in order to study the impact of natural catchment characteristics and anthropogenic activity. Fish were introduced into both lakes in 1991 and a mountain hut lies on the shore of 5 J. Sedimentary grain size (GS) was distinctly coarser in 5 J than 6 J, with arithmetic means ranging between 46 and 60 and 23–36 μm, respectively. In contrast, the mineralogical composition of the two sediments was similar. Calcite predominated strongly, comprising more than 77 % of total minerals, while dolomite and quartz were rare. Organic carbon (OC) and total nitrogen (TN) concentrations were highest in surficial sediments, with levels of 14.4 and 1.8 %, and 19.3 and 2.4 % observed in 5 J and 6 J, respectively. C/N ratios (atomic) were lowest in the same surface sediments, with the two lakes characterized by similar values (9.6 vs. 9.4, respectively), suggesting a predominance of autochthonous organic matter (OM) in both lakes. Contemporary δ¹³C values were lower in 5 J (?21.0 ‰) than 6 J (?18.5 ‰) sediments. Considerable changes in these four parameters were observed in recently deposited material, reflecting a shift in the trophic status of both lakes that was likely induced by the introduction of fish. In addition, the smaller and shallower 6 J seemed to respond to changes faster than the larger and deeper 5 J, indicating the higher sensitivity of the former. δ¹⁵N values in surface sediments of 5 J and 6 J were ?2.9 and ?4.4 ‰, respectively, with levels increasing gradually with depth to approximately +1.0 ‰ in deeper sediments. The observed changes could most likely be attributed to the atmospheric deposition of reactive nitrogen. The mountain hut has seemingly not had a significant enough impact on the lakes to be recorded in their sediments.  相似文献   

Semantically based reclassification of Danish land-use and land-cover information     

Martin Rudbeck Jepsen  Gregor Levin 《International journal of geographical information science》2013,27(12):2375-2390

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Factors contributing to the development of extreme North Atlantic cyclones and their relationship with the NAO     

Joaquim G. Pinto  Stefan Zacharias  Andreas H. Fink  Gregor C. Leckebusch  Uwe Ulbrich 《Climate Dynamics》2009,32(5):739-737

The occurrence of extreme cyclones is analysed in terms of their relationship to the NAO phase and the dominating environmental variables controlling their intensification. These are latent energy (equivalent potential temperature 850 hPa is used as an indicator), upper-air baroclinicity, horizontal divergence and jet stream strength. Cyclones over the North Atlantic are identified and tracked using a numerical algorithm, permitting a detailed analysis of their life cycles. Extreme cyclones are selected as the 10% most severe in terms of intensity. Investigations focus on the main strengthening phase of each cyclone. The environmental factors are related to the NAO, which affects the location and orientation of the cyclone tracks, thus explaining why extreme cyclones occur more (less) frequently during strong positive (negative) NAO phases. The enhanced number of extreme cyclones in positive NAO phases can be explained by the larger area with suitable growth conditions, which is better aligned with the cyclone tracks and is associated with increased cyclone life time and intensity. Moreover, strong intensification of cyclones is frequently linked to the occurrence of extreme values of growth factors in the immediate vicinity of the cyclone centre. Similar results are found for ECHAM5/OM1 for present day conditions, demonstrating that relationships between the environment factors and cyclones are also valid in the GCM. For future climate conditions (following the SRES A1B scenario), the results are similar, but a small increase of the frequency of extreme values is detected near the cyclone cores. On the other hand, total cyclone numbers decrease by 10% over the North Atlantic. An exception is the region near the British Isles, which features increased track density and intensity of extreme cyclones irrespective of the NAO phase. These changes are associated with an intensified jet stream close to Europe. Moreover, an enhanced frequency of explosive developments over the British Isles is found, leading to more frequent windstorms affecting Europe.

Joaquim G. PintoEmail:

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Fluid mixing recorded by mineral assemblage and mineral chemistry in a Mississippi Valley-type Pb–Zn–Ag deposit in Wiesloch,SW Germany     

Katharina Pfaff  Thomas Wagner  Gregor Markl 《Journal of Geochemical Exploration》2009

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Niederschlagsänderungen Während Eines Jahres in Ihrer Beziehung zu den Frontalzonen     

Alois Gregor  Zdenêk Gregor 《Studia Geophysica et Geodaetica》1958,2(4):362-396

Резюме Целью настоящей работы является анализ колебаний осадков последовательно, месяц за месяцем, в течение года, касающийся областей Сев. Америки, Атлантического океана и Европы и сравнение полученных результатов с колебаниями фронтальных зон на названном выше пространстве. Зависимость осадков от изменений температуры исключается, вследствие того, что осадки выражаются в процентах максимального количества осадков, которое могло бы выпасть из нижней половины тропосферы. Во второй части работы приводится приблпженная оценка роли конвекции в осадках в Европе.

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Anschrift: Ke Karlovu 3, Praha 2.

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Anschrift: Letiště Praha-Ruzyně.  相似文献   

Book reviews     

E. M. Yates  W. Manshard  Yrjö Vasari  Jacob O. Maos  C. A. Halstead  Dieter Steiner  Thomas Peucker  Lisbeth Seeley-Heuse  Olof Hedbom  Howard F. Gregor  K.-Seguin Maurice  Klaus-Achim Boesler  C. Koeman  G. H. T. Hart  H. Dequin  M. Richter  Peter H. Nash 《GeoJournal》1980,4(4):381-388

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Some perspectives of the major biogeochemical cycles: Gene E. Likens (ed.), John Wiley & Sons (1981). xiii + 175 pp. $26.50     

Bryan Gregor 《Geochimica et cosmochimica acta》1982,46(6):1145

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Bahamian carbonate platform development in response to sea-level changes and the closure of the Isthmus of Panama   总被引：1，自引：0，他引：1  

John?J.?ReijmerEmail author  Christian?Betzler  Dick?Kroon  Ralf?Tiedemann  Gregor?P.?Eberli 《International Journal of Earth Sciences》2002,91(3):482-489

In this paper we show that the development of the sediment architecture at the leeward toe-of-slope of Great Bahama Bank (Ocean Drilling Project Leg 166, Bahama Transect) during the last 6 Ma is not only a response to sea-level fluctuations, but also to major paleo-oceanographic and climatic changes. A major sequence boundary close to the Miocene/Pliocene boundary (dated at 5.6-5.4 Ma) is interpreted to reflect a major sea-level drop that was followed by a sea-level rise, which led to the re-flooding of the Mediterranean Sea at the end of the Messinian and increasing sea-surface temperatures at Great Bahama Bank. Distinct erosional horizons occurred during the Pliocene (dated at 4.6 and 3.3-3.6 Ma) related to sea-level change and the intensification of the Gulf Stream when the emergence of the Isthmus of Panama reached a critical threshold. The Gulf Stream brings warm, saline and nutrient-poor waters to the Bahamas. Starting at the Early-Late Pliocene boundary at 3.6 Ma this paleo-oceanographic reorganization in combination with enhanced sea-level fluctuations associated with the Late Pliocene main intensification in Northern Hemisphere Glaciation (since 3.2 Ma) led to (1) a gradual change from a ramp-type to a flat-topped type morphology, and (2) a change from a skeletal to a non-skeletal-dominated sedimentary system (mainly peloidal). Increased sea-level fluctuations during the second half of the Pleistocene led to an intensified high stand-shedding depositional pattern within the surrounding basins.  相似文献