排序方式: 共有18条查询结果,搜索用时 31 毫秒
1.
AXEL MUNNECKE HILDEGARD WESTPHAL† JOHN J. G. REIJMER† CHRISTIAN SAMTLEBEN 《Sedimentology》1997,44(6):977-990
Comparison of ultrastructures in Pliocene periplatform carbonates from the Bahamas with Silurian limestones from Gotland (Sweden) reveals that despite the differences in primary sediment composition and age, they reflect a similar mechanism of lithification. In both sequences calcite microspar was formed as a primary cement at an early stage of marine burial diagenesis. Neither significant compression nor meteoric influence are necessary for the formation of calcite microspar. A model is proposed for the process of microsparitic cementation of fine-grained aragonite needle muds comprising four stages: (1) unconsolidated, aragonite-dominated carbonate mud; (2) precipitation of microspar that engulfs aragonite needles; (3) dissolution of aragonite, resulting in pitted surfaces of the microspar crystals; and (4) slight recrystallization. Our results contradict the widespread opinion that microspar necessarily is a product of secondary recrystallization of a previously lithified micrite. 相似文献
2.
The Kyffhäuser Crystalline Complex, Central Germany, formspart of the Mid-German Crystalline Rise, which is assumed torepresent the Variscan collision zone between the East Avalonianterrane and the Armorican terrane assemblage. High-precisionUPb zircon and monazite dating indicates that sedimentaryrocks of the Kyffhäuser Crystalline Complex are youngerthan c. 470 Ma and were intruded by gabbros and diorites between345 ± 4 and 340 ± 1 Ma. These intrusions had magmatictemperatures between 850 and 900°C, and caused a contactmetamorphic overprint of the sediments at PT conditionsof 690750°C and 57 kbar, corresponding toan intrusion depth of 1925 km. At 337 ± 1 Ma themagmaticmetamorphic suite was intruded by granites, syenitesand diorites at a shallow crustal level of some 711 km.This is inferred from a diorite, and conforms to PT pathsobtained from the metasediments, indicating a nearly isothermaldecompression from 57 to 24 kbar at 690750°C.Subsequently, the metamorphicmagmatic sequence underwentaccelerated cooling to below 400°C, as constrained by garnetgeospeedometry and a previously published KAr muscoviteage of 333 ± 7 Ma. With respect to PTDtdata from surrounding units, rapid exhumation of the KCC canbe interpreted to result from NW-directed crustal shorteningduring the Viséan. KEY WORDS: contact metamorphism; UPb dating; hornblende; garnet; Mid-German Crystalline Rise; PT pseudosection 相似文献
3.
BRIAN GERTSCH THIERRY ADATTE GERTA KELLER ABDEL AZIZ A.M. TANTAWY ZSOLT BERNER HAYDON P. MORT DOMINIK FLEITMANN 《Sedimentology》2010,57(6):1430-1462
The response of shallow‐water sequences to oceanic anoxic event 2 and mid‐Cenomanian events 1a and 1b was investigated along the west African margin of Morocco north of Agadir (Azazoul) and correlated with the deep‐water sequence of the Tarfaya Basin (Mohammed Beach) based on biostratigraphy, mineralogy, phosphorus and stable isotopes. In the deeper Mohammed Beach section results show double peaks in δ13Corg for mid‐Cenomanian events 1a and 1b (Rotalipora reicheli biozone, lower CC10a biozone), the characteristic oceanic anoxic event 2 δ13C excursion (Rotalipora cushmani extinction, top of CC10a biozone) and laminated (anoxic) black shale. In the shallow environment north of Agadir, a fluctuating sea‐level associated with dysoxic, brackish and mesotrophic conditions prevailed during the middle to late Cenomanian, as indicated by oyster biostromes, nannofossils, planktonic and benthonic foraminiferal assemblages. Anoxic conditions characteristic of oceanic anoxic event 2 (for example, laminated black shales) did not reach into shallow‐water environments until the maximum transgression of the early Turonian. Climate conditions decoupled along the western margin of Morocco between mid‐Cenomanian event 1b and the Cenomanian–Turonian boundary, as also observed in eastern Tethys. North of Agadir alternating humid and dry seasonal conditions prevailed, whereas in the Tarfaya Basin the climate was dry and seasonal. This climatic decoupling can be attributed to variations in the Intertropical Convergence Zone and in the intensity of the north‐east trade winds in tropical areas. 相似文献
4.
5.
Changes in aerosol size- and phase distributions due to physical and chemical processes in fog 总被引:4,自引:0,他引:4
6.
Phase-partitioning and chemical reactions of low molecular weight organic compounds in fog 总被引:3,自引:0,他引:3
7.
JANOUSEK VOJTECH; GERDES AXEL; VRANA STANISLAV; FINGER FRITZ; ERBAN VOJTECH; FRIEDL GERTRUDE; BRAITHWAITE COLIN J. R. 《Journal of Petrology》2006,47(4):705-744
The Liov Granulite Massif differs from neighbouring granulitebodies in the Moldanubian Zone of southern Bohemia (Czech Republic)in including a higher proportion of intermediatemaficand orthopyroxene-bearing rocks, associated with spinel peridotitesbut lacking eclogites. In addition to dominantly felsic garnetgranulites, other major rock types include quartz dioritic two-pyroxenegranulites, tonalitic granulites and charnockites. Minor bodiesof high-pressure layered gabbroic garnet granulites and spinelperidotites represent tectonically incorporated foreign elements.The protoliths of the maficintermediate granulites (quartz-dioriticand tonalitic) crystallized 360370 Ma ago, as indicatedby laser ablation inductively coupled plasma mass spectrometryUPb ages of abundant zircons with well-preserved magmaticzoning. Strongly metamorphically recrystallized zircons giveages of 330340 Ma, similar to those of other Moldanubiangranulites. For the overwhelming majority of the Liov granulitespeak metamorphic conditions probably did not exceed 800900°Cat 45 kbar; the equilibration temperature of the pyroxenegranulites was 670770°C. This is in sharp contrastto conditions of adjacent contemporaneous Moldanubian granulites,which are characterized by a distinct HPHT signature.The maficintermediate Liov granulites are thought tohave originated during Viséan metamorphic overprintingof metaluminous, medium-K calc-alkaline plutonic rocks thatformed the mid-crustal root of a Late Devonian magmatic arc.The protolith resembled contemporaneous calc-alkaline intrusionsin the European Variscan Belt. KEY WORDS: low-pressure granulites; geothermobarometry; laser-ablation ICP-MS zircon dating; whole-rock geochemistry; SrNd isotopes; Moldanubian Zone 相似文献
8.
Mörner, N.‐A. and Lind, B., 2011. Reply: Comments on ‘Heimdall's stones at Vitemölla in SE Sweden and the chronology and stratigraphy of the surroundings’ by Mörner et al. (2009). Geografiska Annaler: Series A, Physical Geography, 93, 197–199. DOI: 10.1111/j.1468‐0459.2011.00429.x 相似文献
9.
Gerta KELLER Thierry ADATTE Wolfgang STINNESBECK Doris STüBEN Zsolt BERNER Utz KRAMAR Markus HARTING 《Meteoritics & planetary science》2004,39(7):1127-1144
Abstract Yaxcopoil‐1 (Yax‐1), drilled within the Chicxulub crater, was expected to yield the final proof that this impact occurred precisely 65 Myr ago and caused the mass extinction at the Cretaceous‐Tertiary (K/T) boundary. Instead, contrary evidence was discovered based on five independent proxies (sedimentologic, biostratigraphic, magnetostratigraphic, stable isotopic, and iridium) that revealed that the Chicxulub impact predates the K/T boundary by about 300,000 years and could not have caused the mass extinction. This is demonstrated by the presence of five bioturbated glauconite layers and planktic foraminiferal assemblages of the latest Maastrichtian zone CF1 and is corroborated by magnetostratigraphic chron 29r and characteristic late Maastrichtian stable isotope signals. These results were first presented in Keller et al. (2004). In this study, we present more detailed evidence of the presence of late Maastrichtian planktic foraminifera, sedimentologic, and mineralogic analyses that demonstrate that the Chicxulub impact breccia predates the K/T boundary and that the sediments between the breccia and the K/T boundary were deposited in a normal marine environment during the last 300,000 years of the Cretaceous. 相似文献
10.
The Po Valley Fog Experiment 1989 总被引:13,自引:0,他引:13
S. FUZZI M. C. FACCHINI G. ORSI J. A. LIND W. WOBROCK M. KESSEL R. MASER W. JAESCHKE K. H. ENDERLE B. G. ARENDS A. BERNER I. SOLLY C. KRUISZ G. REISCHL S. PAHL U. KAMINSKI P. WINKLER J. A. OGREN^ K. J. NOONE• A. HALLBERG H. FIERLINGER-OBERLINNINGER H. PUXBAUM A. MARZORATI H.-C. HANSSON A. WIEDENSOHLER I. B. SVENNINGSSON B. G. MARTINSSON D. SCHELL H. W. GEORGII 《Tellus. Series B, Chemical and physical meteorology》1992,44(5):448-468