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The middle Cenomanian–lower Turonian deposits of Ohaba-Ponor section (Southern Carpathians) were studied from biostratigraphic and isotopic points of view. Both the qualitative and semiquantitative nannofloral analyses, as well as the stable isotope (δ13C and δ18O) data support significant palaeoenvironmental changes in the investigated interval. Two δ13C positive excursions were recognized: (1) an excursion up to 1.8‰ (PDB) within the middle/late Cenomanian boundary; (2) an excursion up to 2.2‰ (PDB) in the Cenomanian/Turonian boundary interval. The oldest δ13C positive excursion recorded (placed within the Acanthoceras jukes-brownei/Eucalycoceras pentagonum Ammonite Zone boundary interval, and in the NC11 Calcareous Nannofossil Zone respectively) could be assigned to the middle Cenomanian Event II (MCEII). During the above-mentioned event, significant increase in abundance of Watznaueria barnesae, followed by successive blooms of Biscutum constans and Eprolithus floralis, were observed. The youngest δ13C positive excursion was identified in the Cenomanian/Turonian boundary interval (in the NC12 and lower part of the NC13 Calcareous Nannofossil Zones). Even the amplitude of this δ13C positive excursion is lower in the Ohaba-Ponor section, as generally reported, this may represent the regional record of the OAE2. The successive peaks of the nannofossils Biscutum constans, Zeugrhabdotus erectus and Eprolithus floralis indicate episodes of cooler surface water and high fertility, which preceded and lasted the Cenomanian/Turonian boundary event. Additionally, fluctuations of δ18O values between −2 and −6‰ suggest also cooler conditions within the Cenomanian/Turonian boundary interval. 相似文献
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Michael Wagreich Ana-Voica Bojar Reinhard F. Sachsenhofer Stephanie Neuhuber Hans Egger 《Cretaceous Research》2008,29(5-6):965
Ultrahelvetic units of the Eastern Alps were deposited on the distal European continental margin of the (Alpine) Tethys. The Rehkogelgraben section (“Buntmergelserie”, Ultrahelvetic unit, Upper Austria) comprises a 5 m thick succession of upper Cenomanian marl-limestone cycles overlain by a black shale interval composed of three black shale layers and carbonate-free claystones, followed by lower Turonian white to light grey marly limestones with thin marl layers. The main biostratigraphic events in the section are the last occurrence of Rotalipora and the first occurrences of Helvetoglobotruncana helvetica and Quadrum gartneri. The thickest black shale horizon has a TOC content of about 5%, with predominantly marine organic matter of kerogen type II. Vitrinite reflectance and Rock-Eval parameter Tmax (<424 °C) indicate low maturity. HI values range from 261 to 362 mg HC/g TOC. δ13C values of bulk rock carbonates display the well documented positive shift around the black shale interval, allowing correlation of the Rehkogelgraben section with other sections such as the Global Boundary Stratotype Section and Point (GSSP) succession at Pueblo, USA, and reference sections at Eastbourne, UK, and Gubbio, Italy. Sediment accumulation rates at Rehkogelgraben (average 2.5 mm/ka) are significantly lower than those at Pueblo and Eastbourne. 相似文献
3.
Ana-Voica Bojar Harald Fritz Sabine Kargl Wolfgang Unzog 《Journal of African Earth Sciences》2002,34(3-4)
To constrain the post-Pan-African evolution of the Arabian–Nubian Shield, macro-scale tectonic studies, paleostress and fission track data were performed in the Eastern Desert of Egypt. The results provide insights into the processes driving late stage vertical motion and the timing of exhumation of a large shield area. Results of apatite, zircon and sphene fission track analyses from the Neoproterozoic basement indicate two major episodes of exhumation. Sphene and zircon fission track data range from 339 to 410 Ma and from 315 to 366 Ma, respectively. The data are interpreted to represent an intraplate thermotectonic episode during the Late Devonian–Early Carboniferous. At that time, the intraplate stresses responsible for deformation, uplift and erosion, were induced by the collision of Gondwana with Laurussia which started in Late Devonian times. Apatite fission track data indicate that the second cooling phase started in Oligocene and was related to extension, flank uplift and erosion along the actual margin of the Red Sea. Structural data collected from Neoproterozoic basement, Late Cretaceous and Tertiary sedimentary cover suggest two stages of rift formation. (1) Cretaceous strike-slip tectonics with sub-horizontal σ1 (ENE/WSW) and σ3 (NNW/SSE), and sub-vertical σ2 resulted in formation of small pull-apart basins. Basin axes are parallel to the trend of Pan-African structural elements which acted as stress guides. (2) During Oligocene to Miocene the stress field changed towards horizontal NE–SW extension (σ3), and sub-vertical σ1. Relations between structures, depositional ages of sediments and apatite fission track data indicate that the initiation of rift flank uplift, erosion and plate deformation occurred nearly simultaneously. 相似文献
4.
The ability to deduce exhumation mechanisms from thermochronological data is hampered by the fact that assumptions on the thermal state of the lithosphere have to be made. Additional argumentation is generally required to discriminate between erosion-controlled and tectonically induced exhumation. This problem can be overcome by studying the spatial distribution of zircon and apatite (U-Th)/He and fission track data. In this work the variation of four different low temperature isotopic systems generating age trends along a sampling line is used to infer mechanisms of Quaternary exhumation in the Central High Himalayan Metamorphic Belt. Observed zircon age trends with southwards increasing cooling ages (from 0.5 to 1.7 Ma) are attributed to tectonically induced exhumation. The uniform apatite cooling ages clustered c. 0.5 Ma are attributed to erosion. 相似文献
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The Gossendorf volcanic body is the only one in the Styrian basin that shows extensive hydrothermal alteration. K‐Ar dating of primary volcanic biotite and alteration products (alunite) suggests that the emplacement of the volcanic body and hydrothermal alteration took place synchronously, 15 Ma ago. The stable isotope compositions of the alteration products such as opal, barite, pyrite and alunite combined with crystallographia investigations indicate temperatures between 150 and 200 °C for the formation of the alteration zones. The calculated stable isotopic compositions of the parent fluid, responsible for the alteration, show an exogene marine component, which interacted with the host rock. Sulphur isotopic compositions of sulphur, sulphides and sulphates indicate disequilibrium, and progressive oxidation. This fact, combined with the mineral zonation of the alteration zone, reflects not only change in the pH but also change in the fO2 of the ascending fluids. 相似文献
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The granodiorite intrusion at Ocna de Fier-Dognecea in the western South Carpathians, Romania, triggered the formation of
a classic Fe-(Pb-Zn) skarn deposit. The intrusive is related to the larger composite Bocşa Laccolith five kilometres north
that is part of the regional Banatite Suite. Previous work indicated a K/Ar age of 65–57 Ma and postulated an Andean-type
subduction related tectonic setting for the intrusions. We report ion probe U/Pb zircon ages of 79.6 ± 2.5 Ma for the Bocşa
Laccolith and 75.5 ± 1.6 Ma for the Ocna de Fier Pluton, which date their emplacement. Fission track dating on titanite gives
slightly younger ages: 78 ± 4 Ma for Bocşa and 73 ± 4 Ma for Ocna de Fier. Together with zircon and apatite data from the
same samples, average cooling rates of 52 °C/Ma and 83 °C/Ma are calculated for the Bocşa and Ocna de Fier intrusives respectively.
A post-collision tectonic setting is proposed on the basis of field evidence, the timing of intrusions in the context of regional
tectonic evolution, and trace element geochemistry.
Received: 4 August 1998 / Accepted: 20 April 1999 相似文献
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Franz Walter Hans-Peter Bojar Christine E. Hollerer Kurt Mereiter 《Mineralogy and Petrology》2013,107(2):189-199
Galgenbergite-(Ce) from the type locality, the railroad tunnel Galgenberg between Leoben and St. Michael, Styria, Austria, was investigated. There it occurs in small fissures of an albite-chlorite schist as very thin tabular crystals building rosette-shaped aggregates associated with siderite, ancylite-(Ce), pyrite and calcite. Electron microprobe analyses gave CaO 9.49, Ce2O3 28.95, La2O3 11.70, Nd2O3 11.86, Pr2O3 3.48, CO2 30.00, H2O 3.07, total 98.55 wt.%. CO2 and H2O calculated by stoichiometry. The empirical formula (based on Ca + REE ∑3.0) is $ \mathrm{C}{{\mathrm{a}}_{1.00 }}{{\left( {\mathrm{C}{{\mathrm{e}}_{1.04 }}\mathrm{L}{{\mathrm{a}}_{0.42 }}\mathrm{N}{{\mathrm{d}}_{0.42 }}\mathrm{P}{{\mathrm{r}}_{0.12 }}} \right)}_{2.00 }}{{\left( {\mathrm{C}{{\mathrm{O}}_3}} \right)}_4}\cdot {{\mathrm{H}}_2}\mathrm{O} $ , and the simplified formula is $ \mathrm{CaC}{{\mathrm{e}}_2}{{\left( {\mathrm{C}{{\mathrm{O}}_3}} \right)}_4}\cdot {{\mathrm{H}}_2}\mathrm{O} $ . According to X-ray single crystal diffraction galgenbergite-(Ce) is triclinic, space group $ P\overline{1},a=6.3916(5) $ , b?=?6.4005(4), c?=?12.3898(9) Å, α?=?100.884(4), β?=?96.525(4), γ?=?100.492(4)°, V?=?483.64(6) Å3, Z?=?2. The eight strongest lines in the powder X-ray diffraction pattern are [d calc in Å/(I)/hkl]: 5.052/(100)/011; 3.011/(70)/0-22; 3.006/(66)/004; 5.899/(59)/-101; 3.900/(51)/1-12; 3.125/(46)/-201; 2.526/(42)/022; 4.694/(38)/-102. The infrared absorption spectrum reveals H2O (OH-stretching mode at 3,489 cm?1, HOH bending mode at 1,607 cm?1) and indicates the presence of distinctly non-equivalent CO3-groups by double and quadruple peaks of their ν1, ν2, ν3 and ν4 modes. The crystal structure of galgenbergite-(Ce) was refined with X-ray single crystal data to R1?=?0.019 for 2,448 unique reflections (I?>?2σ(I)) and 193 parameters. The three cation sites of the structure Ca(1), Ce(2) and Ce(3) have a modest mixed site occupation by Ca and small amount of REE (Ce, La, Pr, Nd) and vice versa. The structure is based on double layers parallel to (001), which are composed of Ca(1)Ce(2)(CO3)2 single layers with an ordered chessboard like arrangement of Ca and Ce, and with a roof tile-like stacking of the CO3 groups. Perpendicular to (001) the double layers are connected to a triclinic framework structure with good cleavage parallel to (001) by a differently organized and more open part of the structure formed by Ce(3)(CO3)2(H2O). Based on the topology of the CaCe(CO3)2 single layer in galgenbergite-(Ce), structural relationships to rutherfordine, to aragonite and ancylite type minerals, and to lanthanite are outlined. 相似文献
8.
Andrea B. Rieser Ana-Voica Bojar Franz Neubauer Johann Genser Yongjiang Liu Xiao-Hong Ge Gertrude Friedl 《International Journal of Earth Sciences》2009,98(5):1063-1075
Carbon and oxygen stable isotopic composition of Cenozoic lacustrine carbonates from the intramontane Qaidam Basin yields
cycles of variable length and shows several distinct events driven by tectonics and climate changes. From Eocene to Oligocene,
the over-all trend in the δ13C composition of lacustrine carbonates shows a shift toward higher values, possibly related to higher proportions of dissolved
inorganic carbon transported to the lake or lower input of soil derived CO2. At the same time, the δ18O composition of lacustrine carbonates is decreasing in accordance with the global cooling trend and northwards drifting of
the whole region. During the Miocene, distinct isotopic events can be recognized, although their interpretation and linkage
to a certain tectonic event remains difficult. These events may be related to uplift in the Himalayas, to the strongest phase
of uplift in the Altyn Mountains, to pronounced subsidence of the Qaidam Basin or to the expansion of C4 plants on land. Generally
cold, highly evaporative conditions can be deduced from enrichment of δ18O isotopic compositions during Pliocene and Quaternary times. 相似文献
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