Common Lead vs Radiogenic Lead Pb derived from decay of U and Th is described as radiogenic lead. In a system containing U and Th, the isotopic. 2) Concordant U-Pb dates. 3) Discordant U-Pb dates and open. system behavior. 4) Common Pb-Pb dating. 5) The Geochron. Cross-section of a zircon grain. An Introduction to UPb Geochronology – A free PowerPoint PPT presentation to Radioactive Decay and Dating of Geological Materials PowerPoint PPT.
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Absolute ages of multiple generations of brittle structures by U-Pb dating of calcite Collapse of a marine-based ice stream during the early Younger Dryas chronozone, western Canadian Arctic Geospatial analysis of Oklahoma USA earthquakes Quantifying the limits of regional-scale earthquake mitigation measures Mineral changes quantify frictional heating during a large low-friction landslide A Jurassic continental backarc basin oceanic lithosphere in southern Eurasia U-Pb geochronology and geochemistry from the Kumaun Himalaya, NW India, reveal Paleoproterozoic arc magmatism related to formation of the Columbia supercontinent How fast can low-angle normal faults slip?
Insights from cosmogenic exposure dating of the active Mai'iu fault, Papua New Guinea Corrections for the geometry of the host-inclusion system Shahabi Far et al. Identifying externally derived sulfur in conduit-type Cu-platinum-group element deposits: The importance of multiple sulfur isotope studies Limited recycling of crustal osmium in forearc mantle during slab dehydration Deep-basin evidence resolves a year-old debate and demonstrates synchronous onset of Messinian evaporite deposition in a non-desiccated Mediterranean U-Pb dating of calcite cement and diagenetic history in microporous carbonate reservoirs: Paleogeographic correlations So far, there has been no consensus in the place of accretion of the TL and DC and the supposed subsequent sense of movement of the MDAC as a coherent block along the southwestern Gondwana margin.
On the other hand, the possibility of a virtually fixed position for the DYC since its deposition with Patagonia as reference is hampered by the fact that there is no clear indication of a coeval Permian magmatic are at latitude similar to the current position of the MDAC in southern Patagonia e.
This magmatic are could be represented either by the Choiyoi acid magmatic province Kay et al. Conversely, it is well known that the subduction of bathymetrically elevated oceanic features such as ridges or plateau DC and TL in this case can flatten the subducting slab and prevent the magmatic activity in the vicinity of the continental margin. According to the above-mentioned situation, the DYC would not have had displacement since its deposition and the remnants of the associated Permian magmatic are could still be hidden below the Mesozoic sedimentary cover somewhere in the southeastern Patagonia or even farther eastward.
This hy-pothesis would preclude defining the DYC as an allochthonous terrane. In brief, additional and more detailed paleomagnetic, geochronological and isotopic work is needed to give more convincing arguments supporting one of the proposed hypotheses, an autochthonous or an allochthonous origin of the DYC.
Therefore, the possibility of a geological correlation between the geologic units present in western Patagonia and those exposed in the Antarctic Peninsula must be considered. Willan assumed that the TPG could have been derived from a glaciated continental margin, though his result is based only on indirect evidence geochemical weathering and, at this time, there are no palynological reports on this unit.
According to the paleogeographic reconstruc-tions for the late Paleozoic e. However, caution must be taken with this interpretation, mainly because the TPG is part of the Western Domain of the Antarctic Peninsula Vaughan and Storey,which has been regarded as a suspect terrane and even as al-lochthonous to the rest of the terranes of the Antarctic Peninsula Willan, Conclusions This contribution presents the first palynological record for the late Paleozoic in Chile.
The palynological assemblage recorded in the DYC is composed mainly of Gymnospermopsida pollen, with also Pte-ridophyta and fungal spores. The studied association indicates a humid environment of forests with an undergrowth of ferns.
The palynological data indicate a Permian age for the deposition of the DYC. The available data indicate that the allochtho-nous hypothesis for the DYC is not completely proved, and an autochthonous tectonic setting with respect to Patagonia could also be a possible interpretation. Martini are thanked for field support. We are indebted to Dr. Thanks also for Dr. Rapalini Universidad de Buenos Aires for bis paleogeographic reconstructions.
We also thank C.
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Limarino Universidad de Buenos AiresH. Les spores Alpern, B. Detrital zircons as tracers of sedimentary provenance: Academia Nacional de Ciencias: Journal of the Geological Society of London Journal of African Earth Sciences Extreme freshwater release during the late Paleozoic Gondwana deglaciation and its impact on coastal ecosystems.
Rodinia breakup and development of the Pacific and Iapetus margins of Gondwana during the Neoproterozoic and Paleozoic. Linking accretionary orogenesis with supercontinent assembly. Permian fragmentation, accretion and subse-quent translation of a low-latitude Tethyan seamount to the high-latitude east Gondwana margin: Palynostratigraphy of Upper Paleozoic sequences in central-western Argentina.
Paleozoico Superior en Argentina: Permian section at Apillapampa, Bolivia, and its fossil content. Journal of Paleontology 39 6: The Gondwana Glaciation in Chile: Palaeogeography, Palaeoclimatology, Palaeoecology Geological Society of London, Memoirs Anote on the terrane concept, based on a introduction to the Terrane '97 conference, Christchurch, New Zealand, February American Journal of Science Permian phytogeography in Gondwana.
Strike-slip faults in the southern-most Andes and the development of the Patagonian orocline. U-Pb ages of detrital zircons in Jurassic eolian and associated sandstones of the Colorado Plateau: Evidence for transcontinental dispersal and intraregional recycling of sediment. Geological Society of America Bulletin Andean Geology 36 1: Fusulinid foraminifera from southern Chile.
Late Paleozoic Foraminifera from southern Chile.
Geochronology - PowerPoint PPT Presentation
Provenance and depositional setting of pre-Late Jurassic turbidite complexes in Patagonia, Chile. New Zealand Journal of Geology and Geophysics The late Palaeozoic to early Mesozoic evolution of southern South America: A Geological Time Scale A new geochronological approach.
Geological Society of America, Bulletin The Late Paleozoic in Chile: Stratigraphy, structure and possible tectonic framework.
Late Paleozoic subduction and accretion in Southern Chile. In International Geological Congress, No. Detrital zircon age patterns and provenance of the metamorphic complexes of southern Chile. Journal of South American Earth Sciences The western Patagonia terrane collage: Patagonia-Antarctica connections before Gondwana break-up.
The South Patagonian batholith: Metamorphic and plutonic basement complexes. Tectonostratigraphic terranes of the Circum-Pacific region.
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Late Paleozoic-early Mesozoic fore-arc basin sedimentary rocks at the Pacific margin in western Gondwana. Reevaluation of the timing and extent of late Paleozoic glaciation in Gondwana: How extensive was Gondwana glaciation in Antarctica? These lightgray-laminated layers are 2 to 4 cm thick and occur intercalated with organic-rich sediments. Previous studies have interpreted these layers as the product of sporadic rhyolitic volcanism based on petrographic and geochemical data Coutinho et al.
Cathodoluminescence image of zircon grains of bentonic layers from the 3. A dominant population of euhedral, prismatic, elongate to acicular grains interpreted as igneous crystals related to the ash fall volcanism; and a subordinate population Zircon separates from the intermediate betonitic layer of the of rounded to large prismatic grains, interpreted as detrital grains derived from PETROBRAS-Six mine were obtained by conventional gravi- the host rocks.
Error in standard calibration was 0. U and bieites spp. Spores are very scarce Th concentrations were determined relative to the SL13 standard Laevigatosporites vulgaris and microplanctonic fossils were Table 1. Selected level, and uncertainty in the calculated age is reported at the species are illustrated in Fig. Discussion A sample from the same aged layer was processed following the standard palynological method for Paleozoic material in the A Kazanian age, based on pollen grains and palynostrati- Palynological Laboratory of the Geosciences Institute of the Rio graphic correlation with the Euramerican schemes, has been Grande do Sul Federal University.
Carbonates and silicates were traditionally accepted for the Irati Formation see Daemon and removed using hydrochloric acid followed by hydrofluoric acid. The tonsteins interbedded within coal seams from the stratrigraphi- taxonomic study and the microphotographs were carried out cally older Rio Bonito Formation see Fig.
Results The morphology of zircon grains studied by cathodolumi- nescence revealed two different populations Fig. The dominant population comprises euhedral, prismatic, elongate to acicular grains interpreted as igneous crystals related to the ash fall volcanism.
A subordinate population made of rounded to large prismatic grains was interpreted as detrital grains derived from the host rocks. An inherited component at around Ma is present in a few analyzed xenocrysts. The palynological analysis revealed a rich and diversified palynoflora composed predominantly by bisaccate taeniate and non-taeniate and polyplicate pollen grains.
The most important Fig. Selected pollen taxa of the Lueckisporites virkkiae Zone recorded from the studied material. Lunatisporites variesectus Archangelsky and GamerroH49 ; c. Vittatina vittifera Luber and Waltz SamoilovichP44 ; d.
Quantitative and qualitative features of the palynoflora zircons from different populations in the same fraction, but also are typical of the L. Taking into account the Souza and age value for the analyzed zircon population and that lower Marques-Toigopalynostratigraphic scheme, the intercept age defined in their study could be interpreted as a following key index species found are: However, considering the new dating suggests that a short and unique volcanic event at Most zircon grains show the uppermost L interval L3 subinterval seems do not be a small dispersion on the Concordia diagram and define an younger than the Wuachiapingian.
The palynofossils described in the present study suggests The new radiometrical data reveals an Artinskian age for the correlation with biozones from other basins reinforcing the age of Irati Formation, related to the lower Permian Cisuralian taking Ma. For instance, the L. In Argentina, the base of the Striatites Bio- Biostratigraphical correlations between Gondwanan areas zone was dated at Because the levels immediately levels of paleophytogeographical regions of distinct ages.
At least part of the Permian. Toigo and Pons Nevertheless, the species listed by Based on these considerations, the Irati Formation should be Meyer and Marques-Toigo and by Cazzulo-Klepzig et regarded as older than My, as supported by the zircon dating al. While the geochrono- goraiensis Subzone. The source of ash falls with Souza and Marques-Toigoscheme. Gaps and lateral boundaries between the lithostratigraphic units are not A major question concerning the ash layers of the Irati represented.
Ages taken to the Rio do Rasto Formation, top of Formation is the volcanic event which the ash comes from.