Your browser doesn't support javascript.
loading
Mostrar: 20 | 50 | 100
Resultados 1 - 12 de 12
Filtrar
Mais filtros










Base de dados
Intervalo de ano de publicação
1.
Sci Adv ; 1(7): e1500470, 2015 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-26601239

RESUMO

The end-Permian mass extinction was the most severe in the Phanerozoic, extinguishing more than 90% of marine and 75% of terrestrial species in a maximum of 61 ± 48 ky. Because of broad temporal coincidence between the biotic crisis and one of the most voluminous continental volcanic eruptions since the origin of animals, the Siberian Traps large igneous province (LIP), a causal connection has long been suggested. Magmatism is hypothesized to have caused rapid injection of massive amounts of greenhouse gases into the atmosphere, driving climate change and subsequent destabilization of the biosphere. Establishing a causal connection between magmatism and mass extinction is critically dependent on accurately and precisely knowing the relative timing of the two events and the flux of magma. New U/Pb dates on Siberian Traps LIP lava flows, sills, and explosively erupted rocks indicate that (i) about two-thirds of the total lava/pyroclastic volume was erupted over ~300 ky, before and concurrent with the end-Permian mass extinction; (ii) eruption of the balance of lavas continued for at least 500 ky after extinction cessation; and (iii) massive emplacement of sills into the shallow crust began concomitant with the mass extinction and continued for at least 500 ky into the early Triassic. This age model is consistent with Siberian Traps LIP magmatism as a trigger for the end-Permian mass extinction and suggests a role for magmatism in suppression of post-extinction biotic recovery.

2.
Proc Biol Sci ; 282(1811)2015 Jul 22.
Artigo em Inglês | MEDLINE | ID: mdl-26156768

RESUMO

A mid-Permian (Guadalupian epoch) extinction event at approximately 260 Ma has been mooted for two decades. This is based primarily on invertebrate biostratigraphy of Guadalupian-Lopingian marine carbonate platforms in southern China, which are temporally constrained by correlation to the associated Emeishan Large Igneous Province (LIP). Despite attempts to identify a similar biodiversity crisis in the terrestrial realm, the low resolution of mid-Permian tetrapod biostratigraphy and a lack of robust geochronological constraints have until now hampered both the correlation and quantification of terrestrial extinctions. Here we present an extensive compilation of tetrapod-stratigraphic data analysed by the constrained optimization (CONOP) algorithm that reveals a significant extinction event among tetrapods within the lower Beaufort Group of the Karoo Basin, South Africa, in the latest Capitanian. Our fossil dataset reveals a 74-80% loss of generic richness between the upper Tapinocephalus Assemblage Zone (AZ) and the mid-Pristerognathus AZ that is temporally constrained by a U-Pb zircon date (CA-TIMS method) of 260.259 ± 0.081 Ma from a tuff near the top of the Tapinocephalus AZ. This strengthens the biochronology of the Permian Beaufort Group and supports the existence of a mid-Permian mass extinction event on land near the end of the Guadalupian. Our results permit a temporal association between the extinction of dinocephalian therapsids and the LIP volcanism at Emeishan, as well as the marine end-Guadalupian extinctions.


Assuntos
Biodiversidade , Extinção Biológica , Fósseis , Répteis , Animais , África do Sul
3.
Science ; 347(6218): 182-4, 2015 Jan 09.
Artigo em Inglês | MEDLINE | ID: mdl-25502315

RESUMO

The Chicxulub asteroid impact (Mexico) and the eruption of the massive Deccan volcanic province (India) are two proposed causes of the end-Cretaceous mass extinction, which includes the demise of nonavian dinosaurs. Despite widespread acceptance of the impact hypothesis, the lack of a high-resolution eruption timeline for the Deccan basalts has prevented full assessment of their relationship to the mass extinction. Here we apply uranium-lead (U-Pb) zircon geochronology to Deccan rocks and show that the main phase of eruptions initiated ~250,000 years before the Cretaceous-Paleogene boundary and that >1.1 million cubic kilometers of basalt erupted in ~750,000 years. Our results are consistent with the hypothesis that the Deccan Traps contributed to the latest Cretaceous environmental change and biologic turnover that culminated in the marine and terrestrial mass extinctions.


Assuntos
Planeta Terra , Extinção Biológica , Chumbo , Silicatos , Urânio , Zircônio , Animais , Fatores de Tempo , Erupções Vulcânicas
4.
Proc Natl Acad Sci U S A ; 111(9): 3316-21, 2014 Mar 04.
Artigo em Inglês | MEDLINE | ID: mdl-24516148

RESUMO

The end-Permian mass extinction was the most severe loss of marine and terrestrial biota in the last 542 My. Understanding its cause and the controls on extinction/recovery dynamics depends on an accurate and precise age model. U-Pb zircon dates for five volcanic ash beds from the Global Stratotype Section and Point for the Permian-Triassic boundary at Meishan, China, define an age model for the extinction and allow exploration of the links between global environmental perturbation, carbon cycle disruption, mass extinction, and recovery at millennial timescales. The extinction occurred between 251.941 ± 0.037 and 251.880 ± 0.031 Mya, an interval of 60 ± 48 ka. Onset of a major reorganization of the carbon cycle immediately precedes the initiation of extinction and is punctuated by a sharp (3‰), short-lived negative spike in the isotopic composition of carbonate carbon. Carbon cycle volatility persists for ∼500 ka before a return to near preextinction values. Decamillenial to millennial level resolution of the mass extinction and its aftermath will permit a refined evaluation of the relative roles of rate-dependent processes contributing to the extinction, allowing insight into postextinction ecosystem expansion, and establish an accurate time point for evaluating the plausibility of trigger and kill mechanisms.


Assuntos
Evolução Biológica , Ciclo do Carbono/fisiologia , Meio Ambiente , Extinção Biológica , Modelos Biológicos , Isótopos de Carbono/análise , História Antiga , Fatores de Tempo , Erupções Vulcânicas/análise
6.
Science ; 340(6135): 941-5, 2013 May 24.
Artigo em Inglês | MEDLINE | ID: mdl-23519213

RESUMO

The end-Triassic extinction is characterized by major losses in both terrestrial and marine diversity, setting the stage for dinosaurs to dominate Earth for the next 136 million years. Despite the approximate coincidence between this extinction and flood basalt volcanism, existing geochronologic dates have insufficient resolution to confirm eruptive rates required to induce major climate perturbations. Here, we present new zircon uranium-lead (U-Pb) geochronologic constraints on the age and duration of flood basalt volcanism within the Central Atlantic Magmatic Province. This chronology demonstrates synchroneity between the earliest volcanism and extinction, tests and corroborates the existing astrochronologic time scale, and shows that the release of magma and associated atmospheric flux occurred in four pulses over about 600,000 years, indicating expansive volcanism even as the biologic recovery was under way.


Assuntos
Mudança Climática , Planeta Terra , Chumbo , Silicatos , Urânio , Erupções Vulcânicas , Zircônio , Oceano Atlântico , Fatores de Tempo
7.
Science ; 335(6064): 73-6, 2012 Jan 06.
Artigo em Inglês | MEDLINE | ID: mdl-22223803

RESUMO

The continental lithosphere contains the oldest and most stable structures on Earth, where fragments of ancient material have eluded destruction by tectonic and surface processes operating over billions of years. Although present-day erosion of these remnants is slow, a record of how they have uplifted, eroded, and cooled over Earth's history can provide insight into the physical properties of the continents and the forces operating to exhume them over geologic time. We constructed a continuous record of ancient lithosphere cooling with the use of uranium-lead (U-Pb) thermochronology on volcanically exhumed lower crustal fragments. Combining these measurements with thermal and Pb-diffusion models constrains the range of possible erosion histories. Measured U-Pb data are consistent with extremely low erosion rates persisting over time scales approaching the age of the continents themselves.

8.
Science ; 334(6061): 1367-72, 2011 Dec 09.
Artigo em Inglês | MEDLINE | ID: mdl-22096103

RESUMO

The end-Permian mass extinction was the most severe biodiversity crisis in Earth history. To better constrain the timing, and ultimately the causes of this event, we collected a suite of geochronologic, isotopic, and biostratigraphic data on several well-preserved sedimentary sections in South China. High-precision U-Pb dating reveals that the extinction peak occurred just before 252.28 ± 0.08 million years ago, after a decline of 2 per mil (‰) in δ(13)C over 90,000 years, and coincided with a δ(13)C excursion of -5‰ that is estimated to have lasted ≤20,000 years. The extinction interval was less than 200,000 years and synchronous in marine and terrestrial realms; associated charcoal-rich and soot-bearing layers indicate widespread wildfires on land. A massive release of thermogenic carbon dioxide and/or methane may have caused the catastrophic extinction.


Assuntos
Biodiversidade , Ecossistema , Extinção Biológica , Fósseis , Animais , Dióxido de Carbono , Isótopos de Carbono , China , Incêndios , Sedimentos Geológicos , Invertebrados/classificação , Isótopos , Chumbo , Espectrometria de Massas , Metano , Oceanos e Mares , Plantas/classificação , Técnica de Diluição de Radioisótopos , Datação Radiométrica , Água do Mar/química , Tempo , Urânio , Vertebrados/classificação
9.
Nature ; 457(7230): 718-21, 2009 Feb 05.
Artigo em Inglês | MEDLINE | ID: mdl-19194449

RESUMO

The Neoproterozoic era (1,000-542 Myr ago) was an era of climatic extremes and biological evolutionary developments culminating in the emergence of animals (Metazoa) and new ecosystems. Here we show that abundant sedimentary 24-isopropylcholestanes, the hydrocarbon remains of C(30) sterols produced by marine demosponges, record the presence of Metazoa in the geological record before the end of the Marinoan glaciation ( approximately 635 Myr ago). These sterane biomarkers are abundant in all formations of the Huqf Supergroup, South Oman Salt Basin, and, based on a new high-precision geochronology, constitute a continuous 100-Myr-long chemical fossil record of demosponges through the terminal Neoproterozoic and into the Early Cambrian epoch. The demosponge steranes occur in strata that underlie the Marinoan cap carbonate (>635 Myr ago). They currently represent the oldest evidence for animals in the fossil record, and are evidence for animals pre-dating the termination of the Marinoan glaciation. This suggests that shallow shelf waters in some late Cryogenian ocean basins (>635 Myr ago) contained dissolved oxygen in concentrations sufficient to support basal metazoan life at least 100 Myr before the rapid diversification of bilaterians during the Cambrian explosion. Biomarker analysis has yet to reveal any convincing evidence for ancient sponges pre-dating the first globally extensive Neoproterozoic glacial episode (the Sturtian, approximately 713 Myr ago in Oman).


Assuntos
Evolução Biológica , Colestanos/análise , Colestanos/química , Fósseis , Sedimentos Geológicos/química , Poríferos/fisiologia , Animais , Arábia , Biomarcadores/análise , Biomarcadores/química , Colestanos/isolamento & purificação , Cromatografia Gasosa-Espectrometria de Massas , História Antiga , Hidrocarbonetos/análise , Hidrocarbonetos/química , Camada de Gelo , Oceanos e Mares , Oxigênio/análise , Água do Mar/química
10.
Science ; 323(5917): 1048-50, 2009 Feb 20.
Artigo em Inglês | MEDLINE | ID: mdl-19179492

RESUMO

Most of Earth's present-day crust formed at mid-ocean ridges. High-precision uranium-lead dating of zircons in gabbros from the Vema Fracture Zone on the Mid-Atlantic Ridge reveals that the crust there grew in a highly regular pattern characterized by shallow melt delivery. Combined with results from previous dating studies, this finding suggests that two distinct modes of crustal accretion occur along slow-spreading ridges. Individual samples record a zircon date range of 90,000 to 235,000 years, which is interpreted to reflect the time scale of zircon crystallization in oceanic plutonic rocks.

11.
Science ; 308(5718): 95-8, 2005 Apr 01.
Artigo em Inglês | MEDLINE | ID: mdl-15731406

RESUMO

U-Pb zircon dates from volcanic ash beds within the Doushantuo Formation (China) indicate that its deposition occurred between 635 and 551 million years ago. The base records termination of the global-scale Marinoan glaciation and is coeval with similar dated rocks from Namibia, indicating synchronous deglaciation. Carbon isotopic and sequence-stratigraphic data imply that the spectacular animal fossils of the Doushantuo Formation are for the most part younger than 580 million years old. The uppermost Doushantuo Formation contains a pronounced negative carbonate carbon isotopic excursion, which we interpret as a global event at circa 551 million years ago.


Assuntos
Fósseis , Sedimentos Geológicos , Animais , Evolução Biológica , Carbono/análise , Carbono/metabolismo , Isótopos de Carbono/análise , Carbonatos/análise , China , Sedimentos Geológicos/química , Chumbo , Silicatos , Tempo , Urânio , Erupções Vulcânicas , Zircônio
12.
Science ; 304(5674): 1126-9, 2004 May 21.
Artigo em Inglês | MEDLINE | ID: mdl-15105458

RESUMO

We show that intraplate magmatism occurred 1106 to 1112 million years ago over an area of two million square kilometers within the Kalahari craton of southern Africa, during the same magnetic polarity chron as voluminous magmatism within the cratonic core of North America. These contemporaneous magmatic events occurred while the Rodinia supercontinent was being assembled and are inferred to be parts of a single large igneous province emplaced across the two cratons. Widespread intraplate magmatism during Rodinia assembly shows that mantle upwellings required to generate such provinces may occur independently of the supercontinent cycle.

SELEÇÃO DE REFERÊNCIAS
DETALHE DA PESQUISA
...