Geology, geochronology, geochemistry and tectonic implications of the Juchatengo Green Rock Sequence, state of Oaxaca, southern Mexico

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Actitud de docentes de escuelas secundarias ante la inclusión de alumnos con necesidades educativas

Licenciatura en Psicología Educativ

The Chicxulub impact is synchronous with the planktonic foraminifera mass extinction at the Cretaceous/Paleogene boundary : new evidence from the Moncada section, Cuba

The Moncada section, western Cuba, is one of the few sections across the Cretaceous/Paleogene (K/Pg) boundary in the Gulf of Mexico and Caribbean where an Ir anomaly has been identified toward and above the top of a clastic unit, locally called the Moncada Formation (Fm.). The Moncada Fm. is enriched in ejecta (altered glass spherules, shocked quartz, melt rock fragments, etc.) and represents the local Complex Clastic Unit (CCU) linked to the Chicxulub impact event. This CCU is overlain by a 2-3cm thick bed of Ir-rich, dark, calcareous claystone which represents the "K/T Boundary Clay" at Moncada. All lowermost Danian Planktonic Foraminiferal zones and Acme-Stages (PFAS) were identified, suggesting stratigraphic continuity across the Danian and indicating that the Moncada Fm. is K/Pg boundary in age. High-resolution biostratigraphic data suggest that the mass extinction event of planktonic foraminifera at the K/Pg boundary was more severe than previously suggested. The absence of cosmopolitan, generalist Cretaceous species in the Danian deposits of Moncada supports the hypothesis that only Guembelitria survived the mass extinction triggered by the Chicxulub impact event. The high Ir-concentration and the ejecta-rich clay laminations identified in the lowermost Danian of Moncada (Ancón Fm.) are explained partly as the redeposition of ejecta material eroded and reworked from higher topographic levels, still contaminated by toxic trace elements (e.g,. Cu and Ni) of meteoritic origin. These pollutants of meteoritic origin could have affected the ecological conditions of the pelagic environment for thousands of years after the K/Pg boundary, being particularly intense just after the Chicxulub impact. The ecological stress due to the pollutants partly explains the catastrophic mass extinction of planktonic foraminifera at the K/Pg boundary and their subsequent evolutionary radiation

The Chicxulub impact is synchronous with the planktonic foraminifera mass extinction at the Cretaceous/Paleogene boundary: new evidence from the Moncada section, Cuba.

The Moncada section, western Cuba, is one of the few sections across the Cretaceous/Paleogene (K/Pg) boundary in the Gulf of Mexico and Caribbean where an Ir anomaly has been identified toward and above the top of a clastic unit, locally called the Moncada Formation (Fm.). The Moncada Fm. is enriched in ejecta (altered glass spherules, shocked quartz, melt rock fragments, etc.) and represents the local Complex Clastic Unit (CCU) linked to the Chicxulub impact event. This CCU is overlain by a 2-3cm thick bed of Ir-rich, dark, calcareous claystone which represents the “K/T Boundary Clay” at Moncada. All lowermost Danian Planktonic Foraminiferal zones and Acme-Stages (PFAS) were identified, suggesting stratigraphic continuity across the Danian and indicating that the Moncada Fm. is K/Pg boundary in age. High-resolution biostratigraphic data suggest that the mass extinction event of planktonic foraminifera at the K/Pg boundary was more severe than previously suggested. The absence of cosmopolitan, generalist Cretaceous species in the Danian deposits of Moncada supports the hypothesis that only Guembelitria survived the mass extinction triggered by the Chicxulub impact event. The high Ir-concentration and the ejecta-rich clay laminations identified in the lowermost Danian of Moncada (Ancón Fm.) are explained partly as the redeposition of ejecta material eroded and reworked from higher topographic levels, still contaminated by toxic trace elements (e.g,. Cu and Ni) of meteoritic origin. These pollutants of meteoritic origin could have affected the ecological conditions of the pelagic environment for thousands of years after the K/Pg boundary, being particularly intense just after the Chicxulub impact. The ecological stress due to the pollutants partly explains the catastrophic mass extinction of planktonic foraminifera at the K/Pg boundary and their subsequent evolutionary radiation

Study of melt and a clast of 546 Ma magmatic arc rocks in the 65 Ma Chicxulub bolide breccia, northern Maya block, Mexico: western limit of Ediacaran arc peripheral to northern Gondwana

The basement of the Maya block of eastern Mexico is generally covered by Mesozoic and Cenozoic platformal carbonate rocks. However, the 65.5 Ma Chicxulub meteorite impact in the northern Yucatan Peninsula excavated deep into the crust and brought crystalline basement fragments into the impact breccias. Common Pb isotopic data from impact melt and a granitic clast from drill core (Y6) are highly radiogenic, consistent with the Archaean derivation. A granodiorite clast in this breccia from drill core (Yaxcopoil-1) yielded a continuous range of concordant 206Pb/238U laser ablation inductively coupled plasma mass spectrometry zircon ages between 546 5 Ma and 465 Ma, with three discordant zircons having 206Pb/238U ages between 130 Ma and 345 Ma. The ca. 546 Ma age is interpreted as the age of granodiorite intrusion, with younger ages representing variable Pb loss during melting associated with the meteorite impact. This is consistent with previous U-Pb zircon data that gave an upper intercept age of 550 ± 15 Ma at Chicxulub, which becomes 545 ±5 Ma when combined with the zircon data from distal ejecta. Such arc rocks are absent in the southern Maya block, and in the neighbouring Oaxaquia terrane (s.s.) they are replaced by a 546 5 Ma plume-related dike swarm. On the other hand, Ediacaran arc rocks continue through the peri-Gondwanan terranes of the Appalachians and Europe (Florida, Carolinia, Avalonia, Iberia, Armorica, Massif Central, Bohemia, and NW Africa). Arc magmatism in these areas ended between 570 Ma (Newfoundland) and 540 Ma (Carolinia/UK) as the subduction zone was replaced by a transform fault along the northern Gondwanan margin. This age range is synchronous with the two-stage birth of Iapetus, suggesting that both are related to major plate reorganization. The source of plume-related dikes may have been located at the rift-rift-transform triple junction between Laurentia, Baltica, and Gondwana

Seismic stratigraphic evidence of a pre-impact basin in the Yucatán Platform: morphology of the Chicxulub crater and K/Pg boundary deposits

Fifty-four 2D seismic profiles and 13 boreholes were used to describe pre-impact and post-impact deposits in the Yucatán Shelf. Previous work has identified a pre-impact basin in the northwest portion of the Chicxulub structure. The geometry of seismic reflectors associated with the Mesozoic Era shows that this pre-impact depression, here named Yucatán Trough, extends from the southern part of the Yucatán Peninsula to the northern face of the Campeche Escarpment. Stratigraphic data from boreholes of the Yucatán Platform suggest that the main sedimentary fills of the Yucatán Trough are a thin series of Upper Jurassic-Lower Cretaceous red beds, followed by the evaporite-dominated Lower Cretaceous and the carbonate-dominated Upper Cretaceous sedimentary successions. The mapping of the Cretaceous-Paleogene (K/Pg) deposits allowed us to observe the morphology of the Yucatán Shelf by the time of the Chicxulub impact event. The two-way seismic time K/Pg deposits map in conjunction with the free-air gravity anomaly map of the northern Yucatán Block reveals that, before the impact, the carbonate platform was divided into two blocks by a ~ 95–205 km wide and ~ 470-km long trough-shaped depression, probably a rift-basin with a north-south orientation, in which the central structure of Chicxulub impact crater is contained. The seismic reflectors overlying the top of the K/Pg deposits show that, during the Cenozoic Era, both the Yucatán Trough and impact basin were filled by progradational sequences which flattened the surface completely until the current block of the Yucatán Platform was configured. [Display omitted] •A new seismic dataset combined with borehole and gravity data allowed us to define the morphology of a pre-impact basin within the Yucatán Platform.•A ~95-205-km wide and ~470-km long trough-shaped low topographic feature divides the Yucatán Platform into two blocks.•The pre-existing basin, here named Yucatán Trough, is north-south oriented and contains the Chicxulub crater structure.•Deposits that filled the Yucatán Trough during the Mesozoic are mainly Lower to Upper Cretaceous evaporites and carbonates.•The Yucatán Trough is probably a rift basin induced by the Jurassic counterclockwise rotation of the Yucatán Block

Reconnaissance microfossil and magnetic stratigraphy of the Miocene Sayula-Isla sequence, Veracruz, Mexico

Se realizó un estudio piloto de biomagnetoestratigrafía en la bien definida (paleontológicamente) secuencia sedimentaria del Mioceno-Temprano a Medio en Sayula-Isla (sur de Veracruz, México). Se incluyen resultados de magnetismo de rocas como adquisición de magnetismo remanente isotermal (IRM) y experimentos de histéresis. Las curvas de adquisición de IRM resultaron muy parecidas en todas las muestras. Se alcanzó saturación en campos moderados del orden de 150-200 mT, sugiriendo espinelas como portadores de remanencia. De las razones de los parámetros de histéresis, parece que todas las muestras caen en la región del tamaño de grano pseudo-dominio-simple (PSD) o multidominio (MD). En la mayoría de las unidades estudiadas se pudieron observar de una a dos componentes paleomagnéticas. Se eliminaron fácilmente pequeñas componentes secundarias a temperaturas de 100-180°C. Algunas muestras mostraron comportamiento térmico inestable, sugiriendo la presencia de magnetización multicomponente. Se definieron las componentes de magnetización característica después de 250°C para esas muestras. La comparación de las zonas de polaridad de la sección Sayula-Isla muestra algunos problemas a causa de la escasez en el contenido de microfósiles. Se requieren más datos para definir con mayor detalle la Escala Geomagnética Temporal de Polaridad Local; sin embargo, se obtuvo una razonablemente buena correlación para las biozonas del Mioceno-Temprano a Medio de la Cuenca Salina del Istmo. doi: https://doi.org/10.22201/igeof.00167169p.2002.41.2.28