| 1. |
- Cui, Ying, et al.
(författare)
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Carbon cycle perturbation expressed in terrestrial Permian–Triassic boundary sections in South China
- 2015
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Ingår i: Global and Planetary Change. - : Elsevier. - 0921-8181 .- 1872-6364.
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Tidskriftsartikel (refereegranskat)abstract
- Stable isotopes of inorganic and organic carbon are commonly used in chemostratigraphy to correlate marine and terrestrial sedimentary sequences based on the assumption that the carbon isotopic signature of the exogenic carbon pool dominates other sources of variability. Here, sediment samples from four Permian–Triassic boundary (PTB) sections of western Guizhou and eastern Yunnan provinces in South China, representing a terrestrial to marine transitional setting, were analyzed for δ13C of organic matter (δ13Corg). These values were subsequently compared to published δ13C values of carbonates (δ13Ccarb) from the Global Stratotype Section and Point at Meishan and many other marine and terrestrial sections. A similar isotopic trend evident through all four sections is characterized by a negative shift of 2–3‰ at the top of the Xuanwei Formation, where we tentatively place the PTB. This negative shift also corresponds to a turnover in the vegetation and the occurrence of fungal spores, which is generally interpreted as a proliferation of decomposers and collapse of complex ecosystems during the end-Permian mass extinction event. Moreover, the absolute values of δ13Corg are more extreme in the more distal (marine) deposits. The δ13Corg values for the studied sediments are more variable compared to coeval δ13Ccarb records from marine records especially in the interval below the extinction horizon. We contend that the depositional environment influenced the δ13Corg values, but that the persisting geographic δ13Corg pattern through the extinction event across the four independent sections is an indication that the atmospheric δ13C signal left an indelible imprint on the geologic record related to the profound ecosystem change during the end-Permian extinction event.
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| 2. |
- Vajda, Vivi, 1963-, et al.
(författare)
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Nano particles as the primary cause for long-termsunlight suppression athigh southern latitudes following the Chicxulub impact — evidence fromejecta deposits in Belize and Mexico
- 2015
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Ingår i: Gondwana Research. - : Elsevier. - 1342-937X .- 1878-0571. ; 27, s. 1079-1088
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Tidskriftsartikel (refereegranskat)abstract
- Life on Earth was sharply disrupted 66 Ma ago as an asteroid hit the sea-floor inwhat is today Yucatan Peninsula, Mexico. Approximately 600 km3 of sedimentary rock were vapourized, ejected into the atmosphere and subsequently deposited globally as an ejecta apron and fallout layer. Proximal ejecta deposits occur in Belize and southern Mexico where the so called Albion Island spheroid bed is superimposed on the target rock (the Barton Creek Formation). We analysed the spheroid bed via Mössbauer spectroscopy, petrology, XRD, and palynology at several sites ~350–500 km distance from the crater centre. Our results show that the relative concentrations of Fe in nano-phase goethite (α-FeOOH) are very high in the spheroid bed samples from Albion Island (Belize) and from Ramonal South (Mexico), but are low to absent in the spheroid bed at Ramonal North, and in the Cretaceous target rock. Moreover, our study shows that goethite and haematite are the dominant Fe-oxide nano-phases and the XRD results show that the target rock consists of both calcite and dolomite. We suggest that the heterogeneous composition of the spheroid bed between the various sites reflects the different types of target rocks that were dispersed within the rapidly expanding vapour plume and the complex sorting processes involved in the formation of the ejecta blanket. The distribution of the vapourized target rock strongly influenced life on Earth at the close of the Mesozoic. However, the comparatively thin K–Pg boundary clay in high-latitude Gondwanan successions combined with evidence of catastrophic changes to the biota in this region implies that the long-term sunlight suppression in the Southern Hemisphere was mainly governed by the large quantities of hydrous aerosols nucleated around sulphuric acid droplets or nano-sized particles, such as the nano-phase Fe-oxides.
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| 3. |
- Vajda, Vivi, 1963-
(författare)
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Stevns Klint
- 2014
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Ingår i: Geologiskt forum. - : Geological Society of Sweden. ; 21:83, s. 14-19
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Tidskriftsartikel (populärvet., debatt m.m.)
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