Browsing by Author "Ponte, J."
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- Atmospheric halogen and acid rains during the main phase of Deccan eruptions: magnetic and mineral evidencePublication . Font, Eric; Fabre, Sébastien; Nedelec, A.; Adatte, T.; Keller, G.; Veiga-Pires, C.; Ponte, J.; Mirão, José; Khozyem, H.; Spangenberg, J. E.; Gerta Keller, Andrew C. Kerr,Environmental changes linked to Deccan volcanism are still poorly known. A major limitation resides in the paucity of direct Deccan volcanism markers and in the geologically short interval where both impact and volcanism occurred, making it hard to evaluate their contributions to the mass extinction. We investigated the low-magnetic-susceptibility interval just below the iridium-rich layer of the Bidart (France) section, which was recently hypothesized to be the result of paleoenvironmental perturbations linked to paroxysmal Deccan phase 2. Results show a drastic decrease of detrital magnetite and presence of scarce akaganeite, a hypothesized reaction product formed in the aerosols derived from reaction of a volcanic plume with water and oxygen in the high atmosphere. A weathering model of the consequences of acidic rains on a continental regolith reveals nearly complete magnetite dissolution after ~31,000 yr, which is consistent with our magnetic data and falls within the duration of the Deccan phase 2. These results highlight the nature and importance of the Deccan-related environmental changes leading up to the end- Cretaceous mass extinction.
- Atmospheric halogen and acid rains during the major Deccan episode: magnetic and mineral evidencesPublication . Font, Eric; Fabre, Sébastien; Nédélec, Anna; Adatte, T.; Keller, G.; Veiga-Pires, C.; Ponte, J.; Mirão, José; Khozyem, H.; Spangenberg, J. E.Environmental and climatic changes linked to Deccan volcanism are still poorly known. A major limitation resides in the paucity of direct Deccan volcanism markers and in the geologically short interval where both impact and volcanism occurred, making it hard to evaluate their contributions to the mass extinction. We investigated the low magnetic susceptibility interval just below the Iridium-rich layer of the Bidart (France) section, which was recently hypothesized to be the result of palaeoenvironmental perturbations linked to paroxysmal Deccan phase-2. Results show a drastic decrease of detrital magnetite and presence of fine specular akaganeite, a hypothesized reaction product between FeCl2 from the volcanic plume with water and oxygen in the high atmosphere. A weathering model of the consequences of acidic rains on a continental regolith reveals nearly complete magnetite dissolution after about 33,000 years, which is consistent with our magnetic data and the duration of the Deccan phase-2. This discovery represents an unprecedented piece of evidence of the nature and importance of the Deccan-related environmental changes.
- Paleomagnetism in speleothems: influence of calcite growth dip on the natural remanent magnetizationPublication . Font, E.; Ponte, J.; Veiga-Pires, C.; Hillaire-Marcel, C.Recent studies recognized speleothems as excellent recorders of the Earth’s magnetic field. However, some questions remain about the origin of the natural remanent magnetization and about the influence of the speleothem shape on the recorded magnetic directions.
- Speleothem shape and natural remanent magnetizationPublication . Ponte, J.; Font, E.; Veiga-Pires, C.; Hillaire-Marcel, C.Speleothems might be of interest for high-resolution reconstruction of the Earth’s magnetic field. However, little is known about the influence of speleothem morphologies on their Natural Remanent Magnetization (NRM).
- The pre-KPB interval: sedimentary record of a major Deccan Traps pulse?Publication . Font, Eric; Ponte, J.; Nédélec, Anna; Veiga-Pires, C.; Ellwood, B. B.; Camps, Pierre; Figueireido, M. O.; Silva, T. P. da; Nave, Silvia; Pozo, ManuelThe KPB crisis is one of the major biological crises that affected the Earth at Phanerozoic times. There is still an acrimonious debate on the nature and origin of this mass extinction: proponents of the idea that large bolide impacts caused most of the Phanerozoic mass extinctions are opposed to those who favoured a terrestrial origin linked to continental flood basalt eruptions of the Deccan Traps. The major limitations reside in the difficulty to date with precision the stratigraphic position of Deccan traps pulses since direct markers are still missing.