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  • Publication
    Accès libre
    High stress late Maastrichtian – early Danian palaeoenvironment in the Neuquén Basin, Argentina
    (2007)
    Keller, Gerta
    ;
    Adatte, Thierry 
    ;
    Tantawy, Abdel A.
    ;
    Berner, Zsolt
    ;
    Stinnesbeck, W.
    ;
    Stueben, Doris
    ;
    Leanza, H. A.
    During the late Maastrichtian to early Danian the Neuquén Basin of Argentina was adjacent to an active volcanic arc to the west and an extensive land area to the northeast. Mineralogical and geochemical studies of the Bajada del Jagüel in the Neuquén Basin indicate a generally warm climate with seasonal changes in humidity and an open seaway to the South Atlantic that maintained marine conditions. Biostratigraphic and quantitative foraminiferal and nannofossil analyses indicate that sediment deposition during the late Maastrichtian (zones CF4-CF2, N. frequens) occurred in relatively shallow middle neritic (~100 m) depths with largely dysaerobic bottom waters (abundant low O2 tolerant benthics) and fluctuating sea level. Calcareous nannofossils indicate a high stress marine environment dominated by Micula decussata. Planktic foraminifera mimic the post-K/T high stress environment with alternating blooms of the disaster opportunists Guembelitria and low oxygen tolerant Heterohelix groups, indicating nutrient-rich surface waters and an oxygen depleted water column. The high stress conditions were probably driven by high nutrient influx due to upwelling and terrestrial and volcanic influx. The K/T boundary is marked by an erosional surface that marks a hiatus at the base of a 15-25 cm thick volcaniclastic sandstone, which contains diverse planktic foraminiferal zone P1c assemblages and nannofossils of zone NP1b immediately above it. This indicates deposition of the sandstone occurred ~500 ky after the K/T hiatus. No evidence of the Chicxulub impact or related tsunami deposition was detected.
  • Publication
    Accès libre
    Late Cretaceous to early Paleocene climate and sea-level fluctuations : the Tunisian record
    (2002-02-28)
    Adatte, Thierry 
    ;
    Keller, Gerta
    ;
    Stinnesbeck, Wolfgang
    Climate and sea-level fluctuations across the Cretaceous–Tertiary (K–T) transition in Tunisia were examined based on bulk rock and clay mineralogies, biostratigraphy and lithology in five sections (El Melah, El Kef, Elles, Ain Settara and Seldja) spanning from open marine to shallow inner neritic environments. Late Campanian to early Danian trends examined at El Kef and Elles indicate an increasingly more humid climate associated with sea-level fluctuations and increased detrital influx that culminates at the K–T transition. This long-term trend in increasing humidity and runoff in the Tethys region is associated with middle and high latitude cooling. Results of short-term changes across the K–T transition indicate a sea-level lowstand in the latest Maastrichtian about 25–100 ka below the K–T boundary with the regression marked by increased detrital influx at El Kef and Elles and a short hiatus at Ain Settara. A rising sea-level at the end of the Maastrichtian is expressed at Elles and El Kef by deposition of a foraminiferal packstone. A flooding surface and condensed sedimentation mark the K–T boundary clay which is rich in terrestrial organic matter. The P0–P1a transition is marked by a sea-level lowstand corresponding to a short hiatus at Ain Settara where most of P0 is missing and a period of non-deposition and erosion in the lower part of P1a (64.95 Ma). At Seldja, P0 and possibly the topmost part of CF1 are missing. These sea-level fluctuations are associated with maximum humidity. These data suggest that in Tunisia, long-term environmental stresses during the last 500 ka before the K–T boundary and continuing into the early Danian are primarily related to climate and sea-level fluctuations. Within this long-term climatic trend the pronounced warm and humid event within the latest Maastrichtian Zone CF1 may be linked to greenhouse conditions induced by Deccan volcanism. The absence of any significant clay mineral variations at or near the K–T boundary and Ir anomaly suggests that the bolide impact had a relatively incidental short-term effect on climate in the Tethys region.