High stress late Maastrichtian - early Danian palaeoenvironment in the Neuquen Basin, Argentina

During the late Maastrichtian to early Danian the Neuquen Basin of Argentina was adjacent to an volcanic are to the west and an extensive land area to the northeast. Mineralogical and geochemical Studies of the Bajada del Jaguel in the Neuquen 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 (similar to 100 in) depths with largely dysaerobic bottom waters (abundant low 02 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 Heterohelfix 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 Plc assemblages 0 and nannofossils of zone NP 1b immediately above it. This indicates deposition of the sandstone occurred similar to 500 ky after the K/T hiatus. No evidence of the Chicxulub impact or related tsunami deposition was detected. (c) 2007 Elsevier Ltd. All rights reserved.