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
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