ABSTRACT

We constructed a numerical model of the Chicxulub impact event using the Chart-D SQuared (CSQ) code coupled with the ANalytical Equation Of State (ANEOS) package. In the simulations we utilized a target stratigraphy based on borehole data and employed newly developed equations of state for the materials that are believed to play a crucial role in the impact-related extinction hypothesis: carbonates (calcite) and evaporites (anhydrite).
Simulations explored the effects of different projectile sizes (10 to 30 km in diameter) and porosity (0 to 50%). The effect of impact speed is addressed by doing simulations of asteroid impacts (v_i=20 km/s) and comet impacts (v_i=50 km/s). The masses of climatically important species injected into the upper atmosphere by the impact increase with the energy of the impact event, ranging from 350 to 3500 Gt for CO₂, from 40 to 560 Gt for S, and from 200 to 1400 Gt for water vapor. While our results are in good agreement with those of Ivanov et al. (1996), our estimated CO₂ production is 1 to 2 orders of magnitude lower than the results of Takata and Ahrens (1994), indicating that the impact event enhanced the end-Cretaceous atmospheric CO₂ inventory by, at most, 40%. Consequently, sulfur may have been the most important climatically active gas injected into the stratosphere. The amount of S released by the impact is several orders of magnitude higher than any known volcanic eruption and, with H₂O, is high enought to produce a sudden and significant perturbation fo Earth's climate.

COLOR FIGURES

Axially symmetric outputs from the 2D hydrocode simulations at various times after the impact. At left are velocity vectors, whose length is proportional to the velocity of the material. For reference, a vertical vector, representing a speed of 5 km/s, is plotted at right of each diagram. On right are density contours. Colors represent various materials.

(To download GIF files click on the figures)