wwh - Correct again - the presence of that much iridium is a sure indicator of asteroid impact. As mentioned in the previous post however, the impact was during an event of tumultuous vulcanism. The Ir rich layer occurs in the midst of a huge thickness of basalt flows, indicating it was not the cause of the vulcanism. Courtillot postulates that the material released into the atmosphere during the volcanic event exceeded that of the impact.

stales