Final answer:
Flooding during the Late Cretaceous period was primarily attributed to climate change caused by extensive volcanism and possibly the impact of the Yucatan asteroid.
Step-by-step explanation:
The occurrence of flooding during the Late Cretaceous period, approximately 90 million years ago, was primarily attributed to climate change. The release of volcanic gases, particularly sulphur dioxide, during extensive volcanism contributed to the climate change, which may have induced the mass extinction. The impact of the Yucatan asteroid is another possibility that coincided with the volcanic activity and contributed to flooding.