Rapid non cyclic changes are single events such as: digging a new harbor channel and changing the water circulation patterns, or the introduction of a new species.

In general, noncylinic changes such as volcanic eruptions and earthquakes are often an irregular occurrence.

Basically, the deposition of ash from a catastrophic event (volcanic eruption) that caused a mass mortality of foraminifera.  This allows the recolonization of an opportunistic taxa group.