 Like other sequences, the Zuñi was probably caused by a mantle plume - more specifically, the "Mid-Cretaceous Superplume" event.A mass of unusually hot rock rose from the lower mantle to the base of the lithosphere, fueling a dramatic increase in seafloor spreading rates; this caused the hotter mid-ocean ridges to increase in volume, thus displacing the oceans onto the continents.Sea level rose in earnest beginning in the early Cretaceous, until by Cenomanian time it was roughly 250 metres (800+ feet) higher than today.