Geochemical, stratigraphic and palaeolatitudinal data from deep boreholes drilled through Pacific guyots-flat-topped seamounts-help to explain the drowning of these Cretaceous shallow-water carbonate platforms that once thrived through the accumulation of biogenic and inorganic calcium carbonate sediment in mind-oceanic regions. The platforms drowned sequentially over a 60-million-year interval while they were being transported northward by Pacific plate motion through a narrow equatorial zone (similar to 0-10 degrees S). Such platforms were apparently resistant to the effects of Cretaceous oceanic anoxic events. Although the mechanism responsible for drowning remains unknown, the tropics have not always been the refuge for atolls that they are today.