Origin of atoll lagoons

A database of 301 atolls from the Pacific, Indian, and Atlantic Oceans has been analyzed with respect to factors governing max-imum atoll lagoon depth. Statistically significant correlations be-tween maximum atoll lagoon depth and both atoll area and pre-sent-day rainfall are viewed as the combined effect of paleorainfall precipitation and catchment area in contributing to overall atoll morphology. This interpretation is supported by the gross saucer-shaped mor-phology of several of the Lau group of the Fiji Islands, and the subsurface Cretaceous Golden Lane atoll of Mexico, where evi-dence of reef rim construction is lacking but evidence for signifi-cant solution relief is compelling. The contribution of reefs to atoll rim construction appears to be limited generally to;10 m, leaving more than 20 m of relief to be explained at most atolls. At a num-ber of these, the last interglacial highstand surface is;15220 m beneath Holocene rim sediments. Subsidence rates of even 5 cm/ k.y. do not suffice to explain the subsea depth of this unconformity, suggesting the dominating influence of solution on relief expression. Calculations of solution rates relative to the residence time of sea level below given depths during the past 700 k.y. suggest that the observed atoll relief is in part inherited from more than one Pleistocene, or perhaps earlier, glacial stage. Whatever the precise time of origin, the data available strongly suggest that atoll mor-phology is solution determined rather than growth predicated.