Origin of atoll lagoons

A database of 301 atolls from the Pacific, Indian, and Atlantic Oceans has been analyzed with respect to factors governing maximum atoll lagoon depth. Statistically significant correlations between maximum atoll lagoon depth and both atoll area and present-day rainfall are viewed as the combined eff ect of paleorainfall precipitation and catchment area in contributing to ov erall atoll morphology. This interpretation is supported by the gross saucer-shaped morphology of s everal of the Lau group of the Fiji Islands, and the subsurface Cretaceous Golden Lane atoll of Mexico, where evidence of reef rim construction is lac king but evidence for significant solution relief is compelling. The contri bution of reefs to atoll rim construction appears to be limited generally t o similar to 10 m, leaving more than 20 m of relief to be explained at most atolls, At a number of these, the last interglacial highstand surface is s imilar to 15--20 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. Calc ulations of solution rates relative to the residence time of sea level belo w given depths during the past 700 k.y. suggest that the observed atoll rel ief is in part inherited from more than one Pleistocene, or perhaps earlier , glacial stage. Whatever the precise time of origin, the data available st rongly suggest that atoll morphology is solution determined rather than gro wth predicated.