Estimated sedimentation rate data of atoll lagoons show that the accumulation of sand aprons is up to three times higher than lagoonal background sedimentation and therefore suited to fill lagoonal accommodation space and create “filled buckets” in small and intermediately sized platforms (up to hundreds of km 2 size), even during times of high-amplitude sea-level fluctuations of an icehouse world. Because accommodation space became limited, depositional systems of sand aprons prograded toward the lagoon. In general, Holocene sand apron formation started when marginal reefs approached relative sea level some 6–3 kyrs BP. Principal component analyses might allow the separation of Atlantic (Caribbean) from Indo-Pacific atolls, which probably arise from spatial and regional variations in sea-level history, i.e., in the Atlantic (transgressive) and Indo-Pacific region (transgressive–regressive), but more subsurface data are necessary to confirm the interpretation. It is assumed that the lack in correlation can be explained by the limited data set of 16 atolls. There is no statistically significant correlation ( r = −0.364 p = 0.165) between sand apron proportions and depth to Pleistocene surface at platform margins.
Analyses show significant correlations between sand apron proportions and both maximum lagoon depth ( r = −0.420 p = 0.000) and total platform area ( r = −0.226 p = 0.012). Sand apron proportions of 122 atolls and carbonate platforms from the Atlantic, Indian and Pacific Oceans were quantified and correlated to maximum lagoon depth, total platform area and marginal reef thickness, when available. Because data on marginal reef thickness in Holocene atolls and carbonate platforms are limited, maximum lagoon depth was also used as proxy for the depth to the underlying Pleistocene surface.
In the current model, antecedent topography, i.e., the elevation of the underlying Pleistocene karst surface and platform area are major factors controlling Holocene sand apron development.
Though there are studies focusing on sand apron sediment dynamics, the knowledge of Holocene sand apron evolution is limited, because hardly any subsurface data are available. Sand aprons are located in the back-reef area of atolls and carbonate platforms and form transport pathways of reef-derived sediment into adjacent lagoons and platform interiors.
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