Contradicting Barrier Reef relationships for Darwin’s Evolution of reef types

Abstract

The Darwinian progressive subsidence model for the evolution of fringing reefs, barrier reefs and atolls has been generally accepted following the indisputable proof of subsidence provided by drilling results in the Pacific. Nonetheless, there are data that do not fit the expectations of the model, such as the similar lagoon depths of barrier reefs and atolls as opposed to the subsidence theory's implicit prediction that atolls should have significantly greater depths. In contrast, a great deal of evidence supports the influence of meteoric solution on barrier reef morphology. For example, the maximum lagoon depth of 56 modern barrier reefs is statistically correlated with the lagoon catchment area for modern annual rainfall. These modern rainfall patterns would seem to be a reasonable proxy for relative geographic differences in glacial lowstand rainfall, even though the absolute amounts of such rainfall are unknown. The correlation therefore suggests the importance of Pleistocene subaerial solution in contributing to barrier reef morphology. Further support for antecedent influence occurs in the form of barrier reef passes in which the depth of the reef pass is correlated with onshore drainage volumes. On a larger scale, the Cook Island of Mangaia provides evidence that solution can produce barrier reef morphology independent of reef development. In contrast, there are no examples of the subsidence-predicted lagoon transition of fringing reefs to barrier reefs to atolls. Moreover, the common occurrence of fringing reefs within barrier reefs negates subsidence as a causal factor in their 'presumed progressive evolutionary development. Consequently, the evidence to date suggests that a solution morphology template has been accentuated by reef construction to produce the diagnostic barrier reef morphology we see today. The importance of subsidence would seem to be in accounting for the overall thickness of the resulting carbonate caps of oceanic examples and in contributing to lagoon depth variation among the larger continental entities.

Holocene and Pleistocene fringing reef growth and the role of accommodation space and exposure to waves and currents (Bora Bora, Society Islands, French Polynesia)

“…This study and preceding drill projects on Bora Bora (Gischler et al ., ; Isaack et al ., ) have shown that Holocene fringing and barrier reefs developed contemporaneously in the same reef system. Comparable results were obtained elsewhere, for example, in the Mayotte (Zinke et al ., ), Chuuk (Truk) and the New Caledonian barrier reef systems (Purdy & Winterer, , and references therein). It is noteworthy in this context that the fringing reef of Bora Bora apparently developed in water depths somewhat shallower as compared to the nearby barrier reef during ca 9 to 5 kyr bp .…”

Morphometric patterns in Modern carbonate platforms can be applied to the ancient rock record: Similarities between Modern Alacranes Reef and Upper Palaeozoic platforms of the Barents Sea

“…Indeed, it has been demonstrated repeatedly on both regional and local scales that Pleistocene karst relief provided antecedent topography for Holocene reef formation (e.g., Purdy, 1974ab;Halley et al, 1977;Shinn et al, 1977;Shinn, 1980;Purdy and Winterer, 2006;Hudson, 1998, 2004). More recent treatment of the patterns of reticulate ridges of reefs and sediment in Holocene lagoons has suggested biotic self-organization (Blakeway, 2000;Schlager and Purkis, 2014;Blakeway and Hamblin, 2014), though they may develop also as emergent patterns by interaction of air or water with loose sediment (Paola et al 2009 (Blakeway, 2000;Schlager and Purkis, 2014;Blakeway and Hamblin, 2014).…”

Seismic evidence of glacial-age river incision into the Tahaa barrier reef, French Polynesia

“…Each is discussed in more detail below. Spatial differences in upland drainage size, like those noted for Tahiti (Purdy and Winterer, 2006), are also thought to impact lagoon incision during lowstands; however, western Tahaa catchments are, in general, relatively similar in size to each other.…”

“…Backfilling at deltas and deep passes, likely carved by rivers during sea-level lowstands (Fig. 1), are perhaps the most pervasive imprints of fluvial deposition and erosion on reefs, though some have argued that barrier reef morphology itself may be intimately linked to terrestrial drainage networks (Purdy and Winterer, 2006). Makatea islands, which are similar in appearance to uplifted barrier reefs, have been proposed to be modern analogs for how fluvial incision can transform a fringing-reef-bound island into a barrier reef.…”