. Atoll research bulletin. Coral reefs and islands; Marine biology; Marine sciences. limestone surface substrate when we hit hard rock at the base of our probes. These probes confirm the hypothesis that the Pleistocene karst relief is controlling the honeycomb patterns of reef-ridge growth in the Pelican Cays, which commonly results in the formation of ponded areas. The short cores suggest that Acropora cervicornis colonized the areas of slightly elevated relief on the Pleistocene limestone surface when it was flooded by the rising seas of the Holocene Transgression. Differential growth of thi
. Atoll research bulletin. Coral reefs and islands; Marine biology; Marine sciences. limestone surface substrate when we hit hard rock at the base of our probes. These probes confirm the hypothesis that the Pleistocene karst relief is controlling the honeycomb patterns of reef-ridge growth in the Pelican Cays, which commonly results in the formation of ponded areas. The short cores suggest that Acropora cervicornis colonized the areas of slightly elevated relief on the Pleistocene limestone surface when it was flooded by the rising seas of the Holocene Transgression. Differential growth of this fast-growing branching coral community, reported to be accumulating in this area at a rate of up to 8 m/1,000 yrs by Westphall (1986), then formed steep-sided ridges, which on catching up with sea level in some areas, were overgrown by mangrove communities. Although the ponded network pattern of reef ridges is related to polygonal karst relief on a Pleistocene limestone substrate, their relief is mainly the result of differential reef accumulation (Fig. 5). The origin and growth of these Holocene lagoon reefs is therefore related to a combination of karst control (Purdy, 1974a; 1974b) and differential reef growth (Halley et al., 1977). This honeycomb pattern is superimposed on a larger rhombohedral configuration of the shelf atolls, including the one on which the Pelican cays are located (Fig. 1). The parallelism of these rhomboidal atolls suggests that pre-Holocene reef accumulation occurred along the edges of fault blocks (Purdy, 1974a, 1974b; Precht, 1997). The cores from inside Pond C show a distinct transition from a predominantly Acropora cervicornis facies to a predominantly Porites divaricata facies, dating to probably about 500 yrs This facies change documents a shallowing-upward reef sequence similar to that reported in this area by Westphall (1986), where a "catch-up" reef community is being replaced by a very shallow "keep-up" community (N
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