. Atoll research bulletin. Coral reefs and islands; Marine biology; Marine sciences. 11. Figure 14. SEM image showing an area of dense limestone adjacent to an area of chalky calcite. The dense limestone contains fewer tubules than the chalky limestone. Figure 15. SEM image showing a calcified root epidermis with radiating root hairs. DISCUSSION The two reef facies (Fig. 4) consisting of branching Pontes and scattered molluscs, both in a matrix of fine skeletal material in microcrystalline to submicrocrystalline calcite, are readably distinguishable despite the extensive subaerial recrystalliz
. Atoll research bulletin. Coral reefs and islands; Marine biology; Marine sciences. 11. Figure 14. SEM image showing an area of dense limestone adjacent to an area of chalky calcite. The dense limestone contains fewer tubules than the chalky limestone. Figure 15. SEM image showing a calcified root epidermis with radiating root hairs. DISCUSSION The two reef facies (Fig. 4) consisting of branching Pontes and scattered molluscs, both in a matrix of fine skeletal material in microcrystalline to submicrocrystalline calcite, are readably distinguishable despite the extensive subaerial recrystallization of this limestone. The branching Pontes facies is characteristic of lagoonal environments and is well illustrated by the extensive accumulations of branching Pontes in sandy mud and muddy sand in the Bahia Almirante off the Caribbean coast of Panama (Aronson et al. in prep). The "molluscs in muddy sand with occasional corals", particularly Manicina areolata, represent the Thalassia community that is still common to the Belize lagoons ( Macintyre et al., 2000). Thus although this Pleistocene limestone has been greatly altered and much of the original texture lost in our cores, it appears that the Holocene mangroves of Twin Cays became established on a Pleistocene substrate formed by lagoonal accumulations of branching Pontes mounds and Thalassia beds, when this substrate was flooded by the Holocene Transgression. The most striking diagenetic feature in the alteration of this Pleistocene limestone is the widespread mottled chalkification (Constanz, 1989; Fig. 7) associated with a complex tubule pattern (Fig. 12). This appears to be related to the boring activity of a terrestrial plant community. The gradual contact between dense and chalky patches, which appeared to have similar lithology and tubule borings in dense areas, indicates a post-lithification alteration by a penetrating root system that has resulted in extreme recrystallization forming porous chalky
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