. Advances in marine biology: volume 17. Coral fisheries. 254 L. HILLIS-COLINVAUX tEEF INFtUENCE - FUNAFUTI ATOll (BAT* FKOM HINOC, KOYAL SOCIgTr, 1304) n/N«rvri isijino LAGOON eoniNC- - Approilmotaly Vrt miln - ; Oeetmbtr, 1957 100 120' 140' 160' 180' 200' 220' 240' IS I ; 'Slight percentage" .?^ S. 20% Corolt S0% Unconiolldoted skeletal debris .lOpHflMg ^^BS^ IwfSSS SAMPLC 200 220 f, y 240 '"•^"^Flnt Calcite-cemented k^l skeletal debris Practically all orogonite gone First coral costs and moulds , Calcite - cemented skeletal debris, Corals rore Fig. 82. Cross-sectio
. Advances in marine biology: volume 17. Coral fisheries. 254 L. HILLIS-COLINVAUX tEEF INFtUENCE - FUNAFUTI ATOll (BAT* FKOM HINOC, KOYAL SOCIgTr, 1304) n/N«rvri isijino LAGOON eoniNC- - Approilmotaly Vrt miln - ; Oeetmbtr, 1957 100 120' 140' 160' 180' 200' 220' 240' IS I ; 'Slight percentage" .?^ S. 20% Corolt S0% Unconiolldoted skeletal debris .lOpHflMg ^^BS^ IwfSSS SAMPLC 200 220 f, y 240 '"•^"^Flnt Calcite-cemented k^l skeletal debris Practically all orogonite gone First coral costs and moulds , Calcite - cemented skeletal debris, Corals rore Fig. 82. Cross-section of Funafuti Atoll, Ellice Islands, showing some of the results of the cores raised by the Coral Reef Committee of the Royal Society (1904). Halimeda segments were the chief constituent for the first 60 feet below the lagoon floor. They also were the predominant component of the main boring between 652-660 feet, but this depth is not included. (From Ginsburg et al. (1963), original data from Judd (1904) and Hinde (1904); reproduced with permission.) extends the data to various forms of peripheral reef, where Halimeda segments can collect in channels, lagoons and behind sills. At Funafuti the Halimeda-rich stratum of unconsolidated sediment ended with an unconformity which was almost certainly the subaerial exposure surface which had been weathered during the last eustatic lowering of sea-level. In the lower parts of this boring, under the uncon- formity, only one-third of the recognizable parts were Halimeda, the other two-thirds being foraminiferans (Fig. 82). If we accept the Funafuti, Bikini and Enewetak results as correct in suggesting that lagoonal accretions of sediment are likely to be very largely Halimeda segments, then it is reasonable to postulate that the ultimate origin of the mass of an atoll depends on the relative rates of accretion on the lagoon floor and along the reef ridges. We may write: A^={H,L + E,R^)t where A^ is the atoll mass, ^g is the deposition
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