26
majority of the fine sedimentary deposits in this (or any other) part of the
Tanoon (Erery et al., op. cit. p. VI, VIT, 25, 30, 31).
In additicn, seci-
ments near the beach area are eroded and broken by wave action and reductions
in the size of sedimentary material throughout the lagoon arise from the action
of boring organisms.
The abundance of fine debris reaches a maximum of 50%
to 75% several miles off shore.
In general, this band of fine sediments is
widest on the south, west, and northwest half of the atoll's inner perimeter
and is nearly absent from the northeast and eastern regions, except off Bikini
Island (Emery et al.,op. cit. p. 58).
Fine debris comprise less than 10% of
the components of samples in the central region of the lagoon (Emery et al.,
op. cit. p. 58, 62).
With the exception of the deepest regions of the lagoon (Halimeda growth
is limited bv decreasing sunliaht helow about 55 m), Halimeda comprises the
vast renainder of lagoon sediments.
Below the 55 meter zone, remains of some
E> species of benthonic and pelagic foraminifera make up the major proportion
cf tre sediments, although they are present in lesser proportions throughout
tte Tacoon sediments (Emery et al., op. cit., p. 57,62). In a thesis on
the
'#5959 sediments of Rongelap Atoll, Anikouchine (op. cit.) concluded that
vetriy all sediments are produced within the atoll and that no [natural]
sedimrrsery ratertal leaves the lagoon basin after deposition.
{rery et al. (op. cit.) made a limited mechanical particle size analysis
22°" Steves) of a few samples obtained by coring off Bikini Island.
“s*ecactine (op. cit.) performed a more complete particle size
analysis on
" 77 sediment cores from Rongelap Atoll. The distribution of mean grain
fee mite derth in cores and in beach sediments obtained by Anikouchine
are
Veewe te Fig. 6.
- lene
The "average" sediment (curve 3) is seen to have nearly a
'
cistrib
ution of sizes.
i
Forty-one sediments collected by coring
were