The windward perimeter reef shows distinct ecological
and geological zones both at Enewetak and most of the
remaining Marshall Islands (see “Bikini Atoll, Marshall
Islands”). From offshore toward the lagoon, these zones
include the following:
Deep fore reef
Fore reef terrace
Spurs and grooves
Coralline algal reef flat and ridge
Room and pillar caverns (galleries)
Micro-atolls (Porites, Heliopora)
Moated reef flat
Lagoon back reef and
Lagoon floor
The windward reef flat also shows evidence of a higher
(>1 m) sea-level stand between 2,200 and 4,000 years
ago. The zonation along leeward (southwestern) perimeter
reefs shows variable features including
Shallow passes
Sand flats
0
0
500
1,000
1,500
500
1,000
1,500
2,000
2,500
3,000
3,500
4,000
4,500
Total depth 4,620 ft
Total depth 4,222 ft
Total depth 2,556 ft
a
Reef wall
Lagoon and undifferentiated
shallow-water deposits
Open shoal
Core
Unconformity
Numbers 1–15 along drill hole F-1, and 1–3 along
drill hole E-1 indicate cored intervate
No samples recovered
Forereef, outer slope
b
c
d
Explanation
11
10
9
8
7
6 Reef debris abundant
Coral-mollusk-rich zone
top of tertiary b
Lithophyllum-rich zone
Lithophyllum-rich zone
b and d
b and c
c and d
b and c
2A–B
P e n e r o p li s tr il o c u li n a z o n e
O r m a te r o m o li n a z o n e
A s te r ig e r in a z o n e
5
4
3
2
1
Coral-molluskrich zone
Coral-molluskrich zone
Top of tertiary p
Top of tertiary e
Coral-molluskrich zone
To p : L ith o p hy llu m kl a d o su m zo n e
B o tt o m : L it h o p h y ll u m k la d o s u m z o n e
F–1
ENEWETAK
BIKINI
Depth, in feet
Depth in meters
E–1
a and b
12
13
14
15
3
2
1
Pentemic foraminitera with reef debris
from up-stope shallow-water areas
Enewetak Atoll, Marshall Islands, Figure 1 Comparative analysis of drill cores collected at Bikini and Enewetak Atolls, Marshall
Islands (Schlanger, 1963 in Ristvet, 1987).
ENEWETAK ATOLL, MARSHALL ISLANDS
381