Deep Cores of Oahu — Stearns and Chamberlain 
157 
Oahu, opposite Ewa Beach Park. The terrace 
at this locality was a flat, low, emerged coral 
reef of undetermined age, partially covered 
with a thin discontinuous soil layer. The ground 
level is -}- 6.1 ft above mean sea level; all 
depths in the core are measured from ground 
level equaling zero. 
Ewa No. 2 (Table 2) 
The second hole on the Ewa Coastal Plain 
was also located on the 158th meridian but 
2 miles inland from Ewa No. 1. The exact 
locality was within the confines of the West 
Loch of Pearl Harbor Naval Base, at a point a 
few hundred yards south of the West Loch 
shoreline. The ground level at the hole is 
19.7 ft above mean sea level; all depths in the 
core are measured from ground level equaling 
zero. 
PRELIMINARY SEISMIC DATA 
On July 13 and 14, 1965 seismic refraction 
studies were made of the ocean bottom to the 
south of drilling site Ewa No. 1. The following 
results were obtained at a distance of 8.4 km 
seaward from the coast along the 158th merid- 
ian (21°15'N, 158°00'W): (1) water depth 
— 0.36 km; (2) depth from sea surface to 
the upper surface of the basalt basement — 1.1 
km; (3) sound velocity in the sedimentary 
section = 2.8 km/second. 
These data show the sedimentary column to 
be 2,920 ft in thickness at a distance of 4.6 
miles offshore from Ewa No. 1 in a water depth 
of 1,182 ft. The sediment-basalt interface was 
found to be essentially parallel to the sea water- 
sediment interface. 
PRELIMINARY GEOLOGIC HISTORY OF THE EWA 
COASTAL PLAIN 
The following description applies to the 
outer edge of the Ewa Plain in the vicinity of 
Ewa No. 1 : 
1. Prolonged weathering and erosion of the 
upper surface of the Koolau basalts. Formation 
of thick soil deposits, deep incision of stream 
valleys, and deposition of stream cobbles, peb- 
bles, and basaltic sand along the coast. 
2. Gradual submergence. 
3. Accumulation of thick deposits of shallow 
marine lagoonal sediments behind a barrier 
reef. Stream-transported muds and silts pre- 
dominate, with occasional layers of basaltic 
sand and gravel. Inorganically precipitated 
CaC0 3 common to these sediments indicates a 
restricted oceanic circulation. Much of the 
mud is high in organic carbon, indicating 
swamp conditions. Typical lagoonal-deltaic 
sedimentary facies. 
4. With continued submergence, the water 
deepened sufficiently to allow the lagoonal 
deposits to be superseded by calcareous muds 
and coral debris. These sediments indicate the 
barrier reef structure was in close proximity. 
The upper portion of this section grades into 
a hard reef limestone horizon at — 786 ft msl 
in the core. 
5. Following the growth of these corals the 
progradation of the land was sufficient to shift 
the coral reef facies seaward, allowing at first 
the accumulation of gray calcareous mud and 
coral debris, and finally, the progradation of 
the land was sufficient to bring basaltic river 
sands and silts and dark-gray to black organic 
muds into the area. The environment again 
became swampy-lagoonal and eventually peat 
deposits accumulated, now represented by the 
lignite and soils found at — 624 ft msl. At 
this depth a major unconformity occurs which 
probably marks the Pleistocene-Pliocene boun- 
dary. 
6. Following the deposition of the lignite 
beds the sea level rose, allowing the coral facies 
to shift landward. At first calcareous muds 
containing coral debris accumulated, but these 
were followed by the growth of marine coral- 
line reefs more than 50 ft in thickness. 
7. On top of this reef is found at first cal- 
careous mud followed by brown mud and sands 
and soils, indicating a progradation of the 
lagoonal facies. At — 406 ft msl a minor 
unconformity occurs and continues upward 
through brown muds and basaltic sands and 
soils to a major unconformity at — 358 ft msl 
that most likely corresponds to the Kahipa- 
Mamala submarine shelf around Oahu (Stearns, 
1966 ). 
8. Subsequent to the development of this 
