Deep Cores of Oahu, Hawaii and Their Bearing on the 
Geologic History of the Central Pacific Basin 
Harold T. Stearns and Theodore K. Chamberlain * 1 
In the Central Pacific Basin few studies of 
the earth’s crust have been made, and those 
studies that have been undertaken have been 
mainly geophysical in nature: seismic, magnetic, 
heat flow, and gravity surveys. These geo- 
physical data usually require for their correct 
interpretation some knowledge of the geologic 
properties of the crust, especially the upper 
crust; consequently, in order to supplement 
these geophysical data and for other more 
direct reasons, e.g., stratigraphic, palaeon- 
tologic, petrologic, etc., there has been for a 
long time a desire to take actual samples of 
the Central Pacific Basin crust. To realize this 
goal H. S. Ladd, J. I. Tracey, K. O. Emery, 
and others in the last twenty years have drilled 
several deep holes on Central Pacific islands. 
Unfortunately, the drilling techniques used did 
not allow the recovery of a core sample, so that 
actual lithologic sections of the upper crust 
were not obtained. 
In October 1964 a grant was obtained from 
the National Science Foundation by the authors 
to drill a series of deep holes on the edge of 
the Ewa Coastal Plain, Oahu, Hawaii. The 
intent of this research program was to obtain 
complete sections of the upper crust utilizing 
a newly developed core barrel that allows 
nearly 100% core recovery. The Ewa Coastal 
Plain was chosen as the drilling site because it 
is the widest coastal plain in the Central Pacific 
Basin, thereby allowing the drilling to be done 
farther from the central island core than else- 
where in the Pacific. 
The results obtained by drilling the first two 
holes were very rewarding. The first hole (Ewa 
No. 1) was drilled on the 158th meridian 
200 yards inland from the beach (Fig. 2, in- 
set). The basaltic core of Oahu was penetrated 
beneath 1,072 ft of interbedded coral reefs, 
1 Hawaii Institute of Geophysics, University of 
Hawaii, Honolulu, Hawaii. Manuscript received 
I March 25, 1966. 
lagoonal muds, sands, and soils. The second 
hole (Ewa No. 2) was drilled also on the 
158th meridian about 2 miles inland from 
Ewa No. 1. In the second hole 517 ft of sedi- 
mentary rocks were penetrated before the base- 
ment basalts were encountered. More than 85% 
of the core was recovered in both holes, the 
first time in the Central Pacific Basin that such 
complete cores have been obtained from deep 
holes in the upper crust. 
Not only are the recovered cores valuable in 
deducing the geologic history of the Central 
Pacific Basin but, because of their location on 
Oahu, they allow tectonic and eustatic deduc- 
tions to be made concerning the submergence 
and emergence of the Hawaiian Archipelago. 
Furthermore, the Ewa holes are related to other 
deep drilling investigations in the Hawaiian 
area planned for the near future: 
1. It is the desire of the authors to drill 
two more deep holes offshore along the 158th 
meridian to complete the stratigraphic section 
across the Ewa Coastal Plain. These offshore 
holes will be in water about 1,800 ft deep and 
will penetrate approximately 2,000 ft of crustal 
sediments. 
2. Since the Oahu drilling was completed 
Fig. 1 . Map of Oahu showing Ewa Coastal 
Plain on the south shore of the island. 
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