25. site survey report: kana keoki sites 3 and 4 … · 2007. 5. 17. · 25. site survey report:...

25. SITE SURVEY REPORT: KANA KEOKI SITES 3 AND 4HONOLULU TO PONAPE, 1971

R. G. Zachariadis, Hawaii Institute of Geophysics, Honolulu, Hawaii

In May 1971, the University of Hawaii R/V Kana Keokisurveyed two proposed drilling sites north of the CarolineIslands. These sites were to have been drilled on Leg 20;however, equipment problems onboard the D/S GlomarChallenger prevented the drilling. The survey reports arepresented here for possible future use.

Both sites are in sedimentary basins, site 3 beingbetween the Mapmaker and Magellan Seamount groups andSite 4 just north of the Caroline Islands group. Site 3 wouldappear to be suitable for determining the volcanic andpelagic history of the deep-sea floor of the area, as itprobably was effectively isolated from any continental landmass for a long period, if not from the time of its creation.Site 4 may show the effect of the island group in additionto the same influences affecting Site 3.

All times on the records are in GMT.Navigation was satellite-controlled and subsequently

smooth-plotted by computer. Bathymetry was digitized andcomputer-plotted, as was the magnetic field.

The generally low magnetic gradients in the survey areaprobably indicate that the underlying basement has lowrelief. The areas of most prominent magnetic relief on theeast of site 3 and south of site 4 appear to be related tobathymetric features.

The transparent-layer isopachs are obtained from the 3.5kHz records. In most cases the bottom of this layer wasdistinct, but in some places it becomes indistinct. In spiteof this occasional variability, the values at track crossingscorrespond closely. The significance of this layer is notknown.

For site 3 the reflection records generally show fourdistinct reflections at the surface of the upper transparentlayer. Upper intermediate reflector at about 0.05 sectwo-way time, lower intermediate at 0.15 sec, and abasement reflector at approximately 0.4 sec. There are veryfaint indications of a deep reflector at 0.8 to 1 sec on a fewrecords. If these indications are genuine, the section may bemore than one kilometer thick.

The standard low-frequency filter setting was 10 to 55Hz for 15 May, 1600-1800 hours and 50-100 Hz for 15

May, 1800-2400 hours; an 80 cu in. air cannon was used.On 16 May, 0100-0500 hours, a 40 cu in. air cannon wasused, and the low-frequency filter setting was 20 to 80 Hz.For the remainder of the survey the low-frequency settingwas 50 to 100 Hz, and only a sparker source was used. Ahigh-frequency filter setting of 65 to 152 Hz was employedthroughout.

The track goes directly from site 3 to site 4, crossingseveral low features between the Magellan Seamounts andnorthern extension of the Ralik Chain of islands. At 0800on 19 May, the record shows a feature remarkably similarto one seen on records obtained from the Murray FractureZone.

Site 4 reflection records vary in quality. The air cannonwas not operative for the first part of the survey, and therewas no profiler or magnetic coverage on track from 1050on 22 May until approximately 1800-1900 on 22 May (seefigures). However, records are generally good for the majorpart of the survey. Air cannon records indicate goodreflectors down to 0.7 to 0.8 sec two-way time, with tracesof a reflector at about 1.0 sec on some records. The recordsgenerally indicate that the structure is a basin and ourtracks touch the edges to the north, south, west, andpossibly east.

Where only the sparker was running, filter settings onthe low-frequency record were 70 to 100 Hz. Where the aircannon (40-cu in. chamber) was also running, settings weregenerally 30 to 80 Hz. High frequency settings were always65 to 125 Hz. Much of the noise on the records was due tosea state, which was approximately state six for the firstday and then gradually moderated.

3.5-kHz isopachs: Transparent layer isopachs are subjectto the same conditions as for site 3, but the layer isgenerally thinner. The layer appears to be softer than theunderlying materials as free-fall cores dropped in the centerof the survey area came back filled, but one core recoveredat the northern station had only about 45 cm of sediment,and another core did not return at all. The thickness wascalculated using an assumed velocity of 1500 m/sec.

487

R. G. ZACHARIADIS

150"

impfifiecf<tynonaf<ydbymetry

Figure 1. Simplified regional bathymetry, modified from Bathymetry of the North Pacific, sheets 6 and 7,T. E. Chase, H. W. Menard, and J. Mammerickx. I.M.R. Tech Report, Series TR-11.

488

SITE SURVEY REPORT: KANA KEOKI SITES 3 AND 4

iβ 3tfN

W15

woe

—i

KANA KEOKI SITE SURVEY 3

TRACK CHART

»6015

Figure 2. Site 3 - track chart.

489

R. G. ZACHARIADIS

lβ 45'N

l8*3Cf

18*15'

iβ oo'

KANA KEOKI SITE SURVEY 3

BATHYMETRY IN

CORRECTED METERS

1 7 M 5 1 9-30-E

Figure 3. Site 3 - bathymetry.

5640

-5600

-5600

160*00" 160*15' 160*30'

490

SITE SURVEY REPORT: KANA KEOKI SITES 3 AND 4

KANA KEOKI SITE SURVEY 3TRANSPARENT LAYER ISOPACHS , 0

FROM 3.5 khz. V $ E D ' 1.5 km/i c

CONTOUR INTERVAL 5 METERS

15

18*30'

18 15"

18*00

_L159 45'E lóO OO1

Figure 4. Site 3 - transparent layer isopachs.

160 15'

491

R. G. ZACHARIADIS

18 β 30*

8 β 15'

18β 00'

_

\\/

ó

KANA KEOKI SITE SURVEY 3RESIDUAL

IGR

CONTOUR

///

///

/ y'/ y×

i V

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11

i \ i*

i/

MAGNETIC ANOMALIES

F FIELD REMOVED

INTERVAL 25 GAMMAS

× \ i/ v^-75--^v /

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y j

y **"~ '—"~"

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^ -100

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159β45'

Figure 5. Site 3 — residual magnetic anomalies.

160β00 160β150 1 C•

492

SITE SURVEY REPORT: KANA KEOKI SITES 3 AND 4

KANA KEOKI SITE SURVEY 4

TRACK CHART

9 35N

9*20

9*05

15JH01

Figure 6. Site 4 - track chart.

158*40' 158*55

493

R. G. ZACHARIADIS

9*4N

KANA KEOKI SITE SURVEY 4

BATHYMETRY IN

CORRECTED METERS

9 X!

9*15

9 oσ

β'451

5300

* % ^3>

V15^00'E 158*15"

Figure 7. Site 4 - bathymetry.

158*30' 158*45' 159*00' 159*15'

494

SITE SURVEY REPORT: KANA KEOKI SITES 3 AND 4

1

KANA KEOKI SITE SURVEY 4

TRANSPARENT LAYER ISOPACHS

FROM 3.5Wu V^> 1.5 km/> c

5METER CONTOUR INTERVAL C ~ "

./

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V

— 1

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×-

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Figure 8. Site 4 — transparent layer isopachs.

15T401

495

R. G. ZACHARIADIS

9*45"

9 30'

9*15'

9*00'

-

-

-

-125 --100-

-50 -

1 1KANA KEOKI SITE SURVEY

RESIDUAL MAGNETIC ANOMALIES

IGRP FIELD REMOVED

CONTOUR INTERVAL 25 GAMMAS

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158*15' 158*30*

Figure 9. SzYe ̂ - residual magnetic anomalies.

158*45* 159 00

496

SITE 3

END OF SITE 3 AND START OF TRACK TO SITE 4

TRACK BETWEEN SITE 3 AND SITE 4

TRACK BETWEEN SITE 3 AND SITE 4

TRACK BETWEEN SITE 3 AND SITE 4

END OF TRACK TO SITE 4 AND START OF SITE 4

SITE 4