Paleomagnetic stratigraphy, rates of deposition and tephrachronology in North Pacific deep-sea sediments

EARTH AND PLANETARY SCIENCE LETTERS 1 (1966) 476-492.

NORTH-HOLLAND PUBL. COMP., AMSTERDAM

PALEOMAGNETIC STRATIGRAPHY, RATES OF DEPOSITION AND TEPHRACHRONOLOGY IN N O R T H PACIFIC DEEP-SEA S E D I M E N T S * D r a g o s l a v NINKOVICH, N e l l O P D Y K E , B r u c e C. H E E Z E N a n d J o h n H. F O S T E R

Lamont Geological Observatory of Columbia University, Palisades, N. Y., USA Received 2 November 1966

The paleomagnetic stratigraphy of 12 North Pacific d e e p - s e a sediment c o r e s has been investigated and has been used to date volcanic eruptions and to determine r a t e s of deposition of pelagic sediments. Only four of the c o r e s penetrated s e d i m e n t s deposited before the last r e v e r s a l of the e a r t h ' s magnetic field (0.7 m.y.). Of these, one penetrated to the Gauss s e r i e s , two to sediments deposited during the Olduvai event and one penetrated to the middle of the Matuyama s e r i e s . Eight other c o r e s , 10-16 m e t e r s long, taken within 1000 km of the Japan-Kuril-Kamtchatka arc failed to reach the Matuyama s e r i e s . The rate of deposition in North Pacific pelagic s e d i m e n t s vary from > 2 cm/1000 y in the a r e a east of the Asiatic continent to < 0.8 cm/1000 y in the mid Pacific. Assuming continuous deposition, the length of the J a r a m i l l o event can be established as 50 000 y and the Olduvai event as 14 000 y. The apparent length of time during which the dipole field of the earth was reduced during r e v e r s a l s of the e a r t h ' s magnetic field is approximately 20 000 y. In one of the c o r e s the top of the Olduvai event is split. This may r e p r e s e n t the Gilsa event. The brown volcanic ash p r e s e n t in three of the c o r e s apparently originated in an eruption 1.2 m.y. ago in the Aleutian Arc near the Andreanof Islands.

1. ~ T R O D U C T I O N T h e e s t a b l i s h m e n t of a p a l e o m a g n e t i c p o l a r ity r e v e r s a l s t r a t i g r a p h y p r o v i d e s a n e w a n d a c c u r a t e m e t h o d of d e t e r m i n i n g r a t e s of d e p o s i t i o n , a n d of d a t i n g e v e n t s r e c o r d e d in d e e p sea cores. T h e d i p o l e c o m p o n e n t of t h e e a r t h ' s m a g netic field has reversed polarity several times o v e r the p a s t f e w m i l l i o n y e a r s . P a l e o m a g n e t i c s t u d i e s of r a d i o m e t r i c a l l y d a t e d s u b - a e r i a l l a va flows have e s t a b l i s h e d that m a j o r s e m i - p e r manent reversals of p o l a r i t y t o o k p l a c e 0.7, 2.4, a n d 3.5 m . y . ago. T e m p o r a r y r e v e r s a l s of s h o r t d u r a t i o n , c a l l e d e v e n t s , t o o k p l a c e 0.9, 1.9 a n d 3 m . y . a g o ( t a b l e 1 ) [ 1 , 2 ] . A f e w p a l e o m a g n e t i c s t u d i e s h a v e b e e n m a d e on d e e p - s e a c o r e s , and the l a s t m a j o r r e v e r s a l was r e c o g n i z e d in c o r e s f r o m t h e e q u a t o r i a l P a c i f i c b y H a r r i s o n a n d F u n n e l l [3] a n d F u l l e r e t al. [4]. The l a s t r e v e r s a l was found to c o r r e l a t e with a faunal boundary. In t h e f i r s t p a l e o m a g n e t i c s t u d y of d e e p - s e a s e d i m e n t c o r e s at the L a m o n t Geological Obs e r v a t o r y , O p d y k e e t al. [5] e s t a b l i s h e d a p a l e o m a g n e t i c s t r a t i g r a p h y on t h e b a s i s of s e v e n * Lamont Geological Observatory Contribution.

Table 1 K/A age of geomagnetic polarity epochs, m e a s u r e d on rocks f r o m land (after r e f s . [1,2]). Epoch

Event

Age (m.y.) 0.0

Brunhes Normal 0.70 0.71

Jaramillo

0.89

Olduvai

1.9

Matuyama Reversed 2.4±0.1 2,4±0.1 Gauss

Normal 3.35±0.1

A n t a r c t i c c o r e s , which c o r r e l a t e s well with the stratigraphic boundaries previously established b y H a y s [6] on t h e b a s i s of t h e r a d i o l a r i a . T h e b e g i n n i n g of P l e i s t o c e n e g l a c i a t i o n in t h e A n t a r c t i c , i n f e r r e d by C o n o l l y a n d E w i n g [7] on t h e b a s i s of t h e f i r s t a p p e a r a n c e of i c e - r a f t e r m a t e -

90-

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D. NINKOVICH et al. Table 2 L i s t of p i s t o n c o r e s s t u d i e d . Core

107 108 109 119 120 121 122 123 124 125 126 127 128 129 130 131

Long.

Lat. N

43024 ' 45027 ' 47019 ~ 47057 ' 47024 ' 46o58 , 46034 ~ 46o15 T 45050 ' 43o29 , 42o00 ' 40o17 ' 38o47 ' 37o41 ' 36o59 ' 36020 '

Length (era)

178052 ' W 179°14.5'W 179039 ' W 168047 ' E 167045 ' E 164o16 ' E 161°41 ' E 157°55 ' E 154030 ' E 154022 ' E 155052 ' E 156055 ' E 157024 ' E 156035 ' E 152036 ' E 151000 ' E

Depth (m)

1282 1671 1452 1170 1632 1604 1575 1360 854 948 1050 1150 1063 1277 1039 1034

r i a l , w a s p l a c e d b y O p d y k e a n d o t h e r s [5] a t about 2.5 m.y.B.P. The present paper represents a paleomagnetic s t u d y o f L a m o n t G e o l o g i c a l O b s e r v a t o r y cores from the North Pacific starting 20 degrees further north than the red clay core done by Dickson and Foster [17] (fig. 1, t a b l e 2). S a m p l e s approximately 8 c m 3 i n s i z e w e r e c u t a t 10 c m

Earliest Paleomag~etic epoch o r e v e n t penetrated

5872 5625 5629 2739 6216 5859 5563 4903 5534 5545 5515 5583 5612 5766

Olduvai Matuyama Gauss Olduvai Brunhes Brunhes Brunhes Brunhes

5858

Brunhes

N u m b e r of volcanic ash layers colorless

brown 1 1 1

4 6 7 6 10

Brunhes Brunhes Brunhes

to 2 0 c m i n t e r v a l s throughout the length of each core. In intervals where reversals occurred, samples were taken every 2 cm. The specimens were measured on a 5 cps spinner magnetometer [18]. A l l s p e c i m e n s were partially demagnetized i n a n a l t e r n a t i n g f i e l d of 1 5 0 o e r s t e d i n o r d e r t o remove unstable components. Layers of correlative volcanic ash, abundant in the North Pacific

KM$

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V20-110 ! ALEUTIAN V20-106

1

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V20"108

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Fig. 2. T o p o g r a p h i c p r o f i l e a l o n g 1 7 9 o w s h o w i n g l o c a t i o n of p i s t o n c o r e s .

J

52" N~

NORTH PACIFIC DEEP-SEA SEDIMENTS

479

107

109

Fig. 3. Photograph of brown ash in cores V20-107, 108 and 109. c o r e s , c o n f i r m the s t r a t i g r a p h y obtained on the b a s i s of p a l e o m a g n e t i c data. A p r e l i m i n a r y a n a l y s i s was made of eight 10 m e t e r to 16 m e t e r long c o r e s taken within 1000 km of the J a p a n - K u r i l - K a m t c h a t k a A r c (V20 -120, 1 2 1 , 1 2 2 , 1 2 3 , 1 2 6 , 1 2 7 , 1 2 9 , and 131; fig. 1). All failed to p e n e t r a t e to the 0.7 m.y. r e v e r s a l . S e d i m e n t a t i o n r a t e s of the s i l i c i o u s brown lutite in the a r e a m u s t t h e r e f o r e e x c e e d 2 c m / 1 0 0 0 y. T h e s e c o r e s , as well as four o t h e r s (V20-124, 125, 128, and 130) not m a g n e t i c a l l y analyzed, contain 3 to 10 l a y e r s of c o l o r l e s s v o l c a n i c ash 1 c m to 20 cm thick. One c o r e (V20-119, fig. 1 and 5, table 2), taken on the flank of one of the E m p e r o r Seamounts, p e n e t r a t e s the 1.9 m.y. g e o m a g n e t i c event (Olduvai). The c o r e contains d i a t o m s throughout and f o r a m i n i f e r a a r e abundant in the l o w e r half of the c o r e . C o l o r l e s s ash beds ( a p p r o x i m a t e l y 2 c m thick) a r e p r e s e n t at

140 c m and 224 c m within s e d i m e n t s of the B r u n h e s n o r m a l p o l a r i t y s e r i e s . The f i r s t r e v e r s a l (0.7 m.y.) is r e a c h e d at 640 cm. One c o l o r l e s s ash bed at 745 c m is found in s e d i m e n t s d e p o s i t e d during the J a r a m i l l o event (0.9 m.y.), and a fourth bed at 778 c m was d e p o s i t e d during the M a t u y a m a r e v e r s e d epoch. S e d i m e n t s b e tween 1100 c m and the bottom of the c o r e at 1170 c m a r e of r e v e r s e d p o l a r i t y , r e p r e s e n t i n g deposition during the Olduvai event *. C o r e s V20-102 to 110 w e r e taken in the open ocean between the Aleutian T r e n c h and Midway Island (fig. 1 and 2). A d i s t i n c t l a y e r of brown v o l c a n i c ash is p r e s e n t in C o r e s V20-107, 108 * The indices of refraction (n) for the layers are as follows: 138-140 c r n - - n 1.500-1.502; 222-224 e m - n 1.518-1.520; 749-751 c m - - n 1.514-1.516; 777-780 c m - - 1.508-1.510.

480

D. NINKOVICH et al. •

V

COLOR

Grayish Brown 5 YR 512

qEFRACTIVE

1.576

V V Pale • Mg.der at e Yel Iowi sh urown Dark Yellowish Brown Brown 5 YR 514 I0 YR 4 / 2 I0 YR 61Z 1.572

1.560

1.554

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AMPERES Fig. 4. Cumulative separation curves for volcanic glass fractions separated with Frantz isodynamic separator.

and 109 (fig. 3), and is c o r r e l a t e d on the b a s i s of m i n e r a l o g y . All t h r e e c o r e s a r e c o m p o s e d of light b ro wn lutite with s c a t t e r e d d i a t o m s and r a d i o l a r i a , q u a r t z , f r a g m e n t s of r o c k s , and v o l canic g l a s s s h a r d s . E x c e p t f o r the ash beds, the c o r e s a r e u n s t r a t i f i e d and of u n i f o r m c o l o r and a p p e a r to have o r i g i n a t e d f r o m continuous deposition. Only about 5 c m to 15 cm of s e d i m e n t just above the l a y e r of v o l c a n i c ash a r e of a m o r e i n t e n s e brown c o l o r , due to a d i s p e r s a l of fine v o l canic as h p a r t i c l e s (fig. 3). In c o r e s V20-107, 198, and 109, the l a y e r of v o l c a n i c ash is b ro w n (fig. 3), and is much f i n e r in t e x t u r e than the ash l a y e r s in c o r e 119. The s a m p l e s , even those taken f r o m the bottom of the ash l a y e r in c o r e s 107, 108, and 109, show that about 99% of the p a r t i c l e s a r e l e s s than 0.088

m m in s i z e * . Under the m i c r o s c o p e the ash ap p e a r s as p u r e v o l c a n i c g l a s s , r a n g i n g f r o m light brown to d a r k brown, with an index of r e f r a c t i o n of 1.510-1.576. F u r t h e r a n a l y s i s of the brown ash was made with the F r a n t z i s o d y n a m i c s e p a r a t o r (side tilt = 15o, f o r w a r d tilt = 250). The c u m u l a t i v e s e p a r a t i o n c u r v e s (fig. 4) a r e n e a r l y i d e n t i c a l f o r all t h r e e s a m p l e s of brown ash f r o m c o r e s V20-107, 108, and 109. The c o l o r and r e f r a c t i v e index of the v o l c a n i c g l a s s s e p a r a t e d at a given a m p e r a g e a r e i d e n t i c a l f o r each core.

$ The methods used for the study of the volcanic ash have previously been described [12, 13].

NORTH PACIFIC DEEP-SEA SEDIMENTS 2. PALEOMAGNETIC STRATIGRAPHY Since the megascopic e x a m i n a t i o n of the t h r e e m i d - o c e a n c o r e s s u g g e s t s unchanged conditions of s e d i m e n t a t i o n , it can be a s s u m e d that the %2OG~ %~1%~ O

~

V20 ~1.

481

s t r a t i g r a p h y obtained f r o m magnetic data r e p r e s e n t s a chronological s u c c e s s i o n of geomagnetic epochs and events. This is i l l u s t r a t e d in fig. 5. Thus the bottom of core 109 r e a c h e d the upper p a r t of the Gauss s e r i e s ; the bottom of core 107 V20107 ~,.

V20 108 mm.o

V20 119 mm:

o

200

300

400 ¢~RAM/I:/:O

~00 600

700 0

i

~00 ~ ~00 O£DUVA/

~000

2.0

~00 ~200

$

3.0

I

SAMPLES ~

NORMAL

POSITIVE o NEGATIVE

REVERSED

~40G

XEO0

•

~6OO

~700

Fig. 5. Graphic magnetic polarity logs for North Pacific deep-sea cores showing location of volcanic ash beds.

482

D. NINKOVICH et al.

r e a c h e d the Olduvai event; and c o r e 108 p e n e t r a t e d the M a t u y a m a s e r i e s , but did not r e a c h Olduvai. T h e l a y e r of v o l c a n i c ash was d e p o s i t e d in the M a t u y a m a epoch, b e tw e e n the Olduvai and J a r a m i l l o e v e n t s , in a ll t h r e e c o r e s . T h e bottom of c o r e V20-119 p e n e t r a t e d the Olduvai event.

3. MAGNETIC INCLINATION The m a g n e t i c i n c l in a t io n in c o r e s V20-107, 108, and 109 (figs. 6, 7 and 8) v a r i e s v e r y l i t t l e f r o m one s a m p l e to a n o t h e r ; and the m e a n in clination r e m a i n s p r a c t i c a l l y constant to the bottom of the c o r e s , s u g g e s t i n g that t h e r e have been

no si g n i f i can t changes in position of the e a r t h ' s m a g n e t i c p o l e s f o r the l a s t t h r e e m i l l i o n y e a r s . A few e x c e p t i o n s have been detected. At 8 m in c o r e V20-107 and in the u p p er t h r e e m e t e r s of c o r e V20-108, a n o m a l o u s ch an g es in m a g n e t i c inclination o c c u r which r e s e m b l e s h o r t events. Since they cannot be c o r r e l a t e d f r o m c o r e to c o r e , they p r o b a b l y r e f l e c t d i s t u r b a n c e s which o r i g i n a t e d during c o r i n g o p e r a t i o n s . Th e a v e r a g e i n cl i n at i o n s, i r r e s p e c t i v e of sign, a r e 600 f o r c o r e V20-107; 660 f o r c o r e 108 (below 3 m); and 62o f o r c o r e 109. The p r e s e n t i n cl i n at i o n of the m a g n e t i c f i el d in the a r e a w h e r e the t h r e e North P a c i f i c c o r e s w e r e taken is about 57.5o. Since the i n cl i n at i o n

150 O E R S T E D CMS O

/NCLINA T/ON IN DEGREES

-80-60-40

"20

0

/NTENS/TY E M U / ~ f X IO -s

20 4 0 6 0 6 0

0

I

2

3

4

5

6

7

8

~

!00

200

300

400

600

600

700 800

900

VOLCANICI mASH

1000

llO0 1200

1300

Fig. 6. Magnetic inclination and intensity log of Core V20-107.

9

NORTH PACIFIC DEEP-SEA SEDIMENTS

483

150 O E R S T E D CMS

INCLINA T/ON

-80-60-40-20

0

IN DEGREES

INTENSI TY EMU/gr

20 4 0 6 0 80

0

I

2

.3

4

5

X IO - ~

6

7

8

lO0

400

500

600

700

800

900

--%

1000

1100

1200

1300

VOLCANIC"

-'AS

1400 b

150o

1600

1700

Fig. 7. Magnetic inclination ghd intensity log of core V20-108.

/ /

/

484

D. NINKOVICH et al.

~50 O ~ ' R S T r D /NCL/NA T/ON /N DEGREES

CMS

-B0-60-40-20

0

/NTENS/TY

20 40 60 80

0

~00

I

2

3

EMU/gr

4

5

X /0-6

6

7

S

200

:300

500 VOLCANIC:

;ASH

600

700

800

900

2

~000

1100

~200

13GO

1400

----z,

1500 Fig. 8. Magnetic inclination and intensity log of c o r e V20-109.

8

9

NORTH PACIFIC DEEP-SEA SEDIMENTS of an axial dipole field at 450 North would be 63.20, the o b s e r v e d i n c l i n a t i o n values in c o r e s V20-107, 108 and 109 a r e in c l o s e r a g r e e m e n t with a dipole field than they a r e with the p r e s e n t field. Changes in magnetic i n c l i n a t i o n at the points of r e v e r s a l have been m e a s u r e d in detail. Each 1 cm to 2 cm of core V20-108 was s a m p l e d and m e a s u r e d in the v i c i n i t y of each r e v e r s a l (fig. 10). T h e s e m e a s u r e m e n t s showed that the r e v e r s a l s of p o l a r i t y o c c u r r e d abruptly between adja-

485

cent s a m p l e s . One c e n t i m e t e r of s e d i m e n t in core 108 r e p r e s e n t s about 1000 y of deposition which suggests that each complete r e v e r s a l of geomagnetic p o l a r i t y o c c u r r e d in l e s s than 1000 y.

4. MAGNETIC INTENSITY V a r i a t i o n s in i n t e n s i t y a r e r e l a t i v e l y large (figs. 6, 7 and 8). They may in p a r t be due to the

150 O;'RSTED INCLINA T I O N

GM S O

-so -6o-4o -zo ~

IN

DEGREES

20 40 60 80

0

INTENSITY E M U / ~ r X 10-6 I 2 3 4 5 6 7 8

lO0

200

300

400

500

600

700

800

900

lO00 ~,,

ASH LAYER

~00

1200 ~

Fig. 9. Magnetic inclination and intensity log of core V20-119.

9

486

D. NINKOVICH et al. ~50 O E ~ S T E D INCLINATION

CM 700

-80 i

-60 I

-40 I

INTENSITY

IN D E G R E E S

-20 L

0

20

40 I

60 i

80 i

0 A.-

l •

2

EMU/GMXlI3 3 •

4 •

5 •

6 6 A

7 A

AGE (M.Y] 0.65

750

z

0.70

800 850

0.75

900

0.80

950

0.85

1000 0.90 1050 0.95

I100

S

.00

1150 NORMAL F4ELO

REVERSEO FIELD

Fig. 10. Detail of magnetic inclination and intensity log of core V20-108. showing a b r u p t n e s s of r e v e r s a l s . f a c t t h a t t h e i n t e n s i t y w a s m e a s u r e d p e r g r a m of s e d i m e n t a n d n o t p e r g r a m of m a g n e t i z e d m a t e r i a l s . A p r o g r e s s i v e d e c r e a s e in i n t e n s i t y c a n b e o b s e r v e d f r o m t h e t o p t o w a r d t h e b o t t o m of e a c h of t h e t h r e e c o r e s . O p d y k e e t al. [5] h a v e a l r e a d y o b s e r v e d , in t h e i r s t u d y of t h e A n t a r c t i c c o r e s , t h a t t h e i n t e n s i t y of m a g n e t i s m d e c r e a s e d to v e r y low v a l u e s a t t h e p o i n t s of r e v e r s a l s of p o l a r i t y . D u e to t h e h i g h e r r a t e of d e p o s i t i o n in t h e t h r e e N o r t h Pacific cores, this relationship can be more clearly defined. T h e a v e r a g e m a g n e t i c i n t e n s i t y b e t w e e n 700 a n d 1150 c m i n c o r e V 2 0 - 1 0 8 (fig. 10), a l t h o u g h v a r i a b l e , i s b e t w e e n 2.5 a n d 5 × 10 - 6 e m u / g of

s e d i m e n t . N e a r t h e p o i n t s of r e v e r s a l , h o w e v e r , the intensity progressively decreased toward z e r o . T h e p e r i o d of t i m e r e p r e s e n t e d c a n b e e s t i m a t e d a s 1 000 to 1 0 0 0 0 y. D u r i n g t h i s p e r i o d the inclination remains practically unchanged. T h e s a m p l e s c l o s e s t to the r e v e r s a l e x h i b i t e d the lower magnetic intensity, and sometimes a low i n c l i n a t i o n . A f t e r t h e r e v e r s a l , t h e i n t e n s i t y i n c r e a s e s p r o g r e s s i v e l y f o r 1 000 t o 1 0 0 0 0 y o r m o r e . Fig. 11 a n d t a b l e 3 s h o w a p o s s i b l e s u b d i v i s i o n of t h e O l d u v a i e v e n t i n c o r e V 2 0 - 1 0 9 . T h e u p p e r p a r t of t h e O l d u v a i m a y b e c o r r e l a t e d w i t h t h e G i l s a e v e n t , n a m e d f r o m I c e l a n d by M c D o u g a l l a n d W e n s i n k [8]. T h e r e a l i t y of t h i s event still awaits confirmation from other areas

Table 3 Subdivision of Olduvai event in core V20-109. Event

Magnetic polarity

Length (cm)

Duration of interval (× 1000 y)

Normal

924-943

24

Reversed

943-952

11

Normal

952-1037

Apparent age of reversals (m.y.) 1.68

Olduvai

1.69 106

NORTH PACIFIC DEEP-SEA SEDIMENTS

487

15@ OERSTED INCLINATION IN DEGREES

CM 890

-80 - 6 0 - 4 0 - 2 0 I

1

I

[

0

I N T E N S I T Y E M U / G M X IO"~

20

40

60

80

I

I

I

I

0

I A

•

2

3

. 4

•

•

•

5 •

6

7

•

•

,AGE (M.Y) 1.625

900 910

1.650

920

!

930 940 950

!

960 970 980

1.675

1.700

1.725

!

990

I

NORMAL

FIELD

1.750 REVERSED FIELD

Fig. 11. Subdivision of Olduvai event in core V20-109. The upper part of the event, between 924 and 943 cm, may be identified with the Gilsa event [8]. and c o r e s . The p e r i o d of d e c r e a s e and i n c r e a s e of in t en s i t y at both r e v e r s a l s between Olduvai and G i l s a may have b e e n of a s h o r t e r duration than the r e v e r s a l s b e tw e e n the o th e r epochs or events of the g e o m a g n e t i c p o l a r i ty . Thus the int e nsi t y of the g e o m a g n e t i c field p e r i o d i c a l l y d e c r e a s e s ; when it r e a c h e s z e r o , the e a r t h ' s d ipole fi el d is r e - e s t a b l i s h e d with opposite p o l a r i t y but without change in position [9]. As the dipole field d e c r e a s e s , it s e e m s p r o b a b l e that the nondipole components of the e a r t h ' s field would b e c o m e m o r e i m p o r t a n t , leading to the s o - c a l l e d i n t e r m e d i a t e d i r e c t i o n s o b s e r v e d in l a v a s e q u e n c e s on land during t i m e s of r e v e r s a l s [10].

5. RATES OF SEDIMENTATION Rate of deposition in c o r e s 107 and 108 app e a r s to be constant f r o m the bottom to the top

(fig. 12). In c o r e 109, h o w e v e r , an abrupt d ec r e a s e in r a t e of deposition o c c u r r e d n e a r the beginning of the J a r a m i l l o event. Doell and D a l r y m p l e [2] have dated the b e ginning of the B r u n h e s epoch of n o r m a l p o l a r i t y as 0.70 m . y . B . P . :e 3-5% [11]. T h i s date has been u s e d in the p r e s e n t study to e s t a b l i s h the r a t e of deposition in the t h r e e c o r e s (tables 4, 5 and 6).

5.1. C o r e V20-107 The beginning of the B r u n h e s s e r i e s o c c u r s at 525 cm, and the c a l c u l a t e d r a t e of deposition of the upper p o r t i o n of the c o r e is 0.75 c m / 1 0 0 0 y. An e x t r a p o l a t i o n of this r a t e of s e d i m e n t a t i o n s u g g e s t s that the duration of the J a r a m i l l o event was 45 000 y and that the Olduvai event ended 1.64 m,y. B.P. The a s h - f a l l o c c u r r e d 1.19 m.y. ago.

488

D. NINKOVICH et al. 3D v* A e(/'J , ~

NORMAL

2.5

REVERSED

2.O v

w <

1.5

¢3 W U) n., U >, W e,,

•

CORE tO?

•

CORE 108

Q

CORE 109

(~ASH

LAYER

OLDUVAI

X < ~= ~.0

~" JAmAMILLO

0.5

0

=~:

----

0

1

2

3

41

$

6

7

DEPTH

$

9

~

~TERS

IO

11

12

13

141 15

Fig. 12. Depth v e r s u s age of m a g n e t i c p o l a r i t y r e v e r s a l s in c o r e s V20-107,

1•

17

108 and 109.

Table 4 A p p a r e n t age of g e o m a g n e t i c p o l a r i t y e p o c h s and r a t e of d e p o s i t i o n in s e d i m e n t f r o m c o r e V20-107 Epoch

Event

Length (cm)

I B r u n h e s L~ormal

0-525

D u r a t i o n of interval

A p p a r e n t age of reversals

R a t e of deposition

(m.y.)

(m.y.)

(cm/1000 y)

0-0.70

0.75 0.70

Between Brunhes Norm a l and J a r a m i l l o

525-678

0.20

0.75 0.90

Jaramillo

678-712

0.05

0.75 0.95

0)

B e t w e e n J a r a m i l l o and volcanic a s h l a y e r

712-890

B e t w e e n volcanic a s h l a y e r and Olduvai

895-1235

0.24

0.45

0.75 1.19

A s h fall

1.64

0.75

1.64

Olduvai

Between 1235 and the b o t t o m of the c o r e at 1282

0.06

1,70

0.75

NORTH P A C I F I C D E E P - S E A SEDIMENTS

489

Table 5 A p p a r e n t a g e of g e o m a g n e t i c p o l a r i t y e p o c h s and r a t e of d e p o s i t i o n in s e d i m e n t f r o m c o r e V 2 0 - 1 0 8 . Epoch

Event

Brunhes Normal

Length (cm) 0-792

D u r a t i o n of interval (m,y,)

A p p a r e n t a g e of reversals (m.y.)

0-0.70

R a t e of deposition ( c m / l O 0 0 y) 1.13

0.70 Between Brunhes Normal and Jaramillo

792-1005

0,19

1.13

0.89 ~9 > ~D

)

Jaramillo

1005-1070

0,06

1.13 0.95

B e t w e e n J a r a m i l l o and volcanic ash layer

1070-1290

0.19

1.13

N B e t w e e n v o l c a n i c a s h and the bottom ofthe core

1295-1671

0.33

1.14

A s h fall

1.47

i .13

Table 6 A p p a r e n t a g e of g e o m a g n e t i c p o l a r i t y e p o c h s and r a t e of d e p o s i t i o n in s e d i m e n t f r o m c o r e V 2 0 - 1 0 9 . Epoch

Event

Brunhes Normal

Length (cm) 0-270

D u r a t i o n of interval (re.y,)

A p p a r e n t a g e of reversals (m.y.)

0-0.70

R a t e of deposition ( c m / 1 0 0 0 y) 0.38

0.70 Between Brunhes Norm a l and J a r a m i l l o

270-337

0.20

0.34 0.90

Jaramillo

337-346

0.05

0.18 0.95

> ¢9

Between Jaramillo and volcanic ash layer

346-540

0.24

0.80 1.19

Between volcanic ash l a y e r and O1duvai

545-924

0.46

N

A s h fall 0.80

1.65 Olduvai

924-1037

0.14

0.80 1.79

B e t w e e n O l d u v a i and Gauss Normal

1037-1400

0.48

0.80 2.27

Gauss Normal

1400 to t h e b o t t o m of the core at 1671

0.34

2,61

0.80

490

D. NINKOVICH et al. If the date of 0.95 m . y . B . P , is applied f o r the beginning of the J a r a m i l l o ev en t in c o r e 109, then the r a t e of s e d i m e n t a t i o n of 0.80 c m / 1 0 0 0 y below this event g i v e s the following a p p a r e n t a g e s (table 6): 1.19 m.y. f o r the ash l a y e r , and 1.66 m.y. f o r the end of the Olduvai event, both d at es being a l m o s t i d e n t i c a l with t h o se i n f e r r e d f r o m c o r e 107. A c c o r d i n g to the study of c o r e 109, d u r a t i o n of the Olduvai event was 140000 y. Apparent dates of the Olduvai event and the b e ginning of the Matuyama epoch obtained f r o m c o r e V20-109 (table 6) a r e s i m i l a r to t h o se d e t e r mined through m e a s u r e m e n t of lava flows (table 1). H o w e v e r , the a b s o l u t e dating of the J a r a m i l l o event and the beginning of the B r u n h e s epoch (table 6) show that the r a t e of s e d i m e n t a t i o n in c o r e 109 has been l e s s than half its f o r m e r v al u e s i n c e the beginning of the J a r a m i l l o event. The data f r o m t a b l e s 4, 5 and 6 a r e i l l u s t r a t e d in the g r ap h in fig. 13. The a p p a r e n t age of the g e o m a g n e t i c r e v e r s a l s in c o r e s 107, 108, and 109 have been plotted v e r s u s r a t e of d e p o s i t i o n in t h e s e c o r e s . The graph c l e a r l y shows the d i m i n i s h e d r a t e of s e d i m e n t a t i o n in c o r e 109 f o r a p p r o x i m a t e l y the l a s t m i l l i o n y e a r s .

5.2. C o r e V20-108 The beginning of the B r u n h e s s e r i e s o c c u r s at 792 cm, the r a t e of s e d i m e n t a t i o n during the B r u n h e s epoch was 1.13 c m / 1 0 0 0 y. An e x t r a p o lation of this r a t e of deposition to the bottom of c o r e 108 shows that the J a r a m i l l o event l a s t e d 57 000 y. T h e r e f o r e , a c c o r d i n g to c o r e s 107 and 108, the a v e r a g e duration of the J a r a m i l l o event was 50000 y. P a r t i c u l a r l y notable is the s i m i l a r i t y of the a p p a r e n t date of the beginning of the J a r a m i l l o event which has been i n f e r r e d f r o m t h e s e two c o r e s (0.95 y B.P. f o r both). 5.3. C o r e V20-109 Fig. 10 shows that an abrupt change in the r a t e of s e d i m e n t a t i o n has o c c u r r e d in c o r e 109 s i n c e the J a r a m i l l o event. (This is a l s o shown in fig. 5.) F o r e x a m p l e , the t h i c k n e s s of s e d i m e n t s be t ween the J a r a m i l l o event and the ash l a y e r , and between the ash l a y e r and the Olduvai event a r e v e r y s i m i l a r in c o r e s 107 and 109. H o w e v e r , the s e d i m e n t s of the J a r a m i l l o event, the p o r t i o n of the M a t u y a m a s e r i e s b e tw e e n J a r a m i l l o and B r u n h e s , and the whole B r u n h e s s e c t i o n of s e d i ment in c o r e 109 a r e p r o p o r t i o n a t e l y t h i n n e r than in c o r e 107. T h i s e x c l u d e s the p o s s i b i l i t y that p a r t of the s e d i m e n t in c o r e 109 is m i s s i n g , but s u g g e s t s an abrupt d e c r e a s e of s e d i m e n t a t i o n n e a r the beginning of the J a r a m i l l o event in this core.

~RUNHES ~OR~AL

I

5.4. C o r e V20-119 Th e beginning of the B r u n h e s epoch o c c u r s at 638 cm. The J a r a m i l l o ev en t o c c u r s b et w een 739 and 765 cm, and the Olduvai b e t w e e n 1100 c m

l" ~TUYA~A

G&USS INORMAL

RE;VERSED

JARA'~ RLLO

OLDUVA0

V20-108

O~

OE

V20-107

~ o7

~

0. 5

V20-109

O4

03 0.2 01 0

0

m

1

O5

/~ ll

15

AGE

20

( M.Y.I

Fig. 13. Rate of sedimentation versus time in cores V20-107, 108 and 109.

2 5

NORTH PACIFIC DEEP-SEA SEDIMENTS a n d t h e b o t t o m of t h e c o r e . T h e f o l l o w i n g r a t e s of s e d i m e n t a t i o n c a n b e i n f e r r e d : 0.91 c m / 1 0 0 0 y f o r B r u n h e s s e r i e s , 0.57 c m / 1 0 0 0 y f o r t h e M a tuyama series between the Brunhes and Jaram i l l o , a n d 0.47 c m / 1 0 0 0 y b e t w e e n t h e J a r a m i l l o and Olduvai events. This suggests a progressive d e c r e a s e i n r a t e of d e p o s i t i o n w i t h a g e of s e d i ment in core V20-119.

6. S O U R C E O F T H E B R O W N ASH S t r a t i g r a p h y e s t a b l i s h e d o n t h e b a s i s of m a g n e t i c d a t a s h o w s t h a t t h e l a y e r of b r o w n a s h i n c o r e s V 2 0 - 1 0 7 , 108, a n d 109 o r i g i n a t e d i n a n e r u p t i o n a b o u t 1.2 m . y . ago. H o w e v e r , n e i t h e r t h e t h i c k n e s s of t h e l a y e r n o r t h e g r a i n s i z e c a n s h o w t h e s o u r c e of t h e a s h i n t h e s e t h r e e c o r e s . A s a l r e a d y s t a t e d , a l l l a y e r s of v o l c a n i c a s h i n c o r e s t a k e n to t h e w e s t of E m p e r o r S e a m o u n t s a r e c o l o r l e s s . C o r e V 2 0 - 1 1 9 of t h i s g r o u p p e n e t r a t e d s e d i m e n t s of t h e M a t u y a m a s e r i e s a n d e n d e d a t t h e O l d u v a i e v e n t (1.9 m . y . ) , b u t t h i s core did not contain ash which correlated either in composition or in age with ash found in cores 107, 108, a n d 109. S t u d i e s of d i s t r i b u t i o n of a s h l a y e r s i n t h e S o u t h A t l a n t i c [12] a n d t h e E a s t e r n M e d i t e r r a n e a n [13] h a v e s h o w n t h a t t h e m a x i m u m d i s t a n c e f r o m t h e s o u r c e to w h i c h a s h c a n b e t r a n s p o r t e d b y w i n d to f o r m a d i s t i n c t l a y e r i n d e e p - s e a s e d i m e n t s i s a b o u t 1000 k m . T h e d i s t a n c e b e t w e e n c o r e s V 2 0 - 1 0 7 , 108, a n d 109, a n d v o l c a n o e s of K a m t c h a t k a , t h e K u r i l I s l a n d a n d J a p a n i s m o r e t h a n 1500 k m (fig. 1). T h e r e f o r e , t h e b a s a l t i c c o m p o s i t i o n of t h e a s h i n c o r e s 107, 108, a n d 109, a n d t h e p o s i t i o n of t h e s e c o r e s , e x c l u d e s a s o u r c e e i t h e r in t h e Japan-Kuril-Kamtchatl~ Arc or in the Emperor S e a m o u n t s . T h e a b s e n c e of t h e a s h i n c o r e s t a k e n to t h e s o u t h of c o r e 107 s h o w s , on t h e other hand, that the ash did not originate in the a r e a of M i d w a y I s l a n d . A t l e a s t 76 m a j o r v o l c a n o e s l i e i n t h e A l e u t i a n A r c , of w h i c h 17 a r e c a l d e r a s [14]. N a y u d u [15] h a s c o r r e l a t e d t h r e e a s h l a y e r s i n t h e G u l f of A l a s k a . H e d i s t i n g u i s h e d a c o l o r l e s s a s h 25 0 0 0 - 3 0 0 0 0 y old, of u n k n o w n o r i g i n ; a b r o w n a s h 12 0 0 0 - 1 5 0 0 0 y old, w h o s e d i s t r i b u t i o n s u g g e s t s a n A l e u t i a n o r i g i n ; a n d t h e 1912 K a t m a i a s h . D i s t a n c e of t h e t h r e e c o r e s ( V 2 0 - 1 0 7 , 108, a n d 109) f r o m t h e c e n t r a l p a r t of t h e A l e u t i a n A r c i s l e s s t h a n 1000 k m (figs. 1 a n d 2). T h u s v o l c a n o e s i n o r n e a r t h e A n d r e a n o f I s l a n d s of t h e A l e u t i a n A r c [16] c a n b e c o n s i d e r e d the p r o b a b l e s o u r c e of t h e a s h i n c o r e s V 2 0 - 1 0 7 , 108, a n d 109.

491

ACKNOWLEDGEMENTS Professor Maurice Ewing, Director of Lamont Geological Observatory, provided the cores and offered encouragement. A preliminary petr o l o g i c a l e x a m i n a t i o n of N o r t h P a c i f i c c o r e s w a s made by Dr. John Conolly. Bill Glass and David B. E r i c s o n o f f e r e d v a l u a b l e a s s i s t a n c e . D r . J. H e i r t z l e r a n d P r o f . W. S. B r o e c k e r h a v e r e a d t h e manuscript and offered valuable suggestions. T h i s s t u d y w a s s u p p o r t e d b y t h e U.S. N a v y , O f f i c e of N a v a l R e s e a r c h , u n d e r C o n t r a c t NONR 266 (48) a n d b y t h e N a t i o n a l S c i e n c e F o u n d a t i o n u n d e r G r a n t s G P 4004 a n d GA 580.

REFERENCES [1] R. R. Doell, G.B. Dalrymple and A. Cox, Geomagnetic polarity epochs: S i e r r a Nevada Data 3. J. Geophys. Res. 71 (1966} 531. [2] R. R. Doell and G. B. Dalrymple, Geomagnetic polarity epochs: A new polarity event and the age of the B r u n h e s - M a t u y a m a boundary. Science 152 (1966) 1060. [3] C. G. A. H a r r i s o n and B.M. Funnell, Relationship of paleomag~etic r e v e r s a l s and micropaleontology in two Late Cenozoic c o r e s from the Pacific Ocean, Nature 204 (1964) 566; C.G.A. Harrison, P a l e o m a g n e t i s m of deep sea sediments, in: North Pacific Paper, J. Geophys. Res. 71 (1966) 3033. [4] M. D. Fuller, C.G.A. H a r r i s o n and Y.R. Nayudu. Magnetic and petrologic studies of sediment found above basalt in e x p e r i m e n t a l Mohole Core EMT, Am. Assoc. Petrol. Geol. Bull. 50 (1966) 566. [5] N. Opdyke, B. Glass, J.D. Hays and J. Foster. A paleomagnetic study of Antarctic d e e p - s e a sediments. Science (1966), in p r e s s . [6] J. D. Hays, Radiolaria and Late T e r t i a r y and Quat e r n a r y history of Antarctic seas: Am. Geophys. Union, Antarctic Res. Series 5 (1965) 125. [7] J. R. Conolly and M. Ewing, Ice rafted detritus as a climatic indicator in Antarctic d e e p - s e a cores, Science 150 (1965) 1822. [8] I. McDougall and H. Wensink, P a l e o m a g n e t i s m and geochronology of the Pliocene lavas in Iceland, E a r t h Planet. Sci. L e t t e r s 1 (1966) 232. [9] R . J . Uffen, Influence of the e a r t h ' s core on the origin and evolution of life, Nature 198 (1963) 143. [10] J. S. V. Van Zijl, K . W . T . Graham and A. L. Hales, The p a l e o m a g n e t i s m of the S t o r m b e r g lavas. II. The behavior of the magnetic field during a r e v e r sal, Geophys. J. 7 No. 2 (1962). [11] A. Cox, D.M. Hopkins and G. B. Dalrymple. Geomagnetic polarity epochs: Pribilof Islands, Alaska, Geol. Soe. Am. Hull. 77 (1966) 883. [12] D. Ninkovich, B.C. Heezen, J. R. Conolly and L. H. Burckle, South Sandwich t e p h r a in d e e p - s e a sediments, Deep-Sea Res. 11 (1964) 605. [13] D. Ninkovich and B.C. Heezen, Santorini tephra. in: Submarine Geol. Geophys., Colston P a p e r s 17 (Butterworths, London, 1965) 413; Physical and c h e m i c a l p r o p e r t i e s of volcanic glass s h a r d s from

492

D. NINKOVICH et al.

Pozzuolana ash, T h e r a Island. and f r o m u p p e r and lower a s h l a y e r s in E a s t e r n M e d i t e r r a n e a n d e e p - s e a s e d i m e n t s (1966, in p r e s s ) . [14] R. R. Coats. Volcanic activity in the Aleutian Arc, U.S. Geol. Surv. 974B (1950) 35. [15] Y. R. Nayudu. Volcanic a s h d e p o s i t s in the Gulf of Alaska and p r o b l e m s of c o r r e l a t i o n of d e e p - s e a a s h d e p o s i t s , M a r i n e Geol. 1 (1964) 194.

[16] G. D. F r a s e r and H. F. Barnett, Geology of the Del a r o f and w e s t e r n m o s t A n d r e a n o f Islands, Aleutian Islands, Alaska, U.S. Geol. Surv. Bull. 1028J {1959) 211. [17] G. O. Dickson and J. H. F o s t e r , The m a g n e t i c s t r a tigraphy of a d e e p - s e a c o r e f r o m the North P a c i f ic Ocean, E a r t h Planet. Sci. L e t t e r s 1 {1966} 458. [18] J. H. F o s t e r . A p a l e o m a g n e t i c s p i n n e r m a g n e t o m e t e r u s i n g a fluxgate g r a d i o m e t e r . E a r t h Planet. Sci. L e t t e r s 1 (1966) 463.