Marine Geology - Elsevier Publishing Company, Amsterdam - Printed in The Netherlands

ANALYSES OF B, Ga, Rb A N D K IN TWO DEEP-SEA S E D I M E N T CORES, C O N S I D E R A T I O N OF T H E I R USE AS P A L E O E N V I R O N M E N T A L I N D I C A T O R S 1

GEOFFREY T H O M P S O N

Woods Hole Oeeanographtc lnstttutlon, Woods Hole, Mass ( U S A )

(Received November 9, 1967)

SUMMARY

Analyses are presented for B, Ga, Rb and K in a South Atlantic and anEquato-

hal Atlantic deep-sea sediment core These modern deep-sea clays differ from some ancient marine shales and modern shallow water marine clays m the relative abun- dance of B, Ga and Rb, and particularly m B concentration Boron concentration is shown to be independent of sahnlty and of potassium in pelagic clays, other factors possibly influencing boron content are suggested The varmtlon in B con- centration of deep-sea clays implies that the use of the relative concentrations of B, Ga and Rb as indicators of the pelagic enwronment may not always be feasible, complementary data regarding the chemistry and hthology will be required

I N T R O D U C T I O N

Evidence of the environment of deposition of sedimentary rocks 1s fundamental to investigation of their geologic history Certain geochemical charactenstms of sedimentary rocks result from the environment of deposxtlon A survey of such chemical criteria has been made by KEITI~ and DEGENS (1959) The abundance of a given element or group of elements is one of the criteria that have been investigated

DEGENS et al (1957, 1958) have outlined the reqmrements of such environ- mental indicators and the mare factors which ln~uence their dlsmbuttons and con- centratmns They concluded from a study of marine and fresh-water shales of Penn- sylvanlan age that boron, gallium and rubidium appear to be the most sensitive indicators to differentiate the marine from the non-marine environment POTTER

1 Contribution No 2046 from Woods Hole Oceanographic Institution

Marine Geol , 6 (1968) 463-477

4 6 4 (, i ItOMI S()

et al (1963) u~lng trace element abundances 111 alglllaceous sedlment~ lcplesentmg widely varying ,ource areas tc~tom~ condltlon~, rate ol sedimentation, geolog~c,~: ages and sahmtles concluded that B, Cr, Cu Ga, NI and V were the best dlscrlmmatol, of marine from fresh-water envn onment~

lnvesugat~ons of trace element abundances m deep-sea sedmaent~ have beel~ made m recent years (GOLDBtR(, and ARRnENIUS, 1958, EL WAKEEt and RlIl~ 1961a) These authors mdmated high concentratmns of certain elements compared to Igneous rock averages, e g Co, Cu, Mo, NI, Pb and rare earths WEDEPOHL (1960) showed the increasing concentratmn of certain elements going from near-shore to deep-sea sediments The use of geochemmal paleoenwronmental indicators to ascer-

tain whether certain sedlmenta D deposits on continents are of deep-sea origin is lesb frequent HARRISON and JuKcs (1892, 1895), and later EL WAKEEL (1964) have u~ed chemical analyses to support the argument that certain Barbados siliceous earths were of deep-sea origin, MOLENGRAAI- (1920) and EL WAKEEL and Ru.f~ (1961b) made similar studies on fossil red clays [rom Tlmor In all cases overall chemical composition and mineralogy were compared, the use of crmcal trace element abun- dances has not been attempted NICHOLLS (1967) has considered the influence o~ pressure in controlhng trace element concentratmns and concluded that it is small

and inadequate to explain geochemical differences between deep-water and shallo~ water sediments, other factors must be responsible for the differences He lurther suggested that trace element populations may possibly be used as m&catols ot pelagm enwronments

Data is presented below from analyses of deep-sea cores from the South

Atlantm and Equatorml Atlantm for B, Ga and Rb The apphcatmn of the relative concentratmns of these elements is made on these sediments to ascertain if deep-sea

deposits differ from other marine deposits and whether the relative concentratmns may be used as mdmators of the pelaDc environment B, Ga and Rb show no corre- latmn with Mn or Fe, at least m these cores The concentration of the elements Co, Cu, Mo and NJ is closely correlated w~th the concentratmn of authlgemc feno- manganese minerals m the sediments However, these mmerals are not confined to deep-sea deposits (MANHHM, 1965), thus the use of these elements is precluded m this mltml study

EXPERIMENTAL

Matertals

Two deep-sea cores were studted, samphng procedures, treatment and analyses other than those presented here were reported elsewhere (THOMPSON, 1965), and are subject of a paper m preparation

One core, A5797, was taken m the South Atlantm at 31~2'S, 39"33'Wby R V "Atlantis" of the Woods Hole Oceanographm Institution Depth of water was 4279

Marme Geol, 6 (1968) 463-477

,.,.,,

..-4

..-4

TA

BL

E I

CO

NC

ENTR

ATI

ON

OF

B,

Ga

AN

D R

b,

(in

p p

m )

, A

ND

K,

(in

°o) ,

IN

CO

RE

A5

79

7

Dep

th m

co

te

(em

) 7

14

28

35

56

63

70

79

86

100

B

230

2]0

28

5 30

0 28

5 34

5 29

0 29

0 40

0**

345

Ga

12

16

20

16

16

20

19

20

17

13

Rb

n

d

90

120

110

105

nd

11

0 11

5 12

5 13

0 K

2

15

' 2

05

2

22

2

20

2

13

2

22

*

21

6

21

7

21

8

22

2

Dep

th m

co

te (

cm)

170

184

198

219

233

247

261

280

294

308

107

114

128

142

156

235

295

nd

n

d

nd

20

18

19

14

17

n

d

115

120

105

100

nd

2

14

2 13

2

34*

2 07

322

336

350

364

379

B

265

405*

* 29

0 n

d

430

295

31

0'*

30

5 26

0**

~85

275*

* 32

0 29

5**

360

330*

* G

a 18

23

21

18

22

22

22

2

l 22

22

22

21

28

22

19

R

b

105

105

110

115

nd

11

0 11

0 12

0 n

d

110

110

120

110

90

100

K

2 12

2

06

2 16

2

22*

2 17

2

09

2 16

2

14

2 18

" 2

17

2 07

2

14

2 13

2

06

nd

Dep

th t

it co

re (

cm)

392

399

413

420

427

434

441

455

483

490

497

504

511

518

525

B

300

305*

* 33

5 29

5**

245

330*

* 31

0 35

5**

330

380*

* 34

0 36

5**

330

360*

* 37

5 G

a 18

22

15

15

18

19

14

18

15

16

15

18

20

21

14

R

b

nd

11

5 10

5 n

d

110

nd

12

5 11

0 n

d

nd

10

5 n

d

115

nd

10

5 K

2

13

2

09

2

09

2

21

" 2

12

2

34

*

nd

2

09

n

d

21

7"

21

3

23

0*

2

07

2

24

*

20

3

Dep

th m

A

veJ

age

co

le (

era)

53

9 55

3 56

7 58

1 59

5 60

9 61

6 62

3 X

S

CV

°o

B

340*

* 36

0 22

5**

330

250*

* 28

5 34

0**

265

320

44

14

Ga

19

25

13

17

12

19

21

19

18

3 17

R

b

105

110

110

105

85

115

nd

12

0 11

0 9

8 K

2

30

2

0~

2

06

2

09

1

73

2

08

2

27

*

20

8

21

5

01

0

5

nd

=

no

t d

eter

min

ed,

* b

y f

lam

e p

ho

tom

etry

, **

=

o

ne

arci

ng

, A

=

aN

thm

etlc

mea

n,

S st

and

ard

dev

iati

on

, C

V°o

p

erce

nta

ge

coef

fici

ent

of

var

iati

on

Z

t"

O

Z 7~

©

v~

7~

o 4~

466 , i I tOMP'-,()

m (uncorrected), length ,:,t cote ()24 ,...n] fhe cote ~as described a~ homogcncou, red clay throughout it~ length, the uppel 7 cm being a dalker brown colol than th~ remainder Mineralogical exammatlon indicated llhte to be the dominant mme~,tl

minor quartz and lelspar wele present The lnmeralog 5 deduced flom X-~a 3 dliltac- tlon patterns appears lelat~vel~ constant throughout the length of the co~e B[s( AXi (1965) reported mineralogical investigations on the upper parts of piston co, ca m this vicinity of the South Atlantic and l\mnd dhte to predominate

The second core, CH 17-7 was taken b~ the R V 'Chain" from the Romanche Trench00 16 4'S 18 31 0'W m the EquatormlAtlant lc Depth of water was 7610 m length of core 752 cm The upper 200 cm was described as line clay with a number ot layers of ooze present, 200-600 cln is an ooze, the lowei 150 cm clay Data ale pre- sented here only for the clay portions ol the core The mineralogy of the core was quite complex compared to A5797, dllte, montmorillonlte, chlorite and felspars being

present but varying in proportion in different samples

Anal),tlcal techmques

B and Ga were determined by emission spectrographic methods using anode excitation in the d c arc The method, lines used and the instrument were as described by THOMVSON (1965, and in preparation) The composmon of the synthetic clay

matrix used for standardization purposes was $102 56 ~ , MgO 3 25 ~/o, A1203 17 0 ~ , Fe2Oa 7 5 o/, T102 0 75 %, CaCO3 5 0 %, NaCI 7 5 %, KCI 3 0 % Dilution of this matrix was made with suitable proportions of CaCO3 to simulate samples of ooze

Rb was determined by X-ray fluorescence spectrometry using a scintillation counter and LIF analyser crystal The standards used for emission spectrography

were employed but pressed into discs 1 Inch in diameter with a pressure of 400 lb / sq inch The Rb peak was measured at 20 values of 26 65 ~, background at 26 10

K was determined by flame photometry' In the case of samples marked with an asterisk in Table I, on the remainder it was determined by X-ray fluorescence spectro- scopy as for Rb, although in this case a proportional flow counter and E D D T analyser crystal were used The K peak was measured at 20 values ot 19 85 . back- ground at 19 10' A comparison of results by both methods for certain samples Indi- cated agreement within ~- 10°o All the analyses of K in Table II were done by flame photometry

Replicate measurements on the same samples indicated these coefficients of variation B 6 2 %0, Ga 11 1 }o, Rb 3 6 ~o and K 5 0 ~ For samples marked with a double asterisk In Table I, the reported B content is the result of only one arcing, all other results are from triple arcings or irradiations The order of precision indicated for B is such that these single exposure values are of use within the context of this study

The results of the analyses of B, Ga, Rb and K in core A5797 are presented in Table I, for core CH 17-7 in Table II

Marme Geol, 6 (1968) 463-477

C3

a-, i .,M

TA

BL

E I

I

CO

NC

EN

TR

AT

ION

OF

B,

Ga

AN

D R

b (

m p

p m

),

AN

D K

(m

°o)

, IN

CO

RE

17-

7

Dep

th m

C

ote

(cm

) 0

12

20

24

28

36

90

98

12

2 12

7 14

0 14

8 6

52

66

8 6

92

70

8 74

7 X

S

CV

°o

B

195

180

205

24

0

245

160

22

0

20

5

140

120

150

185

20

5

155

160

150

140

180

36

20

G

a

22

14

14

17

17

20

25

18

19

17

22

17

21

2

0

24

2

4

17

19

3 16

R

b

95

95

95

110

80

110

110

110

95

105

125

95

10D

12

5 11

5 11

0 95

10

4 11

11

K

1

31

1 17

1

23

1

29

1

26

1

48

1

67

16

2

1 59

1

46

1

45

1

24

12

5

14

4

1 54

1

42

1

45

1

40

0

15

11

X

=

arit

hm

etic

mea

n

S =

st

and

ard

dev

lan

on

, C

V°o

=

per

cen

t co

effi

cien

t o

fva

na

no

n

Z N

0 -i-1 C~

P 0

" Z

©

m

N

N

Z

C~

©

468 ~, 1 tt()MI"-,( )

DISCUSSION

Apphcatton oJ paleoen vuonmental c rttet m

DEGENS et al (1957) plotted the relative abundances o f B, Ga and Rb, recal-

culated m pairs to 100 °/o, on a mangu la r diagram as shown in Fig 1 The values for

their marine shales are plotted on th~s diagram as are the values for the South Atlanue

core A5797, and the Romanche core 17-7 Since the variation m elemental compo-

smon of oceanic waters m past geological times is uncertam, as are dlagenetic effect~

on the distribution of elements in sediments, some modern marine shallow wate~

clays (taken from data of H1RST, 1962) are included

F rom the diagram it is seen that the deep-sea clays lie m a group separate from

the ancient and modern clays A statistical evaluation of the analytical data sho~n

In Fig 1 is presented m Table I11 From this table it is noted that al though Ga and

Rb are present m these deep-sea clays in amounts that are d~fferent and less variable

than ancient shales, they overlap w~th those of modern shallow water clays in respect

o f G a and are only slightly lower in Rb It is with the element B that the most marked

difference between the deep-sea clays and the others l~ noted, pamcular ly m core A5797

DEGENS et al (1957), also POTTER et al ('1963) showed that the relative concen-

tration o f boron appeared to be the most sensitive mdJcator o f marine condmons

Go

/ ~ + MODERN SHALLOW WATER MARINE CLAYS oV / , \ ~ CFROM H~RST, t962)

o" "7- - ~° ~. o CORE A5797 / " \ % ..NC,E.. M.R,NE S.ALE

~.~7 // \ ~o÷ (FROM DEGENS ET AL 1957)

# / "~ -i+++ 1\

i)oo o

B 80 4O ZO Rb RELATIVE R~ ABUNDANCE RECALCULATED TO iOO%

F=g ] Rclatwe abundance of Ga, Rb and B recalculated m pairs to 100% m core A5797, 17-7, some ancient marine shales (taken from DEGENS et al, 1957), and some modern marine shallow water clays (taken from HIRST, ] 962 )

Marine Geol, 6 (1968) 463-477

ANALYSES OF B, Ga, Rb AND K IN TWO DEEP-SEA SEDIMENT CORES 469

T A B L E I l i

COMPARISON OF MEAN VARIATIONS OF D A T A S H O W N IN FIG 1

E l e m e n t S ta t t ~ttc Core Cot e Anc t en t 1

A 5 7 9 7 17-7 mar ine shales

M o d e l n °~

shal lo~

)~atet c lavs

B mean 320 180 115 79 s tandard deviat ion 44 36 34 11 coefficient o f varmtlon 14°(. 20% 30°o 14°o

Ga mean 18 19 8 20 s tandard devtat lon 3 3 7 4 coefficJent of varmtlon 17% 16°o 88% 20°,,

Rb mean 110 104 281 150 s tandard devmt~on 9 11 147 24 coefficient o f vartaUon 8 % I l °o 52°0 16° .

1 DEGENSetal (1957) 2 HIRST (1962)

GOLDSCHMIDT and PETERS (1932) showed marme shales to be rich in boron, LANDER- GREN (1945) indicated a relationship between boron and sahnlty Other investigators have s~mllarly demonstrated the relationship between boron concentration in the sediments and the environment of deposttton, e g , ERNST et al (1958), KRASINTSEVA and SHISKINA (1959), and FREDERICKSON and REYNOLDS (1960) WALKER (1962) and WALKER and PRICE (1963) have made the proven incorporation of the greater

part of the boron into the llhte lattice as the basis for thetr use of boron as an enwronmental indicator

The consequences of redeposited llhte already containing boron m the lattice have been discussed by HARDER (1959) and by NICHOLLS (1963) For a constant source of detrltal clay minerals containing a constant "inherited" boron content, as core A5797 may well be, the use of "adjusted" and "equwalent" boron values as recommended by Walker and Price may be of some significance

Following Walker and Pmce, the "adjusted" boron contents for core A5797 and CH 17-7 have been computed from the formula

Observed B . 8 5 Adjusted B =

o / K 2 0 / o

(the factor 8 5 being the theoretical concentration of K20 m pure llhte) The dominance of llhte in these deep-sea clays, at least in A5797, lessens the complications from boron being present in other clay minerals From their plots of "adjusted" boron against %K20, Walker and Price considered that the ablhty of llhte or musco- vite to incorporate boron into the structure was determined by its potassmm content They proposed the use of "departure curves" for relating the "adjusted" boron

M a l i n e G e o l , 6 (1968)463-477

470 ~ , I l t O M P ' - , L ) .

values to " 'equivalent ' boron ~alues "Fhe "eqmvalent'" boron is the adlusted' boron content that would exist at eqmllbrmm m llhte from the same sahmt) medium the llhte contammg 5"o K,O They further m&cated tentanve hmmng values lt,~ the "equivalent boron contents of various environments, namely les~ lhan 20(1 p p m for fresh water 300 400 p p m fol normal marine envlronment~ and 80() 1,000 p p m for the upper sahmty hmlts

The "adJusted" boron values for core A5797 and CH 17-7 are plotted against °oKzO m Fig 2 The depalture curves of Walker and Prme are also shown on the same dmgram Two slgmficant leatures are seen from these plots First, the spread of pomts does not follow the proposed departure curves mdmatlng other controls on the boron abundance than potassmm and sahmty Second, they he outside the field of normal marine se&ments and approach the proposed upper sahmty hmlts

Intershtlal water mveshgatlons on cores from this area, (SIEWR et a l , 1965), mdmate normal sahne con&tmns, the dominance and constancy of the dhte contrlbutmn has been indicated Deep-sea sediments from the Pacific investigated bv GOLDBER(, and ARRHENIUS (1958) show slmdar dewatlons when plotted on this dmgram Values for core 230 from the AtlantIc investigated by LANDERGREN (1964) also plot &fferently to the departure curves though the sahmt) mdmated for these se&ments more closeh approaches normal Modern shallow water clays (values taken from HIRSl, 1962) plot at salinity levels m~dway between non-marine and marine

In other stu&es oJ pelagm clays, La, NDERGREN (1964) mdmated the mean B content of eight Pamfic cores to be 135 p p m . with a range from 35-220 and for two

Atlantm cores the mean B content was 130, the range 95-200 Some of the varmtmn

DMODERN MARINE SHALLOW WATER CLAYS {HIRST, ~962)

@CORE f7-7 , EQUATORIAL ATLANT)C • CORE A5797 S ATLANTIC

f2 X PACIFIC PELAOIC SEDS (GOLDBERG ANO ARRNENIUS, [B58 )

(3 ANCIENT MARINE SHALES 0 ANCtENT NON-MARINE SHALES

40 (WALKER AND PRICE,1963) O~ . + CORE 230, ATLANTIC ~<

(LANDERGREN, '1964)

- .~ >

• ~

2- g

lID

, , , i

2~o 4'o0 60o eeo 4oo0 4=00 t4oo

ADJUSTED BORON (p p m )

Fig2 Relationship between "adJusted" boron and K20, and departure curves for "'equwalent" boron m some anment and modern se&ments (taken from WALKER and PRICE, 1963)

Marme Geol, 6 (1968) 463-477

ANALYSES OF B, Ga, Rb AND K JN TWO DEEP-SEA SEDIMENT CORES 471

can be explained by dilution with CaCO3, but m a study of the < 6/1 f ract ion-- predominantly a lummoslhcate- - a mean of 220 p p m was noted for B in a Pacific

core and 135 p p m in an Atlantic core but the variations noted ranged from 60-230 p p m GOLDBERG and ARRHEN~US (1958) from their study of Pacific sediments indi- cated a range in B content from 96-760 p p m with a mean of 300 p p m In the cores A5797 and CH 17-7 the sallmty remained constant and the KzO content was much less varied and independent of the B Core CH 17-7 has lower K20 contents than core 230 m Fig 2 but higher and more varied B concentrations

WALKER and PRICE (1963) noted that modern deep-sea clays &d not plot on the

departure curves m the position of ancient marine se&ments and the) concluded that it would be premature to comment on the results untd more was known of the relative

moblhty of boron and potassium in lllite as compared to other minerals during hthlfi- cat,on However, laboratory leaching experiments (HARDER, 1959, FLEET, 1965, and REYNOLDS, 1965), have demonstrated that clay mineral boron withstands quite severe chemical treatment, interstitial water studies (TAGEEVA and TIKHOMIROVA, 1962, SILVER et a l , 1965) gave no indication of dmgenetlc movement of boron or potassium The K20, Rb, Ga and llhte concentrations m the core are relatively constant The boron shows greater varmblhty but no concentration gra&ent m&catlve of movement is seen Such varmble boron concentration would appear to ln&cate that equilibrium between the boron and llhte is not the controlling factor governing the boron con- centratlon Authlgenac tourmahne, another possible source of boron, ~s very rarely Identified m modern deep-sea clays and was not found m these cores

This prehmmary study of deep-sea clays confirms that differences exist between some pelagic sediments and other marine deposits, particularly with regard to boron content The varmtlon within and between deep-sea cores is quite marked and not easdy explained by sallmty control of boron abundance Other possible factors are &scussed as follows

Rate of deposltton HARDER (1963) indicated that the boron content was greater in more slowly

deposited clays FLEET (1965) confirmed these findings experimentally and, extra- polatlng his results postulated that rate of deposition was a significant factor in con- trolling boron content Core A5797 and many other deep-sea clays were deposited extremely slowly and may be expected to show increased boron content if rate of deposition does control boron incorporation I f this is the case then other marine, or even possibly fresh-water se&ments deposited at similar slow rates, would have h~gh boron contents and indicate higher and anomalous sahnlty environments when plotted on the Walker and Price diagram However, if rate of deposition, or time in contact with boron containing solutions, is a factor controlhng boron content, then deposited clays m contact with mterstitml waters containing boron would con- tmue to incorporate boron into their structure and the Interstitial waters would be progressively depleted in this element This IS not confirmed by observation of waters from cores of many environments, e g , KRASINTSEVA and SH~SK~NA (1959)

Marine Geol, 6 (1968) 463-477

472 ,, I HOM |'",C )\

and TAGEEVA and TIKHOMIRO'~a, (1962) Moreover, the varmble boron t.ontent ,,' pelagic se&ment~ appalentlv ol ~lmllar mineralogy and deposited at qo,a rate~ m&cates other factors than rate of deposition to control boron content

G r a i n 612~ J

HARDER (1959) in experiments on boron adsorption indicated that sorptlon wa~ greater on fine-grained clays L~NDERGREN (1958) also postulated a relationship between boron content and gram size in argillaceous marine sediments, however. SHAW and BUGRY (1966) point out that Landergren's proposed relationship is minera- logical rather than granulometrlc and represents a preferential incorporation of boron by clay minerals whose abundance increases in the finer sized fractions In a more recent study of deep-sea clays, LANDERGREN (1964) once more postulated a correlation between boron content and gram size Although again clay content and type may be of a greatest slgmficance m controlling boron content, the variation m clay mineralogy and abundance in the different fine fractions is not as marked as m shallow water sediments, thus in deep-sea clays the effects of grain sxze may not be entirely discounted However. the finest fractions of those clays stu&ed by Landergren still do not have as high a boron content as core A5797 and some from the Paofic (GOLDBERG and ARRHENIUS, t958) If gram size is a significant factor then either the measured fine fractions from the pelagic clays investigated by Landergren do not represent the true s~ze during sedimentation because of flocculatlon or other mechanisms causing aggregation of particles, or other factors are operatwe m con- trolhng boron lncorporatJ on

Orgamc carbon CURTIS (1964) noted that the operation of Walker and Price "equivalent"

boron computation for deducing sallmties gave anomalous results for certain British Carbomferous se&mentary sequences From data of BADER (1962) that clay minerals quickly and strongly adsorb up to 300 ~ of their own mass of orgamc matter from solution, Curtis explained the anomalous values as being due to variation m the sorptlon of boron because adsorbed organic layers on the clay minerals inhibit the process EAGER and SPEARS (1966) also noted that although the total orgamc carbon- boron relationship predicted earher by EAGER (1962) was redirect, reevaluation of that data and new analyses of BrltJsh Carboniferous sediments showed a direct rela- tlonshlp between carbon and B/K ratios at levels below 10~o orgamc carbon They too postulated boron sorptlon inhibition by soluble organic molecules CHAVE (1965) has also reported organic coatings on mineral grams m sea-water preventing free interaction between sea-water and the particles

EL WAKEEL and RILEY (1961a) observed that the orgamc carbon content of deep-sea clays was appreciably less than that of near-shore sediments Core A5797 and the Pacific clays reported by GOLDBERG and ARRHENIUS (1958) are highly oxldlsed red clays, those analysed by Landergren from core 230 tend to be less oxi&sed as

~tarlne G e o l , 6 (1968) 463-477

ANALYSES OF B, Ga, Rb AND K TN TWO DFEP-SEA SEDIMENT CORES 473

judged from color comparison and manganese content It might be conceivable

that these highly oxIdlsed clays with low organic carbon have less efficient inhlbltlon

of boron sorption by organic matter and hence higher boron content Further inves- tigation of the relationship of boron to orgamc carbon, and the nature of the organic material in pelagic sediments is required It might also be conceivable that in these oxidised clays the ferromanganese minerals, that are typically present, preferentmlly adsorb many of the elements and thus result m less competition for boron adsorbing

on sites on clay minerals

Authtgemc minerals LEVINSON and LUDWICH (1966) presented evidence that boron sorptlon pmma-

rlly takes place at the mixing of fresh and marine waters, further sorptlon from sea- water is not Important The apparent relationship between sahnlty and boron content of sediments is only fortmtous and is due to the fact that the fine-grained clays adsorb

more boron than other phases in the Intermixing zone and are carried out into the more saline areas Although it may well be that a significant proportlon of the boron content is adsorbed at the initial mixing of marine and non-marine waters in deltaic areas, the experimental evidence of HARDER (1959) and FLEET (1965), and the field investigation of workers previously mentioned Indicating a relationship between salinity and boron content of sediments in other areas than deltas, Indicate that sorpt~on can and does Increase with sahnaty Comparison of the boron content of

the fine fraction of pelagic and shallow water sediments of slmdar mineralogy, e g , LANDERGRFN (1958) also indicates some enrichment m boron

Levmson and Ludwlch also postulate that further boron Incorporation after the initial sorptlon in the deltaic region does not occur except in the case of authigenic

minerals, e g , glauconIte The apparent anomalous boron concentrations of the South Atlantic core and of certain Pacific sediments might then be explained as due to the presence of authigenlc minerals The only apparent authlgenic minerals present m these pelagic sediments are the ferromanganese oxides GOLDBERG and ARRHFNIUS (1958) m their studies on the Pacific sediments showed that the greater part of the boron was held in the clay minerals In the South Atlantic core no correlation between boron and manganese or iron is seen, moreover, the ferromanganese oxides represent only a very small proportion of the sediment Incorporation of boron would thus have to be explained by reorganization of the alumlnosflicates and formation of authlgemc clay minerals ARRHENIUS (1954) and GOLDBERG and ARRHENiUS (1958) have postulated formation of clay minerals from true ~olutlon of ionic species of sihcon and aluminum in sea water, the boron proxylng for silicon in the tetrahedral sheets of the clay minerals LANDERGREN (1964) has also postulated red~stmbutlon of boron during the formation of authlgenic clay minerals in pelagic sedlment~

Non-envtronmental factors I t might be argued that the high boron content of core A5797 is not an expre~-

Mal the Geol , 6 (1968) 463 -477

474 ~ , I IIOMP%(~\

slon of any factors controlling sorpUon of boron from normal sea-water 1 here I. the possibility of local ~ olcamc actwlt 5 enrzchmg the enwronment m boron howe~cl the period of time lepresented bx these se&ments with deposition rates of the ordc~

of mdhmeters per 1000 years makes ~t extremely unhkely that such actw~t\ uould have been contmuou~ Charging of the sedHnent by boron rich volcamc e~halates after deposition ~s possible but no evidence of such actlwty is seen in this core. e g absence of ash. zeohtes, montmordlonlte, low Cr and S content There is also the possibility that these clays ate high in "'inherited" boron and the "acqmred ' boron is no higher than usual However, a clay source of such htgh boron content is not known, a similar source for the Pacific clays is also unlikely, other boron phases such as tourmahne, usually the reason lot high boron content, are not found m these

sediments It would appear that the boron enrichment is due to variation m environ-

mental factors m the deep-sea

CONCLUSIONS

Although the question of variation in boron content of ocean waters with time

has not been entirely settled (SHAW and BUGRY, 1966), and there may be some danger in comparing boron content of marine sediments from one geological period to another, the variation In boron content of marine se&ments of the same geological period indicates the effects of local deposltional processes and provenance play a large part in controlling boron content In the absence of some effective method of assessing the relative importance of such factors as rate of sedimentation, "acqui-

red" boron content, potassmm content of alhte, mineralogy, grain size and orgamc matter, it would appear to be more advisable to use the boron content of sediments only as complementary to other criteria for differentiation of environment Boron is enriched in some deep-sea clays but the variation in its relative concentration precludes its single use as an indicator of pelagic environment

The use of the relative abundances of B, Ga and Rb may not always be feasible when plotted on the DEGENS et al 0957) type triangular diagram Although appa- rently successful in the case of the pelagic cores and the sediments plotted in this report, the position of the plots may be markedly affected by the variation in boron concentration and possibly overlap with modern shallow water marine clays Data on all three elements to test the hypothesis further is not yet available

It seems probable that the use of the trace elements examined in this study will only be of real value when used to complement other criteria of pelagic depositmn such as discussed by ARRnEYIUS (1963) Investigation of organic carbon content In relation to boron may be of value in elucidating the processes of boron enrichment, as may investigations of the possible presence of authIgenlc clay minerals

Further studies on trace elements, particularly in different phases of deep-sea se&ments, are also required before such paleoenvlronmental criteria can be applied to the pelagic environment

Marine Geol, 6 (1968) 463--477

ANALYSES OF B, Ga, Rb AND K IN TWO DEEP=SEA SEDIMEN'I CORES 475

ACKNOWLEDGEMENTS

The major part of this work was presented as a portion of the author's Ph D dissertation at the UmversJty of Manchester U K, 1965 Dr G D Nlcholls, Umversity of Manchester gave gmdance at all stages of this work, Dr V T Bowen, Woods Hole Oceanographic Institution constructively crltlclsed the manuscript, the manuscript also benefited from the adwce of Dr E T Degens, Woods Hole Oceanographic Institution and Dr M E L Fleet, Unlversaty of Ontario To all these mdwlduals the author expresses his thanks Th~s work was completed with the aid of grants from the Umversaty of Manchester and the Department of Scientific and Industrial Research, U K , also by the U S Atomic Energy Commission under contracts AT(30-1)-2174 and AT(30-1)-3010 with the Woods Hole Oceanographic Institution Core A5797 was collected by Dr R H Leahe) on cruise 247 of R V "Atlantis" of Woods Hole Oceanographic Insmutton, this crmse was supported by the U S National Science Foundation as a part of the program for the Interna- tional Geophysical Year Core CH 17-7 was taken on cruise 17 of R V "'Chain", supported by the U S Office of Naval Research under contract NONR-2196(00) and by the U S National Science Foundation under Grant 12178 All support is gratefull? acknowledged

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