palaeoecology (stratigraphy of siwalik)

8/3/2019 Palaeoecology (Stratigraphy of Siwalik)

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18Until recently the age of the Siwalik Group was known only from faunalcorrelation (Pilgrim, 1913; Colbert, 1935). However, magnetic polarity strati-graphy analyses (Keller et al., 1977; Opdyke et al., 1979) and radiometricdates (G. D. Johnson et al., 1982) have substantially improved these age esti-

mates for the Upper Siwaliks. Magnetic-polarity stratigraphy has also beenemployed in the vicinity of Dhok Pathan village (Fig.l) to improve the ageresolution o f parts of the Middle Siwaliks (Barndt et al., 1978; Tauxe, 1979).The purpose of this paper is to extend the findings of Barndt et al. (1978)and Tauxe (1979) to other areas of the Potwar Plateau and to synthesize thestratigraphic and paleomagnetic results. Included in this study are the strato-type locations for the Kamlial Formation, the Chinji Formation, the NagriFormation, and the Dhok Pathan Formation. Included also are many of theprincipal faunal levels which have been used to characterize these formations.

~ ~ ~ D ~ ~'_~ ~ '~

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I i - rO h i n j i " -~ . ~ G E - - - . . iI . - q - ~ / . ~ ' ~ . , m R A N ~ l~-..~o,D,,!,;I _ ~ " I " I $ ~ ~ ' i _ - .. , l i . , ~

' / , i ~ l ~ / s I 4 3 D / 1 0 I , I ' ~ " ~~ 2 ~ o ' 1 _ i , j , , o , , f i7 2 J ~ 7 3 7 ~

- 3 3 o 3 0 `

33

3 z O 3 o '

Fig.1. Location of reference population centers and principal magnetic polarity sections(shaded areas). Specific mappe d areas are shown and designated by their Geological Surveyof Pakistan code number s.


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20u p p e r m o s t p a r t o f t h is f o r m a t i o n is n o t r e p r e s e n t e d i n t h e s e c t i o n s g iv e n i nt h o s e s t u d ie s . H o w e v e r , i n t h e B u n h a R i v e r a r e a ( e.g . T a t r o t - - A n d a r , K o t a lK u n d a n d J a la l pu r ) t h e e n t i r e D h o k P a t h a n F o r m a t i o n is p r e se n t .

U p p e r S iw a li le F o r m a t i o nW e h a v e al so s a m p l e d a n d a n a l y s e d t h r e e s t r a t ig r a p h i c s e c t i o n s w h e r e

d e p o s i t i o n e x t e n d s f r o m t h e C h i n ji i n t o t h e U p p e r S iw a l ik s ( in t h e B u n h aR i v e r a re a, K o t a l K u n d , T a t r o t - - A n d a r , a n d J a l a l p u r s e c t io n s , F i g . l ) . T w o o ft h e s e s e c t io n s c o n t a i n t h e U p p e r S i w a li k t u f f c o m p l e x w h i c h h as b e e n ra d io -m e t r i c a l l y d a t e d ( G . D . J o h n s o n e t a l., 1 9 8 2 ) .M ETHODSF i e ld p r o c e d u r e s

P a l e o m a g n e t i c s a m p l e s w e r e c o l l e c t e d f r o m 4 7 2 s it es i n f iv e p r i n c ip a l s ec -t i o n s : 1 1 4 s i te s f r o m a 1 8 0 0 - m s e c t i o n n e a r t h e v il la g e o f K o t a l K u n d , 1 1 3s i te s f r o m a 2 1 0 0 - m s e c t i o n t o t h e n o r t h o f J a l a l p u r v il la ge , 1 1 6 s i t es f r o m a1 5 0 0 - m s e c t i o n in t h e T a t r o t - - A n d a r a re a, a n d 6 6 s i te s f ro m a 1 7 0 0 - m s e c t io ni n t h e C h a k w a l - - B h a u n a re a, a n d 6 3 s i te s f r o m a 1 3 0 0 - m s e c t i o n in t h eC h i n j i- -N a g r i a r e a ( F i g . l ) . T h e s i x t h s e c t i o n w e u s e is t h a t f r o m t h e K h a u ra re a, r e vi se d a n d u p d a t e d b y T a u x e a n d O p d y k e { 1 9 8 2 ) , f ro m t h e D h o kP a t h a n s e c t i o n re p o r t e d e a rl ie r b y B a r n d t e t a l. ( 1 9 7 8 ) a n d T a u x e ( 1 9 7 9 ) . A sa lu l e , s a m p l e s w e r e c o l l e c t e d f r o m o u t c r o p s d e v e l o p e d i n a c t i v e l y d i s s e c t in gs t r e a m c h a n n e l s w h i c h w e r e o r i e n t e d n o r m a l t o r e g i o n al s t ri k e . O n l y c l ay -s t o n e , m u d s t o n e a n d s i l t s t o n e w e r e u s e d a s s a m p l e m a t e r ia l . S a n d s t o n e s a n ds t ra t a s h o w i n g s ig n s o f p o s t - d e p o s i t i o n a l d e f o r m a t i o n o r w e a t h e r i n g w e r ea v o i de d . M o s t s a m p l e s w e r e t a k e n f r o m u n d e r c u t s t re a m b a n k s i n o r d e r t oi n s u r e f r e s h n e s s o f t h e s a m p l e . S a m p l e s w e r e t a k e n o n l y f r o m s t r a t a i n s i tu .T h e f ie ld s a m p l in g p r o c e d u r e is t h a t o u t l i n e d b y N . M . J o h n s o n e t ah ( 1 9 7 5 ) .A m i n i m u m o f t h r e e s a m p l e s w e r e c o l l e c t e d f r o m e a c h s it e. S i t e s e l e c t i o nw a s l a rg e ly p r e d i c a t e d o n t h e a v a i l a b il i ty o f s u i ta b l e l it h o lo g i e s . E x c e p t f o rm u l t i - s t o r ie d s a n ds , w h e r e o v e r b a n k s il ts a n d c l a y a r e n o t p r e s e n t b e t w e e nc y c l e s , o n e s i t e a t l e a s t w a s p l a c e d f o r e a c h f l u v ia l c y c l e . T h e s a m p l i n g p r o -g r a m e x t e n d e d o v e r a 4 - y e a r p e r i o d , e a c h s e c t i o n b e i n g c o l l e c t e d a t le a s tt w i c e t o r e f i n e a n d r e p l i c a t e c r u c i al d a t a p o i n t s . S e c t i o n m e a s u r e m e n t s w e r em a d e w i t h a n A b n e y le ve l m o u n t e d o n a J a c o b ' s s ta f f, o r f o r s t e e p ly d ip -p i n g s t r a ta w i t h a t a p e m e a s u r e . D i p m e a s u r e m e n t s w e r e m a d e w i t h a s p ir it -l ev e l i n c l i n o m e t e r . S t r i k e m e a s u r e m e n t s w e r e t a k e n f r o m o r i e n t e d a e r ia lp h o t o s o r t o p o g r a p h i c m a p s o n r e g io n a l f e a t u r e s s u c h as e x t e n d e d c u e s t a s .M a g n e ti c m e t h o d s

E q u i p m e n t a n d p r o c e d u r e s e m p l o y e d f o r m e a s ur in g r e m a n a n t m a g n e ti s ma r e s p e c i fi e d in a c o m p a n i o n p a p e r b y O p d y k e e t a l. ( 1 9 8 2 ) .


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21Virtual geomagnetic pole (VGP) latitudes were calculated for each site

whose mean polar ity was statis tically significant (k ~> 10), i.e., designatedClass I data according to the classification proposed by Opdyke et al. (1977).In this study we have adopted two other conventions to categorize ourpaleomagnetic site data. We designate a site as Class II if in composite it isnot statistically significant (k < 10), but th at the polarity direction of thesite is not in doubt. Usually this means that two out of the three samplesfrom the site have nearly parallel magnetic vectors with the third being diver-gent. In a few instances one of the three samples was lost or broken, but theremai ning two samples show near ly parallel magnet ic vectors. VGP latit udeswere calculated for Class II sites and included into the data base, althoughgiven less weight than Class I sites. Sites whose mean polarity direction wasstatistically random with all three vectors widely divergent were designatedClass III and were rejected from the data base. The number of Class I, I! andIII sites for each stratigraphic section are given in the discussion of eachsection.DATA AND RESULTS

In this section we present the magnetic data, the magnetic polarity strati-graphy and radiometric data obtained from each of our stratigraphic sections:Kotal Kund section

This section is notable for two reasons: (1) it contains a radiometricallydated ash complex (Fig.2; G. D. Johnson et al., 1982), and (2) it spans theSiwalik sequence from the Chinji Formation to the Upper Siwaliks. We haveestablished the magnetic polarity stratigraphy of this section on the basis of114 paleomagneti c sites, 73 (64%) of which quali fy as Class I; 31 (27%) asClass II and 10 (9%) as Class III. The VGP latitudes are calculated from datather mall y d emagnet ized generally at 550C or in some cases higher tempera-tures (Opdyke et al., 1982). We show in Fig.2 the stratigraphic superpositionof the VGP latitud es for our Kotal Ku nd section. The filled circles representClass-I data while the open circles Class II data. We show also in Fig.2 amagnetic polarity zonation log which has been derived from the VGP databy making the assumptions that (1) magnetic transitions occur mid-waybetween consecutive normal and reversed data points, and (2) that in theinterval between two consecutive sites of like polarity no magnetic transitionshave occurred. We also show in Fig.2 a two-fold portrayal of the lithologiccharacter of the stratigraphic column; the white intervals representing sandsand the black interval muds and silts. The location of the Chinji--Nagri andthe Dhok Pathan--Upper Siwalik boundaries within our stratigraphic columnis based on these boundaries as located by us in the field in confirmation ofthe boundaries as defined on the maps by Pilgrim (1913), Colbert {1935)and E. R. Gee (unpublished). The Nagri--Dhok Pathan boundary in our


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24J a l a l p u r s e c t i o n

L i k e t h e K o t a l K u n d s e c t io n , t h i s s e c t i o n a ls o c o v e r s t h e S i w a l ik s e q u e n c ef r o m m i d -C h i n ji t o U p p e r S i w a li k a n d c o n t a in s t h e U p p e r S i w al ik t u f f c o m -p l e x . A n a s s e m b l a g e o f U p p e r S i w a l i k f o ss il s h a s al s o b e e n r e p o r t e d f r o mh e r e b y O p d y k e e t al. ( 1 9 7 9 ) . M a g n e t ic - p o la r i t y d i r e c ti o n s w e r e o b t a i n e d b yb o t h a .f . a n d t h e r m a l d e m a g n e t i z a t i o n t r e a t m e n t . E x c e p t f o r a f e w s p e c ia lc a se s, t h e p o l a r i t y d i r e c t i o n s o f t h e a .f . d a t a c o n c u r r e d w i t h t h e t h e r m a l d a t a .H o w e v e r , t h e V G P l a t i t u d e d a t a g i ve n h e r e a re b a s e d e x c l u s i v e ly o n t h et h e r m a l d e m a g n e t i z e d s a m p l e s ( 4 2 5 - - 4 4 0 C ) ( O p d y k e e t al. , 1 9 8 2 ) . O f t h e1 1 3 p a l e o m a g n e t i c s i te s f i n a l l y c o l l e c t e d , 8 3 ( 7 3 % ) o f t h e s e a r e C l a ss I , 1 8( 1 6 % ) C l a ss I I a n d 1 2 ( 1 0 % ) C l a ss I I I, w h i c h c o u l d n o t b e u s e d . F i g .4 s h o w st h e m a g n e t i c - p o l a ri t y d a t a f r o m t h e J a l a lp u r s e c t i o n d i s p l a y e d i n t h e s a m ef o r m a t a s t h e K o t a l K u n d d a t a ( F ig . 2 ). T h e d e s i g n a t e d C h i n j i- -N a g r i a n dD h o k P a t h a n - - U p p e r S i w a li k b o u n d a r i e s a r e t h o s e b a s ic a ll y m a p p e d b yP il gr im ( 1 9 1 3 ) , G e e ( 1 9 4 5 , 1 9 4 7 , a n d u n p u b l i sh e d ) . T h e N a g r i - - D h o k P a t h a nb o u n d a r y w a s s et b y u s o n t h e b a s is o f a c o n s p i c u o u s m u l t i- s to r i e d s a n d u n i t .N o t e t h a t l i k e t h e K o t a l K u n d s e c t io n t h e N a g r i F o r m a t i o n h e r e is a ls o d o m i -n a t e d b y a l o n g - n o r m a l m a g n e t i c - p o l a r i t y z o n e , w h i c h w e a g ai n l a b el N o( F ig . 4 ). T h e s e c t i o n a l so c o n t a i n s a n u m b e r o f r a d i o m e t r i c a l l y d a t e d t u f fs .

T h e m a g n e t i c - p o l a r i t y s t r a t ig r a p h y o f t h e U p p e r S i w a l i k p a r t o f t h is s e c t i o nh a s b e e n r e p o r t e d p r e v i o u s l y ( O p d y k e e t a l., 1 9 7 9 ) . S in c e t h e p u b l i c a t i o n o ft h a t r e p o r t , h o w e v e r , m o r e p a l e o m a g n e t i c s am p l i n g h a s a d d e d m o r e p o l a ri t yz o n e s a n d s h a r p e r d e t a il t o t h e m a g n e t i c - p o l a r i t y s t r a t ig r a p h y ( F i g . 4 ). T h eb a s i c i n t e r p r e t a t i o n o f t h e r e s u lt s , h o w e v e r , is e s s e n ti a ll y th e s a m e . W e s h o wi n F i g . 5 t h e g e o g r a p h i c d i s p o s i t i o n o f o u r d e f i n e d p o l a r i t y z o n e s a n d a s so -c i a t e d p a l e o m a g n e t i c s i t e s .C h i n j i a n d N a g r i s t r a t o t y p e s e c t i o n

A s i n d i c a t e d e a rl ie r , t h e C h in j i s t r a t o t y p e a n d t h e N a g ri s t r a t o t y p e c o m -p r i s e o n e c o n t i n u o u s s t ra t i g ra p h i c s e c t i o n s o m e 1 3 0 0 m l o n g . B e s i d e s r e p re -s e n t i n g t h e t y p e l o c a li t ie s f o r t h e s e r o c k - s tr a t ig r a p h i c u n i t s , t h is s e c t i o n a l soc o n t a i n s a n a i r- fa ll t u f f i n t h e N a g ri F o r m a t i o n w h i c h h a s b e e n d a t e d b y t h ef i s si o n - t ra c k m e t h o d a t 9 . 5 0 +- 0 . 6 3 m . y . ( G . D . J o h n s o n e t al ., 1 9 8 2 ) .

T h e s t r a t i g r a p h y a n d p a l e o m a g n e t i c d a t a a n d l o c a t i o n f o r t h is s e c t i o n a r ed e t e r m i n e d b y u s f r o m f i el d o b s e r v a ti o n s an d c o o r d i n a t e d w i t h th e b o u n d a ri es a s i n d i c a t e d o n a v a il a b le p u b l i s h e d m a p s ( C o t t e r , 1 9 3 3 ; C o l b e r t , 1 9 3 5 ) .M a g n e t i c - p o l a r i t y d i r e c t i o n a r e d e r i v e d f r o m s a m p l e s t h e r m a l l y d e m a g n e t i z e da t 6 0 6 C . O f 6 3 p a l e o m a g n e t i c s i te s 3 9 ( 6 2 % ) a r e C l a ss I, 1 9 ( 3 0 % ) C la s s I Ia n d 5 ( 8 % ) C l a ss II I. T h e m a g n e t i c - p o l a r i t y s t r a t ig r a p h y o f t h e N a g ri F o r m a -t i o n is i d e n t i c a l t o t h e p a t t e r n e s t a b l i s h e d p r e v i o u s l y in b o t h t h e K o t a l K u n ds e c t i o n a n d t h e J a l a l p u r s e c t i o n , i .e ., i t is o v e r w h e l m i n g l y c o m p o s e d o f n o r -m a l l y m a g n e t i z e d r o c k s i n t h e f o r m o f a s in g le , l o n g - n o r m a l z o n e ( F i g .6 ) .N o t e t h a t t h e r a d i o m e t r i c a l l y d a t e d s a m p l e ( 9 . 5 0 + 0 .6 3 m . y . ) is s i t u a t e d i n


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C H I N J I - N AG RI

OHOK PATHAN1200 FORMATION

IOOC " / / / / / / / / / / / / / 1 1 1 1 /FOSSI l SITE 3fl

NAGRIFORMATION800 VOLCI~t~IC TUFFL~AAAAAAAA~( ~ ( 9 5 0 1 6 3 m y)

L ~I---uJ 600 / / / / / / / / / / / / / / / / / /

400 CHINJIF O R M A T I O N

2O0' / / / / / / / / / / / / / / / / /

VGP LATIfUDE-90 +90L

R3

~ R~

& A A A A A A ~ A A ~ & ~

N~5 N2"q3R4~ N4c"q~:ZZZ R

l ~ , N5R6N

R7K A M L I A L P: 7F O R M A T I O N

F i g .6 . M a g n e t i c - p o l a r i t y s t r a t i g r a p h y o f t h e C h i n ji a n d N a g r i s t r a t o t y p e a r e as ( F i g . l ) .M a i n f o s si l l o c a l i t y ( Y a l e s i t e 3 1 1 ) i s s h o w n n e a r t o p o f N o. C l a ss I s i t e s a r e i n d i c a t e d b ys o l i d c i r c l e s , C la s s II s it e s b y o p e n c i r c le s .

(1935). The Nagri--Dhok Patha n bou nda ry is placed on our assessment ofthe highest major occurrence of multi-storied sands in the section. Magnetic-polarity directions were determined by means of both a.f. and thermal de-magnetization procedures, the results of which generally concur. The VGPlatitudes s hown in Fig.10, however, are based on the thermal demag netiz atio nresults at 606C. 116 paleomagneti c sites were collected in this section 70(60%) of which were Class I, 39 {34%) Class II and 7 (6%) Class III. It ma ybe no ted that the magnetic-polarity stratigraphy of the Nagri Formati onrepeats the results from the previously described sections, i.e., a simple, long-normal polarity zone bracketed above and below by a more complex zona-tion. The type locality for the Upper Siwalik "Tatrot zone" is represented inthis section (Fig.10) as well as a classic faunal level for the Dhok Path an zone,e.g., the " Bh and ar bone b ed" of Pilgrim (1913) and Colbert (1935).The section we show in Fig.10 is actual ly a composite, involving twosections, the T atr ot and And ar Kas, which are separated along strike by some


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2 8

) N

~ a n F o r m a t i o n~ i te 3 1 1 ) I N A G R J~ ] e n to n it e J F O R M A T I O Nn o t i o n) r m a t i o nl e o m a g ne f i c o m p l e S i re

Fig.7. Detailed location of the magnetic-polarity section for the Chinji and Nagri strata-types. Indexed magnetic-polarity zones (Fig.6) are locate d by arrows. Fossil locality 311is shown within N 0. A r adiom etri call y dated volcanic ash (be nton ite ) is locate d near thevillage of Qadirpu r.

5 kms {Fig.3). The two sections, however, share a common magnetic polarityzone, N ~ of Figs.10 and 11. N ~ has been trac ed and ide nti fie d in five inter-mediate sections between the Tatrot--Bhandar section and the Andar Kassection (McMurtry, 1980). Cont ained within N 6 is a distinctive sandstonest rat um which also serves as a stratigraph ic tracer.Because of the proximity of the Tatrot--Andar area and the Kotal Kundarea (Fig.3) and the presence of numerous fossil sites in that area, we haveat te mp ted to correlate the magnetic-pol arity stratigraphy of these two sec-tions. A step in this direction was made w ith the correlation of the Tatrot- -Bhandar and the Andar Kas sections by means of magnetic and stratigraphiccriteria (McMurtry, 1980). Similarly, we have replicated a portion of theKotal Kund magnetic stratigraphy some 14 kms away from Kotai Kund in asection called Dhala Nala (Figs.3 and 11). The magnetic polarit y stratigraphyof th e Dhala Nala section ( Fi g. ll ) is based on 25 paleomagnetic sites, 23 ofwhich are Class I and the remaining 2 are Class II. Distinctive and laterallycontinuous sandstone beds were traced along strike to correlate the DhalaNala section with bot h the Kotal Ku nd and the Tatrot-- Bhandar sections.


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3 0

alik Formation (Tpsu)In Formation (Tmsdp)~ation Trnsn)lot ion (Tmsc)~ornaqnetic Sam ple Site

F i g . 9 . D e t a i le d l o c a t i o n o f t h e m a g n e t i c - p o l a r i t y s e c t io n n e a r C h a k w a l - - B h a u n ( F i g . l ) .I n d e x e d m a g n e t i c - p o l a r i t y z o n e s a r e l o c a t e d b y a r r o w s .

z o n e , w h i c h h a s s u b s e q u e n t l y b e e n ca ll ed t h e K h a u r N o r m a l Z o n e ( T a u x e,1 9 7 9 ) . O n t h e b a si s o f f a u n a f r o m t h e K h a u r N o r m a l Z o n e , B a r n d t e t a t.( 1 9 7 8 ) h a v e c o rr e l a t e d it w i t h C h r o n 9 o r m a r i n e m a g n e t i c a n o m a l y 5 , w h o s et i m e r a n g e is e s t i m a t e d a t 8 . 6 - - 1 0 . 0 m . y . ( M a n k i n e n a n d D a l r y m p l e , 1 9 7 9 ) .T h e r a d i o m e t r i c d a t e w e h a v e o b t a i n e d f r o m t h e K h a u r N o r m a l Z o n e in t h eN a g r i s t r a t o t y p e , 9 . 5 0 + 0 . 6 3 m . y . ( F i g . 6 ), a g r e es w e l l w i t h t h e r a d i o m e t r i ca g es t h a t M c D o u g a l l e t al. ( 1 9 7 6 ) h a v e o b t a i n e d f r o m C h r o n 9 b a s a lt s inI c e l a n d a s w e l l a s t h e M a n k i n e n a n d D a l r y m p l e ( 1 9 7 9 ) a g e a s s ig n m e n t s .T a k e n t o g e t h e r , t h e f a u n a l e v i d e n c e a n d t h e r a d i o m e t r i c d a t e a r g u e s t r o n g l yt h a t t h e K h a u r N o r m a l Z o n e i n th e P o t w a r r e g io n i s c o r re l at iv e w i t h C h r o n 9 .

T h e r a d i o m e t r i c d a t e s w e ha v e o b t a i n e d f r o m t h e U p p e r S i w a li k F o r m a -t i o n a t K o t a l K u n d a n d i n t h e J a l a l p u r s e c t i o n ( G . D . J o h n s o n e t a l., 1 9 8 2 )a l so ai d o u r i n t e r p r e t a t i o n o f t h e m a g n e t i c - p o l a r i t y s t r a ti g r a p h y . T h e s e a g eso f a b o u t 2 . 5 m . y . u n i q u e l y i d e n t i f y th e C h r o n 2 - - C h r o n 3 b o u n d a r y i n t h e


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3 8

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| m i i l l i N I I I I m I m l l ~ :I ,~ 1 , ~ 1 , ~ [ , , I ,o [ ~ I ~ I ~ ' ILo BTecque,e lol ( 1 9 7 7 ) M o g n e l ic P o l o r J ly T i m e Stole L o B r e c q u e , e t o l , ( 1 9 7 7 ) M a g n e t i c P o l a r i t y T im e S c a r e

F i g . 1 5 . C o m p a r i s o n o f t h e K h a u r c o m p o s i t e m a g n e t i c - p o la r i t y st r a ti g ra p h y ( T a u x e a ndO p d y k e , 1 9 8 2 ) w i t h t h e L a B r e c q u e e t a l. ( 1 9 7 7 ) t i m e s c a l e . S l o p e is d i r e c t ly p r o p o r t i o n a lt o s e d i m e n t a t i o n r a t e ( T a b l e I ) .F i g . 1 6 . C o m p a r i s o n o f t h e T a t r o t -- B h a n d a r m a g n e t i c - p o l a r it y s t r a ti g ra p h y w i t h t h e L aB r e c q u e e t a l. ( 1 9 7 7 ) t i m e s c a le . S l o p e i s d i r e c t ly p r o p o r t i o n a l t o s e d i m e n t a t i o n r a t e( T a b l e I ) .w e r e p o r t h er e ( T a b l e I ) . T h i s c o r r e s p o n d e n c e b e t w e e n t h e r a te o f u p l i ft int h e s o u r c e a r e a a n d t h e r a te o f s e d i m e n t a c c u m u l a t i o n i m m e d i a t e l y d o w n -s t r e a m i m p l i e s t h e e x i s t e n c e o f a h i g h l y i n t e g r a t e d f l u v ia l s y s t e m . A s u p l i f to c c u r r e d i n t h e s o u r c e a r ea s, l o c a l b a s e l e v el s d o w n s t r e a m w e r e a p p a r e n t l yr a is e d in r e s p o n s e . T h e H i m a l a y a - - S i w a l i k f lu v i a l s y s t e m i n t h e p a s t 1 5 m . y .t h u s a p p e a r s t o h a v e b e e n w e l l a d j u s t e d w i t h r e g a r d t o o v e r a l l e r o s i o n r a t e ,l o a d t r a n s p o r t a n d s e d i m e n t d e p o s i t i o n .Assessm ent o f paleomagnet ic sampling

E s t a b l i s h i n g a l o c a l m a g n e t i c - p o l a r i t y s t r a ti g r a p h y f r o m a l im i t e d s e t o fd i s c r e te , p a l e o m a g n e t i c d a t a p o i n t s , i s e s s e n t i a ll y a s t a ti s ti c a l p r o b l e m , l a rg e lyb e c a u s e o f t h e in f o r m a t i o n g a p s i n h e r e n t in a n y d i sc r e te s a m p l e n e t w o r k a n dt h e i n f e r e n c e s a s s o c i a t ed w i t h t h e g a p s ( M c G e e a n d J o h n s o n , 1 9 8 0 ) . W i t hp r e s e n t t h e o r i e s i t is p o s s i b l e t o r e t r o s p e c t i v e l y t e s t t h e a d e q u a c y o f a g i v e ns a m p l i n g p r o g r a m o n a s t a ti st ic a l b a s is if ( 1 ) t h e t i m e i n t e rv a l b e i n g s a m p l e dis k n o w n , ( 2 ) t h e n u m b e r o f p a l e o m a g n e t i c s it e s in t h e t i m e in t er v a l isk n o w n , a n d (3 ) t h e m o d e o f d i s tr i b u t io n o f th e s a m p l e s i t es i s k n o w n . O u rK o t a l K u n d , K h a u r , T a t r o t - - A n d a r a n d J a la l p u r s e c t i o n s m e e t th e s e cr it er ia ,


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palaeoecology (stratigraphy of siwalik)

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