EARTH AND PLANETARY SCIENCE LETTERS 16 (1972) 189-194. NORTH-HOLLAND PUBLISHING COMPANY
THE PALEOMAGNETISM OF THE SALT PSEUDOMORPH BEDS OF MIDDLE
CAMBRIAN AGE FROM THE SALT RANGE, WEST PAKISTAN
H. W E N S I N K
Geological Institute. Oude Gracht 320. Utrecht, The Netherlands
Received 1 April 1972
Revised version received 10 July 1972
Oriented cores for a paleomagnetic investigation were collected from ten sites in the sedimentary redbeds of the
Salt Pseudomorph Beds of Middle Cambrian age m the Salt Range near Khcwra. All samples were subjected to progressive, thermal demagnetization procedures which revealed the characteristic direction of magnetization.
The material of ten sites with a total number of 71 specimens was included in the analysis, giving an overall mean
direction with D = 215.9 ° , I = +42.4 °, C,9s= 13.7 '~. In the ultimate analysis the material of six sites was included, because four site~ shox~ fairly strong deviations from the mean direction. The virtual magnetic pole position is located
at 26.6 ° S, 33.5 ° F, with A9s = 5.1 °. A Phanerozoic polar wander curve is given for lndiaq'akistan. The result presented here supports the view that in Gondwana reconstructions the west coast of-the Indian subcontinent is best
fitted alongside the northeast coast of Africa.
1. Introduction
In the Salt R a n g e o f West Pakistan, w h e r e e x c e l l e n t
o u t c r o p s are available o f s e d i m e n t s o f C a m b r i a n and
P e r m o - C a r b o n i f e r o u s age, o r i e n t e d samples were collected from the Salt P s e u d o m o r p h Beds o f Middle
C a m b r i a n age for p a l e o m a g n e t i c research, In this area
M c E l h i n n y [ 11 c o l l e c t e d m a t e r i a l f r o m the Purple
S a n d s t o n e s o f L o w e r C a m b r i a n age w h i c h revealed
reliable c h a r a c t e r i s t i c d i r e c t i o n s o f m a g n e t i z a t i o n .
~',~--~--, ~
,#
a
I,
.
',.s
.
p
~
I
The Salt R a n g e is s i t u a t e d in West P a k i s t a n b e t w e e n
the rivers I n d u s to the west a n d J h e l u m to the east
(fig. 1). T h e range is little m o r e t h a n the scarped
s o u t h e r n l y m a r g i n o f the P o t w a r plateau w h e r e sedim e n t s of m a i n l y T e r t i a r y age are m e t with. T h e r e are
a n u u t b e r or" deep r a v i n e s / ' a c i n g t o w a r d s the s o u t h ,
w h i c h offer e x c e l l e n t o u t c r o p s .
T h e basal series, the Saline Series, w h i c h has an
U p p e r P r e c a m b r i a n to L o w e r C a m b r i a n age, consists
o f g y p s e o u s lnarls, marls, a n d salt d e p o s i t s ; the minim u m t h i c k n e s s is 4 5 0 m. T h e Saline Series is overlain
.
.
.
13Tr s ~, >
72=E
2. G e o l o g y of the area
O RAWALPIND)
g,,~
,f
/f
t
75°E
Fig. 1. Geological map of tile Salt Range, West Pakistan, with
sampling locality.
by the J h e l u m Series of L o w e r to Middle C a m b r i a n
age w i t h a thickness up to 3 6 0 m. T h e J h e l u m Series
is s u b d i v i d e d into four stages (fig. 2): the Purple
S a n d s t o n e , the N e o b o l u s Shales, the M a g n e s i u m
S a n d s t o n e , a n d the Salt P s e u d o m o r p l t Beds successively
[21.
T h e Purple S a n d s t o n e consists o f fine-grained, mar o o n to reddish, j o i n t e d s a n d s t o n e s with t h i n b a n d s
o f shale. T h e unfossiliferous s e d i m e n t s have s o m e
ripple-marks. T h e N e o b o l u s Shales have d a r k shales
H. h'ensink, Paleomagnctisnt o.[ salt pset~domorpl beds .l)om the Salt Range. It'. Pakistan
190
3. Field sampling
Talchlr BoulderBeds
o{--..---- ~-__, Salt PseudomorphBeds
__ --~-80m
I~[
l
/
/
O[lllllrl
II
I
l/
--II
~.~1
i
/
i
/[ /l/l/]
/
I
/
/
/
I
1
,"
I
I
I
/
I
[
1
/
i
/
I
I
I
J
MogneslumS a n d s t o n e
BOrn
Neobolus Shales
25-50m
Purple
Sandstone
Ahmg the road from Khewra to the north there are
excellent exposures of the Salt Pseudomorph Beds. lit
an ahnost undisturbed sequence of about 15 m thickness, immediately overlain by the Talchir Boulder Bed,
samples were collected for paleonragnetic research.
Cores were sampled with the aid of a portable diamond
drill: at each site 8 to 10 independently oriented cores
were drilled. In fig. 5 the sites are indicated at their
respective elevations in the section.
80-150m
•
C'.
V
--
4. Laboratory studies
__ I
Saline
Series
[ is. 2. S t r a t i g r a p l n c a l c o l u n m a t tilt.' rock:, o ( ( ' a m b r i a n age
h a m the S a h R a n g e .
associated with sandy and calcareous beds. Fossils are
l\mnd, including trilobites of the genus Rcdliz'hia. The
Magnesium Sandstone is a creant-coloured or white
massive sandy, dolomite with some intercalated clay
beds. At this stage fossils are met with as well.
Tire Salt Pseudomorph Beds consist of shales with
intercalated thin-bedded flaggy sandstones. The flags
are sometinles sun-cracked. Tile shales are characterized by their deeply red colour and by tire numerous
pseudomorph casts of salt crystals which cover the
bedding surface. The origin of rite crystals lnUSt be due
to the evaporation of salt water and the subsequent
covering of the crystals by, sediment. The unl\~ssiliferous beds must have been laid down under arid conditions.
The exact age of the Jhelum Series was discussed
by several authors. On account of the assemblage at
fossils Schindewolf and Seilacher [3] place the units
in the Lower Cambrian: Opik [4], on the other band,
has shown that the occttrrence of the trilobite species
Redlk'hia noetlblgi points to a late early, as well as
early Middle Cambrian age.
The Upper Carboniferous Talchir Boulder Bed overlies the Cambrian sediments. In the Salt Range the
Boulder Bed transgresses westwards over ever older
stages of the Jhelum Series.
Apart from southward directed overthrusting at
various places at the margm of the range, also dome
structures can be observed, that are due to tire local
thick deveh~pment of the salt of the Saline Series.
The material collected was treated at the Paleomagnetic Laboratory of the Utrecht State University. The
cores with a diameter of about 25 mm were sawn into
cylinders of 22 mm length.
The measurentelltS for the detectioi] of the intensities and directions of the natural retnanent mag0etization were carried Otlt o11 astatic magnetotneters. The
initial natural remanent magnetization (n.r.m.) nearly
always is, however, composite. For the elimination of
the secondary conlponent( s} of magnetization, the
specimens were subjected to progressive thermal demagnetization which was carried out in a furnace, positioned
I.O
M/Mo 0.6°8
~
~
0.4
•
0.2
0
I
200
TemperatureL°C)
i
400
I
600
l i~. 3. C u r ; ' c s silo,,,, in F tile n o r m a l i z e d i n t e n s i t i e s o f n a t u r a l
r o m a n c n t m a g n e t i z a t i o n f r o n l specimen,, o f ttle Salt P s e u d o m o r p h Beds d u r i n g t h e r m a l t r e a t m e r t t .
H. h'eusink, Paleomagnetism o f salt pseudomorph heds j?om the Salt Range, W. Pakistan
191
in a set of Helmholtz coils• A trlinimum of ten successive steps of heating was applied: after each step the
\
specimens were relneasured
The decrease in the intensity of the n.r.m, during
themml treatment can be presented in a diagram,
where the tmrmalized intensities, i.e. the ratio of the
remaining to the initial intensity, are plotted to tire
applied temperatures. In fig. 3 the themral decay
curves are given ['or three specimens front three different sites. These curves are strikingly consistent with
slight increases in the intensity at about 200°C and
at about 530°C. An increase in the intensity can be
attributed to the complete demagnetization of one of
tire components of magnetization. Above about
580°C tire intensities drop rapidly [6]: this is the
characteristic magnetization of which the direction
remains unchanged. It is fairly certain that haematite
is an important carrier of the n.r.m, of these redbeds.
One can inter from fig. 3 that the n.r.m, is composite
and consists of a characteristic component and two
secondary components of magnetization.
5. Paleomagnetic results
The characteristic directions of magnetization of
the specimens of three sites are plotted in individual
equal area projections(fig. 4): the fourth projection,
below to the right, shows the mean directions of the
sites as well as the overall site-mean direction. The
latter projection indicates that two sites have northseeking directions upwards (negative inclinations) attd
eight sites north-seeking directions downwards (positive inclinations). Moreover, it appears that four sites,
one with negative and three with positive inclinations,
have fairly strongly deviating characteristic directions
of tnagnetization with respect to the site-mean direction.
It can be seen from fig. 5 that the upper two sites
have negative inclinations. Tire sites with deviating
directions of magnetization are the sites E, G, I, and
K, The decimations and inclinations of the successive
sites at the polarity change in fig. 5 seem to indicate
a gradual transition in direction. However, polarity
transitions generally occur within a short interval of
about 50 000 yr: in our section the distance between
successive sites is too large, unless an extremely low
rate of sedimentation has occurred.
~
*i DTE H
'
9TE if/
SITE E
t
t
""
":I
-.%
I
J
['ig. 4. Equal-area p r o j e c t i o n s w i t h the characterD, tic d i r e c t i o n s
o f m a g n e t i z a t i o n after t e c t o n i c c o r r e c t i o n s o I the s p e c i m e n s
of three i n d i v i d u a l sites: site tt and site E have positive and
negative i n c l i n a t i o n s r e s p e c t i v e l y ; site K with positive inclinat i o n s has a m e a n value d e v i a t i n g l r o m the overall mean. The
p r o j e c t i o n b e l o w to the right s h o w s the m e a n charamerist~c
d i r e c t i o n s o f m a g n e t i z a t i o n o t all t e n sites and also the sitemean d i r e c t i o n p r o v i d e d w i t h its 95~; circle o f c o n f i d e n c e .
Full dots and open circles denote north-seckin~ d i r e c t i o n s
p o i n t i n F d o w n w a r d s and upwards respectively. ('ross is the
local d i r e c t i o n o f the axial geomagnetic d i p o l e field.
0
"cDo-c~,~
~
TALCHIR
BOULDER
BEDS
¢n
~,
INCL;NATION
r- -9o" -60• -~o- o° ÷30" °60" .90"
--4
200
Q
SqTES
--
I
Im
4OO C
I°
\
o
',~
,:~
L
./
6-
~oleo"
DECLINATION
I,
A
/'!l
z70-
Fig. 5. Diagram showing the values of the declinations and
inclinations or" the characteristic directions of magnetization
of ten successive sites in a Salt Pseudomorph Beds section.
192
H. Wensink, Paleomagnetism oJ'salt pseudomorph beds front the Salt Range, It( Pakistan
Table 1
Site mean dlrecnons at magnetization after themml cleaning with corresponding virtual pole positions*. The locality' at" the sites
is 32.66~N tat.. 72.97°F long.
Sites
[
E
G
I1
A
g
C
1)
1
K
All
:V
Mean direction of magnetization
7
8
8
6
8
8
6
8
7
6
10"*
Pole pt~sition
D
(deg)
I
(deg~
k
a , .5
~deg)
69.1
3%8
173.7
211).6
220.6
224.1
215.1
212.7
265.1
20t.5
215.9
-45.6
--24.9
+ 19.4
+ 37.6
+ 40.1
+ 33.4
+ 37.5
+ 39.9
+ 68.9
+ 57.1
+ 42.4
19.3
95.5
83.6
168.1
17.2
20.6
18.7
20.7
298. I
57.7
13.4
14.1
5.7
6.1
5.2
13.7
12.5
15.9
I 2.5
3.5
8.9
13.7
Lat. S
ldeg~
1.2
30.5
46.9
28.9
22.3
23.9
26.7
26.5
22.5
16.8
23.3
Long. E
ldegl
6p
~deg~
6m
[deg)
16.6
26.6
82.1
40.1
32.6
26.7
36.0
39.2
31.8
55.3
37.5
! 1.4
3.3
3.3
3.6
9.9
8.1
11.0
9.0
5.1
9.4
10.4
17.9
6.1
6.4
6.1
16.6
14.2
18.7
15.0
5.9
12.9
16.8
The locations of the bites are indicated on fig. 6; N is the number of samples: D and 1 are the declination and inclination o l the
magnetizatmn direction; k is the precision parameter [ 171; o,9,~ i~ the ,,emi-angle of the cone of 95(; confidence:,Sp and am are
the semi-axe¢, of the oval of 95% confidence for the pole position of the site.
** Number of sites included m the analysis.
*
Table 2
Pole positions calculated by combining positions of the sites "~.
N
K
.4,)5
(deg)
Latitude S
{deg)
Longitude E
ldegt
10
6 *~
1l
176
15.0
5. I
21.2
26.6
37.2
33.5
* N is the number of site poles included m the analysis: K is the precision of the site poles:Ags is the semi-angle of the cone of
95"; confidence for the mean pole position.
** Selected poles ~see textJ.
The deviations in d i r e c t i o n o f m a g n e t i z a t i o n o f the
sites E, G, 1, attd K are too large to be e x p l a i n e d in
t e r m s o f secular variation o f g e o m a g n e t i c field. But,
tile d i r e c t i o n s tnust have a p r i m a r y cause as well, because the sampled section shows n o inconsistencies.
Tile strongly d e v i a t i n g c h a r a c t e r i s t i c d i r e c t i o n s can
be due to s h o r t e x c u r s i o n s o f the g e o m a g n e t i c field,
such as was described by W a t s o n [7].
T h e site-mean d i r e c t i o n s after t h e r m a l cleaning
w i t h their c o r r e s p o n d i n g pole p o s i t i o n s are listed in
table 1. T h e site-mean pole p o s i t i o n is given in table
2, w h e r e the p a l e o m a g n e t i c pole p o s i t i o n c o m p u t e d
from the poles o f six selected sites is listed too. T h e
latter pole is c o n s i d e r e d to be r e p r e s e n t a t i v e for the
Salt P s e u d o u t o r p h Beds.
6. Discussion
Tile results o f a p a l e o m a g n e t i c s t u d y o n tile L o w e r
C a t n b r i a n Purple S a n d s t o u e o f tire Salt R a n g e in
P a k i s t a n [1] are in very good a g r e e m e n t w i t h those
p r e s e n t e d in this paper. In fig. 6 the polar w a n d e r
curve is d r a w n for tile India-Pakistan s u b c o n t i n e n t
d u r i n g the P h a n e r o z o i c . T h e selected virtual magnetic pole p o s i t i o n s o b t a i n e d from P h a n e r o z o i c rocks
o f India a n d Pakistan, w h i c h were used in fig. 6, are
listed in table 3. T h e polar w a n d e r i n g curve is very
similar to t h a t o f McDougall a n d M c E I h i n n y ( 1 9 7 0 ) .
A few p o s i t i o n s o f t e n used have b e e n o m i t t e d : the
pole p o s i t i o n a c q u i r e d frt)m K a m t h i beds of U p p e r
P e r m i a n age [181, w h i c h c o n s i d e r a b l y deviates from
11. Wensink, Paleomagnetism of salt pseudomorph beds from the Salt Range, W. Pakistan
193
beds [15] : the ages, p r e s e n t e d in table 3, are n o t irre-
",o ~'°,~
¢.
G"
vocable.
T h e q u e s t i o n m a y be p o s e d w h e t h e r it is w a r r a n t e d
c" /
to use i n d i s c r i m i n a t e l y the p a l e o m a g n e t i c d a t a f r o m
India a n d P a k i s t a n in the same c o n f i g u r a t i o n . It is n o t
c e r t a i n t h a t since the early P h a n e r o z o i c the Salt Range
has h a d the same relative p o s i t i o n w i t h respect to the
I n d i a n p a r t o f the s u b c o n t i n e n t .
P a l e o m a g n e t i c studies on r o c k s o f a particular age
w h i c h are f o u n d b o t h in I n d i a a n d in the Salt Range
m a y resolve this p r o b l e m . In I n d i a Paleozoic rocks
older t h a n U p p e r C a r b o n i f e r o u s in age are virtually
a b s e n t . In the Salt Range the T a l c h i r B o u l d e r Bed is
overlain b y reddish a n d p u r p l i s h s a n d s t o n e s o f the
S p e c k l e d S a n d s t o n e Stage w h i c h has an U p p e r C a r b o n iferous age; p a l e o m a g n e t i c research on these rocks
are in progress. Here, the covering s e d i m e n t s m a i n l y
are m a r i n e l i m e s t o n e s o f P e r m i a n age.
2-',", ))
f
R e c e n t l y it was p o i n t e d o u t [19] t h a t at the recons t r u c t i o n s o f G o n d w a n a l a n d for the L o w e r Paleozoic
the I n d i a - P a k i s t a n s u b c o n t i n e n t s h o u l d be placed
n e a r East Africa r a t h e r t h a n alongside Western
Australia. T h e p a l e o m a g n e t i c results p r e s e n t e d in this
p a p e r strongly s u p p o r t this view. This a r r a n g e m e n t
is n o t fully in a g r e e m e n t with the c o m p u t e r fit o f the
s o u t h e r n c o n t i n e n t s p r o p o s e d b y S m i t h a n d Hallam
[ 1, 20]. T h e U p p e r Paleozoic p a l e o m a g n e t i c data o f
the s u b c o n t i n e n t d o n o t s u p p o r t a p o s i t i o n near East
Africa [9]. More research is n e e d e d to c o n c l u d e
w h e t h e r this d i s c r e p a n c y is significant.
Fig. 6. Map showing the Phanerozoic polar wander curve for
the India-Pakistan subcontinent. The poles are numbered as
in table 3. The positions L, M, and U near pole no. 10 are the
pole positions from the respective Lower, Middle, and Upper
Deccan traps.
K a m t h i pole, no. 4 in table 3, is n o t listed, b e c a u s e ,
in o u r o p i n i o n , the s e c o n d a r y m a g n e t i z a t i o n s were
n o t c o m p l e t e l y r e m o v e d ; the p o o r c o r r e l a t i o n can
also be due to a d i f f e r e n c e in time. T h e r e is some
c o n t r o v e r s y o n the ages o f a n u m b e r o f G o n d w a n a
Table 3
Phanerozoic paleomagnetic results from ln clia and Pakistan.
Pole
Formation
Age
no.
1
2
3
4
5
6
7
8
9
10
1l
Purple sandstone
Salt pseudomorph
beds
Talchir shales
Kamthi redbeds
Mangli redbeds
Pachmarhi sandstones
Sylhet traps
Rajmahal traps
Tirupati sandstones
Deccan traps
Siwalik redbeds
Site locality
Pole position
Lat. N
Long. E
Lat.
Long.
A9s
Ref.
Lower Cambrian
Middle Cambrian
32.7 °
32.7 °
73.0 °
73.0 °
28°S
27°S
32 °E
33°E
I 1°
5°
79.0 °
79.0 °
79.0 °
78.4 °
91.4 °
87.4 °
31°N
22°N
7° N
10°S
16°S
7°S
134°E
130°E
124 ° E
129°E
120°E
117°E
3°
10°
9°
13°
8°
7°
[ 1]
this
paper
[8]
[9]
[9 ]
[9]
[101
[ l 1,15]
Upper Carbonif.
Upper Permian
Lower Triassic
Upper Triassic
Jurassic-Cret.?
Middle Cret.
105-100 my
Upper Cretaceous
Lower Eocene 6 0 m y
Miocene
21.4 °
20.0 °
20.5 °
22.4 °
25.3 °
24.6 °
16.4 °
16 ° - 2 5 °
32,8 °
81.1 °
72 ° 79"
73.0 °
28°S
34°S
72°S
107°E
101°E
69°E
5°
4°
-
[12]
[13, 16]
[141
194
H. ll'e#ts'i,tk, Paleomag,tetism oJ'xalt pseudomorph heals Jrom the Salt Ra#~ge. W. Pakistan
Acknowledgements
I a m g r a t e f u l to P r o f e s s o r V e l d k a m p for c r i t i c a l l y
r e a d i n g the m a n u s c r i p t . T h a n k s are also d u e to Dr.
A.A. B u t t and Mr. C.T. K l o o t w i j k for t h e i r a s s i s t a n c e
in the field.
This w o r k was u n d e r t a k e n w i t h the s u p p o r t o f the
N e t h e r l a n d s O r g a n i z a t i o n for Pure S c i e n t i f i c R e s e a r c h
( Z . W . O . ) . This s u p p o r t is g r a t e f u l l y a c k n o w l e d g e d .
References
[ I ] M.\V. McFlhmny, Paleomagnctl~m o l the Cambrian
Purple Sandstone t'ro,n the Sail Range, West Pakistan,
I arth. Planet. Sci. Letters 8 ~19701 149.
[2] I(. Pascoe, A manual of the geology of hrdia and Burma,
vol. II 11959 I, Government o f h:dia Press, Calcutta,
1345.
[3] O.H. Sehindex~,oh and A. Seilacher, Beitrage zur Kennmis
tics Kanlbrituns in der Salt Range (Pakistani. Akad.
Wi,,s., Lit. (MainzJ: Abh. Math.-naturvc. KI. I0 (19551
190p.
[4] 4.A. Opik, The Cambrian tribolite Redhchia: organisatlon and geneiic concept. Austral. Bur. Min. Res., Geol.,
Geoph. Bull., 42 119581 38.
[5] .I.D.A. Zijderveld, A.C. demagnetization of rocks, in:
D.W. ('ollinson et al. I Fditors), Methods in Paleomagnetism.
IL-lsevler, Amsterdam t I19671 254.
[6] K.M. Storetvedt, Ttmrmal analysis o f the natural remanent magnetization of some Upper Silurian red sandstones in the Oslo region. Iectonophysics, 5 (19681 413.
[7] N.D. Watkms. Non-dipole behaviour during an Upper
Miocene geonlagnetJc polarity transition in Oregon,
Geoph_vs. J. Roy. astr. Soc., I 7 ( 19691 12 I.
[8] 11. \\"en,.ink and C.T. Kloot~ ijk, Tile Palaeonlagnetisnr of
tile Talehir Series of the Lower Gondwana System, Central
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