We report here the occurrence of an aborted reversal (geomagnetic excursion) in the Late Pleistocene sediments of Pinjor Dun near Chandigarh, NW Himalaya. The event discovered at ~697.5 cm level from the base of Kiratpur section corresponds to the OSL date of 40±5 Ka coinciding with the Laschamp excursion and palaeointensity minima elsewhere. The Pinjor Dun sediments are deposited at a high rate of sedimentation that enables quite enlarged records of remanent geomagnetic field, hence suitable for further high resolution study of the excursion (under progress) to extend its utility as a stratigraphic marker in the Quaternary sediments at the foothills of the Himalaya

Bagati, T. N.

Bloemendal, J.

Kumar, Rohtash

Sangode, S. J.

Suresh, N.

Thakur, V. C.

English

Publications of the IAS Fellows

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CURRENT SCIENCE, VOL. 82, NO. 2, 25 JANUARY 2002 210
#For correspondence. (e-mail: sangode@rediffmail.com) 
Discovery of an aborted reversal 
(geomagnetic excursion) in the Late 
Pleistocene sediments of Pinjor Dun, 
NW Himalaya 
S. J. Sangode†,#, N. Suresh†, T. N. Bagati†, 
J. Bloemendal*, Rohtash Kumar† and 
V. C. Thakur† 
†Wadia Institute of Himalayan Geology, 33, G. M. S. Road, 
Dehradun 248 001, India 
*Environmental Magnetic Laboratory, Department of Geography, 
University of Liverpool, Liverpool, L69 7ZT, UK 
We report here the occurrence of an aborted rever-
sal (geomagnetic excursion) in the Late Pleistocene 
sediments of Pinjor Dun near Chandigarh, NW Hi-
malaya. The event discovered at ~ 697.5 cm level 
from the base of Kiratpur section corresponds to the 
OSL date of 40 ± 5 Ka coinciding with the Laschamp 
excursion1 and palaeointensity minima2 elsewhere. 
The Pinjor Dun sediments are deposited at a high 
rate of sedimentation that enables quite enlarged 
records of remanent geomagnetic field, hence suit-
able for further high resolution study of the excur-
sion (under progress) to extend its utility as a 
stratigraphic marker in the Quaternary sediments at 
the foothills of the Himalaya. 
GEOMAGNETIC excursions are the records of departure 
of the earth’s magnetic field from its usual near-axial 
configuration for brief periods without establishing a 
reversal3. Such excursions are well established for the 
Brunhes Normal polarity event (< 0.78 Ma) that contin-
ues to the present geomagnetic field (see Jacobs1 for 
review). Excursions have been reported in lava flows, 
marine sediments and lake sediments of various ages in 
different parts of the world1,4. Previously, Opdyke5 dis-
covered the 40 Ka Laschamp excursion in the marine 
cores from the Indian Ocean. Kotlia et al.6 reported an 
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CURRENT SCIENCE, VOL. 82, NO. 2, 25 JANUARY 2002 211 
excursion of 26–28 Ka (Mono Lake event) from Bhim-
tal lake in Kumaun Himalaya. We report here an excur-
sion from the fine-grained facies (silt–mudstone) of the 
fluvial sediments of Pinjor Dun in NW Himalaya.  
 Pinjor Dun sediments are deposited by high-energy 
fluvial and fluvio-lacustrine conditions in a longitudi al 
basin (or valley) created by the latest orogenic folding 
of the frontal Himalaya7–9. Similar basins occur laterally 
in various parts of the Outer Himalaya, explained as 
Duns by Wadia10 (e.g. Dehra Dun, Kothri Dun, Patli 
Dun, etc.). The Pinjor Dun basin is mainly filled by 
several southwardly-trending alluvial fans controlled by 
the piedmont rivers from the higher rang s at the north. 
The alluvial fan geometry created a proximal t  distal 
grain-size variation and rapid lateral lithogenic changes, 
making it difficult to correlate different exposed sec-
tions in this basin as well as the rest of the Quaternary 
basins in the foothills. Magnetic polarity being inde-
pendent of such facies variations, we selected a silt–
mud dominant section near Kiratpur (Figure 1) initially 
to reconstruct the magnetic polarity stratigraphy. 
 Ongoing incision by the rivers flowing across the 
long axis of Pinjor Dun basin has exposed several e-
carpments with their base level around 40–60 Ka and 
upper part around 20–25 Ka through a thickness of 20–
35 m that suggests a very high sedimentation rate of the 
order 100 to 150 cm/Ka (the average rate of sedimenta-
tion in the Siwalik basin is around 45 cm/Ka)11. Such a 
high rate of sedimentation is quite conducive to pre-
serve the enlarged records of remanent mag tic events.  
 
 
 
Figure 1. Geological map of the study area after Karunakaran and 
Ranga Rao22. The studied section is located at Kiratpur and the Pinjor 
Dun basin extends up to Pinjaur. Several tributaries from NE meet 
Sirsa Nadi to expose many such sections like Kiratpur. 
Moreover the grain-size variants from silt to mudstone 
are quite suitable for ideal depositional remanent mag-
netization (DRM) due to abundance of the grains falling 
in stable single domain (SSD) range12. W  sampled a 
35 m thick incised escarpment along the Nangal Hydel 
Canal near Kiratpur in the Ropar district; Punjab for the 
mag etic analysis. The details on sediment lithofacies, 
grain-size analysis and luminescence dating will be 
published elsewhere.  
 We collected 7 oriented block samples (measuring 
approximately 40 cm ´  20 cm ´  30 cm) judiciously 
placed near the OSL dates of 40± 5Ka and the top (ex-
pected 24 ± 5 Ka) in the Kiratpur section envisaged at 
the globally reported excursion events of Laschamp 
(~ 40 Ka) and Mono Lake (25 Ka). The oriented block 
samples were cut into vertical and horizontal sections 
using a hacksaw to get 2.5 cm cubes. The cubes were 
cleaned using a blower to remove the dust and hacksaw 
contaminations. Since the sediments are soft and fri-
able, a layer of non-magnetic resin was applied for dust-
proof and secure handling during the demagnetization 
process. A minimum 20 cubes were obtained from each 
s mple block for palaeomagnetic and rock magnetic 
analyses. Separate un-oriented bulk samples were col-
lected at 38 sites in the studied section using 10 ml non-
magnetic (styrene) pots at a mean sampling interval of 
75 cm, to study the change in susceptibility with litho-
facies and the rock magnetism of representative sam-
ples.  
 The natural remanence was analysed at the laboratory 
in the Wadia Institute of Himalayan Geology usin  
Digital Spinner Magnetometer (DSM-2) and thermal 
demagnetizer (TSD-2) of Schonstedt Instruments, USA 
and alternating field demagnetizer (AFD) of Molspin, 
UK. Since there is no ideal intensity decay using AFD 
due to insufficient field available (100 mT) for the 
complete spectrum of demagnetization, the results were 
discarded from further interpretation and only the de-
tailed thermal demagnetization (TSD) up to 700°C used 
successfully. Magnetic susceptibility measurements 
were made after each step of thermal demagnetization 
to monitor the change in susceptibility with tempera-
ture. Bulk magnetic susceptibility for rock magnetism 
was calculated by average of six directions of the cubi-
cal specimens each at low (0.47 kHz) and high 
(4.7 kHz) frequencies of applied field. More detailed 
rock magnetic analysis (remanent hysteresis properties) 
on the representative samples was conducted at the En-
vironmental Magnetic Laboratory (EML) of University 
of Liverpool, UK to determine the magnetic mineralogy 
and granulometry. XARM, a parameter sensitive to the 
abundance of SD magnetite was measured at EML using 
the DTech ARM equipment. An isothermal remanent 
magnetization was imparted up to a forward field of 
4000 mT and back-field of 500 mT to determine the 
saturation remanence (SIRM) and remanence coercivity 
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CURRENT SCIENCE, VOL. 82, NO. 2, 25 JANUARY 2002 212
 
Figure 2. Rock magnetic properties of the representative samples from the studied section. a, Commonly 
used environmental magnetic parameters13; and b, Result of stepwise acquisition of isothermal remanent mag-
netization in forward and back-field directions to find the saturation levels of the bulk natural sample. 
 
 
(B0Cr) and to calculate the ratios SIRM/Xlf and Soft%. 
Hard remanent magnetization (HIRM in mAm2/kg) was 
calculated to depict the total concentration of rema-
nence carrying canted antiferromagnetic hematites13 and 
was derived using the vibrating sample magnetometer 
(Molspin-VSM). 
 The mean mass specific susceptibility (Xlf) for the 38 
bulk samples is 10 ´  10–8 m3/kg (minimum = 3 and 
maximum = 35), with the mean coefficient of frequency 
dependence (Xfd) of 4.8%. It is at the lower side than 
nearby records of (i) loess in China14, (i) lake sedi-
ments in Ladakh15 and Kumaun6, (iii) marine sediments 
of Bengal fan16, but quite comparable to the overbank 
deposits of Siwaliks11,17 (the bedrock for Dun sedi-
ments). The mean XARM for the representative samples 
is 150 ´  10–8 m3/kg and suggests an abundance of single 
domain (SD) grains, that results in preservation of sta-
ble remanent magnetization. Figure 2 a d picts the in-
terrelation of studied rock magnetic properties of 
representative samples. A very good correlation 
amongst Xlf, XARM, Xfd and Soft% and their inverse re-
lation to the HIRM and SIRM/Xlf indicate that the peaks 
in magnetic susceptibility are expressed by ferromag-
netic assemblage, whereas the drop may be inferred as 
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CURRENT SCIENCE, VOL. 82, NO. 2, 25 JANUARY 2002 213 
the haematite reach assemblage. The XARM and Xfd val-
ues suggest tha  the ferrimagnetic component mainly 
comprises SD magnetite, whereas BoCr and HIRM indi-
cate that the antiferromagnetic component is of haema-
titic origin.  
 The remanence hysteresis derived from stepwise iso-
thermal remanent magnetizations up to a forward field 
of 4000 mT and back-field of 300 to 500 mT is plotted 
in the Figure 2 b. The plots for BGK –3, –17, –18, –24 
and –27 infer that the complete saturation is n t ac-
quired even by the 4000 mT field, although about 70% 
of the field is acquired below 700 mT suggesting an 
admixture of the ferri- and antiferromagnetic minerals 
with predominant magnetization of the ferrimagnetic 
minerals. However, BGK 35 indicates an overall domi-
nance of the ferrimagnetic component. Figure 3 de-
scribes the magnetic susceptibility and its relation to 
different lithogenic factors in the studied section. There 
is no close correlation amongst the curves, however the 
magnetic susceptibili y appears to be controlled by silt 
content, suggesting that the SSD grains are quite abun-
dant in siltstones than any other lithotype. A peak in Xlf 
at ~ 970 cm coincides with that of organic carbon and 
inversely to the sand content. The Xlf is controlled by 
SD magnetite that favours restricted climate conditions 
and is supported by the preservation of organic matter 
with relatively low detrital influx. Another peak in Xlf 
beginning at 2950 cm too supports similar conditions. 
The magnetic susceptibility variation from 470 cm 
to 2950 cm is restricted to a window 3 to 15  
(´  10–8 m3/kg), suggesting fairly constant sediment  
 
 
 
Figure 3. Analytical description of the studied section of Kiratpur 
(38 bulk samples) analysed to get the param ters: (1), Lithocolumn 
using the field observations; (2), Low-frequency magnetic suscepti-
bility (Xlf, 10–8 m3/kg); (3), Frequency dependency of susceptibility 
(Xfd%); (4), Total organic carbon (%) using weight loss on combus-
tion at 450°C; (5), Inorganic carbon using the weight loss at 1100°C 
minus total organic carbon; (6)–(8), Sand, silt and clay percentage 
using conventional methods; (9) Location of the palaeomagnetic sites 
and luminescence dating sample. 
 
Figure 4. Decay in the intensity of magnetic moments normalized 
to the intensity at room temperature of the respective samples. X-
axis: temperature increments (°C), Y-axis: Normalized intensity of 
magnetic moments (%).
 
input conditions; it increases suddenly after 3000 cm till 
the top of the escarpment. More detail d work is under 
progress to find whether this peak in magnetic suscepti-
bility could be correlated with the top parts of the other 
sections in this basin with the reference of the excursion
event at the base.  
 Thermal demagnetization was conducted at intervals
of 100°C up to 700°C for all the studied samples. The 
specimens showing change in susceptibility with tem-
perature are discarded from the analysis. The intensity 
decay curves (Figure 4) show two major drops, one at 
300°C and the other at 600°C, common to all. The vec-
tor end-point plots (Zijderveldt diagrams, Figure 5) 
have shown uni-component system for most of the 
specimens and 1–3 secondary components for a consid-
erable number of specim ns. BGK M1/5 indicates the 
normal polarity trajectory with a viscous component 
cleared below 100°C and ferrimagnetic (magnet-
ite/maghemite) component removed at blocking tem-
perature below 600°C. A secondary component with 
blocking temperature at < 300°C was removed for most 
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CURRENT SCIENCE, VOL. 82, NO. 2, 25 JANUARY 2002 214
 
Figure 5. Vector end-point diagrams (Zijdervedt plots)12 of the representative samples from each site after stepwise 
thermal demagnetization at steps: 1, Room temperature; 2, 100°C; 3, 200°C; 4, 300°C; 5, 400°C; 6, 500°C; 7, 600°C; 
and 8, 700°C (see text for details). 
 
of the samples. Except the site BGK M3, all the other 
samples show their secondary component too as normal
polarity making low angles with primary component, 
indicative of overlapping coercivity spectra. The  
Zijderveldt plots for the specimens of BGK M3  
have shown entirely different trajectories characteristic 
of aborted reversal/excursion. Finally, the excursion  
at BGK M3 can be assigned using the following criteria. 
 
(1) After the removal of the viscous component at 
100°C the intensity is increased, instead of the usu-
ally expected decay as observed in all other sam-
ples. This may be due to the antiparallel acquisition 
of the viscous component (present-day ormal po-
larity) to the reversed component of excursion. 
(2) The virtual geomagnetic pole (VGP) latitudes, fall 
in the lower hemisphere with the low latitude values 
and are thus characteristic of excursion1 rather than 
a full reversal. 
(3) The demagnetized Natural Remanent Magnetization 
(NRM) intensity is reduced dramatically in the 
sample M3 despite Xlf being constant (see NRM/Xlf 
ratio in Figure 6). This is a behaviour suggestive of 
an excursion event2,18. 
(4) The maximum angular deviation (MAD) values for 
the principle-component derived directions (D and 
I) infer that the primary component is highly clus-
tered after 400°C for the M3/3 than the samples be-
low and above it (i.e. M3/4 and M3/1), suggesting 
transition of the excursion. 
(5) For all the samples, except BGK M3, the Zi-
jderveldt plots (Figure 5) show highly overlapping 
coercivity spectra for the secondary components,  
as the primary as well as secondary directions  
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CURRENT SCIENCE, VOL. 82, NO. 2, 25 JANUARY 2002 215 
are acquired in the same polarity (i.e. Brunhes 
Normal). 
(6) The scattered nature of the secondary component as 
well as the short record of excursion is probably 
due to the insufficient ‘remanence lock-in time’19 
and/or stronger Post-Depositional Remanent Mag-
netization (PDRM) overprinting of the primary sig-
natures20. 
(7) The sample BGK M3 occurs just above the OSL 
date of 40 ± 5 Ka and thus coincides with the Las-
champ Excursion1,5. 
 
 
 
Figure 6. Variation in the lithogenic (Xlf, Xfd% and XARM) and 
geomagnetic (declination, inclination and virtual geomagnetic pole 
(VGP) latitude) parameters. Note that the lithogenic factors remain 
fairly constant, although the geomagnetic parameters are varied, 
particularly during BGK M3 authenticating the occurrence of excur-
sion.  
Thus the selective sampling in the Kiratpur section di-
covered a geomagnetic excursion coinciding with the 
~ 40 Ka Laschamp event1. The high rate of sedimenta-
tion in this basin is quite suitable to get enlarged re-
cords from the sediments. A more detailed close 
sampling for palaeomagnetic and rock magnetic analy-
si  is under progress, to study the behaviour of this ex-
cursion for its successful correlation as a bench-mark 
for the Late Pleistocene sediments in Pijor Dun and 
adjacent area. Study of the excursions is of vital impor-
tance to understand the non-dip le nature of the geo-
magnetic field4 and the production of cosmogenic 
radionuclides21.  
 
1. Jacobs, J. A., Reversals of the Earth’s Magnetic Field, Cam-
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6. Kotlia, B. S. et al., Palaeogeogr. Palaeoclimatol. Palaeoecol., 
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Pandey, M. R. and Stein, R. S., Ann. Tecton., Spl. Issue, 1992, 
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and Frontiers, Cambridge University Press, 1997, p. 573.  
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Allen and Unwin Publishers, London, 1986, p. 220. 
14. Evans, M. and Heller, F., Earth Sci. Rev., 2001, 54, 129–144 
15. Sangode, S. J. and Bagati, T. N., J Himalayan Geol., 1995, 6, 
51–60 
16. Sangode, S. J., Suresh, N. and Bagati, T. N., Curr. Sci., 2001, 
80, 660–664. 
17. Sangode, S. J., Bloemendal, J., Kumar, R. and Ghosh, S. K., 
Curr. Sci., 2001, 81, 387–392. 
18. Levi, S., Audunsson, H., Duncan, R. A., Kristjansson, L., Gillot, 
P. Y. and Jacobsson, L., Earth Planet. Sci. Lett., 1990, 96, 219.  
19. Tauxe, L., Herbert, T., Shackleton, N. J. and Kok, Y. S., Earth 
Planet. Sci. Lett., 1996, 140, 133–146.  
20. Coe, R. S. and Liddicoat, J. C., Nature, 1994, 367, 57–59 
21. Mazaud, A., Laj, C., Bard, E., Arnold, M. and Tric, E., Geo-
phys. Res. Lett., 1991, 18, 1885. 
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Dehradun, 1976, p. 86. 
 
ACKNOWLEDGEMENTS. This work was funded by Department 
of Science and Technology, (Government of India) project grant 
ESS/CA/A-9/1996–97, and the funds for analysis at Liverpool to 
S.J.S. under DST-BOYSCAST fellowship HRU/BYS/A-08/98. We 
are grateful to the Directo , Wadia Institute of Himalayan Geology 
for his encouragement. Mr Senthyl Kumar is acknowledged for help 
during fieldwork and analysis. 
 
Received 8 August 2001; accepted 12 October 2001 


Discovery of an aborted reversal (geomagnetic excursion) in the Late Pleistocene sediments of Pinjor Dun, NW Himalaya

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Discovery of an aborted reversal (geomagnetic excursion) in the Late Pleistocene sediments of Pinjor Dun, NW Himalaya

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