Basin Research (2009) 21, 61–90, doi: 10.1111/j.1365-2117.2008.00374.x
Magnetic polarity stratigraphy of the Neogene
foreland basin deposits of Nepal
T. P. Ojha, R. F. Butler, P. G. DeCelles and J. Quade
Department of Geosciences, University of Arizona,Tucson, AZ, USA
ABSTRACT
The early Miocene Dumri Formation and middle Miocene^Pliocene Siwalik Group were deposited
in the Himalayan foreland basin in response to uplift and erosion in the Himalayan fold-thrust belt.
We report magnetostratigraphic data from four sections of these rocks in Nepal.Three of these
sections are in the Siwalik Group in the hanging wall of the Main Frontal thrust, and one section is
from the Dumri Formation in the hanging wall of the Main Boundary thrust (MBT).Thermal
demagnetization experiments demonstrate that laminated siltstones yield palaeomagnetic data
useful for tectonic and magnetostratigraphic studies whereas other lithofacies yield data of
questionable reliability. Magnetostratigraphic data have been acquired from 297 sites within a
4200-m-thick section of Siwalik deposits at Surai Khola.The observed sequence of polarity zones
correlates with the geomagnetic polarity time scale (GPTS) from chron C5Ar.1n to chron C2r.2n,
spanning the time frame ca. 12.5^2.0 Ma. At Muksar Khola (eastern Nepal), 111 palaeomagnetic sites
from a 2600-m-thick section of the Siwalik Group de¢ne a polarity zonation that correlates with the
GPTS from chron C4Ar.2n to chron C2Br.1r, indicating an age range of ca. 10.0^3.5 Ma. At Tinau
Khola, 121 sites from a 1824 -m-thick section of the Siwalik Group are correlated to chrons C5An.1n
through C4r.1n, equivalent to the time span ca. 11.8^8.1 Ma. At Swat Khola, 68 sites within a
1200-m-thick section of lower Miocene Dumri Formation are correlated with chrons C6n through
C5Bn.2n, covering the time span ca. 19.9^15.1 Ma.Together with previous results from Khutia Khola
and Bakiya Khola, these data provide the ¢rst magnetostratigraphic correlation along nearly the
entire NW^SE length of Nepal.The correlation demonstrates that major lithostratigraphic
boundaries in the Siwalik Group are highly diachronous, with roughly 2 Myr ofvariability. In turn, this
suggests that the major sedimentological changes commonly inferred to re£ect strengthening of the
Asian monsoon are not isochronous. Sediment accumulation curves exhibit a 30^50% increase in
accumulation rate in four of the ¢ve sections of the Siwalik Group, but the timing of this increase
ranges systematically from 11.1 Ma in western Nepal to 5.3 Ma in eastern Nepal. If this increase in
sediment accumulation rate is interpreted as a result of more rapid subsidence owing to thrust
loading in the Himalaya, then the diachroneity of this increase suggests lateral propagation of a major
thrust system, perhaps the MBT, at a rate of ca. 103 mm year 1 across the length of Nepal.
INTRODUCTION
The Himalayan thrust belt is the type example of an oro genic belt formed by intercontinental collision (Argand,
1924; Gansser, 1964; Dewey et al., 1989). Much of what is
known about the tectonic and palaeogeographic histories
of the Himalaya is constrained by the subsidence history,
depositional systems, exhumation history, provenance
and structure of Neogene foreland basin deposits that are
preserved in the frontal part of the thrust belt (Raiverman
et al., 1983; Sakai, 1983; Raynolds & Johnson, 1985; Harrison
et al., 1993; Critelli & Ingersoll, 1994; Quade et al., 1995;
Burbank et al., 1996; DeCelles et al., 1998a, b, 2004; Najman
Correspondence: T. P. Ojha, Department of Geosciences, University of Arizona, Tucson AZ 85721, USA. E-mail: ojha
@email.arizona.edu
& Garzanti, 2000; Huyghe et al., 2001, 2005; White
etal., 2002; Mugnier etal., 2004; Najman etal., 2004; Bernet
et al., 2006; Najman, 2006; Szulc et al., 2006; van der Beek
et al., 2006). In Pakistan and parts of northern India, the
chronology of deposition in the Neogene synorogenic
Himalayan record is relatively well known from a combination of palaeontology, magnetostratigraphy and radio metric dating of tu¡aceous deposits (Opdyke et al., 1979;
Johnson et al., 1982, 1983; Tauxe & Opdyke, 1982;
Sangode et al., 1996; see summaries in Burbank et al., 1996;
Gautam & R˛sler, 1999). On the other hand, in the
800-km-long segment of the Himalayan orogenic arc
occupied by Nepal (Fig. 1), the chronostratigraphy of the
Neogene synorogenic sediment record is poorly known,
mainly owing to a lack of tu¡aceous deposits and chronostratigraphically signi¢cant fossils (see reviews in Gautam
& R˛sler, 1999; Corvinus & Rimal, 2001). A number of
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Journal Compilation r Blackwell Publishing Ltd, European Association of Geoscientists & Engineers and International Association of Sedimentologists
61
T. P. Ojha et al.
previous magnetostratigraphic studies of the Nepalese Siwalik Group have been published (Appel et al., 1991; Appel
& R˛sler, 1994; Gautam & Appel, 1994; R˛sler et al., 1997;
Gautam & R˛sler,1999; Gautam & Fujiwara, 2000; Gautam
et al., 2000). However, these studies were based on sparse
sampling (typically a single sample from a given bed; R˛sler et al., 1997), generally of lithofacies (sandstones and
strongly cemented palaeosols; e.g. R˛sler et al., 1997; Gautam & Fujiwara, 2000) that have been shown to produce inconsistent palaeomagnetic results (Tauxe & Badgely, 1988;
Tauxe et al., 1990; Ojha et al., 2000). Moreover, only middle
Miocene to Pliocene Siwalik Group strata have been
sampled for magnetostratigraphic analysis, leaving a large
part of the synorogenic record undated. In particular, the
age of the Dumri (or Suntar) Formation is based only on
its stratigraphic position above fossiliferous Eocene marine deposits of the Bhainskati Formation (Sakai, 1983) and
the presence of detrital muscovite grains that yielded early
Miocene 40Ar/39Ar ages (DeCelles et al., 1998a). Because a
continuous, reliably dated stratigraphic section containing
both the Dumri Formation and the Siwalik Group is not
known to exist in surface exposures in Nepal, the younger
age limit of the Dumri remains conjectural.The lack of precise chronologies for sections of the Siwalik Group and
Dumri Formation in Nepal hampers e¡orts to determine
the tectonic development of the central Himalayan foreland
basin system and timing of major thrusting events; the timing of climate changes proxied by isotopic and palaeobotani-
80°
cal evidence (Harrison et al.,1993; Quade etal.,1995; Quade &
Cerling, 1995; Cerling et al., 1997; Hoorn et al., 2000); and the
Sr-isotopic evolution of Himalayan palaeorivers (Quade
et al., 1997, 2003; English et al., 2000).
The purpose of this paper is to present a synthesis of three
new and two previously published magnetostratigraphic
sections in the Siwalik Group, and the ¢rst magnetostratigraphic section from the Dumri Formation. The sections
span nearly the entire along-strike length of the Himalayan
foreland basin system in Nepal, and provide the ¢rst
integrated magnetostratigraphic data set from this region.
GEOLOGICAL SETTING
The synorogenic sediments of the Himalayan foreland basin system fringe the Himalayan range from Assam, India,
to western Pakistan. In Nepal and northern India, the
northern deformed edge of this foreland basin is formed
by the sub-Himalayan range, or the ‘Siwalik foothills’. The
Siwalik foothills are characterized by southward asymmetric, parallel ridges and valleys, with maximum elevation of 1500 m. The Siwalik Group outcrop belt in
Nepal is bounded on the north by the Main Boundary
thrust (MBT) and on the south by the Main Frontal thrust
(MFT) (Fig. 1). North of the MBT lies the Lesser Himalayan zone, which is composed of a thick succession of slightly
metamorphosed to unmetamorphosed sedimentary and
Tibet
84°
Nepal
100
0
30°
Bhutan
km
India
Bangladesh
KK
SWK
RT
RT
MCT
28°
28°
MBT
SK
TK
Kathmandu
MFT
Siwalik Group
Miocene Leucogranite
Tibetan Himalayan zone
Greater Himalayan zone
Lesser Himalayan zone
80°
Section Locations:
KK = Khutia Khola
SWK = Swat Khola
SK = Surai Khola
TK = Tinau Khola
BK = Bakiya Khola
MK = Muksar Khola
84°
Hetauda
BK
MK
Thrust fault
Normal fault
88°
Fig. 1. Generalized geological map of Nepal modi¢ed from DMG Maps with nomenclature and description given by DeCelles et al.
(1998b, 2001). Palaeomagnetic sampling locations are shown by stars, and major faults are Main Frontal Thrust (MFT), Main Boundary
thrust (MBT), Ramgarh thrust (RT) and Main Central thrust (MCT).
62
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Journal Compilation r Blackwell Publishing Ltd, European Association of Geoscientists & Engineers and International Association of Sedimentologists
Magnetic polarity stratigraphy of the Neogene foreland basin deposits of Nepal
local intrusive rocks of Proterozoic, late Palaeozoic and
Cretaceous^Palaeocene age, capped by a roughly 1.5-kmthick package of Eocene (Bhainskati Formation) and early
Miocene (Dumri Formation) strata that are separated
from each other by a disconformity representing a roughly
15 Myr hiatus (DeCelles et al., 1998a). Because the Bhainskati and Dumri Formations crop out only to the north of
the MBT in Nepal, no continuous stratigraphic section of
Eocene through Pliocene rocks is exposed.To the south of
the Siwalik foothills lies the Terai Plain, which constitutes
the active foredeep and wedge-top depozones of the modern alluvial foreland basin system between the topographic
front of the Himalaya and the southern fringe of the
Ganges River drainage basin (Fig.1). Subsurface data from
the Terai Plain indicate that the Tertiary stratigraphic
equivalents of the Siwalik Group and the Dumri and
Bhainskati Formations are up to 6 km thick (Raiverman
et al., 1983).
The geological structure of the Siwalik foothills is a system of mainly SSW verging imbricate thrust faults (Chalaron et al., 1995; Powers et al., 1998; Mugnier et al.,
1999a, b) that branch upward from a regional de¤ collement
that merges northward with the Main Himalayan detachment at the base of the Himalayan orogenic wedge (Raiverman et al., 1983; Gahalaut & Chander, 1992; Biswas, 1994;
Hauck et al., 1998; Avouac, 2003). In far western and midwestern Nepal, this de¤ collement occurs below ca. 13 Ma
sediments of the Siwalik Group (DeCelles et al., 1998b;
Ojha et al., 2000, 2004). Several north-dipping thrusts
repeat sections of the Siwalik Group.The system of thrusts
called the Main Dun Thrusts (Schelling et al., 1991; Mugnier et al., 1999a, b) consists of a series of three to four
branching, laterally overlapping imbricates that tip out in
laterally propagating anticlines or lateral transfer zones
(Mugnier et al., 1999a, b).
The Dumri Formation is at least 1200 m thick at Swat
Khola and consists of £uvial channel sandstones and red
overbank mudstone with palaeosols. Palaeocurrent data
show a southwestward pattern of palaeodrainage, perhaps
because the sandstones were deposited in a southwestward
£owing axial river system (DeCelles et al., 1998a).The thickest reported section of the Siwalik Group in Nepal is approximately 5.3 km (Szulc et al., 2006). On depth-converted
seismic sections, however, maximum thickness may be closer to 6 km (Schelling et al., 1991). The Siwalik Group is informally subdivided into lower, middle and upper members
that form an overall upward coarsening sequence (Auden,
1935; Quade et al., 1995; DeCelles et al., 1998b; Szulc et al.,
2006). The lower member is characterized by numerous
several-metre-thick lenticular channel sandstone bodies
and associated red £oodplain siltstones and calcic palaeosols.The middle member contains very thick (420 m) multistory channel sandstones and generally more histic,
chemically reduced palaeosols and organic-rich overbank
siltstones.The upper member is dominated by conglomeratic £uvial and stream-dominated alluvial fan deposits.
We place the boundaries between the Siwalik members
in the ¢eld according to the system utilized by geologists
from the Nepal Department of Mines and Geology for
more than 30 years: (1) the lower^middle Siwalik boundary
is placed at the transition from generally o10-m-thick,
single- story channel sandstones and red palaeosols/overbank deposits, to thick (420 m) multistory channel sandstones with grey overbank and palaeosol facies; and (2)
the middle^upper Siwalik boundary is placed at the ¢rst
appearance of frequent extraformational conglomerate
units more than a metre thick, and where these conglomerates begin to dominate the section (Quade et al., 1995).
The placement of these boundaries is subject to interpretation in the ¢eld, but most workers have found this
scheme practicable. The lower^middle boundary is more
clear- cut than is the middle^upper boundary, mainly because the ¢rst conglomeratic deposits may be present
more than a kilometre below the ¢nal middle-to -upper
transition as described above.
Palaeocurrent and sedimentological data indicate that
the Siwalik Group was probably deposited in a system of
£uvial megafans similar to those that dominate the modern foredeep depozone of the Himalayan foreland basin
(Mohindra et al., 1992; Sinha & Friend, 1994; Gupta, 1997;
DeCelles & Cavazza, 1999; Szulc et al., 2006). The timestratigraphic transition from the Dumri Formation
through the Siwalik Group may therefore be interpreted
simply as the result of southward progradation of a foreland depositional mosaic consisting of a distal axial river
that was fed by transversely oriented £uvial megafans,
similar to the modern situation.
The Dumri Formation and Siwalik Group in Nepal
contain few fossils that have chronostratigraphic signi¢ cance. The most thorough collections are reported in the
Surai Khola section by Corvinus & Rimal (2001) and previous papers that are summarized therein. Although these
fossils are important for controlling the age of the Surai
Khola section, comparable collections have not been reported elsewhere in Nepal, and it remains impossible to
erect a biostratigraphy for regional age correlations.
Therefore, magnetostratigraphy has proved to be a vital
tool for determining the age of the Siwalik Group.
An additional source of age information from the Siwalik Group deposits is carbon isotope values (d13C) from
palaeosols. These values increased abruptly during the
late Miocene in response to a dramatic expansion of C4
plants on £oodplains across the Indian subcontinent. The
carbon isotope shift is best documented on the Indian
sub- continent in Pakistan (Quade et al., 1989, 1995; Behrensmeyer et al., 2007) where it commenced at 7.9 Ma
and ended at 5.0 Ma. The carbon isotope shift is also
visible in sediments of the Bengal submarine fan at
6.8 Ma (France-Lanord & Derry, 1994), demonstrating
that the shift was a late^Miocene (7.9^6.8 Ma) continentwide event. Thus, the carbon isotope shift serves as an
age anchor for our palaeomagnetic sections, and should
fall anywhere from C4n.2n (7.695^8.108 Ma) to C3Ar
(6.733^7.140 Ma). As discussed in subsequent sections
of this paper, the stratigraphic position of the carbon iso tope shift (Table 1) is incorporated into our correlations of
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Journal Compilation r Blackwell Publishing Ltd, European Association of Geoscientists & Engineers and International Association of Sedimentologists
63
T. P. Ojha et al.
Table 1. Age of carbon isotope transition in Siwalik Group palaeosols
d13C carbonate
4 8%
Section
Surai Khola
Bakiya Khola
Khutia Khola
Muksar Khola
Tinau Khola
d13C organic matter
4 22%
6.7
1.5
4.2
Not detected
21.7
Not detected
Stratigraphic
level (m)
Polarity interval
GPTSn
1723
1799
2842
1237.5
Base of H
Not numbered
Not measured
Base of J
base C3.Br
C3Bn
C3Ar
Estimated
age (Ma)
7.5
7.2
o7.5
7.1
47.9
n
Lourens et al. (2004).
GPTS, geomagnetic polarity time scale.
individual magnetostratigraphic sections to the geomagnetic polarity time scale (GPTS).
We sampled sections of the Siwalik Group at Surai
Khola, Tinau Khola and Muksar Khola in the Siwalik
foothills, and the Dumri Formation at Swat Khola in the
Lesser Himalayan zone (Fig. 1). Our previously published
sections from Khutia Khola (far western Nepal, Ojha et al.,
2000) and Bakiya Khola (east- central Nepal, Harrison
etal.,1993; Quade etal.,1995) are integrated into this analysis.
SAMPLING AND LABORATORY
METHODS
As discussed in Ojha et al. (2000), we targeted laminated
siltstone layers that typically occur directly below major
basal erosional surfaces of channel sandstone bodies. The
stratigraphic spacing of these layers is generally on the order of 15 m in the lower parts of the sections, and increases
to 20^30 m in the upper parts. Gautam & R˛sler (1999)
argued that, given the frequency of magnetic reversals
during the Neogene and the average long-term rate of sediment accumulation in the Siwalik Group, an average
spacing of 30 m should be su⁄cient to record most of the
major polarity zones. The same authors also suggested
that a minimum section thickness of 1000 m should be
sampled in order to provide su⁄cient reversals for a reasonably good tie to the GPTS. All of our sections satisfy
these criteria.
Three to ¢ve oriented samples were collected from each
sedimentary horizon. Most samples were cored in situ with
standard drilling equipment and oriented as described by
Butler (1992). Samples from clay-rich layers too poorly indurated for drilling were sampled using an electric rock
cutter (Ellwood et al., 1993). After trimming to specimen
dimensions, all palaeomagnetic samples were stored, measured, and thermally demagnetized in a magnetically
shielded room with average ¢eld intensity o200 nT. Natural remanent magnetization (NRM) was measured using
a three-axis cryogenic magnetometer (Model 755R, 2G). Initial NRM intensities ranged from 10 1 to 10 3 A m 1.
Prior research on palaeomagnetism of Siwalik Group sedimentary rocks in Pakistan and Nepal has established that
thermal demagnetization is required for isolation of the
components of NRM (Tauxe & Opdyke, 1982; Johnson
64
et al., 1985; Appel et al., 1991; Harrison et al., 1993; Gautam
& Appel, 1994; Ojha et al., 2000). After initial NRM
measurements, samples were subjected to progressive
thermal demagnetization. Samples were demagnetized
at 12 temperature steps to 680 1C with six to seven steps
between 600 and 680 1C.Typical thermal demagnetization
behaviours are illustrated in Fig. 2. The high unblocking
temperature components are carried by specular haematite that acquired a magnetization either as detrital remanent magnetization or chemical remanent magnetization
soon after deposition (Tauxe & Badgely, 1988; Tauxe
et al., 1990; Ojha et al., 2000). Our preliminary sampling
included collection of sandstone, laminated siltstone and
palaeosol (i.e. massive, pedoturbated and bioturbated siltstone with characteristic micromorphologic features of
soils). Results showed that palaeosols and medium- to
coarse-grained sandstones exhibit erratic thermal demagnetization behaviours (Ojha et al., 2000). In contrast, samples from laminated siltstone and ¢ne sandstone (Fig. 2)
display coherent demagnetization trajectories; this guided
our exclusive sampling of laminated siltstones and ¢ne
sandstones.
Principal component analysis of NRM remaining at
four to six successive temperature steps generally above
600 1C was used to determine the ChRM (Kirschvink,
1980). Samples yielding maximum angular deviation
(MAD) 4151 were rejected from further analysis. Sitemean ChRM directions were determined using methods
of Fisher (1953) and examined using the test for randomness of Watson (1956). Sites with three or more samples
yielding ChRM directions that are non-random at the
5% signi¢cance level are the most reliable results and are
designated Class A sites. Sites with two or more samples
with more dispersed ChRM directions but generally
unambiguous polarity are designated Class B sites. Class
A and B sites are used to construct the magnetic polarity
columns. Sites yielding only one sample ChRM direction
were rejected from further analysis. Further analyses of
Class A site-mean directions included examination of fold
and reversal tests following the procedures of Watson &
Enkin (1993) and McFadden & McElhinny (1990), respectively. Concordance/discordance analyses of section-mean
directions were done using reference palaeomagnetic
poles for India (Besse & Courtillot, 2002) and procedures
of Beck (1980) and Demarest (1983).
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Journal Compilation r Blackwell Publishing Ltd, European Association of Geoscientists & Engineers and International Association of Sedimentologists
Magnetic polarity stratigraphy of the Neogene foreland basin deposits of Nepal
Muksar Khola
Surai Khola
GK026B
Up, W
NRM
SK123B
Up, West
188
398
499
581
665
671
647
S
NRM
188
Down, E
Surai Khola
298
410
608
S
N
673
652
581
671
665
499 647
398
1X10–3 A /m
SK209D
Up, West
N
682
–3
677 1X10 A /m
671
666
635
646
532
495 243
NRM
Down, East
Swat Khola ST085A
Up, W
614571
377
642
625
NRM
673
602
S
N
642 664
664 625
499
560
632
651
S
666
614
N
673
1X10–4 A/m
1X10–4
602
571
377
A/m
NRM
Down, East
Down, E
Tinau Khola UA034B
Up, West
416
526
Fig. 2. Representative vector- component
diagrams of thermal demagnetization
behaviour (Zijderveld, 1967) for siltstones
and very ¢ne-grained sandstones within
Siwalik Group deposits of Nepal. Diagrams
are labelled indicating locality of collection.
Open circles are projections onto vertical
plane and ¢lled circles are projections onto
horizontal plane. Numbers adjacent to data
points indicate temperature in 1C.
CARBON ISOTOPE RESULTS FROM
SIWALIK GROUP STRATA
Although a detailed presentation of our extensive carbon
isotope data from the Siwalik Group in Nepal is beyond
the scope of this paper, these data provide an independent constraint on the age of the Siwalik Group because
of the nearly synchronous, continent-wide nature of the
shift in d13C values. The shift in C3^C4 biomass, as
re£ected in the d13C value of palaeosol carbonates and
organic matter, is visible in all but one of the Siwalik study
sections (Table 1). The onset of the shift is denoted by
d13C values of palaeosol carbonate 4 8% and for organic matter of 4 22% (see Quade et al. (1995) for discussion). For example, d13C values of palaeosol carbonates
exceeding 8% are ¢rst found at 1723 m at Surai Khola
NRM
624
653
S
674
684
669
624
653
N
Horizontal Plane
Vertical Plane
416
526
1X10–3 A/m
NRM
Down, East
(Table 1, 6.7%; Quade et al., 1995) and at 1799 m at
Bakiya Khola ( 1.5 and 0.8%) (Quade et al., 1995).
At Muksar Khola, palaeosol carbonate is not present high
in the section but organic matter is, and the d13C value of
palaeosol organic matter increases abruptly at 1237.5 m
( 21.7%). At Khutia Khola, the carbon isotope shift
occurs between 2600 and 2842 m, above the palaeomagnetically dated portion of the section, which is no younger than about 7.5 Ma (Ojha et al., 2000, 2004). At Tinau
Khola the carbon isotope shift was not detected; all d13C
values of palaeosol carbonates are o 8%. In this paper,
we use the carbon isotope shift to roughly correlate our
sections to the GPTS, assuming that the shift occurred
sometime between 7.9 and 6.8 Ma (Quade et al., 1989,
1995; France-Lanord & Derry, 1994; Behrensmeyer
et al., 2007).
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Journal Compilation r Blackwell Publishing Ltd, European Association of Geoscientists & Engineers and International Association of Sedimentologists
65
T. P. Ojha et al.
PALAEOMAGNETISM OF SWAT KHOLA
DEPOSITS
At Swat Khola (28.70951N, 81.55131E), palaeomagnetic
samples were collected at 68 sites within a 1200-m-thick
section of Dumri Formation £uvial deposits (cf. DeCelles
et al., 1998a). Class A site-mean ChRM directions were obtained from 41 sites whereas Class B site-mean directions
were obtained from 22 sites (Table A1). Figure 3 illustrates
Class A site-mean directions in geographic and
stratigraphic coordinates.Three site-mean directions more
than two estimated angular standard deviations from the
preliminary means for normal and reversed polarity
groups were not used for reversal and fold tests. The mean
of seven normal polarity sites is Inc. 5 4.51, Dec. 513.31,
a95 522.51 (k 5 8.2) whereas the mean of 46 reverse polarity
sites is Inc. 5 8.11, Dec. 5197.51, a95 510.81 (k 510.0).
The angle between the mean of normal polarity sites
and the antipode of the mean of the reversed polarity sites
is 4.31 whereas the critical angle is 23.91. However, the
k-values for both polarity groups are low and the reversal
test is indeterminate.
A fold test of Class A site-mean ChRM directions from
Swat Khola yields the somewhat unexpected result of
optimum unfolding at 1.2% with 95% con¢dence limits of
14.6 and 17.6% unfolding. However, given the limited
variation in bedding attitudes and low k-values (large
dispersion), the implications of this fold test are uncertain.
Comparing the Swat Khola section-mean direction
(Inc. 5 6.91, Dec. 515.91, a95 5 7.81) in stratigraphic
coordinates to the expected 15 Ma direction indicates clockwise vertical-axis rotation of 13.1 6.91, and 35.2 7.11 £attening of inclination (Fig. 3). The large £attening of
inclination is a common observation in palaeomagnetic studies of Neogene £uvial and overbank deposits in Pakistan
and Nepal (Tauxe & Kent, 1984; Appel et al., 1991; Gautam &
Appel, 1994; Gautam & R˛sler, 1999; Gautam & Fujiwara,
2000; Ojha et al., 2000). This shallowing of palaeomagnetic
directions is likely the result of plate-like detrital haematite
particles settling with long-axes sub parallel to bedding
(Tauxe & Kent, 1984; R˛sler & Appel, 1998; Ojha et al., 2000)
or post-depositional sediment compaction (Kodama, 1997).
The polarity stratigraphy for the Dumri Formation at Swat
Khola is illustrated in Fig. 4b. A maximum age constraint is
Fig. 3. Equal-area projections of site-mean ChRM directions
from Swat Khola. Filled circles are in lower hemisphere and open
circles are in upper hemisphere. (a) Directions in geographic
(in situ) coordinates. (b) Directions in stratigraphic coordinates
following restoration of bedding to horizontal. Mean of normalpolarity sites is shown by ¢lled square surrounded by 95%
con¢dence limits. Mean of reverse-polarity sites is shown by
open square surrounded by 95% con¢dence limits. Site-mean
directions labelled in grey were not used for fold or reversal tests
or determination of vertical-axis rotation. (c) Comparison of
observed section mean direction and the expected direction.
Implied vertical-axis rotation (R DR) is clockwise 13.1 6.91;
£attening of inclination (F DF) is 35.2 7.11.
66
provided by detrital muscovite 40Ar/39Ar ages of 19 Ma from
Dumri exposures 50 km NWof Swat Khola (DeCelles etal.,
2001), but a strong minimum age constraint is not available.
Most likely the minimum age of the Dumri Formation is
14 Ma, given the maximum age of the Siwalik Group. However, the Dumri consists of £uvial lithofacies very similar to
r 2009 The Authors
Journal Compilation r Blackwell Publishing Ltd, European Association of Geoscientists & Engineers and International Association of Sedimentologists
Magnetic polarity stratigraphy of the Neogene foreland basin deposits of Nepal
those of the lower Siwalik Group (DeCelles etal.,1998a) and no
continuous Dumri^Siwalik section is present in Nepal, leaving open the possibility that an age continuum exists between
the 2 units. Although there is some uncertainty in
correlating the base of the section to the GPTS, magnetic
polarity zones D1 through I show very good correlation
(coe⁄cient 5 0.66) to chrons C5Dn through C5Bn.2n
of the GPTS (Lourens et al., 2004). The age range of
the Dumri Formation deposits at Swat Khola is therefore
indicated in the interval 19.9 to 15.1Ma (Fig. 4b).
Additional support for the notion that the Dumri
completely predates the Siwalik Group comes from
petrographic and Nd isotopic provenance data that show
distinct changes between the 2 units and their equivalents to
the west in northern India (DeCelles et al., 1998a, 2004;
Huyghe et al., 2001; Robinson et al., 2001; White et al., 2002;
Szulc et al., 2006).
PALAEOMAGNETISM OF SURAI KHOLA
DEPOSITS
At Surai Khola (27.74761N, 82.84491E), palaeomagnetic samples were collected at 297 sites within a 4200-m-thick section
of Siwalik Group. Class A site-mean ChRM directions were
obtained from117 sites, and class B site-mean directions were
obtained from 48 sites (Table A2). Figure 5 illustrates Class A
site-mean directions in geographic and stratigraphic coordinates. Sixteen site-mean directions more than two estimated
angular standard deviations from the preliminary means for
normal and reversed polarity groups were not used for reversal and fold tests. The mean of 55 normal polarity sites is
Inc. 519.61, Dec. 5 358.71, a95 5 4.81 whereas the mean of 46
reverse polarity sites is Inc. 5 21.01, Dec. 5178.71,
a95 5 6.01. These polarity-mean directions pass the reversal
test with classi¢cation B and are similar to those observed
by Appel et al. (1991).
The stratigraphic sequence at Surai Khola is north dipping but with only minor variation in bedding attitudes.
The fold test of site-mean ChRM directions from Surai
Khola shows only minor variation in grouping of sitemean directions between geographic coordinates
(k 5 14.9) and stratigraphic coordinates (k 5 13.7). Applying the fold test of Watson & Enkin (1993) yields the somewhat unexpected result of optimum unfolding at 37.2%
(k 5 16.3) with 95% con¢dence limits of 29.9 and 45.7% unfolding. However, given the limited variation in grouping
of site-mean directions over the full range of unfolding,
we doubt that these results indicate a synfolding origin
for the ChRM. Comparing the Surai Khola section-mean
direction (Inc. 5 20.21, Dec. 5 358.71, a95 5 3.91) in stratigraphic coordinates with the expected 10 Ma direction indicates counterclockwise vertical-axis rotation of 4.5 4.4
and 22.4 4.71 £attening of inclination (Fig. 5).
A key observation in the Surai Khola magnetic polarity
zonation is a thick normal polarity zone within the Lower Siwalik part of the section (C1) that correlates with chron
C5n.1n and C5n.2n (Fig. 6b; see also R˛sleretal.,1997). An ad-
ditional thick normal polarity zone spanning the lower^middle Siwalik boundary (G1) correlates with chron C4n.1n and
C4n.2n. Correlations between polarity zones in the Surai
Khola section and the GPTS are reasonably secure up
through zone I1. However, correlations between the magnetic polarity sequence in the upper part of the section and
the GPTS are tenuous because this portion of the section is
dominated by conglomerates and was probably deposited in
the wedge-top part of the foreland basin system (DeCelles
et al., 1998b), where syndepositional folding could have
strongly a¡ected sediment accumulation and preservation.
An important result is that the carbon isotope transition
commences at 1723 m at the base of magnetic polarity zone
H . Correlation of zone H with the base of chron C3.Br
implies an age of 7.5 Ma for the transition in the Surai
Khola section, which is consistent with the 6.8^7.9 Ma age of
the transition elsewhere. Detrital apatite ¢ssion track (AFT)
ages reported by van der Beek et al. (2006) provide additional
constraints on the maximum ages of sampled beds above polarity zone I1 (Fig. 6b).These ages are from apatites that were
not annealed by post-depositional burial (van der Beek et al.,
2006), and therefore they provide a maximum depositional
age for each horizon from which they were collected. These
maximum depositional ages are indicated in Fig. 6b. van der
Beek et al. (2006) also noted that the detrital AFT ages are
consistent with our polarity zonation and correlation to the
GPTS, whereas most of the mean AFTages are younger than
the depositional ages of host beds according to the Gautam &
R˛sler (1999) GPTS correlation.
Because of its continuous exposure, great thickness and
ease of access along the Mahendra highway, the Surai
Khola section has acquired reference section status in
Nepal.The section has been logged and sampled for chronostratigraphy by three studies (Appel & R˛sler, 1994; Corvinus & Rimal, 2001; and this study). A number of distinctive
landmarks along the Surai Khola section were noted in the
logs of all three studies, permitting cross-comparison and
consideration of the two biostratigraphic constraints on the
section relative to the palaeomagnetic age estimates. Corvinus & Rimal (2001) reported ¢rst appearances at Surai Khola
of Hexaprotodon sivalensis at 3000 m (2600 m in our section)
and Elephus planifrons in their ‘Dobatta Formation’ (between
about 2900 and 3400 m in our section). In the well-dated Siwalik sections of Pakistan (Barry et al., 1982), these fossils are
recorded at o5.9 and o3.6 Ma, respectively. Our estimated
palaeomagnetic ages are 4.9 Ma for the site containing
H. sivalensis, and 4.2^3.4 Ma for the interval (Dobatta Formation) reported to contain E. planifrons.Thus, our palaeomagnetic age estimates for this part of the section are in
agreement with the existing biostratigraphic age estimates.
PALAEOMAGNETISM OF TINAU KHOLA
DEPOSITS
At Tinau Khola (27.72031N, 83.46791N), palaeomagnetic
samples were collected at121sites from a1824-m-thick stratigraphic section of the Siwalik Group. Sixty sites yielded
r 2009 The Authors
Journal Compilation r Blackwell Publishing Ltd, European Association of Geoscientists & Engineers and International Association of Sedimentologists
67
T. P. Ojha et al.
(a)
GPTS
Lourens et al., 2004
Age Chron
C5ABn
14 C5ACn
C5ADn
15 C5Bn.1n
C5Bn.2n
16
(b)
C5Cn.1n
C5Cn.2n
C5Cn.3n
Polarity
Magnetostratigraphy
1200
I–
1000
H+
G–
F+
17
C5Dn
18
E–
C5En
500
D+
19
C–
0
B+
A–
Si SS Cg
–90
–45
0
45
VGP latitude (°)
90
Class A site-mean ChRM directions and 54 sites yielded
Class B site-mean ChRM directions (Table A3,
Fig. 7). Seven sites yield MAD4151 and were rejected from
further analysis. Class A site-mean ChRM directions in
geographic coordinates and stratigraphic coordinates are illustrated in Fig. 7. Five Class A site-mean directions more
than two estimated angular standard deviations from the
preliminary means for normal and reversed polarity groups
were not used for reversal and fold tests (Fig. 7). The mean
of 32 normal polarity sites is Inc. 5 8.81, Dec. 5 342.61,
a95 5 6.01 (k 5 26.40) and the mean of 18 reverse polarity
sites is Inc. 5 21.21, Dec. 5154.31, a95 5 6.21 (k 5 20.45).
The angle between the mean of normal polarity sites and
the antipode of the mean of the reversed polarity sites is
8.31 whereas the critical angle is 12.21 indicating failure of
the reversal test. However, the ratio of the k-values from
the opposing polarity groups is 41.3 so the validity of the
reversal test is questionable.
Variations in bedding attitude within the stratigraphic
section at Tinau Khola allow application of a fold test.
Optimum unfolding occurs at 93.7% with 95% con¢dence
68
C6n
20
Fig. 4. (a) Map showing location of the Swat
Khola section. For more detailed
information review 1 : 25 000 scale
topographic map, sheet no. 2881-07A,
published byTopographical Survey
Department, Government of Nepal. (b)
Lithostratigraphy and magnetostratigraphy
from Swat Khola. In magnetostratigraphic
plot, solid circles are Class A virtual
geomagnetic pole (VGP) latitudes and open
circles are class B VGP latitudes. Black
intervals in polarity column are normal
polarity; white intervals are reverse polarity.
Polarity zone designations are shown at left
of polarity column. Correlation of Swat
Khola polarity column to the GPTS
(Lourens et al., 2004) is shown at right.
GPTS, geomagnetic polarity time scale.
limits of 88.2% unfolding and 98.8% unfolding.
The implications of the result that optimum unfolding occurs at a percent unfolding distinguishable from 100% are
unclear, in part because of the larger dispersion of normal
polarity site-mean directions compared with the dispersion
of reversed polarity directions. Converting Class A site-mean
directions in stratigraphic coordinates to normal polarity
and determining the section-mean direction yields:
Inc. 514.81, Dec. 5 343.41, a95 5 4.61. Comparing the Tinau
Khola section-mean direction to the 10 Ma expected
direction indicates counterclockwise vertical-axis
rotation of 19.0 4.7 and 26.7 5.01 £attening of
inclination (Fig. 7). Gautam & Appel (1994) observed
comparable £attening of inclination and counterclockwise
vertical-axis rotation of mean palaeomagnetic directions
at Tinau Khola.
As in the Surai Khola section, a key observation in the
Tinau Khola magnetic polarity zonation is a thick normal
polarity zone within the lower Siwalik part of the
section (E1) that correlates with chron C5n.2n (Table A3;
Fig. 8b). In addition, thick normal polarity zone O1 corre-
r 2009 The Authors
Journal Compilation r Blackwell Publishing Ltd, European Association of Geoscientists & Engineers and International Association of Sedimentologists
Magnetic polarity stratigraphy of the Neogene foreland basin deposits of Nepal
linear sediment accumulation curve and an age span for the
section of 11.8 to 8.1Ma. d13C values from palaeosol carbonates from the entire measured section at Tinau Khola are all
o 8%, consistent with the palaeomagnetic age assignment of 47.9 Ma for the whole section. Unfortunately, most
of the detrital AFTages reported by van der Beek et al. (2006)
from theTinau Khola section have been partially annealed by
post-depositional burial heating. The mean age
(11.2 1.8 Ma) for the single unreset sample is from
4500 m above magnetic polarity zone E1, which is easily
correlated with chron C5n.2n.Therefore, although the apatite
ages are consistent with our correlation to the GPTS, they
provide no additional constraints on the correlation.
PALAEOMAGNETISM OF MUKSAR
KHOLA DEPOSITS
Fig. 5. Equal-area projections of site-mean ChRM directions
from Surai Khola. (a) Directions in geographic (in situ)
coordinates. (b) Directions in stratigraphic coordinates following
restoration of bedding to horizontal. (c) Comparison of observed
section mean direction and the expected direction. Implied
vertical-axis rotation (R DR) is counterclockwise 4.5 4.41;
£attening of inclination (F DF) is 22.4 4.71. Symbols as in
Fig. 3.
lates with chron C4An.The magnetic polarity zonation from
theTinau Khola section can be con¢dently correlated to the
GPTS of Lourens et al. (2004) (Fig. 8b), yielding a nearly
At Muksar Khola (26.87001N, 86.38001E), palaeomagnetic
samples were collected at 146 sites from a 2551-m-thick
stratigraphic section of the Siwalik Group. Seventy-nine
sites yielded Class A site-mean ChRM directions and 33
sites yielded Class B site-mean ChRM directions (Table
A4, Fig. 9). Class A site-mean ChRM directions in geo graphic (in situ) coordinates and stratigraphic (bedding corrected) coordinates are illustrated in Fig. 9. Two Class A
site-mean directions are anomalous and were not used in
the following stability tests. The mean of 39 normal polarity sites is Inc. 515.21, Dec. 5 358.91, a95 5 4.41, and the
mean of 38 reverse polarity sites is Inc. 5 20.01,
Dec. 5175.51, a95 55.11.These directions pass the reversal
test with classi¢cation B.
The sampled section at Muksar Khola is a northdipping sequence with su⁄cient variations in bedding
attitude to allow application of the fold test. Optimum
unfolding occurs at 95.4% with 95% con¢dence limits
of 82.8% unfolding and 109.4% unfolding; the Class A
site-mean ChRM directions thus pass the fold test,
consistent with a primary origin for the characteristic remanent magnetization. Converting Class A site-mean
directions in stratigraphic coordinates to normal
polarity and determining the section-mean direction
yields: Inc. 517.51, Dec. 5 357.21, a95 5 3.31. Comparing
the Muksar Khola section-mean direction to the expected
direction indicates counterclockwise vertical-axis
rotation of 5.4 3.9 and 23.4 4.31 £attening of
inclination (Fig. 9).
Lithostratigraphy and magnetostratigraphy of the Siwalik Group deposits at Muksar Khola are illustrated in
Fig. 10b. Site-mean ChRM directions are listed in Table
A4 . Almost all polarity zones are determined by more than
one palaeomagnetic site and no major stratigraphic gaps
are present between palaeomagnetic sites. From magnetostratigraphic and geochronologic studies, it is known
that a thick normal polarity zone correlative with chrons
C5n.1n and C5n.2n occurs within Lower Siwalik deposits
or spanning the lower to middle Siwalik transition (R˛sler
& Appel, 1998; Gautam & R˛sler, 1999; Ojha et al., 2000).
r 2009 The Authors
Journal Compilation r Blackwell Publishing Ltd, European Association of Geoscientists & Engineers and International Association of Sedimentologists
69
T. P. Ojha et al.
(a)
82°44'0"E
Belauti
Bagahasoti
82°46'0"E
82°48'0"E
82°52'0"E
82°50'0"E
27°52'0"N
27°52'0"N
Bagahasoti
Lahareni
Lahaveni
Pakhapani
27°50'0"N
27°50'0"N
Tanda
Lami Damar
Juraune
27°48'0"N
Ransin
27°48'0"N
Dobata
27°46'0"N
27°46'0"N
Shivagadhi
Surai Khola
Siddha Paira
27°44'0"N
Surahi Naka
27°44'0"N
Chirai Naka
Ramawadahawa
27°42'0"N
82°44'0"E
0
1.5
82°46'0"E
Shiwapur
Daumai
Gokhahawa
27°40'0"N
27°42'0"N
Bichagauri
3
Village
Trail
Road
Measured section
27°40'0"N
River
Stream
6 KM
82°48'0"E
Legend
82°50'0"E
82°52'0"E
Fig. 6. (a) Map showing location of Surai Khola section. For more detailed information review 1 : 25 000 scale topographic map, sheet
no. 2782-04C, 097-11, published byTopographical Survey Department, Government of Nepal. (b) Lithostratigraphy and
magnetostratigraphy from Surai Khola section of the Siwalik Group. Correlation of Surai Khola polarity column to the GPTS (Lourens
et al., 2004) is shown at right. Symbols as in Fig. 4b. Locations of detrital apatite ¢ssion track (AFT) ages that provide maximum
stratigraphic ages are also shown (van der Beek et al., 2006). GPTS, geomagnetic polarity time scale.
70
r 2009 The Authors
Journal Compilation r Blackwell Publishing Ltd, European Association of Geoscientists & Engineers and International Association of Sedimentologists
Magnetic polarity stratigraphy of the Neogene foreland basin deposits of Nepal
GPTS
Lourens et al., 2004
Age Chron
Polarity
Magnetostratigraphy
(b)
C1n
4300
X–
4000
W+
V–
U+
T–
S+
Upper
Siwalik
Middle
Siwalik
0
1
2
C1r.1n
C1r.2n
C2n
C2r.1n
C2r.2n
3500
R–
Elephus
planifrons
3
4.4, 4.1
C2An.3n
Q+
3000
Hexaprotodon
sivalensis
2500
C2An.1n
C2An.2n
5.9
6.1
4
C3n.1n
O+
N–
M+
L–
K+
C3n.2n
J–
5
C3n.3n
C3n.4n
C3Br.1r
6
C3An.1n
I+
7.0
C2Br.1r
P–
C3An.2n
2000
1500
Lower
Siwalik
1000
Detrital AFT ages
van der Beek et al., 2006
Middle
Siwalik
H–
7.6
C–isotope
shift
G+
7
8
C3Bn
C3Br.2n
C4n.1n
C4n.2n
C4r.1n
F–
9
E+
C4An
C4Ar.1n
C4Ar.2n
D–
10 C5n.1n
C+
C5n.2n
500
11
C5r.1n
C5r.2n
C5An.1n
B–
0
meters SiSSCg
A+
–90
0
45
–45
VGP Latitude (°)
12
90
13
C5An.2n
C5Ar.1n
C5Ar.2n
C5AAn
Fig. 6. (continued)
r 2009 The Authors
Journal Compilation r Blackwell Publishing Ltd, European Association of Geoscientists & Engineers and International Association of Sedimentologists
71
T. P. Ojha et al.
polarity zone S1 with the older portion of chron
C2An.3n at 3.6 Ma. The carbon isotope transition in
the Muksar Khola section commences at 1237.5 m at the
base of a roughly 400-m-thick reverse magnetic polarity
zone (J ) (Table 1). To honor the timing constraints on
the carbon isotope shift as discussed previously, we correlate the base of zone J with the base of chron C3Ar
(6.733^7.140 Ma; Fig. 10b preferred correlation). An alternative correlation shown on the right side in Fig. 10b
equates zone J with chron C3Br.1r. Although this correlation is more attractive in terms of matching the overall
polarity zonation throughout the late Miocene and Plio cene, it places the carbon isotope shift at 6 Ma, considerably later than the 7.9^6.8 Ma time frame in which the
shift normally occurs. At this point, we favour the older
age ( 7.1^6.7 Ma) for the start of the carbon isotope shift
at Muksar Khola because it is consistent with the
6.8 Ma age of the shift across the palaeo -Gangetic Plain
as recorded by the Bengal Fan record (France-Lanord &
Derry,1994).The lower and upper parts of each correlation
are identical, and either correlation is reasonable in terms
of sediment accumulation history.
DISCUSSION
Regional correlations and lithostratigraphic
patterns
Fig. 7. Equal-area projections of site-mean ChRM directions
from Tinau Khola. (a) Directions in geographic (in situ)
coordinates. (b) Directions in stratigraphic coordinates following
restoration of bedding to horizontal. (c) Comparison of observed
section mean direction and the expected direction. Implied
vertical-axis rotation (R DR) is counterclockwise 19.0 4.71;
£attening of inclination (F DF) is 26.7 5.01. Symbols as
in Fig. 3.
The lower 120 m of the Muksar Khola section has normal polarity (zone A1), contains the lower^middle Siwalik
boundary, and is probably correlative with the upper part
of chron C5n.1n at 9.9 Ma. We correlate the uppermost
72
Combined with magnetic polarity zonation from previously worked sections at Khutia Khola (Ojha et al.,
2000) and Bakiya Khola (Harrison et al., 1993), our new
data allow for a regional correlation in the Siwalik Group
across nearly the entire length of Nepal (Fig.11).The Siwalik Group correlations are keyed on the presence of the
long normal polarity zone that correlates with chron
C5n.2n at 10^11.1 Ma, which is present in all of the sections. A second key reverse polarity interval C2Br.1r
( 3.5^4.2 Ma; Lourens etal., 2004) is recorded in the Surai and Muksar Khola sections. Polarity zones J , K1 and
L in Surai Khola, the Y polarity zone in Bakiya Khola
and the J polarity zone in Muksar Khola correlate with
reversed polarity chron C3Br.1r. Dominantly reversed
polarity zones U at Khutia Khola, F at Surai Khola,
P at Tinau Khola, L , N1 and O at Bakiya Khola,
and D
at Muksar Khola are correlated with
chron C4r.2r. If our correlations of the Dumri Formation
and the Siwalik Group at Khutia Khola are correct, a
temporal gap of 1 Myr is present between the top of
the Dumri and the base of the Siwalik Group. However,
we emphasize that this is not evidence for an unconformity
because the two units are not exposed in a single
continuous section; the upper boundary of the Dumri
Formation in the Swat Khola section is a major thrust fault
(Pearson & DeCelles, 2005).
The regional correlation suggests that the age of the
lower to middle Siwalik transition is dated at ca. 10.5 0.5 Ma in all sections except Surai Khola, where instead it
r 2009 The Authors
Journal Compilation r Blackwell Publishing Ltd, European Association of Geoscientists & Engineers and International Association of Sedimentologists
Magnetic polarity stratigraphy of the Neogene foreland basin deposits of Nepal
Tin
au K
hol
a
(a)
GPTS
Lourens et al., 2004
Age Chron
C3An.1n
(b)
Magnetostratigraphy
Polarity
1824
1000
Middle
Siwalik
7
P–
11.2
O+
N– M+
L–
K+
J–
I+ H–
G+
F–
Detrital AFT ages
van der Beek et al., 2006
1500
R–
Q+
C3An.2n
E+
500
Lower
Siwalik
8
C3Bn
C3Br.2n
C4n.1n
C4n.2n
C4r.1n
9 C4An
C4Ar.1n
C4Ar.2n
10 C5n.1n
C5n.2n
0
meters Si SS Cg
D–
C+
B–
A+
–90
–45
0
45
VGP latitude (°)
11
C5r.1n
C5r.2n
C5An.1n
90
12
C5An.2n
C5Ar.1n
Fig. 8. (a) Map showing location of Tinau Khola section. For more detailed information review 1 : 25 000 scale topographic map, sheet
no. 098-12, published byTopographical Survey Department, Government of Nepal. (b) Lithostratigraphy and magnetostratigraphy
from Tinau Khola. Symbols as in Fig. 4b. Location of detrital apatite ¢ssion track (AFT) age that provides a maximum stratigraphic age
is also shown (van der Beek et al., 2006).
r 2009 The Authors
Journal Compilation r Blackwell Publishing Ltd, European Association of Geoscientists & Engineers and International Association of Sedimentologists
73
T. P. Ojha et al.
extrapolation of a constant sedimentation rate would place
it at 4.6 Ma or younger; at Surai Khola the transition is
dated at 3.0 Ma; and at Muksar Khola it is dated at
3.5 Ma. Some of this variability could result from the imprecise nature of picking this contact in the ¢eld.
The Siwalik Group chronostratigraphy presented here
allows for assessment of regional lithostratigraphic patterns.The variation in the age of the lower^middle Siwalik
contact may be attributed to several causes. Our sections
could be representing slightly di¡erent across- strike parts
of the foreland basin system owing to variable displacement and/or erosion along the MFT, or the age di¡erence
could re£ect a true cul-de- sac in the progradational front
of middle Siwalik sandy lithofacies. In any case, the variation in age of the lower^middle Siwalik boundary poses a
challenge to models for monsoon intensi¢cation based on
the increased discharge of £uvial channels as manifested in
this lithostratigraphic transition. If this lithofacies change
is truly a result of monsoon intensi¢cation, then we would
expect it to be a regionally isochronous event. In order to
test for regional isochroneity, additional chronostratigraphic data are needed from thrust sheets in the Siwalik
foothills that are located north of the MFTsheet.
Sediment accumulation history
Fig. 9. Equal-area projections of site-mean ChRM directions
from Muksar Khola. (a) Directions in geographic (in situ)
coordinates. (b) Directions in stratigraphic coordinates following
restoration of bedding to horizontal. (c) Comparison of observed
section mean direction and the expected direction. Implied
vertical-axis rotation (R DR) is counterclockwise 5.4 3.91;
£attening of inclination (F DF) is 23.4 4.31. Symbols as in
Fig. 3.
occurs at 8.0 Ma (Fig. 11). The middle^upper Siwalik
transition is present in three of our sections (Khutia, Surai
and Muksar Kholas) and is more variable in age: at Khutia
Khola it is not directly dated by magnetic stratigraphy, but
74
The rates of sediment accumulation in foreland basins
provide useful information about lithospheric properties,
the kinematic history of the thrust belt, and the rates of
subsidence and £exural wave migration (Jordan et al.,
1988). This approach has been exploited in the Pakistan
and northern Indian part of the Himalayan foreland basin
by Burbank et al. (1996). The foreland lithosphere
migrates through the standing £exural wave set up by
the load of the adjacent thrust belt (Sinclair & Allen,
1992). Because the two-dimensional shape of the £exural
pro¢le steepens exponentially towards the thrust belt load,
the rate of subsidence should generally increase through
time as the £exural wave migrates past a given locality in
the foreland (Angevine et al., 1990). This pattern has been
demonstrated in many foreland basins (e.g. Angevine
et al., 1990; Dorobek, 1995; DeCelles & Currie, 1996; Tensi
et al., 2006).
Relatively abrupt changes in the slope of a sediment
accumulation curve are commonly taken to indicate the
timing of major thrusting events. Strictly speaking, the
rate of sediment accumulation is an accurate proxy
for subsidence rate only when the elevation of the depositional surface is known through time and the rates of sediment compaction are calculable (Van Hinte, 1978;
Dickinson et al., 1988). In the case of the Nepalese Himalayan foreland basin, the depositional environment was exclusively nonmarine, such that the surface elevation
through time is unknown. However, carbon and oxygen
isotopic data from palaeosol carbonate in the Siwalik
Group provide no evidence to suggest that the palaeoelevation of the Himalayan foreland basin was signi¢cantly
di¡erent from its modern elevation (o200 m above sea
r 2009 The Authors
Journal Compilation r Blackwell Publishing Ltd, European Association of Geoscientists & Engineers and International Association of Sedimentologists
Magnetic polarity stratigraphy of the Neogene foreland basin deposits of Nepal
(a)
GPTS
Lourens et al., 2004
Age Chron
(b)
Upper
Siwalik
Middle
Siwalik
Preferred
correlation
2700
3
Polarity
2500
C2An.1n
Alternate
correlation
C2An.2n
Polarity
S+
C2An.3n
S+
R–
C2Br.1r
R–
4
C3n.1n
Q+
P–
O+
N–
L–M+
K+
2000
5
C3Br.1r
6
1500
I+
H–
G+
F–
E+
1000
C3An.1n
C3An.2n
J–
C–isotope
shift
C3n.2n
C3n.3n
C3n.4n
7
8
C3Ar
C3Bn
C3Br.2n
C4n.1n
C+
Middle
Siwalik
Lower
Siwalik
9
B–
0
meters Si SS Cg
A+
–90
45
0
–45
VGP latitude (°)
I+
C4r.1n
C4An
D–
C+
C4Ar.1n
C4Ar.2n
B–
C4n.2n
10 C5n.1n
90
J–
H–
G+
F–
E+
D–
500
Q+
P–
O+
N–
M+
K+ L–
A+
C5n.2n
11
C5r.1n
C5r.2n
Fig. 10. (a) Location map for the Muksar Khola section. For more detailed information review 1 : 25 000 scale topographic maps, sheets
no. 2686 -02B, 2686 -02C, 2686 -02D published byTopographical Survey Department, Government of Nepal. (b) Lithostratigraphy and
magnetostratigraphy from Muksar Khola. Symbols as in Fig. 4b. Preferred and alternative correlations of Muksar Khola polarity column
to the GPTS are shown at right. GPTS, geomagnetic polarity time scale.
r 2009 The Authors
Journal Compilation r Blackwell Publishing Ltd, European Association of Geoscientists & Engineers and International Association of Sedimentologists
75
T. P. Ojha et al.
Fig. 11. Regional correlation from west to east across Nepal. Grey areas highlight major correlation intervals, and the section is hung on
the top of chron C5n.2n.
level; Quade et al., 1995). Although the depositional systems
recorded in the Dumri Formation and Siwalik Group exhibit an obvious upward coarsening in response to increasing proximity to the front of the Himalayan thrust belt, the
modern elevation gain from the Ganges River to the front
of the thrust belt is o150 m.Therefore, no attempt is made
to correct for palaeoelevation. Although sediment decompaction is a routine process, Burbank et al. (1996)
argued that decompaction of the Neogene strata of the Himalayan foreland basin is compromised by the fact that
they were substantially lithi¢ed by pedogenic and early
diagenetic processes before burial. In support of this,
Quade & Roe (1999) showed that calcite cements and
pedogenic carbonates formed pervasively in the Siwalik
Group within a few metres of the surface.We concur with
the view that decompaction is unnecessary and could lead
to erroneous interpretations (Burbank et al., 1996), and we
view the curves derived from cross- correlation plots in
Fig.12 as representative of long-term sediment accumulation rates.
The rates of sediment accumulation in our palaeomagnetic sections are in the range typical for foredeep depo zones in foreland basin systems (0.1^0.6 mm year 1). All
of the accumulation rate curves exhibit upward concavity,
as expected for increasing accumulation rates in response
to migration of an upward convex exponential £exural pro ¢le (Fig.12). At least one abrupt increase in sediment accu-
76
mulation rate is observed on all but one of the curves (the
Tinau Khola curve is linear, but only covers 3 Myr of
geologic time). The timing of this increase changes systematically from west to east (Fig. 13): at Khutia Khola an
80% increase occurred at 11.1 Ma; at Surai Khola, a 27%
increase took place at 8.8 Ma; at Bakiya Khola the rate
increased by 28% at 7.5 Ma; and at Muksar Khola the rate
increased by 32% at 5.3 Ma. Because all of these sections are located in the MFTsheet, we may interpret them
as more or less palaeogeographically equivalent sections.
In other words, each of these sections represents facies
that accumulated in a tectonically analogous position
within the foreland basin.
Meigs et al. (1995) and Burbank et al. (1996) attributed a
nearly synchronous doubling in the rate of sediment accumulation at 11Ma in several sections from northern Pakistan to northern India to enhanced loading in the foreland by
initial slip on the MBT. If this interpretation is correct, and if
our data are a further re£ection of this important tectonic
event, then it may be inferred that the MBTwas emplaced almost simultaneously along a roughly1000-km-long segment
of its trace in Pakistan and India, and that the thrust propagated approximately 600 km laterally eastward from western
to eastern Nepal over a time span of 5.8 Myr at a rate of
103 mm year 1. This rate is approximately two times
greater than typical rates of lateral propagation on thrust systems in the Himalaya (Mugnier et al., 1999a, b; van der Beek
r 2009 The Authors
Journal Compilation r Blackwell Publishing Ltd, European Association of Geoscientists & Engineers and International Association of Sedimentologists
m/
yr
Surai Khola
Thickness (m)
r
/y
m
0.
31
0.
39
m
m
/y
r
m
11.1 Ma
4.9 Ma
Thickness (m)
0.5
6m
Khutia Khola
0.5
9m
m/
yr
Magnetic polarity stratigraphy of the Neogene foreland basin deposits of Nepal
8.8 Ma
Age (Ma)
/yr
r
/y
m
28
m
0.
m
Swat Khola
31
0.
m
18.8 Ma
Age (Ma)
m
m
41
0.
5.3 Ma
/yr
m
34
Thickness (m)
m
m
/y
r
0.
36
0.5
7m
m/
yr
Thickness (m)
7.5 Ma
Muksar Khola
Thickness (m)
Tinau Khola
0.4
6m
m/
yr
Bakiya Khola
/yr
Age (Ma)
m
0.
Age (Ma)
Age (Ma)
Fig. 12. Cross- correlation plots showing the derivation of sediment accumulation curves.
et al., 2002), suggesting that the MBT in Nepal might have
originated as a series of independent, unlinked local thrusts
that eventually merged laterally to form the single trace of the
MBT. A similar process may be occurring presently on the
MFTsystem (Mugnier et al., 1999a, b, 2004).The one exception to the regional trend of eastward younging in the rate
change is at Tinau Khola, where our correlation with the
GPTS indicates a nearly linear sediment accumulation
history and that the portion of the section that we sampled
may completely predate the change in accumulation rate at
that location (Fig.13).
It is also conceivable that, at least in some sections
(e.g. Surai Khola), the subsidence event was driven by emplacement of thrust sheets farther north than the MBT,
such as the Ramgarh thrust (Pearson & DeCelles, 2005).
The timing of slip on the Ramgarh thrust has been
dated by 40Ar/39Ar muscovite cooling ages as 11^12 Ma in
western Nepal north of the Khutia Khola section
(Robinson et al., 2006), and 10 Ma in central Nepal
(Kohn et al., 2004), but no age data are presently available
from eastern Nepal. The only independent constraint
on the timing of slip on the MBT in Nepal is that it
cuts upper Miocene deposits in the Siwalik Group, and
therefore must have experienced at least some signi¢cant
slip after the end of the Miocene. This would preclude
neither earlier nor regionally time-transgressive slip on
the MBT.
A second increase (by 49%) in the rate of sediment
accumulation is apparent at 4.9 Ma in the Surai
Khola section (Fig. 12). Rocks of this age and slightly
younger are only documented in one other section ^
Muksar Khola ^ so it is not possible at this point to
speculate on whether or not this second rate increase
re£ects a younger thrusting event. Similarly, in the
Swat Khola section an increase at 18.8 Ma is evident.
This is within the range of reported times for the
initial emplacement of the Main Central thrust sheet
in western and central Nepal (Copeland et al., 1996;
Hodges et al., 1996; DeCelles et al., 2001; Robinson et al.,
2006).
The rate of sediment accumulation in most of the
Swat Khola section of the Dumri Formation was
0.28 mm year 1, on trend with the rates recorded in the
lower Siwalik Group at nearby Khutia Khola. A composite
Dumri^Siwalik section in western Nepal exhibits the typical upward concave pattern of sediment accumulation that
r 2009 The Authors
Journal Compilation r Blackwell Publishing Ltd, European Association of Geoscientists & Engineers and International Association of Sedimentologists
77
T. P. Ojha et al.
EAST
Muksar Khola
Bakiya Khola
Siwalik Gr.
Tinau Khola
Surai Khola
Khutia Khola
Fig. 13. Sediment accumulation curves
plotted against the GPTS of Lourens et al.
(2004), and arrayed from east (top) to west
(bottom).Thick stippled line highlights the
timing of major kinks in accumulation
curves, with an eastward decrease in the age
of the major increase in accumulation rate.
Swat Khola
results from the forelandward migration of an elastic £exural wave, with slower rates giving way to progressively
more rapid rates as the distal foredeep is replaced by the
proximal foredeep (Fig. 12).
WEST
Age (Ma)
Dumri Fm.
the frontal Lesser Himalaya. Future magnetostratigraphic research in theTertiary of Nepal should focus on sampling laminated siltstones from the Siwalik Group in thrust sheets north
of the MFTsheet, as well as additional sections of the Dumri
Formation.
CONCLUSIONS
Magnetostratigraphically consistent and useful results are
obtained from laminated siltstones in the Siwalik Group and
Dumri Formation. The Dumri Formation spans 19.9 to
15.1Ma. The dated portions of the Siwalik Group range
in age from 13.5^2.0 Ma. Major lithostratigraphic boundaries in the Siwalik Group exhibit ca. 2 Myr of diachroneity,
and cannot be used simply to estimate the timing of palaeoclimatic changes associated with the Asian monsoon. Sediment
accumulation rates range from 0.28 to 0.56 mmyear 1,
generally increasing through time in both the Dumri
Formation and the Siwalik Group. A major increase in accumulation rate in the Siwalik Group took place at progressively
younger times across Nepal, from 11.1Ma in western Nepal
to 5.3 Ma in eastern Nepal. Increased accumulation rates
suggest lateral propagation of a major thrust system in
78
Acknowledgments
We are grateful to reviewers Andrew Meigs, Bet Beamud,
and Wolfgang R˛sler, and editor Hugh Sinclair, whose critiques of the manuscript corrected errors and resulted in
many improvements. This research was funded by U.S.
National Science Foundation grant EAR97-25607. We
thank B.N. Upreti, Bill Hart, Carmala Garzione, Gratian
Quade, David Richards, and Orestes Mor¢n for assistance
in the ¢eld and the laboratory.
Appendix A
Tables A1^A4
r 2009 The Authors
Journal Compilation r Blackwell Publishing Ltd, European Association of Geoscientists & Engineers and International Association of Sedimentologists
Magnetic polarity stratigraphy of the Neogene foreland basin deposits of Nepal
Table A1. Site-Mean ChRM directions for Dumri Formation at Swat Khola
Site
Level m
Class
N
SW002
SW020
SW038
SW160
SW173
SW190
SW207
SW248
SW283
SW304
SW335
SW351
SW354
SW366
SW371
SW378
SW387
SW452
SW467
SW473
SW478
SW497
SW501
SW505
SW509
SW515
SW529
SW550
SW565
SW592
SW596
SW600
SW608
SW618
SW628
SW635
SW649
SW672
SW677
SW695
SW712
SW738
SW763
SW795
SW831
SW855
SW884
SW907
SW922
SW938
SW980
SW983
SW997
ST012
ST030
ST045
ST070
ST085
2.0
20.0
38.0
160.0
173.0
190.0
207.0
248.0
283.0
304.0
335.0
351.0
354.0
366.0
371.0
378.0
387.0
452.0
467.0
473.0
478.0
497.0
501.0
505.0
509.0
515.0
529.0
550.0
565.0
592.0
596.0
600.0
608.0
618.0
628.0
635.0
649.0
672.0
677.0
695.0
712.0
738.0
763.0
795.0
831.0
855.0
884.0
907.0
922.0
938.0
980.0
983.0
997.0
1012.0
1030.0
1045.0
1070.0
1085.0
A
B
B
B
A
A
A
B
A
B
A
B
B
A
B
B
A
A
A
A
A
A
A
B
A
B
B
A
A
B
B
A
A
B
A
A
A
A
A
A
B
B
A
B
B
A
A
A
B
B
A
A
A
A
A
A
A
A
3
3
3
2
3
4
4
2
9
2
7
6
5
4
5
5
5
4
3
3
5
4
3
2
4
3
4
6
8
2
2
4
4
2
3
3
3
3
3
4
3
2
3
2
2
4
4
3
2
3
3
3
3
3
3
3
3
4
a95, deg
30.4
88.7
K
17.5
3.0
n
n
n
n
43.0
11.8
13.6
n
11.9
9.3
61.2
46.4
n
14.9
n
n
3.9
243.4
n
n
89.9
11.7
76.1
82.7
11.0
20.4
20.0
56.6
9.1
10.1
3.2
n
6.6
95.8
n
55.5
27.3
n
1.7
47.7
2.0
1.8
49.0
21.3
39.0
5.8
47.2
57.0
1442.4
n
115.3
2.8
n
2.4
5.1
n
n
n
5.7
8.4
139.2
121.8
n
n
18.1
11.0
11.1
8.0
33.5
11.3
26.76
70.7
124.8
93.54
8.47
66.9
n
n
n
n
31.9
15.9
n
n
n
n
15.6
9.6
12.6
n
143.2
11.9
36.8
10.2
23.9
16.4
12.5
9.8
20.8
25.02
40.21
37.73
n
1.9
42.25
12.3
145.9
13.2
66.3
97.7
160.7
20.4
Geographic
Stratigraphic Coordinates
I, deg
I, deg
47.6
9.8
48.8
66.5
32.2
59.6
31.9
66.4
56.1
31.4
17.8
9.3
42.1
44.7
38.4
24.9
70.6
8.7
15.5
13.4
14.0
74.2
60.0
70.3
53.2
23.3
47.9
52.7
53.4
4.8
66.9
48.3
55.8
41.9
60.9
58.9
41.7
74.7
70.0
54.1
69.7
35.8
68.4
40.0
3.4
48.5
61.8
34.7
27.7
34.0
49.4
73.5
57.7
43.0
51.1
49.0
47.8
61.1
D, deg
107.9
92.7
326.0
85.5
0.2
143.3
57.8
115.5
109.3
94.0
130.9
39.5
244.3
193.1
164.6
0.5
165.2
185.4
193.0
182.5
156.9
176.4
146.6
341.1
176.6
318.6
340.6
354.1
324.6
327.2
149.5
165.2
172.6
159.3
158.4
158.4
150.3
139.5
195.3
167.9
268.0
232.7
249.7
330.3
303.2
196.1
351.8
300.2
321.9
229.7
158.5
179.7
192.4
173.4
190.2
148.6
189.6
207.1
24.1
34.0
5.7
36.1
38.4
10.6
77.6
29.6
36.4
30.4
12.3
64.5
24.9
2.5
14.4
10.9
24.2
61.4
46.6
40.7
19.1
17.1
21.8
32.6
4.3
13.4
10.2
7.8
27.1
10.0
16.2
0.6
8.3
6.3
11.5
10.5
13.2
37.2
29.3
21.7
28.3
70.2
35.5
15.6
8.9
6.1
12.9
16.5
28.0
24.3
3.5
8.3
17.3
2.3
15.0
11.1
10.5
8.0
D, deg
191.2
106.5
4.4
199.4
357.8
186.6
179.2
189.0
190.5
93.6
154.2
0.9
243.9
210.9
192.0
6.4
224.9
144.4
179.7
167.9
153.5
220.9
199.5
254.2
202.3
340.4
11.1
23.3
16.1
323.9
200.8
189.3
200.7
184.4
201.9
193.5
183.5
187.5
223.3
212.3
251.9
19.2
11.9
354.9
305.9
192.0
15.0
279.1
278.5
228.8
192.6
218.1
213.8
187.9
206.8
181.5
203.7
215.3
Lat, 1N
70.8
22.9
58.1
54.6
39.6
65.8
52.5
71.9
77.6
30.6
56.8
51.8
2.7
48.9
65.8
55.2
45.4
11.6
33.4
36.7
44.2
45.1
64.8
41.6
56.2
61.3
70.0
56.8
69.3
45.6
56.1
59.2
58.5
64.1
60.9
62.1
67.7
79.4
49.6
55.2
22.8
60.9
75.8
68.5
51.7
61.9
53.5
1.7
0.1
27.2
60.3
46.4
52.5
62.2
41.2
66.8
49.0
48.4
r 2009 The Authors
Journal Compilation r Blackwell Publishing Ltd, European Association of Geoscientists & Engineers and International Association of Sedimentologists
Long, 1E
46.1
180.9
253.1
269.6
264.2
65.3
261.0
59.2
47.1
190.0
133.7
244.2
8.1
27.0
51.3
250.3
3.0
107.5
81.8
95.4
117.9
8.7
31.2
355.7
38.8
305.4
235.5
215.4
212.1
313.2
22.7
64.4
39.0
71.3
35.3
45.0
72.3
32.6
1.8
15.0
346.3
104.8
209.0
281.7
300.2
59.9
236.9
339.8
334.4
25.9
52.7
18.5
16.8
57.5
39.1
77.8
43.8
21.3
79
T. P. Ojha et al.
Table A1. (Continued)
Site
Level m
Class
N
a95, deg
ST092
ST106
ST112
ST126
ST150
1092.0
1106.0
1112.0
1126.0
1150.0
A
A
A
B
A
4
3
3
4
3
11.1
9.7
30.0
126.8
17.1
K
Geographic
Stratigraphic Coordinates
I, deg
I, deg
69.1
163.2
17.9
1.6
52.9
D, deg
56.8
31.9
26.5
59.8
66.7
146.7
202.6
1.2
175.2
353.7
21.4
21.2
16.3
13.3
26.2
D, deg
Lat, 1N
185.8
204.9
5.1
193.9
21.4
71.6
43.6
52.7
64.4
65.2
Long, 1E
63.4
46.7
253.2
48.0
203.9
Site, identi¢cation number for paleomagnetic site; Level, stratigraphic level of collecting site in meters; N, number of samples used to determine site^
mean direction; k, best estimate of Fisher precision parameter; a95, radius of cone of 95% con¢dence about site^mean direction; Geographic, in situ
directions of ChRM; Stratigraphic Coordinates, ChRM direction after restoring bedding to horizontal; I and D, inclination and declination of site^mean
direction; Lat and Long, latitude and longitude of the site^mean virtual geomagnetic pole (VGP) computed from the stratigraphic directions.
n
Sites that do not permit calculation of statistical parameters but do provide unambiguous polarity determinations.
Table A2. Site-mean ChRM directions for Siwalik Group at Surai Khola
Site
SK112
SK114
SK115
SK119
SK120
SK121
SK122
SK123
SK124
SK125
SK127
SK128
SK129
SK130
SK132
SK133
SK134
SK135
SK136
SK138
SK140
SK141
SK010
SK011
SK012
SK013
SK014
SK015
SK016
SK017
SK018
SK019
SK022
SK024
SK025
SK026
SK027
SK028
SK033
SK035
80
Level (m)
0
8
9
18
20
23
25
26
27
28
35
40
42
45
53
60
64
73
88
117
136
147
204
216
224
236
248
261
273
283
295
305
322
345
351
376
380
397
415
443
Class
N
a95 (1)
B
B
A
A
A
A
B
A
A
A
A
A
B
B
A
B
B
A
A
A
A
A
A
A
A
A
B
A
A
B
A
A
A
B
A
B
B
A
A
A
3
2
3
3
3
3
2
3
3
3
4
4
2
2
4
2
2
3
4
3
3
3
3
3
3
3
2
3
3
2
3
3
3
2
3
2
2
3
4
3
n
n
n
n
46.0
40.2
22.8
6.8
8.2
10.5
30.4
330.1
k
n
n
10.6
42.7
13.5
12.0
13.0
136.5
9.4
84.4
59.9
51.2
n
n
n
n
4.6
406.7
n
n
n
n
11.8
27.2
8.8
14.3
5.9
29.1
15.9
18.0
54.5
110.9
12.4
198.8
75.4
436.1
19.1
61.0
47.8
6.2
n
18.7
52.4
n
44.4
6.6
n
n
7.1
14.5
26.2
302.1
73.5
23.3
n
34.9
n
13.6
n
n
n
n
19.7
8.4
23.0
40.2
121.9
29.9
Geographic
Stratigraphic coordinates
I (deg.)
I (deg.)
26.7
69.4
71.1
37.5
72.7
73.2
69.6
49.7
78.6
75.6
83.5
77.9
74.0
76.0
76.6
75.4
64.0
60.1
51.9
63.2
87.3
75.6
66.3
76.5
81.8
59.5
80.9
74.8
62.5
73.2
64.8
62.8
58.9
25.4
61.4
68.8
60.1
62.1
69.5
84.1
D (deg.)
235.6
22.6
308.0
324.6
347.4
353.5
67.4
329.4
349.2
70.5
348.4
217.4
154.0
294.7
21.7
33.5
131.2
134.8
158.0
105.1
286.5
321.8
183.2
236.2
334.2
7.2
43.8
261.1
241.8
282.2
72.3
155.5
96.0
287.8
181.1
123.1
126.5
91.5
47.3
87.4
3.3
55.5
24.3
7.3
18.8
14.2
26.1
1.4
13.6
14.1
34.5
19.1
15.9
37.0
22.0
22.4
11.6
25.4
14.8
12.7
21.2
26.7
2.0
26.9
22.2
55.0
30.9
27.7
20.7
34.5
21.3
1.3
20.5
32.2
9.2
35.7
40.9
29.5
25.2
31.4
D (deg.)
224.9
159.9
340.7
325.6
345.8
349.6
5.7
334.6
346.7
8.4
164.5
181.9
169.1
190.2
0.7
4.0
150.6
129.9
158.0
141.4
172.6
176.3
174.1
336.2
351.0
139.9
159.2
178.0
183.8
170.0
12.2
162.3
23.1
254.8
165.7
15.5
24.6
30.4
0.9
348.7
Lat. (1N)
37.8
71.1
66.5
44.4
67.5
67.2
75.0
52.5
65.6
67.9
73.3
71.9
67.8
78.3
73.6
73.4
54.5
41.3
61.0
47.7
71.8
75.9
61.0
64.2
72.0
55.1
68.0
77.1
72.8
77.5
70.0
58.3
62.5
21.2
63.1
73.7
67.4
59.5
75.8
75.2
Long.(1E)
19.5
203.7
316.8
314.8
302.0
290.3
241.0
307.6
296.5
240.1
144.3
76.6
112.6
27.8
260.5
249.1
140.1
166.2
132.7
149.8
106.8
97.6
94.8
326.5
292.2
196.1
147.4
91.3
69.6
131.9
225.2
117.8
205.7
343.6
116.0
198.9
178.4
189.5
258.7
309.7
r 2009 The Authors
Journal Compilation r Blackwell Publishing Ltd, European Association of Geoscientists & Engineers and International Association of Sedimentologists
Magnetic polarity stratigraphy of the Neogene foreland basin deposits of Nepal
Table A2. (Continued)
Site
Level (m)
Class
N
a95 (1)
SK036
SK037
SK038
SK039
SK040
SK041
SK042
SK043
SK044
SK045
SK046
SK051
SK047
SK049
SK050
SK052
SK053
SK054
SK055
SK056
SK057
SK058
SK059
SK061
SK062
SK143
SK144
SK145
SK146
SK147
SK148
SK149
SK150
SK063
SK064
SK065
SK067
SK080
SK078
SK081
SK079
SK077
SK076
SK075
SK074
SK072
SK070
SK068
SK082
SK084
SK086
SK087
SK088
SK089
SK091
SK108
SK109
SK110
456
470
482
497
505
518
525
534
550
595
608
623
624
659
685
758
788
808
817
837
862
874
889
915
928
940
943
948
950
959
969
974
977
985
1013
1032
1065
1110
1115
1119
1139
1167
1185
1214
1244
1312
1368
1403
1479
1604
1641
1653
1673
1695
1725
2021
2048
2064
A
A
A
B
A
B
A
B
A
A
A
A
A
B
B
A
B
B
A
A
A
B
A
A
A
B
A
B
B
A
A
A
B
A
A
A
A
B
A
A
A
A
A
A
B
A
B
A
A
A
A
A
A
A
B
B
B
B
3
3
4
2
3
2
4
3
3
3
3
4
3
2
2
3
2
3
3
3
3
2
3
3
3
2
3
3
2
4
4
3
2
4
4
3
3
3
3
3
3
3
3
3
2
3
3
3
3
3
3
3
3
3
2
2
2
2
14.8
6.6
16.3
n
7.1
k
70.5
345.4
32.8
n
305.3
n
n
9.4
110.3
24.8
5.5
26.1
9.6
4.3
95.9
2.4
25.7
510.0
23.4
93.5
830.6
n
n
n
n
21.1
n
76.9
23.2
18.2
16.3
35.0
n
3.7
29.4
47.0
58.5
n
n
5.9
23.3
23.8
437.1
28.9
27.9
n
n
7.1
65.7
301.0
4.6
n
n
7.3
12.8
13.2
159.3
52.9
88.8
n
n
21.7
16.9
21.3
29.0
100.5
26.6
21.8
9.3
12.0
17.9
9.5
18.9
30.4
34.5
19.2
2.6
22.6
33.1
175.7
107.3
48.7
170.2
n
n
13.5
75.2
16.4
17.5
10.4
10.4
11.1
28.9
14.7
84.7
3.8
57.3
50.6
140.8
141.1
123.4
19.3
71.5
n
n
n
n
n
n
n
n
Geographic
Stratigraphic coordinates
I (deg.)
I (deg.)
75.9
78.4
59.1
80.3
69.7
67.4
62.4
53.9
60.0
64.6
60.0
68.2
55.8
71.0
80.9
74.8
67.8
74.8
54.4
63.2
65.0
41.6
56.1
69.9
55.7
70.3
86.7
72.3
77.4
85.2
60.8
73.5
79.8
56.6
30.1
66.5
45.0
64.6
72.7
61.0
68.6
64.4
45.2
45.7
74.5
61.2
39.2
82.5
49.3
72.8
64.5
51.5
61.7
70.1
78.7
76.7
70.9
70.7
D (deg.)
3.6
43.3
334.4
45.9
40.9
33.2
355.7
357.5
111.6
25.3
350.6
90.2
16.9
46.4
299.0
98.5
59.9
52.2
5.3
61.9
197.0
283.4
295.3
154.8
295.3
216.2
263.2
162.2
91.3
110.6
203.0
187.7
212.8
20.7
273.3
257.2
240.4
29.5
305.1
29.4
57.7
171.6
155.7
215.5
155.5
43.8
210.9
42.1
39.0
16.8
177.3
306.3
28.8
3.2
358.6
194.2
95.4
56.6
22.0
49.5
24.3
31.2
30.8
9.3
0.4
5.6
46.1
21.0
23.2
41.5
19.1
31.9
23.9
6.0
10.3
31.7
14.8
3.7
11.5
29.5
40.3
33.7
37.6
5.7
29.4
11.3
41.2
9.3
0.4
2.1
9.7
5.1
11.8
42.2
1.9
5.5
32.8
6.7
22.8
12.7
4.2
6.7
39.1
53.1
6.1
34.5
1.4
30.1
1.6
10.3
7.8
10.3
52.3
19.9
36.2
24.8
D (deg.)
345.3
331.9
330.3
340.9
355.8
4.0
356.4
353.2
12.6
348.5
337.6
345.0
345.3
356.3
333.5
359.0
4.0
10.0
357.0
32.2
184.3
217.3
208.1
3.2
170.6
173.1
168.8
164.2
123.4
162.9
184.3
176.4
182.2
8.9
290.6
190.1
206.7
9.1
347.1
22.0
4.6
190.3
166.5
212.0
195.3
7.4
201.6
3.4
26.4
8.3
163.8
334.1
26.3
8.3
177.8
202.4
18.5
15.3
Lat. (1N)
68.8
65.3
58.6
69.4
78.5
66.9
62.2
58.7
78.8
70.2
64.0
76.0
67.6
79.2
61.0
65.5
67.4
76.2
69.9
50.0
68.0
53.5
64.2
80.2
79.1
64.2
74.1
63.3
39.3
61.8
62.1
63.0
67.0
63.7
21.0
80.5
53.2
63.8
74.8
58.1
73.8
66.8
61.5
46.4
75.1
81.1
58.1
81.0
53.2
76.3
57.7
56.8
55.6
66.3
84.2
62.8
71.6
69.6
r 2009 The Authors
Journal Compilation r Blackwell Publishing Ltd, European Association of Geoscientists & Engineers and International Association of Sedimentologists
Long.(1E)
306.1
5.8
330.5
325.3
283.2
252.2
270.6
276.0
171.6
297.8
320.7
341.1
303.4
281.9
326.7
264.9
252.0
218.4
271.1
206.6
71.1
4.0
357.2
244.5
136.7
98.8
126.0
120.0
181.7
121.0
73.7
90.8
77.2
242.1
348.2
8.8
34.0
241.5
316.2
217.6
246.2
55.7
111.8
32.3
10.1
126.5
38.5
241.4
214.7
226.3
114.0
315.0
211.1
241.5
243.9
27.4
192.1
214.7
81
T. P. Ojha et al.
Table A2. (Continued)
Geographic
Stratigraphic coordinates
I (deg.)
I (deg.)
Site
Level (m)
Class
N
a95 (1)
SK151
SK152
SK153
SK154
SK159
SK160
SK161
SK162
SK163
SK164
SK165
SK166
SK168
SK169
SK171
SK172
SK173
SK174
SK175
SK176
SK178
SK177
SK179
SK182
SK183
SK184
SK185
SK186
SK187
SK188
SK189
SK191
SK201
SK200
SK199
SK198
SK197
SK194
SK193
SK192
SK202
SK203
SK204
SK205
SK206
SK207
SK208
SK209
SK210
SK212
SK214
SK215
SK216
SK217
SK218
SK219
SK220
SK222
2139
2140
2165
2255
2415
2444
2502
2504
2526
2535
2570
2580
2618
2670
2695
2720
2738
2741
2775
2798
2805
2808
2846
2932
2934
2944
2954
2958
2982
2988
2990
3021
3047
3055
3060
3062
3064
3098
3103
3108
3155
3170
3190
3220
3240
3280
3350
3386
3435
3525
3578
3601
3620
3635
3694
3707
3729
3776
A
B
A
B
B
A
A
A
A
A
A
A
A
B
A
A
A
A
A
A
A
A
A
A
A
A
B
B
A
A
A
A
B
A
A
A
B
A
A
A
A
A
B
A
A
B
A
B
A
A
A
A
A
A
A
A
B
A
4
2
3
5
2
5
4
3
8
4
3
5
3
2
5
5
4
5
6
4
4
5
3
5
3
3
2
2
4
3
3
3
3
8
9
5
2
5
3
4
4
4
5
5
3
2
5
2
5
3
4
4
4
5
6
3
3
3
7.9
82
r 2009 The Authors
Journal Compilation r Blackwell Publishing Ltd, European Association of Geoscientists & Engineers and International Association of Sedimentologists
k
136.8
n
n
5.8
74.9
445.5
2.0
n
n
5.6
17.9
11.6
8.9
27.0
40.9
8.0
18.4
186.9
27.2
114.9
39.8
12.6
10.1
92.3
46.0
n
n
11.5
7.9
78.8
20.7
12.6
15.4
19.5
10.0
26.5
18.0
31.8
41.3
n
45.3
94.9
2.4
14.6
29.4
36.6
23.3
59.6
22.7
18.9
16.1
10.0
n
n
n
11.6
19.3
5.9
49.5
63.4
41.9
434.6
7.3
n
n
8.9
9.2
9.0
39.6
32.2
73.3
n
n
15.8
13.9
41.7
32.3
21.3
73.4
6.9
24.8
24.5
79.3
5.8
9.1
19.5
2.0
122.3
25.8
n
n
11.5
44.9
n
n
22.1
37.3
20.4
44.3
28.0
17.7
23.9
44.3
n
15.3
12.9
12.0
21.3
5.3
11.7
19.6
8.8
8.8
n
66.0
61.3
68.0
40.9
81.6
35.2
78.9
64.5
62.4
66.9
71.9
50.0
66.0
56.6
57.8
85.5
60.7
27.7
82.2
64.0
80.3
65.7
61.1
68.2
26.2
28.4
11.1
62.7
28.4
34.4
41.1
37.1
11.8
60.2
61.7
79.1
75.7
32.5
58.5
83.7
78.6
50.6
73.3
71.6
76.9
67.5
63.0
68.8
80.2
66.7
54.4
82.3
43.9
59.3
67.5
70.8
70.8
68.2
27.0
D (deg.)
38.9
27.4
28.0
290.1
273.0
49.8
177.0
240.5
106.4
25.6
9.9
349.9
233.8
32.5
275.9
347.3
251.8
303.8
18.5
82.9
349.0
295.9
212.9
340.6
337.9
331.2
25.5
335.2
151.8
189.3
164.9
29.7
238.4
293.4
122.1
193.1
333.6
53.1
284.8
283.2
4.0
211.7
187.3
290.4
48.1
86.9
214.7
124.1
219.1
270.2
38.9
58.7
300.4
260.8
228.5
19.9
25.2
281.5
42.3
45.2
13.6
33.2
16.8
49.3
2.9
18.3
8.3
17.9
4.9
5.7
2.3
39.7
38.2
1.9
3.9
17.4
9.6
23.1
2.8
9.8
9.1
72.6
75.2
41.8
52.0
66.5
69.2
84.0
76.4
48.8
18.8
39.5
33.5
3.8
69.9
6.2
32.8
34.2
44.2
5.7
14.0
13.0
20.6
11.2
0.2
7.3
17.4
16.0
9.2
2.9
54.2
33.0
31.1
63.8
48.7
13.5
D (deg.)
123.5
134.2
16.0
157.5
304.5
173.0
170.1
193.2
159.4
11.6
8.2
344.0
187.7
119.2
352.3
352.8
237.0
352.3
359.2
12.4
351.9
329.4
196.5
351.9
289.7
309.5
164.7
264.5
78.8
294.9
94.8
46.4
185.5
205.0
155.3
175.6
238.3
14.2
348.9
344.6
111.2
179.5
179.0
183.8
133.1
144.6
186.9
156.8
188.3
204.3
3.1
30.2
195.5
195.2
196.0
160.2
180.0
300.2
Lat. (1N)
39.6
49.5
64.2
67.2
34.4
83.4
62.0
67.8
59.3
68.4
58.8
55.7
62.4
35.3
80.6
60.5
27.7
69.8
67.0
70.5
62.5
53.0
62.0
4.0
15.8
18.9
76.0
24.0
28.4
32.2
22.8
17.4
71.2
66.8
65.4
63.8
40.6
61.9
75.8
73.3
29.4
65.1
69.3
68.5
42.9
49.8
61.4
57.3
69.6
59.8
66.7
50.9
75.0
73.0
71.6
66.4
88.1
29.9
Long.(1E)
182.8
182.4
223.8
152.5
343.9
195.8
104.2
46.2
126.2
230.2
246.9
292.0
66.1
182.0
312.6
277.6
11.5
285.3
264.9
223.9
280.5
320.3
45.8
267.1
290.1
311.0
196.8
308.5
125.3
70.1
110.8
221.6
65.7
0.5
155.5
92.9
304.3
231.6
310.9
323.6
188.5
84.1
85.7
72.5
161.1
146.0
68.2
129.5
58.8
28.7
255.1
209.9
321.4
24.6
26.1
226.4
262.1
344.4
Magnetic polarity stratigraphy of the Neogene foreland basin deposits of Nepal
Table A2. (Continued)
Site
Level (m)
Class
N
a95 (1)
SK223
SK225
SK228
SK230
SK232
SK231
SK233
SK235
SK236
3790
3872
3990
4030
4052
4078
4108
4170
4220
A
B
B
B
A
B
A
B
A
4
2
2
2
4
3
3
2
4
5.9
k
245.4
n
n
n
n
n
n
65.4
123.3
22.1
n
21.9
Geographic
Stratigraphic coordinates
I (deg.)
I (deg.)
27.3
25.8
50.2
79.9
77.0
19.5
58.4
35.4
61.3
3.0
2.2
32.3
n
18.5
D (deg.)
241.3
300.9
348.9
200.2
349.5
182.3
149.6
170.4
174.3
30.8
68.1
0.2
47.4
64.9
27.1
27.7
59.2
22.2
D (deg.)
271.3
252.7
350.4
165.6
174.8
183.2
158.9
140.3
182.9
Lat. (1N)
8.8
31.9
60.8
77.3
70.5
47.8
66.5
12.8
73.5
Long.(1E)
7.0
307.6
282.9
179.6
252.2
78.2
143.4
112.9
72.7
n
Sites that do not permit calculation of statistical parameters but do provide unambiguous polarity determinations.
Site, identi¢cation number for palaeomagnetic site; Level, stratigraphic level of collecting site in metres; N, number of samples used to determine sitemean direction; k, best estimate of Fisher precision parameter; a95, radius of cone of 95% con¢dence about site-mean direction; Geographic, in situ directions of ChRM; Stratigraphic coordinates, ChRM direction after restoring bedding to horizontal; I and D, inclination and declination of site-mean
direction; Lat. and Long., latitude and longitude of the site-mean virtual geomagnetic pole (VGP) computed from the stratigraphic directions.
Table A3. Site-Mean ChRM directions for Siwalik Group at Tinau Khola
Site
UT026
UT028
UT029
UT030
UT031
UT032
UT033
UT034
UT035
UT036
UT037
UT038
UT039
UT040
UT041
UT001
UT014
UT002
UT015
UT003
UT016
UT004
UT017
UT005
UT018
UT019
UT006
UT020
UT007
UT021
UT023
UT008
UT009
UT010
UT025
UT011
Level m
3.5
34.2
47.8
56.5
63.0
79.9
107.9
123.4
133.4
174.0
199.0
212.2
215.7
224.0
238.0
253.6
264.0
266.9
277.0
281.4
289.6
291.6
303.7
311.6
313.5
322.0
337.4
342.4
347.4
351.6
382.0
383.0
396.0
407.4
412.0
422.6
Class
N
A
A
A
B
A
B
B
B
B
B
B
B
A
A
B
A
A
B
A
B
B
B
B
A
B
B
B
B
A
A
B
A
B
A
B
A
3
3
3
2
3
2
2
2
2
2
2
2
3
3
2
1
3
2
3
3
2
1
3
3
2
3
2
2
3
3
2
3
1
3
2
3
a95, deg
11.6
28.1
11.3
n
13.8
k
113.7
20.3
120.7
n
80.3
n
n
n
n
n
n
n
n
n
n
n
n
n
5.3
16.8
n
n
15.8
n
19.4
80.8
n
535.0
55.1
n
n
62.1
n
41.5
3.4
n
n
n
n
77.7
8.5
n
128.0
n
n
5.2
11.1
n
20.4
n
17.7
n
6.9
3.6
212.8
n
2.1
n
n
568.1
123.5
n
37.7
n
49.5
n
316.7
Geographic
Stratigraphic Coordinates
I, deg
I, deg
46.8
21.7
11.7
5.3
13.0
7.2
17.9
8.1
14.7
23.4
21.8
27.1
25.2
34.7
58.1
52.3
20.9
40.5
28.6
69.9
42.5
51.0
64.9
39.5
17.3
25.6
22.8
30.6
17.4
39.1
20.8
20.2
40.3
32.2
8.2
27.5
D, deg
186.9
131.8
334.9
338.2
303.4
157.3
131.9
138.7
120.9
42.4
132.4
145.9
151.2
149.9
35.37
45.2
322.6
315.5
328
318.33
283.2
23.1
10
333.1
315.3
26.8
304.2
344.4
342.8
321.9
328.2
320.5
330.53
346
313.7
345.2
24.0
34.7
9.4
7.5
8.2
32.5
43.7
8.6
18.0
4.8
13.9
0.3
16.3
18.0
68.3
40.9
9.7
25.4
11.1
43.5
36.0
23.9
34.9
25.6
5.1
3.0
15.1
7.0
8.4
17.8
3.5
1.9
8.4
16.0
3.1
17.3
D, deg
167.9
154.5
324.5
337.2
301.4
143.8
133.7
138.8
128.6
41.3
139.1
152.1
155.8
153.3
93.8
35.2
330.4
333.0
336.1
349.6
304.3
17.4
8.5
350.6
319.9
22.4
309.9
347.2
344.2
337.0
329.3
324.2
23.7
351.4
318.5
353.4
Lat, 1N
71.1
65.1
42.9
51.6
29.5
32.6
20.6
44.4
38.3
40.2
46.2
51.6
60.0
58.8
23.6
58.0
53.8
61.1
58.3
80.4
38.9
67.9
78.4
73.5
44.2
56.1
38.7
63.1
54.9
61.5
51.0
46.6
57.6
69.1
42.6
70.4
r 2009 The Authors
Journal Compilation r Blackwell Publishing Ltd, European Association of Geoscientists & Engineers and International Association of Sedimentologists
Long, 1E
121.8
157.9
314.9
301.3
341.0
124.7
127.0
149.5
162.2
203.3
152.5
131.7
137.0
141.6
220.1
171.7
319.1
328.8
312.9
342.5
356.9
211.7
218.4
296.4
326.6
219.7
339.6
291.7
290.6
316.6
316.6
321.0
214.1
287.1
326.6
282.4
83
T. P. Ojha et al.
Table A3. (Continued)
Site
Level m
Class
N
UT013
UA001
UA030
UA002
UA031
UA032
UA033
UA003
UA034
UA004
UA005
UA035
UA036
UA006
UA037
UA038
UA039
UA008
UA040
UA009
UA041
UA010
UA042
UA011
UA043
UA012
UA044
UA013
UA045
UA046
UA014
UA047
UA015
UA048
UA049
UA016
UA050
UA017
UA051
UA018
UA052
UA019
UA020
UA054
UA021
UA053
UA022
UA055
UA22R
UA023
UA056
UA057
UA024
UA058
UA025
UA059
UA026
UA027
436.2
467.0
488.2
492.0
503.0
513.5
520.5
534.0
546.0
567.0
602.0
604.1
629.0
644.0
651.0
667.0
687.0
692.0
704.0
724.0
730.1
767.0
776.9
784.5
794.1
807.4
828.4
832.0
836.7
847.0
850.0
867.6
887.5
902.0
928.0
947.3
971.0
987.8
994.0
1037.5
1057.0
1066.0
1096.0
1115.0
1134.0
1150.0
1163.0
1179.0
1199.0
1226.0
1234.0
1250.0
1265.0
1272.0
1281.0
1289.0
1318.0
1344.0
A
A
A
B
A
A
A
B
B
A
A
A
A
A
A
B
B
B
B
A
B
B
B
A
B
A
A
B
A
A
B
B
A
B
B
A
B
A
B
A
A
B
A
B
A
B
A
B
A
A
A
A
B
A
A
A
A
A
3
3
4
2
3
3
3
3
2
3
3
3
3
3
3
1
1
3
1
3
3
1
2
3
2
3
3
2
3
3
1
2
3
2
2
3
1
3
2
3
4
3
3
2
3
1
3
2
3
3
3
3
1
4
3
3
3
3
84
a95, deg
46.9
14.6
6.4
n
15.4
19.9
34.9
78.4
n
13.0
6.9
36.6
24.9
9.2
16.4
n
n
13.5
n
27.7
k
8.0
72.8
206.6
n
64.9
39.3
13.5
3.6
n
91.4
322.8
12.4
25.6
179.4
57.9
n
n
84.6
n
20.9
n
n
n
n
n
17.2
n
2.4
16.4
n
11.1
40.3
n
n
8.2
n
n
19.8
n
18.4
n
55.8
5.8
8.9
27.2
n
12.7
n
8.7
n
27.7
23.1
10.1
21.7
n
13.9
6.6
9.6
2.9
8.0
n
52.2
n
2723.8
57.4
n
123.4
10.4
n
n
227.4
n
n
39.9
n
46.0
n
6.0
254.7
194.6
21.6
n
95.5
n
200.8
n
20.9
29.6
150.3
33.2
n
44.4
354.3
165.1
1791.1
237.2
Geographic
Stratigraphic Coordinates
I, deg
I, deg
34.9
8.1
26.2
49.3
31.1
41.3
45.6
72.2
23.8
15.1
29.8
38.2
32.2
37.3
39.2
1.7
42.4
39.4
4.2
40.3
26.1
27.2
35.2
39.3
46.1
43.1
31.8
36.7
47.1
2.8
12.6
52.2
37.3
41.7
36.6
47.4
26.9
47.3
59.7
57.2
54.3
46.1
55.8
28.6
3.6
42.1
48.5
57.2
37.0
63.7
52.4
50.8
30.5
69.5
53.5
46.6
44.5
43.7
D, deg
276.1
332.6
325.5
341.9
337.1
331.8
350.6
286
315.2
343.6
334.5
331.3
316.2
341.5
340.2
294.08
352.04
315.2
31.32
330.5
46.5
299.83
328.7
333.7
331.8
348.1
334.5
314.6
5.8
70
139.22
108.1
350.2
3.5
327.2
118.7
144.4
354.9
358.9
144.6
149.5
331.8
159.9
115.6
275.1
280.74
289.4
301.4
0.7
82.7
115
351
239.35
158.1
146.7
135.7
312.4
344
47.0
5.2
5.2
23.7
12.3
2.1
21.3
60.5
8.9
1.2
0.1
25.7
21.3
10.9
6.2
1.5
16.9
10.3
22.6
11.3
0.3
7.1
16.1
18.5
12.9
21.5
5.2
20.1
18.7
12.1
2.7
42.9
0.6
2.2
1.2
32.8
13.7
12.4
18.9
14.5
29.3
4.0
19.9
19.5
3.7
24.7
22.3
40.2
2.4
48.2
29.9
9.8
7.2
28.1
15.4
9.7
14.0
3.0
D, deg
307.1
333.5
331.8
4.4
343.8
348.4
1.5
350.5
321.6
346.5
339.8
344.3
328.4
1.1
346.7
294.1
355.0
324.9
33.6
334.3
42.3
306.9
331.6
337.8
343.1
345.3
334.6
320.8
355.6
72.6
140.1
130.4
351.2
0.5
335.9
132.9
148.0
353.4
3.2
170.1
149.6
152.1
162.4
128.2
275.1
249.5
300.4
334.3
358.4
133.5
137.4
357.2
235.2
179.2
158.4
153.1
337.1
346.2
Lat, 1N
43.6
50.6
53.2
74.4
63.5
59.2
73.2
74.0
46.7
60.2
56.4
69.6
56.0
68.0
62.3
20.8
70.3
49.9
38.8
57.3
41.0
34.1
56.9
62.4
63.4
68.6
51.0
49.4
71.4
12.3
42.0
45.8
61.0
63.4
53.4
45.8
43.5
67.9
71.7
67.8
59.4
50.1
66.1
38.3
3.6
24.0
32.2
66.3
61.3
49.3
49.0
67.1
28.5
77.2
61.7
55.7
60.3
58.2
Long, 1E
6.4
307.1
314.8
246.3
301.4
285.8
257.6
55.9
327.4
290.5
301.2
311.7
329.7
259.5
292.4
340.3
277.6
325.3
218.8
315.5
199.8
337.0
322.1
316.1
303.0
305.7
305.8
335.4
276.7
186.6
142.3
181.0
280.9
261.6
306.1
170.3
129.4
280.2
252.8
109.5
155.9
129.4
129.8
163.3
348.5
350.4
349.1
346.9
265.9
186.3
165.4
270.1
13.7
86.5
132.7
135.9
313.6
289.3
r 2009 The Authors
Journal Compilation r Blackwell Publishing Ltd, European Association of Geoscientists & Engineers and International Association of Sedimentologists
Magnetic polarity stratigraphy of the Neogene foreland basin deposits of Nepal
Table A3. (Continued)
Site
Level m
Class
N
a95, deg
UA028
UA060
UA061
UA062
UA063
UA064
UA065
UA066
UA067
UA068
UA069
UA070
UA071
UA072
UA073
UA074
UA075
UA077
UA078
UA079
1372.0
1383.0
1392.0
1406.0
1419.0
1455.0
1499.0
1504.0
1511.0
1549.0
1564.0
1582.9
1607.5
1620.0
1648.1
1658.0
1674.0
1720.0
1740.7
1761.0
A
A
A
B
B
A
A
A
B
A
B
B
B
A
B
B
B
A
B
A
3
3
3
2
2
3
3
3
2
4
1
1
2
3
1
2
2
3
2
3
18.9
6.4
17.1
k
43.8
369.6
53.3
n
n
n
n
16.5
13.1
13.3
56.8
89.2
86.6
n
n
6.4
210.1
n
n
n
n
n
n
6.5
357.1
n
n
n
n
n
n
19.6
40.8
n
n
15.3
66.1
Geographic
Stratigraphic Coordinates
I, deg
I, deg
D, deg
43.4
27.7
57.8
70.6
46.2
46.4
43.9
51.5
39.2
50.1
69.0
21.6
59.0
65.0
57.3
57.8
16.6
28.5
56.3
35.8
317
313.3
15.9
316.8
323.2
138.9
114.8
160.9
222.2
149.8
114
135.1
42.7
109.2
117.47
138.1
107
295.3
232.4
140.2
22.3
10.8
8.8
8.3
9.3
35.1
24.1
10.8
5.1
0.7
34.0
11.8
56.1
32.8
23.9
13.7
6.0
1.9
23.0
2.0
D, deg
Lat, 1N
336.1
320.6
16.0
355.6
337.1
70.9
138.9
175.6
215.8
164.7
169.9
139.1
160.0
151.6
148.4
149.1
112.2
309.9
208.6
147.4
62.6
39.5
62.2
66.0
58.3
25.3
48.8
67.3
44.1
58.9
77.0
38.1
70.9
62.1
56.7
54.1
18.0
34.1
59.0
48.9
Long, 1E
321.9
317.8
226.9
273.8
310.3
163.3
159.7
94.3
28.3
113.6
130.6
138.6
205.8
158.2
151.9
143.2
159.3
330.6
17.6
137.8
Site, identi¢cation number for paleomagnetic site; Level, stratigraphic level of collecting site in meters; N, number of samples used to determine site^
mean direction; k, best estimate of Fisher precision parameter; a95, radius of cone of 95% con¢dence about site^mean direction; Geographic, in situ
directions of ChRM; Stratigraphic Coordinates, ChRM direction after restoring bedding to horizontal; I and D, inclination and declination of site^mean
direction; Lat and Long, latitude and longitude of the site^mean virtual geomagnetic pole (VGP) computed from the stratigraphic directions.
n
Sites that do not permit calculation of statistical parameters but do provide unambiguous polarity determinations.
Table A4. Site-Mean ChRM directions for Siwalik Group at Muksar Khola
Site
GK002
GK003
GK004
GK005
GK001
GK006
GK008
GK009
GK010
GK011
GK012
GK013
GK014
GK015
GK016
GK018
GK021
GK022
GK023
GK024
GK025
GK026
GK027
GK028
GK029
Level (m)
0.3
2.2
4.5
11.8
39.0
55.0
68.0
86.0
91.0
98.0
102.0
111.0
223.0
276.0
280.0
285.0
386.0
487.0
517.0
542.0
563.0
576.0
650.0
654.0
673.0
Class
N
A
A
A
A
A
A
A
A
A
A
B
A
A
A
A
A
A
A
A
A
A
A
A
A
A
4
4
4
3
4
4
4
3
4
4
4
4
3
4
3
3
3
3
3
3
4
3
3
3
3
a95 (deg.)
10.4
6.1
19.9
18.0
9.8
49.0
10.1
15.1
13.4
5.5
78.1
11.2
7.8
22.0
11.5
10.1
15.7
18.7
21.1
24.6
10.7
4.1
14.1
14.6
7.9
k
79.2
226.3
22.2
48.0
88.0
4.5
84.4
67.9
47.7
285.1
2.4
67.7
250.7
18.4
116.0
148.7
62.4
44.6
35.3
26.3
74.8
893.8
77.7
72.4
245.2
Geographic
Stratigraphic coordinates
I (deg.)
I (deg.)
31.7
26.1
33.1
14.3
40.8
24.0
53.8
43.0
43.7
57.8
43.5
44.2
72.5
21.0
78.8
72.7
64.6
35.0
64.2
63.4
45.5
61.0
67.4
56.8
62.6
D (deg.)
3.3
19.8
17.1
343.1
28.4
359.2
357.0
353.1
334.6
14.7
22.9
20.4
170.1
84.1
126.8
215.8
166.4
34.5
345.6
349.4
137.9
163.1
169.4
176.4
354.6
9.0
6.3
19.3
3.5
20.8
1.5
34.8
8.1
4.9
16.5
6.5
7.9
38.6
14.9
27.6
19.0
18.3
1.9
10.5
13.3
11.5
13.0
9.4
1.0
11.9
D (deg.)
0.4
15.7
11.3
342.8
3.2
357.3
357.0
352.8
339.4
4.3
11.7
12.8
173.7
103.4
168.1
188.3
175.0
23.9
350.9
6.4
152.6
162.5
169.2
173.1
359.6
Lat. (1N)
67.7
61.9
70.0
56.9
73.6
63.7
81.9
66.2
58.6
71.1
63.9
64.0
82.3
15.4
73.5
71.2
71.9
53.9
66.7
69.0
56.5
63.8
65.6
61.8
69.2
r 2009 The Authors
Journal Compilation r Blackwell Publishing Ltd, European Association of Geoscientists & Engineers and International Association of Sedimentologists
Long. (1E)
265.3
231.3
232.0
299.1
255.2
272.6
286.6
284.4
308.8
253.0
239.0
236.1
135.9
177.2
130.8
60.0
102.3
223.0
290.0
248.3
142.4
128.8
113.3
101.2
267.4
85
T. P. Ojha et al.
Table A4. (Continued)
a95 (deg.)
k
Geographic
Stratigraphic coordinates
I (deg.)
I (deg.)
Site
Level (m)
Class
N
GK030
GK031
GK032
GK033
GK034
GK035
GK036
GK037
GK038
GK039
GK040
GK041
GK042
GK045
GK047
GK048
GK049
GK050
GK051
GK056
GK057
GK060
GK064
GK065
GK067
GK069
GK070
GK073
GK074
GK076
GK077
GK079
GK080
GK081
GK082
GK083
GK084
GK085
GK086
GK089
GK087
GK090
GK091
GK092
GK095
GK096
GK097
GK099
GK100
GK102
GK103
GK104
GK105
GK107
GK106
GK109
GK110
GK108
690.0
706.0
751.0
825.0
835.0
852.0
908.0
915.0
990.0
1023.0
1046.0
1078.0
1086.0
1131.0
1161.0
1162.0
1164.0
1170.0
1182.0
1238.0
1254.0
1277.0
1373.0
1377.0
1512.0
1559.0
1564.0
1612.0
1651.0
1669.0
1671.0
1675.0
1698.0
1704.0
1709.0
1717.0
1719.0
1746.0
1752.0
1782.0
1784.0
1795.0
1809.0
1811.0
1849.0
1862.0
1886.0
1894.0
1897.0
1911.0
1929.0
1932.0
1954.0
1958.0
1980.0
1985.0
1990.0
2002.0
A
A
A
A
A
B
B
B
A
A
A
A
B
B
B
A
A
B
A
B
B
A
A
B
A
A
A
B
B
A
B
B
B
A
A
A
A
A
A
B
A
A
B
A
A
A
B
B
A
A
A
A
A
B
B
B
A
B
3
3
3
3
3
2
3
3
3
3
3
3
4
2
2
3
3
2
3
2
2
3
4
2
4
3
4
2
3
3
3
2
4
3
4
3
4
3
3
2
3
3
2
3
4
4
2
2
3
3
3
3
4
3
3
3
3
2
86
r 2009 The Authors
Journal Compilation r Blackwell Publishing Ltd, European Association of Geoscientists & Engineers and International Association of Sedimentologists
44.5
16.2
6.7
24.1
11.7
n
74.8
68.9
9.1
14.5
7.1
8.7
142.3
8.7
59.0
343.1
27.2
111.6
n
3.8
4.3
185.7
73.7
301.9
200.9
1.5
n
n
n
n
13.7
10.2
n
14.2
n
n
9.2
10.4
n
54.2
8.1
10.0
n
122.4
23.8
64.3
n
61.3
37.1
8.5
17.6
6.5
28.2
11.1
n
6.8
53.6
n
26.9
5.1
16.2
82.3
146.4
n
76.5
n
n
179.6
78.5
n
3.9
234.7
86.1
n
2.2
27.8
4.8
n
3.2
12.1
117.8
49.8
202.4
20.2
124.8
n
327.7
6.4
n
22.1
325.0
33.0
n
n
n
n
16.6
56.4
16.4
16.5
26.9
56.5
5.9
57.7
56.9
12.6
n
n
n
n
n
n
17.8
n
48.8
n
82.6
67.5
53.1
74.5
64.7
64.4
47.4
48.1
52.3
86.5
67.8
11.3
50.6
61.6
81.5
64.7
55.8
20.4
62.1
58.4
71.7
65.0
61.1
82.4
74.8
87.2
67.8
74.7
75.2
73.2
75.8
69.5
35.5
56.8
83.3
76.8
51.6
73.3
67.9
84.1
85.6
77.1
49.6
67.0
60.6
67.2
24.5
4.0
65.1
75.2
69.6
65.7
59.0
62.7
53.5
82.9
74.6
45.8
D (deg.)
29.6
15.7
348.5
260.9
312.3
189.6
267.7
336.5
4.0
87.1
163.8
98.5
163.0
355.2
6.8
347.9
25.6
317.2
0.5
110.8
249.3
188.2
129.0
303.2
82.5
178.1
147.7
143.8
181.6
39.8
219.8
298.0
315.9
146.3
317.8
352.5
43.1
151.6
206.6
119.8
53.6
77.3
309.9
8.0
190.4
177.4
103.8
190.1
326.0
228.0
320.2
7.5
23.7
347.6
141.6
121.4
174.5
32.3
26.0
20.8
11.4
38.9
23.9
19.8
32.2
2.1
3.8
51.2
18.0
2.2
3.2
19.6
34.6
18.3
14.7
17.4
19.1
28.0
34.1
14.8
5.4
33.0
35.8
26.2
22.4
12.0
4.2
21.3
45.6
24.3
11.4
5.1
24.7
22.0
7.8
12.4
6.6
36.6
30.2
30.5
9.7
10.1
9.7
12.2
2.5
55.1
6.3
36.8
7.4
1.4
3.0
14.2
10.1
19.0
27.9
7.8
D (deg.)
357.9
9.4
352.2
344.5
339.7
183.3
235.8
343.8
359.7
176.4
176.8
102.4
167.4
356.6
2.9
355.7
10.8
317.9
359.2
136.2
199.1
179.0
152.0
177.7
151.2
179.9
174.1
162.4
180.4
12.9
349.6
341.8
322.5
157.7
352.3
1.2
17.2
167.5
187.1
356.7
350.7
5.0
328.2
3.8
187.7
175.3
115.9
202.0
345.0
343.9
341.3
358.3
9.8
354.2
157.9
162.5
166.4
21.0
Lat. (1N)
76.7
71.6
67.6
75.1
66.2
73.0
37.8
59.9
65.0
84.1
72.1
10.6
62.0
73.0
81.7
72.1
68.1
35.8
73.0
47.6
70.6
70.6
53.9
80.9
62.7
76.9
73.8
63.3
65.2
70.0
80.7
67.9
41.2
57.7
74.3
74.5
61.8
66.2
65.5
82.8
76.3
78.6
52.5
68.0
66.8
68.8
22.3
24.1
62.3
73.9
60.8
63.8
62.9
69.6
59.7
66.3
72.5
59.5
Long. (1E)
275.4
235.9
287.1
340.6
323.3
75.2
354.5
300.1
267.0
234.8
96.8
169.7
114.0
277.8
247.3
280.2
236.6
321.1
269.0
169.0
17.3
89.3
139.1
100.1
167.7
86.8
107.7
128.4
85.4
226.4
359.9
320.3
320.0
131.4
295.2
262.0
227.8
118.5
69.0
291.9
307.3
241.4
326.0
256.4
66.6
99.3
162.8
66.9
300.1
336.4
307.2
270.1
244.3
283.1
134.3
133.6
135.5
221.6
Magnetic polarity stratigraphy of the Neogene foreland basin deposits of Nepal
Table A4. (Continued)
Site
Level (m)
Class
N
GK112
GK113
GK114
GK115
GK118
GK119
GK121
GK123
GK128
GK125
GK127
GK126
GK129
GK130
GK131
GK132
GK133
GK134
GK136
GK137
GK138
GK139
GK140
GK141
GK142
GK144
GK145
GK146
2019.0
2023.0
2052.0
2075.0
2112.0
2136.0
2160.0
2170.0
2182.0
2190.0
2211.0
2246.0
2266.0
2280.0
2303.0
2310.0
2342.0
2374.0
2383.0
2396.0
2406.0
2422.0
2444.0
2451.0
2462.0
2530.0
2548.0
2551.0
B
A
A
B
A
A
B
A
A
A
A
A
A
B
A
A
A
A
A
A
B
A
A
B
A
B
A
B
2
3
4
2
3
3
2
3
3
3
4
3
3
2
3
4
4
4
3
4
2
3
3
3
3
3
4
2
a95 (deg.)
n
38.4
16.6
n
5.2
27.7
n
20.2
25.1
18.1
33.5
15.7
21.7
n
33.7
17.7
10.7
18.1
15.3
25.1
n
23.1
13.8
67.4
14.3
94.7
4.6
n
k
Geographic
Stratigraphic coordinates
I (deg.)
I (deg.)
n
11.4
31.4
n
559.0
20.9
n
38.1
25.2
47.6
8.5
62.9
33.3
n
14.4
27.9
74.9
26.9
66.2
14.4
n
29.6
80.4
4.4
75.1
2.8
403.3
n
0.2
63.3
66.4
80.8
55.1
71.5
12.1
62.9
60.3
85.5
79.2
73.3
75.5
61.6
63.5
84.2
65.1
76.2
65.9
78.4
61.8
69.1
67.7
79.9
81.2
70.0
71.6
61.2
D (deg.)
146.9
272.9
248.2
44.2
340.6
344.4
196.3
171.9
155.2
217.4
223.4
154.4
150.6
156.8
135.1
194.8
221.1
212.5
217.4
144.2
168.7
157.9
202.4
3.0
223.7
358.7
332.7
22.8
37.6
37.1
25.2
38.6
3.1
15.0
45.0
15.5
9.1
34.9
29.1
21.5
23.9
8.4
14.6
32.8
12.8
14.9
6.2
16.9
1.3
15.2
15.8
47.1
30.3
20.1
27.2
15.0
D (deg.)
135.4
216.3
200.9
174.1
352.7
353.6
201.5
178.9
166.8
174.1
186.8
170.9
170.8
169.1
152.9
170.2
192.4
190.0
197.7
176.3
176.8
159.2
189.9
181.8
188.7
3.3
355.5
14.8
Lat. (1N)
25.5
56.3
66.2
82.6
63.8
69.8
32.7
71.0
64.4
80.6
77.0
72.1
73.2
65.1
57.8
77.3
66.5
68.5
60.8
71.5
62.3
62.5
69.0
87.9
76.7
73.2
76.8
66.2
Long. (1E)
132.9
359.0
27.1
133.9
283.1
285.1
63.4
89.8
118.2
124.3
55.9
116.7
119.3
113.0
144.3
133.5
54.0
58.5
47.9
98.0
93.2
136.0
58.0
313.7
47.2
254.9
286.0
227.6
n
Sites that do not permit calculation of statistical parameters but do provide unambiguous polarity determinations.
Site, identi¢cation number for palaeomagnetic site; Level, stratigraphic level of collecting site in metres; N, number of samples used to determine site mean direction; k, best estimate of Fisher precision parameter; a95, radius of cone of 95% con¢dence about site-mean direction; Geographic, in situ directions of ChRM; Stratigraphic coordinates, ChRM direction after restoring bedding to horizontal; I and D, inclination and declination of site-mean
direction; Lat. and Long., latitude and longitude of the site-mean virtual geomagnetic pole (VGP) computed from the stratigraphic directions.
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r 2009 The Authors
Journal Compilation r Blackwell Publishing Ltd, European Association of Geoscientists & Engineers and International Association of Sedimentologists
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