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 r 2009 The Authors 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 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 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 r 2009 The Authors 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). 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 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). r 2009 The Authors 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. REFERENCES Angevine, C.L., Heller, P.L. & Paolo, C. (1990) Quantitative Sedimentary Basin Modeling. AAPG Continuing Ed. 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