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Quaternary International 159 (2007) 102–118

Environmental magnetic studies on some Quaternary sedimentsof varied depositional settings in the Indian sub-continent

S.J. Sangodea,�, Rajiv Sinhab, B. Phartiyalc, O.S. Chauhand, R.K. Mazaria, T.N. Bagatia,N. Suresha, Sheila Mishrae, Rohtash Kumara, P. Bhattacharjeeb

aWadia Institute of Himalayan Geology, Dehradun 248 001, IndiabIndian Institute of Technology, Kanpur 208 016, IndiacBirbal Sahni Institute of Palaeobotany, Lucknow, India

dNational Institute of Oceanography, Goa, IndiaeDepartment of Archeology, Deccan College, Pune, India

Abstract

The efficacy and limitations of routine environmental magnetic approaches to characterize and compare the Quaternary sediments of

varied depositional settings (fluvial, fluvio-lacustrine and marine) from the Indian sub-continent are discussed. The various studied

profiles fall under tropical wet and dry, subtropical humid, cold arid and alpine climatic zones at altitudes varying from �2000m below

sea level to �4500msl. The magnetic mineral assemblages are characterized by magnetic susceptibility, high field hysteresis parameters

and their ratios and bivariate plots. Besides applying the conventional models, we produced new and multi-parametric environmental

magnetic models for finer discrimination of the mineral magnetic assemblages (MMA) amongst these deposits.

In similar hinterland setup and climate zones, independent MMA characteristics are shown by the Late Quaternary frontal Himalayan

basins: the Ganga basin, the intermontane Pinjor Dun and the folded Siwalik sequence. Such variations are attributed to diverse energy

conditions due to varied basin morphology, climate and the source to sink proximity. Contrasting channel to overbank MMA relations

are discernible during the glacial and interglacial periods within the Ganga Basin. The Siwalik sediments are notably restricted to

antiferromagnetic region of the bivariate plots indicating formation and stability of iron oxides under warm humid to arid conditions.

The post-Siwalik intermontane sediments show steep gradients in MMA domain within a short distance from proximal to distal fan

regime. In the tropical Peninsular region, the ‘source to sink’ relation is marked by the Deccan Trap province (source) and Bengal

submarine fan (sink) at least since the Last Glacial Maxima (LGM) in the Middle fan region. The MMAs for the lacustrine and fluvio-

lacustrine deposits in the Himalayan foothills as well as the Higher Himalaya indicate detrital variations governed by the fluvial

dynamics in the region. This demands a more detail catchment to sink studies in each basin and to explore the climatic tele-connections

amongst the varied altitudinal regions. Overall, this study indicates a strong detrital control on MMA governed by the energy conditions

of the transporting media that in turn is controlled by catchment morphology, regional tectonics and climatic fluctuations. In the absence

of suitable unmixing models, the new bivariate and diamond plots attempted here are helpful in describing the detrital modes within the

basin and its comparison to other basins.

r 2006 Elsevier Ltd and INQUA. All rights reserved.

1. Introduction

Discrimination and quantification of authigenic anddetrital inputs in a basin and identification of themechanism of detrital processes are crucial to understandthe climate and/or tectonic variability. Environmental

e front matter r 2006 Elsevier Ltd and INQUA. All rights re

aint.2006.08.015

ing author.

ess: sangode@wihg.res.in (S.J. Sangode).

magnetism provides such a tool suitable to most deposi-tional settings due to the ubiquitous occurrence of the ironoxides, their sensitivity to climate, depositional setting andtransporting media and the ease with which the magneticproperties can be measured (Thompson and Oldfield, 1986;Verosub and Roberts, 1995; Dekkers, 1997; Maher andThompson, 1999; Evans and Heller, 2003).The oxides of iron are sensitive to climate with a short

response time, but once formed, they can preserve stable

served.

ARTICLE IN PRESSS.J. Sangode et al. / Quaternary International 159 (2007) 102–118 103

records over longer geological times. Environmentalmagnetic techniques have so far been developed to enablequalitative and quantitative estimates of iron minerals inbulk state thus allowing discrimination and quantificationof different modes of authigenic and detrital iron oxides.Their dilution due to diamagnetic and paramagneticsilicate and carbonate minerals plays an important role indeciphering the environmental magnetic signatures. Thechanges due to diagenetic and dissolution processes need tobe evaluated under many of the depositional environments(Frolich et al., 1979; Tarling and Turner, 1999; Garrels andMackenzie, 2001; Zhang et al., 2001).

Environmental magnetic methods are inexpensive andrapid with little need for sample preparation, and theanalysis of large number of samples in bulk state enables amore representative estimation. Although widely used,these methods have been developed for depositionalsettings and hinterland configurations that are not asdiverse and dynamic as in the Himalaya, Bengal fan andthe Indian subcontinent in general. A comprehensiveattempt is therefore warranted to know the abundance ofthe commonly occurring magnetic minerals (Table 1) andtheir style of dispersal under tropical, subtropical andalpine climatic conditions at varied tectonic and geo-morphic settings. This paper considers some of theseclimatic and depositional settings in order to facilitate acomparison of mineral magnetic response for regionalclimatic variation signatures.

2. Geographic setting

The Indian sub-continent (Fig. 1) geographically coverstropical to subtropical climatic zones and experiencesstrong seasonality from warm humid to arid and cold aridconditions. The gradient of climatic zones is greatlymodified by the sharp altitudinal changes in the northernhalf where the Himalaya forms the major relief. Most partsof the Indian sub-continent experience a tropical monsoonclimate, with significant seasonal variations in rainfall and

Table 1

Magnetic minerals, their magnetic status and occurrence (compiled from Schw

Schwertmann, 1999)

Minerals Formula Magnetic status

Magnetite Fe3O4 Ferrimagnetic

Maghemite gFe2O3 Ferrimagnetic

Hematite aFe2O3 Canted

antiferromagnetic

Goethite aFeOOH Parasitic ferromagnetism

Lepidocrocite gFeOOH Paramagnetic

Ferrihydrite 5Fe2O3.9H2O Paramagnetic

temperature. The Himalaya, acting as a barrier to the coldnorth winds from Central Asia, maintains the pattern ofthe Indian Ocean monsoon circulation. The Thar Desertallows oceanic atmospheric circulation and sediment dust-aerosol influx deep into the continent.There are two branches of the SW monsoon, the Bay of

Bengal and the Arabian Sea branch. The Arabian Seabranch extends the low-pressure area over the Thar Desertin Rajasthan whereas the Bay of Bengal branch results inturbulence in the region due to the rapid altitudinaldifferences and narrowing orography. The Arabian Seabranch is roughly three times stronger than the Bay ofBengal branch. During strong monsoons, cyclones occur inthe coastal region, causing large-scale changes in theclimate-induced sedimentation processes. The Quaternarybasins in the northern latitudes (4201N) thus manifestlarge base level changes from the submarine fans of the Bayof Bengal and Arabian Sea (4100m below sea level),Ganga plains (0–150m), the Himalayan foothills(150–1000m), the Lesser Himalaya (1000–4500m) andthe Higher and Trans-Himalaya (43000m) within a shortlatitudinal difference of o101. Furthermore, all thesebasins individually have also experienced base levelchanges through time due to tectonoclimatic modulationsat regional scale.Geomorphologically, the Indian sub-continent consists

of a large portion of the alluvial plains of the Indus,Ganges and Brahmaputra Rivers and their deltas linked tothe submarine fans of the Bay of Bengal and the ArabianSea. Terraces and the incised valleys form commongeomorphic features in plains as well as mountainousregions. The Himalayan Frontal Thrust (HFT) separatingthe Himalayan foothills from the Ganga plains representsthe youngest amongst the Himalayan thrust systems,broadly demarcating the zone of deposition and erosionin the northern half of the continent. Although informationon the modern climate and its variability is ample in thisregion, the role of sediment response to climate change andits relation to tectonics is not well explored. The coupling

ertmann and Fischer, 1973; Maher and Thompson, 1999; Scheinost and

Color Occurrence

Grayish black Occurs widely as detrital and authigenic

fraction in Quaternary environments and well

preserved in restricted less oxidizing

conditions

Dark brown Abundant in highly weathered tropical/sub-

tropical soils

Red Relatively dry, highly oxidized soils, usually in

areas of elevated temperature

Yellow Abundant in moist soils well drained

temperate regions

Reddish yellow Occurs in poorly drained soils

Dark red Poorly drained and podzolized soils

ARTICLE IN PRESS

Fig. 1. Physiographic map of the major part of the Indian subcontinent showing the locations of the studied sites (numbered white trangles). 1: Lamayuru

paleolake (Lp), 2: Spituk Leh paleolake (Sptl), 3: Kioto paleolake (Kp), 4: Mansar lake (Ml), 5: Khajjiar lake (Kjl), 6: Sumdo paleolake (Sp), 7: Asan lake

(Asl), 8: Pinjor Dun (Pf), 9: Ghaggar section Siwaliks (Sf-Gh), 10: Moginand section Siwaliks (Sf MG), 11: Haripur section Siwaliks (Sf HP), 12:

Jagdishpur valley fill (Gf JP), 13: Kanpur interfluve (Gf Inf), 14: Firozpur valley fill (Gf FP), 15: Bhima–Godavari basin Quaternary (BGf), 16: Bengal fan

peninsular source (Bf pe),17: Bengal fan Himalayan source (BF Hm), 18: Bengal fan deep core (BF dp).

S.J. Sangode et al. / Quaternary International 159 (2007) 102–118104

of climate and tectonics has largely controlled the regionalgeomorphology of the Quaternary basins, especially in thenorthern half of the subcontinent.

The classical methods of geomorphology, facies char-acterization, grain size analysis and geochemistry canprovide a basic understanding of the evolution of theQuaternary basins. However, these methods are moredescriptive, time consuming and rarely allow a quantitativediscriminations as facilitated by environmental magnetism,especially to understand the source to sink relation, anddetrital to authigenic characterization (Thompson et al.,1975; Thompson and Mortan, 1979; Oldfield et al., 1985;Yu and Oldfield, 1989, 1993; Dearing 1992). This paperpresents a comprehensive environmental magnetic assess-ment of the Quaternary fluvial, fluvio-lacustrine and deltaicto deep marine sediments from Himalaya, Indo-Gangeticplains, Bay of Bengal and Peninsular India between 161Nand 341N. The depositional milieu includes (a) Freshwaterchannel, floodplain and interfluve sediments of the Siwalik

molasses, the Pinjor Dun, the Ganga basin, and theGodavari basin, (b) Fluvio-lacustrine sediments of themonsoon fed Assan reservoir, the Mansar and the Khajjiarlake (SW monsoon); (c) Cold alpine Himalayan lacustrineand fluviolacustrine sediments of the Kioto and the Sumdolakes in Spiti, and the Lamayuru and the Spituk lakes inLadakh (Fig. 1).

3. Environmental magnetic methods

The environmental magnetic methods are based uponestimation of inherent mineral characteristics in responseto a variety of magnetic fields of known direction andintensity (Collinson, 1987; Thompson and Oldfield, 1986;Dunlop and Ozdemir 1997). As a result, weakly magneticsediment samples are also analyzed and characterized quitesuitably by using the high field environmental mag-netic parameters (Thompson and Oldfield, 1986; Maherand Thompson, 1999; Evans and Heller, 2003). These

ARTICLE IN PRESSS.J. Sangode et al. / Quaternary International 159 (2007) 102–118 105

techniques require little sample preparation, and are rapid,nondestructive and often grain size sensitive. They allowdeterminative analysis without physical separation, and alarge sample quantity can be analyzed in a short time.Measurements include field and temperature-dependenceof various types of induced and remanent magnetizations.

The low-field magnetic susceptibility (jlf) is the mostfundamental and extensively used parameter at roomtemperature. The mass normalized susceptibility (vlf) is afirst order estimate of ferrimagnetic concentration and isalso an important parameter when used as a ratio withother hysteresis parameters. Magnetic susceptibility mea-sured under different frequencies of applied fields allowsdistinction and quantification amongst certain grain sizes,taking advantage of the phenomenon of magnetic viscosityand is expressed as frequency-dependent susceptibility(vfd). The parameter vfd% is defined as percentage measureof change in magnetic susceptibility per decadal increase offrequency of the applied field (Collinson, 1987).

The coercivity of isothermal remanant magnetization[B0(CR)] is another parameter to distinguish amongstferrimagnetic and antiferromagnetic assemblages and theirgranulometric relation (Dunlop and Ozdemir, 1997). Theferrimagnetic multi domain (MD) grains (415 mm) showsvery low B(0)CR (o20mT) whereas the ferrimagnetic singledomain (SD) grains (o0.03 mm) have B(0)CR values in therange of 20–50mT. The canted antiferromagnetic mineralhematite show B(0)CR values larger than 100mT and veryhigh values are shown by goethite.

S-Ratio is an empirical parameter based upon the ideathat the coercivity of isothermal remanent magnetization(IRM) for natural samples containing mixtures of magneticminerals of varied grain sizes exhibits the greatest degree ofseparation at 100–300mT backfield. When 100mT back-field is used, high negative S-ratios (4�0.75) are indicativeof MD ferrimagnetic particles followed by less negativeratios (��0.75 to �0.5) for SD–PSD grains. Very lownegative (5�0.5) to zero S-ratios indicates admixtures offerrimagnetic and antiferromagnetic oxides. Low positivevalues (�0–0.3) indicate pure canted antiferromagneticminerals. The higher S-ratios (40.3) can be due tostoichiometric substitution and magnetocrystalline aniso-tropy of the antiferromagnetic grains. All these parametersare used successfully in describing the relative variationswithin a single profile (Dekkers, 1997; Evans and Heller,2003; Peters and Dekkers, 2003).

3.1. Magnetic domain—grain size relation

Magnetic domain size is a concept based upon the factthat the magnetic mineral grains form domains ofstable–unstable magnetization depending upon the grainvolume and geometry (Stacey and Banerjee, 1974; Dunlopand Ozdemir, 1997). The environmental magnetic para-meters are particularly sensitive to these domain sizes andhave great implication in determining the grain sizecharacteristics of the depositional environment. A broad

relationship amongst magnetic domain size and thephysical grain size for the commonly occurring iron oxideminerals is shown in Fig. 2. The ranges of physical grainsize (in microns) are plotted in the top row from fine clay tocoarse sand. The magnetic minerals can range in size froma few nanometers to several hundred microns, exhibitingindependent characteristics. For any specific MMA, sets ofmagnetic properties characterize the abundance, composi-tion and grain size of magnetic particles. Suites of magneticminerals with different grain sizes and compositions havedifferent magnetic characteristics. Thus, the mineralmagnetic assemblage can be characterized from indepen-dent mixing of different sources or varied depositionalconditions.

3.2. Magnetic mineral assemblage (MMA)

Magnetite, hematite, maghemite and goethite (Table 1)are the most abundant magnetic minerals occurring in theQuaternary sediments, yet they form less than 2% of thetotal mineral assemblage. In this instance the rest of theminerals constituting 480% of paramagnetic, diamagneticand their varieties with ferrimagnetic inclusions haveconsiderable influence on the environmental magneticproperties. The compositional and grain size variants ofall these minerals are unique to the contemporarydepositional environments and the catchment configura-tions. Therefore, the term magnetic mineral assemblage(MMA) is used to express the net response of theenvironmental magnetic approach.Most of the established magnetic properties and models

for environmental magnetism were originally developed formono-mineralic ferrimagnetic assemblages and their subtlevariation in grain size; or where the antiferromagneticcontent is minor (see Thompson and Oldfield, 1986). Thisrestricts the straightforward use of the standard models inwide ranging assemblages of ferri- and antiferromagneticminerals (e.g., Table 1) and their stoichiometric substitutedvariants which are common in tropical and subtropicalclimates (Schwertmann and Fischer, 1973; Schwertmann,1988; Martini and Chestworth, 1992). Therefore, thedefined domains in these models for the monomineraliccomposition may deviate for the MMA from such regions.The variations in the MMA are required to be linked to

site-specific explanatory mechanisms for the environmentalmagnetic signatures (Bradshaw and Thompson, 1985;Oldfield et al., 1985; Caitcheon, 1993). Secondly, many ofthe available studies have used a saturating fieldo1000mTthat is insufficient to saturate minerals of high coercivity(e.g., goethite and hematite). The commonly used fre-quency dependence parameter (vfd, based upon thefrequencies 0.47 and 4.7 kHz) is unable to detect theviscous fractions of the canted antiferromagnetic (hema-tite) and parasitic ferromagnetic (goethite) forms and alsogreatly varies among the ferrimagnetic minerals. Suchstudies are not available for the Quaternary sediments fromthe Indian subcontinent. In this scenario, a detailed

ARTICLE IN PRESS

Fig. 2. Magnetic domain and physical grainsize relation for the commonly occurring iron oxide minerals (compiled from various sources). Details

described in text. Question tag indicates information not available.

S.J. Sangode et al. / Quaternary International 159 (2007) 102–118106

approach using magnetic mineral separates (extracts) iswarranted. The environmental magnetic approach tocharacterize the MMA here demonstrates the depositionalsystem in order to understand the distribution andconcentration of the magnetic minerals in response to thevaried depositional settings.

4. Depositional settings and magnetic mineral variation

A summary of site location, depositional setting anddepositional environments for all the studied sites is givenin Table 2. Broad relationships amongst the depositionalenvironments, catchment/source configurations and mag-netic mineral variation in the respective basins aredescribed below.

4.1. Quaternary fluvial sequences of Siwalik (Sf)

The Siwalik fluvial sequence of the Himalayan forelandbasin is a continuous record of channel to overbank faciesfrom Early Miocene to Late Pleistocene. The entire

Pleistocene part of the Siwalik has experienced the mostdynamic phase in the Himalayan foreland, expressed in therapid coarsening upward of lithofacies. The hinterland(source area) configuration as well as basin morphology isgreatly varied at a scale of hundreds of kilometers laterallythroughout the Himalayan foreland basin. Therefore, thesource to basin relation also appears to have variedindividually for each sub-basin. The latest Quaternaryphase in the Siwalik sequence is characterized by a majorityof truncated and weak to moderately developed paleosolprofiles. These paleosols are the only widespread authigenicfacies in the Himalayan realm covering the entire Plioceneto Pleistocene periods. Environmental magnetic data ispresented for pedogenic and nonpedogenic (detrital) layerssampled in three different sections of the PleistoceneSiwaliks between the Ghaggar and the Ganga rivers(Fig. 1).The environmental magnetic properties in the Siwalik

sediments are dominated by antiferromagnetic and para-sitic ferrimagnetic minerals (hematite and goethite respec-tively) especially in the pedogenic facies (Sangode et al.,

ARTICLE IN PRESSTable

2

DistributionofthestudiedQuaternary

basins,theirdepositionalsettingandenvironments

Quaternary

basin

Age

Sitelat/long

Sampledthickness

Bedrock/countryrock/

catchment

Depositionalsetting

Depositionalenvironment,mean

annualprecipitationandtemperature

Siwalik(Sf)

�18–0.5Ma

(Samplingdone

for�2–0.5Ma

interval)

321N771E

Approx.

3800m

thickcombination

ofChannel

sandstone,

overbankmudstoneand

paleosols

Allsortsofolder

sedim

entary

and

metamorphic

rockswith

theirvaryingprevalence

in

timeandspace

Typicalforelandbasin

settingwithactive

orogenic

frontandthrust

loadingdepositedbelow

o500msl(?)

Molassetype,

typicallyfreshwaterhigh

energyfluvialenvironments

separated

bythefloodplain

andinterfluveregions

withpaleoprecipitationand

temperature

varyingin

between500and

2000mm/yearand10–301C

Ganga(G

f)o0.5Ma

261300 N

801E

Total85m

strata

offine

silt-sandandmud

interfluve

sequence+

medium

to

coarsesandchannel

sedim

ents

Mainly

Siwaliksandthe

hinterlandofSiwaliks

Typicalforelandbasin

activesedim

entation

mainly

byalluvialfans

(0–150msl)

Predominantlyalluvialfan

sedim

entationwithgeomorphic

expressionsoftheuplandandinterfluve

area.Precipitationandtemperature

varyingin

between800and1000mm/

yearand35–451C

Interm

ontane

PinjorDun(Pf)

o0.5Ma

321N771E

Approx.

50m

thicknessoffriable

sand-siltandmud

sequence

Siwaliks,Lower

Tertiaries

andLesserHim

alayan

sedim

ents

and

metasedim

ents

Interm

ontanebasinwith

alluvialfansedim

entation

(100–600)msl

Fresh

waterfluvialsedim

entationand

occasionalpondingconditions.

Predominance

ofrapid

sedim

entationin

theinitialpart

andincisionin

thelater

part.Precipitationandtemperature

varyingbetween500–1000mm/yrand

20–451C

Bhim

a-

Goadavaribasins

(Bgf)

o2Ma

191N751E

13m

totalthicknessof

grayto

dark

graymainly

overbanksiltandmud,

rarely

sand

DeccanBasalt

Low

gradientalluvialfan

sedim

entation

200–500msl

Fresh

waterfluvialandinterfluve

sedim

entationPrecipitationand

temperature:500–1000mm/yr;20–471C

MansarLake

(Ml)

o50Ka

32148N,75123E

34m

thickcore

ofgrayto

dark

graysandsiltand

mud

Interm

ontanesubtropical

lakebasin670msl

Interm

ontanelakebasin.Precipitation

andtemperature:500–1500mm

KhajjiarLake

(Kjl)

o50Ka

32130N

76124E

6m

oflightyellowishgray

todark

graysurface

core

samples

Granite-Gneisses

Highaltitudesubtropical

1900msl

Interm

ontanelakebasin.Precipitation

andtemperature:500–1500mm

AsanLake(A

sl)

o100yr

30127N

77142E

3m

thickfinesandsiltand

mud

Sedim

ents

and

metasedim

ents

Interm

ontanesubtropical

freshwaterlake390msl

Fluvio-lacustrine,

Precipitation

300–1000mm/yr,temp:20–381C

Kioto

Paleolake

(Kp)

�50–5Ka

32110N

78105E

23m

thickyellow

graysilt

tosiltyclay

Kioto

Lim

estone

DammingofRiver

2500msl

Fluvio-lacustrine,

Sem

iaridAlpine

clim

ate

Lamayuru

Paleolake(Lp)

�45–1Ka

34120N

76150E

8m

thickyellow

siltto

siltyclay

Argillaceousand

calcareousLamayuru

flysch

Dammingofriver

basin

3600msl

Fluvio-lacustrine,

Sem

iaridAlpine

clim

ate

Spituk-Leh

Paleolake(Sptl)

�50–1Ka

34110N

77130E

14m

thickyellow

graysilt

andsiltyclay

LadakhBatholith

and

Indusmolasses

Dammingofriver

3090msl

Fluvio-lacustrine,

Sem

iaridAlpine

clim

ate

Sumdo

Palaeolake(Sp)

o50Ka

6m

thickyellow

graysilt

andclaysilt

Quartzite,Shale,

Lim

estone

Dammingofriver

3200msl

Fluvio-lacustrine,

Sem

iaridAlpine

clim

ate

Bengalfan(Bf)

o50Ma

(sampledfor

o20Ka)

Dark

grayto

black

sand,

siltandmud

Him

alayanandDeccan

trapsource

Deltaicto

deepmarinefan

deposits

Gravityflow

andturbiditycurrents

S.J. Sangode et al. / Quaternary International 159 (2007) 102–118 107

ARTICLE IN PRESSS.J. Sangode et al. / Quaternary International 159 (2007) 102–118108

1999; Kumaravel et al., 2005; Sangode and Bloemendal,2005). The channel sediments show relatively higherferrimagnetic content. As a result, there is magneticsusceptibility depletion due to pedogenesis in general.The environmental magnetic results on channel sandstones(Sf-Ch), paleosols (Sf-Pedo) as well as the total (Sf-All)comprising the channel sandstone, pedogenic and non-pedogenic mudstones and siltstones are presented here forcomparison (Table 3, Figs. 3–7).

4.2. Alluvial plains in the Himalayan foreland (Ganga

plains—Gf)

The Ganga basin is the continuation of the distalforeland sedimentation of the Himalayan Foreland Basin(HFB) system with its linkage to the modern sedimenta-tion, in contrast to the cessation of the Siwalik sedimenta-tion during Late Quaternary. Understanding the modernsedimentation processes in the Ganga plains gives a betterinsight to investigate the Siwalik sequences. However, since

Table 3

Volume specific magnetic susceptibilities (jlf: 10e–11 SI units) for the studied pr

Table describes their interrelations using routine statistical parameters

Sf-All Sf-Ch Sf-Pedo Gf-All (except modern)

Mean 22.09 33.19 16.41 17.47

Median 10.67 11.77 10.53 15.00

SD 31.23 43.55 17.12 13.73

SV 975 1896 293 188

Kurtosis 15.90 6.64 10.13 41.45

Skewness 3.63 2.45 3.12 5.30

Range 214 214 87 139

Minimum 3.80 3.80 4.67 3.00

Maximum 218.35 218.35 91.73 142.00

Count 131 54 48 171

Ml Kjl Asl Kp

Mean 12.54 10.81 24.83 8.

Median 7.79 10.90 23.83 7.

SD 18.07 5.08 8.13 3.

SV 326.65 25.82 66.02 10.

Kurtosis 20.16 1.30 17.90 5.

Skewness 4.18 0.88 3.36 2.

Range 111.60 20.05 59.17 17.

Minimum 1.67 2.73 11.83 4.

Maximum 113.27 22.78 71.00 21.

Count 52 22 58 104

Bf All Bf Hm

Mean 21.25 24.40

Median 19.00 23.99

SD 10.64 8.65

SV 113.15 74.89

Kurtosis 2.53 -0.41

Skewness 1.40 0.12

Range 69.81 37.97

Minimum 2.12 7.40

Maximum 71.93 45.37

Count 468 44

only the Late Pleistocene to Holocene sediments areexposed as cliffs along the river banks (Sinha et al., 2002;Gibling et al., 2005), a direct link between the Siwalik andthe Ganga plains is not discernible based on fieldobservations. The environmental magnetic studies pre-sented here are based on samples from drill cores and someexposed bank sections in the Ganga basin. The results aredistinguished for channel facies (Gf-Ch), modern sands(Gf-Mod) and the interfluve deposits (Gf-Inf).These sediments are dominated by ferrimagnetic miner-

als, in contrast to the antiferromagnetic mineral dominancein the Siwalik sequences. Thus the channel as well asfloodplain facies in the Ganga plains are characterized byferrimagnetic minerals and their MMAs are distinguishedbased upon grain size sensitive magnetic parameters. Allthe escarpments exposed in the Ganga plains are char-acterized by channel to floodplain couplets. The environ-mental magnetic studies therefore can help to characterizethe channel- floodplain relations in time and space over theGanga basin.

ofiles and cores from the Indian subcontinent localities as shown in Fig. 1.

Gf-Inf Gf-All-ch Gf-Mod Pf-Mid Pf-Dist BGF

20.16 16.20 153.26 19.72 18.75 306.92

17.71 14.00 139.30 18.30 12.96 273.50

10.18 15.00 46.90 8.25 16.79 185.41

103 224 2199 67 281 34,378

5.26 44.91 5.61 �0.95 4.73 6.09

2.02 5.89 2.04 0.22 2.37 2.12

54 139 197 30 66 1169

7.16 3.00 108.96 7.00 5.23 73.00

61.33 142.00 306.26 37.02 71.43 1242

55 116 19 41 38 182

Lp SLp Sp Gtp

64 14.02 25.41 8.43 17.77

60 7.33 21.20 8.00 16.68

19 15.46 28.26 3.41 4.79

15 239.06 798.71 11.65 22.97

76 6.28 25.26 2.06 28.25

34 2.56 4.28 1.33 3.95

70 63.67 233.07 11.48 49.70

00 5.03 3.70 5.00 9.62

70 68.70 236.77 16.48 59.32

29 140 11 201

BF dp Bf pe Clp

15.68 40.36 79.30

15.20 39.00 68.57

5.51 10.33 44.33

30.32 106.76 1965.03

0.05 1.74 1.40

0.23 0.93 1.23

25.00 45.00 224.81

4.00 23.00 10.77

29.00 68.00 235.58

56 28 1490

ARTICLE IN PRESS

Fig. 3. The jlf bubble plots expressing the mean values as center of the bubble on abscissa with, minimum on ordinate; and the area is indicated by the

spread of the maximum value.

S.J. Sangode et al. / Quaternary International 159 (2007) 102–118 109

4.3. Alluvial fan in intermontane basin (Pinjor Dun fluvial—

Pf)

‘Dun’ is a general term given to the post-Siwalik(younger to �0.5Ma) intermontane valley in the Hima-layan foreland. The Himalayan Frontal Thrust (HFT)separating the Ganga basin and the folded Himalayanforeland sequence is the southernmost boundary for theseintermontane basins. Their northern limit is marked by theforeland margin thrusts and partitioning thrusts. Thesebasins display a sedimentation pattern with proximal todistal alluvial fan gradation. Fan entrenchment and terracedevelopment are the later processes dominated in thesebasins after the fan aggradation. More detailed descrip-tions of the sedimentation processes in these sequences aregiven by Singh and Tandon (this volume) and Kumar et al.(this volume).

Three sections were sampled, one each from proximal,medial and distal fan regions, in the Pinjor Dun area. Thesubtle facies variation within the sand-silt sequences in thisregion makes it difficult to identify and relate thesedimentation process to high-resolution tectonic/climaticchanges. However, high amplitude environmental magneticchanges indicate their utility to characterize the deposi-tional and pedogenic events, to assess their duration andstyle of occurrence, and to relate them to the knownclimatic and tectonic variations during the Quaternary.Magnetic minerals in these sediments are characterized bymixtures of ferri- and antiferromagnetic oxides. Their

variations in a single profile thus allow demarcation ofpedogenic and detrital events.

4.4. Himalayan lacustrine and fluvio-lacustrine settings

(Mansar:Ml, Khajjar:Kjl, Asan:Asl, Lamayuru:Lp,

Spituk-Leh:Sptl, Sumdo:Sp and Kioto:Kp)

The lacustrine and fluvio-lacustrine sedimentation in theHimalayan region can be broadly distinguished intopaleolake and active lake sedimentation. The paleolakedeposits mostly occur in the Higher and Trans-Himalayanregion beyond the monsoonal barrier. The majority ofthese lake deposits are formed by the dynamic glacio-fluvial and tectonic changes such as blockages of rivers (seeBurgisser et al., 1982; Fort et al., 1989; Shroder andHiggins, 1989). The palaeolakes formed during LatePleistocene were drained during the Holocene and theeroded profiles are exposed as scarps along the rivervalleys. These sediments occur as interbedded fine- tocoarse-grained gray to yellowish silts. Several present-dayhigh-altitude lakes in the Himalayan region, fed by highersediment influx during monsoonal precipitation, were alsosampled for this study. These lake and paleolake sedimentsprovide a modern link to the neotectonic and climaticfluctuations in the region. Understanding the process andmechanism of sediment accumulation in these lake basinsthus becomes a prerequisite for their detailed investigation.These lake sediments show varied mineralogy betweenferri- and antiferromagnetic mixtures, but those with

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Fig. 4. SIRM vs jlf plots based on Thompson and Oldfield (1986). The magnitudes of SIRM and jlf parameters are sensitive to concentration of MMA

while their ratio is sensitive to grainsize. The standard plot 4 (A) is based upon 1000 natural samples and about 25 natural separates of magnetite (see text

for citation).

S.J. Sangode et al. / Quaternary International 159 (2007) 102–118110

strong visible detrital influx lean towards the ferrimagneticcomposition of larger grain size.

4.5. Bhima–Godavari Peninsular river basin (BGf)

A large part of the Quaternary sedimentation over theDeccan plateau region forms erosional landscapes. Themajority of the rivers originate in the region of steepescarpments in the western margin of the Deccan plateau.A steep rainfall gradient occurs from west to east(3000–600mm) within a stretch of 40–50 km due to the

rain shadow effect of the Western Ghats. Sedimentationand erosion in this basin is thus mainly governed by thechanges in sediment-water ratio driven by climatic changes.Magnetic susceptibility and other environmental mag-

netic parameters from the studied sections along thetributaries of the Godavari and the Bhima suggestsignificantly high ferrimagnetic content as they arecomposed of weathering products of the Deccan Basalt.Stratigraphic correlation of individual sites based uponrock magnetic studies is possible only after understandingthe basic MMA characteristics.

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Fig. 5. Concentration and grainsize distribution of the MMAs for the studied set of profiles after standard plot of Peters and Dekkers (2003). Ht:

Hematite, Gt: Goethite, Mt: Magnetite, SPMt: Superparamagnetic magnetite, MDMt: multidomain magnetite, SDHt: single domain hematite.

S.J. Sangode et al. / Quaternary International 159 (2007) 102–118 111

4.6. Bengal fan Submarine sedimentation (Bf)

Sedimentation in the Bengal fan is mainly driven by thegravity flow and turbidity currents with major sedimentflux from the Ganga–Brahmputra river systems. The othercontrasting source influx to the Bay of Bengal is from theeast coast of the Peninsular. India through the Mahanadi,Godavary and Cauvery river systems. The Bengal fan thusprovides a unique repository to study the climate and/ortectonic controlled sediment supply from the Himalayanand the Peninsular India. A total of 17 gravity cores (each1–3m) obtained from the Upper and Middle fan regionhave been studied for the present study. The cores aredivided into three sub-groups: (a) cores off the Gang-a–Brahmputra region as the Himalayan source (Bf-Hm),(b) cores off the Godavari delta as characteristic peninsularsource (Bf-Pe) and (c) cores from the deeper part (Bf-dp).The samples consist of pelagic-hemipelagic clays, silt andmud and silt turbidites deposited under deep marine to

shallow marine conditions during Late Pleistocene-Holo-cene. All these regions (a,b,c) show ferrimagnetic mineralassemblage with regional variation in grainsize andconcentration. The Bf-Hm shows larger ferrimagneticgrain size and lower concentration compared to Bf-Peand Bf-dp.

5. Results and discussion

5.1. Low-field volume susceptibility (jlf)

The bubble plots (Fig. 3) show the mean values (centerof the bubble) on abscissa, minimum on ordinate and themaximum values expressed by the size of the bubble. Thefluvial sediments of the Siwalik, Ganga basin and theintermontane Pinjor Dun cluster in the low value regionwith mean jlfo50 (Fig. 3(a)). The proximal facies of thePinjor fan (Pf-Prox) shows higher values and the modernriver sediments of the Ganga basin (Gf-Mod) and the

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Fig. 6. Plot indicating remanence coercivity (B(O)CR) and S-ratio. Mean values for the studied profiles are shown to indicate their distribution and

interrelations.

S.J. Sangode et al. / Quaternary International 159 (2007) 102–118112

Bhima–Godavari basin sediments (BGf) show significantlyhigh mean values. The high values of BGf sediments aredue to their enrichment by ferrimagnetic basaltic weath-ering products. It is interesting to note that the modernchannel sand (Gf-Mod) in the Ganga basin shows entirelydifferent MMA than the older Ganga basin sediments andthe Siwaliks by its ferrimagnetic mineral enrichment. Thissuggests that the modern sand in the Ganga basin isdetritus from the hinterlands farther north, predominatingover the contributions of the local hinterlands.

The Siwalik, Ganga basin and the Pinjor Dun sedimentshave been plotted separately for clarity (Fig. 3(b)) toillustrate their interrelations. The lower values of Siwalikpaleosols (Sf-Pedo) compared to the associated channelsediments (Sf-Ch) indicates depletion of susceptibility,previously explained as antiferromagnetic mineral enrich-ment in the paleosols compared to the ferrimagneticassemblage of the channel sands (Sangode and Bloemen-dal, 2005). This is in contrast to the pedogenic enhance-ment of susceptibility reported elsewhere, particularly inthe Chinese Loess-Paleosol sequence. It is also interestingto note that the Ganga plains interfluve facies (Gf-inf)shows relatively higher values than the associated channelfacies (Gf-Ch) and is entirely different from the modernsands (Gf-Mod). This indicates a change in catchment (i.e.hinterland setup) during the flood events. This aspect needsspecial attention.

The Pinjor Dun fan sediments clearly show a decreasingtrend of jlf from proximal to distal fan regions (Figs. 3(a)and 3(b)) indicating the trend of the alluvial fansedimentation. Amongst the fluvial sediments the jlf forSiwalik sediments (Sf-All) are larger than the Ganga fluvialsediments (excluding the modern sand) and are comparableto the intermontane Pinjor Dun sediments (Table 3). TheGanga basin shows more peakedness (Table 3) comparedto the Siwalik system. Moreover, the modern sand in the

Ganga basin behaves entirely differently from otherassemblages and needs special attention for more detailedwork.Amongst the active lakes, the Asan lake sediments from

the Dun valley show high values of jlf with low standarddeviation, suggesting suitability for reconstruction of highresolution records of sediment response to climate varia-bility. The Mansar lake sediments show low to intermedi-ate values with relatively larger standard deviation,probably indicating linkage to the catchment dynamics.Detailed catchment sampling could relate the environmen-tal magnetic signatures to the tectonic and climatic changesin the region. The Khajjiar lake surface sediments showlower values probably due to diamagnetism from organicmatters, as the lake sediments were observed to be enrichedin organic content. The Mansar lake sediments show ahigher peakedness compared to the Asan and the Khajjiarlake sediments, most probably due to multiple inputs fromthe catchment of varied lithology.Amongst the paleolakes, the Spituk-Leh (Sptl) shows the

highest mean jlf with very large standard deviation andpeakedness, indicating a highly dynamic ‘catchment tosink’ relationship. This suggests a good scope to investigatethe sediment source mechanism based on environmentalmagnetic approach. Similar conditions are also observed inthe Lamayuru paleolake (Lp) which is a closed lake basin.These lacustrine sediments in the Ladakh Himalaya arerepositories to document the fluvial response to dynamicclimatic and tectonic changes in the region during the LateQuaternary. The Kioto and Sumdo (Kp and Sp) paleolakesin the Higher and Lesser Himalaya, on the other hand,show lower standard deviation and peakedness, suggestingstable catchments with uniform bedrock composition.The Bengal fan samples representing the Peninsular

source off the Godavari mouth (Bf-Pe) show the highestmean values of jlf compared to the deeper (Bf-dp) and the

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Fig. 7. Mean, minimum and maximum values for the B(O)CR vs. S-ratio plots for the Siwalik–Dun–Ganga basin system and the Deccan trap-Bay of

Bengal system to indicate their source to sink relations.

S.J. Sangode et al. / Quaternary International 159 (2007) 102–118 113

Himalayan source (Bf-Hm) samples, suggesting affinity tothe weathering products from the Deccan Basalt province.Previously, Sangode et al. (2001) noted a trend in jlf off the

Godavari coast particularly during the Holocene inter-glacial period. There is depleted susceptibility in the deeperpart of the Bengal fan, probably due to a decrease in

ARTICLE IN PRESSS.J. Sangode et al. / Quaternary International 159 (2007) 102–118114

ferrimagnetic grain size or mixing from the Himalayansource. The Himalayan source (Bf-Hm) shows intermediatevalues between Bf-Pe and Bf-dp. To summarize, the jlf

values and their variations are quite distinct amongst allthese basins, and are mainly controlled by proximity andstyle of catchment erosion due to fluvial processes that arein turn controlled by climate and tectonics at different timescales.

5.2. SIRM vs. jlf plots

The SIRM is the summation of saturations acquired bythe remanence carrying minerals. Therefore, its ratio with jlfis sensitive to concentration and grain size of ferri- andantiferromagnetic minerals. The magnitudes of SIRM andjlf are independently sensitive to concentrations, whereastheir ratios are sensitive to grain size. The classical bivariatestereogram of SIRM versus jlf (Thompson and Oldfield,1986) is therefore used here (Fig. 4) to discriminate theMMAs amongst the varied depositional settings. Thestandard plot (Fig. 4(a), Thompson and Oldfield, 1986) isderived from the data of 1000 natural samples and about 25natural separates of magnetite. They indicate high magnetiteconcentration diagonally towards top right, high hematiteto magnetite ratio laterally towards right at the base andincreasing paramagnetic concentration towards far left withthe ordinate. The MD magnetites and MMA with highconcentration of SP magnetite plot towards the top.

In this diagram, all fluvial sediments plot intermediate tomagnetite and hematite regions indicating their mixtures(Figs. 4(b) and (c)). The Bhima–Godavari (BGf) sedimentsshow the highest ferrimagnetic content amongst all due tothe Deccan trap source. In the fluvio- lacustrine sediments,the subtropical monsoonal lakes in the Himalayan foothills(Asan-Asl and Mansar-Ml) are high in ferrimagneticcontent, with Asl showing relatively larger grain size thanMl, suggesting predominance of detrital control by fluvialinflux for Asl. The high altitude Himalayan lake, Khajjiar(Kjl) with overall gneissic bedrock composition, plots inthe intermediate fields of ferri-, para- and diamagnetic.This is in agreement with its weak fluvial influx and highorganic matter content. Amongst the paleolakes, theSumdo (Spl) in the Spiti valley and the Lamayuru (Lp) inLadakh indicate mixtures of weakly ferrimagnetic andmore paramagnetic assemblages. These lakes are situatedin a catchment of weakly magnetic siliciclastic and lime-stone terrain. However, the Kioto paleolake (Kp) in theSpiti valley with predominantly limestone bedrock plots ina different field indicative of a mixture of ferrimagnetic tocanted antiferromagnetic MMA.

The Spituk-Leh (Sptl) paleolake sediments plot in amore ferrimagnetic region. These deposits exposed alongthe Indus river valley represent high energy fluvial settings(Phartiyal et al., 2005). The discrete nature of Sptl on theSIRM vs. jlf plots, relative to all the other lake-paleolakesediments even in the adjoining region (e.g., Lamayurulake) suggests a different configuration of the lake basin

and its catchment relation that needs to be explored indetail. This suggests that although most of these lakes andpaleolakes are coeval, they are governed by their owncatchment and hence can not be regionally correlatedwithout a proper source to sink study.The Bengal fan sediments with peninsular sources (Bf-

Pe) show higher ferrimagnetic contents than those from thedeep marine sites (Bf-dp). Sangode et al. (2001) observed aclear gradient from the Peninsular source off the Godavaridelta to the deep marine cores based on their magneticsusceptibility core correlation approach. The Bengal fansediments from the Himalayan source (Bf-Hm) also plot inthe ferrimagnetic fields with larger grain size than Bf-Peand Bf-dp. This indicates high energy conditions for thesedimentation in the Bf-Hm region.In general, the SIRM vs. jlf plots indicate the largest

spread for the Ganga basin sediments and notablyconstricted fields for the Siwalik sediments. This is despitethe fact that the Siwalik sediments represent significantlylarger time and space domains. Thus, it is essential toinvestigate the catchment (hinterland) dynamics for boththe Ganga and Siwalik foreland basins. Sangode andBloemendal (2005) have discussed the changes in magneticmineralogy of the Siwalik paleosols due to burial. Moredetailed attempts are awaited to investigate the overallconstricted nature of the Siwalik basin sediments as shownhere.The SIRM vs. jlf plots thus indicate discrete fields for

each basin. Detailed catchment sampling for all thesebasins is suggested in order to reconstruct the regionaltectonic/climatic history based upon environmental mag-netic approach on respective sediment profiles and cores.

5.3. SIRM/ vlf vs. B(0)CR bivariate plots

This plot (Fig. 5) is mainly indicative of distribution ofmagnetic domain sizes for ferri- and antiferromagneticminerals. These plots, initially suggested by Thompson andOldfield (1986), were further improved after more data onnatural separates by Peters and Thompson (1998) andothers (Peters and Dekkers, 2003). Magnetite and goethitefields plot diagonally opposite to each other. The hematiteand titanomagnetite plots intermediate to magnetite andgoethite. The SIRMs are sensitive to grain size. However,the vlf is relatively insensitive to it and decreases with theenrichment of antiferromagnetic minerals. The high SIRM/vlf ratios for dominantly ferromagnetic MMA suggest anincrease in SD content. For mixtures, it may suggestincreased content of canted antiferromagnetic minerals.These ratios thus require careful interpretation in combi-nation with other concentration-independent but grainsize-sensitive parameters such as B(0)CR. This model is usedhere for relative comparison of MMAs amongst differentdepositional environments.The Siwalik (Sf) and the Ganga basin (Gf) clearly show

distinct fields with the Siwalik plotting in hematite rich andthe Ganga basin in hematite-depleted regions. The Pinjor

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fan (Pf) plots in the region similar to the Siwaliks, exceptthe proximal fan data, and shows high ferrimagneticcontent. The Bhima–Godavari fan (BGf) sediments essen-tially plot near the ferrimagnetic fields. The mean SIRM/vlf and the B(0)CR increases for the Siwalik paleosolsgeographically from east to west for the coeval sectionsof Haripur (HP), Moginand (MG) and Ghaggar (GH).This occurs within an antiferromagnetic assemblagesuggesting increasing percentage of higher coercivityminerals (goethite over hematite) laterally towards thewest indicating more warm-humid conditions for soildevelopment. The distribution amongst the lake andpaleolake sediments is clustered in the SIRM/ vlf–B(0)CR

bivariate plots. This probably indicates that the bivariateplot is not very useful for the comparison of these lakebasins.

5.4. S-ratio vs. B(0)CR plots

In order to understand a finer discrimination anddistribution amongst the MMAs, S-ratio is plotted againstB(0)CR (see Figs. 6–8). These parameters are mainly basedupon the shape of the remanence hysteresis curve and aremore ideal for intercomparisons. Both these parametersshow good discrimination over grain size and compositionfor most of the abundant iron oxides. This can defineregions of specific grain size with respective minerals andtheir mixtures when plotted together on the scatterogram.For example, more negative values for S-ratio (o�0.75)and significantly low B(0)CR define a region for MD grainswhereas S-ratio ranging in between �0.25 and 0.25 withvarying B(0)CR can define variants of MMA with ferri- andantiferromagnetic minerals. When studying a profile andcatchment to sink relation, the MMA path can be tracedon such a plot (Fig. 6). Also, it is possible to define more

Fig. 8. Empirical plot based upon B(O)CR and S-ratio parameters. The regions

artificial simulation to describe the utility of the plot (See text for details).

regions and better quantification based upon database onnatural separates.Fig. 6 is able to indicate the separation among the

depositional settings and also ‘proximal to distal’ or‘source to sink’ relations. The proximal, middle and distalfan variation for the Pinjor Dun sediments is elaborated byPath I in this figure. The sediments in the proximal fanregion are the mixture of ferri- to antiferromagneticminerals which change to predominantly antiferromagneticmixtures (higher goethite to hematite ratio) in the middlefan region and then returns to more hematitic compositionin the distal fan region. This path thus clearly indicates agradient from larger ferrimagnetic grain composition fromproximal fan, well drained (goethitic) depositional condi-tions in the middle fan region and more warm-arid(hematitic) conditions in the distal region. This depicts adistribution of alluvial fan sedimentation in this basinwhere the distal region appears to have remained uplifteddue to upwarping along the frontal thrust (HFT).Path II indicates a gradient amongst the Siwalik

paleosols [Sf-Pal(HP)–SfPal(MG)–Sf Pal(Gh)] laterallywith their geographic distribution from east to west inthe Himalayan foreland basin. It demonstrates thedistribution of paleosol development under relativelywarm-arid conditions at HP in the east to more humidconditions in the west at Gh that may be related to thechannel proximity and its dynamics.Similarly, interbasinal comparison can be made for the

lacustrine and fluviolacustrine basins. The Asan (Asl) andthe Sumdo (Sl) lakes clearly indicate the dominance oflarger ferrimagnetic grains. This is in agreement with thedepositional setting and the lithofacies for these lake basinsthat indicate high energy fluvial influx. Similarly, theLamayuru paleolake (Lp) which originated by riverblockage indicates a composition intermediate to MD

are defined based upon available information, while the paths indicate an

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and SD ferrimagnetics. The remainder of the lakesediments plot as mixtures of ferri- and antiferromagneticgrains and require a detailed catchment to sink and profiledescriptions (to be published elsewhere).

For the Bengal fan, the peninsular source and the deepmarine core overlap each other indicating their closeaffinity. The Himalayan source is quite distinct from thesetwo cores. Fig. 7 displays the variations in paths for mean,minima and maximum. These are indicative of differentfractions within the basin (e.g., authigenic-detrital orvarious combinations of MMA within the authigenicsource) that needs to be explored in detail.

The objective of the above exercise was to test the utilityof the B(0)CR vs. S-ratio scatterogram for inferring variousQuaternary depositional environments in the Indiansubcontinent. More detailed work is in progress for asystematic approach of ‘source/catchment to sink’ studiesin the individual basins. Fig. 8 demonstrates the possibleMMA regions by simulating two hypothetical cases ofsource to sink variations. Path I indicates a simple casewhere the source is canted antiferromagnetic-rich catch-

Fig. 9. The diamond plot defining the regions of MMA distribution for the fl

given in text).

ment and the sink is enriched with SD ferrimagnetics. Thiscan imply significant authigenic enhancement of the sink inaddition to the detrital influxes. Path II is a single profilefor the sink whose source is articulated by the MDdominant mineralogy (dashed line rectangle). The variationin the path of the sink with profile depth is indicative of theevents of prevalent source influx as well as regions ofMMA mixing.

5.5. B(0)CR–SIRM/ vlf–vARM–S-ratio ‘Diamond plots’

These are the most reliable and widely used independentparameters covering almost all the aspects of environ-mental magnetic procedures at room temperature. Theseparameters are plotted on a single diagram (Fig. 9) in orderto demonstrate the domains of fluvial regime in theHimalaya foreland region. In this plot, the sides of theparallelogram represent the axis for the respective para-meters. Thus, the axis named as B(0)CR ¼ 500 indicates theline joining all the points whose values are 500mTremanence coercivity. The parallel lines away from this

uvial sediments in the Himalayan foreland including Ganga basin (details

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axis end at zero at an interval of 50mT. The SIRM/vlf ¼ 500 axis can be explained in a similar manner. Thecentral horizontal axis represents the vARM value of 500,which decreases below and above towards the apices of thediamond. These apices are defined by S-ratio ¼+1 and�1 with the central horizontal line axis coinciding with S-ratio ¼ 0. The horizontal lines fall at an interval of 0.1 ofthe S-ratio, both at positive and negative sides. The vARM

values divide the plot in the negative or positive sidedepending upon preference to the sign of mean S-ratiovalue. The vertical bars with the numbers at the centerrepresent S-ratio for the respective numbered index of thedata, the center represents the mean value and the top andbottom as minima and maxima.

In the diamond plot the Siwalik channel and paleosoldomains can be seen overlapping each other (marked bythe gray and the hexagonal filling). The largest spread isshown by the Siwalik paleosols (Sf-Pal) indicating a largevariation in the mineralogy and grain size, followed byPinjor fan distal facies (Pf-Dist) and Siwalik channel (Sf-Ch). The Ganga basin channel as well as interfluve, and thePinjor fan proximal settings show the most constrictednature falling in the range of larger ferrimagnetic grain size.It can be observed that the channel sediments aredominated by more ferrimagnetic MMA than are theinterfluve sediments. The MMA in the Pinjore Dun fanproximal (Pf-prox) shows more ferrimagnetic affinity thanthe distal fan (Pf-dist). It is interesting to note the gradientof spread of MMA in the Pf-Dist that lies within a shortdistance of �20 km from Pf-Prox region. This eitherindicates a geomorphic break in topography or channelmorphology and demands detailed field studies. Theentirely discrete nature of the Ganga basin sedimentssuggests that the Siwalik foreland is not its predominantcatchment. More hinterland sampling in the Lesser and theHigher Himalayan terrain is required to further delineatethe hinterland/catchment relation for the Ganga basin todecipher the ‘source to sink’ evolution and its tectonic orclimatic implications.

6. Concluding remarks

This paper presents an attempt to characterize andcompare a variety of depositional settings across the Indiansubcontinent using environmental magnetic signatures forthe first time. Besides using the conventional models, newmodels were found successful in describing and comparingvaried sets of depositional conditions. The environmentalmagnetic approach on selective profiles of some of theQuaternary basins representing varied depositional condi-tions (including marine sediments) has indicated predomi-nantly detrital control.

The detrital processes are governed by the climate ortectonically induced sediment influx from catchment tobasin. Within profile environmental magnetic processesshould be linked to such processes by extensive catchmentsampling in order to investigate the climate proxies and for

the regional comparison with other basins. The Siwalik,Ganga basin and the intermontane Pinjor Dun sedimentshave a complex relation that can be resolved by extensiveand detailed analysis for the environmental magnetism.The characteristics from the magnetic parameters synchro-nously vary with the lithofacies and source and can beexpressed in its unique mineral magnetic assemblage(MMA). Detailed rock magnetic studies are warranted tocharacterize the MMA in each basin for wider use of themore simplistic environmental magnetic parameters likethe magnetic susceptibility.The magnetic signatures generated from the controlled

high field approach of the environmental magnetism showslarge amplitudes even when there is subtle lithofaciesvariation in a profile. Different minerals and their grainsizeconstituents are recognizable using the combination ofenvironmental magnetic parameters without the need forphysical separation. The ability to quantify is an addedadvantage for modeling and comparison of the deposi-tional processed. This makes environmental magnetism afast, economic and robust approach for characterization ofthe Quaternary sedimentation processes in the Indian sub-continent.

Acknowledgements

We are grateful to Prof. B.R. Arora, Director, WadiaInstitute of Himalayan Geology (WIHG), Dehradun forhis suggestions, encouragement and liberal funding for thisresearch. The Ganga plains work was supported throughfunding from the Department of Science and Technology,New Delhi to R. S. We profusely thank the Directors andHeads of the respective Institutions for encouraging thesecollaborative efforts. We acknowledge the improvement ofthis manuscript by the critical reviews and healthysuggestions from M. J. Dekkers and M. E. Evans. Mr.Rakesh Kumar is acknowledged for his assistance duringanalysis in the Palaeomagnetic lab of WIHG.

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