Holocene climatic ﬂuctuations in the Gujarat Alluvial Plains based on a multiproxy study of the...

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Palaeogeography, Palaeoclimatology, Palaeoecology 421 (2015) 60–74

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Palaeogeography, Palaeoclimatology, Palaeoecology

j ourna l homepage: www.e lsev ie r .com/ locate /pa laeo

Holocene climatic fluctuations in the Gujarat Alluvial Plains based on amultiproxy study of the Pariyaj Lake archive, western India

Rachna Raj a,⁎, L.S. Chamyal a, Vandana Prasad b, Anupam Sharma b, Jayant K. Tripathi c, Poonam Verma b

a Department of Geology, Faculty of Science, The M.S. University of Baroda, Vadodara 390 002, Indiab The Birbal Sahni Institute of Palaeobotany, 52 University Road, Lucknow 226 007, Indiac School of Environmental Sciences, Jawaharlal Nehru University, New Delhi 110067, India

⁎ Corresponding author. Tel.: +91 9376220681 (mobilE-mail address: naveenrachna@gmail.com (R. Raj).

a b s t r a c t

Article history:Received 2 January 2014Received in revised form 8 December 2014Accepted 6 January 2015Available online 10 January 2015

Keywords:HolocenePalaeoclimateLakesGujarat Alluvial PlainsWestern India

A sediment core from Pariyaj Lake, from the Vatrak River basin, located at the desert margin in the GujaratAlluvial Plains of western India, was investigated in a multidisciplinary aspect. The goal was to reconstruct thepalaeoclimate, palaeoenvironment and tectonic history and to understand the role these factors played in thegeomorphological evolution of the area during the Holocene. Palaeoclimatic interpretations also shed light onthe factors responsible for the rise and fall of the Harappan civilisation. The results obtained based onmultiproxystudies show five climatic phases during the last 11,000 yr BP. Phase 1 (~11,000 cal yr BP) represents a veryhumid climate and high precipitation/discharge leading to high lake stand as attested by the high pollenconcentration of semi-evergreen tree taxa, phytoliths belonging to cool and moist grasses, and large proportionof algae, marking the onset of Holocene. In phase 2 (~8000 to 9000 cal yr BP) a significantly reduced yield ofpollen, phytoliths and aquatic algae indicates shrinkage of the lake. Phase 3 (~7630 cal yr BP) shows moderateyield of pollen and phytolith pointing towards fluctuating precipitation conditions. Phase 4 (~5864 to4680 cal yr BP) shows very low pollen and phytolith counts, indicating a very dry spell. Finally, phase 5(~4680 to 3500 cal yr BP) shows a good density and diversity of flora. The wet climate and high lake stand~11,000 cal yr BP, 7630 cal yr BP and after ~4680 cal yr BP are synchronous with the lacustrine, marine andaeolian records of western India. The contribution of winter precipitation at 7630 cal yr BP and after~4680 cal yr BP can be correlatedwith similar records from Rajasthan Lake. Decrease in the precipitation activity,the low lake stand and the onset of dry climatic condition between 8000 and 9000 cal yr BP corresponds to a nearglobal anomaly of this period. Another dry event between ~5864 and 4680 cal yr BP documented in Pariyaj Lakerecord is synchronous with various proxy records of the mid–late Holocene Afro-Asiatic monsoonal belt.

1. Introduction

The Holocene spans the time period of the last 11.6 ka (Walker et al.,2009). In recent studies (Bond et al., 2001;Mayewski et al., 2004; Prasadand Enzel, 2006; Staubwasser and Weiss, 2006; Prasad et al., 2007,2014a; Fletcher et al., 2013) it has been established that during theHolocene, whichwas traditionally considered a climaticallymore stableperiod than the Late Pleistocene, the climate varied significantly. Abruptclimate change during the early Holocene is also documented by variousworkers in Asia (Enzel et al., 1999, 2003; Weiss and Bradley, 2001;Parker et al., 2004; Migowski et al., 2006; Staubwasser and Weiss,2006). During the first 5 ka of the early Holocene, a reorganisation ofthe hydrographical system due to the melting of the large ice-sheetstook place (Carlson et al., 2008; Renssen et al., 2009)whereas the periodof the last 7 ka was dominated by the decrease in solar insolation in thenorthern hemisphere during boreal summer (Berger, 1978; Wanner

et al., 2008). Recent decades have been influenced by climate changedue to anthropogenic forcing. Due to this redistribution of solar energythe global climatic system experienced a rearrangement that is classifiedin twomain Holocene climate patterns, i.e. Holocene ThermalMaximum(HTM between ~7 and 4.5 ka BP) and the Neoglacial, which startedaround 4.2 ka BP and ended with the modern industrialisation in the19th century (Wanner et al., 2008; Wanner and Bronnimann, 2012).The HTM witnessed enhanced heating of the northern hemisphereduring the boreal summer leading to warming, generating intensifiedheat lows, and higher activity of the Afro-Asian summer monsoonsystem, thus transportingmoremoisture to the corresponding continen-tal areas. An almost opposite pattern existed during the Neoglacial whensummer monsoons were less active and the corresponding continentalareas were exposed to an increased dryness (Gasse, 2000; Wang et al.,2005). With the better understanding of Holocene climatic fluctuationsand rapid oscillations (Mayewski et al., 2004; Duplessy et al., 2005)multidisciplinary studies for this period are gaining importance. Theperiod has widespread socio-economic impacts on human activitiesand defines the period during which civilisation developed.

61R. Raj et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 421 (2015) 60–74

According to Force and McFadgen (2012) the effect of tectonicactivity should be considered along with other factors such as climatechange in evaluating human activity and development. The Holoceneof Gujarat Alluvial Plains of western India has captured the interest ofearth scientists due to several factors as, the area is very sensitive toclimate change, a great part of it falls in the tectonically active Cambaybasin and it has also witnessed strong human influence during thistime (Hegde, 1995; Gaur and Vora, 1999). The area is presently under-going various forms of stresses due to increased climatic variability andtectonic activity, so understanding the interactions between pastclimates versus palaeoenvironmental response and the geomorphicevolution of land, and relating these to rise and fall of agriculture-based societies is important in today's context. There is also a specialinterest attached to climate change as it relates to Indian agriculturesince it affects the livelihood of over one billion people. These studiesalso help in developing an understanding of present day local climaticresponses to regional and global climatic changes.

Tectonism has been evoked by previousworkers (Raj et al., 1999a,b;Chamyal et al., 2002, 2003; Raj, 2004, 2007, 2012; Raj and Yadav, 2009)in studies of the early Holocene of western India to explain the regionaluplift of Gujarat Alluvial Plains. A study of theMahi River (Maurya et al.,1998) also suggests that seismic event that took place between 3320 ±90 and 2850 ± 90 yr BP may have played a major role in shaping theGujarat Alluvial Plains in general. A recent study in the Vatrak Riverbasin in the northwest part of Gujarat Alluvial Plains (Raj, 2012) hasestablished an eastward tilting of the Vatrak and its tributaries, a rela-tively rapid uplift of the basin, and a strong role of tectonic elements

Fig. 1. A. Map of NW India showing climatic zones (indicated as brown lines), isohyets (indicatindicated as yellow line). B. Geological map of the Vatrak River basin (Raj, 2012) showing vast stC). D. Structuralmap of NW India showing the extent of Cambay basin and its various blocks (mthe lower reaches of the River.

in the overall landscape evolution of the area. For the climatic changestudies, within the terrestrial archives, lacustrine sediments providethe best record of Holocene climatic fluctuations and their potentiallinks with rise and collapse of Indus Valley civilisation (Singh, 1971;Singh et al., 1974, 1990, 2007; Prasad et al., 1997, 2014a). In a recentstudy by Prasad et al. (2014a) of a lake in the central part of Gujarat Al-luvial Plains, a number of arid and humid phases during the Holocenewere linked with the rise and fall of Harappan civilisation using multi-proxy approach.

To gain a better understanding of the Holocene climatic fluctuationsof the Gujarat Alluvial Plains, a multiproxy record was generated fromthe Pariyaj Lake, a large natural lake in the area. The primary aim ofthis study is to understand the palaeoclimatic fluctuations during theHolocene and to offer a regional correlation of the data generated bythis study with that of the marine, lacustrine, aeolian and culturalrecords of West Asia. The role of climate in the rise and fall of theHarappan civilisation is also critically assessed.

1.1. Regional setting

1.1.1. Geology and tectonicsThe Vatrak River basin, in the lower part of which Pariyaj Lake is

situated, is bordered by the Thar Desert in the northwest, the Gulf ofCambay in the south and the Deccan Trap highland in the east, makingit suitable for the palaeoclimatic studies (Fig. 1A–D). The river originatesin the Aravalli upland and flows through a constricted course in theupper reaches of the Aravalli terrain. In the middle and lower reaches

ed as blue lines) and the maximum fossil extent of the Thar Desert (after Juyal et al., 2003,retch of Gujarat Alluvial Plains in the lower reaches where lake Pariyaj is located (see insetodified after Biswas, 1982). Blue dashed line is Vatrak Fault which controls the drainage in

62 R. Raj et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 421 (2015) 60–74

it flows through the Quaternary deposits of Gujarat Alluvial Plains(Fig. 1B). The lower part of the basin falls within the tectonically activeCambay basin; an intracratonic rift graben (Fig. 1 D). Mathur et al.(1968) have divided the Cambay basin into four transverse blocks andthe lower part of the Vatrak River basin falls within the Tarapur block.The fault (Fig. 1D) known as Vatrak Fault (it is the fault separating theTarapur block from Ahmedabad–Mehsana block) passes through thecourse of Vatrak River in the lower reaches (Fig. 1D). The geomorphologyof the area is influenced by the activity along the fault in the area(Raj, 2012). The Pariyaj Lake is situated close to these faults (Fig. 1C, D).A series of palaeochannels and lakes can be seen in the area (Figs. 1C,2A, B). Geologically, the northeast part the basin is bound by Archaeanrocks of the Aravalli Super Group and rocks of Lameta Formation ofLower Cretaceous (Fig. 1B). Towards the east and southeast there areDeccan volcanics of Upper Cretaceous to Palaeocene age with isolatedpatches of Lower Cretaceous sediments (Fig. 1B). The sediment supply

Fig. 2. A. Lower reaches of Vatrak River showing structural and tectonic setup of the area aroundGujarat (1987) and Raj (2012). Box shows the area in (B). B. Figure showing series of lakes andseen in Fig. 3A.

(Fig. 1B) is from the eastern and northeastern part of the exposedPrecambrian rocks of Aravalli Super Group, the Mesozoic sedimentsand the Deccan volcanics (Raj, 2012). Previous studies in the VatrakRiver basin (Raj, 2012) have been confined to understanding the role oftectonics in the landscape evolution of the basin. The studies have alsoobserved continuing active tectonics in the region and highlightedtheir role in shaping the Vatrak River basin. The presence of variouspalaeochannels, meander cut-offs, lakes and ponds aligned in a NE–SWdirection has been noted (Fig. 2A, B).

1.1.2. Study region and siteThe steep rainfall gradient in NW India (Fig. 1A) makes this entire

region particularly sensitive to small climate fluctuations. The lake islocated in the transitional part between semi-arid and arid climaticzones (Fig. 1A). The transitional climatic zone is very sensitive to smallfluctuations in the precipitation and therefore provides a very good

the lake. The faults and lineaments are after Biswas (1982), Sahai (1981), Planning atlas ofponds in the area aligned in the NE–SWdirection, box shows the area of the Google image

record of climatic changes. The Pariyaj Lake (22°32′ N and 72°35′ E;Fig. 2A) lies in a natural depression, at places surrounded by an embank-ment; having a circumference of ~10 km. It is rich in aquatic vegetation,unlike most other wetlands in Gujarat. The total area of the Pariyaj Lakeas calculated from the recent Google image is about 2.5 × 3.5 km2 andthe depth varies from 1.5 at the fringe to 3 m in the centre. The areahas dry, tropical monsoon climate with an average annual rainfall ofabout 700 mm concentrated in the months of July, August and Septem-ber. The distance of the lake from the present day margin of the Gulf ofCambay is ~30 km. There is no river draining the lake today, isolatingit from riverine inflows and the main source of water input is throughsurface run off during the monsoon. Pariyaj Lake offers a variety ofhabitats fromponds andmarshes to patches of open grassland and scrub.

2. Lithostratigraphy

The present paper though is based on one sediment core of ~1 m(Fig. 3A, B); however, 3 smaller cores were retrieved from around thelake in the month of May, 2010, during the lowest water level andcompared for their physical and textural characteristics. The core onwhich detailed studies were taken was raised from the southern partof the lake (Fig. 3A). This core enabled a detailed sampling of variouslithostratigraphic units as it was cut into continuous 5 cm thick slices.The grain size and carbonate content of the units contributed to thesediment classification (Fig. 4). The core is comprised of three majorunits (Fig. 3B). The top half (PV-1 to PV-9, i.e. top 45 cm) comprisesfiner units of clayey sand with two darker bands of high clay content(PV-4 and 8). The second unit between PV-10 to 13 is comprised of

Fig. 3. A. Google image of Pariyaj Lake showing the location fromwhere the corewas raised. B Linterpolated ages (PV = Pariyaj Lake, Vatrak River basin).

fine calcrete nodules in clayey silt whereas the third unit betweenPV-14 to 18 contains coarser calcrete nodules in sandy horizon withmm thin clayey partings. The grain size change in the core showslarge variation in the sand and clay components whereas silt is some-what consistent (Fig. 4). There is a gradual loss in sand size with acomplementary gain in clay content till PV-3. From sample PV-12 toPV-4 sand remains below 50% whereas clay varies between ~20 and28%. A significant variation in silt content from sample PV-12 to PV-8indicates a transitory phase, from where the clay content increasesover silt. Organic carbon and carbonate variation is also following thegrain-size trend showing maximum values for moisture and organiccarbon where the clay content is maximum (Fig. 4). The carbonateremains above 10% up to sample PV-13. A successive but large drop incarbonate (from 9.8 to 2.6) is translated into gain in organic carbonand moisture, though the variation is relatively small. The higherconcentration of carbonates usually indicates evaporating conditionssupplemented by higher surface temperature as it reduces the solubilityof carbon dioxide in the water bodies. An overall decrease, however,indicates that the conditions became more favourable, initially at aslow pace, and peaking sometime around deposition of sample PV-10.

3. Analytical work: material and method

Radiometric dating and age–depth calculations were used to estab-lish a geochronological framework for the last ~11,000 yr BP. Data frompalynological and phytolith studies, as well as the sand–silt–clay ratios,organic/inorganic carbon percentage,major and trace element distribu-tions and claymineralogywere generated to infer palaeoenvironmental

ithology and photograph of the core alongwith the radiocarbon dates (blue coloured) and

Fig. 4.A. Geochemical (recalculated on carbonate free basis) and grain size variation plots of Pariyaj sediment core alongwith the lithology. Note that the variation observed does not fit incompletely with the biological proxy parameters; however, the discrepancy is dealt in the text. B. A–CN–K triangular diagram based on CIA calculation of the Pariyaj sample plot close toUCC (UCC: upper continental crust having CIA= ~50). Note that the CIA values ~50 indicate the presence ofmafic components derived from basalt, else the CIA valuesmust be relativelyhigh if the sediment is moderately or highly weathered.

changes the area has undergone during this period. Since vegetationresponds very well with the changing climatic conditions, detailedpalynological and phytolith studies were carried out to infer pastprecipitation related climatic changes.

3.1. Phytolith studies

Phytoliths are microscopic opal particles that are deposited in orbetween cells of living plant tissue. They occur in many plant familiesbut are especially abundant and diverse and distinctive in the grassfamily Poaceae. After the decay and decomposition of the plant tissues,phytoliths are liberated into the soil and are easily transported alongwith the silt size fraction to the depositional site. The main advantageof phytolith as palaeoecological microfossils is due to their preservabil-ity in soils and sediments under oxidising conditions where pollen andspores and other organic microfossils are scarce. Various methods havebeen described for the extraction of phytoliths from soil sediments. Dueto their resistance to decay and distinctive morphology in C3 and C4

grasses, fossil phytoliths are now being increasingly used for the recon-struction of palaeovegetation patterns and related palaeoclimaticreconstruction (Barboni et al., 1999; Blinnikov et al., 2002; Prasadet al., 2007, 2014a; Singh et al., 2007). In the present study phytolith as-semblages have been used to understand themonsoonal variability as a

result of climate change during the Holocene in this region. For the phy-tolith studies, deflocculation of the sediment was achieved by placing5 g of the sediment sample in a 10% Calgon solution overnight. Thesuspended claywas siphoned out and the residuewaswashedwith dis-tilled water several times. The sample was then treated with 10% HCl,and heated in a sand bath for 10–20 min to remove the carbonate con-tent from the sediment (Prasad et al., 2007). The residue was washedtwice using distilled water and dried. The organic content was then re-moved by heating the residue in 30% H2O2 in a sand bath for 20–30mindepending on the richness of organic content of the sediment. Theremaining residue was again washed twice with distilled water anddried. Phytolith extraction was achieved using heavy liquid solution ofCdI2 and KI (specific gravity 2.3) and centrifuged at 1000 r.p.m. for5 min. This step was repeated until all the material lighter than 2.3 wasrecovered. The phytoliths were washed, dried and weighed.Dried phytoliths were mounted on a glass slide using Canada balsam.Several slides were also mounted in immersion oil to view the three-dimensional images of phytoliths. Phytolith identification was madeunder 400× and 1000×magnification on an Olympus BX51microscope.The extracted phytoliths were counted and classified according to theclassification of Mulholland and Rapp (1992), Fredlund and Tieszen(1994), Alexandre et al. (1997), Barboni et al. (1999), Runge (1999),Wang (2003), and Li et al. (2010). Seven different types of grass short

Table 1Sample number, depth in cm, (14C) isotope dated sediment character and three calibrated(14C) radiocarbon ages (marked with asterisks *) and interpolated ages of other samples.

Samplenumber

Depth(cm)

Sediment character datedfor (14C) radiocarbon

Radiocarbon ages(cal yr BP)

PV-3 10–15 Organic carbon 3510 ± 130*PV-5 20–25 – 4680 ± 300PV-7 30–35 – 5864 ± 560PV-10 45–50 Organic carbon 7630 ± 210*PV-13 60–65 Organic carbon 8630 ± 110*PV-17 80–89 – 10,970 ± 930

silica cells (GSSC) were identified: rondel, square, cross, bilobate,bambusoid, multifaceted, and some burnt phytoliths. The rondel GSSCdominantly occurs in the subfamily Pooideae. Mainly C3 grasses areadapted to cool and considerably high soil moisture conditions (Tieszenet al., 1979; Livingstone and Clayton, 1980). Cross and bilobate GSSCoccur predominantly in the Panicoideae grass subfamilywhich are chieflyC4 grasses adapted to warm and humid climate with high soil moistureconditions (Tieszen et al., 1979; Twiss, 1980; Scott, 2002). In Indianplains the dominance of Panicoideae grasses (Pennisetum, Cenchrus,Andropogon, Sorghum) in the regions of high precipitation during south-west/summer monsoons (July–September) is a common feature.Bambusoid phytolith is derived from members of the Bambusoideaesubfamily. Bambusoideae grasses occur in moist and shady placesclose to awater source so their dominance in the phytolith assemblagesindicates the prevalence of wet climatic conditions (Wang, 2003; Liet al., 2010). Multifaceted, blocky polygon phytolith structures arederived from the epidermal cells and woods of ligneous dicotyledontrees (Wang and Lu, 1993; Bremond et al., 2005; Lu et al., 2006; Guet al., 2008; Li et al., 2010).

3.2. Palynological studies

The reliable autographs of climate change are provided in na-ture through climate responsive material. Among biological prox-ies, palynology has been used to understand the palaeovegetationand palaeoclimate of the Quaternary (Erdtman, 1943; Faegri andIverson, 1989; Moore et al., 1991; Birks and Birks, 2006). For recov-ering pollen and spores, 100 g of sediment samples was boiled in10% aqueous KOH solution for 5 min to deflocculate the sedimentand to remove humus. This was followed by treatment of the sam-ples with 10% HCl and 40% HF solution in order to remove carbon-ates and silica respectively. After washing with distilled water, thesamples were dehydrated in glacial acetic acid and then acetolysed(Erdtman, 1943) using the acetolysing mixture (9:1 ratio of aceticanhydride and concentrated sulphuric acid). Finally, after rinsingwith distilled water, concentrated macerals were preserved in50% glycerine solution for microscopic examination and counting.Slides were prepared and were examined under Olympus Micro-scope (BX-51) at 200× and 400× magnification. The identificationof pollen and spores recovered from all the sediment samples wasdone on the basis of the morphological characters of thepalynomorphs such as number and type of apertures, sculpturing,shape and size (Erdtman, 1943; Faegri and Iverson, 1989; Mooreet al., 1991; Punt et al., 2007). Various catalogues and identificationkeys were consulted for identification of pollen and spores (Guptaand Sharma, 1986; Nayar, 1990; Punt et al., 2007). A total of 17 to280 palynomorphs were counted per sample. The palynomorphswere grouped in order viz. trees, shrubs, herbs, ferns, and algal andfungal remains. The absolute values of each taxon were counted foreach sample and were displayed in the pollen diagram to show thetemporal changes of all the pollen taxa including algae, Pteridophytesand fungal remains with time scale and lithological details. In addition,to analyse and deduce the environmental changes a relative proportionof ratio of pollen belonging to environmental sensitive plants such asdry deciduous (Holoptelea, Prosopis, Acacia, Azadirachta, Ailanthusand member of Anacardiaceae family) and semi-evergreen (Madhucaindica, Symplocos, Syzygium) tree taxa were taken into consideration.Their ratios give an indication of dry/wet climatic condition in the re-gion. The arboreal pollen sum and non-arboreal pollen sum ratioswere calculated to estimate the total vegetation density of the region.The Artemisia and Chenopodiaceae/Amaranthaceae are the markersfor winter precipitation and can also give better clue of aridity fromtheir ratio with Poaceae. Cyperaceae and aquatic herb ratios indicaterelative lake margin shift. The exposed lake margin offers better prolif-eration of sedges at lakemarginswhereas submergedmarginswill havemore aquatic herbs.

3.3. Geochemical studies

Climate plays a major role in chemical weathering processes (Zhonget al., 2012). The chemical weathering is initiated by water, which isseen as the first order controlling agent. It also determines the intensityof major chemical reactions (White and Blum, 1995; Blands and Rolls,1998; Sun et al., 2010). Temperature and precipitation conditions of aregion largely control the chemical weathering processes (Lasagaet al., 1994; White and Blum, 1995; Sharma and Rajamani, 2000a,b).In a lake setup, materials derived from various sources in the watershedas the products of chemical weathering are delivered to the lake. Thus,the chemical weathering history of a lake catchment can be understoodby the characteristics of the chemical elements present in the lakesediments. Geochemistry tells us about weathering/erosion intensity(low or high), provenance of sediments (felsic or basic) and geomor-phology of the reach and nature of anthropogenic activity in the catch-ment. Based on the geochemical analysis of the samples of Pariyajsediment core plots and A–CN–K triangular diagram (based on Chemi-cal Index of Alteration (CIA))were prepared for detailed interpretations(Fig. 4A, B).

3.3.1. X-ray diffractionClayminerals, being neoformed and thermodynamicallymore stable

under surface geological conditions, are useful palaeoenvironmentalindicators. The assemblage of clay minerals is controlled by the climateaswell as the parentmaterial fromwhich they are derived. Palaeoclimaticinterpretations based on clay mineralogy have been used effectively byvarious workers (Curtis, 1990; Pal et al., 2000, 2003; Prasad et al., 2007;Garzanti et al., 2011). Clays were separated by the Atterberg method(Muller, 1967) and also identified by X-ray diffraction with a SeifertX-ray diffractometer, using Cu/Ni radiation at 40 kV/30 mA, from 5° to40° 2θ value.

3.4. Chronology

The radiocarbon (14C) dating of the organic carbon in the sedimentwas carried out at the radiocarbon laboratory of Birbal Sahni Instituteof Palaeobotany (BSIP), Lucknow. The sediments were manuallycleaned, sieved and subjected to hydrochloric acid to remove carbonatecontent. After repeated rinsing with distilled water for pH stabilisation,the sediment was combusted in the continuous flow of oxygen. Theresulting carbon-dioxide was collected and converted to acetylene andfinally into benzene using standard catalyst and procedures. Thecounting was carried out in a Liquid Scintillation Counter (Quantulus,1220). Of six bulk samples only three sediment samples rich in organiccarbon were radiocarbon dated. Radiocarbon dates were calibratedusing IntCal09 (Stuiver et al., 1998) and are referred to as calibratedyear before present (cal yr BP).

Three radiocarbon dates generated on the sediment core of PariyajLake are 6680 ± 110, 5680 ± 210, and 1560 ± 130 cal yr BC (or 8630,7630, 3510 cal yr BP respectively) at 65, 50 and 15 cm levels respectively(Fig. 3, Table 1). Extrapolation of ages was done for various other hori-zons based on age–depth model (Fig. 5). The graph of age–depthmodel shows the sedimentation rate of 0.009 ± 0.001 cm/year (for the

Fig. 5. Age–depth graph of Pariyaj Lake showing sedimentation rates.

upper part) and 0.015 ± 0.005 cm/year (for the lower part) with theaverage being 0.0118 ± 0.046 cm/yr. Extrapolation to 90 cm (base)gives an age estimate of 10,970+930 cal yr BP, encompassing the entireHolocene time span.

4. Results and interpretations

Based on a combined interpretation of data generated throughvarious proxies, the 90 cm profile of Pariyaj Lake has been divided intofive zones that correspond to five climatic phases (Figs. 6 and 7).

Fig. 6. Plot showing phytolith, pollen, algal and fu

4.1. Zone 1 (PV-17 to PV-16, ~20 cm thick)

The basal 20 cm zone starts with the fine calcrete nodules in a sandyhorizon showing thin clayey partings at the base, which becomes coars-er in the upper part. The maximum density and variety of vegetationwere recorded in this zone. Phytolith recovery was high in this zoneand includes a large proportion of well-preserved rondel, trapezoid,and bambusoid phytolith morphotypes including multi-facetedphytoliths along with burnt phytoliths and micro-charcoal. The maxi-mum dry deciduous (mean 49) and semi-evergreen (mean 4.5) treepollens were found in this zone (Fig. 6). The pollen of tree taxa likeMadhuca, Acacia, Azadirachta, Ailanthus, Symplocos, Syzygium and a fewbelonging to the family Anacardiaceae has been recovered. The terres-trial, marshy and aquatic herb pollens of Solanaceae, Brassicaceae,Asteraceae, Poaceae, Cannabinaceae, Caryophyllaceae, and Cyperaceaefamilies have been dominant. Typha and Potamogeton (freshwaterswamp taxa), trilete and monolete fern spores and algal and fungal re-mains have also been dominant in this zone. Moderate Cheno/AMSand low Artemisia pollen values were recorded. The most characteristicfeature of this zone is the presence of micro-charcoal that occurs in alarge proportion in the lower part of the zone (Fig. 6).

The sample PV-17 to PV-14 shows a dominance of illite oversmectite and lower CIA (Figs. 4 and 7) indicating sediments from acomposite source of both weathered basalt and less weatheredAravalli sediment source (Sharma et al., 2013). The trend showinga contribution from relatively less chemical weathering is supportedby less enrichment of TiO2 (Fig. 4A). The relatively lower CIA valuesindicate a regional provenance for the lake including weatheredcomponents of basalts and less weathered felsic componentsof Aravalli (low TiO2, Fig. 4A). Together these point to a regional

ngal spore distributions along with lithology.

Fig. 7. Comparison between values of clayminerals (chlorite, smectite, illite and kaolinite), winter precipitation, SWprecipitation, dry deciduous and semi-evergreen tree ratios, freshwa-ter algae and related increase and decrease of lake level.

humid condition, although sub-humid conditions prevailed in thenorth-northeast part of the region.

4.2. Zone 2 (PV-15 to PV-13, ~10 cm thick)

This zone is characterised by sand-dominated facies. Phytolithrecovery is reduced compared to Zone 1 and only trapezoid, rondeland bambusoid phytoliths are found. There is also a notable reductionin the pollen yield as arboreals almost swept and non-arboreals weresignificantly reduced. Cheno/Ams prevailed and Poaceae was depleted.The Cyperaceae dried up and aquatic plants were reduced, indicatingarid conditions and shrinkage of the lake (Figs. 6 and 7). The geochem-ical record during the sedimentation between PV-15 to PV-11 indicatesthat the weathering conditions started changing towards a supply frommore weathered components from basaltic region (higher CIA and TiO2

values, Fig. 4A) to more physically weathered sediments from northernprovenances (high silica fromquartz rich sediments of felsic rocks). Thispoint towards an arid–semiarid condition in the north-northeasternpart and sub-humid conditions in the south-southwest part of prove-nance, where weathered material from the previous humid weatheringconditions was available for the supply.

4.3. Zone 3 (PV-12 to PV-8, ~25 cm)

This zone showed a fairly good yield of phytoliths aswell as terrestrial,marshy and aquatic herb pollen. Rondel, trapezoid multifacetedphytoliths appear with another good representation of charcoal(Fig. 6). Dry deciduous tree pollens occurred in moderate numbers(mean 13.4). In contrast, there were very less semi-evergreen treepollens (mean 1). Cheno/Ams and Artemisia developed in this zone,showing the prevalence of aridity along with winter precipitation(Fig. 7).

A sudden decrease in CIA and TiO2 has been noted in the core for thesample PV-10. Here, the majority of sediments are in the silt size range(Fig. 4A). The high silica values (Fig. 4B) and also sediments of maficcharacter as seen in ACNK diagram (Fig. 4B) indicate a mixing ofquartz-rich sediments (e.g., from the felsic rocks of the Aravallis)

with the Deccan basalts. This is most likely an event of drainagereorganisation (tectonic) or high rainfall (flash flood) in the northernpart of the catchment, bringing quartz-rich mineral (SiO2 = 71 wt.%)resulting in a dilution effect of the other parameters. Na and K valuesalso show the lowest values at this point (Fig. 4A). The six trace ele-ments analysed (Ba, Sr, Ni, Cr, Cu and Zn) showed the lowest values atPV-10 (Fig. 4A). An increase in the chlorite content in clay fraction andincreasing trends in kaolinite along with organic content also supportthe inference of humid conditions.

The above data are well corroborated by the prevalence of a varietyof tree taxa pollen grains observed in these sediments. It is interesting tonote here that the sediment chemistry is different from that of samplePV-10. The high TiO2 values in these samples reflect increasinglyfavourable conditions for weathering of Ti-rich basalts. The anomaloushigh silica values may be related to an increased clastic supply fromthe Aravallis as discussed above. The almost similar trend of silicawith CIA and TiO2 is a bit unexpected because in general, with increas-ing weathering, silica typically leaves the system. However, this couldbe explained as the result of the high precipitation event (may becyclonic storm/flash flood or something similar to it) in the Aravalliranges, bringing more silica from the upland regions as discussedearlier.

4.4. Zone 4 (PV-7 to PV-5, ~15 cm)

This is a very well-marked zone showing complete absence of anytaxa of pollen and phytolith. Sandy facies is dominant with silt andclay percentages being almost equal (Fig. 4A). Values of carbonatecarbon decrease with increase in organic carbon values upward in theprofile. Smectite still remains the dominant clay mineral (Fig. 7). Highvalues of CIA, FM (Fe2O3, MnO, Mg2O3), and K and low values of CaOare also observed in this zone. A remarkable feature of this time zone(~5864 to 4680 cal yr BP) is the near complete absence of any phytolithor pollen with only few traces of fungal and algal spores (Fig. 6). Anoverall declining/fluctuating but inverse trend in CIA and SiO2 in samplePV-7 to PV-5 with increase in smectite and illite clay minerals suggestschange in climate from humid to drier conditions (Fig. 7).

4.5. Zone 5 (PV-4 to PV-1, ~25 cm)

The good density and diversity of flora have been exhibited inthis zone. Herb pollen yield shows a very good population of mem-bers of Solanaceae, Brassicaceae, Asteraceae, Cheno/AMS, Poaceae,Cannabinaceae, Caryophyllaceae, and Cyperaceae families. Moder-ate semi-evergreen tree pollen and dry deciduous tree pollen haveshown a mean of 4.6 and 26 respectively. Cheno/Ams and Artemisiaincreased showing persistence of aridity with winter precipitation(Fig. 6). Cyperaceae and other aquatics increased depicting lenticcondition of lake. The higher values of silica and increased grainsize in two uppermost samples could be an effect of eluviations,where the relatively fine material may have trickled down in theprofile or in some cases if the area gets exposed, finer material isblown away by wind leaving behind coarser material.

The increasingly antipathetic trend of silica with TiO2 and CIA fromsample number PV-4 (Fig. 4A) again points to an expanded catchmentand contribution of more quartz-rich sediments from the Aravallirocks. The relatively higher contribution from the Aravallis is supportedby decrease in CIA and increase in illite contribution in the clay fractionof the sediments and sand domination (Figs. 4A and 7). The antipatheticrelationship, mentioned above, could be explained in two ways. If thehumid conditions became more intense covering much larger catch-ment, then it would have brought more sediment from the Aravalliacidic rocks in the uplands, thereby increasing the silica content. How-ever, this could not be the case because both CIA and TiO2 values shouldhave increased with increased weathering in catchment. Moreover, thehumid conditions favour better vegetation in uplands limiting thecoarse grain fluvial supply, which is not the case here. Alternately, it islikely that the conditions might have become drier and along with thisdue to some tectonic activity (eastward tilting of the Vatrak and its trib-utaries, Raj, 2012) the lake got cut off for receiving the sediments fromthe Deccanmafic sources. As a result, though the sediment supply is re-duced it is restricted to northern upland regions of the Aravalli only andtherefore bringingmore siliceous unweathered sediments justifying therelatively low CIA and TiO2 values. The increase in illite contributionover the smectite in the clay fraction of the sediments and dominationof sand in bulk samples (Figs. 4A and 7) also support change in thecatchment and relatively drier conditions somewhat similar to presentday conditions. The weathering being a relatively slow process, thereis always a time lag in supply of the geochemically mature sedimentsto the depositional site and hence the variation is commonly observedbetween the geochemical data and the biological proxy parameters.

5. Discussion

Studies on Holocene records of lakes in the alluvial plains are impor-tant in understanding environment as well as the evolutionary historyof humans. The ongoing discussion on climate change, which alsoaffects water budgets, shows that lakes may also be altered by thesechanges. But to understand the changes in these lakes during the past,particularly their water levels and to know if all these changes wereclimate-controlled and if the changes in the water-table affect humanhistory of a region, a detailed multiproxy study of a lake is an effectivetool in finding all these answers. Previous studies have shown that innorth-western India the lake levels were fluctuating during the earlyHolocene. The onset of aridity in NW India could have begun as earlyas ~5.3 cal kyr BP, after which thereweremultiplewet events of shorterduration and smaller magnitude than during the mid-Holocene asshown in various proxy records (Prasad et al., 1997, 2014a). The land-scape evolution and climatic fluctuation estimation have been donebased onmultiproxy data generated on Pariyaj Lake and the data reflectthe rise and fall of the water table and vegetation changes in thesurrounding region indicating temporal fluctuations in the climate.The regional significance of the data is discussed by comparing it withthe regional marine, lacustrine and dune records.

5.1. Holocene landscape evolution

The Pariyaj Lake falls in the lower reaches of the Vatrak River basinwhich is a major tributary of the Sabarmati River. Neotectonic activityalong the various pre-Quaternary tectonic structures has been envis-aged in Gujarat Alluvial Plains by various workers during the last twodecades (Pant and Chamyal, 1990; Maurya et al., 1998, 2000; Raj et al.,1999a,b, 2003, 2004; Srivastava et al., 2001; Chamyal et al., 2002,2003; Raj, 2004, 2007, 2012; Raj and Yadav, 2009). The landform ofthe mainland Gujarat as it appears today has been attributed to theHolocene tectonism (Maurya et al., 2000). The entire area experiencedtectonic uplift during early Holocene which was also a period of warmand humid climate (Maurya et al., 1998, 2000; Singh, 1998; Raj andYadav, 2009). Tectono-geomorphic studies of the lower Narmadabasin by Raj (2007) indicated active deformation driven by NarmadaSon Fault system and a very recent phase of tectonic uplift (after1200 yr BP) in the area (Raj and Yadav, 2009). The change in the courseof Orsang River (a tributary of Narmada River), which earlier flowedthrough the present day Dhadhar River has been attributed to earlyHolocene uplift along the major faults in the area (Raj, 2004) andwhich also resulted in the formation of several ponds and lakes inthe area. Srivastava et al. (2001) have placed the adjustment of theSabarmati River around 12 ka BP.

The geomorphology of the area around the Pariyaj Lake is carved bythe active tectonics. Early Holocene uplift in the Vatrak River basin ledto the formation of present day drainage (Raj, 2012) in the area. It isenvisaged that the various blocks in the NW–SE corridor bounded byCambay basin margin fault and various other sympathetic and crossfaults through which the Vatrak River and some of its tributaries usedto flow, underwent differential uplift during early Holocene leavingabandoned/defunct channels which turned into isolated closed bodiesof water and which were fed during monsoon. Tectonics and climaticfluctuations all through the Holocene have resulted in the constantchange in the course of the Vatrak and its tributaries and as a result wedo not get any well-developed Holocene terrace surface in this riverbasin as compared to the neighbouring river basins. Several defunctpalaeocourses mostly in the western part of the present day channelcan be seen on the topographic sheets as well as the Google/satelliteimages in the lower reaches (Raj, 2012). The presence of various pondsand lakes all along this NE–SW corridor as shown in Fig. 2, many ofwhich are also trending NE–SW is noted in this study.

5.2. Regional climatic fluctuations

The data has provided evidence in support of a humid phase~11,000 cal yr BP during phase 1, indicating high run off and pondingcondition due to high precipitation. It shows high chlorite, high semi-evergreen and dry deciduous tree ratio and high percentage of freshwa-ter algae. A dry spell is indicated by the decrease in yield of pollen alongwith the decrease in freshwater algae due to low SW precipitation~8000 cal yr BP during phase 2. It indicates the N-NE part of the prove-nance area being under arid–semiarid conditions and S-SW part undersub-humid condition. At ~7630 cal yr BP during phase 3, the recordpoints towards high rainfall seasonality due to decreasing SW mon-soonal activity with active winter precipitation and a sudden and briefperiod within this phase (~ PV-10) represents flash flood/tectonicevent in the area which might have led to drainage reorganisation.The period also shows high freshwater algae and low arboreal ratios.Phase 4 between ~5860 and 4680 cal yr BP is again a severe dry phasein the area with absolutely no biotic record for the entire phase, follow-ed by a phase between ~4680 and 3510 cal yr BP showing good densityand diversity of flora indicating warm and humid climate due to SWmonsoonal activity as well as persistence of winter precipitation activi-ty. A correspondence analysis (CA) (Fig. 8)was carried out for the pollenand phytolith values of the lake samples to see the temporal relationbetween the samples as well as to distinguish different environmental

Fig. 8. Correspondence analysis of pollen and phytolith data from Pariyaj Lake sediments showing temporal relationship between samples and different depositional regimes.

settings based on the pollen and phytolith data. The CA analysis is amultivariate method to distinguish correlations between constraintsand variables. Results reveal that, samples 17–13 are clustered in apositive field of factor axes F1 and F2. However sample 12-1 nested inthe negative field of factor axes F1 and F2. CA analysis of the pollenand phytolith frequency data indicates four groups of depositionalsetting. Group I is indicative of deposition in a cool and extremely wetclimatic condition with low rainfall seasonality since both winter pre-cipitation and summer precipitation were active, Group II also indicateswetter climate but with increased rainfall seasonality due to decline inthe summer precipitation. Group III suggests warm and humid mon-soonal climate with high rainfall seasonality due to increased SWmon-soonal activity. Group IV is barren for biotic proxies and is indicative ofwarm and dry climate, probably drought condition as a result of declineof both winter as well as summer rainfall. The climatic phases werecompared with the published regional palaeoclimatic data generatedon marine, lacustrine, aeolian and cultural records of this time.

5.2.1. Comparison with marine recordPreviousworks (Hong et al., 2003; Gupta et al., 2005 andWang et al.,

2005) have emphasised on a link between the weak Indian/Asian sum-mer monsoon and the cool north Atlantic climate, which was possiblytriggered by solar influence. Continuous records from the NorthernArabian Sea (Staubwasser and Weiss, 2006) show a complex Holoceneclimate evolution, which is attributed to the combined influence ofwinter and spring rain as well as summer monsoon rain in the region.Some of the records from the Arabian Sea core were broadly comparedwith terrestrial records (Fig. 9). Palaeoclimatic records (Fig. 9A) fromthe Arabian Sea (Sirocko et al., 1993; Overpeck et al., 1996; Von Radet al., 1999) indicate a step wise increase in the southwestern monsoonactivity ~12,000 cal kyr BP, weakening of summer monsoon winds/aridification ~5000 cal yr BP (Overpeck et al., 1996; Staubwasser et al.,2003). Monsoon proxy records of Gupta et al. (2003) revealed severalintervals of weak summermonsoon duringHolocene and lows between5000 and 6000 cal yr BP and 8200 cal yr BP coincidewith lows indicatedin Pariyaj records (Fig. 9B). A study by Gupta et al. (2005) reported thatthe summer monsoon was stronger with more abrupt changes in theearly Holocene (10–8 kyr). Thamban et al. (2007) from their studiesin the eastern Arabian Sea sediments suggested several abrupt eventsin monsoon precipitation throughout the Holocene. They reportedthat the early Holocenemonsoon intensification occurred in two abruptsteps at 9500 and 9100 years BP and weakened gradually thereafter,

starting at 8500 years BP. Staubwasser and Weiss (2006) indicateabrupt climate change events, such as widespread droughts around8200, 5200 and 4200 cal yr BP. Rohling and Palike (2005) have showna collection of proxy records which are well dated and it identifiesanomalies around 8.2 kyr BP (Fig. 9C). The anomaly in palaeoclimatearchive ~8.2 kyr is on a near global scale (Rohling and Palike, 2005)and the correlations with well dated palaeoclimate proxy records ofDongge cave in east China, Tibetan Plateau, sediment core fromPakistan Margin, Hoti Cave in north Oman, Qunf Cave in south Oman,North Africa and Pariyaj Lake (Fig. 9C).

Sharma et al. (2004) also reported a gradual weakening of summermonsoon over the past 8 kyr with amore or less stable dry phase begin-ning ~5 kyr BP, that coincideswith the onset of an arid phase in India andtermination of the Indus Valley civilisation (Staubwasser et al., 2003;Gupta, 2004). The Pariyaj Lake records of early Holocene show a wetphase at ~11,000 cal yr BP followed by a period of dry phase ~9000 yrBP which continues until ~8000 yr BP showing the correlativity withthe Holocene marine records of the Arabian Sea (Fig. 9A, B and C).A dry phase in Pariyaj record, which peaked ~8500 yr BP and which isshort-lived can be compared to palaeoclimatic archive which occurredon a near global scale (Alley and Agustsdottir, 2005; Rohling andPalike, 2005; Wanner and Bronnimann, 2012). Rohling and Palike(2005) found a broad Holocene monsoon minimum in the Indian andAsian domains from around the Arabian Sea records. Together, theserecords portray a broad reduction of Indian summer–monsoon activitybetween roughly 8.5 and 8.0 kyr BP, which both started and endedwitha century-scale peak minimum. Another drying event of Pariyaj Lakereflected ~5864 to 4680 cal yr BP can be related to a bracket of theclimate change event of ~4200 yr BP that is observed on a globalscale, includingmany places in Asia and Africa, where a severe and last-ing drought is indicated (Gasse, 2000; Weiss and Bradley, 2001; Boothet al., 2005; Staubwasser and Weiss, 2006; Berkelhammer et al.,2012). Thamban et al. (2007) recorded one of the most significantlyweak monsoon periods between 6000 and 5000 yr BP in their studies.Gupta et al. (2003) indicate the beginning of aridity around 4800 and4200 cal yr BP in theNWArabian Sea records (Fig. 9B). The 5.2 ka dryingevent is well known in the palaeoclimatic data from the Arabian Sea(Fig. 9A) (Sirocko et al., 1993; Overpeck et al., 1996) and according toBerkelhammer et al. (2012) an abrupt shift in Indian monsoon aroundthis period is documented in number of different proxy records acrossNorth Africa, the Middle East, the Tibetan Plateau, southern Europeand North America.

Fig. 9. A. Figure showing palaeoclimatic changes from the three cores raised from theArabian Sea, based on lithofacies, biofacies, inorganic geochemistry, sedimentology, δ13Cproxies and G. bulloides abundances by Von Rad et al. (1999), pollen and G. bulloidesabundances by Overpeck et al. (1996), and δ13C and dust proxies by Sirocko et al., 1993(figure redrawn from Prasad and Enzel, 2006). B. G. bulloides percentage (normalised byremoving the trend related to insolation by Gupta et al., 2003) from Arabian Sea, used assouthwest monsoon proxy record. Yellow lines indicate drying at 4.2, ~5–6 and ~8.2 calkyr BP. C. Palaeoclimate proxy records of a. Dongge cave in east China, b. Tibetan Plateau,c. sediment core from Pakistan Margin, d. Hoti Cave in north Oman, e. Qunf Cave in southOman, f. North Africa and g. Pariyaj Lake showing anomaly at ~8.2 kyr BP (figure redrawnfrom Rohling and Palike, 2005).

Fig. 10. Comparison of Pariyaj Lake record with Lunkaransar Lake (Enzel et al., 1999),Didwana Lake (Wasson et al., 1984), Nal Lake (Prasad et al., 1997), and Wadhwana Lake(Prasad et al., 2014a) andwith the cultural records given by Giosan et al. (2012). The tem-poral extent of eachHarappan phase is indicated by green vertical dashed lines (E=early;M=mature; L= late). Yellow lines are indicative of drying events. Inset figure shows thelocations for these lakes.Figures for Rajasthan Lake and Nal Lake redrawn from Prasad and Enzel (2006).

5.2.2. Comparison with lacustrine recordAt 11 ka cal BP a rise in temperature and precipitation could be re-

constructed, marking the onset of the Holocene (Felauer et al., 2012).In their study on lake archives of central Asia, Felauer et al. (2012)reported that the humid period of the Holocene lasted until about4 ka cal BP, interrupted by shorter dry/cold reversals at 8.5–7.5 ka calBP and 5–4.5 ka cal BP. Pariyaj records when compared to lacustrinerecords of the NW India revealed interesting correlations. The dataindicate a wet phase at ~11,000 yr BP (Fig. 9) and are correlatable tothe lacustrine conditions in Sāmbhar, Lunkaransar and Didwana lakes(Singh et al., 1974). A study by Singh et al. (1990) showed that~12,800–9300 yr BP there was saline to deep freshwater conditions inDidwana Lake (Fig. 10). In another work on Didwana Lake by Wassonet al. (1983),fluctuations between hypersaline and freshwater conditionsbetween 12,500 and 6000 yr BP have been reported. The Pariyaj records

indicate drying event between 8000 and 9000 cal yr BP and find its corre-lation in a very recent study on Riwasa palaeolake of NW India, whereDixit et al. (2014) have provided the first terrestrial evidence of the8.2 kyr drying from Indian subcontinent which coincided with the

‘8.2 kyr BP’ cold event in the North Atlantic. The third phase in PariyajLake of ~7630 yr BP, which is again a wet phase, finds similarity inLunkaransar, Didwana and Wadhwana records in western India(Fig. 10). Singh et al. (1990) infer high precipitation and freshwaterinflux followed by high mean precipitation between ~7500 and6200 yr BP resulting in the Didwana Lake acquiring the deepestlevel during this period. Lunkaransar experienced the wettestphase ~7200–6000 yr BP (Enzel et al., 1999).

The Pariyaj records between ~5864 and 4680 cal yr BP indicate thatthemonsoonweakened. This correlates well (Fig. 10)with drying out ofLunkaransar and Didwana lakes at ~5000 and ~4700 yr BP respectively(Prasad and Enzel, 2006). Similar drying trend was reported fromSambhar Lake at ~4700 yr BP (Prasad and Enzel, 2006). Prasad et al.(2014b) in their studies on palaeoclimatic records based on multiproxyreconstruction from the Lonar Lake, falling within the central Indiancore monsoon zone, show prolonged droughts between 4.6 and3.9 cal ka. They exclude any contribution from the winter westerliesas the region is under the influence of the Indian SummerMonsoon dur-ing the Holocene (Prasad and Negendank, 2004). A study inWadhwanaLake (Prasad et al., 2014a) which is about 85 km SE of Pariyaj Lake hasalso shown a wet phase between ~6800 and 5628 yr BP. Nal Sarovarshows a short lived wet phase ~7200 to 6100 yr BP (Prasad et al.,1997). Nal Sarovar is about 50 kmNW of Pariyaj and is adjoining Rajas-than. In Pariyaj Lake which is located in between Nal Sarovar andWadhwana Lakes (Fig. 10 inset) the cessation of winter rainfall activityaround ~5864 cal yr BP matches well when compared to cessation ofwinter rain activity at ~6100 yr BP for Nal and ~5628 yr BP forWadhwana Lakes. The period after ~4680 cal yr BP is a general wetphase in Pariyaj and the fluctuations of SW monsoon are balanced bywinter rains. It has been noticed that there is an inverse relationship be-tween winter rains and SW monsoons except for the period between~5864 and 4680 cal yr BP.

5.2.3. Comparisons with aeolian recordsLarge amplitude changes in the Holocene monsoon intensity have

been reported by the studies based on environmental changes in theThar Desert (Singhvi and Kar, 1992). Singhvi et al. (2001) in theirpalaeoclimatic studies in dune activity of Thar Desert indicated that~13,000–9000 yr BP was the time when the southwest monsoon wasbecoming re-established in the region, and around this period theYounger Dryas cooling episode resulted in an enhanced wintermonsoon (Sirocko, 1996). Gupta et al. (2003) indicate an absence ofdune formation in NW India during the earliest Holocene. The EarlyHolocenewet phase of ~11,000 cal yr BP seen in the Pariyaj Lake recordsis consistent with the dune records of NW India and also with theHolocene Thermal Maximum. The second episode of drying eventstrongly reflected in Pariyaj record between ~5864 and 4680 cal yr BPis consistent with the 5.2 ka drying event and is also reflected in the re-cords of the Gulf of Oman (Cullen et al., 2000). Singhvi and Kar (1992)indicated a northward shift in dune forming climate during theHolocene and they reported that the southern margin of the Mega-Thar in Gujarat did not experience any dune building activity after10 ka whereas the north Gujarat plain experienced dune aggradationactivity up to 5 ka. According to them parts of west Rajasthan, contain-ing the core of the Thar experienced dune activity even after 2 ka and upto the present in some parts. When we compare the lake records ofGujarat from NW to SE it shows that the dune forming activity tookplace in Nal Sarovar until ~3500 yr BP whereas in Pariyaj last dryphase lasted until ~4680 cal yr BP, thus providing important clues to-wards the spatial shifts in the monsoon through time.

5.2.4. Comparison with cultural recordsHolocene witnessed co-occurrence of rise and collapse of various

agricultural based societies due to abrupt climate change. Sedimentsunearthed and dated by Giosan et al. (2012) showed a remodelling ofthe landscape over time with the changing climate. About 10,000 years

ago, flooding rivers in parts of India, Pakistan and Afghanistan changedbehaviour as monsoon rains weakened. Gangal et al. (2010) in theirstudies on growth and decline of Indus Valley civilisation reportedthat there was a delayed decline of culture in Gujarat. According toStaubwasser andWeiss (2006) around 8.2 ka dry event, farming socie-ties ofWest Asiawere reducedwith somehabitat-tracking to sustainableenvironments (Weninger et al., 2006). Climate and societal change alsoco-occurred prominently during the late mid-Holocene and early lateHolocene, roughly 5500 to 3500 yr BP. Clift et al. (2012) in their studiesestablished that the Harappan Culture, thrived on the northwest edge ofthe Thar Desert (India and Pakistan) between 3200 and 1900 BCE andlinked its demise to rapid weakening of the summer monsoon at thattime. Such co-occurrences have led to the discussion of the link betweenclimate events and cultural change in both palaeoclimatic and archaeo-logical communities, where the causal links have been criticised orrejected by some (e.g., Possehl, 1997a,b; Coombes and Barber, 2005;Madella and Fuller, 2006; Staubwasser andWeiss, 2006). The social im-pact of precipitation change is discussed, particularly for the eventsaround 8500 cal yr BP (8.2 ka event) and ~6000–4000 yr BP (5.2 kaevent and 4.2 ka event). At around 3900 cal yr BP Possehl (1997a,b,2000) reported transition from urbanised to a rural (post urban) society.By the end of the third millennium, the Great Bath and Granary atMohenjo–Daro were abandoned, settlements in Sindh, the Indus–Sarasvati valley and the Baluchi highlands collapsed and shifted towardsthe east, the headwaters of the Sarasvati and south to the SaurashtraPeninsula (Possehl, 1997b, 2000). Earlier the climate factor in this reloca-tion was disputed for the lack of clear records. However, such climaterecords and comparisons are now available (Staubwasser et al., 2003;Prasad and Enzel, 2006; Prasad et al., 2014a) and the transition fromurban to post-urban, as recorded inMohenjo Daro, beganwith the aban-donment of the Great Bath, which preceded the abandonment of thewhole city (Possehl, 1997a), apparently just after 4200 cal yr BP. TheHarappan and pre-Harappan civilisations in the northern part of the de-sert flourished during awaning phase of the SWmonsoon,when rainfallevents weremore aberrant, and high aeolian activities (Singhvi and Kar,1992). Giosan et al. (2012) also showed that precipitation from bothmonsoon and westerly sources that fed rivers of the western Indo-Gangetic Plains decreased since approximately 5000 yrs ago (Fig. 10).This supports the hypothesis that adaptations to arid climate contributedtowards urbanisation and social complexity (Giosan et al., 2012; Prasadet al., 2014a). An intense drought period around 4.2 ka is also linked tomajor disruptions in Egypt and Mesopotamia (Weiss et al., 1993)which coincides instead with the flourishing of Harappan urbanism. Acomparison with the drought periods reported in the culture of NWIndia, the Indianmonsoon precipitation reconstructedwith temporal ex-tent of eachHarappan phasewith the synthetic reconstruction for Indianmonsoon and westerly precipitation records given by Giosan et al.(2012) with that of Pariyaj record (Fig. 10) shows a good correlation.The records of winter rains from the Pariyaj Lake are in conformitywith the delayed decline of civilisation from the area during the periodssuggested by Gangal et al. (2010).

6. Conclusions

1. A multi-proxy study from Pariyaj Lake of the Vatrak River basin,which is situated in the northern part of Gujarat Alluvial Plains ofWestern India, has provided evidence of Holocene climate fluctua-tions from the semi-arid to arid transitional climatic zones.

2. The study indicated wet climate and high lake stand during~11,000, 7630 and between 4680 and 3500 cal yr BP in PariyajLake. Records have indicated possible contribution by winter pre-cipitation at 7630 cal yr BP and between 4680 and 3500 cal yr BPin the Pariyaj Lake, which is a regional phenomena as winterprecipitation activity of 7500–6795 cal yr BP is a synchronousphenomenon and can be seen in various lake records of Gujaratand Rajasthan.

3. A decrease in the precipitation activity, low lake stand and onset ofdry climatic condition between 5864 and 4680 cal yr BP andbetween 8000 and 9000 cal yr BP is envisaged in Pariyaj Lake.

4. Drying between 5864 and 4680 cal yr BP is a globally spreadphenomenon and can be correlated with the drying out trend ofLunkaransar (5700 cal yr BP), Didwana (~5900 cal yr BP), andSambhar (~5590–5290 cal yr BP) lakes of Rajasthan, Nal Lake(~6100–5400 cal yr BP) and Wadhwana Lake (~5565 cal yr BP) ofcentral Gujarat Alluvial Plains regionally and can also be correlatedglobally to an abrupt shift in Indianmonsoon ~4000 yrs ago with cli-mate change documents in the records of North Africa, the MiddleEast, the Tibetan Plateau, southern Europe and North America. Thedrying event reflected between 8000 and 9000 cal yr BP finds its cor-relation in the 8.2 ka dry event of farming societies of West Asia asreported from lake archives of central Asia.

5. The broader significance of the study is the correlatability of thePariyaj record to the near global drying events of ~5.2 and 8.2 kyrBP, to the Harappan cultural records and to the winter precipitationrecord of the various lakes of western India.

Acknowledgements

This study was supported by the Department of Science andTechnology, New Delhi, project nos. SR/WOS-A/ES-13/2008 andSR/WOS-A/ES-07/2012 granted to Dr. Rachna Raj. We are thankfulto the Director, BSIP for his support and Dr. Siddharth Prizomwalaand Sri Vishal Ukey for help in raising the core during the fieldwork. Manoj MC is thanked for help in the statistical analysis.

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Holocene climatic ﬂuctuations in the Gujarat Alluvial Plains based on a multiproxy study of the...

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