Palaeogeography, Palaeoclimatology, Palaeoecologyecfont/publications/Fantasia et al., 2015.pdfprobably underwent excessive desiccation/oxidation processes under semi-arid conditions.

Palaeogeography, Palaeoclimatology, Palaeoecology xxx (2015) xxx–xxx

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Palaeogeography, Palaeoclimatology, Palaeoecology

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

Palaeoenvironmental changes associated with Deccan volcanism,examples from terrestrial deposits from Central India

Alicia Fantasia a,⁎, Thierry Adatte a, Jorge E. Spangenberg b, Eric Font c

a Institute of Earth Sciences (ISTE), University of Lausanne, Building Géopolis, 1015 Lausanne, Switzerlandb Institute of Earth Surface Dynamics (IDYST), University of Lausanne, Building Géopolis, 1015 Lausanne, Switzerlandc Instituto Dom Luís, Faculdade de Ciências (IDL-FCUL), Universidade de Lisboa, Portugal

⁎ Corresponding author.E-mail address: [email protected] (A. Fantasia).

http://dx.doi.org/10.1016/j.palaeo.2015.06.0320031-0182/© 2015 Elsevier B.V. All rights reserved.

Please cite this article as: Fantasia, A., et al., Pfrom Central India, Palaeogeogr. Palaeoclima

a b s t r a c t
a r t i c l e i n f o
Article history:Received 2 March 2015Received in revised form 17 May 2015Accepted 24 June 2015Available online xxxx

Keywords:Deccan volcanismIntertrappean sedimentsMulti-proxy approachWeatheringAcid rain

We analysed the geochemical and mineralogical aspects of sedimentary beds associated with Deccan volcanismexposed in the eastern part of the volcanic sequence in the Jabalpur–Mandla–Chhindwara (JMC) sector (MadyhaPradesh) and in theNand–Dongargaon (ND) basin in Central India. These sedimentswere deposited in terrestrialenvironments before the onset of the volcanic activity or during periods of quiescence inmainly alluvial-limnic tolacustrine facies. Deposited at different stratigraphic levels within the Deccan lava pile, they provide crucialevidence to evaluate environmental changes on land induced by the onset of the volcanism in the central partof India. Our results indicate that sediments (intertrappeans) deposited during Deccan volcanism do not reflectthe same depositional characteristics as sediments (Lameta Formation) preceding volcanic eruptions. Thesedimentological and mineralogical observations indicate alluvial-limnic environments under semi-arid climateduring deposition of the Lameta sediments. This could explain the low concentration of organic matter, whichprobably underwent excessive desiccation/oxidation processes under semi-arid conditions. The eruption ofDeccan volcanic flows severely affected environmental conditions. Intertrappean sediments associated withDeccan phase-1 and phase-2 were deposited in terrestrial to lacustrine environments under semi-arid climateswith dry and humid seasons, which are highlighted by the predominance of smectites resulting frombasalt alter-ation. Organic matter is well preserved in the sediments deposited in phase-1 and indicates a mixed source withwell-preserved lacustrine organic matter and terrestrial inputs. The subsequent intertrappean sediments withinphase-2 are strongly influenced byDeccan volcanism characterized by high volcanic content associated elements(Ti and Fe) and high chemical alteration (CIA-K) that likely reflects increasing acid rains rather than climaticchange. In addition, a sharp decrease in pollen and spores coupled with the appearance of fungi mark increasingstress conditions, which is likely a direct result of volcanic activity. Bulk organic geochemistry points to a strongdegradation of the autochthonous organic matter, suggesting that the biomass was oxidized in acidic conditionstriggered by intense volcanic activity.

© 2015 Elsevier B.V. All rights reserved.

1. Introduction

The Phanerozoic time was punctuated by several mass extinctions(Sepkoski, 1996). Amongst them, the Cretaceous–Tertiary boundary(KTB) event, 65 Ma ago, is characterized bymassive species extinctions(about 75%). Some studies show a link between an extraterrestrial im-pact and the KT boundary event, but since the 1980s numerous authorshave established the connection between Deccan Traps and KT events(e.g., Mclean, 1985; Courtillot et al., 1986, 1988; Duncan and Pyle,1988). TheDeccan volcanic province (DVP) is oneof themost importantLarge Igneous Provinces (LIPs) in the world and covers an area of about512,000 km2 in the Western Ghats and central Deccan Plateau ofIndia. The sediments associated with the DVP are represented by

alaeoenvironmental changestol. Palaeoecol. (2015), http:/

infratrappean (Lameta Formation) and intertrappean beds. The dura-tion of intermittent volcanic activity spanned about 4 Ma across theCretaceous–Tertiary boundary (Jerram and Widdowson, 2005).

In the Western Ghats, the Deccan Traps erupted in three mainphases with 6% of the total Deccan volume in phase-1 (base C30n),80% in phase-2 (C29r), which included N1.1 million cubic km of basalt,and 14% in phase-3 (C29n). Recent studies indicate that the bulk(80%) of Deccan trap eruptions (phase-2) occurred over a relativelyshort time interval in magnetic polarity C29r (Chenet et al., 2008).Moreover, U–Pb zircon geochronology shows that the main phase-2began 250 ka before the Cretaceous–Tertiary (KT) mass extinction,suggesting a cause-and-effect relationship (Schoene et al., 2015).

Deccan volcanic activity released huge amounts of acid volcanicaerosols in the atmosphere and stratosphere, including SO2 and HCl(Self et al., 2006, 2008) leading to global environmental perturba-tions by increasing acid conditions (Ward, 2009; Gertsch et al.,

associated with Deccan volcanism, examples from terrestrial deposits/dx.doi.org/10.1016/j.palaeo.2015.06.032

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2 A. Fantasia et al. / Palaeogeography, Palaeoclimatology, Palaeoecology xxx (2015) xxx–xxx

2011; Font and Abrajevitch, 2014; Font et al., 2014; Keller, 2014). InIndia, palynological and palaeontological studies advanced ourunderstanding of Deccan-induced activity in terrestrial environ-ments (Samant and Mohabey, 2005, 2009, 2014), and a strongfloral response is observed as a direct response to Deccan volcanicphase-2. In Lameta (infratrappean) sediments preceding phase-2volcanic eruptions, palynoflora are dominated by gymnospermsand angiosperms with a rich canopy of gymnosperms (Conifers andPodocarpaceae) and an understory of palms and herbs. Immediatelyafter the onset of Deccan phase-2, this floral association was deci-mated leading to dominance by angiosperms and pteridophytes atthe expense of gymnosperms. In subsequent intertrappean sedi-ments a sharp decrease in pollen and spores coupled with theappearance of fungi mark increasing stress conditions apparentlyas a direct result of volcanic activity (Samant and Mohabey, 2014).The aim of this study is to compare continental (terrestrial to lacus-trine) sedimentary successions located below the basalt pile (LametaFormation) and at different stratigraphic levels (intertrappean sedi-ments) within the DVP, in order to determine the environmentalconsequences induced by the Deccan volcanic activity. For this pur-pose, we focus on five sections: the Dongargaon section locatedbelow the volcanic sequence, and the Government Well, Daiwal,Podgawan and Umaria–Isra sections deposited during periods ofvolcanic quiescence. The stratigraphic positions of the Lameta andintertrappean sediments within the three Deccan phases are based onpalynologic, biostratigraphic and palaeomagnetic data (Mohabeyet al., 1993; Hansen et al., 2005; Samant and Mohabey, 2014).

Our investigations are based on a multi-proxy approach, includ-ing (1) sedimentology, whole-rock mineralogy, microfacies andmicrofaunas (e.g., ostracods) in order to evaluate the depositionalenvironment; (2) clay mineralogy, bulk organic matter and stable iso-topes analyses to determine palaeoclimatic and palaeoenvironmentalconditions; and (3) major and trace element distributions to evaluatethe causal-relationship between the onset of the Deccan volcanic activ-ity and basalt weathering.

2. Geological settings

During our investigation in Central India, infratrappean andintertrappean sediments in different stratigraphic levels at fivelocalities on the eastern side of the DVP were studied, including theNand–Dongargaon basin and adjoining area of Yeotmal–Nanded(Maharashtra) and in the Chhindwara–Mandla–Jabalpur sector(Madhya Pradesh) (Fig. 1A–B).

In the Nand–Dongargaon basin (ND basin) (Fig. 1B–C), theinfratrappean sediments of Dongargaon were deposited during thelate Maastrichtian C30n (Hansen et al., 2005). This succession is un-conformably underlain by Precambrian and Gondwana sediments(Carboniferous to Jurassic) and overlain by the Deccan volcanic se-quence of the Sahyadri Group comprising a 500 m thick sequenceof a total of 29 basaltic flows grouped in four Formations (GSI map,2000). Amongst these, the Ajanta Formation includes intertrappeansediments of Daiwal (DA) between flow F1 and F2. Palaeomagneticdata indicate that the DA intertrappean was deposited during theupper Maastrichtian in the geomagnetic polarity chron 29r and there-fore corresponds to the onset of the main phase-2 (Mohabey et al.,1993; GSI map, 2000; Hansen et al., 2005; Samant and Mohabey,2014) (Fig. 2). Moreover, the accumulation time for this sequence isaround 100 ka (Hansen et al., 1996). The intertrappean sediments ofPodgawan (PO) are intercalated between flow F8 of the Ajanta Forma-tion and flow F2 of the Karnja Formation (GSImap, 2000). Palynologicaldata (Samant and Mohabey, 2014) indicate an early Palaeocene ageequivalent or slightly younger than the Jhilmili intertrappean (Fig. 2)(Keller et al., 2009) and therefore corresponds to the upper part ofphase-2 (C29r).

Please cite this article as: Fantasia, A., et al., Palaeoenvironmental changesfrom Central India, Palaeogeogr. Palaeoclimatol. Palaeoecol. (2015), http:/

In the Jabalpur–Mandla–Chhindwara sector (JMC sector) (Fig. 1B–C), the Deccan volcanic sequence of the Amarkantak Group comprisesthe Mandla, Dhuma, Pipardhi and Linga Formations in ascending order(GSI, 2000). The Governmental Well sediments are equivalent to theMohgaon Kalan Well sediments described by Samant and Mohabey(2009, 2014). Therefore, these sediments were deposited during aperiod of quiescence between phase-1 (C30n) and phase-2 (C29r).The Umaria Isra section is stratigraphically located above the Jhilmilisection (upper basalt is in C29n; Keller et al., 2009;Widdowson, Khadri,personal communications) and is therefore deposited during phase-3(C29n) (Fig. 2).

3. Location and methods

The Dongargaon (20°12′39.8″ N, 79°05′40.6″ E) and Daiwal (20°16′45.8″N, 78°55′00.8″ E) sections are located in the ChandrapurDistrict ofMaharashtra where the Daiwal section is exposed in a tributary of theDaiwal River near the village of Panjurni. The Podgawan section(20°22′17.1″ N, 78°26′20.7″ E) is located in the Yavatmal District ofMaharashtra near the town of Yeotmal. The Umaria Isra section(22°02′03.1″ N, 79°04′50.8″ E) is located in Chhindwara District inMadhya Pradesh near the road that links Chhindwara to Chaurai (Fig. 1).

Infratrappean and intertrappean sedimentswere trenched to exposefresh sediments,whichwere carefully examined for lithological changesand fossil content. The sections were described, measured, photo-graphed and methodically sampled at an average of 10 cm intervals.In the laboratory samples were dried in an oven at 45 °C and thencrushed in an agate mortar before analyses.

Mineralogic analyses were carried out at the University of Lausannewith a Thermo Scientific ARL X-TRA diffractometer using a semi-quantitative method following the procedures described by Klug andAlexander (1974), Kübler (1983) and Adatte et al. (1996). Whole rockmineralogic analyses were performed on powdered samples pressedinto a powder holder. Clay minerals were analysed for the b2 μm frac-tion. Carbonates were removed from the samples with HCl (10%).Then, following Stokes law the granulometric fraction b 2 μmwas pipet-ted and deposited on a glass plate and air-dried.

Major and trace element concentrations were determined by X-rayfluorescence spectrometry (XRFS) using a PANalytical PW2400 spec-trometer at the University of Lausanne. Major elements were deter-mined on fused lithium tetraborate glass disc. For this purpose,samples were first heated to 1050 °C in an oven in order to calculatethe loss of ignition (LOI). Then, 1.2000 ± 0.0002 g of ignited samplewas mixed with 6.0000 ± 0.0002 g of lithium tetraborate (Li2B4O7)and placed in a Bead machine PerlX'3 at 1250 °C to obtain the fusedtablet. The obtained concentrations are given in weight percentages(wt.%). Trace element analyses were performed on pressed tabletsafter mixing 15% of the powered samples with Mowiol 2%. The pressedtablets were then placed in an oven at 110 °C for at least 6 h before anal-ysis by XRFS. The trace element concentrations are given in parts permillion (ppm).

Stable isotope analyses were performed at the Institute of Earth Sur-face Dynamics of the University of Lausanne. Stable carbon and oxygenisotope ratios (δ13Ccarb and δ18Ocarb values) were measured in wholerock samples containing N10 wt.% CaCO3 following the procedure de-scribed previously (Spangenberg and Herlec, 2006). Samples showingclear evidence of diagenetic neoformed or recrystallized carbonate(calcite) were not analysed. The analyses were performed in aliquotsof powdered whole rock samples (variable size depending on theCaCO3 content) using a Thermo Fisher Scientific (Bremen, Germany)Gas Bench II carbonate preparation device connected to a Delta PlusXL isotope ratio mass spectrometer. The CO2 extraction was done by re-action with anhydrous phosphoric acid at 70 °C. The stable carbon andoxygen isotope ratios are reported in the delta (δ) notation as the permil (‰) deviation relative to the Vienna Pee Dee belemnite standard(VPDB). The standardization of the δ13Ccarb and δ18Ocarb values relative



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3A. Fantasia et al. / Palaeogeography, Palaeoclimatology, Palaeoecology xxx (2015) xxx–xxx

Please cite this article as: Fantasia, A., et al., Palaeoenvironmental changes associated with Deccan volcanism, examples from terrestrial depositsfrom Central India, Palaeogeogr. Palaeoclimatol. Palaeoecol. (2015), http://dx.doi.org/10.1016/j.palaeo.2015.06.032


KT

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Fig. 2. Block diagram showing the stratigraphic position of the studied infratrappean and intertrappean sediments in relation to the Deccan phases-1, -2 and -3. Note the stratigraphicposition of the Dongargaon section corresponding to infratrappean sediments, the Governmental Well sediments deposited during phase-1 and the Daiwal intertrappeans correspondingto the onset of themain phase-2. The intertrappean sediments of Podgawan are equivalent to the early Palaeocene Jhilmili section (Keller et al., 2009) and correspond to the upper part ofphase-2. The Umaria Isra section represents the intertrappean sediments at the highest stratigraphic level deposited during phase-3.


to the international VPDB scale was done by calibration of the referencegases andworking standardswith IAEA standards. Analytical uncertain-ty (2σ) monitored by replicate analyses of the international calcitestandard NBS-19 and the laboratory standard Carrara Marble was notgreater than ±0.05‰ for δ13C and ±0.1‰ for δ18O.

The organic carbon isotope ratio (δ13Corg values in‰ VPDB) was de-termined from decarbonated (10% HCl treatment) samples based oncontinuous flow elemental analyser/isotope ratio mass spectrometry(EA/IRMS), as described previously (Spangenberg et al., 2010). Aliquotsof samples were flash-combusted on a Carlo Erba 1108 (Milan, Italy)elemental analyser connected to a Thermo Fisher Scientific Delta V(Bremen, Germany) isotope ratio mass spectrometer that was operatedin the continuous heliumflowmode via a Conflo III split interface for thedetermination of the isotopic composition of the produced CO2. Repro-ducibility and accuracy are better than ±0.1‰ for δ13Corg.

The characterization and quantification of the organic matter wereperformed on powered whole rock at the Institute of Earth Sciences ofthe University of Lausanne using a Rock-Eval 6 following the methoddescribed by (Behar et al., 2001). The samples were placed in an ovenand first heated at 300 °C under an inert atmosphere and then graduallypyrolysed up to 650 °C. After the pyrolysis is completed, the samples aretransferred into another oven and gradually heated up to 850 °C in thepresence of air. The determined parameters are total organic carbon(TOC), the Hydrogen Index (HI as mg HC/g TOC) and the OxygenIndex (OI as mg CO2/g TOC), which permit an overall characterizationof the sedimentary organic matter.

4. Lithology and mineralogy

4.1. The Dongargaon section

The Lameta section of Dongargaon (Figs. 1 and 3) is 5.4 m thick(the contact with the Precambrian basement was not visible) and

Fig. 3. Lithology and mineralogy of the Dongargaon infratrappean sequence.Whole rock compophyllosilicates as main component. Clay minerals consist exclusively of smectite and poorly cr


mainly composed of green claystones and siltstones with carbonatenodules and finely laminated marly limestone layers, which containrare ostracods (Unit 1). The overlying Unit 2 consists of massive ba-salts of the Sahyadri Group, which erupted at the beginning of C29r(Samant and Mohabey, 2014) and hence at the onset of phase-2(Chenet et al., 2008).

Whole rock compositions reflect the dominant lithology of claystonewith phyllosilicates (10–85%) as main component. The unquantifiedpart (0–47%) consists of poorly crystallized minerals (e.g., opal CT, Fe-oxides). Calcite content is low (0–12%) but reaches 50% in the marlylimestone intervals, which are characterized by low phyllosilicatecontent (Fig. 3). Ankerite (Fe-rich dolomite) is present in small amounts(0–7%) but reaches a maximum of 13% in the marly limestoneintervals at 370 cm. Small amounts of quartz (0–4%), K-feldspar andNa-plagioclase (b4%) are sporadically present. Clay minerals consistexclusively of smectite (10–55%) and illite (45–90%), which may havebeen derived from a partial degradation of smectite (Fig. 3).

4.2. The Daiwal section

The section spans nearly 4.5 m between the lower and upper basaltflows (Figs. 1 and 4). The lower flow is characterized by stronglyweath-ered basalt with holocrystalline texture (Unit 1). Vertical fractures filledwith grey siliceous sediments are present. The contact with thesediments is irregular and weathered basalts clasts are present. Sedi-ments of Unit 2 consist of laminated porcelanite (Fig. 4F) with variousdegrees of silicification and black chert nodules (DA9, DA14, DA19;Fig. 4). This Unit is characterized by the presence of ostracods, gastro-pods and fishes (Fig. 4C). Unit 3 is composed of grey to black cherts(Fig. 4G). Thewhole rock composition is dominated byquartz of biogen-ic origin formed by diagenetic transformation of opal-A from diatomstests into opal-CT and finally into quartz. Unit 1 contains sedimentsinfilling the sub-vertical fractures in the lower basalt trap, which is

sitions reflect the dominant lithology of claystones alternating with carbonate layers withystallized illite.






Fig. 4. Lithology,mineralogy andmicrographs of theDaiwal intertrappean sequence (onset of phase-2). The lithology reflects lacustrine environments and is dominated by porcelanite andcherts. Thewhole rock compositions consistmainly of quartz reflecting thediagenetic transformation of opal-A fromdiatoms tests into quartz. Clayminerals are exclusively representedbysmectite.Micrographs: DA2: recrystallized ostracods, DA3:weathered basalt clast, DA12: laminatedporcelanite, DA13: ostracod, DA16: laminationwith ostracods shells, DA18:fish debris.


dominated by quartz (27–81%), largely unquantified minerals (5–61%)and relatively uniform phyllosilicate content (12–17%). In Unit 2, quartzis the dominant mineral and increases upward (33–78%). Only the

Fig. 5. Characteristics, lithology and mineralogy of the Podgawan intertrappean sequence (uppalternating with carbonate layers. Unit 3 is marked by more fluctuating lithologies showing lapalaeosoil. Unit 4 is composed of marly carbonates. The mineralogy is dominated by phyllosilireferences to colour in this figure legend, the reader is referred to the web version of this artic


mudstone sample DA19 contained significant calcite (32%). Wholerock minerals of Unit 3 reflect a lithology dominated by cherts withabundant quartz (80–87%), phyllosilicates (5%), minor unquantified

er part of phase-2). The base of the section (Unit 2) is composed of monotonous siltstonecustrine environments, a charcoal-rich layer and a red clay layer likely corresponding to acates and clay minerals are represented by smectite and zeolite. (For interpretation of thele.)







minerals (6–13%) and low calcite content (1–4%). At Daiwal, the clayfraction is exclusively composed of smectite (Fig. 4).

4.3. The Podgawan section

The Podgawan section has been trenched in two small hills located100 m apart. These two segments are separated by an outcrop gap ofapproximately 2 m (Fig. 5). This composite section spans nearly 5 mbetween the lower and upper basalt flows. Unit 1 marks the top of thelower flow and consists of vesicular basalt (Fig. 5A). Unit 2 is about2 m thick and consists of monotonous green siltstone, which gradesupwards into brownish siltstone alternating with 2–5 cm thick carbon-ate layers (Fig. 5B). Unit 3 is about 1.45 m thick and consists of fossilif-erous brown silty claystones intercalated with 2–5 cm thick marlylimestone layers (Fig. 5C to F). The upper part of Unit 3 shows three pe-culiar levels consisting of a 5 cm thick grey chert layer (PoA12, Fig. 5E)overlain by 1–2 cm thick coal-rich level (PoA14, Fig. 5F), which istopped by a 1 cm thick reddish clay-rich layer (PoA16, Fig. 5F). Gastro-pods and ostracods are scarce at the base of Unit 3 and become moreabundant between 80 and 105 cm. Both are rare to absent in theupper part of this unit. Most of the ostracods are apparently of thenon-marine genus Frambocythere COLIN, 1980, which seems to beparticularly tolerant to environmental variations (Bhandari et al.,1995; Bhandari and Colin, 1999). Unit 4 consists of marly limestone in-cluding one level enriched in gastropods with preserved aragoniticshells (Fig. 5G–H).

The whole rock composition of Unit 2 reflects claystone–siltstonelithologies with phyllosilicates reaching 40–80%. Calcite content isgenerally very low (b5%) but reaches 57% in the marly limestone inter-vals of units 2, 3 and 4 (Fig. 5); quartz and Na-plagioclase contents areuniformly low (b7%). The clay fraction consists exclusively of smectite,which are often associated with zeolite (Fig. 5).

4.4. The Umaria Isra section

The section spans nearly 80 cm between the lower and the upperbasalt traps (Fig. 6). The lower flow (Unit 1) is characterized by weath-ered basalt with holocrystalline texture. The sediments of Unit 2 arecomposed by white silty claystone laminated at the base, which gradesupward into more massive claystone. Unit 3 is typified by brown siltyclaystone, which grades upward into clayey siltstone. Unit 4 consistsof white siltstone. Unit 5 consists of orange coarse-grain siltstone withsmall clayey clasts. The top of Unit 5 is characterized by clayey siltstone(Fig. 6A). Unit 6 consists of white claystone. Unit 7 consists of blue-greycoarse-grain laminated siltstone, which grades upward into a greenclaystone with polygenic and heterometric clasts (Fig. 6B–C). Unit 8corresponds to the upper basalt flow.

The whole rock composition is mainly dominated by unquantifieds(38–65%), which mainly consist of poorly crystallized minerals(opal-CT, zeolite, iron oxides and hydroxides). Units 2 to 4 have similarwhole rock compositions with phyllosilicates (10–37%) as the mostabundant mineral. Quartz, Na-plagioclase and K-feldspar are alsopresent, but in minor quantities (0–10%) though they increaseupsection to the top of Unit 4. Calcite (up to 12%) is mainly representedin units 2 and 4, whereas quartz (15–29%), Na-plagioclase (8%) andK-feldspar (9–10%) increase in units 5 and 6. Unit 7 and is dominatedby phyllosilicates (31–42%) and unquantifieds (54–59%). Illite (10–90%)and smectite (9–90%) are the dominant clay minerals (Fig. 6).

5. Major and trace element geochemistry

Major elements (MEs) and trace elements (TEs) have been mea-sured in the Lameta and intertrappean sediments. For most of sedimen-tary deposits, Al can be considered as indicator of the aluminosilicatefraction of the sediments that is more or less immobile during diagenet-ic processes (Tribovillard et al., 2006 and references therein). TEs are


therefore normalized with Al following Van der Weijden (2002) andTribovillard et al. (2006) because (1) the detrital fraction composed ofphyllosilicates, Na-plagioclases and K-feldspars (quartz is mainly frombiogenic origin in most of the sections) is dominant and calcite contentis generally low; and (2) Al shows generally the lowest coefficient ofvariation (0.1–0.65).

MEs trends show significant fluctuations through the Deccanbasalt sequence (Fig. 7). Al2O3 lacks significant variations in Dongargaon(except for the carbonate-rich intervals). Al2O3 values are lower (2.7–10.8 wt.%) than the Post-Archean average shale (PAAS) and quite closeto the Average Deccan basalt composition (ADBC). Daiwal sedimentsare characterized by very low Al2O3 contents (1–4 wt.%). In contrast,the Podgawan section shows more contrasted Al2O3 fluctuations(0.6–11.5 wt.%), whereas, the Umaria section is characterized bypredominantly highest steady values between 9 and 12.8 wt.%,close to the ADBC, similar to the infratrappean Dongargaon section.

TiO2 and Fe2O3 display similar trends; the Dongargaon sedimentsshow values (TiO2 b 1 wt.%; Fe2O3: 2–10 wt.%) close to the Post-Archean average shale (PAAS) and the Daiwal section displays lowerbut steady values (TiO2 ≪ 1 wt.%; Fe2O3: 0.5–3 wt.%). Important fluctu-ations are observed in the Podgawan section with the highest values ofTiO2 and Fe2O3 with 2.42 and 12.3 wt.% respectively, therefore close toADBC within the interval of 120 and 165 cm.

MgO show maximum values in the Dongargaon section (4.9–12.7 wt.%) and minimum values in the Dawail section (b0.9 wt.%). ThePodgawan intertrappean is characterized by highly fluctuating MgOcontents (0.7–10.2 wt.%). Maximum values are observed in the clayeysiltstones, while the lowerMgO amounts typify themarly limestone in-tervals. At Umaria–Isra MgO amounts are quite comparable to those ofthe infratrappean sediments of Dongargaon, with values betweenPAAS and ACDB.

P2O5 content is generally very low (b0.2 wt.%) largely below PAASvalues, except for the Podgawan intertrappean sediments, whichshow elevated P2O5 exceeding PAAS values, especially in the clay–siltintervals of Unit 3. Highest P contents (0.5 wt.%) are observed inPoA13 and 14, which correspond to a charcoal rich layer.

TEs, such as Cu, Ni, Zn, V, U lack significant fluctuations through theDongargaon (infratrappeans), Daiwal (intertrappean, phase-2) andUmaria Isra (phase-3) sections and are comparable to ADBC and/orPAAS. In contrast, the intertrappean section of Podgawan (phase-2)shows generally highest values compared with the other sections.High V/Al ratios in Podgawan samples are related to the widespreadCa–Fe-rich vanadates particles observed by Font et al. (in this issue).

6. Stable carbon and oxygen isotopes

The Dongargaon section (Do 5, 7, 17, 18, 21) and the Daiwal section(DA 12, 15, 19, 20) show relatively high δ13Ccarb values (−4.8 to−3.0‰and −3.0 to −0.0‰, respectively). δ18Ocarb values range from −4.7 to0.0‰ (Fig. 10C). In contrast, δ13Ccarb values measured in the Podgawansection vary between −9.0 and −7.2‰ in the marly limestone layers(PoB1, PoA3b, PoA5, PoA7 and PoA10) and δ18O values vary between−2.3 and−1.3‰. Lower δ13Ccarb values in the −10.8 to −9.4‰ rangeare measured in samples from shaly intervals (PoA9, PoA11, PoA13)and marly limestone beds in the upper part of the section (PoA20:−10.1‰, PoA21: −10.3‰, PoB14: −10.3‰). For these beds, δ18Ocarb

values are significantly lower and range between −10.6 and −6.3‰.The lowest δ13Ccarb value is in the calcite within the charcoal rich layer(−12.6‰, PoA14).

The organic C isotope composition was determined only in samplesfrom the Podgawan section. δ13Corg values are quite stable in the lowerpart of Unit 2, ranging between −26 and −22‰ (Fig. 9). Above, theδ13Corg values (Fig. 9) show a reverse trend relative to δ13Ccarb, showinga gradual positive excursion (from −29.3 to −17.0‰) culminating inthe layer (PoA17) just above the red clay layer located in the upperpart of Unit 3.



Fig. 6. Lithology andmineralogy of the Umaria Isra intertrappean sequence (phase-3). The lithology is dominated by claystones to siltstones. Thewhole rock composition ismore variablethan in underlying intertrappeans and clay minerals are composed of smectite and illite as in the Dongargaon infratrappean section.


7. Organic matter

With the exception of the Governmental Well and Podgawan sec-tions, all other infratrappean and intertrappean deposits are very poorin organic matter (TOC b 0.2%). Samples from the brown shales in theGovernmental Well show the highest TOC content (up to 10 wt.%).Hydrogen and oxygen indexes (HI and OI) are variable (HI: 37–450 mg HC/g TOC and OI: 37–240 CO2/g TOC), indicating a mixture oflacustrine and terrestrial organic matter (Espitalié et al., 1985;Lafargue et al., 1998) (Fig. 10A). This is consistent with the abundantpresence of ostracods, gastropods and wood debris in these deposits.Moreover, Podgawan sediments show very low TOC values (≪0.1%) inthe lower part of the section, followed by a gradual increase in themiddle part of the section (up to 1.3 wt.% TOC), corresponding to acharcoal rich layer. For TOC values N 0.2%, HI values are between 7 and


37 (mg HC/g TOC) and OI values are between 105 and 260 CO2/g TOC(Fig. 10A). Low HI and high OI values point to a strong oxidative degra-dation of the organicmatter in the sediments depositedwithin themainphase-2 of volcanism, suggesting oxidation of the biomass during thevolcanic activity. These results are in agreement with the observationsof Samant andMohabey (2009), which show a sharp decrease in pollenand an increase in fungal spores for these deposits.

8. Discussion

8.1. Clay minerals as environmental proxies

Clay mineral assemblages reflect continental morphology, tectonicactivity, climate changes and sea level fluctuations and are therefore ex-cellent environmental proxies (Chamley, 1989, 1998; Adatte et al.,



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Fig. 7.Major and trace elements from a Lameta section (Dongargaon) and different intertrappean sections (Daiwal: onset of phase-2; Podgawan: upper phase-2; Umaria–Isra: phase-3) located at different stratigraphic levels within the Deccan pile.Note the Podgawan section marked by highly variable MEs and TEs compared to other infra and intertrappean sections, thus indicating increased basalt weathering.

10A.Fantasia

etal./Palaeogeography,Palaeoclimatology,Palaeoecology

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CentralIndia,Palaeogeogr.Palaeoclimatol.Palaeoecol.(2015),http://dx.doi.org/10.1016/j.palaeo.2015.06.032



2002). The clay minerals recognized in the studied section can be sepa-rated in two categories. (1) A smectite and illite assemblage character-izing the infratrappean (Dongargaon) and the intertrappean depositedduring phase-3 (Umaria Isra) and (2), an exclusive smectite contenttypifying the intertrappean deposited during themain phase-2 (Daiwaland Podgawan). Smectite generally forms in intermittently poorlydrained soils, characterized by strongly seasonal precipitations. Thepoorly crystallized illite may have been derived from a partial degrada-tion of smectite (Deconinck et al., 1988). Illitization of smectite at sur-face temperature is known from lacustrine environments (Singer andStoffers, 1980) and from calcrete palaeosols (Robinson and Wright,1987) as a result of successive wet and dry cycles under alkaline condi-tions (Eberl and Karlinger, 1986). The K necessary for the illitization ofsmectite may have been supplied from plant debris present in the soiland/or provided by the leaching of metamorphic basement (e.g., mus-covite, feldspar). The second assemblage reflects the exclusive and in-tense leaching of basalts under the same kind of semi-arid climate andreflects therefore the Deccan phase-2, during which basalt emissionwas the highest. This would lead to intensive leaching of the extendedbasalt outcrops, accelerated by acid rains linked to SO2 emissions. Thissemi arid seasonal climatic regime has already been inferred by Ghoshet al. (1995) for the infratrappean Lameta Fm and by Keller et al.(2009) for the Jhimili intertrappean section, which is nearly coevalwith the Podgawan section. Local aridity in the DVP is interpreted byKhadkikar et al. (1999) as a result of « mock aridity ». This term refersto volcanic induced xeric conditions linked to fresh barren landscapesproduced by volcanism. Such new landscapes lack well-developedsoils to sustain vegetation inducing therefore drier climate. However,the Lameta beds (Dongargaon section) are traditionally considered aspre-Deccan in age in absence of underlying lava flows and therefore vol-canism inducedmock ariditywould be unlikely to explain the semi-aridconditions characterizing these sediments. Recently, Boucot et al.(2013) showed that South and Central India are characterized by subtropical-arid conditions during the Coniacian–Maastrichtian interval.But a late Maastrichtian age for the Lameta beds is indicated by thenannofossil marker Micula murus (Saxena and Misra, 1995) and istherefore not incompatible with the Deccan phase-1, which startedaround 67.1 Ma (Schöbel et al., 2014). Moreover Salil et al. (1997)show that the Lameta smectitic clays derived from the weathering ofDeccan basalt, based on REE elements and hence their deposition canbe coeval with the onset of Deccan volcanism.

8.2. Elemental geochemistry as environmental proxies

8.2.1. Volcanism vs detritismThe influence of volcanism is evaluated based on the Ti/Al and the

K/(Fe + Mg) ratios. Titanium has very low mobility under almost allenvironmental conditions, mainly due to the high stability of the insol-uble oxide TiO2 under all, but themost acid conditions (Brookins, 1988).Therefore, titanium behaves as a refractory element during weatheringprocesses. In Podgawan sediments, Ti and Fe enrichments suggesthigh weathering as it is indicated by the high correlation with Al(R2(Al–Ti)=0.9, R2(Al–Fe)=0.8). The remarkable high value detectedin sample PoA16 could be related to the development of lithotrophic Fe-oxidizer bacteria described by Font et al. (this volume). K/(Fe + Mg)ratio represents the balance between detrital and volcanogenic inputs(Sageman and Lyons, 2003).

In Lameta sediments (Dongargaon section), the Ti/Al ratio is steadyand reaches 0.19 (mean value 0.13), whereas the Ti/Al ratio in Daiwalsediments (intertrappean at the base of phase-2) remains very low(0.02–0.09) and close to PAAS. In intertrappean sediments of Podgawandeposited during themain Deccan phase-2, the Ti/Al ratio is high (0.14–0.27,mean value: 0.19) and close to ADBC values (mean value for ADBC:0.19; Crocket and Paul, 2004). Moreover, the K/(Fe + Mg) ratio is verylow and close to ADBC (mean value for ADBC: 0.03; Crocket and Paul,2004), indicating a mafic igneous provenance (basalt weathering).


These changes could be related to the intense leaching of large portionsof newly erupted basalt during the main phase-2 (Fig. 8). Ti/Al ratioscharacterizing the samples from Umaria Isra intertrappean, coevalwith the phase-3 are fairly similar to those typifying the infratrappeansediments with values ranging from (0.02–0.16), confirming that thisphase is minor compared with phase-2. High K/(Fe + Mg) ratios con-firm that trend and is explained by the presence of significant amountsof detrital K-feldspar and to a lesser extent illite, similar to theintertrappean (Figs. 3 and 6).

8.2.2. Chemical index of alterationEnvironmental consequences of Deccan volcanism were assessed

using geochemical proxies calculated with major elements. The chemi-cal index of alteration is used to estimate the intensity of alterationrelated to climatic conditions and/or potential acid rains (Nesbitt andYoung, 1982, 1989). The CIA-K method developed by Sheldon et al.(2002), based on a soil-weathering index developed by Harnois(1988) and Maynard (1992) was used. This method compares abun-dances of soluble cations of calcium and sodiumagainst relatively stablealuminium to determine the relative amount of chemical weathering.This index does not include potassium (K) because diagenetic processescan yield elevated concentrations of K (Sheldon et al., 2002; Adamset al., 2011). The calculation is based on molar proportions: CIA-K =Al2O3/[Al2O3 + Na2O + CaO*] ∗ 100, where the CaO* represents theCaO in silicate minerals (Nesbitt et al., 1980; Nesbitt and Young,1982). In this study, a CaO* correction is needed due to the presenceof carbonates (e.g., McLennan et al., 1993). In the case of a remainingamount of CaO* after the correction higher than Na2O content, it is as-sumed that the CaO* is equivalent to the Na2O content (McLennan etal., 1993).

The CIA-K values of the Dongargaon infratrappean sediments com-prise between 80–90 (mean value is 85), followed by a decrease to amean value of 77 in the Daiwal intertrappean sediments (lower partof phase-2). The Daiwal sediments were deposited in a lacustrineenvironment dominated by a siliceous productivity (diatoms), whichexplains the lower CIA-K values. A gradual increase is observed culmi-nating in the intertrappean sediments of Podgawan (upper part ofphase-2) with maximum values of 97 (mean value is 93), followed bya sharp decrease in the Umaria Isra intertrappean sediments (phase-3) (mean value is 68) (Fig. 8). The Podgawan sediments (final stagesof the main phase-2) are characterized by the highest CIA-K values co-incident with very low magnetic susceptibility values and presence ofvanadates (Font et al., this issue). This reflects increasing acidic condi-tions due to volcanic gas (SO2) rather than global climatic changessince clayminerals are quite identical in all infra and intertrappean sed-iments. Moreover, the presence of a charcoal layer and a red clay bedcontaining iron fossil bacteria may indicate deterioration of environ-mental conditions such as wildfires and bacterial blooms (Font et al.,this issue).

8.2.3. Mean annual precipitationQuantitative mean annual precipitation (MAP) values (mm/year)

(Sheldon et al., 2002; Sheldon and Tabor, 2009; Adams et al., 2011)were calculated using CIA-K index in order to evaluate whether the in-tensity ofweathering is linked to the quantity or quality of precipitation.

The MAP values for the Lameta sediments (Dongargaon) are be-tween 1060 and 1295 mm/year (mean value is 1197 mm/year). Forthe subsequent intertrappean sediments MAP values range from 819to 1333 mm/year (mean value: 1004 mm/year) for Daiwal, from 1220to 1500 mm/year (mean value: 1384 mm/year) for Podgawan andfrom 512 to 1362 mm/year (mean value: 899 mm/year) for UmariaIsra (Fig. 8). These MAP values are typical for hot and semi-arid climateconditions with seasonal rainfall, similar to the current climate prevail-ing in Central India characterized by a monsoonal regime (1200 mm,Rao, 1976). Mean annual precipitation values for the Lameta depositsprior to basalt eruptions do not vary from intertrappean sediments



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Fig. 9.TOC content, δ13Corg, δ13Ccarb and δ18Ocarb (for sampleswith CaCO3 content N 10wt.%) of Podgawan section (upper phase-2). TOC content is generally low (b0.25wt.%) except for thecharcoal-rich layer (PoA14). δ13Corg curve shows a positive excursion in Unit 3 suggesting oxidation/reworking of organic matter. δ13Ccarb and δ18Ocarb curves show a gradual negativeexcursion in the same interval (upper Unit 3 and Unit 4).


within the lava flows. This indicates that the onset of Deccan volcanismin the nearby areas did not change the quantity of precipitation appre-ciably and that the increasing chemical weathering ismore likely linkedto more acidic rains.

8.3. Stable isotopes as environmental proxies

Several geochemical proxies (CIA-K, Ti/Al, K/Fe + Mg) combinedwith sedimentology and palynology (Samant and Mohabey, 2014) and

Fig. 8. Summary of environmental proxies used in this study (volcanism vs detritism, chemicalNote themajor change in CIA-K index culminating in Podgawan section (upper phase-2). Ti/Al,position of Podgawan sediments. MAP values indicate a semi-arid seasonal climatic regime wi


magnetic susceptibility (Font et al., this volume) show that thePodgawan intertrappean, which is coeval with the main DVP phase-2,was marked by extreme and detrimental events culminating in theupper part (units 3 and 4) (Figs. 8 and 5). The δ13Corg values graduallyincrease in Unit 3 to reach maximum values in the upper Unit 3 and 4(Figs. 9 and 10). δ13Corg higher values coincide with the red clay layer,which is marked by the presence of iron oxide bacterial colonies (Fontet al., in this issue). The observed trend of 13Corg enrichment points to in-creased oxidation and reworking of organic matter (e.g., Meyers and

index of alteration and mean annual precipitation) based onmajor element geochemistry.K/(Fe+Mg) ratios are close to ADBC indicating a major volcanic influence during the de-th maximum of precipitation in Podgawan.



Fig. 10. (A)HI vsOI (for sampleswith TOC content N 0.2wt.%). Scatter plot for theGovernmentalWell samples and the Podgawan section TheGovernmentalWell section deposited duringphase-1 shows typical HI–OI values for a mixture of lacustrine and terrestrial organic matter (OM). Podgawan sequence deposited within the main phase-2 of volcanism shows HI–OIvalues reflecting a strong oxidative degradation of the OM. This is consistent with the sharp decline in pollen observed by Samant and Mohabey (2009, 2014). (B) δ13Corg vs. TOC scatterplot of Podgawan (phase-2) shows higher δ13Corg values in units 3 and 4 than in the lower part of the section (Unit 2 and lower Unit 3). (C) The trend tomore negative values (Podgawansection, units 3 and 4) in both δ13Ccarb and δ18Ocarb suggests increased diagenetic overprint resulting from dissolution–recrystallization processes linked to extreme events (e.g., acidifica-tion). (D) Close-up of the charcoal-rich interval (PoA14) and the red clay layer (PoA16) in the Podgawan section. (For interpretation of the references to colour in this figure legend, thereader is referred to the web version of this article.)


Ishlwatari, 1993). Moreover, the δ13Corg vs. TOC scatter plot shows thatall the samples corresponding to Units 3 and 4 are characterized byhigher δ13Corg values than those of Units 2 and 3 (Fig. 10B). This trendis confirmed by the HI vs. OI plot (Fig. 10A), in which samples fromPodgawan with very low HI (b100) but high OI values (75–350) com-pared to the GW section are located between DVP phases-1 and -2(Fig. 10A). Thus, these combined data reflect a strong oxidative degra-dation of the organic matter in the sediments deposited within themain phase-2 of volcanism, suggesting that oxidation of the biomasswas associated with Deccan volcanic activity.

Both δ13Ccarb and δ18Ocarb profiles show a gradual negative excursionin the same interval (Fig. 9). The δ13Ccarb vs. δ18Ocarb plot also reflects anincreased diagenetic overprint related to oxidation and dissolution–recrystallization processes probably linked with volcanism inducedacidification (Fig. 10C). The Dongargaon infratrappean sediments andDaiwal intertrappeans, whichmark the onset of phase-2, are character-ized by δ13Ccarb and δ18Ocarb characteristic of freshwater lacustrineenvironments (−6 to −4‰). Some samples from Daiwal are closelyassociated with abundant chert but show less negative δ13Ccarb and


δ18Ocarb values, whichmay be explained by diagenetic processes imply-ing opal dissolution and incorporation of heavy oxygen into the calcite(e.g., Swann et al., 2006).

However all samples located in the upper part of Units 3 and 4show very negative δ13Ccarb and δ18Ocarb values, which likely resultsfrom diagenetic dissolution–recrystallization processes, includingbacterial recycling as also observed by Font et al. (this issue). Thechemical weathering of the Deccan silicate and carbonate rocks(δ13C = −14‰; Das and Krishnaswami, 2007) may also explainthese negative values. Higher CIA values observed at the same inter-val support therefore the connection between increasing weatheringintensity and the observed changes in both carbonate and organicmatter stable isotopes.

9. Depositional scenario

The Lameta sediments of theNand–Dongargaon basin are composedof green to reddish clays with carbonate nodules and more continuouslayers, which contain ostracods. These sediments were deposited in




alluvial-limnic environments (Mohabey et al., 1993) under semiarid toarid climates with strong seasonality, which are confirmed by the pres-ence of smectite associated with poorly crystallized illite derived from apartial degradation of smectite (Deconinck et al., 1988). Illitization ofsmectite is known as a result of successive wet and dry cycles underalkaline conditions (Eberl and Karlinger, 1986). The near absence oforganic matter in the sediments could be explained by the arid condi-tions implying high biodegradation. The presence of thin carbonatelayers within the clays, as well as the carbonate nodules, may be indic-ative of groundwater level fluctuations. Palynological (Samant andMohabey, 2009, 2014) and palaeontological (Mohabey et al., 1993;Mohabey and Udhoji, 1996) studies reveal the presence of a gymno-sperm–angiosperm-rich palynoflora and a diversified fauna (turtles,frogs, crocodylomorphs, dinosaurs, etc.).

The onset of the Deccan volcanism dramatically changed the ecosys-tems. Small lakes and ponds developed on basaltic bedrocks as attestedby the presence of fishes, ostracods and gastropods in GovernmentalWell, Daiwal and Podgawan intertrappean beds.

The sediments of Governmental Well in phase-1 contain abundantostracods, gastropods and wood debris. Organic matter is well pre-served and poorly oxidized in these deposits. The volcanic activity likelyinfused a huge nutrient supply leading to high productivity in lakes andponds. These deposits seem to be equivalent to theMohgaon KalanWelldescribed by Samant and Mohabey (2009, 2014), which yielded dino-saur eggshells and a megaflora dominated by angiosperms.

Deccan volcanism reached its maximum (phase-2) during the last250 ky of the late Maastrichtian up to the early Palaeocene (C29r),depositing 80% of the total lava thickness (Chenet et al., 2007, 2008).Palynological studies indicate that immediately after the onset of Dec-can phase-2, the pre-existing floral association was decimated leadingto dominance by angiosperms and pteridophytes at the expense ofgymnosperms. In subsequent early Palaeocene intertrappean sedimentsof Podgawan, a sharp decrease in pollen and spores coupled with thedominance of Mycorrhizal fungi mark increasing stress conditions ap-parently as a direct result of volcanic activity (Samant and Mohabey,2009, 2014). The volcanic activity and the associated gas SO2, HCl (Selfet al., 2008) changed the environmental conditions leading to strongvolcanic influence and more acidic conditions. This is indicated byCIA-K values thatmark increased chemical weathering in the Podgawansequence (phase-2), which is more likely due to acidic conditions (acidrain) than climatic change.

The increased volcanic influence is also indicated by high Ti and Fevalues, which mark the intensive leaching of large basalt portions.Organic matter is characterized by high OI (oxygen index), low HI (hy-drogen index) and heavier δ13C values, which indicate that the organicmatter in the intertrappean sediments deposited within phase-2 wasreworked and oxidized due to the severe leaching of acid rain inducedby intense volcanic activity. Moreover, the presence of a charcoal richlayer suggests intense land fires.

The sediments associated with phase-3 are dominated by soils,which were probably formed in more alkaline conditions under semi-arid conditions. The subsequent deposits are marked by floral recovery(Samant and Mohabey, 2009, 2014).

10. Conclusions

1) Sedimentologic, mineralogic and facies analyses indicate modifica-tions of the environments with the onset of the Deccan volcanism.Lameta sediments were deposited in alluvial-limnic environmentswhile intertrappeans are typical for terrestrial to lacustrine environ-ments.

2) Clay minerals suggest a semi-arid climate with alternating humidand dry cycles. Two assemblages are recognized. The illite and smec-tite assemblage from the Dongargaon infratrappeans results fromthe illitisation of smectite as a result of successivewet and dry cyclesunder alkaline conditions. The exclusive smectite composition for


intertrappeans (Daiwal and Podgawan) within the main phase-2 ofvolcanism reflects the sole and intense leaching of basalts likelyaccelerated by acid rains linked to SO2 emissions.

3) In the Podgawan section high Fe and Ti values, aswell as culminatingCIA-K values, indicate strong leaching of newly erupted basalt. Thiscoincides with abrupt lithological changes and very low magneticsusceptibility values and point to more increasingly acidic condi-tions. MAP values are almost steady in all infratrappean andintertrappean sections reflecting more likely a change in the qualityof the precipitation (acidic rains).

4) The organic matter content is very low in all infratrappean andintertrappean sediments, except in Governmental Well (phase-1)and in Podgawan section (phase-2). The Governmental Wellshows high organicmatter contentwith a typically terrestrial and la-custrine origin. The organic matter content in Podgawan is low andstrongly oxidized-alterated, suggesting that this degradationwas as-sociated with volcanism and the onset of the most detrimentalDeccan phase-2. This is also marked by less negative δ13Corg valuesin the upper part of Podgawan section.

5) This increased alteration is coeval with the sharp decline in pollenand an increase in fungal spores and corresponds to the mainphase of Deccan activity. These observations indicate that Deccanvolcanism played a key role in increasing atmospheric CO2 and SO2

levels that resulted in globalwarming and acidification, thus increas-ing biotic stress that predisposed faunas to eventual extinction at theKTB.

Acknowledgements

We thank Nicolas Tribovillard and one anonymous reviewer forinsightful comments. We are grateful to the Department of Geology inNagpur (India) for logistical support during fieldwork and to BandanaSamant, Deepali Thakre and Dhananjay Mohabey for field assistance.We thank Jean-Claude Lavanchy for XRF measurements, Laurent Nicodfor thin sections preparation, Pierre Vonlanthen for SEM micrographsand TiffanyMonnier for laboratory assistance and Gerta Keller (Univer-sity of Princeton) for her helpful comments on a earlier version of thismanuscript. This research was supported by the Swiss Academy ofSciences (SCNAT) (01-2012).

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Palaeogeography, Palaeoclimatology, Palaeoecologyecfont/publications/Fantasia et al., 2015.pdfprobably underwent excessive desiccation/oxidation processes under semi-arid conditions.

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