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Precambrian Research 238 (2013) 120– 128

Contents lists available at ScienceDirect

Precambrian Research

journa l h om epa ge : www.elsev ier .com/ locate /precamres

New age constraints for the Proterozoic Aravalli–Delhi successions ofIndia and their implications

N. Ryan McKenziea,b,∗, Nigel C. Hughesb, Paul M. Myrowc, Dhiraj M. Banerjeed,Mihir Debd, Noah J. Planavskye

a Department of Geological Sciences, Jackson School of Geosciences, University of Texas at Austin, TX 78712, USAb Department of Earth Sciences, University of California, Riverside, CA 92521, USAc Department of Geology, Colorado College, Colorado Springs, CO 80903, USAd Department of Geology, Delhi University, Chattra Marg, Delhi 110007, Indiae Department of Geology and Geophysics, Yale University, New Haven, CT 06520, USA

a r t i c l e i n f o

Article history:Received 24 April 2013Received in revised form19 September 2013Accepted 2 October 2013Available online 12 October 2013

Keywords:ProterozoicAravalliVindhyanDetrital zirconPhosphoriteBoring billion

a b s t r a c t

Proterozoic sedimentary successions of India are important archives of both the tectonic history of theIndian subcontinent and the geochemical evolution of Earth surface processes. However, the lack of firmage constraints on many of these stratigraphic units limits their current utility. Here, we present newdetrital zircon age data from strata of the southern Aravalli–Delhi Orogenic Belt (ADOB) and the RajasthanVindhyan successions. The Alwar Group of the southern Delhi Supergroup yielded a large population of∼1.2 Ga detrital zircon grains, which refutes the 1.9–1.7 Ga age assertion for this unit. Detrital zircon agedistributions from the southern Alwar Group differ strongly from the Alwar Group of the “North DelhiBelt”, demonstrating miscorrelation between these two regions. The Jhamarkotra Formation of the LowerAravalli Group contains a large population of 1.9–1.7 Ga detrital zircon grains. Therefore, the unit cannotbe ∼2.1 Ga as traditionally assumed. Age distributions of the Aravalli and Delhi supergroups are similarto those of the lower and upper Vindhyan successions, and we postulate contiguous sediment sources forboth regions, with strata of the tectonically deformed ADOB representing the distal margin equivalentsof the Vindhyan successions. Additionally, a late Paleoproterozoic age for the Jhamarkotra Formationnullifies the hypothesis that the markedly positive carbonate �13C values in this unit are linked to the2.3–2.0 Ga Lomagundi–Jatuli positive isotope excursion. The potential of a large late Paleoproterozoic(ca. 1.7 Ga) positive �13C excursion contrasts with the long-held view of a prolonged period of carbonisotope stasis during the so-called ‘boring billion’.

© 2013 Published by Elsevier B.V.

1. Introduction

Thick Proterozoic sedimentary successions that cover the Indianshield are considered deposits of discrete isolated basins that areoften referred to as the “Purana Basins” (Purana means ancient)(e.g., Holland, 1909; Valdiya, 1995; Chakraborty, 2006; Chakrabortyet al., 2010). Modern physiographic features and differences intectonic deformation typically define the boundaries of the so-called Purana Basins. The degree of continuity or isolation of thesebasins from one another during the time of sediment accumulationremains unclear. Interbasinal correlation has largely been hinderedby a lack of depositional age constraints on the strata within them.

∗ Corresponding author at: Department of Geological Sciences, Jackson School ofGeosciences, University of Texas at Austin, USA.

E-mail addresses: [email protected], [email protected](N.R. McKenzie).

However, there are recently developed chronostratigraphic frame-works for these various successions (e.g., Patranabis-Deb et al.,2007; Bengtson et al., 2009; Malone et al., 2008; Pradhan et al.,2010; Bickford et al., 2011; McKenzie et al., 2011; Mukherjeeet al., 2012; Pradhan et al., 2012). These are critical to further-ing understanding of the tectonic–sedimentary evolution of theIndian subcontinent. Additionally, these successions preserve crit-ical information about the Proterozoic evolution of the biosphere(e.g., Bengtson et al., 2009; Papineau et al., 2009, 2013). The AravalliSupergroup, in particular, contains carbonate rocks with markedlypositive carbonate �13C values that have been linked to the∼2.3–2.1 Ga Paleoproterozoic Lomagundi–Jatuli carbonate carbonisotope excursion (Sreenivas et al., 2001; Maheshwari et al., 2002,2010; Purohit et al., 2010). The Aravalli Supergroup has also beenproposed to contain the oldest phosphorites in the rock record,which along with additional geochemical data, have been used forinferences on biogeochemical cycling following the ∼2.4 Ga GreatOxidation Event (Papineau et al., 2009, 2013; Papineau, 2010).

0301-9268/$ – see front matter © 2013 Published by Elsevier B.V.http://dx.doi.org/10.1016/j.precamres.2013.10.006


N.R. McKenzie et al. / Precambrian Research 238 (2013) 120– 128 121

In this study we present new U-Pb detrital zircon age data frommajor stratigraphic units of the southern Aravalli and Delhi super-groups and the Vindhyan successions of Rajasthan, India. Thesedata provide new constraints that drastically revise the deposi-tional ages of the Aravalli and Delhi supergroups. Furthermore,these new age constraints appear to redefine the significanceof carbonate carbon isotope trends from Proterozoic Aravallistrata.

2. Geologic setting

2.1. Aravalli–Delhi Orogenic Belt

The roughly north–south trending Aravalli–Delhi Orogenic Belt(ADOB) of western India exceeds 700 km in length (Deb et al.,1989; Roy and Jakhar, 2002) (Fig. 1). Two major stratigraphic unitsare defined in the ADOB: the lower Aravalli Supergroup and theupper Delhi Supergroup (Fig. 2). The ADOB is divided into north-ern and southern “belts” with strata of both the Aravalli andDelhi supergroups recognized in the southern belt, whereas allstrata of the northern belt are classified as Delhi Supergroup, andthus it is commonly termed the “North Delhi Belt”. At least twomajor tectonothermal events are recorded in the ADOB that canbe broadly defined as late Paleoproterozoic (1.9–1.6 Ga) and lateMesoproterozoic–early Neoproterozoic (1.1–0.8 Ga) in age (Debet al., 1989, 2001; Buick et al., 2006; Bhowmik et al., 2010; Meertet al., 2010).

The Aravalli Supergroup overlies the ∼2.5 Ga Banded GneissComplex-I (BGC-I) Deb and Sarkar, 1990 (Deb et al., 1989;Wiedenbeck et al., 1996; Buick et al., 2006; Meert et al., 2010;Pradhan et al., 2010) and is divided into lower, middle andupper groups. The Lower Aravalli Group includes the basal Del-wara Formation, which consists mostly of siliciclastic strata withinterspersed volcanics, and the overlying carbonate-dominated

VINDHYAN SUCCESSIONS

Aravalli Sgr.

Lower Aravalli Gr.

Delwara Fm.Jhamarkotra Fm.

Middle Aravalli Gr.Upper Aravalli Gr.

Delhi Sgr. Ajabgarh Gr.Alwar Gr.

Upper Vindhyan

Lower Vindhyan

Bhander Gr.Rewa Gr.Kaimur Gr.

Semri Gr.

ARAVALLI-DELHI OROGENIC BELT

mixed siliciclastic-carbonatesiliciclasitic dominated

siliciclastic dominated

siliiclastic with interspersed mafic volcanics

carbonate dominated

mixed siliciclastic-carbonatesiliciclastic dominatedsiliciclastic dominated

mixed siliciclastic-carbonate

siliciclastic dominated

Fig. 2. Simplified stratigraphic nomenclature and general lithologies for strata ofthe Aravalli–Delhi Orogenic Belt and the Vindhyan successions (units listed in strati-graphic order). Sgr. = Supergroup; Gr. = Group; Fm. = Formation.

Jhamarkotra Formation, which contains localized phosphorite(Banerjee, 1971; Banerjee et al., 1986). It has been suggested thatthe Aravalli Supergroup was deposited in a series of “sub-basins”along an active rift margin (Roy and Paliwal, 1981; Roy and Jakhar,2002) but, just as with the definition of the Purana Basins, theso-called “sub-basins” of the Aravalli Supergroup are defined bymodern day outcrop limits and lithological facies variations, pri-marily the presence or absence of phosphatic stromatolites. Asa result, these sub-basins have been subsequently divided into“phosphatic” and “non-phosphatic” domains (Papineau et al., 2009,2013; Purohit et al., 2010). Their status as isolated basins dur-ing deposition has yet to be adequately verified, as there are no

Fig. 1. (a) Small-scale map illustrating locations of major Purana Basins of India (ADOB = Aravalli–Delhi Orogenic Belt; RV = Rajasthan Vindhyan; SV = Son Valley Vindhyan;Ch = Chhattisgarh Basin, IB = Indravati Basin; Cu = Cuddapah Basin; CITZ = Central Indian Tectonic Zone). (b)Simplified Geologic map of Vindhyan and Aravalli successions(modified after Buick et al., 2006; Malone et al., 2008). Published data: NAQ = Northern Alwar Quartzite (Kaur et al., 2011); RVB = Rajasthan Vindhyan Bhander Group (Maloneet al., 2008); SVS, SVK, SVR, and SVB = Son Valley Semri, Kaimur, Rewa, and Bhander groups, respectively (McKenzie et al., 2011). GPS coordinates for sample localities:RSV1 = 24◦ 50.513′ N, 74◦ 35.458′ E; RSK1 = 24◦ 53.750′ N, 74◦ 38.586′ E; RA05 = 24◦ 27.492′ N, 73◦ 52.372′ E; RA10 = 24◦ 49.971′ N, 73◦ 46.029′ E; RA11 = 24◦ 36.002′ N, 73◦

40.688′ E; RD4 = 24◦ 45.173′ N, 73◦ 21.510′ E.


122 N.R. McKenzie et al. / Precambrian Research 238 (2013) 120– 128

well-constrained synsedimentary faults or evidence for basementonlap of strata between the sub-basins. This, combined with lithos-tratigraphic similarities between “sub-basin” deposits throughoutthe region, supports arguments against the suggestion that thesesedimentary units were originally laterally discontinuous or thateach “sub-basin” was a separate depositional system. Furthermore,regardless of the validity of the sub-basin model, Papineau et al.(2013) used integrative data to argue for contemporaneous depo-sition of the Jhamarkotra Formation strata throughout the region.

The Lower Aravalli Group is considered to have depositionalages from 2.1 to 1.9 Ga, although geochronologic constraints forthis age range are contentious. A minimum age constraint is ofteninferred from a ∼1.9 Ga Rb–Sr isochron for the Darwal granitethat is believed to intrude the base of the Lower Aravalli Group(Choudhary et al., 1984). However, Deb and Thorpe (2004) noteda complicated contact relationship between the Darwal intrusionand basal Aravalli strata, and questioned its usefulness for provid-ing a minimum age constraint. Ahmad et al. (2008) presented aseries of whole-rock Sm–Nd model ages for ultramafic–mafic vol-canic rocks in the basal Delwara Formation that ranged from 2.3to 1.8 Ga. The wide range of calculated ages for this series of vol-canic flows (a ∼0.5 billion year interval) illustrates a problem withusing these data for reliable age constraints. Sparse Pb–Pb modelages from galena extracted from barite veins in Delwara volcanicsyielded ages around 2.1–2.0 Ga, whereas the majority of Pb–Pbgalena model ages from various units within the Lower AravalliGroup consistently yielded ages around 1.8–1.7 Ga (Deb et al., 1989;Deb and Thorpe, 2004). A 2.2–2.0 Ga depositional age has also beensuggested for the Jhamarkotra Formation based on correlation ofanomalously 13C-enriched carbonate in the Jhamarkotra Forma-tion with the Lomagundi–Jatuli isotope excursion (Sreenivas et al.,2001; Maheshwari et al., 2002, 2010; Purohit et al., 2010; Papineauet al., 2009, 2013), as this global event is roughly constrained tobetween 2.3 and 2.05 Ga (Melezhik et al., 2007).

The Delhi Supergroup is divided into the lower Alwar andupper Ajabgarh groups with depositional ages suggested to rangebetween 1.7 and 1.5 Ga (Choudhary et al., 1984). However, recentage data for the Delhi Supergroup are conflicting. Strata of the NorthDelhi Belt are well constrained to 1.8–1.7 Ga with minimum andmaximum age depositional ages provided by cutting relationshipof intrusive igneous rocks and detrital zircon age data, respectively(Biju-Sekhar et al., 2003; Kaur et al., 2011), whereas rocks associ-ated with the upper Delhi Supergroup in the southern belt may be asyoung as ∼1.0 Ga (Deb et al., 2001). It is also noteworthy that DelhiSupergroup rocks of the southern belt lack ∼1.7 Ga intrusive rocksknown from the North Delhi Belt, and these strata have not yieldedPb–Pb model ages older than ∼1.0 Ga (Deb and Thorpe, 2004).

2.2. Vindhyan successions

The Great Boundary Fault marks the eastern limits of the ADOBand is the present structural boundary with the Vindhyan basin. TheVindhyan basin is regionally divided into the western Rajasthan andeastern Son Valley sectors (Fig. 1). Vindhyan strata are divided intolower and upper successions by a prominent unconformity, withthe lower Vindhyan succession consisting of the Semri Group andthe upper Vindhyan succession consisting of the Kaimur, Rewa, andBhander groups, in ascending order (Fig. 2). The upper part of theSemri Group is well dated at ∼1.6 Ga (Rasmussen et al., 2002; Rayet al., 2002; Ray, 2006; Bengtson et al., 2009), and strata of the upperVindhyan succession are constrained to between ∼1.1 and 1.0 Ga(Gregory et al., 2006; Malone et al., 2008; McKenzie et al., 2011;Pradhan et al., 2012; Gopalan et al., 2013). Thus, the unconformitybetween the upper and lower Vindhyan successions represents anapproximate 500 million year interval.

3. Methods

Detrital zircon geochronology has proven useful for establish-ing depositional age constraints on siliciclastic strata and resolvingcorrelation problems across the Indian craton (e.g., Malone et al.,2008; McKenzie et al., 2011). In this study, new detrital zircon U–Pbage data were generated from siliciclastic rocks of the Aravalli andDelhi supergroups of the southern ADOB and Vindhyan successionsof Rajasthan (Figs. 3 and 4). Individual zircon grains were separatedusing standard heavy mineral separation procedures and analyzedby means of laser ablation multicollector inductively coupled massspectroscopy (LA-MC-ICPMS) at the University of Arizona Laser-Chron Center (see supplementary materials for analytical detailsand data tables). Back-scattered electron (BSE) images of polishedgrain mounts were used to help target portions of zircon grains withclear growth zoning for spot analysis and to avoid inherited cores,un-zoned rims, and fractures. Sandstone samples analyzed from theAravalli Supergroup include the basal Delwara Formation (RA10),the Jhamarkotra Formation (RA5), and the Middle Aravalli Group(RA11). A Delhi Supergroup sample was analyzed from the AlwarGroup (RD4). Vindhyan samples collected near Chittorgarh includethe Semri (RSV1) and Kaimur groups (RVK1). Unfortunately, sam-ples collected from the Upper Aravalli Group and the AjabgarhGroup of the upper Delhi Supergroup did not yield zircon grains.

4. Results and discussion

4.1. Revised ages for the Aravalli Supergroup

The basal Delwara Formation sample (RA10) contains a range ofArchean zircon grains with only a single concordant zircon youngerthan ∼2.5 Ga, which yielded a 207Pb/206Pb age of 1709 ± 8 Ma. TheJhamarkotra Formation sample (RA05) contains a large populationof 1.9–1.7 Ga detrital zircon (∼1772 Ma age peak) and the youngestsingle grain yielded a 207Pb/206Pb age of 1762 ± 9 Ma. A samplefrom the middle Aravalli group (RA11) contained a broad popula-tion of 1.8–1.6 Ga detrital zircon with abundant ∼2.5 Ga grains andthe single youngest zircon yielded a 207Pb/206Pb age of 1576 ± 7 Ma(Fig. 4).

The single 1709 ± 8 Ma grain provides a problematic age con-straint for the Delwara Formation. The Delwara sample wascollected less than 10 m above the depositional contact with theBGC-I basement. The large population of Archean grains was likelyderived directly from proximal BGC-I rocks, and the near-absenceof ∼1.7 Ga grains might be the result of dilution from locally deriveddetritus. A similar dilution problem may exist with a sample fromthe Semri Group of the lower Vindhyan succession (discussedbelow). The possibility that the single ‘young’ 1709 ± 8 Ma grainresulted from contamination during sample processing must alsobe considered, although this is unlikely as grains around this par-ticular age are not common in any sample. Alternatively, the single‘young’ grain may represent an inaccurate age from erroneousmeasurement or later alteration of the grain through Pb loss ormetamorphic overprinting during a ∼1.7 Ga tectonothermal event(see Buick et al., 2006). Therefore, the single ∼1.7 Ga grain onlyprovides a tentative age constraint for the Delwara Formation andfurther investigation of this unit is required.

The presence of a large population of 1.9–1.7 Ga zircon grains inthe Jhamarkotra Formation nullify assertions of 2.2–2.0 Ga depo-sitional ages for the formation and for all overlying strata of theAravalli Supergroup. The detrital zircon data presented here con-strain only the maximum depositional age. However, Deb et al.(1989) reported numerous ∼1.7 Ga Pb–Pb model ages for syn-genetic ore deposits associated with the Jhamarkotra Formationthat provide tentative minimum depositional age constraints for



Fig. 3. (a) Semri Group sample locality (RSV1): fluvial feldspathic pebble to very coarse grained sandstone/conglomerate overlying cross-bedded coarse-medium grainedsandstone; (b) Kaimur Group sample locality (RVK1): wave ripple imprints on sole of bed; (c) Delwara Formation sample locality (RA10): massive quartzite above BGC-Icontact; (d) Jhamarkotra Formation locality (RA05): fresh surface of white massive, medium-grained sandstone of the Jhamarkotra Formation; (e) cut and polished sectionof Delwara Formation sample (RA10); (f) cut and polished section of Jhamarkotra Formation sample (RA05).

the unit. Therefore, the Jhamarkotra Formation is interpreted tohave a ∼1.7 Ga depositional age. This age is further supported by alack of younger ∼1.6 Ga zircon grains that are present in the overly-ing Middle Aravalli Group and a lack of Mesoproterozoic grains thatare common in younger strata of the ADOB and other Indian cra-tonic successions (e.g., Malone et al., 2008; McKenzie et al., 2011)(Fig. 4). The Aravalli region experienced considerable magmaticactivity between 1.9 and 1.7 Ga (Deb et al., 2002; Biju-Sekhar et al.,2003; Buick et al., 2006; Kaur et al., 2007, 2009), with Andean-type

subduction and arc magmatism postulated along the margin(Kaur et al., 2009, 2013). A similar contemporaneous tectonicsetting existed along the north Indian margin as well (Kohn et al.,2010). The abundance of relatively young 1.9–1.7 Ga zircon grainsin the Jhamarkotra Formation may result from syntectonic deposi-tion along the active convergent margin, which is common alongsimilar tectonic settings (e.g., Cawood et al., 2012). The introduc-tion of younger ∼1.6 Ga zircon grains into the Middle Aravalli groupis consistent with a younger depositional age for this unit.



0.5 1.0 1.5 2.0 2.5 3.0 3.5 Age (Ga)

RA10-040112

Delwara Fm.

n = 96

RA5-033112

Jhamarkotra Fm.

n = 73

RA11-040112

Middle Aravalli Gr.

n = 77

RD4-040512

Alwar Gr.

n = 98

RVS1-032712

Semri Gr.?

n = 50

RVK1-032712

Kaimur Gr.

n = 81

Bhander Gr.

n = 196

(Malone et al.,2008)

0.5 1.0 1.5 2.0 2.5 3.0 3.5 Age (Ga)

Semri Gr.

n = 84

McKenzie et al., (2011)

Kaimur Gr.

n = 94


Rewa Gr.

n = 83


Bhander Gr.

n = 52


0.5 1.0 1.5 2.0 2.5 3.0 3.5 Age (Ga)

Southern Aravalli-Delhi Belt Rajasthan Vindhyan Son Valley Vindhyan

Ea

rlie

r

Pa

leo

pro

tero

zo

ic?

La

te

Pa

leo

pro

tero

zo

ic

La

te M

es

op

rote

rozo

ic-

Ea

rly

Ne

op

rote

rozo

ic

REGIONAL UNCONFORMITY

? ? ?

??

1187

1175 1586

1586

1172

1709 (n = 1)

1586

1772

1870 (n = 2)

17721596

1174

17291554

1713

1851

1003

16471729

17721646

12121589

1022

1713

Relative Probability

Fig. 4. Detrital zircon age distributions and suggested correlation of strata from the southern Aravalli–Delhi Orogenic Belt and the Vindhyan successions.

4.1.1. Late Paleoproterozoic phosphatic stromatolites in northIndia

The Jhamarkotra Formation sample analyzed for detrital zircongrains was collected stratigraphically below the phosphatic carbon-ate in the Jhamarkotra mine. The ∼1.7 Ga maximum depositionalage for the Jhamarkotra Formation nullifies the interpretationthat this unit was deposited during a ∼2.0 Ga global phospho-genic event following the Great Oxidation Event (Papineau et al.,2009, 2013; Papineau, 2010). Phosphatic stromatolites are knownin ca. 1.6 Ga late Paleoproterozoic rocks in both the upper SemriGroup of the lower Vindhyan succession and the GangolihatDolomite of the Lesser Himalaya (e.g., Valdiya, 1969; Banerjeeet al., 1986; McKenzie et al., 2011). The Himalayan–Vindhyanphosphatic deposits consist of branching columnar stromatoliticbioherms with columns exceeding 10 cm in diameter. The phos-phatic horizons in those deposits are restricted to within only afew meters of the bioherm with the phosphate occurring in theinter-columnar spaces as phosphatic grainstone, as coatings onterrigenous material, and as crusts on the stromatolite columns,whereas the stromatolite build-ups themselves are mostly dolo-stone (Banerjee et al., 1986; Bengtson et al., 2009; McKenzie et al.,2011). In both the Vindhyan and Himalayan deposits the phos-phate does not occur throughout the stromatolitic lamination, andthe phosphatic crusts around the individual columns appear topinch-out along the stromatolitic heads in a discrete interval of thebioherms (e.g., McKenzie et al., 2011). These specific similaritiesmay suggest a common mode of phosphogenesis in both regions.

The phosphate-bearing Jhamarkotra stromatolitic bioherms areup to 10’s of meters in stratigraphic thickness (e.g., Banerjee,1971) and are dominated by infrequently branching, elongate

columnar stromatolites that are only a few centimeters indiameter (Fig. 5). In the Jhamarkotra deposits the stromatoliticcolumns are phosphatic, with the intercolumnar space consistingprimarily of massive dolostone. Therefore, there are some differ-ences in mode of carbonate-fluorapatite deposition between theHimalayan–Vindhyan and Jhamarkotra phosphatic stromatolites,despite both being shallow water, stromatolitic phosphorites. Thesimilar age among all of these phosphatic deposits suggests theremay have been similar over-arching controls on carbonate fluo-rapatite precipitation across the north Indian margin during thelate Paleoproterozoic. Whatever the cause, various stromatolitebioherms created local environments that permitted phosphogen-esis in northern India during this discrete interval of time. This isnoteworthy given the general dearth of Precambrian phosphorites.

4.1.2. A mid-Proterozoic ı13C excursion?The revised age determination for the Lower Aravalli Group also

brings into question claims that �13C enrichments in the Jhamarko-tra Formation are related to the ∼2.1 Ga Lomagundi–Jatuli event.The Jhamarkotra Formation has yielded variable �13C values. Phos-phatic horizons yield �13C values around 0‰ whereas thick sectionsof massive dolostone yield variable �13C values that range up to+11‰ (Sreenivas et al., 2001; Maheshwari et al., 2002, 2010; Purohitet al., 2010). Nitrogen and organic carbon isotopic values are sim-ilar for both phosphatic and non-phosphatic sections (Papineauet al., 2013). The dolostone with isotopically heavy carbon val-ues is considered to sit stratigraphically below the phoshpatichorizons (e.g., Sreenivas et al., 2001). Following the argumentsof Papineau et al. (2013) for contemporaneous deposition of all



Fig. 5. Phosphatic stromatolites of the Jhamarkotra Formation from the Jhamarkotra mine. (a) Out-of-place block with cross-sectional view of stromatolitic columns. Arrowpoints in “up” direction as inferred from stromatolitic laminae. (b) Polished cross-section of stromatolitic column. Note white phosphatic stromatolitic column and dark graydolostone filling intercolumnar space. (c) Quasi-planar view of stromatolitic bioherm. (d) Polished quasi-planar section of stromatolitic bioherm. Scale bars = 2 cm.

Jhamarkotra strata, the 13C-rich Jhamarkotra deposits would havebeen deposited around ∼1.7 Ga.

The positive values in the Jhamarkotra Formation are likelyto record depositional �13C signatures. Foremost, the carbonatesare found in a relatively pure, organic-lean carbonate succession(rather than a carbonate-cemented siliciclastic unit) and most dia-genetic processes drive the �13C values negative. The fact that theisotope excursion is found in a thick (>55 m stratigraphic inter-val) unit with �13C values exceeding +7‰ (Maheshwari et al., 2002,2010) also points toward a depositional, rather than diagenetic,origin for the anomalous �13C values; typical methanic-zone �13Cenrichment in carbonate constitutes a relatively minor aspect ofsedimentary successions (e.g., Irwin et al., 1977). Although theJhamarkotra Formation has been metamorphosed to greenschistfacies (Papineau et al., 2009, 2013), a metamorphic origin of theanomalously high positive carbonate �13C values is highly unlikely.Therefore, all available evidence suggests that the Jhamarkotra For-mation may host a previously unidentified late Paleoproterozoicpositive �13C excursion (Fig. 6).

The prevailing view is that the mid-Proterozoic (1.8–0.8 Ga)was characterized by carbonate isotope and general biogeochem-ical stasis (Brasier and Lindsay, 1998), which has given rise tothe moniker the ‘boring billon’ (e.g., Holland, 2006). The potentialimplications of a billion years of carbon isotope stasis have beenfar reaching. For example, this framework has shaped models ofeukaryotic diversification (e.g., Anbar and Knoll, 2002), and playeda central role in models of environmental change and carbon iso-tope chemistry bracketing the Proterozoic (e.g., Swanson-Hysellet al., 2010; Bekker and Holland, 2012). If both the age and pri-mary nature of this isotope excursion are corroborated, and if it infact reflects global-scale marine processes, the presence of a signifi-cant late Paleoproterozoic positive carbon isotope excursion would

-4048

1216

Phaner. ProterozoicNeo- Meso- Paleo-

ArcheanMeso- Paleo-Neo-

0 0.5 1.0 1.5 2.0 2.5-4048

12

3.0 3.5

16

Age (Ga)

Lomagundi Excursion

‘Boring Billion’Great Oxidation

Event

δ13C (

‰, V

-PDB

) δ13

C (‰

, V-P

DB) Aravalli

Excursion

a

b

Fig. 6. (a) A generalized carbonate carbon isotope curve through time and (b) arevised curve assuming a ca. 1.7 Ga depositional age for the Jhamarkotra Formationbased on a new maximum age constraints presented here (modified from Planavskyet al. (2012)).

dramatically affect views of the evolution of the carbon cycle duringthe Precambrian. Given the potential for the Jhamarkotra Forma-tion to fundamentally reshape our view of biogeochemical cyclingfor a billion years of Earth’s history, additional work to rigorouslytest the validity of a ca. 1.7 Ga positive carbonate carbon isotopeexcursion is certainly warranted.

4.2. Revised ages of the Delhi Supergroup and miscorrelation ofthe North and South Delhi belts

A sample from the Alwar Group (RD4) of the southern DelhiSupergroup possesses a large population of 1.2–1.1 Ga detritalzircons (∼1187 Ma age peak) (Fig. 7). Therefore, the southernDelhi Supergroup cannot be 1.9–1.7 Ga as previously asserted. The∼1.2 Ga depositional age constraint together with reports of 987 ± 6



Alwar Group

North Delhi Belt

n = 14 4

(Kaur et al., 2011)

0.5 1.0 1.5 2.0 2.5 3.0 3.5 Age (Ga)

Alwar Group

South Delhi Belt

n = 98

Fig. 7. Comparison of detrital zircon age distributions from the so-called AlwarGroup from the northern and southern ADOB.

and 986 ± 2 Ma rhyolites associated with the uppermost part of theDelhi Supergroup (Deb et al., 2001) brackets the depositional agesof the southern Delhi Supergroup between ∼1.2 and ∼1.0 Ga. Theage distribution from the southern sample differs from publishedage data from the Alwar Group of the North Delhi Belt (Kaur et al.,2011) as the northern sample contains a large population of ∼1.7 Gazircon grains with nothing younger (Fig. 7). A potential age discrep-ancy between the northern and southern Delhi groups has beenpreviously recognized (Biju-Sekhar et al., 2003), although this dis-crepancy was attributed to differences in tectonic history of each“basin”. On the basis of data presented here, we suggest that thediscrepancy results from a longstanding miscorrelation of stratabetween the two regions.

The age distribution from the ∼1.7 Ga northern Alwar Group issimilar to the Jhamarkotra Formation, which we have estimatedto have a depositional age of ∼1.7 Ga. Based on the similar depo-sitional ages and detrital zircon age distributions, strata of theso-called North Delhi Belt likely represent the northern equiv-alents of the Aravalli Supergroup. Kaur et al. (2013) suggestsyntectonic deposition for strata of the North Delhi Belt alongan active continental arc system and based on data presentedherein, we suggested a similar depositional environment for theAravlli Supergroup. Deposition along a convergent margin con-trasts the long-standing hypothesis that the Aravalli Supergroupwas deposited along an active rift margin.

4.3. The Rajasthan Vindhyan successions and correlation acrossthe north Indian margin

Forty-eight of the fifty zircon grains analyzed from the SemriGroup sample (RVS1) yielded 207Pb/206Pb ages between 2515 ± 4and 2588 ± 41 Ma and the two other grains yielded ages of 1877 ± 7and 1885 ± 17 Ma. This sample was acquired from coarse-grainedfeldspathic sandstone (Fig. 3a) and the abundance of ∼2.5 Ga zircongrains likely reflects almost exclusive derivation of detritus froma proximal ∼2.5 Ga felsic igneous source. The two ∼1.8 Ga grainsare close in age to the 1854 ± 7 Ma volcanic Hindoli rocks located∼150 km northeast of the Semri Group locality (Deb et al., 2002),as well as ∼1.9–1.7 Ga plutons of the North Delhi Belt (e.g., Biju-Sekhar et al., 2003; Kaur et al., 2009, 2013), and the BGC-II of thesouthern ADOB (Buick et al., 2006). The Semri Group age distribu-tion from Rajasthan is considerably different from a Semri Groupage distribution from the Son Valley (Fig. 3) and direct correla-tion between these regions is not possible based on data presented

here. Kaimur Group sandstone (RVK1) contains large populationsof ∼1.2 Ga (∼1175 age peak) and ∼1.6 Ga zircon grains. This is simi-lar to both a published age distribution from the Son Valley KaimurGroup, which also produced a youngest age peak of ∼1172 Ma, andage distributions from both the Rajasthan and Son Valley Bhandergroups (McKenzie et al., 2011) (Fig. 4). Together, these similaritiessupport correlation of upper Vindhyan successions between theRajasthan and Son Valley sectors.

While the abundance of grains from distinct age populationswithin each distribution is variable, the Kaimur Group distribu-tions are strikingly similar to the age distribution of the southernDelhi Group. Most notable are the similar age peaks around ∼1.2and ∼1.6 Ga in the Rajasthan Kaimur Group and Delhi Group, withboth samples lacking ∼2.5 Ga grains, which are common in all otherage distributions (Fig. 4). Overall, strata of the ADOB have similarage-relationships to lower and upper Vindhyan successions, andit is suggested here that the Aravalli–Delhi supergroups representthe tectonically deformed equivalents of the Vindhyan successions,with the Aravalli–Delhi supergroups separated by the same ∼500million year unconformity present in the Vindhyan successions(Fig. 4). The similarity of detrital zircon age distributions in theVindhyan successions and strata of the ADOB likely resulted fromshared sediment sources, and thus these strata were deposited aspart of a contiguous margin with Vindhyan strata deposited inepicontinental settings and the Aravalli deposited along the con-tinental margin, rather than in discrete isolated basins as generallyassumed.

5. Conclusions

We provide new age constraints on the sedimentary succes-sion of the ADOB. The Aravalli Supergroup is constrained to be latePaleoproterozoic in age. The Jhamarkotra Formation has an esti-mated depositional age of ∼1.7 Ga. Based on these revised ages, it isdoubtful that the positive carbonate �13C values measured in thisunit are linked to the 2.2–2.0 Ga Lomagundi–Jatuli event. There-fore, this presents the intriguing possibility of an unrecognized latePaleoproterozoic positive �13C excursion. If verified, this would callinto question the idea of mid-Precambrian carbon isotope stasis,which has become a key facet of current models on the evolutionof biogeochemical cycling in the Precambrian.

The Delhi Supergroup of the southern ADOB has a depositionalage range of 1.2–1.0 Ga and is not correlative with the Delhi Super-group of the North Delhi Belt. Strata of the northern belt arelikely correlative with the Aravalli Supergroup. These late Paleo-proterozoic strata were deposited syntectonically along an activeconvergent margin, rather than an active rift margin. Age rela-tionships of the Aravalli–Delhi supergroups reflect those of thelower–upper Vindhyan successions and similar age distributionsof detrital zircon grains from all regions are used to suggest thatthese strata were deposited across a contiguous margin, with Vin-dhyan strata representing epicontinental deposits and strata of theADOB representing the distal continental margin equivalents.

Acknowledgements

We thank Dr. N.K. Chauhan for local support in Udaipur, G.Gehrels, M. Pecha, and N. Giesler for analytical assistance atthe Arizona LaserChron Center, JS. Lackey for providing facilitiesand assistance for sample processing, and C. Lee for analyticalassistance. Comments from M. Bickford, S. Long, J. Meert, H. Frim-mel, and anonymous reviewers greatly improved the manuscript.This work was supported by National Science Foundation GrantsEAR-1124303 to N. Hughes and EAR-1124518 to P. Myrow. McKen-zie acknowledges the UT Austin Jackson Postdoctoral Fellowship



Program and N. Planavsky acknowledges the NSF-EAR-PostdoctoralFellowship Program. The Arizona LaserChron Center is supportedby NSF-EAR-0732436.

Appendix A. Supplementary data

Supplementary data associated with this article can befound, in the online version, at http://dx.doi.org/10.1016/j.precamres.2013.10.006.

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