Regressive depositional architecture on a Mesoproterozoic siliciclastic ramp: Sequence stratigraphic and Nd isotopic evidences from Bhalukona Formation, Singhora Group, Chhattisgarh

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Precambrian Research 200– 203 (2012) 129– 148

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egressive depositional architecture on a Mesoproterozoic siliciclastic ramp:equence stratigraphic and Nd isotopic evidences from Bhalukona Formation,inghora Group, Chhattisgarh Supergroup, central India

artha Pratim Chakrabortya,∗, Priyabrata Dasb, Kaushik Dasb, Subhojit Sahaa, S. Balakrishnanc

Department of Geology, University of Delhi, Delhi 110007, IndiaDepartment of Earth Sciences, Bengal Science and Engineering University, Howrah 711103, IndiaDepartment of Earth Sciences, Pondicherry University, Pondicherry, India

r t i c l e i n f o

rticle history:eceived 6 July 2011eceived in revised form1 December 2011ccepted 17 January 2012vailable online xxx

eywords:halukona Formationhhattisgarh Supergroupaleofacies analysism–Nd isotopic signaturesorced regression

a b s t r a c t

A paleo-environmental and sequence stratigraphic study of the Mesoproterozoic Bhalukona Formation,Singhora Group, central India provides new interpretations applicable to understanding sedimentationand stratigraphic architecture in the Proterozoic siliciclastic ramp settings under falling and lowstand sealevel conditions. Beside delineation of two diachronous surfaces, process-based facies analysis identifiedfourteen facies types that are grouped under five different facies associations. Paleo-environments rangeamong continental fluvial, beach-foreshore, upper shoreface, lower shoreface and wave-dominated deltafront. From the paleocurrent measurement within the fluvial channel sandstones and measurement ofcrest line orientations of wave generated swash bedforms, it is inferred that the Bhalukona Sea had NNE-SSW shoreline trajectory and the south-easterly flowing river system carried sediment on the shorelinefrom a source in the west-northwest. Such inference though in clear discordance with the earlier proposedsouth-southeastern sediment source for the Singhora basin, finds support in the shift in εt

Nd (t = 1.42 Ga)values (from −3.5 ± 3.3 to −9.3 ± 2.2) indicating change in sediment provenance at the early Bhalukonasedimentation history; sediments in the Bhalukona Formation derived from more evolved or older con-tinental crustal sources in comparison to those of the underlying Saraipalli Formation. A tectonic forcingbehind the shift in sediment provenance and fall in relative sea level is inferred that established the forcedregressive and lowstand shoreline in the Singhora basin during the Bhalukona time.

Abrupt basin-ward shift of facies tract and incision on shelf is exhibited by the occurrence of poorlysorted, coarse granular Bhalukona fluvial system (carrying rip-up mud clasts) directly above the argilla-ceous highstand Saraipalli shelf with ∼10 m incision and is inferred as the signal for forced regression anddevelopment of Type-I sequence boundary. In low-gradient Proterozoic ramp settings without shelf-slopebreak, we interpret that the Bhalukona fluvial system incised the coastal prism developed on the Saraipallihighstand coastline. The low-gradient of the ramp, however, prompted long distance (∼15 km) regressionrepresented by the offlapped and detached delta front lobe away from the shoreline. The slow, steadyrise in sea level, onset of lowstand and establishment of a wave-dominated coastline caused reworkingof fluvial sediments in the basinal part (within the wave base) and resulted development of ravinementdeposit. Basin-ward, the surface grades into correlative conformity. With aggradational and weak ret-

rogradational stacking the beach-foreshore, upper- and lower-shoreface, in order of superposition, recordthe lowstand depositional history. The basin-scale transgression is witnessed with formation of Trans-gressive surface of erosion (TSE) and establishment of the Chuipalli shelf system, dominantly beyondstorm wave base. Taking into consideration ∼23 m preserved shoreface succession, 1 m per year eustaticrise consistent with present day rate and average rate of shoreface retreat 0.5 m per year, ∼11.5 km retreatfor the Bhalukona shoreline is estimated in its lowstand history.

∗ Corresponding author.E-mail address: [email protected] (P.P. Chakraborty).

301-9268/$ – see front matter © 2012 Published by Elsevier B.V.oi:10.1016/j.precamres.2012.01.004

© 2012 Published by Elsevier B.V.

1. Introduction

Interest shown by sedimentologists, stratigraphers and explo-rationists for the products of sea level regression stem not onlyfrom the urge of understanding the timing and forcing/s of breakin sedimentation and unconformity formation, but also from

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he appraisal that the products of regressive shoreline representany of the largest and most significant hydrocarbon reserves

round the World. Application of sequence stratigraphic insight onegressive shoreline successions allow distinction between prod-cts deposited under three different ‘Systems tract’s of varyingelative base level positions, i.e., from highstand (HST) throughalling (forced regression; FSST) to early rise (Lowstand; LST)Posamentier and Allen, 1993; Walker and Wiseman, 1995; Huntnd Gawthorpe, 2000). Because the three regressive trends occupypecific stratigraphic position, distinctions between their prod-cts are convincingly done in subsurface dataset where preservedecords are undisturbed by later effects. Incomplete stratigraphicecord often results in tentative field-based interpretation (see

alker and Wiseman, 1995; MacEachern et al., 1998 for review).he complexity increases further in case of long-distance regres-ion in low-gradient ramp setting where a zone of bypass separateshe products of forced regression located in basin margin andhe deposits of lowstand located further seaward (Christe-Blickt al., 1995; Hunt and Gawthorpe, 2000). Low-gradient Protero-oic shelves without shelf-slope break may offer an ideal set-upo investigate and document products of long-distance regres-ion, more so if the basin is forced by flexural tectonics, whereintages of subsidence (and base level rise) are significantly shortern time relative to the stages of isostatic renounce (base level fall)Catuneanu, 2004). Despite the understanding, such studies aretrikingly restricted (Gehling, 2000; Sarkar et al., 2001; Chakrabortynd Paul, 2008), principally because of limited interest shown byydrocarbon sector in Precambrian successions. Moreover, limita-ions are inherent in application of sequence stratigraphic rationalen Precambrian sedimentary successions because chances for over-ooking marker horizons (unconformity, ravinement, maximumooding, etc.) are high in these basin-fills in absence or sparsevailability of biostratigraphic and chronostratigraphic controlChriste-Blick et al., 1995).

Encroachment of continental or shallow marine system on dis-al shelf is resulted both in fall (forced regression) and slow riselowstand) of base level. Whereas forced regressive products over-ie regressive surfaces of erosion cut by wave action during thealling stage of relative sea level (regressive surface of marinerosion; RSME), the lowstand shoreline overlies the marine partf the sequence boundary, also cut by wave erosion. As forcedegressive deposits are often not preserved in the stratigraphicecord because of erosion both at sea level fall and subsequentea level rise, their absence thus result in putative stratigraphicomenclature for the detached erosive-based shoreface complexesforced regressive or lowstand) (Posamentier and Morris, 2000).or example, the sharp-based shoreface sandstone units have beenariably assigned to progradation of late highstand successionse.g., Van Wagoner, 1995), forced regression (falling stage) sys-ems (e.g., Hunt and Tucker, 1992; Walker and Bergman, 1993;ergman, 1994; Davies and Walker, 1993) or lowstand systemse.g., Posamentier et al., 1992; Posamentier and Chemberlain, 1993;

ellere and Steel, 1995; Walker and Wiseman, 1995) in litera-ure.

The present article is an attempt in this direction as it dealsith depositional facies, facies associations and cross-basin cor-

elation for a Mesoproterozoic arenaceous succession from centralndia, i.e., the Bhalukona Formation, Singhora Group, Chhattisgarhupergroup. This field-based study aims towards, (i) identifica-ion of depositional discontinuities through sequence stratigraphicationale, (ii) differentiation between the regressive products -orced and lowstand, and (iii) documentation of relative domi-

ance of continental and shallow marine agents (fluvial, wave andide) in different ‘Systems tracts’. From stratigraphic architecturehe paper describes products of two ‘Systems tracts’ viz. fallingnd lowstand in regressive Bhalukona depositional history. Though

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the study is essentially field-based, clues obtained from sedimentpetrographic modal analysis and Nd-isotope geochemistry helpedin constraining paleo-environmental settings and operative depo-sitional agencies at different stages of ‘Systems tract’ developmentbesides provenance analysis.

2. Geological setting and age control

The Chhattisgarh Supergroup, Proterozoic epicratonic succes-sion in Peninsular India, comprises ∼2300 m thick succession ofmixed siliciclastic–carbonate strata that unconformably overliegranitic/gneissic basement of Bastar craton (Fig. 1a) and is clas-sified into three Groups, viz. Singhora Group, Chandarpur Groupand Raipur Group (Das et al., 1992; Fig. 1b). With ∼400 m thick-ness, the Singhora Group of rocks (200 km2 in aerial extent) isclassified under four lithostratigraphic Formations viz. Rehtikhol,Saraipalli, Bhalukona and Chuipalli, in order of superposition(Fig. 1b and c). Whereas the coarse arenaceous Rehtikhol Formationexemplifies a pre-vegetation alluvial fan and braid-delta deposi-tional set-up (Chakraborty et al., 2009), the argillaceous Saraipalliand Chuipalli Formations represent widely varying shelf condi-tion ranging between storm-infested inner shelf and distal outershelf below the storm wave base. From the fining-upward stack-ing of alluvial fan – braid-delta – shelf succession, Chakrabortyet al. (2009) postulated a deepening-upward transgressive deposi-tional motif across the Rehtikhol- Saraipalli transition in the earlySinghora sedimentation history. Except for the short perturba-tion/s, represented by the Bhalukona sandstone (discussed later),the deepening tendency continued up to the Chuipalli Formation.Distal shelf green/black shales without any large-scale wave orcurrent structure represent the Chuipalli Formation (Das et al.,2001). A stratified tuffaceous unit present at the contact betweenthe Rehtikhol and Saraipalli Formation has yielded ∼1500 Ma agethrough EPMA U–Th–Pb monazite dating (Das et al., 2009) and1405 ± 9 Ma age through U-Pb SHRIMP zircon dating (Bickford et al.,2011). Recently, diabasic intrusive within Saraipalli Formation hasyielded an emplacement age of 1421 ± 23 Ma (Das et al., 2011).Recent data thus firmly establish a Mesoproterozoic time framefor the Singhora succession.

Detailed regional- to outcrop-scale structural mapping withinthe Singhora basin identified definite signatures of compressionaldeformation in basin-scale (Fig. 1c). The notable difference betweenthe earlier published map of Das et al. (2003) (later followed byPatranabis-Deb and Chaudhuri, 2007, 2008; Bickford et al., 2011)and that of the present geological map lies in the recognition ofnorth-south trending regional faults dissecting the lithopackage.Our structural data exclude the possibility of presence of suchregional-scale faults in the basin and instead, document occur-rence of regional non-plane non-cylindrical fold geometry withinthe sandstone. This is in striking contrast with the undeformed, verylow dipping (<10◦), sub-horizontal stratal attitude observed withinthe Chandarpur Group of rocks. On the basis of stratal attitudeand field relationship, Chakraborty et al. (2009, 2011) suggestedan angular unconformable relationship between the rocks of theSinghora and Chandarpur Groups and strongly argued in favour ofan independent status for both groups, with Singhora Group beingthe older one. However, some recent studies (Patranabis-Deb andChaudhuri, 2008; Bickford et al., 2011) offer a new stratigraphicclassification of Chhattisgarh Supergroup without any independentstatus for Singhora Group and equated it with overlying Chan-darpur Group. Further studies are needed to resolve this problem

of stratigraphy, particularly the status of Singhora Group vis-à-visChandarpur Group.

Encased between two argillaceous units of shallow to deepmarine origin, i.e., Saraipalli Shale below and the Chuipalli Shale

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Fig. 1. Chhattisgarh Basin with surrounding crustal provinces (a) and generalized stratigraphic subdivisions (Group level) for Chhattisgarh Supergroup and the SinghoraGroup (Formation level) with recent geochronological database, (b) geological map of the study area, Singhora basin showing attitudes of beds and locations of studieds al. (2

atttet(m

ections, (c) the western boundary for the Singhora basin is drawn following Das et

bove, the detached outcrops of the Bhalukona clastic wedge israced within the study area between the Singhora section inhe east, Padampur Road section in the west and Deodarah sec-ion in the southeast (Fig. 1c). The Formation wedges out in the

xtreme east and north-east part of the basin and in its absencehe demarcation between the Saraipalli and Chuipalli Formationboth argillaceous in nature), often turns speculative. The maxi-

um thickness recorded for the sandstone is ∼23 m (Bhaludungri

003) and Babu and Singh (2011).

section). The beds within the sandstone show low to moderatedip (10–30◦) except at near the southern margin of the basin. Inabsence of subsurface data and detailed process-based sedimento-logical analysis, a generalized shallow-marine origin is invoked for

the spatially detached outcrops of the Formation (Das et al., 2001).Correlation between the detached outcrops and their genetic mod-eling in the backdrop of basin evolution are long-awaited. Frombasin-scale observations spanning over 430 km2 area the present

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aper attempts depositional modeling of Bhalukona Formation inpace-time framework.

. Methodology

Seven sections spreading across the exposure belt are stud-ed (Fig. 1c). Facies types are delineated and interpreted while

utually associated facies types are clubbed under different faciesssociations (FA). The sandstone bodies are studied by describ-ng measured sections and photomosaics. Depositional processesnd environments are interpreted from primary sedimentologicaleatures (sedimentary structures, grain size, paleoflow indicators)nd shifts in paleogeography are interpreted through variationsn interpreted bathymetry across the stratigraphic column. Withinhe fluvial parts the geometrical expressions of genetically relatedacies types, i.e., ‘architectural elements’ are delineated follow-ng the definitions of Miall (1978, 1985, 1988). Considering theeformed nature of the strata, measurements of paleoflow indi-ators were restricted within the low-dipping (<12◦) normal limbsf regional-scale fold to avoid effect of tilting. Grain size measure-ents were carried out on thin sections by use of a transmitted

ight petrographic microscope fitted with an ocular micrometer.he values of statistical parameters determined from grain sizeeasurement data viz. Median grain size (Md�), grain size sort-

ng (inclusive graphic standard deviation, �I) are cited in the paperollowing Folk (1974).

Surfaces across which the depositional succession revealedbrupt change in interpreted bathymetry are identified as “key sur-aces” (unconformity, ravinement, flooding surface, etc.) and takens marker for correlating different studied sections and to identifyajor paleogeographic shifts in the depositional history those can

e traced basin-wide.Samples were collected from different facies associations and

bout 50 thin sections were prepared for modal analysis. Followinghe Gazzi-Dickinson’s QFL method (Gazzi, 1966; Dickinson, 1970),andstone petrography, i.e., estimation of quartz (Q), feldsparF; also identified by acid-staining), and lithic fragments (L)f selected samples, was studied by a standard point-countingethod wherein ∼300 points were counted for each sample. The

esults are projected against the measured lithologs of Bhalukonaormation.

Sm–Nd isotopic analyses were carried out on the sandstonesf Bhalukona Formation and sandstone and shale units of underly-ng Saraipalli Formation. Sampling within the Bhalukona Formations done from younger to older horizons in correlated balancedections having normal sequence. The whole-rock samples weigh-ng around 2–3 kg were crushed using a hardened steel mortar,omogenized, and by quartering and coning about 100 g of sam-le was ground using a tungsten carbide ball mill to <10 micronize. Precisely weighed (∼0.1 g) samples were taken in pre-weighed

ml Savillex screw-capped vials. About 2 ml of hydrofluoric acidHF) + 1 ml HNO3 + few drops of HCl were added to the sample vialsnd tightly closed and kept on a hot plate at 120 ◦C overnight forigestion. To the clear sample solution Nd and Sm isotope tracerolution was added and standard chemical separation proceduressing ion exchange resin filled columns as described in detail bynand and Balakrishnan (2010) was followed. Once separated, Smnd Nd were loaded onto pre-cleaned Re filaments and isotopenalyses were carried out using a solid source thermal ionizationass spectrometer (TIMS, Triton, Thermo-Finnigan) in static mul-

icollector mode at the National facility for isotope geosciences,epartment of Earth Sciences, Pondicherry University, India. The

nternal precision for 143Nd/144Nd ratios was checked with AMESd standard analyzed ten times during the course of this study. The

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yielded mean 143Nd/144Nd ratio was 0.511968 ± 10, (quoted valueis 0.511970, Govindaraju, 1994).

4. Facies and facies associations

Table 1 summarises the delineated facies types and their plau-sible depositional conditions. The facies types are clubbed underfacies associations belonging to nonmarine and marine settingsand assigned specific depositional environments based on theirsedimentary attributes and lateral facies relationships. Further,specific depositional processes and events within the fluvial systemare identified through delineation of genetically related pack-ages of strata, i.e., ‘architectural elements’. Bounded between theargillaceous marine shelf deposits of Saraipalli Formation belowand Chuipalli Formation above, the Bhalukona sandstone wedgeexhibits five major facies associations viz. fluvial, foreshore-beach,upper shoreface, lower shoreface and wave-influenced delta frontwhich are discussed below.

4.1. Facies Association I (FA I): fluvial

Granule rich, coarse grained (Md� = 0.16˚), poorly-sorted sand-stones of this association, constituted of facies types A–D (Table 1),overlies the argillaceous inner shelf sediments of Saraipalli For-mation with erosional contact, and are exposed in the westernand north-western parts of the basin viz., Padampur road andBhalukona village sections (Fig. 1c). Maximum thickness observedis ∼10 m. In the best-exposed section (Padampur Road), stacking offour meter-thick tabular fining-upward (grain size varies betweengranule (average −1.40˚) and medium sand (average 1.47˚) sizefrom base to top) successions is observed (Fig. 2a). Each successionbegins with a ‘Channel’ (CH) or ‘Lateral Accretion’ (LA) element,and in turn, topped by thin bedded sheet like medium-grainedsandstones (SS element) dominated by horizontal laminated (Sh),planar cross-stratified (Sp) and trough cross-stratified (St) lithofa-cies (Figs. 2a and 3c). Planar or broadly undulated master erosionsurface, extensive over ∼75 m wide outcrop area, is found toseparate vertically stacked tabular units. Coarse sandstone withdispersed rip-up mud intraclast pebbles (max. diam. 8.1 cm) (Gm;Fig. 2a) with cosets of St and Sp characterizes the CH element(Fig. 3a and b). The SS elements are found marginally to the CHunits or overlying and typically arranged in a multi-storey fash-ion (Fig. 3c). The paleocurrent readings (from Sp and St) fromboth CH and SS element are towards a mean azimuth of 167◦

(Fig. 2a). The LA macroforms (Fig. 2a), consist of medium- to coarse-grained sandstone, are only a maximum 2.40 m long, 0.55 m thickand recognized with foresets dipping towards east. Broad, shallowscours (average width:depth ratio 6.4:1), filled with very coarseand granular sandstone (SF), disrupt the fining-upward tendency(Fig. 3d). Occasionally, lensoidal bodies of cross-stratifications(average set thickness 8.6 cm) with granules concentrated at fore-set bases are found to fill the scours. In Padampur road section,the top of the association is replete with large-scale symmet-rical bedforms (average wave length and amplitude 70 cm and8.9 cm, respectively) with straight, bifurcated crest lines; concen-tration of coarsest grains observed on the crest lines (Fig. 2a).In the Bhalukona village section, ‘Overbank Fine’ (OF) element,constituted of alternation between thinly-bedded and laminatedfine-grained lenticular sandstone and siltstones, are exposed withup to 4.35 m of thickness (Fig. 2b).

Thin section study reveals poorly-sorted, clast-supported sub-

arkose to sub-litharenite characters for the sandstones. Matrix isgenerally rare; wherever present is <8% in volume and identifiedas opaque iron oxide or clayey pseudomatrix formed by squash-ing of labile lithic fragments. In addition to quartz [mono- (mc)

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Table 1Lithofacies and Facies Associations of Bhalukona Formation and their inferred depositional environments.

Architectural element Geometry and lithofacies descriptions Average thickness Associated elements Interpretation

Nonmarine facies associationFA I: Braided fluvial system(architectural element and faciescode adapted from Miall (1978,1985, 1996)A. Medium- to coarse-grained

cross-stratified poorly sortedsandstone (with mudstone andsiltstone intraclasts) (CH)

Solitary or grouped sets withhigh-angle trough cross-bedding(sandy, St) and horizontal laminatedbed (Sh); planar cross bed (Sp) climbingor stacked over the top. Rareoverturned cross-beds. Usually solitaryand rare multi-storey complex. Troughcross-beds (St) show unimodalpaleocurrent towards southeast

1.8 to 3.2 m Associated with SS, LAand OF elements.Upward thinning andfining packages

Braided fluvialchannels anddistributary channels(CH) with sporadic lags.Amalgamated channeldeposits common

B. Medium grained sheetsandstone (SS)

Sheet-like bodies with erosive toslightly concave basal surfaces. Planar(Sh) and cross-stratified (St) bed;granule/pebble filled shallow scours(SF) with occasional crudecross-bedding (Sp, St)

Extend >80 m laterallywith 0.8–1.35 mthickness. Scours arewith 24 cm wide and7.5 cm deep on average

Overlies and laterallyassociated with CHelement

Sand sheets (SS),braided fluvial channeland distributarychannels, shallowscour fills

C. Lateral accretion macroform (LA) In cross-section wedge-shapedsandstone lenses constitutedprincipally of Sp and St . Distinctiveinternal grading from granule tocoarse- and medium-grainedsandstones. Cross-beds show easterlypaleocurrent direction, at high angle tothe paleocurrent obtained from the CHunits

Lenticular unit,laterally tracedmaximum for 4.3 m, av.thickness 0.85 m

Laterally associatedwith CH element; alsooccasionally overlainby CH element

Accretion laterallyacross channel

D. Overbank fines (OF) Red coloured, fine grained sand, siltand mud (Fh) with minor Sh, Sp andrare St . Sandstones of broad lenticulargeometry with average width andthickness 2.12 m and 0.26 m,respectively

Vary in thicknessbetween 2.23 m and4.35 m; Laterallyextensive in specificlocations viz.Bhalukona section

Underlain by CHelement. Exposureconstraint did notallow documentationof lateral and uppercontact relationship forthis element

Overbank and/orwaning flood deposits

Marine facies association (FA)sFA II: Foreshore-beachE. Medium-grained tabular

sandstoneE1. Tabular units of well-sortedsandstone; trough cross-stratified.Rare small-scale planar cross-stratawith tabular geometry. Average setthicknesses of trough and tabularcross-stratification are 0.15 m and0.08 m, respectively

0.17 to 1.16 m Overlies waveravinement surface(facies I) and overlainby the rocks of FA III

Traction currentdeposition under lowerflow regime conditions,deposited fromsinuous-crested rippleand linear-cresteddune bedforms

E2. Parallel-stratified sandstone withungraded stratification bands. Lowangle truncations

0.03 to 0.86 m Upper flow regimetractive transport ofsand grains. Commonin beach environment

FA III: Upper shorefaceF. Thick-bedded lenticular

sandstonesLenticular beds (av. width 0.78 m) withplanar base and convex-up top,massive or planar-curvedcross-laminated (Average set thickness9.4 cm). Symmetrical ripple forms (av.wave length 11.4 cm, amplitude0.9 cm; Ripple Index (RI = 12.6) on thebedding surfaces. Amalgamated bedsconstitute packages (average 1.35 m inthickness)

0.22 to 0.87 m inthickness; widthvarying between 23 cmand 1.46 m

Facies F and G changeover laterally oralternate verticallywith one another

Lower flow regimedune deposits in awave dominatedsetting, bedform index>8 suggestive of swashorigin

G. Thin-bedded lenticularsandstones

Smaller scale lenticularity incomparison to facies F, rare siltstonestringers

0.08 to 0.38 m inthickness; widthvarying between 0.08and 0.62 m

Relatively lower energyinterdune deposits inwave dominatedshoreface setting

FA IV: Lower shorefaceH Lenticular beds (av. width 0.28 m)

internally constituted of H1. Cosets oftrough cross-stratification withaverage set thickness 4.5 cm; rareplanar lamination H2. Planartabular/curved cross-strata arranged inchevron pattern. Average set thickness4.3 cm Tops of sandstones commonlyreworked by ripples

0.12–0.29 m In association withfacies types I and J

Mixed wave/currenttwo- andthree-dimensionalbedforms

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Table 1 (Continued)

Architectural element Geometry and lithofacies descriptions Average thickness Associated elements Interpretation

I. Quasi-planar laminatedsandstone

Thin (<4 cm) planar-laminatedsandstone. Multiple low-angletruncation surfaces; lower laminaecommonly downlap onto basal surface

0.24–0.68 m Associated with faciesH

Combined flow (?)plane bed related tohigh energy (storm)event

J. Bi-directional cross-stratifiedsandstone

Herringbone cross-stratifiedsandstone, Laterally and verticallydiscontinuous. Surfaces of reactivation

Set and coset thickness7.5 and 19.3 cmrespectively

Dominant in the upperpart of the associationin alternation withfacies H

Reversing unsteadyflow related to tidalaction

FA V: Wave dominated Delta frontK. Tabular, parallel-sided

massive/normal-gradedsandstone

Decimetre- to meter-thick parallelsided sandstone beds; base of bedssharp, nonerosional/feeblyerosional and top varying betweensharp and gradational. Bed tops areoften replete with symmetricalwave ripples (av. wave length andamplitude 3.5 cm and 0.6 cm,respectively). Beds thicken andamalgamate upwards through thesuccession. Observed with twointernal structural sequences:K1. Poorly sorted coarse to mediumgrained sandstone. Ungraded tocoarse-tail normal graded, with flatbasal contacts, rarely scoured. Crudehorizontal or wavy laminae; climbingcurrent ripple cross-laminations onlyin the uppermost part (Bouma Ta, Tab,Tbc)

Decimetre to meterthick. Traceable formore than 500 m inexposure

Occur in amalgamationor in alternation withfacies L

Rapid deposition fromsandy dispersionsassociated with waningturbulent flow. Nearbed suspensiongenerated by mixingwith ambient fluidalong the upper surfaceof the basal dense flow

K2. Featureless (massive, lacking anygrading), rarely the beds are draped byparallel-laminated sandstone(maximum thickness 0.26 m)

Decimeter (0.35 to0.76 m) thick, laterallytraceable for more than500 m

Gradual aggradationfrom sustained highdensity turbiditycurrent (cf. Branneyand Kokellar, 1992)and upward migrationof depositional flowboundary due to grainhyperconcentrationand hindered settlingin a steady andquasi-steady current

L. Ripple laminatedsiltstone/mudstone

Siltstone with lesser very fine arenite.Sporadic current ripple

0.03 to 0.13 m Alternates with faciesK with gradational andsharp contacts at itsbase and top,respectively

Offshore fines

Key (diachronous) surfacesM. Polymictic conglomerate Cm- thick bed set (s) of clast- and

matrix-supported conglomeratecontaining pebble to cobble sizedclasts of vein quartz, sandstone andshale; coarse sandy matrix. Clasts arewith moderate to well roundness, butwith poor sorting. Beds are tabularover 100s of meter exposure length.Internally massive; matrix is with highfeldspar content (>9.5%)

0.79 m thick inBhalukona section and0.37 m thick inDongrijharan section

Overlies FA I andoverlain by FAII andFAIII

Product of waveravinement

N. Sandstone with dispersedgranules and pebbles

Lenticular bed set(s) containingdispersed granules and pebbles ofsandstone set within glauconitic coarse

Centimeter- todecimeter thick(maximum recordedth

Erosionally overlyingFA IV and overlain bythe distal shelf shale of

Erosional product oftransgression;Transgressive surface

asstaoawmh

sandstone matrix

nd poly-crystalline (pc)], feldspar and lithic fragments (quartzite,iltstone and shale) constitute the clast population of the sand-tones. Clasts of glauconite are present in the topmost part ofhe association at the Padampur Road section. Quartz (mc) grainsre subangular, coarse- to fine-grained and with occasional ironxide coatings and overgrowths. Polycrystalline quartz grains (pc)

re subordinate, consist mainly of sutured, semicomposite crystalsith preferred crystallographic fabric (Fig. 2a), probably of meta-orphic origin. Muscovite, rutile and zircon (rare) are the main

eavy minerals.

ickness 0.55 m) Chuipalli Formation of erosion

4.1.1. InterpretationFeatures supporting the fluvial interpretation include poor sort-

ing, sharp-based fining-upward sequences and predominance ofcross-beds with a unimodal south-eastward (seaward) paleocur-rent direction (cf. Bridge, 2006). Overbank fines are rare andrestricted to thin units of red siltstone. Defining the channel pat-

tern is problematic because local lateral continuity of outcrops islimited. The general lack of channel morphology and low disper-sion of paleocurrent, however, are suggestive of a broad, shallow(<2 m deep) and unconfined braided channel system (sinuosity

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Fig. 2. Measured lithologs of FAI (a) Padampur Road section, (b) Bhalukona Village section. Note (i) stacked meter-scale fining-upward successions, (ii) south-eastward (solidrose) and eastward (vertically striped rose) paleocurrent directions obtained from the CH and LA elements, respectively, and (iii) occurrence of swash bedforms with NE-SWc f OF eo atificas s of C

vantoa

Fs

rest line tend in the topmost part of Padampur Road section (a); and occurrence of Gm and LA elements indicate the rip-up shale clasts and accretionary cross-strtretched and preferred orientated sub-grains and lithic clasts within the sandstone

alue 1.03; after Le Roux, 1992). The dominant trough cross-bedsre related with megadune migration, whereas the minor pla-

ar cross-bedded units represent smaller dunes migrating overhe banks. The downstream migrating dune fields are commonlyverlain by poorly-defined laterally extensive sand sheets. The rel-tively larger-scale lateral accretionary foresets are the results of

ig. 3. Architectural elements and facies types within FA I; Multi-storeyed channel phoand sheets (SS; c) and granule/pebble filled shallow scours (SF; d) Hammer length: 27 cm

lement in the Bhalukona village section (b). The white arrows in the photographstion, respectively. Also note the occurrence of polycrystalline quartz grains withH element at the Padampur Road section (a) and Bhalukona village section (b).

marginal bar migration. Coarse grained, solitary nature of the unit,with erosional top and base, is comparable with simple cross-

bedded bars described from the low-sinuosity braided systems inthe Brownstones (Lower Devonian) Welsh Borders (Allen, 1983).Rapid variability in discharge is documented in form of scours filledwith coarse sediments including granules and commonly present

tomosaic (a), interpretation from photomosaic (b), decimeter-thick amalgamated, Pen length 14 cm, coin diam. 2.5 cm.

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36 P.P. Chakraborty et al. / Precambr

eactivation surfaces within the St units. In fact, the granule-filledcours incised on top of all other fluvial facies presumably rep-esent a stage of strongest turbulence and bed shear. Occasionalide-filling of the scours suggests emergence, thus we are inclinedo take scours as ultimate products of sheet flow during a fallingater stage when bed shear and grain entrainment capacity are

t maximum (cf. Bose and Chakraborty, 1994). The overbank fine-rained siltstones and sandstones present at the Bhalukona villageection are interpreted as deposits of flood stages and followinganing stages (cf. Jones et al., 2001). From wavelength:amplitude

atio (>8:1), the large scale bedforms present at the top of thessociation at Padampur road section are identified as of swashrigin (Clifton, 1969, 2006). Concentration of coarse grains athe bedform crests corroborates wave churning (Galloway, 2002;atuneanu, 2002). Reworking of fluvial sediment by marine agent

s inferred.

.2. Facies Association II (FA II): Beach-Foreshore

Sandstones of this association are observed at the Bhaludungrind Dongrijharan sections overlying granular/pebbly ravine-ent deposit (discussed later) with sharp, erosional contact.

abular (tens of meter wide) beds of medium-grained sand-tone, made up of subfacies E1 and E2, often in amalgamationmaximum thickness recorded ∼2.23 m) constitute the associa-ion. Individual bed thickness varies between 0.65 and 1.32 m.he sandstones preserve horizontal lamination (parting lineatednd with low-angle truncations), very low-angle trough cross-tratifications (set thickness ranging between 10 cm and 45 cm;verage ∼15 cm) and rare tabular cross-stratifications. Paleocur-ent measurements from troughs reveal bimodal west-southwestrientation (Fig. 4).

.2.1. InterpretationHorizontal-laminated sheet sandstones with parting lineation

uggest upper flow regime condition. Such sandstones are reportedrom widely different environmental conditions, viz. beach, eolian,phemeral fluvial or tidal channel environments (Clifton, 1969;cKee et al., 1967; Tirsgaard, 1993; Eriksson et al., 1995). Absence

f inverse grading, eolian translatant strata or tidal symmetricalnd bipolar paleocurrent pattern allows us to negate those pos-ibilities. On the contrary, good sorting, plane lamination (witharting lineation), low-angle truncation, alteration with troughross-stratified units and stratigraphic position below shorefaceacies association (FA III) suggest deposition of these sandstonesn a beach condition. The trough cross-stratified units, in associ-tion, are interpreted as the product of shallow-marine currentsn the foreshore associated with the beach. Similar products areecorded from several modern wave-dominated clastic shorelines,herein the surf–swash transition results in planar lamination

long with landward- and seaward-dipping trough cross stratifi-ation (cf. Clifton, 2006).

.3. Facies Association III (FA III): Upper Shoreface

From landward to basin-ward, sandstones of this associationverlie the beach- foreshore sandstones (FAII), ravinement lagRL) or gray shale of the Saraipalli Formation with thicknessarying between 0.12 m and 0.23 m (Fig. 4). Either in amalgam-tion or separated by cm-thick mudstone partings, stacked sets ofecimetre-to meter-thick tabular units of fine- to medium-grainedoderate- to poorly-sorted sandstones make up this association

Fig. 5a). Internally each tabular unit is constituted of intermin-ling between two different sub-associations (I and II) at variouscales (Fig. 5b), both subassociations are constituted of lenticu-ar beds of medium (Md� ∼ 0.23˚) to fine (Md� ∼ 2.47˚) grained

search 200– 203 (2012) 129– 148

sandstones, but differ in grain size sorting (�I), bed thickness anddegree of lenticularity. Despite intermingling, dominance of sub-associations I and II is observed in the lower and upper partsof the tabular units, respectively. Sub-association I sandstonesare moderately-sorted (�I = 0.87), uniformly thick bedded (aver-age bed thickness ∼46 cm), broad lensoid (width 0.28 m, maximumlength 1.46 m) in geometry, internally structureless, and troughcross-stratified (average set thickness 18 cm) or low-angle planar-curved cross-stratified (average set thickness 12 cm). In contrast,sandstones of sub-association II are either sandwiched betweenunits of sub-association I, or present in amalgamation towards theupper parts of the tabular units. Constituted of thin (average thick-ness ∼11 cm) bedded, poorly-sorted (�I = 1.22) sandstones, thesub-association II units internally comprise alternations of troughcross-stratification (average set thickness ∼5.4 cm) and plane lam-inations. Trough cross-stratifications from both sub-associationsshow a bimodal west northwest- west southwest orientation(Fig. 4). Sub-association I, when directly overlies the Saraipallishale, show presence of rip-up shale clasts at its basal part. Oscil-lation ripples, in trains, represent the dominant surface bedforms(Fig. 6a). The ripples are symmetrical in profile, straight-crested(rarely three-dimensional) and occasionally with crest bifurca-tions (crestline orientation ∼NNE-SSW) (Fig. 4). On average, wavelength and amplitude of the ripples are 12.8 cm and 1.2 cm, respec-tively. Confined at the basal part of this association soft-sedimentdeformations in form of crumpled and distorted beddings arerecorded.

Sandstones of this association are sub-arkose to quartz arenite[Q(t) = 87.53–92.66%, F = 8.34–4.84%, L = 0.00–0.53%, glauconite andheavies = 0.00–0.42%; matrix content, in general, <8%] in composi-tion and show variable grain size sorting. Glauconites are presentboth as clast and matrix. Rutile and zircon are most common heavyminerals.

4.3.1. InterpretationDominance of trough cross-strata with bimodal foreset ori-

entations and frequent occurrence of wave generated bedformsindicate deposition in a shallow, wave-dominated environmentabove fair-weather wave base (Walker and Plint, 1992). Wavelength:amplitude ratio (>8:1) for the wave ripples suggest theirswash origin (Clifton, 1969, 2006; Sarkar et al., 1996) in uppershoreface set-up. Bimodal, land (west) ward directed paleocurrentrecorded from trough cross-stratifications within sub-associationsI and II suggest landward migration of lunate bedforms, varyingin scale (centimetre to decimetre high). Similar landward migrat-ing decimetre-high lunate megaripples are described from the areaof most intense wave build-up just seaward from the surf zone inmedium to coarse-grained sandy nonbarred nearshores in southernOregon (Clifton, 1976; Posamentier and Walker, 2006). Whereasthe thick beds (average cross-bed set thickness 18 cm) with broadlenticular geometry are interpreted as products of bar migration,the thin bedded units (average set thickness 5.4 cm) with overridingsmall-scale ripple bedforms are possibly of interbar origin (Tamuraet al., 2007).

4.4. Facies Association IV (FA IV): Lower Shoreface

This association comprises the uppermost part of Bhalukonasuccession and is represented by stacked sets of tabular units con-stituting facies types H, I and J (Table 1). While lower boundary ofthis association with FA III is gradational and difficult to delineatein field, the upper boundary is sharp and can easily be demarcated

by cms-thick bed/s of clast-supported coarse granular sandstone.Two laterally equivalent facies, H1 (cosets of troughs capped bywave rippled sheets) and H2 (tabular cross-strata arranged in criss-cross chevron pattern) constitute the basic motif of tabular units.

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Fig. 4. Detailed measured litholog of FA II, III and IV exposed at the Bhaludungri section. Note presence of ravinement deposit and transgressive surface of erosion (TSE) atthe base and top of the section, respectively. Detailed architecture of stacked tabular unit is shown on the right. Paleocurrent directions and variation in modal abundanceof framework elements and matrix content of sandstones at different stratigraphic levels are shown on the left. Note steady decline in feldspar content up the stratigraphicc

T1uwosAetBsJ

tc

olumn.

he troughs are with average set and co-set thickness 4.5 cm and1.6 cm, respectively and their paleocurrent measurement indicatenimodal westward direction of migration (Fig. 4). The associatedave ripples show north northeast - south southwest crest line

rientation. The bedform size decreases steadily upward in thetratigraphic section (set thickness recorded ∼1.85 cm at the top).t places, the cross-laminated units are cut by shallow, concave-uprosional surfaces. The concordant laminations (facies I) overlyinghese surfaces are intermittently intervened by truncation surfaces.ipolarity in the orientation of cross-stratifications is observed atome selected intervals in the upper part of the association (facies

; Fig. 6b).

Sandstones of this association are bimodal in grain size dis-ribution (Md�1 = 0.096˚, Md�2 = 4.02˚) and quartz arenite inomposition [Q(t) = 97.79%, F = 0.45%; matrix content <2%].

4.4.1. InterpretationA perpetually wave-agitated relatively deep neritic environ-

ment is inferred. Meter-thick chevron cross-stratification co-setsuggests that the water depth was sufficient to accommodatevertically accreted bedforms ∼2 m or more in height, possiblyencompassing middle and lower shoreface domain. In an overallwave-dominated set up, the vertically accreted bedforms mighthave acted as barriers that led to local enhancement of tide rep-resented by bipolar cross-stratified units in the upper part of theassociation. Although the association lacks any definite signatureof hummocky cross-stratification, the low-angle truncations with

conformable overlying laminae are suggestive of possible stormaction (Tamura et al., 2007). The coarser grain fraction in thebimodal grain population was possibly carried by storm currentswithin the relatively deeper neritic domain where otherwise fine

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F the ii FA IIu rms a

s2

4

p(bmcspwcspl

Fw

ig. 5. Stacked meter-thick tabular units within FA III (a). Photomosaic detailingntermingling between thick- (TBL) and thin-bedded (ThBL) lenticular units withinnits are shown in (c). Larger scale cross strata within TBL represents the bar bedfo

and size grains equilibrated with fair weather waves (Clifton,006).

.5. Facies Association V (FA V): Wave influenced delta front

This is best exposed at the Deodarah section in the south-easternart of the study area and constituted of facies types K and LTable 1). Rocks of this association are deformed and folded. Despiteeing folded, the gently dipping limb (average dip < 10◦) of asym-etric folds allowed documentation of detailed sedimentological

haracters. Non-amalgamated (separated by cm-thick silty greyhale intervals; facies L) to amalgamated decimeter- to meter-thickarallel sided sandstone beds (facies K) made up the general frame-ork for the association (Fig. 7). Individual bed, with indistinct

oarse-tail normal grading, is characterized by a distinctive verticaluccession of structures: massive successively followed upward bylanar-parallel laminations and non-climbing current ripple cross-

amination (Bouma Ta, Tab, Tbc). Beds are invariably planar, sharp at

ig. 6. Plan view of facies J showing trains of wave ripple. Rose diagram showing NNE–SSWithin facies J of lower Shoreface facies association (FA IV) (b).

nternal structures of one such tabular unit (T2) is shown on the right (b). NoteI. A detailed view representing chevron cross-stratification pattern within the TBLnd thin ripple laminated bedforms within ThBL represent the interbar.

the base and their upper boundaries vary between sharp and gra-dational. Continuity of the beds with unchanged thickness is tracedin the outcrop for more than hundred meters. Adjacent coarser(sandstone beds; facies K) and finer (facies L) interbeds show poorcorrelation (r = 0.12) between their thickness values. Bed tops arereworked by symmetric ripples with average wave length andamplitude 4.2 cm and 0.8 cm, respectively. Massive (unstratified)sandstone beds, without any grading, are also common.

Sandstones of this association are silica-cemented, quartz aren-ite (Q(mc) > 90%; matrix content <5%) in composition, poorly-sortedwith variation in grain size between 9.96 ̊ and 0.45˚.

4.5.1. InterpretationThe sandstone beds are interpreted as products of gravity flows

ranging in rheology between highly concentrated granular dis-persion and dilute noncohesive turbidity current. Low correlationcoefficients (r = 0.12) between adjacent coarser (sandstone beds,facies K) and finer (facies L) interbed thicknesses suggest their

trend for the ripple crest lines of the s is in the inset (a). Bipolar cross-stratifications

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F lid ror nds ofl nd po

iutba(gru(DeT

ig. 7. Measured litholog of FA V exposed at the Deodhara section. Whereas the soipple cross-stratifications within facies K, the stippled rose indicates crest line treaterally traceable parallel-sided character of beds, wave reworking at the bed top a

ndependent origin (Schwarzacher and Fischer, 1982). The massive,nstratified beds are interpreted as products of gradual aggrada-ion and consequent upward migration of the depositional flowoundary due to grain hyperconcentration and hindered settling in

sustained steady and/or quasi-steady, high-concentration currentBranney and Kokellar, 1992; Kneller and Branney, 1995). Amal-amated mass-flow units, separated infrequently by facies L shale,esemble delta front sandstone lobes (shale encased, thickeningp, Bouma Ta, Tab, Tbc beds, etc.) ahead of the coeval alluvial system

FA I) present at the landward part of the basin (Pattison, 2005).eposition within fair weather wave base is attested by the pres-nce of wave-formed symmetrical ripples on the bedding surfaces.he stacked event beds (i.e., Bouma-like Tab, abc beds) with diffuse

se in the right demarcates south-easterly paleocurrent measured from the current wave generated bedforms. Photographs on the right (from base to top) illustratesorly sorted character for the sandstones.

contacts between the ripple-laminated division and overlyingmassive (Ta) or plane-laminated (Tb) divisions, are interpreted asevidences for waning to waxing to waning flow conditions. Veryhigh sandstone: shale ratio and medium- to coarse-grain size inthese sandstones allowed us to confirm their derivation within ariver-delta fed by a low-sinuosity, bedload channel system (FA I).

5. Key surfaces

In addition to the inferred unconformity at the base of FA I, thepresent study identifies two other key surfaces; both are erosionalin character (Fig. 8). Out of these one is present at the base of FAII and the other at the top of FA IV. While the surface at the base

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F ons oE ph at

oDtCisct

flsfbfbim

sstntto

6

o

ig. 8. Detailed litholog of Bhaludungri and Dongrijharan sections showing positirosion (TSE) with field photographs for the both. The black arrows in the photogra

f FA II is traced in outcrop for 3.5 km between Bhaludungri andongrijharan sections, that at the top of FA IV is traced between

he Bhaludungri and Sisupal sections, spanning more than 7.5 km.last-supported cms-thick polymictic conglomerate beds contain-

ng clasts of vein quartz, chert and sandstone demarcate the keyurface at the base of FA II and glauconitic granular sandstone bedsontaining clasts of sandstone (Fig. 8) constitute the other at theop of FA IV.

The surface at the base of FA II is interpreted as an erosion sur-ace produced by wave ravinement at the lowstand of relative seaevel (Dominguez and Wanless, 1991). Occurrence of ∼23 m thickhallow marine succession on this surface suggests that the uncon-ormity and its overlying forced regressive products are reworkedy wave ravinement, resulting in a situation where the uncon-ormable contact directly overlain by marine facies (discussedelow). Landward, the sequence boundary is marked by alluvial

ncision. At the base of FA II the sequence boundary is cut within aarine setting (MacEachern et al., 1999).The surface at the top of FA IV represents the boundary where

hallower marine strata are sharply overlain by deeper marinetrata without significant erosion. Such surface correlates landwardo Transgressive Surface of Erosion (TSE), and is interpreted here asear conformable marine flooding surface (FS) formed at the base ofransgressive systems tract of relative sea level. Above this surface,he occurrence of storm-infested middle-to distal-shelf successionf Chuipalli Shale records the history of transgression.

. Paleocurrent and Nd isotope signatures of sandstones

Detailed mapping of Bhalukona Sandstone reveals confinementf continental alluvial sediments in the western and north-western

f key (diachronous) surfaces viz. ravinement deposit and Transgressive surface ofthe top indicate sandstone clasts. Both scale and Pen have length of 14 cm.

corners of the study area; the shallow-marine and deltaic sedi-ments dominate in the east and southeast (Fig. 9). Distribution offacies types in space, paleocurrent directions measured form differ-ent facies associations and crestline orientation of swash bedformspresent within FA I (Padampur road section) – these signaturestogether suggest that the Bhalukona Sea had ∼northeast-southwestshoreline orientation and the basin opened to the east and south-east. This is also supported by the paleocurrent direction obtainedfrom the FA I fluvial association, which shows predominanteast–southeast directed sediment transport indicating the land wasin the west and northwest. This inference is in striking contrastwith the understanding of north-westward opening of Chhattis-garh basin, suggested from the works carried out in the RehtikholFormation (Chakraborty et al., 2009) of Singhora Group and alsoin the Lohardi and Kansapathar Formations of Chandarpur Group(Paul and Chakraborty, 2006; Patranabis-Deb and Chaudhuri, 2007;Chakraborty and Paul, 2008), respectively. A reversal in sedimentprovenance in the Singhora basin during the Bhalukona deposi-tion is inferred, corroboration of which is sought from independentgeochemical study.

Total eleven samples from all the units of both the SaraipalliFormation (four samples from stratigraphic bottom to top) and theBhalukona Formation (seven samples from stratigraphic bottomto top) are analyzed for their Sm–Nd isotopes. In the absence ofany evidence of post-depositional fractionation, the Sm/Nd ratio ofthe sediments could represent the source rocks (Armendáriz et al.,2008). The initial Nd isotopic composition represented by εt

Nd is

considered to be a robust parameter to identify the provenance aswell as any sudden shift in the provenance. The εt

Nd values calcu-lated for the time of formation of the Singhora Group (t = 1.42 Ga)for all the samples are showing negative values (Fig. 10a). For the

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Fig. 9. Facies association (FA) map of Bhalukona Formation, Singhora basin. FA II, III and IV are clubbed as shallow marine and shown. Representative paleocurrent directionsand directional attributes are given on the map. Also given are the measured lithologs of studied sections. Please note the proximal-distal relationship of different faciesassociations.

Table 2Sm–Nd isotopic compositions of representative samples from the Saraipalli and Bhalukona Formations.

Sample Sm (�g/g) Nd (�g/g) 147Sm/144Nd 143Nd/144Nd* ε0Nd

TDM (Ga) εtNd

fSm/Nd

Bhalukona Sst Topmost 1.084 5.843 0.1110 0.511253 ± 4.0 −27.0 2.79 −11.5 −0.4356Bhalukona Sst Top 0.220 1.113 0.1116 0.511369 ± 7.0 −24.7 2.64 −9.3 −0.4326Bhalukona Sst Top 1.114 5.912 0.0998 0.511267 ± 2.8 −26.7 2.51 −9.1 −0.4927Bhalukona Sst Middle 0.358 1.726 0.1100 0.511471 ± 8.4 −22.8 2.46 −7.0 −0.4406Bhalukona Sst Middle 2.881 13.900 0.1250 0.511581 ± 6.0 −20.6 2.68 −7.6 −0.3645Bhalukona Sst bottom 0.377 1.935 0.1128 0.511300 ± 3.0 −26.1 2.77 −10.9 −0.4263Bhalukona Sst contact zone 0.401 2.106 0.1008 0.511731 ± 3.8 −17.7 1.91 −0.2 −0.4877Saraipalli Sst 3.175 15.791 0.1064 0.511594 ± 5.0 −20.3 2.21 −4.0 −0.4589Saraipalli Sst 8.837 46.672 0.1146 0.511711 ± 5.0 −18.1 2.20 −3.2 −0.4173Sariapalli Shale 7.883 41.886 0.0996 0.511721 ± 3.0 −17.8 1.90 −0.2 −0.4935

Ss−Iwsah−(t

Saraipalli Shale 2.684 13.667 0.1185

* The errors quoted are 2 × S.E.

araipalli Formation, these values range from −0.2 to −6.6, whereasix samples from the Bhalukona Formation range from −7.0 to11.5 with exception of a sample having a value of −0.2 (Table 2).

f the sediments of both the Saraipalli and Bhalukona Formationsere derived from the same provenance then their εt

Nd valueshould be similar. However, sediments of the Saraipalli Formationnd lowermost Bhalukona Formation (at the contact region) must

ave derived from rocks that had less negative εt

Nd values (−0.2 to6.6), and major part of the sediments of the Bhalukona Formation

Middle and Top) were derived from distinctly different sourceshat had more negative εt

Nd values (−7.0 to −11.5).

0.511570 ± 5.0 −20.8 2.51 −6.6 −0.3976

If we assume that the source rocks (or their protoliths) that sup-plied the sediments were of igneous parentage then they could havebeen similar in age and had different εt

Nd values. For example, sed-iments derived in different proportions from a granite (εt

Nd = −14)and gabbro (εt

Nd = +6), both formed at the same time, can alsoexplain the variations observed in them. The granitoid rocks typ-ically would have lower Sm/Nd ratios than the gabbro and in the

sediments representing different proportions of granite and gab-bro will have a range of Sm/Nd ratios correlated with εt

Nd valueswill be expected in the sediments. However, sediments of theboth Saraipalli and the Bhalukona Formations have nearly uniform

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200– 203 (2012) 129– 148

Fig. 10. Nd isotopic composition of rocks from Saraipalli Formation and Bhalukona Formation. The time-corrected Nd isotopic compositions (εtNd

, t = 1.42 Ga), enrichment factors (fSm/Nd) and depleted mantle model ages (TDM) areplotted in (a), (b) and (c), respectively. The Y-axis represents the relative stratigraphic positions of the samples. The maximum error in calculation of εt

Ndis ±0.2. The samples collected from continuous exposures are connected

by thin line. Note that there is a change of Nd isotopic composition in the early Bhalukona sedimentation history, possibly indicating a sudden provenance change.

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m/Nd ratio and show no correlation with εtNd values indicating that

heir provenance also had similar Sm/Nd ratios. The enrichmentactor, fSm/Nd is the deviation of 147Sm/144Nd of the sample fromhe chondritic uniform reservoir (CHUR) value which is similar forhese two formations in the range of −0.364 to −0.494 (Fig. 10b).ence, the differences in the εt

Nd values can be explained if therovenances are made up of similar rocks but of different ages.

The Nd model ages are useful to evaluate relative antiquityf the provenance (Faure, 1986). Depleted mantle Nd model ageTDM) implies the time of extraction of the source rock of the sed-ment from a depleted mantle source. The TDM ages are in theange of 1.9 to 2.5 Ga for the Saraipalli Formation, whereas, in thehalukona Formation this shows much higher values towards 2.5o 2.8 Ga excepting a sample from the base level (Table 2, Fig. 10c).he actual ages of the source rocks could be few hundred mil-ion years younger than their respective TDM ages (Dickins, 2005).hus, from the calculated εt

Nd values, more contributions from juve-ile continental sources for the Saraipalli Formation that changespward in stratigraphy with contributions from older upper con-inental crustal material are apparent. However, within Saraipallind Bhalukona Formations variations in the εt

Nd values to extentf 3 and 2 units are seen, respectively. This could be as a resultf variations in relative contributions of sediments from rocksf slightly different crustal residence ages that occurred in theirrovenance.

. Discussion

Sequence stratigraphic models for low-gradient shelf settingsonsider the depositional sequences as composed of transgressivend highstand deposits; falling stage and lowstand deposits typ-cally restricted or absent (Baum and Vail, 1988). The paucity inocumentation of falling stage records always remains a concern in

dentifying the depositional breaks and thereby predisposes inter-retations towards an incomplete stratigraphic framework biasedith half of a sea level cycle. Proterozoic basins, without shelf-slope

reak, although can be cited as ideal analogues for low-gradienthelfal settings (estimated mean dip less than 1 m/km; Walker,995) such as those that characterise very large platform (Everts,995) or ramp margins, absence of geophysical data and incom-lete outcrop-based stratigraphic records commonly do not allowifferentiation between regressive products in terms of their forcedegressive or lowstand origin. Through process-based facies, faciesssociation and key surface delineation, the present study alloweddentification of ‘Systems tract’s within the Bhalukona Formationnd subdivide the regressive Bhalukona depositional history inwo-stages viz. forced regressive and lowstand.

An interpreted sequence stratigraphic framework for thehalukona succession is presented in Fig. 11. The thickening- andoarsening-upward stratal stacking pattern recorded at the upperart of the Saraipalli Shale Formation (Chakraborty et al., 2009) bear

ndication that the Saraipalli shelf attained highstand sea level con-ition at its terminal sedimentation history. That the shelf attainedear-equilibrium physiographic profile with progradation by thend of Saraipalli time with appreciable reduction in clastic supplys attested in the growth of patchy, biohermal stromatolites in theppermost Saraipalli succession (Sisupal section).

A drastic basin-ward dislocation of facies belt is inferred thatrought the coarse, granular alluvial sandstones (FA I) of thehalukona Formation right onto the Saraipalli highstand shelf.xposure limitation and non-availability of borehole data did not

llow physical documentation of contact relationship between thelluvial Sandstone and its underlying shelf deposits. However,ccurrence of mud clasts, boulder-sized at times, within the sand-tones of FA I suggest that the Bhalukona fluvial system encroached

search 200– 203 (2012) 129– 148 143

the Saraipalli shelf with incision. Such alluvial incision of shelf isattributed to the fall in the base level of erosion and formation ofType-I sequence boundary (Posamentier et al., 1992; Posamentierand Allen, 1993; Hunt and Gawthorpe, 2000). From the preservedthickness of FA I, it is estimated that the Bhalukona fluvial sys-tem incised more than 10 m on the Saraipalli shelf. Recognitionof decimetre-thick channel- bar complexes stacked within meter-thick alluvial succession (FA I) suggest that the erosional relief isgreater than the single channel fill, a criteria commonly used foridentification of incised valleys. The occurrence of wave generatedbedforms and sandstones with glauconitic matrix in the uppermostpart of FAI at the Padampur Road section (Fig. 2) indicate rework-ing of alluvial sediments by marine agents on the forced regressiveshoreline of the Bhalukona Sea.

The southeasterly paleocurrent measured from the fluvialassociation, in striking contrast with the northwestward pale-ocurrent documented from the underlying Rehtikhol river system(Chakraborty et al., 2009), is noteworthy. Changes in regionaldrainage patterns associated with the development of incisedvalleys are documented in literature (Dalrymple et al., 1994;Fitzsimmons and Johnson, 2000). In such instances, the distributarychannels are pulled towards the vector of maximum base level fall,and accordingly, the progradation direction of associated shore-line may also get realigned. However, near-reversal of paleocurrent(about 180◦ out of phase), as documented in the present study,cannot be accounted by this reasoning and calls for operation ofsome allokinetic forcing. A tectonic perturbation possibly causedthe reversal of basinal slope and change in sediment provenancefrom east-southeast to west- northwest in the Bhalukona time.The idea finds support in the shift of Nd- isotope values in courseof deposition of Bhalukona succession. The εt

Nd change recordedfrom the lower part of Bhalukona succession (except one samplefrom the contact zone) can be caused either due to lack of sequencepreservation, or, merely as an artifact of post-depositional diage-netic alteration. Overlapping and similar fSm/Nd values across theboundary between Saraipalli and Bhalukona Formations suggest noperceptible loss of record (or hiatus) and hence, the sharp change ofTDM and εt

Nd values are interpreted as characters of their respectivesources. The contact zone sample at the base of Bhalukona yield-ing anomalous data, though show the mixing of isotopic charactersof Saraipalli Formation, could also be explained by its derivationfrom greenstone belt rocks, particularly basaltic type. These rockspresent at the western part of the studied basin will have higher εNdvalues than the surrounding granites. With the present databasesuch provenance correlation would be speculative. However, achange in the provenance right in the early history of Bhalukonasedimentation is distinct. Contribution of relatively juvenile mate-rials during the deposition of Saraipalli rocks changed to morecontributions from older and less radiogenic crustal componentsduring the depositional history of the Bhalukona Formation. Fur-ther, there is an increase in the proportion of older materials addedupward within the Bhalukona succession. We interpret this prove-nance change in the early history of Bhalukona sedimentation andsubsequent progressive change during Bhalukona basin-fill his-tory as a result of protracted tectonic disturbance in and aroundthe basin. Here, it is noteworthy that the Singhora basin is struc-turally disturbed and the tectonic disturbance was pulsative withsuperposition of at least two phases of deformation. With such abackground, the above-mentioned provenance shift is a distinctpossibility.

The sediment gravity flow units within FA IV reflect deposi-tion from hyperpycnal density underflows generated at the river

mouth during high discharge floods (Mulder and Syvitski, 1996;Chakraborty et al., 2009). Coarse grain size (medium to coarsesand) and evidences of fair weather wave reworking suggest thatthe delta system developed in shallow water, essentially restricted

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144 P.P. Chakraborty et al. / Precambrian Research 200– 203 (2012) 129– 148

Fig. 11. Graphic log correlation in depositional-dip profile across the Bhalukona Formation showing transition from underlying Saraipalli to overlying Chuipalli sediments inSinghora basin, central India; numbers of log locations are from Fig. 1c. Locations of ‘key surfaces’ viz. unconformity, ravinement surface and Transgressive surface of Erosiona hicht indicas

wricfwdtidstiecodflfltcwtbatbvsM

o

re shown. Note the presence of unconformity in the western part of the basin, whe wave base. The distally pinching foreshore-beach-shoreface facies associationsurface of erosion.

ithin the shelf domain. Poor grain sorting of FA IV sandstones andestriction of wave reworking signatures only at the top of bedsmply fluvial dominance in the delta. The mixing of wave- andurrent-produced structures is typical of wave-influenced deltaront (Bhattacharya and Walker, 1991), but relative scarcity ofave-produced structures suggests wave influence rather thanominance. Though a physical link between marginal fluvial sys-em (FA I) and related delta front (FA IV) cannot be established,t can be appreciated that the hyperpycnal flow deposits in theelta front relate to the time during which sediment flux to theea attains its maximum. Studies in the modern settings revealedhat the degree of shelf incision by a forced regressive river systems driven by the exposure of convex-up coastal profile that occursither at the shelf edge or at the preceding highstand coastline (theoastal prism) (Posamentier et al., 1992; Talling, 1998). In absencef shelf-slope break and slope control in the Proterozoic basins,ownstream increase in the stream power of Bhalukona inciseduvial system is unlikely. Hence, it is possible that the Bhalukonauvial system incised the highstand coastal prism developed onhe Saraipalli shelf and debouched sediment load ahead of channelonfinement in the shallow water delta front setting (within faireather wave base). The base of FA IV is demarcated as correla-

ive conformity related to the Type-I unconformity inferred at thease of FA I association in the landward direction. Offlapped anderially separated from the fluvial association (Padampur section),he delta front sandstone lobe is deposited at the distal part of theasin (Deodarah section). The gentle dip of Bhalukona sea floor pro-oked such long-distance regression of deltaic sandstone (∼15 km

outheastward) in course of forced regression (cf. Posamentier andorris, 2000).The cessation of forced regression and inception of stillstand

r slow rise of base level established wave-dominated lowstand

turns into correlative conformity basinward; development of ravinement withinte its wedge nature. Top of the Bhalukona sandstone represents the Transgressive

coastline. The soft sediment deformation features at the basal partof FA III bear indication of basinal instability that contributed inthe turn over from the forced regression to the lowstand of sealevel. The amalgamated pebble bedset at the sole of FA II, tracedbasin-ward for more than 3.5 km between Bhaludungri and Dongri-jharan sections, demarcate the diachronous ravinement depositionformed by wave reworking associated with slow landward retreatof the coastline truncating deposits of preceding forced regres-sion (Cattaneo and Steel, 2003). Backstepping incised shorefacesare described in literature from several stratigraphic sections pre-serving nearshore successions (Cardium E4, E5; Walker and Eyles,1988; Pattison and Walker, 1992; Shannon sandstone, Bergman,1994; Beaverhill Lake shoreface, Viking Formation, Walker andWiseman, 1995). It is inferred that the forced-regressive shorelinetrajectory became steeper than the shelf dip in the Bhalukona Seabecause of increased wave stress on the sea bed (cf. Carey et al.,1999). To regain the equilibrium geometry as a function of prevail-ing wave energy during subsequent base level rise, wave erosionand ravinement resulted in the coastal areas, where forced regres-sive profile gradient was steepest and waves are also with highestenergy. Occurrence of anomalous coarse sized grains, unavailable inboth underlying and overlying sediment column, within the ravine-ment lag bears proof for complete reworking of fluvial products.This is also supported by steady decline in feldspar content up in thestratigraphic column of nearshore succession from the foreshore-beach (FA II) and basal part of upper shoreface (FA III) sandstonesto the lower shoreface sandstones (FA IV). Absence of lag at thebase of nearshore sandstones at the Sisupal and Singhora sections

and in lieu, gradational transition between the Saraipalli shelf andBhalukona shoreface in these sections represent basin-ward cor-relative conformity. In the east and northeast of the basin, absenceof Bhalukona rocks and juxtaposition of Saraipalli and Chuipalli

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P.P. Chakraborty et al. / Precambrian Research 200– 203 (2012) 129– 148 145

Fig. 12. Interpretation of the events that led to the formation of Bhalukona regressive succession (i) base level fall, formation of incised fluvial valley and detached delta lobe( nd upf orefact

ap

wWbptblfnrss(

iITmaioutoloetJmas‘oot(

Type-I unconformity), (ii) slow, stepwise increase in relative sea level, landward aormation of ravinement deposit and (iii) the landward and upward migration of shhe section preserved as a result of transgression.

rgillaceous sediments suggest wedge out of regressive sedimentackage in the basin-ward direction.

The cms-thick cycles represented by bar-interbar stackingithin FA III are interpreted as ‘parasequences’ sensu lato (Vanagoner et al., 1988). The meter-tick tabular units bounded

y planar surfaces, occasionally overlain by shale, represent thearasequence sets with large-scale linkages of facies or systemsracts (Brown and Fisher, 1977; Proust et al., 2001). The surfacesounding the units without significant erosion or clear break in

ithology represent within-trend conformable marine flooding sur-aces (FS; Catuneanu, 2006). The stacking of tabular units withear-uniform thickness is indicative of aggradational to weakly ret-ogradational stacking in the early lowstand history as the rate ofediment supply matches or occasionally falls behind the slow butteady creation of accommodation on flattened shoreface profilePosamentier and Morris, 2000; Hampson, 2000).

With slow, steady rise in relative sea level and concomitantncrease in bathymetry, the sediments of lower shoreface (FAV) overlie the sediments of upper shoreface (FA III) association.he rise in base level and increase in the accommodation spacearginally exceeded the sedimentation rate in the lower shoreface

nd thereby a time-equivalent, landward onlap back across therregular lowstand topography resulted in the enhanced strengthf tidal currents, recorded as bipolar cross-stratified beds in thepper part of FA IV association (cf. Mellere and Steel, 1995). Fur-her steepening in the gradient of relative sea level rise resultedutpacing of sediment supply and transgression at the shore-ine. The glauconite-bearing granular sandstone beds at the topf FA IV represents ravinement deposition associated with thestablishment of transgressive Chuipalli shelf system. Followinghe Transgression-Regression (T-R) sequence model (Embry andohannesen, 1992), the upper boundary of the lowstand section

arks the point between regression and following transgressionnd is termed as ‘maximum regressive surface’. The occurrence ofhelf shale of Chuipalli Formation above the surface confirms itsmaximum regression’ status (cf. Catuneanu, 2002). The coupling

f the surface of maximum regression with the interpreted surfacef transgression and ravinement allowed us to pick it as a ‘Sys-ems Tract’ boundary. Lying above forced regressive fluvial depositFA I) and bounded between the wave ravinement deposit at its

ward migration of shoreface causing erosion of underlying alluvial sediment ande during transgressive erosion formed a TSE. Vertical double-headed arrow shows

base and transgressive ravinement deposit at the top, the nearshoresedimentary package, constituted of FA II, III and IV, records thelowstand depositional history of Bhalukona Sea.

Sequence stratigraphic models (Plint, 1988; Plint andNummedal, 2000; Posamentier et al., 1992; Van Wagoner, 1995;MacEachern et al., 1999) involving forced regressive and lowstandshoreface succession often document fairly thin character for thedeposits. The thin deposit character is commonly tagged with, (i)decline in accommodation space and (ii) horizontal TransgressiveSurface of Erosion (TSE) that cause large-scale transgressiveerosion and removal of shoreface succession. While decreasingaccommodation can be well-perceived for forced regression, theslow base level rise in lowstand goes against the idea. Also, thepresumption of horizontal TSE cannot be unequivocal unlesssediment supply to the shoreface is reduced to zero and sea levelrise is an absolute minimum (cf. Walker and Wiseman, 1995). Inthis context, the ∼23 m thick foreshore-shoreface succession ina lowstand depositional motif demands analysis for the extentof shoreface retreat on the Bhalukona coastline that allowed itspreservation. Working on Joarcham sandstone of Alberta Walkerand Wiseman (1995) considered 1 mm rise in relative sea levelper year, in consistence with the rate of present day eustatic risein sea level, and 1 m per year as the rate of shoreface retreat,as observed in the east coast of USA and estimated 15 m risein TSE with a gradient of 0.04◦ for 20 km retreat of shoreface.Recognising geographic and chronologic variations, it is generallyagreed upon from average global conditions that the continentalfreeboard remained constant since 2.5 Ga in the entire Proterozoicand Phanerozoic time (Eriksson, 1999 and references therein).Considering continental crustal growth, the freeboard and sealevel changes as interdependent variables, we assume that therate of present day eustatic rise in sea level can be extended toProterozoic systems as well. However, we differ from Walker andWiseman (1995) in making estimation for rate of shoreface retreat.Working on the muddy (sand <1% in volume) Amazon river mouth,Allison et al. (1995) estimated shoreface retreat rate varying

between 0.5 and 1 m per year with highest rates recorded in areaswith dentate or terraced shorelines with large tidal amplitude.Sandy (medium to coarse-grained) Bhalukona coastline without(i) any large-scale tidal signature and (ii) evidences favouring

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8

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2

3

4

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46 P.P. Chakraborty et al. / Precambr

erraced shoreline character allowed us to favour the lower boundf shoreface retreat rate, i.e., 0.5 m per year. Though the exposureonstraint and deformed nature of the terrain did not allow usstimation of net shoreface retreat in the Bhalukona Sea thatllowed preservation of ∼23 m of shoreface succession, if we go byresent day rate of eustatic rise, i.e., 1 m per year and average ratef shoreface retreat 0.5 m per year, it requires ∼11.5 km retreatf the shoreline (Fig. 12). It may be pertinent to mention herehat the measured total exposure width of FA II and FA III rocksn the studied area in paleoshoreline (NNE-SSW) perpendicularection is also consistent with the obtained value i.e., around 12 kmFig. 9).

. Conclusions

. Process-based facies and paleo-environmental analysis in theBhalukona Formation, Singhora Group, Chhattisgarh Supergrouprevealed deposition in both continental and marine domains.While the continental setting is represented solely by the fluvialsystem, the marine products vary widely in environment span-ning between wave-dominated near shore to wave-influenceddelta front. Five facies associations are defined (1) fluvial, (2)foreshore-beach, (3) upper shoreface, (4) lower shoreface, and(5) wave-influenced delta front.

. Above highstand Saraipalli shelf, the Bhalukona fluvial sys-tem encroached with incision and together with its overlyingnearshore and shallow-marine succession records a regressivedepositional history built up at two stages viz. forced regres-sion and lowstand. The base of fluvial association, though couldnot be documented physically, is inferred as a Type-I sequenceboundary formed in course of forced regressive base level fall.

. The southeastward paleocurrent recorded from the fluvial sys-tem and sharp negative shift of Nd isotope values of Bhalukonarocks in comparison to those of underlying Saraipalli rocksprompted us to suggest change in sediment provenance fromeast-southeast in the Rehtikhol and Saraipalli time to west-northwest in the Bhalukona time. A possible tectonic forcingis inferred, which gets support from the occurrence of soft-sediment deformation structures at the basal part of Bhalukonasuccession.

. The slow rise in relative sea level in subsequent lowstandresulted in the establishment of a wave-dominated coastline.In the near-shore sections above wave base, the forced regres-sive deposits are thoroughly reworked by wave action and thesequence boundary is substituted by surface of ravinement.Basin-ward, the gradational transition between the highstandshelf and lowstand shoreface, is interpreted as correlative con-formity.

. The nearshore succession constituted of foreshore-beach, upperand lower shoreface sediments represent the lowstand deposi-tion in the Bhalukona coastline. The upper boundary of lowershoreface association (FA IV) is interpreted as ‘Maximum sur-face of regression’, and identified as ‘Systems Tract’ boundarycoinciding with Surface of transgression (TS) that established theChuipalli shelf system.

. The preservation of ∼23 m of lowstand succession in the regres-sive Bhalukona coastline supports the conjecture of Walker andWiseman (1995) that the gradient of TSE and the preservationof lowstand succession depend on rate of sea level rise, depth tofair weather wave base and the rate of coastal retreat. Though it

is difficult to quantitatively reconstruct the controlling parame-ters, considering 1 mm per year rate of eustatic sea level rise andaverage rate of shoreface retreat 0.5 m per year, we qualitativelypredict ∼11.5 km retreat for Bhalukona shoreface in course of itslowstand depositional history.

search 200– 203 (2012) 129– 148

Acknowledgements

The authors are thankful to Department of Science and Tech-nology, Government of India for providing necessary funding.Department of Geology, University of Delhi had provided the nec-essary infrastructural facilities. Thanks are also due to severalmasters’ students who took active initiatives in field in course ofmapping and litho-section measurement. P.D. and S.S. acknowl-edge CSIR and DST, respectively for financial help in form offellowship. K.D. is thankful to ISEI, Misasa for their support dur-ing his visit. Thorough and incisive reviews of Drs. P.G. Erikssonand A. Basu helped us to improve this manuscript to a great extent.Dr. Basu has kindly shared his experience in Chhattisgarh basin andhighlighted some critical issues.

References

Allen, J.R.L., 1983. Studies in fluviatile sedimentation: bars, bar complexes and sand-stone sheets in low sinuosity braided streams) in the Brownstones (L. Devonian)Welsh Borders. Sedimentary Geology 33, 237–293.

Allison, M.A., Nittrouer, C.A., Faria Jr., L.E.C., 1995. Rates and mechanisms of shorefaceprogradation and retreat downdrift of the Amazon River mouth. Marine Geology25, 373–392.

Anand, R., Balakrishnan, S., 2010. Pb, Sr and Nd isotope systematics of metavolcanicrocks of the Hutti greenstone belt, Eastern Dharwar craton: constraints on age,duration of volcanism and evolution of mantle sources during Late Archean.Journal of Asian Earth Science 39, 1–11.

Armendáriz, M., López-Guijarro, R., Quesada, C., Pin, C., Bellido, F., 2008. Genesisand evolution of a syn-orogenic basin in transpression: insights from petrog-raphy, geochemistry and Sm–Nd systematics in the Variscan Pedroches basin(Mississippian, SW Iberia). Tectonophysics 461, 395–413.

Babu, R., Singh, V.K., 2011. Record of aquatic carbonaceous metaphytic remains fromthe Proterozoic Singhora Group of Chhattisgarh Supergroup, India and theirsignificance. Journal of Evolutionary Biology Research 3, 47–66.

Baum, G.R., Vail, P.R., 1988. Sequence stratigraphic concepts applied to Paleogeneoutcrops, Gulf and Atlantic basins. In: Wilgus, C.K., Hastings, B.S., Kendall,C.G.St.C., Posamentier, H.W., Ross, C.A., Van Wagoner, J.C. (Eds.), Sea LevelChanges–An Integrated Approach. SEPM Special Publication 42, pp. 309–327.

Bergman, K.M., 1994. Shannon Sandstone in Hartzog Draw- Heldt Draw fields rein-terpreted as detached lowstand shoreface deposits. Journal of SedimentaryResearch B64, 184–201.

Bickford, M.E., Basu, A., Patranabis-Deb, S., Dhang, P.C., Schieber, J., 2011. Deposi-tional history of the Chhattisgarh basin, central India: constraints from newSHRIMP zircon ages. Journal of Geology 119, 33–50.

Bose, P.K, Chakraborty, P.P., 1994. Marine to fluvial transition: Proterozoic UpperRewa Sandstone, Maihar, India. Sedimentary Geology 89, 285–302.

Branney, M.J., Kokellar, B.P., 1992. A reappraisal of ignimbrite emplacement: pro-gressive aggradation and changes from particulate to nonparticulate flow duringemplacement of high-grade ignimbrite. Bulletin Volcanologique 54, 504–520.

Bhattacharya, J.P., Walker, R.G., 1991. River- and wave-dominated depositionalsystems of the upper Cretaceous Dunvegan Formation, northwestern Alberta.Bulletin Canadian Petroleum Geology 39, 165–191.

Bridge, J.S., 2006. Fluvial facies models: recent developments. In: Posamentier, H.W.,Walker, R.G. (Eds.). Facies model revisited. SEPM special publication 84, pp.85–170.

Brown, L.F. Jr., Fisher, W.L., 1977. Seismic stratigraphic interpretation of depositionalsystems: Examples from Brazilian rift and pull-apart basins. In: Payton, C.E. (Ed.)Seismic stratigraphy - Applications to Hydrocarbon Exploration. AAPG Memoir26, pp. 213–248.

Carey, J.S., Swift, D.J.P., Steckler, M., Reed, C.W., Niedoroda, A., 1999. High-resolutionsequence stratigraphic modelling 2: effects of sedimentation processes. In: Har-bugh, J.W., Watney, W.L., Rankey, E.C., Slingerland, R., Goldstein, R.H., Franseen,E.K. (Eds.) Numerical Experiments in stratigraphy: recent advances in strati-graphic and sedimentologic computer simulations. SEPM Special Publication62, pp. 151–164.

Catuneanu, O., 2002. Sequence stratigraphy of clastic systems: concepts, merits andpitfalls. Journal of African Earth Science 35, 1–43.

Catuneanu, O., 2004. Basement control on flexural profiles and the distribution offoreland facies: the Dwyka Group of the Karoo Basin, South Africa. Geology 32,517–520.

Catuneanu, 2006. Principles of Sequence Stratigraphy. Elsevier, 375 p.Cattaneo, A., Steel, R.J., 2003. Transgressive deposits: a review of their variability.

Earth Science Review 62, 187–228.Chakraborty, P.P., Paul, S., 2008. Depositional pattern across Forced regressive-

Transgressive sea-level history on a Neoproterozoic siliciclastic shelf:Chandarpur Group, central India. Precambrian Research 162, 227–247.

Chakraborty, P.P., Das, K., Sarkar, A., Das, P., 2009. Fan-delta and storm-dominatedshelf sedimentation in the Proterozoic Singhora Group, Chattisgarh Supergroup,central India. Precambrian Research 70, 88–106.

Chakraborty, P.P., Das, K., Tsutsumi, Y., Horie, K., 2011. Depositional history of theChhattisgarh basin, central India: Constrints from new SHRIMP zircon ages by

Page 19

ian Re

C

CC

C

D

D

D

D

D

D

D

D

D

D

E

E

E

E

FF

F

G

G

G

G

H

H

P.P. Chakraborty et al. / Precambr

M.E. Bickford, A. Basu, S. Patranabis-Deb, P.C. Dhang, J. Scieber: A discussion.Journal of Geology 119, 549–552.

hriste-Blick, N., Dyson, I.A., Von der Borch, C.C., 1995. Sequence stratigraphyand the interpretation of Neoproterozoic earth history. Precambrian Research,3–26.

lifton, H.E., 1969. Beach lamination: nature and origin. Marine Geology 7, 553–559.lifton, H.E., 1976. Wave-formed sedimentary structures—a conceptual model. In:

Davis, R.A., Ethington, R.L. (Eds.), Beach and Nearshore Processes: Society ofEconomic Paleontologists and Mineralogists, vol. 24. Special Publication, pp.126–148.

lifton, H.E., 2006. A reexamination of facies models for clastic shorelines. In: Posa-mentier, H.W., Walker, R.G. (Eds.), Facies Models Revisited, vol. 84. SEPM SpecialPublication, pp. 293–337.

alrymple, R.W., Boyd, R., Zaitlin, B.A., 1994. Incised valley systems: origin andsedimentary sequences. Society of economic Paleontologists and Mineralogists.Special Publications, p. 51.

as, D.P., Kundu, A., Das, N., Dutta, D.R., Kumaran, K., Ramamurthy, S., Thangavelu,C., Rajaiya, V., 1992. Lithostratigraphy and sedimentation of Chattisgarh basin.Indian Minerals 46, 271–288.

as, D.P., Dutta, N.K., Dutta, D.R., Thanavellu, C., Baburao, K., 2003. Singhora Group-the oldest Proterozoic lithopackage of Eastern Bastar craton and its significance.Indian Minerals 57, 127–138.

as, N., Dutta, D.R., Das, D.P., 2001. Proterozoic cover sediments of southeasternChattisgarh state and adjoining parts of Orissa. Geological Survey of India SpecialPublication 55, 237–262.

as, K., Yokoyama, K., Chakraborty, P.P., Sarkar, A., 2009. Basal tuffs and con-temporaneity of the Chattisgarh and Khariar Basins based on new dates andgeochemistry. Journal of Geology 117, 88–102.

as, P., Das, K., Chakraborty, P.P., Balakrishnan, S., 2011. 1420 Ma diabasic intrusivesfrom the Mesoproterozoic Singhora Group, Chhattisgarh Supergroup, India:Implications towards non-plume intrusive activity. Journal of Earth System Sci-ence 120, 1–14.

avies, S.D., Walker, R.G., 1993. Reservoir geometry influenced by high frequencyforced regressions within an overall transgression; Caroline and Garringtonfields. Viking Formation (Lr. Cretaceous) Alberta. Bulletin Canadian PetroleumGeology 41, 407–421.

ickins, A.P., 2005. Radiogenic Isotope Geology, 2nd ed. Cambridge University Press,492 pp.

ickinson, W.R., 1970. Interpreting detrital modes of graywacke and arkose. Journalof Sedimentary Petrology 40, 695–707.

ominguez, J.M.L., Wanless, H.R., 1991. Facies architecture of a falling sealevelstrandplain, Doce River Coast, Brazil. In: Swift, D.J.P., Oerteal, G.F., Tillman, R.W.,Thorne, J.A. (Eds.), Shelf Sand and Sandstone Bodies, vol. 14. International Asso-ciation Sedimentologists Special Publication, pp. 259–281.

mbry, A.F., Johannesen, E.P., 1992. T–R sequence Stratigraphy, facies analysisand reservoir distribution in the uppermost Triassic-lower Jurassic succession,western Sverdrup Basin, Arctic Canada. In: Vorren, T.O., Bergsager, E., Dahl-Stamnes, O.A., Holter, E., Johansen, B., Lie, E., Lund, T.B. (Eds.), Arctic Geologyand Petroleum Potential, vol. 2. Norwegian Petroleum Society (NPF) SpecialPublication, pp. 121–146.

riksson, P.G., Reckzo, B.F.F., Boshoff, A.J., Schrieber, U.M., Van Der Neut, M., Snyman,C.P., 1995. Architectural elements from Lower Proterozoic braid-delta and highenergy tidal flat deposits in the Magaliesberg Formation, Transvaal Supergroup,South Africa. Sedimentary Geology 97, 99–117.

riksson, P.G., 1999. Sea level changes and the continental freeboard concept: gen-eral principles and application to the Precambrian. Precambrian Research 97,143–154.

verts, A.J.W., 1995. Sequence stratigraphy at the margin of the Vercors platform(Cretaceous, France): stratal geometry and facies patterns in a productivity-dominated setting. In: Hunt, D., Gawthorpe, R., Docherty, M. (Eds.), SedimentaryResponses to Forced Regression: Recognition, Interpretation and ReservoirPotential. Manchester University Press, pp. 47–49.

aure, G., 1986. Principles of Isotope Geology, 2nd ed. John Wiley & Sons, 589 pp.itzsimmons, R., Johnson, S., 2000. Forced regressions: recognition, architecture

and genesis in the Campanian of the Bighorn Basin, Wyoming. In: Hunt, D.,Gawthorpe, R.L. (Eds.), Sedimentary Responses to Forced Regressions, vol. 172.Geological Society of London Special Publication, pp. 113–140.

olk, R.L., 1974. The Petrology of Sedimentary Rocks. Hemphill Publishing Co, Austin,Texas, pp. 182.

alloway, W.E., 2002. Paleogeographic setting and depositional architecture of asand dominated shelf depositional system, Miocene Utsira Formation, NorthSea basin. Journal of Sedimentary Research 72, 476–490.

azzi, P., 1966. Le arenarie del flysch sopracretaceo delrAppennino modenese;correlazioni con il flysch di Monghidoro. Mineralogica e Petrografica Acta 12,69–97.

ehling, J.G., 2000. Environmental interpretation and a sequence stratigraphicframework for the terminal Proterozoic Ediacara member within the RawnsleyQuartzite, South Australia. Precambrian Research 100, 65–95.

ovindaraju, K., 1994. Computation of working values and sample description for383 geostandards. Geostandards Newsletter 18, 1–158.

ampson, G.J., 2000. Discontinuity surfaces, clinoforms, and facies architecture

in a wave-dominated, shoreface–shelf parasequence. Journal of SedimentaryResearch 70, 325–340.

unt, D., Tucker, M.E., 1992. Stranded parasequences and the forced regressivewedge systems tract: deposition during base level fall. Sedimentary Geology81, 1–9.

search 200– 203 (2012) 129– 148 147

Hunt, D., Gawthorpe, R.L. (Eds.), 2000. Sedimentary Response to Forced Regressions,vol. 172. Geological Society of London, Special Publication, p. 383.

Jones, S.J., Forstick, L.E., Austin, T.R., 2001. Braided stream and flood plain archi-tecture: the Rio Vero formation, Spanish Pyrenees. Sedimentary Geology 139,229–260.

Kneller, B.C., Branney, M.J., 1995. Sustained high density turbidity currents and thedeposition of thick massive sands. Sedimentology 42, 607–616.

Le Roux, J.P., 1992. Determining the channel sinuosity of ancient fluvial systemsfrom paleocurrent data. Journal of Sedimentary Petrology 62, 283–291.

MacEachern, J.A., Zaitlin, B.A., Pemberton, S.G., 1998. High-resolution sequencestratigraphy of early transgressive deposits, Viking Formation, Joffre Field,Alberta, Canada, AAPG Bulletin, vol. 82, pp. 729–756.

MacEachern, J., Zaitlin, B.A., Pemberton, S.G., 1999. A sharp-based sandstone of theViking Formation, Joffre Field, Alberta, Canada: Criteria for recognition of trans-gressively incised shoreface complexes. Journal of Sedimentary Research 69,876–892.

McKee, E.D., Crosby, E.J., Berryhill Jr., H.L., 1967. Flood deposits, Bijou Creek, Colorado,June 1965. Journal of Sedimentary Petrology 34, 829–851.

Mellere, D., Steel, R., 1995. Variability of lowstand wedges and their distinction fromforced regressive wedges in the Mesaverde Group, southesat Wyoming. Geology23, 803–806.

Miall, A.D., 1978. Lithofacies types and vertical profile models in braided riverdeposits: a summary. In: Miall, A.D. (Ed.), Fluvial Sedimentology, vol. 5. Memoirof Canadian Society of Petroleum Geology, pp. 597–604.

Miall, A.D., 1985. Architectural-element analysis: a new method of facies analysisapplied to fluvial deposits. Earth Science Reviews 22, 261–308.

Miall, A.D., 1988. Architectural elements and bounding surfaces in fluvial deposits:Anatomy of the Kayenta Formation (Lower Jurassic), southwest Colorado. Sedi-mentary Geology 55, 233–262.

Mulder, T., Syvitski, J.P.M., 1996. Climatic and morphologic relationships of rivers:Implications of sea level fluctuations on river loads. Journal of Geology 104,509–523.

Patranabis-Deb, S., Chaudhuri, A.K., 2007. A retreating fan delta system in the Neo-proterozoic Chattisgarh rift basin, central India: major controls on its evolution.AAPG Bulletin 91, 785–808.

Patranabis-Deb, S., Chaudhuri, A.K., 2008. Sequence evolution in the easternChhattisgarh basin: constraints on correlation and stratigraphic analysis. Pale-obotanist 57, 15–32.

Pattison, S.A.J., Walker, R.G., 1992. Deposition and interpretation of long, narrowsandbodies underlain by a basinwide erosion surface; Cardium Formation,Cretaceous Western Interior Seaway, Alberta, Canada. Journal of SedimentaryPetrology 62, 292–309.

Pattison, S.A.J., 2005. Storm-influenced prodelta turbidite complex in the lowerKenilworth member at Hatch Mesa, Book Cliffs, Utah, U.S.A.: implications forshallow marine facies models. Journal of Sedimentary Research 75, 420–439.

Paul, S., Chakraborty, P.P., 2006. Depositional discontinuity in Neo-Mesoproterozoicrocks of Chandarpur Group, Chhattisgarh Supergroup, central India. Indian Jour-nal of Geology 78, 159–174.

Posamentier, H.W., Allen, H.W., James, D.P., Tesson, M., 1992. Forced regressionsin sequence stratigraphic framework: concepts, examples and sequence strati-graphic significance. American association of Petroleum Geologists Bulletin 76,1687–1709.

Posamentier, H.W., Chemberlain, C.J., 1993. Sequence stratigraphic analysis ofViking Formation lowstand beach deposits at Joarcham field, Alberta, Canada.In: Posamentier, H.W., Summerhayes, C.P., Haq, B.U., Allen, G.P. (Eds.),Stratigraphy and Facies Associatios in a Sequence Stratigraphic Framework,vol. 18. International Association of Sedimentologists Special Publications,pp. 469–485.

Posamentier, H.W., Allen, G.P., 1993. Variability of sequence stratigraphic model:effects of local basin factors. Sedimentary Geology 86, 91–109.

Posamentier, H.W., Morris, W.R., 2000. Aspects of the stratal architecture of forcedregressive deposits. In: Hunt, D., Gawthorpe, R.L. (Eds.), Sedimentary Responsesto Forced Regressions, vol. 72. Geological Society of London Special Publication,pp. 19–46.

Posamentier, H.W., Walker, R.G., 2006. Facies Model Revisited, vol. 84. SEPM SpecialPublication, 527 p.

Plint, A.G., 1988. Sharp-based shoreface sequences and ‘offshore bars’ in the CardiumFormation of Alberta: their relationship to relative changes in sea level. In: Wil-gus, C.K., Hastings, B.S., Kendall, C.G.St.C., Posamentier, H.W., Ross, C.A., VanWagoner, J.C. (Eds.), Sea Level Changes—An Integrated Approach, vol. 42. SEPMSpecial Publication, pp. 357–370.

Plint, A.G., Nummedal, D., 2000. The falling stage systems tract: recognition andimportance in sequence stratigraphic analysis. In: Hunt, D., Gawthorpe, R.L.(Eds.), Sedimentary Responses to Forced Regressions, vol. 172. Geol. Soc. Lond.Spl. Publ., pp. 1–17.

Proust, J., Mahiux, G., Tessier, B., 2001. Field and seismic images of sharpbasedshoreface deposits: implications for sequence stratigraphic analysis. Journal ofSedimentary Research 71, 944–957.

Sarkar, S., Chakraborty, P.P., Bose, P.K., 1996. Proterozoic Lakheri Limestone, Cen-tral India: facies, paleogeography and physiography. In: Bhattacharya, A. (Ed.),Recent Advances in Vindhyan Geology, vol. 36. Memoir Geological Society of

India, pp. 5–25.

Sarkar, S., Chakraborty, S., Banerjee, S., Bose, P.K., 2001. Facies sequence andoccult imprint of sag tectonics in Sirbu Shale. In: Altermann, W., Corcoran,P.L. (Eds.), Precambrian Sedimentary Environments. Blackwell, Oxford, pp.168–183.

Page 20

1 ian Re

S

T

T

T

V

V

48 P.P. Chakraborty et al. / Precambr

chwarzacher, W., Fischer, A.G., 1982. Limestone-shale bedding perturbations of theEarth’s orbit. In: Einsele, G., Seilacher, A. (Eds.), Cyclic and Event Stratification.Springer-Verlag, pp. 72–95.

amura, T., Nanayama, F., Saito, T., Murakami, F., Nakashima, R., Watanabe, K., 2007.Intra-shoreface erosion in response to rapid sea-level fall: depositional recordof a tectonically uplifted strand plain Pacific coast of Japan. Sedimentology 54,1149–1162.

alling, P.J., 1998. How and where do incised valleys form if sea level remains abovethe shelf edge? Geology 26, 87–90.

irsgaard, H., 1993. The architecture of Precambrian high energy tidal channeldeposits: an example from the Lyell Lond Group (Eloomore Bay Supergroup),northeast Greenland. Sedimentary Geology 88, 137–152.

an Wagoner, J.C., 1995. Overview of sequence Stratigraphy of foreland basin

deposits. In: VanWagoner, J.C., Bertram, G.T. (Eds.), Sequence Stratigraphy ofForeland Basin Deposits, vol. 64. AAPG Memoir, pp. ix–xxi.

an Wagoner, J.C., Posamentier, H.W., Mitchum Jr., R.M., Vail, P.R., Sarg, J.F., Loutit,T.S., Hardenbol, J., 1988. An overview of the fundamentals of Sequence stratig-raphy and key definitions. In: Wilgus, C.K., Hastings, B.S., Kendall, C.G.St.C.,

search 200– 203 (2012) 129– 148

Posamentier, H.W., Ross, C.A., Van Wagoner, J.C. (Eds.), Sea Level Changes–AnIntegrated Approach, vol. 42. SEPM Spec. Publ., pp. 39–45.

Walker, R.G., Bergman, K.M., 1993. Shannon sandstone in Wyoming: a shelf-ridgecomplex reinterpreted as lowstand shoreface deposits. Journal of SedimentaryPetrology 63, 839–851.

Walker, R.G., Eyles, C.H., 1988. Geometry and facies of stacked shallow marinesandier upward sequences dissected by an erosion surface, Cardium Formation,Willesden Green, Alberta. AAPG Bulletin 72, 1469–1494.

Walker, R.G., Plint, A.G., 1992. Wave and storm-dominated shallow marine systems.In: Walker, R.G., James, N.P. (Eds.), Facies Models: Response to Sea-Level Change.Geological Association of Canada, St. John’s, Newfoundland, pp. 219–238.

Walker, R.G., Wiseman, T.R., 1995. Lowstand shorefaces, transgressive incisedshorefaces, and forced regressions: Examples from the Viking Formation, Joar-

cam area, Alberta. Journal of Sedimentary Research B65, 132–141.

Walker, R.G., 1995. An incise valley in the Cardium Formation at Ricinus, Alberta:reinterpretation of an estuarine fill. In: Plint, A.G. (Ed.), Sedimentary Facies Anal-ysis, vol. 22. International Association of Sedimentologists, Special Publication,pp. 47–74.