proterozoic intracontinental basin: the vindhyan example

Proterozoic intracontinental basin:The Vindhyan example

Chandan Chakraborty

Geological Studies Unit, Indian Statistical Institute, 203 B.T. Road, Kolkata 700 108, India.e-mail: [email protected]

The Vindhyan basin is a classic example of Proterozoic intracontinental basin that developed inthe central part of the Indian shield along with several other basins such as Cuddapah, Chattis-garh, etc. The strata are exposed in three major sectors: Son valley, Bundelkhand and Rajasthan.Substantially thick Vindhyan rocks have also been recognized under the Gangetic alluvium. Theconstituent stratigraphic units of the Vindhyan Supergroup are laterally correlatable and verti-cally stacked in similar fashion in individual sectors, but their stratigraphic and sedimentologicattributes vary from one sector to the other. The basin fill in the Son valley (around 3 km thick)exhibits an asymmetric cross-sectional geometry normal to the regional strike (ENE–WSW), withthe thickest part occurring to the south, and is divisible into four groups: Semri, Kaimur, Rewaand Bhander, from bottom to top. The boundary between the Semri and Kaimur Groups is markedby a pronounced unconformity. The dominant lithologies include conglomerate, sandstone, shale,limestone as well as volcaniclastics. The Vindhyan strata define a broad, regional syncline trendingENE–WSW. The axis of the syncline is slightly curved (convex towards north) and plunges gen-tly towards west. The average dip of the southern limb is greater than that of the northern limbrendering the axial plane to dip southerly.

The Vindhyan succession can be divided into five major sequences separated by unconformities.The unconformities are manifested in the field by angular discordances and/or long-term subaer-ial exposure features. Unconformity surfaces are disposed in the succession defining what is knownas progressive unconformity, indicating contemporaneous tectonic activity during sedimentation.Individual sequences comprise of a spectrum of depositional systems that include alluvial fan,fan delta, braidplain, braidplain delta, eolian sandsheet, siliciclastic/carbonate tidal flat, siliciclas-tic/carbonate shoreface, siliciclastic/carbonate shelf. The paleocurrents revealed by the Vindhyanstrata are typically northerly suggesting that the evolving Satpura orogen served as the source forthe Vindhyan sediments. However, the source for the clastics occurring within the Semri and thelower parts of the Kaimur and Rewa Groups in the Bundelkhand sector was perhaps the Bun-delkhand Granite Gneiss, Bijawar and Gwalior Group of rocks as manifested by the southerlypaleocurrent.

The sequences of the Vindhyan succession are composed of several systems tracts. The differ-ent paleogeographic settings characterizing the systems tracts within individual sequences are asfollows:

Sequence 1:

• TST – alluvial fan–fan delta–shelf (Deoland and Arangi Formations)• HST – carbonate ramp (Kajrahat Formation)

Keywords. Intracratonic basin; Proterozoic; depositional environments; sedimentation; sequence stratigraphy.

J. Earth Syst. Sci. 115, No. 1, February 2006, pp. 3–22© Printed in India. 3

4 Chandan Chakraborty

Sequence 2:

• TST – shelf (Deonar Formation)• FSST to TST – braid/fan delta–shelf (Koldaha Formation)• HST – tidal flat–shoreface–shelf (Chorhat and Koldaha Formations)• TST – shelf (Rampur Formation)• TST – carbonate ramp (Rohtas Formation)

Sequence 3:

• TST – shoreface–shelf (Sasaram Formation)• FSST – shoreface (Ghaghar Formation)• TST – shelf (Bijaygarh Formation)• HST – braidplain–braid delta–shelf (Mageswar and Dhandraul Formations)

Sequence 4:

• TST – shelf (Panna Formation)• FSST to TST – shoreface (Assan and Jhri Formations)• HST – braidplain–braid delta–shelf (Jhiri, Drammondgunj and Govindgarh Formations)

Sequence 5:

• TST – tidal flat (Ganurgarh Formation)• HST – carbonate platform (Bhander Formartion)• TST – tidal flat to coastal lagoon (Bundihill and Sirbu Formations)• FSST – tidal flat–braidplain–eolian (Shikhaoda Formation)

1. Intracratonic basin: An overview

The middle to late Proterozoic was the period ofdevelopment of intracratonic basins on the conti-nental shields all over the world (Windley 1977;Condie 1989). The basin fills, often several kilo-meters thick, are typically unmetamorphosed,varyingly deformed sedimentary strata that gotdeposited in an unvegetated landscape. The stratalie unconformably on the Archean–early Protero-zoic gneisses, high-grade rocks, granite-greenstonesor metasedimentaries of Proterozoic mobilebelts.

There are significant differences between Pre-cambrian sedimentary deposits of intracratonicbasin and their Phanerozoic-modern equivalents.For example, epeiric seas constitute an impor-tant depositional setting characterizing most ofthe Proterozoic intracratonic basins, but do nothave any exact modern analogue (Friedman et al1992; Eriksson et al 1998). Precambrian and someyounger deposits sharing the features of mod-ern tide-wave affected shoreface and shelf sedi-ments have been ascribed as products of epeiricseas. These epeiric seas were much wider (hun-dreds of kilometers), and had a very low gradientwith a maximum paleobathymetry around 100 m(Friedman et al 1992; Eriksson et al 1998). Thebasins, however, virtually lacked a discernible shelf-slope break that characterizes present day conti-nental margin shelf seas (Shaw 1964; Irwin 1965;

Schopf 1980; Friedman et al 1992; Aspler et al1994; Runkel et al 1998).

Accumulation of a huge thickness of shallowwater sediments in intracratonic basins clearlyindicates synsedimentary subsidence. The drivingforces of subsidence have remained unclearfor many cratonic basins. Cratons are stablecontinental interiors or continental intraplateregions relatively free from tectonic effects, whichare preferentially localized along their boundaries.However, intracontinental regions do experienceintraplate stresses inducing subsidence and upliftthough at much slower rates than that at plateboundaries (Park and Jaroszewski 1994). Tradi-tionally cratonic basins have been thought tohave suffered subsidence and uplift independentlyof the activities at the craton margin or plateboundary. Sediment loading, subcrustal loadingand thermal subsidence have been considered tobe the dominant mechanisms of subsidence in suchbasins. However, Sloss (1988a, b) pointed out thatexclusion of cratons from the dynamics of platetectonics is not a valid proposition and intraplatetectonic activities in many cases can be related tocompressional or extensional events at the mar-gin of the craton. In many basins, the subsidenceis related to thermal contraction or subcrustalloading; these basins are typically oval in shape,and show symmetric isopach distribution (e.g., Illi-nois and Michigan basins, Angevine et al 1990).Subsidence induced by extensional tectonism has

Proterozoic intracontinental basin 5

Figure 1. Outcrop of the Vindhyan basin as revealed by SRTM data. Note: (i) confinement of the basin between the GreatBoundary Fault and the Son–Narmada lineament; (ii) occurrence of the Bundelkhand Gneiss at the middle of the basin;(iii) the Gangetic plain covering the northern part of the basin; (iv) occurrences of the Vindhyan strata in three differentsectors – Rajasthan, Bundelkhand and Son valley. Locations of illustrative outcrops and sections are also shown.

been invoked for basins that are conspicuouslynarrow and linear (e.g., Pranhita–Godavari valleybasin, Naqvi and Rogers 1987). The subsidence inbasins located in front of Proterozoic mobile belts,on the other hand, has been thought to be dueto supracrustal, thrust loading in the hinterland(Allen and Homewood 1986); the thickness of thebasin fill in these basins systematically increasestowards the orogenic front resulting in stronglyasymmetric isopach distribution.

The Vindhyan basin of central India offersunique scope to resolve all these issues concern-ing the development and evolution of intracratonicbasins during the Proterozoic. In the Indian shield,there are four large intracratonic basins of Protero-zoic age:

1. Vindhyan basin,2. Cuddapah basin,3. Pranhita–Godavari basin, and4. Chattisgarh basin barring the smaller Indra-

vati, Kaladgi, Bhima and Badami basins.

Despite many differences in details, the sedi-mentaries developed in these widely separatedbasins display marked similarities in their lithology,depositional setting and stratigraphic architecture(Naqvi and Rogers 1987). This note sum-marises the stratigraphy, stratal architecture, sed-imentology and geochronology of the Vindhyan

Supergroup occurring in the Son valley region(figure 1).

2. The Vindhyan basin

The Vindhyan strata are exposed in three sectors:

1. Rajasthan sector2. Bundelkhand sector and3. Son valley sector (figure 1).

In the west and south of the Vindhyan outcropoccur the fold-belts of Aravalli–Delhi and Satpura.At the central part of the basin occurs an isolatedinlier of basement gneiss designated as the Bun-delkhand massif. Along the southern edge of theVindhyan outcrop and the eastern flank of the Bun-delkhand massif are exposed a low-grade metamor-phic group of volcano-sedimentary rocks, termedas the Mahakoshal Group and the Bijawar Grouprespectively. The northern part of the basin is hid-den under the Gangetic alluvium (figure 1).

The southern margin of the Vindhyan basin ismarked by a major ENE–WSW trending lineamenttermed Narmada–Son lineament south of whichoccurs the Satpura orogen (figure 1). The westernmargin of the Vindhyan basin in the Rajasthan sec-tor is also marked by a NE–SW trending major lin-eament known as Great Boundary Fault separating


Figure 2. Strike-wise stratigraphic column of the Vindhyan Supergroup in the Son valley prepared by combining severaldiscrete logs constructed at different locations along the structural strike. The upper boundary of the column representsthe present-day topography. Maihar town has been shown as a reference location on the topographic profile.

the Aravalli–Delhi orogen from the Vindhyan(figure 1).

2.1 Lithostratigraphy

The entire Vindhyan succession, maximum thick-ness estimated to be around 3 km, and comprisingmainly sandstone, shale and limestone is assigned

as the Vindhyan Supergroup (Bhattacharyya1996). The Supergroup is divisible into fourgroups:

1. Semri Group,2. Kaimur Group,3. Rewa Group and4. Bhander Group,


from bottom to top (figure 2). Each group is againsubdivided into several formations. An outline ofthe lithostratigraphy of the Vindhyan Supergroupof the Son valley is presented in table 1 (see alsofigure 2).

The Semri Group in the Son valley rests uncon-formably on a variety of pre-Vindhyan rocks suchas granites and metamorphics. In the Bundelkhandarea, the group overlies the Bundelkand Gran-ite Gneisses and Bijawar Group of metamorphics,whereas in the southern Son valley, Mahakoshal isthe basement in most places (figure 3A); however,in some localities (e.g., Deoland, M.P.) the base-ment is granite.

The Semri succession of the Bundelkhand areahas two detached outcrops around Chitrakut andBijawar respectively, and is only a few tens ofmeters thick (figure 1). The successions in thesetwo outcrops are dissimilar. Moreover, these twosuccessions have several dissimilarities with that ofthe southern Son valley:

• The succession in the Bundelkhand area is muchthinner and dominated by carbonates, whereasin the southern Son valley both carbonates andsiliciclastics are prevalent,

• The lithological attributes of the carbonates ofthe Bundelkhand area are quite different fromthat of the carbonates occurring in the southernSon valley,

• In the southern Son valley, volcaniclasticdeposits form a major lithostratigraphic unit ofthe succession but are absent in the Bundelk-hand area (Singh and Kumar 1978; Sastry andMoitra 1984).

The basal part of the Kaimur Group in the Bun-delkhand area is represented by arkosic, pebblysandstones and has no analogue in the Son valley.However, the overlying rocks are similar in the tworegions.

The basal part of the Rewa Group occurring inthe northern part of the Son valley is representedby conglomerates and arkosic sandstones, whichhave no equivalent in the southern part (Bose et al1997). However, the overlying units are correlat-able across the entire outcrop of the Vindhyans inthe Son valley.

The field appearances of different formationsare presented through a series of photographs (fig-ures 3–6).

3. Structural style of the Vindhyanstrata

The outcrop of the Vindhyan lithounits in the Sonvalley shows a parabolic pattern with easterly clo-sure (figure 1). The northern arm has southerly dip,

whereas the southern arm dips northerly with thebasal units showing steep dips (figure 3A, B, C).This indicates a regional scale syncline with west-erly plunge (figure 7). The trace of the axial planeis mildly curved with an overall ENE–WSW trend.In the Rajasthan sector near the Great Bound-ary Fault, the Vindhyan strata show tight andlocally overturned folds trending parallel to thefault (Banerjee and Sinha 1981; Prasad 1984).

The geological profiles across the regionalstrike (ENE–WSW) in the Son valley (figure 8)revealed the presence of several sub-regional foldson the southern limb of the regional syncline(Chakraborty and Karmakar 1998). The differ-ent folds are recognizable in different stratigraphicunits. However, integration of all the profiles leadsto reconstruction of the overall structural patternof the Vindhyan strata (figure 9). The salient fea-tures are:

• The cross-sectional geometry of the Vindhyanbasin fill, normal to the regional strike, is asym-metric with the thickest part occurring towardssouth.

• The Vindhyan strata define a broad, regionalsyncline trending ENE–WSW. The axis of thesyncline is slightly curved and plunges gentlytowards west. The average dip of the southernlimb is greater than that of the northern limbrendering the axial plane to dip southerly.

• The preserved southern limb of the regionalsyncline shows two smaller, local anticlines inter-vened by two synclines. In contrast, the low-dipping northern limb is homoclinal (<5◦).

• The smaller folds are asymmetric in nature withone limb longer and steeper (northern limb incase of anticlines and southern limb in case ofsynclines) than the other. Their axial planes dipsoutherly. In other words, the fold geometry isthat of successive monoclines defining a terracelike or ramp-and-flat pattern.

4. Stratal discontinuities in theVindhyan succession

The profiles constructed have also revealed thepresence of angular discordances between differentlithostratigraphic units of the Vindhyan successionat various levels (figure 9) as mentioned below.

• Between Kajrahat and Deonar Formations of theSemri Group.

• Between Rohtas Formation of the Semri Groupand Sasaram Formation of the Kaimur Group.This is the most conspicuous unconformity sur-face within the Vindhayn succession.

• Between Dhandraul Formation of the KaimurGroup and Rewa Group.

8 Chandan ChakrabortyTable

1.

Lithost

ratigr

aphy

and

dep

osi

tionalen

viro

nm

ents

ofth

eV

indhya

nSupe

rgro

up

(Son

valley

).

Bhander

Gro

up

Shik

haoda

Form

ati

on

(Shard

aForm

ati

on??

)

The

low

erpart

of

the

form

ati

on

isof

mix

edlith

olo

gy

conta

inin

gsa

ndst

one

bed

sen

case

dw

ithin

shale

.T

he

upper

part

isdom

inate

dby

med

ium

-gra

ined

sandst

ones

.T

he

low

erpart

repre

sents

dep

osits

ofst

orm

-influen

ced

tidalflat

syst

em,w

her

eas

the

upper

sandst

one-

dom

inate

dpart

conta

ins

bra

idpla

inand

eolian

stra

ta(S

ingh

1980;

Chakra

bort

y2001;B

ose

etal

1999;C

hakra

bort

yand

Chakra

bort

y2001).

Sir

bu

Shale

This

form

ati

on

beg

ins

wit

hooliti

cand

stro

mato

liti

clim

esto

nes

follow

edby

shale

sw

ith

stri

nger

sof

sandst

one

and

silt

stone.

Ala

goonal

environm

ent

has

bee

nin

ferr

ed(S

ingh

1980;C

hakra

bort

y2001;Sark

ar

etal

2002).

Bundih

illForm

ati

on

(Maih

ar

Form

ati

on??

)

The

form

ati

on

consist

sof

sandst

ones

wit

hin

terlay

ers

of

reddish

mudst

one.

The

dep

ositi

onal

syst

emis

consider

edas

ati

de-

storm

influen

ced

coast

al

flat

(Bose

and

Chaudhuri

1990;C

hakra

bort

y2001).

Lakher

iForm

ation

(Doln

iLim

esto

ne?

?)

This

form

ati

on

isch

ara

cter

ized

by

lim

esto

nes

,at

pla

ces

stro

mato

liti

c,w

ith

an

inte

rven

ing

unit

of

silici

clast

ics

(sandst

one-

shale

het

erolith

icunit

).T

he

dep

osi

tional

envir

onm

ent

has

bee

nin

ferr

edas

ast

orm

-influen

ced,hom

ocl

inalca

rbonate

ram

p(S

ark

ar

etal

1996;C

hakra

bort

y2004).

Ganurg

arh

Form

ation

The

form

ati

on

isre

pre

sente

dby

shale

sw

ith

inte

rven

ing

layer

sof

silt

stone

and

sandst

one.

Ati

de-

affec

ted,

coast

al

flat

syst

emhas

bee

nin

ferr

edfo

rit

sdep

ositi

on

(Chakra

bort

yet

al

1998).

Rew

aG

roup

Gov

indgarh

Sandst

one

Peb

bly

toco

ars

e-gra

ined

sandst

one

repre

senti

ng

dep

osits

ofa

bra

idpla

inw

ith

patc

hes

ofeo

lianit

es(C

hakra

bort

yand

Chaudhuri

1990;B

ose

and

Chakra

bort

y1994).

Dra

mm

ondgunjSandst

one

Med

ium

-gra

ined

sandst

one

dep

osi

ted

insh

ore

face

environm

ent

(Chakra

bort

yand

Chaudhuri

1990;B

ose

and

Chakra

bort

y1994).

Rew

aShale

(Panna

Shale

,A

san

Sandst

one,

Jhir

iShale

)

Purp

leto

gre

ensh

ale

wit

hsa

ndst

one

inte

rbed

sup

tose

ver

alm

eter

sth

ick

and

met

erth

ick

and

volc

anic

last

icbed

s(C

hakra

bort

yP

etal

1996).

The

infe

rred

dep

osi

tional

environm

ent

isin

ner

shel

fw

ith

the

sand

inte

rbed

sem

pla

ced

by

storm

flow

s(C

hakra

bort

yand

Chaudhuri

1990).

Kaim

ur

Gro

up

Dhandra

ulSandst

one

This

form

ati

on

isre

pre

sente

dby

med

ium

toco

ars

e-gra

ined

sandst

ones

.T

he

dep

ositi

onalen

vironm

ents

incl

ude

bra

idpla

in,eo

lian

sandsh

eet

(upper

part

),bra

idpla

indel

ta(l

ower

part

)(B

hatt

ach

ary

ya

and

Mora

d1993;C

hakra

bort

y1993,1996).

Manges

war

Form

ati

on

This

form

ati

on

isre

pre

sente

dby

fine

tom

ediu

m-g

rain

ed,dec

imet

erto

met

er-t

hic

k,ta

bula

rsa

ndst

one

bodie

sw

ith

shale

part

ings.

The

infe

rred

dep

osi

tionalen

vironm

ent

isst

orm

-influen

ced

inner

shel

f(C

hakra

bort

yand

Bose

1992).

Bijay

gart

hShale

The

low

erpart

of

this

form

ati

on

isch

ara

cter

ized

by

asa

ndst

one-

shale

inte

rcala

ted

unit

wit

hth

esa

ndst

one/

shale

rati

odec

reasing

upw

ard

s;w

her

eas,

the

upper

part

isre

pre

sente

dby

clay

stones

wit

hsi

gnifi

cant

pyri

teco

nce

ntr

ati

on

at

Am

jhore

,R

ohta

sD

istr

ict,

Bih

ar.

The

succ

essi

on

reco

rds

gra

dualtr

ansi

tion

from

inner

shel

fto

oute

rsh

elf(C

hakra

bort

y1995).

At

the

top

volc

anic

last

ics

occ

ur

loca

lly

(Chakra

bort

yet

al

1996).


Ghaghar

Sandst

one

This

isa

med

ium

-gra

ined

sandst

one

unit

dep

osi

ted

insh

ore

face

envir

onm

ent

under

the

influen

ceofw

ave

and

tide

(Chakra

bort

y1999).

Sasa

ram

Form

ati

on

This

form

ati

on

beg

ins

wit

hm

ediu

m-g

rain

edsa

ndst

one

and

isfo

llow

edby

asa

ndst

one-

shale

inte

rcala

ted

unit

.T

he

low

erpart

repre

sents

dep

osits

ofti

de-

affec

ted

shore

face

envir

onm

ent

and

the

upper

part

ast

orm

influen

ced

inner

shel

fse

ttin

g(C

hakra

bort

yand

Bose

1990).

Sem

riG

roup

Rohta

sForm

ati

on

This

form

ati

on

beg

ins

wit

hm

ass

ive,

pla

ne-

lam

inate

dand/or

stro

mato

liti

clim

esto

nes

follow

edby

an

inte

rcala

ted

unit

of

lim

esto

ne

and

shale

.In

the

wes

tern

part

at

Jukeh

i,Satn

aD

istr

ict,

M.P

.,th

elim

esto

nes

ofth

efo

rmati

on

are

over

lain

by

thic

k(3

0m

)volc

anic

last

icdep

osi

ts.T

his

volc

anic

last

ichorizo

nth

insto

ward

sea

st.T

he

over

all

dep

osi

tionalen

vironm

ent

isin

ferr

edto

be

aca

rbonate

pla

tform

wit

ha

dis

tally

stee

pen

edra

mp

(Chakra

bort

y,T

etal

1996).

Ram

pur

Form

ati

on

This

form

ati

on

consist

sofgre

enish

shale

sw

ith

inte

rbed

sofsa

ndst

one

repre

senti

ng

dep

osits

ofst

orm

-influen

ced

inner

and

oute

rsh

elf(S

ark

ar

etal

2002).

Salk

han

Form

ati

on

This

form

ati

on

isw

elldev

eloped

inth

eea

ster

npart

ofth

eSon

valley

inM

irza

pur

distr

ict

and

isre

pre

sente

dby

stro

mato

litic

as

wel

las

non-s

trom

ato

liti

clim

esto

nes

.T

his

form

ati

on

isa

late

raleq

uiv

ale

nt

ofC

horh

at

Form

ati

on.A

per

itid

alen

vorn

men

tis

infe

rred

for

its

dep

osi

tion

(Baner

jee

and

Jee

vankum

ar

2003).

Chorh

at

Form

ati

on

This

form

ati

on

isre

pre

sente

dby

sandst

ones

wit

hand

wit

hout

mud

part

ings

and

layer

s.T

he

form

ati

on

isw

elldev

eloped

inth

ew

este

rnpart

ofSon

valley

inth

eC

horh

at

are

aofSid

hiD

istr

ict,

M.P

.T

he

infe

rred

dep

ositi

onalen

vir

onm

entva

ries

from

shore

face

toti

de-

storm

influen

ced

coast

alflat.

The

form

ati

on

yie

lded

som

em

ark

ings

claim

edto

be

oftr

ails

oftr

iplo

bla

stic

met

azo

ans

(Sark

aret

al

1998;Sei

lach

eret

al

1998).

Kold

aha

Form

ati

on

The

Kold

aha

Form

ati

on

beg

ins

wit

ha

sandst

one-

shale

inte

rcala

ted

unit

and

gra

dually

bec

om

escl

ayey

.T

her

eare

thre

edis

tinct

coars

erunit

sw

ithin

the

form

ati

on,

the

bott

om

-most

of

whic

his

conglo

mer

ati

cco

nta

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Figure 3. Field appearances and vertical disposition of different stratigraphic units of the Semri Group in Son valley. Note:(i) steep dips of the Deoland Formation in A and B; (ii) tight, upright folds in the Kajrahat Limestone in C; (iii) dippingbeds of Deonar Formation in D; (iv) vertical section through the Koldaha Formation in E; (v) vertical lithological variationwithin the Koldaha Formation in F.


Figure 4. Field appearances and vertical disposition of different strati-graphic units of the Kaimur Group in the Son valley. Note: (i) Verticalsuccession of the Kaimur Group occurring between Rohtas Lime-stone of the Semri Group and Panna Shale of the Rewa Group in A.(ii) Continuous section of the whole Kaimur Group occurring aboveSemri Group in B and below Rewa Group in C.


Figure 5. (A) Field appearance of the vertical transitionfrom Dhandraul Sandstone (Kaimur Group) to the RewaGroup. (B) Vertical lithological variation within the RewaShale overlying the Kaimur Group.

• Between Govindgarh Formation of the RewaGroup and Ganurgarh Formation of the Bhan-der Group.

These angular discordances are recognizable in thesouth and they gradually grade into conformi-ties, paraconformities or disconformities towardsnorth.

Besides the angular unconformities, the stratalarchitecture is also suggestive of ‘cumulative wedgesystems’ or ‘progressive unconformities’ indicating“a depositional surface which is tilted by uplift ofone side and the subsidence of the other, with nointerruption of sedimentation. Such features wouldbe generated over an anticlinal flank and wouldespecially well develop on the flanks of overfolds,overthrusts. . . ” (Riba 1976).

It is, therefore, logical to infer that synsedimen-tary tectonism played an important role in thedevelopment of the Vindhyan succession and thedeformation pattern shown by the Vindhyan stratawas not a result of the post-Vindhyan tectonicevent.

5. Depositional systems

In the Vindhyan succession many depositional sys-tems have been recognized, the products of whichoccur at different stratigraphic levels, within dif-ferent lithostratigraphic units (table 2).

5.1 Description of depositional systems

5.1a Alluvial fan

Lithosomes of gravity-flow dominated alluvial fandepositional system are characterized by disor-ganized, poorly-sorted breccias and conglomer-ates comprising angular to subangular fragments(1–20 cm long) of igneous and metamorphic rocks,vein quartz and jasper set in a matrix of coarsesand and granules. The content of matrix variesresulting in both clast-supported and matrix-supported texture. The sediment bodies are usuallymassive; however, at places crude layering definedby weakly oriented clasts may be observed. Thegrains of breccias at places show matching bound-aries. Lithosomes are laterally impersistent andapparently appear to be lenticular in shape.

Lithosomes of stream-flow dominated alluvialfan depositional system are characterized by sedi-ment bodies of conglomerates and pebbly to coarsegrained sandstones. The conglomerates are mod-erately sorted, dominantly clast supported. Clastsare of metamorphic rocks, vein quartz, jasper, etc.and range in length from 10–15 cm. The bodiesmay be massive, horizontally stratified or cross


Figure 6. Field appearances of different stratigraphic units of the Bhander Group.

stratified. Channel cuts with stratified or mas-sive fills are common. At places laterally extensive,graded (normal as well and reverse) beds have beenobserved.

5.1b Fan delta

Lithosomes of the fan delta plain depositional sys-tem are characterized by sheet-like, laterally exten-sive conglomerate beds with or without interbedsof granular sandstones. The clasts are poorlysorted, and mostly of vein quartz and jasper witha few fragments of basic and schistose rocks. Thelength of the clasts ranges from 1 to 15 cm. Theyare dominantly subangular, supported by variableamounts of coarse sandy to granular matrix andare mostly unoriented; however, where the pro-portion of matrix is less they may be orientedwith their long axis parallel to the bedding. The

conglomerates are usually normally graded. Theinterbedded sandstones may be horizontally strat-ified, cross stratified or massive. At places, the sys-tem is represented by multistoreyed sandstones.The sandstones are cross stratified and often showpreserved dunes of transitional flow regime.

Lithosomes of the delta front depositional sys-tem are characterized by parallel-sided beds ofpebbly sandstones that become gradually pebble-free towards the top of the beds. The bedsoften show Tabc type succession. The pebblesare subangular and dominantly of vein quartzand jasper and range in size from 0.5 to 5 cm.There are also sandstone lithosomes with inter-nal low-angle cross-stratification and with segre-gated pebble layers; on bedding planes wave ripplesare common suggesting wave reworking of the deltafront deposit. Pebble segregation can also be inter-preted to be the result of wave reworking processes.


Figure 7. Sectional view of the Vindhyan Supergroup along the line A–B constructed from the DEM provided by SRTMand field observations. Note plateaus formed by the Semri, Kaimur, Rewa and Bhander Groups of rocks.

5.1c Prodelta/shelf

Lithosomes of the prodelta/shelf depositional sys-tem are represented by regular alternation betweenfine-to-medium grained sandstones and claystone.The sandstone beds are sharp based, parallel sidedand show parting lineated parallel laminae.

5.1d Braidplain and braid delta

Lithosomes of braidplain depositional system aretypically represented by vertically superimposedsheet-like, several meters thick sandstone bodieswith little mudstones. The sandstone bodies haveerosional lower contacts, at places replete withflutes, mud clasts and showing broad concave-upward geometry. Sandstones are dominantlymedium grained; however, pebbly and gritty vari-eties are also common in some lithostratigraphicunits. The sandstones are thoroughly cross strati-fied with trough, tabular and lenticular set geome-try. The shape of cross-strata within a set may varylaterally from planar to concave-up to sigmoidal.The sigmoidal cross-sets often grades verticallyinto parallel-laminated units with parting lin-eation and current crescent. The cross-set thicknessranges between 30 cm and 70 cm and they showdifferent types of reactivation surfaces. There arealso solitary sets of planar cross-strata with a set

thickness of more than a meter. Down current dip-ping cross-sets pertaining to ‘foreset macroform’and small-scale channel fill sandstones have alsobeen observed. Patches of eolianites characterizedby adhesion ripples, translatent strata, along withrain prints are common.

The sandstone bodies show a systematic ver-tical distribution of sedimentary structures fromcross-stratification to parallel-lamination suggest-ing deposition from flood events.

Lithosomes of braid delta depositional systemshare the features of braidplain depositional sys-tem. However, they are comparatively finer-grainedand often show effects of reworking by waveand tide and altogether lack subaerial exposurefeatures.

5.1e Aeolian sandsheet

Aeolian sandsheets have been recognized in theDhandraul, Govindgarh and Shikhaoda Forma-tions wherein they occur sandwiched betweenlithosomes of braidplain and coastal plain deposi-tional system. The deposits include:

• sheet-like sandstones with internal translatentstrata, capped by aeolian and adhesion ripples,

• sandstones internally showing adhesion ripplecross-lamination,


Figure 8. Downdip structural profiles of the Vindhyan succession in the Son valley.


Figure 9. Inferred depositional sequences of the Vindhyan succession. Not to scale.

• lenticular sandstones showing cross-stratificationcharacteristic of meter-scale longitudinal (seif)dunes, and

• lenticular sandstones with transverse aeoliandune cross-strata. The proportions of the lasttwo types of lithosomes are much lower than theother types in the aeolian deposit.

5.1f Siliciclastic tidal flat

Upper tidal flat deposits include interlayeredrippled-sandstones and mudstones with thesand:mud ratio varying widely resulting in lentic-ular bedding, wavy bedding, flaser bedding, etc.The lower tidal flat deposits are cross-stratifiedsandstones with little mud and the cross-strata arearranged in herring-bone pattern. The deposits arecharacterized by interference ripples, ladder-backripples, flat-topped ripples, abundant rain prints,adhesion structures, desiccation cracks, mud clasts.Within the tidal deposits, there are also thickersandstone beds (parallel and/or cross-laminated)showing sole marks, gutters, mud pebbles, etc. rep-resenting deposition from storm induced shootingflows on the tidal flat setting.

5.1g Shoreface

Shoreface deposits are represented by decimeterto meter thick sandstone beds with minor silt-stones and claystones. Two types can berecognized: wave/storm dominated shoreface andtide-dominated shoreface.

Wave/storm dominated shoreface deposits showsharp based (often with sole marks), parallel-sided,cross-stratified sandstone beds grading upward into

ripple bedded muddy sandstones. Cross-strata aredominantly low angle, planar to concave-up, uni-directional and anisotropic, hummocky. Ripplesmay be symmetric and asymmetric in profile withinternal wave-diagnostic lamination. The featuressuggest deposition from sediment-laden combinedflows induced by storms. The vertical variation insedimentary structure and texture indicate domi-nance of unidirectional current component in thecombined flow during the initial stage of depositionwhile oscillatory flow dominated the later phaseof sedimentation. Amalgamation of beds is alsocommon.

Tide-dominated shoreface deposits include sand-stone beds showing compound cross-stratificationcharacterized by horizontal and dipping cross-setswith the internal cross-strata arranged in herring-bone pattern along with reactivation surfaces,mud drapes, mud clasts. The features suggest ashoreface surfaced by asymmetric dunes of tidalorigin with superimposed smaller dunes.

5.1h Inner shelf

The indigenous deposits of inner shelf settingare muds. However, sands may be introduced bystorm flows resulting in interbedded sandstoneand mudstone. Storm deposited sandstone bedsare sharp based with sole marks such as grooves,prods, flutes, gutters, etc. The beds depositedunder the dominance of oscillatory componentshow hummocky cross-stratification and/or wave-ripple bedding grading vertically into the mud-stone. Beds deposited under the dominance ofunidirectional current are typically parallel sidedwith sole marks and internally show Bouma


Table 1. Systems tracts of the Vindhyan Supergroup (Son valley).

Depositional systems Systems tracts Formations

Sequence 5

Braidplain, eolian, tidal flat Falling stage ShikhaodaLagoon, tidal flat Transgressive Sirbu, BundihillSubtidal to peritidal

carbonate platformHighstand Bhander

Tide-influenced coastal flat Transgressive Ganurgarh

Sequence 4

Outer to inner shelf to braid deltato braidplain with eolian patches

Highstand Jhiri, Drammondgunj,Govindgarh

Shoreface Falling stage AsanInner to outer shelf Transgressive Panna

Sequence 3

Inner shelf to braid delta to braid-plain with eolian sandsheets

Highstand Mangeswar, Dhandraul

Inner to outer shelf Transgressive BijaygarhStorm-tide influenced shoreface Falling stage GhagharTide-influenced shoreface to shelf Transgressive Sasaram

Sequence 2

Carbonate ramp Transgressive RohtasStorm-influenced shelf Transgressive RampurShelf to shoreface to tidal flat Highstand Koldaha, Chorhat (Salkhan)Inner to outer shelf with fan delta Overall transgressive with

several intervening fallingstage packages

Deonar, Koldaha

Sequence 1

Subtidal to peritidalcarbonate platform

Highstand Kajrahat

Alluvial fan to fan delta to shelf Transgressive Deoland, Arangi

type sequences. Amalgamation of beds is alsocommon.

5.1i Outer shelf

The deposits of outer shelf depositional systemare typically mudstones with or without thin,parallel-sided layers of parallel laminated and/ormicro cross-laminated fine sandstones depositedfrom storm suspensions with or without the influ-ence of unidirectional current.

5.1j Peritidal carbonates

Peritidal carbonate deposits are characterized byintraclastic, flat pebble conglomerates, tepee struc-tures, desiccation cracks, molar tooth structures,wavy or lenticular bedded limestones, micro-bial laminites, microdigitate or mini stromato-lites (tufa), domal stromatolites, chert nodules andbirds-eye structures.

5.1k Shallow subtidal carbonates

Carbonates of shallow subtidal regime can bedivided into two types:

1. Biohermal and2. Clastic.

Biohermal carbonates show columnar stromato-lites. Clastic carbonates show unidirectional (bothhigh angle and low angle) as well as hummockycross-stratification and horizontal stratification.

5.1� Deep water carbonates

Biohermal deep water carbonates are character-ized by conical stromatolites. The other types ofdeposits include carbonate mud-encased suspen-sion flow deposits characterized by massive carbon-ate conglomerates and calcareous sandstone bedsshowing vertical variation in structure from paral-lel lamination to ripple drift cross-lamination. Thedistal deposits are typically represented centimeterthick interlayers of limestone-shale rhythmites.

6. Sequence stratigraphy

The whole Vindhyan succession in the southernSon valley can be divided into five sequences sep-arated by unconformities with one sequence in the


Bundelkhand region (figure 9). The unconformitiesare manifested in the field by angular discordancesand/or long-term subaerial exposure features. Eachindividual sequence again can be subdivided intoseveral systems tracts represented in the successionas a sediment package defining a particular pale-ogeographic setting (table 2). The systems tractsare bounded by chronstratigraphically significantsurfaces across which a change in paleogeographicsetting can be inferred.

6.1 Sequences of Vindhyan succession

6.1a Sequence 1

Sequence 1 is represented by Deoland, Arangi andKajrahat Formations (figures 2, 3A, B). It consistsof two systems tracts (table 2). The lower tractreflects a paleogeography characterized by alluvialfan, fan delta and prodeltaic shelf and the systemsare arranged in the succession retrogradationallydefining what is known as transgressive systemstract (TST). The TST is followed by a sedimentpackage representing the paleogeography of a car-bonate platform – a homoclinal carbonate ramp. Inthis package, the deep-water carbonates are over-lain by shallow subtidal carbonates with the peri-tidal carbonates occurring at the top. The stackingpattern indicates a highstand systems tract (HST).The boundary between the two systems tracts is,therefore, a maximum flooding surface.

The strata of the alluvial fan system mostly havehigh (>50◦) dips. As a result, true paleocurrentdirections could not be determined; however, thedata suggest northerly transport of sediments witha source towards the south. The mean paleocurrentof the fan delta plain system is towards north, butthe cross-strata azimuths show wide scatter (Boseet al 1997).

6.1b Sequence 2

Sequence 2 is represented by Deonar, Koldaha,Chorhat, Salkhan, Rampur and Rohtas Forma-tions (figure 2). It consists of four major systemstracts (table 2). The first (from the bottom)systems tract is represented by the volcaniclasticsof the Deonar Formation and claystones of theKoldaha Formation. The volcaniclastics and theclaystones were deposited in shelfal water depthsand the package shows a deepening-upwards trenddefining a transgressive systems tract. However,this tract is often intervened by packages ofcoarser clastics (conglomerate, medium to coarsesandstone) deposited in shoreface region in theform of fan delta and braidplain delta represent-ing falling stage systems tracts within the over-all transgressive tract (figure 3F). The second

systems tract represents a paleogeography char-acterized by tidal flat, shoreface and shelf depo-sitional systems. Several parasequences could berecognized in this tract represented by prograda-tional packages of shoreface to tidal flat strataand bounded by flooding surfaces. The parase-quences show an aggradational to progradationalstacking pattern. The systems tract is, therefore, ahighstand systems tract consisting of upper partsof Koldaha Formation and Chorhat Formation(figure 3F).

The tidal flat deposits of the highstand systemstract are sharply overlain by shelf strata belongingto the Rampur Formation (figure 2). The upperbounding surface of the highstand systems tractmay thus be interpreted as a transgressive surfacerepresenting a submarine discontinuity. The sys-tems tract overlying the transgressive surface isrepresented by inner and outer shelf strata defin-ing a deepening upwards trend and thus a trans-gressive systems tract. The top-most or the fourthsystems tract of sequence 2 represents a paleogeog-raphy as a distally steepened carbonate ramp inwhich deposits of deeper systems occur upwards inthe package. The tract is, therefore, a transgres-sive systems tract comprising the Rohtas Forma-tion (figure 2).

Sequence 2 ends with a transgressive systemstract instead of a highstand systems tract. Theupper bounding surface of the top-most TST ofsequence 2 is a major unconformity surface of theVindhyan succession delineating the Lower Vin-dhyan (Semri) from the Upper Vindhyan (fig-ure 4A). In addition to angular discordances, thissurface is also marked by long term subaerialexposure features, e.g., karstic dissolution, baux-itization, etc. Therefore, the absence of the HSTcould be due to erosional removal of the highstandstrata.

The mean crestal trend of the wave ripples occur-ring in the shelf deposits of the second systemstract is along NW–SE. The cross-strata azimuthsof the sandy braid delta systems of the sametract of the sequence indicates a mean paleocurrenttowards NNW, whereas the mean paleocurrentindicated by the conglomerating fan delta systemsis towards NE.

6.1c Sequence 3

Sequence 3 is represented by Sasaram, Ghaghar,Bijaygarh, Mangeswar and Dhandraul Forma-tions of the Kaimur Group and consists of twosystems tracts (figures 2 and 4). The lower sys-tems tract reflects a paleogeography character-ized by shoreface and shelf depositional systems(table 2). This tract contains several parase-quences represented by progradational successions


of tide-dominated shoreface to inner shelf strata,and each parasequence is bounded at the top byflooding surfaces. The parasequences are stackedretrogradationally. This set of retrogradationalparasequences is topped by a regressive surfaceon which sharply occurs a parasequence definedby a progradational succession of storm-dominatedshoreface strata which is bounded at the top by aflooding surface representing a falling stage depositwithin the lower systems tract. The rest of the suc-cession of the lower systems tract is representedby shelfal strata showing a deepening upwardstrend. The lower systems tract, therefore, repre-sents an overall transgressive tract with an inter-vening falling stage (regressive) wedge.

The upper systems tract represents a paleogeog-raphy characterized by braidplain, braid delta andshelf depositional systems arranged in prograda-tional pattern defining a highstand systems tract.The boundary between the two systems tracts is,therefore, a maximum flooding surface.

In the TST, the azimuths of the cross-strataassociated with tidal dunes reveal a bipolar,tri-modal distribution and indicate an averagetidal flow along NE (ebb)–SW (flood) direction.The storm-generated cross-strata in the regres-sive wedge of the TST show wide divergence ofazimuths, but a mean orientation towards northis indicated suggesting offshore transport of sed-iments. The wave ripples of the TST show widescatter with a mean orientation along NNW–SSE.The sole marks occurring in the inner shelf depositsof the TST are typically oriented along NW–SEsuggesting that the storm flow had along-shorecomponents.

In the HST, the cross-strata/lamina of the innershelf deposits shows a mean orientation towardsNNW. The associated sole marks are dominantlyoriented towards NW, although bipolar distri-bution is also common. The paleocurrent pat-tern of the braidplain and braid delta systemsshows a mean sediment transport direction towardsNNW.

6.1d Sequence 4

Sequence 4 is represented by Panna, Assan, Jhiri,Drammondgunj and Govindgarh Formations of theRewa Group (figures 2 and 5). It consists of threesystems tracts (table 2). The lower tract repre-sents a paleogeography characterized by inner toouter shelf depositional systems. The tract is dom-inantly represented by shelfal strata with deep-ening upwards trend, i.e., a transgressive systemstract. This tract is sharply overlain by a packageof shoreface strata bounded below by a regressivesurface and above by a flooding surface (fallingstage deposits). The uppermost systems tract is

represented by braidplain, braid delta and shelfdepositional systems arranged in progradationalpattern defining a highstand systems tract. Theboundary between the two systems tracts is evi-dently a maximum flooding surface.

In the braid delta system of the HST, the cross-strata azimuths show a wide scatter with a meantrend towards WNW, whereas the cross-strata ofthe braid-plain systems are more consistently ori-ented with a mean direction towards NNW.

6.1e Sequence 5

Sequence 5 is represented by Ganurgarh, Bhander,Bundihill, Sirbu and Shikhaoda Formations of theBhander Group (figures 2 and 6). There are foursystems tracts in the succession (table 2). The firsttract is represented by siliciclastic tidal flat, pre-sumably with a carbonate domain in the subtidalpart. The systems are arranged in retrogradationalpattern and thus define a transgressive systemstract. The second tract is represented by a homo-clinal carbonate ramp with a progradational arrayof the depositional systems defining a highstandsystems tract. The third tract reflects a paleogeog-raphy characteristic of siliciclastic, coastal lagoon-tidal flat depositional system overlain by marinestrata representing a transgressive systems tract.The third tract is sharply overlain by coarser,proximal peritidal deposits and thus its top maybe interpreted as a regressive surface. The fourthtract overlying the regressive surface is representedby strata reflecting progradation of a braidplainover the peritidal domain, i.e., a falling stagetract.

The cross-strata of the carbonate platform showa bipolar distribution along NE–SW with thestronger mode towards NE. The associated asym-metric ripples also reveal a mean migration direc-tion towards NE, whereas the symmetric rippleshave a mean crestal trend along NS.

The wave ripple trends in all the peritidalsystems, although boxing the compass, reveal amean trend along 140◦–320◦. The asymmetric rip-ples in the Bundihill Formation show a mean ori-entation towards 35◦, whereas the sole marks inthe Sirbu Formation are grossly oriented along71◦–249◦. Only three flute cast orientations couldbe measured from the lower unit of the ShikhaodaFormation which indicate flows towards 215◦, 10◦

and 357◦. In Bundihill Formation sole mark ori-entations could not be measured due to exposurelimitations. It is thus inferred that the gross orien-tation of the shoreline was NNW–SSW. The WNWdirected paleocurrent of the fluvial deposit in theupper Shikhaoda Formation suggests that the landwas located south of the inferred shoreline. Thewind-induced currents operating in the peritidal


flat thus appear to have had strong cross-shorecomponents.

6.2 Systems tracts at the Bundelkhandsector

It has already been mentioned that there are sed-iment packages in the Vindhyan succession at theBundelkhand region that, lithologically as well asin respect of paleocurrent, stand out from thedepositional systems represented in the southernpart of the Son valley. These packages should thusbe considered as representing separate systemstracts and sequences from those of the southernSon valley.

The entire Semri Group of the northern partperhaps represents a sequence. Absence of vol-caniclastics (represented by the widespread DeonarFormation in southern Son valley and Rajasthan)in this sequence suggests that the sequence post-dates TST-1 of sequence 2 in the southernpart. Interestingly, the paleocurrent data of thissequence demonstrate southerly transport of sedi-ments from a northerly occurring source land.

There are two other sediment packages, at thebase of the Kaimur and Rewa Groups, in the north-ern part standing apart from the depositional sys-tems of the southern Son valley. These packagesrepresent fan delta depositional systems prograd-ing southerly from a northerly occurring scarp(Bose et al 1997).

7. Summary

• The features of the Vindhyan succession clearlyindicate a vast intracratonic basin that remainedwithin tens of meters of sea level throughoutits lifetime. Apparently, shallow water conditionwas maintained over a large area for a longperiod of time suggesting that the sub-Vindhyanlithosphere suffered subsidence over a larger areaproducing a wide shallow ramp type basin. Hun-dreds of meters thick accumulation of peritidalstrata in sequence 5 of the Vindhyan successionindicates that the subsidence rate was in perfectconcert with the rate of sediment supply for aconsiderably long period of time during the endphase of Vindhyan basin evolution – the hall-mark of cratonic basins Sloss (1988a, b). It isinferred that during the terminal period of theVindhyan sedimentation a self-regulating systemof uplift, erosion, sedimentation and subsidencecontrolled the accumulation of strata.

• The Vindhyan basin-fill in the Son valleyexhibits an asymmetric cross-sectional geometrynormal to the regional strike (ENE–WSW) withthe thickest part occurring to the south.

• The Vindhyan strata define a broad, regionalsyncline trending ENE–WNW. The northernlimb of the syncline is homoclinal and has lowdip. In contrast, the southern limb is steeperand shows several sub-regional anticlines inter-vened by synclines arranged in a terrace-like(ramp and flat) fashion.

• In the southern part of the Son valley, theVindhyan basin fill shows several angular uncon-formities that grade into conformities, para-conformities and/or disconformities towardsnorth.

• The different depositional systems recognized inthe Vindhyan succession are: alluvial fan, fandelta, braid delta, braidplain, eolian sand sheet,tidal flat (carbonate as well as siliciclastic),shoreface (tide and storm dominated), stormdominated shelf, homoclinal carbonate ramp,distally steepened carbonate ramp and epeiricperitidal flat (siliciclastic).

• The overall paleocurrent directions of the depo-sitional systems in the Son valley are northerlysuggesting a source towards south.

• The unconformities divide the Vindhyan suc-cession of Son valley into five sequences. Eachsequence consists of several systems tracts rep-resenting different paleogeographic settings andmarking paleogeographic shifts.

• The different strata of the Vindhyan succes-sion show evidences of soft-sediment deformationsuggesting synsedimentary tectonic activity.

• The progressive and successive angular uncon-formities suggest that the deformation patternshown by the Vindhyan strata is a reflection ofsynsedimentary tectonic activity.

• It is postulated that the individual sequences ofthe Vindhyan succession are related to discreteepisodes of tectonism that induced the subsi-dence necessary for accumulation of sedimentsand resulted into deformation of the older strata.Angular unconformities resulted due to erosionof the uplifted crest of the anticlines on whichthe next sequence of strata was deposited withan angular discordance.

• There are sediment packages at the northernpart of the Vindhyan basin developed from anortherly source and thus representing differ-ent tracts and sequences from those of thesouthern part. These packages are representedintermittently in the succession and have beeninterpreted as representing periods of uplift ofthe Bundelkhand Granite and subsequent ero-sion in the north.

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