Integrated Borehole and Outcrop Study for Documentation of Sea Level Cycles Within the Early Eocene Naredi Formation Western Kutch Ind-libre

8/11/2019 Integrated Borehole and Outcrop Study for Documentation of Sea Level Cycles Within the Early Eocene Naredi For

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Journal of Palaeogeography2012, 1(2): 126-137

DOI: 10.3724/SP.J.1261.2012.00010

Lithofacies palaeogeography and sedimentology

Integrated borehole and outcrop study fordocumentat ion of sea level cycles within

the Early Eocene Naredi Formation, western Kutch, India

Urbashi Sarkar, Santanu Banerjee*, P. K. Saraswati

Department of Earth Sciences, Indian Institute of Technology Bombay, Powai, Mumbai-400076, India

Abstract A combined micropalaeontological and sedimentological investigation of the

Early Eocene Naredi Formation (thickness varying between 20 m and 60 m) reveals a com -plete third-order cycle and six fourth-order sea level cycles. Within the third-order cycle the

foraminiferal abundance and diversity gradually increase upwards and reach their maximum

values at about 41 m thickness above the base of the formation and subsequently decrease

upward and nally give way upward to an unfossiliferous zone at the topmost part. Within a

fourth-order cycle foraminiferal abundance and diversity exhibit a similar increasing and de-

creasing pattern. Bounded between two unconformities the Naredi Formation represents a

sequence. A highly fossiliferous Assilina-bearing limestone interval represents the maximum

ooding zone which separates the transgressive systems tract at the base from the highstand

systems tract at the top.

Key words Early Eocene, Naredi Formation, sea level cycle, Foraminifera, westernKutch, India

1 Introduction*

A combined micropalaeontological, microfacies and

eld documentation of the mixed siliciclasticcarbonate

succession of the Early Eocene Naredi Formation allows a

better reconstruction of the palaeoenvironment and palaeo

bathymetry. This, in turn, helps to interpret the sequencestratigraphic architecture, as well as the evolution of the

basin. The Early Eocene Naredi Formation in the west

ern Kutch has been studied extensively from the biostrati

graphic point of view but little work has been done on the

sea level cyclicity, sequence stratigraphy and depositional

environment for this formation. Raju (2008) presented a

broad overview of sequences and sea level cycles in Kutch

in a stratigraphic compilation of sedimentary successions

* Corresponding author: Professor. Email: [email protected].

Received: 20120712 Accepted: 20120821

of India. Chattoraj et al.(2009) reported glauconitic shale

within the outcrop of the Naredi formation and discussed

mineralogical characteristics of the glauconite. A recent

recovery of borehole samples in this area has indicated

that a complete succession of the Naredi Formation is

present only in the subsurface. The outcrop of the Naredi

Formation represents only the upper part of the formation.Saraswati et al.(2012) constrained the age of the Naredi

Formation as Early Eocene, ranging from shallowbenthic

zones SBZ 6 to SBZ 11. The exposed part of the Naredi

is referred to SBZ 8 to SBZ 11. The extended section in

the borehole thus further incorporates the present under

standing of sea level cycles in this region. Sequence strati

graphic interpretation of the Naredi Formation is likely to

provide new insights about the PalaeoceneEocene ther

mal maxima in the Indian subcontinent. The objectives of

the present study include: 1) interpretation of the depo

sitional environment based on detailed eld and microfa


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Vol. 1 No. 2 127

Urbashi Sarkar et al.: Integrated borehole and outcrop study for documentation of sea levelcycles within the Early Eocene Naredi Formation, western Kutch, India

cies investigations, 2) to propose sequence stratigraphic

architecture, as well as the sea level cycles of the Naredi

Formation, based on detailed micropalaeontological and

sedimentological investigations, and to compare it with

the global sea level curve of the Early Eocene (cf.Haq et

al., 1987; Miller et al., 2005).

2 Geological setting

The Kutch Basin originated as a rift basin on the west

ern margin of India during the Jurassic and subsequently

evolved as a passive margin (Biswas, 1987). The onshore

Palaeogene sediments crop out to the south of the Great

Rann of Kutch around the Deccan trap exposures (Fig. 1).

The Cenozoic sediments of the western Kutch unconform

ably overlie either the Deccan Trap (69-63 Ma, Pande,

2002) or Mesozoic sediments. The beds are almost atto low dipping at 13 towards WSW to NW. Biswas

(1992) has classied the Palaeogene succession of western

Kutch into ve formations, viz., the Matanomadh, Naredi,

Harudi, Fulra and Maniyara Fort formations from the bot

tom to top (Table 1). The basal Matanomadh Formation is

poorly exposed and consists of unfossiliferous sandstones

and shales with minor lignites. The formation occurs lo

cally and is absent in places; the overlying Naredi Forma

tion may rest directly on the Deccan Trap. Biswas (1992)

has identied three members of the Naredi Formation, viz.,

Gypseous Shale Member,AssilinaLimestone Member and

Ferruginous Claystone Member. However, the thickness

of the Naredi Formation is highly variable and all three

members rarely occur together in the outcrop. Lignite and

carbonaceous shales of variable thickness occur locally

within the formation. The Naredi Formation is mainly ma

rine, containing diverse kinds of fossils, including inverte

brate fossils (mostly bivalve and gastropod), Foraminifera

(mostly Assilina, Nummulites) and ostracoda and it con

tains glauconites in places (Chattoraj et al., 2009). The

contact between the Naredi Formation and the Harudi Formation is locally marked by a laterite horizon.

3 Samples and methods

Samples for the present study were collected from

the Kakdi River section from the Naredi village (Naredi

cliff section; N233949; E684038), the stratotype of

the formation, as well as from a borehole (N233100;

E683626) drilled near the village Baranda (Fig. 1). De

tailed eld documentation was carried out in the Naredi

cliff section. The borehole samples provided a nearly com

plete documentation of the Naredi Formation, as the lower

part of the Naredi Formation is not exposed in the cliff

section (Saraswati et al., 2012).

Standard thin sections were prepared from samples for

microfacies studies. Petrographic analysis were carried out

using a Leica DM 4500P polarizing microscope attachedwith Leica DFC420 camera using both transmitted and re

ected light. The foraminiferal species were handpicked

under Nikon SMZ 1000 stereo zoom microscope from

nearly 45 processed samples. Quantitative distribution

of foraminiferal genera per gram of processed samples

were recorded. Identication and classication of the Fo

raminifera were carried out using standard techniques (cf.

Loeblich and Tappan, 1988). Altogether 17 genera of Fo

raminifera were identied from both surface and subsur

face sections. The planktonic/benthic ratio along with their

diversity and abundance and known environmental afnity of foraminifers were used for the palaeoenvironmental

analysis and sea level cyclicity (cf. Hallock and Glenn,

1986; Geel, 2000; Wakeeld and Monteil, 2002; Murray,

2006; VaziriMoghaddam et al., 2006).

4 Lithological variations in the NarediFormation

The Naredi Formation is composed of shallow marine,

mixed carbonatesiliciclastic sediments (Chattoraj, 2012).

The formation overlies directly on the weathered basalt of

the Deccan Trap. The Naredi Formation is dominated by

grey, green and reddish grey shale in outcrop. The shale is

thinly bedded and planar laminated to massive and ssile

in nature. The shale comprises the bulk of the sediments in

the lower and middle part in the borehole and also appears

at the top (Fig. 2). The shale is characterized by the vary

ing amount of glauconites and marine fossils. The glauco

nite content may be as high as 50% of the total sediment

in places. The intervening glauconitefree, red shale often

exhibits desiccation cracks in the outcrop indicating emergence of the substrate. The facies thickness varies from 12

m (in outcrop) to 40 m (in borehole). Carbonate replaces

the shale in the upper part of the formation. Dominance of

Assilinacharacterizes the carbonates. The lower part of this

carbonate is composed of loose, wackestone, but its upper

part comprises relatively harder packstone. The carbonate is

overlain by shale with minor siltstone intercalations at the

topmost part of the Naredi Formation. The top part of the

shale, near the contact with the overlying Harudi Forma

tion, is locally marked by a 2.3 mthick laterite in outcrop.

However, no laterite is observed in the borehole, but thick


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128 Oct. 2012JOURNAL OF PALAEOGEOGRAPHY

Fig. 1 Geological map showing the Cenozoic outcrops in western Kutch and location of the study area (modied from Biswas and

Raju, 1973) (inset showing map of India).

unfossiliferous red shale is found (Figs. 5, 6, 7).

5 Microfacies

Microfossil, texture and primary sedimentary features

are used to recognize three microfacies within the Naredi

Formation. The description and classication of the facies

aims to describe the sedimentary processes and deposi

tional environment. Carbonate microfacies is compared

with the standard ramp microfacies of Flgel (2004) for

the interpretation of depositional environment.

5.1 Shale

Shale is the most frequently occurring facies in the

Naredi Formation. The colour of the facies may be red,

brown, grey or green. The greenness of the rocks depends


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Vol. 1 No. 2 129


on proportion of glauconite (Fig. 3A). This facies is thinly

bedded, planar laminated to massive in nature. Vertical to

highly inclined burrows disrupts original laminae in places. It contains Foraminifera, ostracodes, echinoderms and

other invertebrate fossil fragments. The abundance and di

versity of the fossils (Fig. 3B) within the shale may vary

widely, ranging from fossiliferous, grey to green shale to

completely unfossiliferous red shale. Preservation of fos

sils is medium to good. In highly fossiliferous parts the

fossils do not exhibit any specic orientation.Nummulites,

Rotalia, Cibicides, Asterigerina, Bolivinaand planktonic

foraminifers Acarinina, Chiloguembelina and Jenkinsina

(Fig. 4) commonly occur within the shale. The diversity

and abundance of Foraminifera are generally lower com

pared to the rest of the Paleogene sections of the Kutch

(Chattoraj, 2012). In certain intervals ostracodes domi

nate over Foraminifera (Fig. 5). A few pyrite and Feoxidepatches are encountered within and outside the skeletal

fragments.

Deposition of clayey sediments suggests a low energy

depositional environment. Lack of preferred orientation

of the fossils suggests a considerably weak current. The

presence of glauconite indicates a slow rate of sedimenta

tion. Quantitative analysis of foraminifers reveal a depth

range of 0 to 10 m (Figs. 5, 6).Bolivina,Rotaliaand Cibi-

cidesindicate inner shelf depositional conditions (Murray,

1991).Nummulitesoccur in a wide range of environment

from back reef to midramp setting (Racey, 1994; Gilham

Fig. 2 Field photograph of the Early Eocene Naredi Formation, western Kutch, India. A-Field photograph of brown shale from the

Naredi cliff section (hammer length = 35 cm); B-Field photograph of green shale from the Naredi cliff section (pen length = 12 cm);

C-Field photograph of red shale from the Naredi cliff section (pen length = 12 cm); D -Field photograph of laterite at the top of the

Naredi cliff section (swiss knife length = 7.5 cm).


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Fig. 3 Microphotograph of the Early Eocene Naredi Formation, western Kutch, India. A-Photomicrograph (plane polarized light)

showing glavconite grains from the shale facies; B-Photomicrograph (plane polarized light) of shale microfacies from a Nummu

litesdominated layer; C-Photomicrograph (plane polarized light) showing blocky calcite crystals within a void space in the Assilina

packstone facies; the white arrow marks a dissolved bioclast later lled by blocky calcite crystals; D-Photomicrograph (crossed polar

ized light) showing cubic pyrite crystals (marked with arrow) within Assilina; E-Photomicrograph (plane polarized light) showing Fe

patches from the Assilina wackestone microfacies; F-Photomicrograph (plane polarized light) of a halfstained thin section showing

Assilina packstone facies (arrow indicates Assilina); G-Photomicrograph (plane polarized light) of a boring (marked by a white arrow)

cutting across a foraminiferal shell; H-Photomicrograph (plane polarized light) showing ostracode shell inlled by calcite cement

(marked with arrow).


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Vol. 1 No. 2 131


and Bristow, 1998; Sinclair et al., 1998). The presence of

pyrite within the shale indicates local suboxic conditions.

5.2 AssilinaWackestone

The nonrepetitive facies (up to 3 m thickness) occurs

at the upper part of the Naredi Formation and is associated

with Assilinapackstone. Assilinacomprises 50% of the

bioclastic component. The other foraminifers includes

Nummulites, Rotalia, Cibicides, Eponides, Asterigerina,

Nonionella,Bolivina,Bulimina, Triloculina, Quinqueloc-

ulina, Spiroloculinaand planktonic foraminifersAcarinina

and Chiloguembelina(Fig. 4). Overall, the abundance and

Fig. 4 Scanning electron micrographs of the external views of Foraminifera. 1-Assilina sp.; 2-Eoannularia sp.; 3-Num-

mulites burdigalensis; 4-Nummulites globules nanus; 5-Rotalia sp.; 6-Eponides sp.; 7-Asterigerina sp.; 8-Cibicides sp.;

9-Nonionella sp.; 10-Quinqueloculina sp.; 11-Spiroloculina sp.; 12, 13-Bolivina sp.; 14-Acarinina sp.; 15-Chiloguembelina sp.;

16-Jenkinsina sp.


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diversity of foraminifers are high and it increases gradu

ally upward. Although planktonic foraminifers are present,

their abundance is considerably less (planktonic/benthic

ratio ~ 1: 99). The degree of fragmentation of shells is me

dium, but the shells do not exhibit any specic orienta

tion. Chambers of the fossils are often lled with blocky

calcite cements (Fig. 3C) although primary porosities are

still preserved in many larger foraminiferal tests. Pyrites

and Feoxides are found within and outside the chamber

of the foraminifers (Figs. 3D, 3E). Glauconite occurs lo

Fig. 5 Vertical facies succession of the Naredi Formation in the borehole section showing quantitative foraminiferal assemblage, third

(dotted curve) and fourthorder (solid curve) palaeobathymetric variation (arrows indicate sample positions for micropalaeontological

and petrographic investigations).

Late

CretaceoustoPaleocene

SBZ6

SBZ7(?)

SBZ8

SBZ9(?)SBZ10

60

50

40

30

20

10

0

6

5

4

3

2

1

SBZ11

EarlyEocene

Eocen

e

Harudi

Age

Shallow

benthiczones

Sampleposition

Lithology

Heightfrom

Naredibase(m)

Juven

ilean

do

ther

fourth

ordercycle

Relativesea levelcurve (m)

0 10 20 30

Basalt

Weatheredbasalt

Shale

Packstone

Solitary

2-5

6-10

11-25

26-50

>50

Barren

INDEX

Foraminiferal

count

M.

Nummu

lites

Ass

ilina

Cibicides

Rota

lia

Asterigerina

Qu

inque

locu

lina

Sp

iro

locu

lina

Tri

locu

lina

Non

ione

lla

Bo

liv

ina

Bu

lim

ina

Briza

lina

Bcarin

ina

Jen

kins

ina

Chiloguem

be

lina


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Vol. 1 No. 2 133


cally and its concentration is less compared to the green

shale. Micrite is recrystallized in places to form calcite

pseudospar. The facies is comparable to the microfacies

RMF 20 of Flgel (2004).

The dominance of micrite and nonoriented fossils

suggest a low energy environment. The dominance of

microfossils suggests a curtailment of ner siliciclasticssupply to the depositional setting. Quantitative study of

foraminiferal data suggests a bathymetric range between

10 m and 30 m (Figs. 5, 6). Occurrence of miliolid fora

minifers suggests sheltered environment. The presence of

abundant pyrite in places suggests local suboxic conditions.

5.3 AssilinaPackstone

The facies (up to 3.5 m thickness) occurs immediate

ly above the Assilina wackestone facies and is nonre

peti tive. The main constituent of the facies is Assil ina

comprising nearly 50%of the allochemical components

(Fig. 3F). Other species of larger benthic foraminifers,

smaller benthic foraminifers and ostracodes constitute

the remaining allochems. The foraminiferal assemblage

is similar to the Assilinawackestone but the abundance

of the miliolids is low. In some samples Foraminifera and

other fossils are completely broken and it is difcult to

carry out quantitative analysis. The abundance and diversity of Foraminifera decrease gradually upward. The

chambers of the foraminifers and other microfossils are

mostly lled with calcite cements (Fig. 3H). Borings may

cut across the foraminiferal chambers and are lled with

the blocky calcite cement (Fig. 3G). Some of the bioclasts

are completely dissolved and are subsequently lled by

calcite cements (Fig.3C). Meteoric diagenesis may be the

reason for the dissolution of bioclasts and precipitation of

calcite. Feoxide and pyrite occur locally within and out

side the bioclasts. The facies can be compared with the

standard microfacies RMF 20 (Flgel, 2004).

Fig. 6 Vertical facies succession of the Naredi Formation from the outcrop section showing quantitative foraminiferal assemblages,

third (dotted curve) and fourthorder (solid curve) palaeobathymetric variation.

Late

CretaceousDeccan Trap

SBZ8

SBZ9

SBZ10(?)

20

10

0

5

4

SBZ11

EarlyE

ocene

Eocen

eHarudi

Age

Shallow

benthiczones

Heightfrom

Naredibase(m)

Lithology

Grainsize

Mud Sand Grain

Mud

Wacke

Pack

Grain

Rud&

Bound

fourth

ordercycle

Relative

sea levelcurve (m)

0 10 20 30

Basalt

Wackestone

Shale

Packstone

Laterite

Barren

Solitary

2-5

11-25

26-50

>50

6-10

INDEX

Foraminiferalcount

M.

N

ummulites

A

ssilina

T

riloculina

Q

uinqueloculina

S

piroloculina

E

oannularia

B

olivina

B

ulimina

C

ibicides

E

ponides

A

sterigerina

N

onionella

A

carinina

Jenkinsina

C

hiloguembelina

J

uvenile

ando

ther


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Quantitative analysis of foraminifers suggests a ba

thymetric range between 5 m and 20 m (Figs. 5, 6). The

microfacies indicates slight increase in energy conditions

compared to theAssilinawackestone microfacies.

6 Palaeogeography and palaeoenviron-ment

The Naredi Formation, consisting of ner clastics and

carbonates, marks the rst marine transgression of the Ce

nozoic succession of Kutch. It contains marine biota in

cluding benthic and planktonic Foraminifera. Quantitative

analysis of the foraminifers suggests a palaeobathymetric

range between 0 to 30 m. The shale facies records a bathy

metric range from 0 to 10 m and represents the shallowest

depositional conditions. The red shale layers in the out

crop bear evidences of emergence and are totally devoidof marine fossils while the alternating grey to green shales

are fossiliferous, often containing glauconite and pyrite.

Perfectly gradational contacts between different types of

shales represent a sedimentation continuum within a low

energy depositional regime. The shallow marine, low en

ergy depositional setting, representing fossil assemblage

characteristic of a restricted setting may be best interpreted

as a lagoon. The colour variation of the shale facies is re

lated to the variation in organic content, variable duration

of exposure of the substrate, and variation in glauconite

content. The red shale possibly represents the marginal part

of the lagoon while the grey and green shale represents the

deeper part of the lagoon. Although glauconite is abundant

in the outer shelf depositional setting the mineral is report

ed from lagoonal conditions (El Albani et al., 2005 and

references therein). Glauconite is also reported from the

lagoonaloriginated Palaeogene Maniyara Fort Formation

and the inner shelforiginated Harudi Formation within the

Palaeogene succession of Kutch (Banerjee et al., 2012a,

2012b; Chattoraj, 2012).Assilinawackestone andAssilina

packstone facies represent relatively open marine conditions and possibly formed in proximity to the barrier. The

occurrence of these two facies over shale facies, therefore,

suggests a relative sea level rise. Foraminiferal data re

veal a bathymetry up to 30 m for these two facies. In the

absence of any reef/bar in the seaward side it is inferred

that the elevated areas of the Deccan Trap possibly formed

a protected lagoonal condition. Evidence of meteoric di

agenesis in such a shallow water setting are manifested by

partial to complete dissolution of bioclasts and precipita

tion of blocky cements. Meteoric diagenesis took place as

the relative sea level fall after the deposition of theAssilina

packstone facies.

7 Sea level cycles

The variation in faunal assemblages provides two differ

ent orders of cyclicity within the Naredi Formation (Figs.5, 6). The higher order cycle thickness varies ~5 m to ~12

m, while the lower order cycle thickness ranges from 20

m to 60 m. Six higher order cycles have been identied

within the borehole section against one lower order cycle

(Figs. 5, 6).

Within each higher order cycle the foraminiferal abun

dance and diversity increases from the bottom, exhibits

maximum values at the middle and nally decreases to

wards the top part. Benthic Foraminifera Nummulites,

Assilina, Bolivina, Bulimina, Eponides, Asterigina, Non-

ionella, Cibicides, Rotalia and planktonic ForaminiferaAcarinina, Chiloguembelinaare found at the middle of the

cycle. The remaining portion of the cycle is characterized

by the low abundance of benthic foraminifersNummulites,

Rotalia and Cibicides (Figs. 5, 6). Each cycle therefore

represents an initial deepeningupward trend of the relative

sea level which is followed upward by a shallowingup

ward trend (Figs. 5, 6). The fossil abundance and diversity

may vary from cycle to cycle. While the entire formation is

developed within the borehole section, the outcrop section

exhibits incomplete development of the Naredi Formation.

Two higher order cycles (No. 4, No. 5) occurs both in out

crop and subsurface while four of the higher order cycles

have not developed in the outcrop (Fig. 7).

Relative sea level appears to have increased in the sec

tion up to ~41 m from the base of the Naredi Formation

(corresponding to Assilina packstone) and subsequently

records the fall and ultimate exposure of the depositional

substrate. Therefore, a smaller order cyclicity has been re

corded which shows transgressive trend at the base and

regressive trend at the top. The species diversity and abun

dance of Foraminifera is generally low near the base of theformation, but increases gradually at the upper part of the

lower order cycle indicating rise of relative sea level (Figs.

5, 6). Maximum diversity and abundance of Foraminifera

have been observed at a height of ~41 m from the base of

the formation. The smaller order cyclicity is also observed

in the outcrop section.

Considering the age range of the Naredi Formation

from SBZ 6 to SBZ 11 (Saraswati et al., 2012), the total

duration of sedimentation (4.5 Ma to 5 Ma, SerraKiel et

al., 1998) and the thickness of sediments, these two orders

are dened as thirdand fourthorder sea level cyclicity. It


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Vol. 1 No. 2 135


may be mentioned that six smaller order cycles have been

mentioned from the Early Eocene (cf. Haq et al., 1987;

Miller et al., 2005) and it is likely that the six fourthorder

cycles of the Naredi Formation represents the global sea

level cycles.

8 Sequence stratigraphy

The studied succession of the Naredi Formation is

bounded by two unconformities at the bottom and at the

top which marks the sequence boundaries. The bottom is

marked by a disconformity between the Paleocene Matano

madh Formation (Biswas, 1992) and Early Eocene Naredi

Formation (Biswas, 1992). The upper sequence boundary

is a paraconformity between the Early Eocene Naredi and

Middle Eocene Harudi Formation, often marked by a lat

erite cover in the outcrop (Biswas, 1992; Chattoraj, 2012).

The Naredi Formation, therefore, reects deposition dur

Fig. 7 Correlation of thirdand fourthorder cycles between the borehole section and the outcrop section

TST

TST

Early

Eocene

SBZ8

SBZ6

SBZ7(?)

SBZ8

SBZ9(?)-SBZ10

SBZ11

Early

Eocene

INDEX

Basalt

Shale

packstoneAssilina

wackestoneAssilina

Laterite

MFS (Fourth-order cycle)

TST (Fourh-order cycle)

HST (Fourth-order cycle)Paleocene to

Late Cretaceous

Weathered basalt

SBZ11

SBZ9-

SBZ10(?)

MFZ

MFZ

H

ST

HST

20

10 50

60

40

30

20

10

0

0

4

4

3

2

1

5

6

5

Late

NE SW

Cretaceous

third-ordercyc

le

third-ordercyc

le

fourt

h-ordercyc

le

fourt

h-ordercyc

le

Age

Age

SBZ

SBZ

Nare

dibase

(m)

Litho

logy

Litho

logy

He

ightfrom

Nare

dibase

(m)

He

ightfrom


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ing a single thirdorder cycle and it represents a sequence.

The rst marine transgression in the Early Eocene starts

at the bottom of the Naredi Formation. Species diversity

and abundance of Foraminifera is generally low near the

bottom, but increases gradually in the upper part indicating

a rise of relative sea level (Figs. 5, 6). The transgressivetrend continued up to a height of 40-41 m from the base of

the formation in borehole section (up to theAssilinapack

stone). Minor oscillations in the relative sea level curve

during the transgression is related to fourthorder cyclic

ity. This part of the formation is therefore considered as

the transgressive systems tract (TST). It includes the entire

shale facies occurring below the Assilinabearing lime

stone.

Assilinawackestone andAssilinapackstone covering a

broad zone (nearly 3.5 m to 5 m thick) contains the maxi

mum species diversity and frequency. The foraminiferalassemblage also indicates a relatively open marine condi

tion. The maximum ooding surface is characterized by

the maximum species frequency and diversity as well as

highest planktonic/benthic ratio (cf.Wakeeld and Mon

teil, 2002). Since it is found in a zone rather than a surface

it is termed as maximum ooding zone (MFZ) instead

of maximum ooding surface (MFS) (cf.Montaez and

Osleger, 1993; Osleger and Montaez, 1996; Strasser et

al., 1999; Colombi and Strasser, 2005). The diversity and

abundance of Foraminifera gradually decrease upward

above the maximum ooding zone in response to the rela

tive sea level fall (Figs. 5, 6). The high stand systems tract

(HST), occurring above the maximum ooding zone and

extending up to the laterite, consists of poorly fossiliferous

to unfossiliferous shale. The top part of the HST is barren

in both borehole and outcrop section and the HST is trun

cated at the top by a laterite (in the outcrop) or red shale

(in the borehole). A similar depositional trend has been ob

served in the outcrop section, although the thicknesses of

both transgressive systems tracts and high system tract are

much reduced (Figs. 5, 6).The zone with maximum foraminiferal richness within

a fourthorder cycle is referred to as a marine ooding sur

face (MFS) of the fourthorder cycle. The lower part of the

MFS has a gradual increasing sea level trend and this can

be attributed as the TST. A decreasing sea level trend has

been noted above the MFS which is considered as HST

of the fourth order cycle (cf. Strasser et al., 1999). An

attempt has been made to correlate the fourthorder TSTs

and HSTs of the borehole section with the outcrop section

(Fig. 7). Apparently, the cliff section developed on top

of a basement high and it remained emerged for most of

the early part of sedimentation. The sedimentation com

menced in the outcrop section in response to rapid rise

of the relative sea level (Fig. 7) representing SBZ 8. The

borehole section, however, represents sedimentation con

tinuum representing SBZ 6 to SBZ 11.

9 Conclusions

Microfacies study and foraminiferal assemblages of the

Naredi Formation has led to the following conclusions.

1. The Early Eocene Naredi Formation consisting of

ner clastics and carbonates were deposited in a lagoonal

depositional environment.

2. Shale facies represents the marginal part of the la

goon attached to the land whereas the wackestone and

packstone facies belong to more open, external part of the

lagoon.3. On the basis of foraminiferal abundance and diver

sity, two orders of cyclicity have been identied within the

Naredi Formation; the smaller order cycle thickness rang

ing from 20 m to 60 m and higher order cycle thickness

ranges between 5 m and 12 m.

4. A thirdorder sea level cycle with transgressive sys

tems tract, maximum ooding zone and highstand systems

tract has been documented from this formation.

5. Six fourthorder cycles have been identied. Out of

these, ve cycles belong to the transgressive systems tract

and one belongs to the highstand systems tract. While all

the cycles are well developed in the borehole section, the

outcrop represents incomplete preservation of the cycles.

Acknowledgements

The authors are thankful to the Department of Science

and Technology for the nancial support (project No. SR/

S4/ESe281/2007). The authors acknowledge the infra

structural support provided by Indian Institute of Technol

ogy Bombay. The authors acknowledge Tadeusz Peryt andJianbo Liu for careful review and constructive criticisms

of the earlier version of the manuscript.

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Documents

Integrated Borehole and Outcrop Study for Documentation of Sea Level Cycles Within the Early Eocene Naredi Formation Western Kutch Ind-libre