Integrated borehole and outcrop study for documentation of sea … · 2017. 2. 9. · (mostly...

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

DOI: 10.3724/SP.J.1261.2012.00010

Lithofacies palaeogeography and sedimentology

Integrated borehole and outcrop study fordocumentation of sea level cycles within

the Early Eocene Naredi Formation, western Kutch, India

Urbashi Sarkar, Santanu Banerjee*, P. K. SaraswatiDepartment 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 finally 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 flooding 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, western Kutch, India

1 Introduction*

A combined micropalaeontological, microfacies and field documentation of the mixed siliciclastic‑carbonate succession of the Early Eocene Naredi Formation allows a better reconstruction of the palaeoenvironment and palaeo‑bathymetry. This, in turn, helps to interpret the sequence stratigraphic 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]: 2012‑07‑12 Accepted: 2012‑08‑21

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 shallow‑benthic 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 Palaeocene‑Eocene ther‑mal maxima in the Indian subcontinent. The objectives of the present study include: 1) interpretation of the depo‑sitional environment based on detailed field and microfa‑

Vol. 1 No. 2 127Urbashi Sarkar et al.: Integrated borehole and outcrop study for documentation of sea level cycles 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 etal., 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 flat to low dipping at 1°−3° towards WSW to NW. Biswas (1992) has classified the Palaeogene succession of western Kutch into five 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 identified three members of the Naredi Formation, viz., Gypseous Shale Member, Assilina Limestone 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 For‑mation 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; N23°39′49″; E68°40′38″), the stratotype of the formation, as well as from a borehole (N23°31′00″; E68°36′26″) drilled near the village Baranda (Fig. 1). De‑tailed field 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 attached with Leica DFC420 camera using both transmitted and re‑flected light. The foraminiferal species were hand‑picked under Nikon SMZ 1000 stereo zoom microscope from nearly 45 processed samples. Quantitative distribution of foraminiferal genera per gram of processed samples were recorded. Identification and classification of the Fo‑raminifera were carried out using standard techniques (cf.Loeblich and Tappan, 1988). Altogether 17 genera of Fo‑raminifera were identified from both surface and subsur‑face sections. The planktonic/benthic ratio along with their diversity and abundance and known environmental affin‑ity of foraminifers were used for the palaeoenvironmental analysis and sea level cyclicity (cf. Hallock and Glenn, 1986; Geel, 2000; Wakefield and Monteil, 2002; Murray, 2006; Vaziri‑Moghaddam et al., 2006).

4 Lithological variations in the Naredi Formation

The Naredi Formation is composed of shallow marine, mixed carbonate‑siliciclastic 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 fissile 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 glauconite‑free, red shale often exhibits desiccation cracks in the outcrop indicating emer‑gence 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 Assilina characterizes 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 m‑thick laterite in outcrop. However, no laterite is observed in the borehole, but thick

128 Oct. 2012JOURNAL OF PALAEOGEOGRAPHY

Fig. 1 Geological map showing the Cenozoic outcrops in western Kutch and location of the study area (modified 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 classification of the facies aims to describe the sedimentary processes and deposi‑

tional environment. Carbonate microfacies is compared with the standard ramp microfacies of Flügel (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


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 plac‑es. 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 specific orientation. Nummulites, Rotalia, Cibicides, Asterigerina, Bolivina and 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 Fe‑oxide patches 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, Rotalia and Cibi-cides indicate inner shelf depositional conditions (Murray, 1991). Nummulites occur in a wide range of environment from back reef to mid‑ramp 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).


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‑lites‑dominated 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 filled 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 half‑stained 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 infilled by calcite cement

(marked with arrow).


and Bristow, 1998; Sinclair et al., 1998). The presence of pyrite within the shale indicates local sub‑oxic conditions.

5.2 Assilina Wackestone

The non‑repetitive facies (up to 3 m thickness) occurs at the upper part of the Naredi Formation and is associated

with Assilina packstone. Assilina comprises 50% of the bioclastic component. The other foraminifers includes Nummulites, Rotalia, Cibicides, Eponides, Asterigerina, Nonionella, Bolivina, Bulimina, Triloculina, Quinqueloc-ulina, Spiroloculina and planktonic foraminifers Acarininaand 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.


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 specific orienta‑

tion. Chambers of the fossils are often filled with blocky calcite cements (Fig. 3C) although primary porosities are still preserved in many larger foraminiferal tests. Pyrites and Fe‑oxides 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 fourth‑order (solid curve) palaeobathymetric variation (arrows indicate sample positions for micropalaeontological

and petrographic investigations).

LateCretaceous

toPaleocene

SB

Z 6

SB

Z 7

(?)

SB

Z 8

SB

Z 9

(?)-S

BZ

10

60

50

40

30

20

10

0

6

5

4

3

2

1

SB

Z 1

1

Ear

ly E

ocen

eE

ocen

e

Haru

di

Age

Sha

llow

bent

hic

zone

sS

ampl

e po

sitio

n

Lith

olog

y

Hei

ght f

rom

Nar

edi b

ase

(m)

Juve

nile

and

oth

er

four

th-o

rder

cyc

le

Relativesea levelcurve (m)

0 10 20 30

Basalt

Weatheredbasalt

Shale

Packstone

Solitary

2-5

6-10

11-25

26-50

>50

Barren

INDEX

Foraminiferalcount

M.

Num

mul

ites

Ass

ilina

Cib

icid

es

Rot

alia

Ast

erig

erin

a

Qui

nque

locu

lina

Spi

rolo

culin

a

Trilo

culin

a

Non

ione

llaB

oliv

ina

Bul

imin

a

Briz

alin

a

Bca

rinin

aJe

nkin

sina

Chi

logu

embe

lina


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 Flügel (2004).

The dominance of micrite and non‑oriented fossils suggest a low energy environment. The dominance of microfossils suggests a curtailment of finer siliciclastics supply 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 sub‑oxic conditions.

5.3 Assilina Packstone

The facies (up to 3.5 m thickness) occurs immediate‑ly above the Assilina wackestone facies and is non‑re‑petitive. The main constituent of the facies is Assilinacomprising 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 Assilina wackestone but the abundance of the miliolids is low. In some samples Foraminifera and other fossils are completely broken and it is difficult to carry out quantitative analysis. The abundance and di‑versity of Foraminifera decrease gradually upward. The chambers of the foraminifers and other microfossils are mostly filled with calcite cements (Fig. 3H). Borings may cut across the foraminiferal chambers and are filled with the blocky calcite cement (Fig. 3G). Some of the bioclasts are completely dissolved and are subsequently filled by calcite cements (Fig.3C). Meteoric diagenesis may be the reason for the dissolution of bioclasts and precipitation of calcite. Fe‑oxide and pyrite occur locally within and out‑side the bioclasts. The facies can be compared with the standard microfacies RMF 20 (Flügel, 2004).

Fig. 6 Vertical facies succession of the Naredi Formation from the outcrop section showing quantitative foraminiferal assemblages, third‑ (dotted curve) and fourth‑order (solid curve) palaeobathymetric variation.

LateCretaceous Deccan Trap

SB

Z 8

SB

Z 9-S

BZ

10

(?)

20

10

0

5

4

SB

Z 1

1

Ear

ly E

ocen

eEo

cene Harudi

Age

Sha

llow

ben

thic

zon

es

Hei

ght f

rom

Nar

edi b

ase

(m)

Lith

olog

y

Grainsize

Mud Sand Grain

Mud

Wac

kePa

ck

Gra

in

Rud

&B

ound

four

th-o

rder

cyc

le

Relativesea 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.

Num

mul

ites

Ass

ilina

Trilo

culin

aQ

uinq

uelo

culin

aSp

irolo

culin

aEo

annu

laria

Boliv

ina

Bulim

ina

Cibi

cide

sEp

onid

esA

sterig

erin

aN

onio

nella

Aca

rinin

aJe

nkin

sina

Chilo

guem

belin

aJu

veni

le a

nd o

ther


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 the Assilina wackestone microfacies.

6 Palaeogeography and palaeoenviron-ment

The Naredi Formation, consisting of finer clastics and carbonates, marks the first 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 devoid of 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 lagoonal‑originated Palaeogene Maniyara Fort Formation and the inner shelf‑originated Harudi Formation within the Palaeogene succession of Kutch (Banerjee et al., 2012a, 2012b; Chattoraj, 2012). Assilina wackestone and Assilinapackstone facies represent relatively open marine condi‑tions 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 the Assilina

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 identified 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 finally decreases to‑wards the top part. Benthic Foraminifera Nummulites, Assilina, Bolivina, Bulimina, Eponides, Asterigina, Non-ionella, Cibicides, Rotalia and planktonic Foraminifera Acarinina, Chiloguembelina are found at the middle of the cycle. The remaining portion of the cycle is characterized by the low abundance of benthic foraminifers Nummulites, Rotalia and Cibicides (Figs. 5, 6). Each cycle therefore represents an initial deepening‑upward trend of the relative sea level which is followed upward by a shallowing‑up‑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 the formation, 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, Serra‑Kiel etal., 1998) and the thickness of sediments, these two orders are defined as third‑and fourth‑order sea level cyclicity. It


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 fourth‑order 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, reflects deposition dur‑

Fig. 7 Correlation of third‑and fourth‑order cycles between the borehole section and the outcrop section

TS

T

TS

T

Ear

ly E

ocen

e

SB

Z 8

SB

Z 6

SB

Z 7

(?)

SB

Z 8

SB

Z 9

(?)

-SB

Z 1

0S

BZ

11

Ear

ly E

ocen

e

INDEX

Basalt

Shale

packstoneAssilina

wackestoneAssilina

Laterite

MFS (Fourth-order cycle)

TST (Fourh-order cycle)

HST (Fourth-order cycle)Paleocene to

Late Cretaceous

Weathered basalt

SB

Z 1

1S

BZ

9-S

BZ

10 (

?)

MF

Z

MF

Z

HS

T

HS

T

20

10 50

60

40

30

20

10

0

0

4

4

3

2

1

5

6

5

Late

NE SW

Cretaceous

third

-ord

er c

ycle

third

-ord

er c

ycle

four

th-o

rder

cyc

le

four

th-o

rder

cyc

le

Age

AgeSB

Z

SB

Z

Nar

edi b

ase(

m)

Lith

olog

y

Lith

olog

y

Hei

ght f

rom

Nar

edi b

ase(

m)

Hei

ght f

rom


ing a single third‑order cycle and it represents a sequence.The first 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 transgressive trend continued up to a height of 40-41 m from the base of the formation in borehole section (up to the Assilina pack‑stone). Minor oscillations in the relative sea level curve during the transgression is related to fourth‑order 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 Assilina‑bearing lime‑stone.

Assilina wackestone and Assilina packstone covering a broad zone (nearly 3.5 m to 5 m thick) contains the maxi‑mum species diversity and frequency. The foraminiferal assemblage also indicates a relatively open marine condi‑tion. The maximum flooding surface is characterized by the maximum species frequency and diversity as well as highest planktonic/benthic ratio (cf. Wakefield and Mon‑teil, 2002). Since it is found in a zone rather than a surface it is termed as ‘maximum flooding zone’ (MFZ) instead of maximum flooding surface (MFS) (cf. Montañez and Osleger, 1993; Osleger and Montañez, 1996; Strasser etal., 1999; Colombié and Strasser, 2005). The diversity and abundance of Foraminifera gradually decrease upward above the maximum flooding zone in response to the rela‑tive sea level fall (Figs. 5, 6). The high stand systems tract (HST), occurring above the maximum flooding 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 fourth‑order cycle is referred to as a marine flooding sur‑face (MFS) of the fourth‑order 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 fourth‑order 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 finer 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 identified 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 third‑order sea level cycle with transgressive sys‑tems tract, maximum flooding zone and highstand systems tract has been documented from this formation.

5. Six fourth‑order cycles have been identified. Out of these, five 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 financial 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 and Jianbo Liu for careful review and constructive criticisms of the earlier version of the manuscript.

References

Banerjee, S., Chattoraj, S. L., Saraswati, P. K., Dasgupta, S., Sarkar, U., 2012a. Substrate control on formation and maturation of glauconites in the Middle Eocene Harudi Formation, western Kutch, India. Marine and Petroleum Geology, 30: 144-160.

Banerjee, S., Chattoraj, S. L., Saraswati, P. K., Dasgupta, S., Sarkar, U., Bumby, A., 2012b. The origin and maturation of lagoonal


glauconites: a case study from the Oligocene Maniyara Fort For‑mation, western Kutch, India. Geological Journal, doi: 10.1002/gj.1345.

Biswas, S. K., 1987. Regional tectonic framework, structure and evolution of the western marginal basins of India. Tectonophys‑ics, 135: 307-327.

Biswas, S. K., 1992. Tertiary stratigraphy of Kutch. Journal of the Palaeontological Society of India, 37: 1-29.

Biswas, S. K., Raju, D. S. N., 1973. The rock‑stratigraphic classifica‑tion on the Tertiary sediments of Kutch. Bull. ONGC., 10(1-2): 37-46.

Chattoraj, S. L., Banerjee, S., Saraswati, P. K., 2009. Glauconites from the Late Palaeocene‑Early Eocene Naredi Formation, West‑ern Kutch and their Genetic Implications. Journal Geological So‑ciety of India, 73: 567-574.

Chattoraj, S. L., 2012. Glauconite formation in stratigraphic frame‑work of Palaeogene succession in Kutch. Unpublished Ph.D. Thesis, Indian Institute of Technology Bombay, 222.

Colombié, C., Strasser, A., 2005. Facies, cycles, and controls on the evolution of a keep‑up carbonate platform (Kimmeridgian, Swiss Jura). Sedimentology, 52: 1207-1227.

El Albani, A., Meunier, A., Fursich, F., 2005. Unusual occurrence of glauconite in a shallow marine lagoonal environment. Terra Nova, 17: 537-544.

Flügel, E., 2004. Microfacies analysis of limestone: analysis, inter‑pretation and application. Berlin: Springer, 1-976.

Geel, T., 2000. Recognition of stratigraphic sequences in carbonate platform and slope deposits: empirical models based on microfa‑cies analysis of Palaeogene deposits in southeastern Spain. Pal‑aeogeography, Palaeoclimatology, Palaeoecology, 155: 211-238.

Gilham, R. F., Bristow, C. S., 1998. Facies architecture and geometry of a prograding carbonate ramp during the early stages of fore‑land basin evolution: Lower Eocene sequences, Sierra del Cadí, SE Pyrenees, Spain. Geological Society, London, Special Publi‑cations, 149: 181-203.

Hallock, P., Glenn, E. C., 1986. Larger Foraminifera: a tool for paleoenvironmental analysis of Cenozoic carbonate depositional facies. Palaios, 1: 55-64.

Haq, B. U., Hardenbol, J., Vail, P. R., 1987. Chronology of Fluctu‑ating Sea Levels since the Triassic. Science, New Series, 235: 1156-1167.

Loeblich, A. R., Jr., Tappan, H., 1988. Foraminiferal Genera and their Classification. New York: Van Nostrand Reinhold, 1-970.

Miller, K. G., Kominz, M. A., Browning, J. V., Wright, J. D., Moun‑tain, G. S., Katz, M. E., Sugarman, P. J., Cramer, B. S., Chris‑tie‑Blick, N., Pekar, S. F., 2005. The Phanerozoic Record of Global Sea‑Level Change. Science, 310: 1293-1298.

Montañez, I. P., Osleger, D. A., 1993. Parasequence stacking pat‑terns, third‑order accommodation events, and sequence stratigra‑phy of Middle to Upper Cambrian platform carbonates, Bonanza King Formation, southern Great Basin. In: Loucks, R. G., Sarg,

J. F., (eds.), Carbonate Sequence Stratigraphy. AAPG Mem., 57: 305-326.

Murray, J. W., 1991. Ecology and Palaeoecology of Benthic Fo‑raminifera. Avon UK: Longman Scientific and Technical, 1-397.

Murray, J. W., 2006. Ecology and Applications of Benthic Foraminif‑era. UK: Cambridge University Press, 1-343.

Osleger, D. A., Montañez, I. P., 1996. Cross‑platform architecture of a sequence boundary in mixed siliciclastic carbonate lithofacies, Middle Cambrian, southern Great Basin, USA. Sedimentology, 43: 197-217.

Pande, K., 2002. Age and duration of the Deccan Traps, India: a re‑view of radiometric and paleomagnetic constraints. Proceedings of the Indian Academy of Sciences (Earth and Planetary Scienc‑es), 111: 115-123.

Racey, A., 1994. Biostratigraphy and palaeobiogeographic sig‑nificance of Tertiary nummulitids (foraminifera) from northern Oman. In: Simmons, M. D., (ed). Micropalaeontology and Hy‑drocarbon Exploration in the Middle East. London: Chapman and Hall, 343-370.

Raju, D. S. N., 2008. Phanerozoic Cycles of Sea‑Level Change on Indian Plate: An Overview with a Base Chart. New Delhi, India: GEO India Convention & Exhibition.

Saraswati, P. K, Sarkar, U., Banerjee, S., 2012. Nummulites solitar-ius‑Nummulites burdigalensis lineage in Kutch with remarks on the age of Naredi Formation. Journal Geological Society of In‑dia, 79: 476-482.

Serra‑Kiel, J., Hottinger, L., Caus, E., Drobne, K., Ferrandez, C., Jauhri, A. K., Less, G., Pavlovec, R., Pignatti, J., Samso, J. M., Schaub, H., Sirel, E., Strougo, A., Tambareau, Y., Tosquella, J., Zakrevskaya, E., 1998. Larger foraminiferal biostratigraphy of the Tethyan Paleocene and Eocene. Bull. Soc. Geol. Fr., 169: 281-299.

Sinclair, H. D., Sayer, Z. R., Tucker M. E., 1998. Carbonate sedi‑mentation during early foreland basin subsidence: the Eocene succession of the French Alps. In: Wright, V. P., Burchette, T. P., (eds.), Carbonate Ramps, Geological Society of London Special Publication, 149: 205-227.

Strasser, A., Pittet B., Hillgärtner, H., Pasquier, J. 1999. Depositional sequences in shallow carbonate‑dominated sedimentary systems: concepts for a high‑resolution analysis. Sedimentary Geology, 128: 201-221.

Vaziri‑Moghaddam, H., Kimiagari, M., Taheri, A., 2006. Deposition‑al environment and sequence stratigraphy of the Oligocene‑Mio‑cene Asmari Formation in SW Iran, Lali Area. Facies, 52: 41-51.

Wakefield, M. I., Monteill, E., 2002. Biosequence stratigraphical and palaeoenvironmental findings from the Cretaceous through Ter‑tiary succession, Central Indus Basin, Pakistan. Journal of Micro‑paleontology, 21: 115-130.

(Edited by Liu Min, Wang Yuan)

Integrated borehole and outcrop study for documentation of sea level cycles within the Early Eocene Naredi Formation, western Ku1 Introduction*2 Geological setting3 Samples and methods4 Lithological variations in the Naredi Formation5 Microfacies6 Palaeogeography and palaeoenvironment7 Sea level cycles8 Sequence stratigraphy9 ConclusionsAcknowledgementsReferences

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