CHAPTER-2

STRATIGRAPHIC UNITS

2.1 Introduction

The Mesozoic rocks exposed in the study area range in age from

Callovian to Albian i.e. Upper Jurassic to Lower Cretaceous and are overlain

by the Deccan Traps. Milliolitic sandstones of Quaternary age are exposed

along valleys and on gentle hill slopes. As per the lithostratigraphic

classification of Biswas (1977) the Mesozoic sediments are classified in to four

units - Jhurio Formation, Jumara Formation, Jhuran Formation and Bhuj

Formation. These are co-relatable to Patcham, Chari, Katrol and Umia Series

respectively as per the chronostratigraphic classification. The boundaries of

both the classifications are not exactly match except the Jumara-Jhuran

boundary to that of Chari-Katrol boundary. In the present study the author is

following the lithostratigraphic classification of Biswas ( 1977). Of these four

units, rocks of Jhurio Formation and some part of Lower Jumara Formation are

not exposed in the study area. So, the sediments exposed in the present study

area starts from Lower Jumara Formation. Along with Lower Jumara

Formation, rocks of Jhuran and Bhuj Formation are exposed extensively. In

fact most part of the study area is covered by Jhuran and Bhuj Formation. In

the extreme south, Bhuj Formation is overlain by Deccan Trap Formation.

These sediments were laid down in two mega-cycles, a Middle Jurassic

transgressive cycle and a Late Jurassic-Early Cretaceous regressive cycle. The

two mega cycles include short phases of transgressive-regressive sub-cycles

(Biswas, 1991 ). These rock formations include various alternations of shales,

limestones, siltstones and sandstones. Overall the shales are dominant in the

lower part- in Jumara Formation and in Lower and Middle Jhuran Formation,

while sandstones are more prominent in the upper part - in Upper Jhuran and

Bhuj Formation. Fossil content is also abundant in the lower part and it

becomes decreases towards the top part. Trace fossils are also found present in

almost all the successions and abundant at the partings of shale-siltstone

34

intercalations. Fossil wood and leaf impressions are also found preserved in

various successions.

Based on field observations, these sediments for this study area are

further sub-divided in to ten stratigraphic units or members. For this purpose

different parameters have been checked during the filed work, such as rock

types, sedimentary structures, grain size variation, types of contacts, thickness

of strata, vertical and lateral extension and presence of body and trace fossils.

Mainly based on the lithic changes and distinct contacts, these ten members are

formed, which are included under the three main Formations such as Jumara,

Jhuran and Bhuj. These members are listed in the lithostratigraphic

classification of the study area as given in Table 7.

Table 7: Lithostratigraphic classification of the study area

FORMATION MEMBER STAGE AGE Bhuj Rukmavati Member Neocomian to Lower Cretaceous

God_!)_ar Member Santonian Sir Edmund Lake Kimmeridgian Upper Jurassic to

Jhuran Member to Lower Lower Cretaceous Rathi Dungar Member Neocomian Kandawari Wadi Member Dhosa Oolite Member Oxfordian Piludi Lake Member

Jumara Samtiya Dun gar Callovian Upper Jurassic Member Chadwa Dun gar Member Bharasar Member

The brief descriptions of all these Members are as follows.

A unique feature of the Kachchh basin is meridional high occurnng

across the basin hinge zone, which passes through the study area. This is

affecting ·the thickness of sediments deposited in this part of the basin. The

Median High seems to have been developed during the sedimentation. The Pre­

Callovian beds (Jumara Formation) show uniform thickness and facies across

this high, whereas the Post-Callovian sedimentation (Jhuran and Bhuj

Formation) have been controlled by it. Evidence of sediment thickness and the 35

facies indicate that this high came into existence in Late Oxfordian time and

remained as an active synchronous high till the end of Mesozoic sedimentation

in Late Cretaceous. The rise of the median high at the beginning of the Late

Jurassic is the earliest tectonic movement marked by the Late Oxfordian

unconformity (Biswas, 1991 ).

2.2 Jumara Formation

Jumara Formation has been named after its type section in Jumara Hill

near the Rann, north of Jumara village. The formation is exposed in form of

inliers at the centers of the domal and anticlinal hills and particularly in

Charwar range it is found in more or less circular and elliptical outcrops as a

whole. According to lithostratigraphy (Biswas, 1977) it has been sub-divided in

to four informal members - number I to IV from below on the basis of the

limestone or sandstone intercalations dividing the continuous shale sequence.

Towards the eastern part, as found in Jhurio and Habo dome and Charwar

range, it is more arenaceous in the lower part. This formation is the richest in

fossil content of all the formations. More commonly different genera and

species of ammonites, belemnites, brachiopods, bivalves and gastropods found

along with some scattered vertebrate remains throughout the formation. The

upper boundary with Jhuran Formation is distinct. The contact is marked by

topmost oolitic band which is conglomeratic and separates the unfossiliferous

shales of Jhuran Formation from the fossiliferous shales found along with

Dhosa Oolite bands. From the lithological and biologic aspects it appears to

have been deposited below the wave base in circa-littoral environment (Biswas,

1977). Ghosh (1969), based on fossil assemblages, fixed a Callovian-Argovian

age for the "Chari Series" of Jumara dome. The equivalent Jumara Formation

ranges in age between Callovian to Oxfordian (Biswas, 1977).

Rocks of Jumara Formation are exposed around following localities:

East of Wandhaya village, South of Samatra village, Near Prag Sar, Samtiya

Dungar block, Chadwa Dungar block, South of Bharasar village in Bharasar

36

dome, near Shiv-parasnath temple at Wala-Khawas on Bhuj-Mandvi road, and

near Bhata talav on Bhuj-Mundra road.

Overall thickness of the Formation is approximately 234 m. Based on

major lithological changes and distinct contacts; Jumara Formation has been

divided in to five members in ascending order as follows:

(1) Bharasar Member

(2) Chadwa Dungar Member

(3) Samtiya Dungar Member

( 4) Piludi Lake Member

(5) Dhosa Oolite Member

The oldest beds exposed in the study area are shales along with thin

intercalations of siltstones and limestones. It is overlain by thick sandstones,

siltstone-shale intercalations and finally at the top Dhosa Oolite bands are

exposed, which are unconformably overlain by Jhuran Formation. These rocks

appear to have been involved in a number of tectonic events. They are also

found penetrated by basic igneous intrusions - dykes and laccoliths at various

localities as discussed earlier. So, the rocks have became folded, faulted and

baked at places. All these dykes along with major almost north-south trending

faults divide the area in to different blocks from east to west named as

Bharapar block, Bharasar Dome block, Chadwa Dungar block, Samtiya Dungar

block, Prag Sar block and W andhaya block.

2.2.1 Bharasar Member (BM):

The oldest rocks of the study area are exposed 2 km south of Bharasar

village in the Bharasar dome. The location is situated at 23° 1 0' 45" N latitude

and 69° 33' 31" E longitude with 175 m elevation above mean sea level. This is

the type section as well as only one exposed section in the study area from

which it is named as "Bharasar Member". The total thickness of Bharasar

Member is more than 56 m. This member is typically exposed in the northern

flanks of the Bharasar dome, which is lying south of the east-west trending

Katrol Hill Fault and east of the prominent basic dyke (God par dyke) trending

37

in NNE-SSW direction. This member is depicted in the Geological map of the

study area (Figure 6).

As a whole, the Bharasar Member is shaly in nature. In the lower part, in

between shales, thin bands of limestones are common, which is the main

characteristic of the Bharasar Member. Shales are yellowish to greenish in

colour. Shales are exposed due to the hard partings of red ferruginous bands

and limestones and also due to their upheaval along the up throw side of Katrol

Hill fault. In the upper part shales are yellowish to pinkish in colour due to

presence of ferruginous material with beautiful lamination. Here at places

offshoots of the prominent basic God par dyke are exposed, nearer to which the

shale sequence becomes baked and found in form of black shale. Limestones

are grayish in colour, fine grained and it becomes cherty in upper layers.

Limestone becomes reddish-highly ferruginous in the upper part, which is

highly fossiliferous, although the fossils are smaller in size. They are minute

shells of bivalves. Some bands of limestones are crystalline. Thickness of

limestones ranges from 0.4 m - 2.5 m. Intraformational conglomerate bands

(Plate la) are also found in shale sequence. Pebbles in the intraformational

conglomerate are clayey - yellowish and limonitic-highly ferruginous enclosed

in calcareous matrix. Fossils of bivalves-astarte and belemnites are common in

conglomerate. Average thickness of intraformational conglomerate is 0.15 m.

Uppermost boundary of the Bharasar Member is fixed at the top of hard­

projected sandstone bed which is purple-ferruginous and medium to coarse

grained with inverse grading and gravelly top. At places it becomes gritty. It is

about 2.0 m thick bed. Throughout the sequence thin gypsum layers or lenses

and red-ferruginous bands are common.

Strata are disturbed by Katrol Hill Fault. Due to Katrol Hill Fault, the

oldest rocks of the area are directly come in contact with much younger rocks

of Bhuj Formation, which are exposed Northward of the fault. Many small

faults associated with Katrol Hill Fault also displace the strata. Folding is also

common here along with igneous intrusions. The most prominent basic dyke-

38

Figure 6: Geological Map of the Study Ar1

pur eMirjapur

N ,.;.I~ "I'·

3 9 (For Legend refer next page)

Legend for Geological Map -==== Faults

--Dykes

D Rukmavati Member

D Godpar Member

D Sir Edmund Lake Member

D Rathi Dungar Memebr

D Kandawari Wadi Member

D Dhosa Oolite Member

D Piludi Lake Member

D Samtiya Dungar Member

D Chadwa Dungar Member

D Bharasar Member

D Plugs and sill

Lakes

D Deccan Trap Formation

40

Plate 1

~,.-.. .._. ""' _,.., ~· ~£ ~,~~ • • liO ... ~· - ~- -~~ -~--::--~.:~;;_-----~ ... ~~~~·: ~~~=a; .. ,_~~··~·"--~~~-- ~ ~ . -;.;l-:~-: : .... ~ ~-;::-~:::.~-~~i:-~: _.__ - - . --- <t_;.-~.;~ ..;~ -.] I ~· y .. ~ ~ -- '"''"'~ f f - !

' ~ ·' .,.. .. \ ·\ ·.- .~:,:·

. T ·A,.-.

(a) Intraformational conglomerate band, Bharasar Member of Jumara Formation, Bharasar dome.

(b) Sandstone ofMFSS facies, Chadwa Dungar Member of Jumara Formation; quarry section, Bharasar dome.

(c) Rounded to sub-rounded cobbles found enclosed within the matrix of sandstone, Samtiya Dungar Member of Jumara Formation, Samtiya Dungar.

(d) Topmost conglomeratic band ofDhosa Oolite, Dhosa Oolite Member of Jumara Formation, Kandawari Wadi.

Scale for Plate 1 & 2: 1 rupee coin= 2.5 em, 2 rupee coin= 2.6 em, Diary = 19 em, Pen = 15 em, Brush = 15 em, Hammer = 31 em

41

doleritic is exposed at Bharasar, extends towards South up to Jamora lake.

Displacement of strata has been noticed along this dyke.

Bibalves are abundant in Bharasar Member- mainly astarte. Among

other fossils belemnites, gastropods and ammonoids are noted in the field.

Fossils mainly found from intraformational conglomerate as well as from

shale-limestone intercalations. Some unidentifiable plant remains are also

found. Trace fossils are abundant in the thin partings and different varieties

include Bergaueria, Dendrotichnium, Didymaulichnus, Monocraterion,

Ophiomorpha, Palaeophycus, Phymatoderma, Taenidium, arthropod trails and

ammonoid reel marks.

Based on fossil content, the Bharasar Member is assigned to Lower to

Middle Callovian age according to Spath (1924, 1933), Pascoe (1959), Rajnath

(1932, 1942), and Krishnan (1968).

2.2.2 Chadwa Dungar Member (COM):

The rocks of Chadwa Dungar Member are best exposed in the Chadwa

Dungar block lying SW of the Bharasar village and west of NNE-SSW

trending Godpar dyke. The location is 23° 10' 51" N latitude and 69° 33' 09" E

longitude. This type section is exposed along the stream near Bharasar quarries,

which is 1.94 km away from Bharasar village in SW direction. Rocks of CDM

are also exposed in Bharasar dome, overlies Bharasar Member conformably as

well as in Samtiya Dungar block, which is lying west of Chadwa Dungar block.

The total thickness of CDM is approximately 70 m.

The rocks composing the CDM are shales, siltstones, sandstones and

intraformational conglomerate. Entire section is best exposed in Chadwa

Dungar block and Bharasar Dome, while in Samtiya Dungar block only upper

part of the member is exposed.

In the lower part of CDM as found in Bharasar Dome, there are

numerous intercalations of shale-siltstone. The intercalations are lying

conformably over the hard, gritty, ferruginous sandstone of Bharasar Member.

Thickness of these intercalations are about 1 0 m. Abundant bioturbation is

42

found preserved in these partings. Lower part of CDM in Chadwa Dungar is

more arenaceous than the Bharasar dome along with intercalations of shale­

sandstone.

Middle part is arenaceous with about 9 m thick beds of massive

sandstones. The lower 3 m thick sandstone is pink in colour-ferruginous with

feldspar content and upper 6 m thick sandstone is yellowish. Both are separated

by thin shale bed. Sandstones are hard, medium grained with uniform grain

size. It is quarried for various purposes (Plate 1 b).

In upper part of CDM again shales and shale-siltstone partings are

abundant along with one band of intraformational conglomerate. Shales are

thick (total thickness is about 50 m), yellowish as well as grayish and red­

ferruginous in colour. Fine lamination due to colour variation is distinct. There

are 5 partings of siltstone (0.5 m thick) with abundant bioturbation preserved in

it within this thick shale sequence at various levels. Thin gypsum layers are

common throughout the sequence. A band of intraformational conglomerate

with calcareous matrix and clayey pebbles - yellowish to reddish-limonitic

with fossils of belemnite guard (abundant) and bivalve (astarte) is distinct in

thick shale sequence near to the top of CDM. Overall CDM is more

argillaceous with sandstones along with shale-siltstone intercalations in the

middle part, while in underlying Bharasar Member limestone intercalations are

more with shales and accordingly the lower boundary of CDM is fixed on the

bases of the commencement of shale on inverse graded gritty-gravelly

sandstone of the top part of Bharasar Member. The upper boundary of CDM is

fixed on the top of thick shale sequence with lamination which is followed by

thick sandstones of Samtiya Dungar Member having erosional contact with

underlying shale.

Chadwa Dungar block and Samtiya Dungar block are two larger

anticlines in which these rocks are exposed. In the centre part of the blocks, the

upper part of CDM is exposed. While in the northern part of blocks, along

Katrol Hill Fault younger rocks are exposed and in the southern part along with

other younger rocks Dhosa Oolite Member is found. These blocks on both east

43

and west sides are bounded by prominent and almost north-south trending

faults occupied by basic dykes. Both the dykes are doleritic in composition -

one with NNE-SSW orientation is Godpar dyke, another with north-south trend

is Dahisara dyke. Chadwa Dungar block is confined on east by Godpar dyke

and on west by Dahisara dyke, which also confines the eastern part of Samtiya

Dungar block. Further westward, a prominent fault which runs from north of

Phat Sar bounding the Samtiya Dungar block on west. Dip of the beds are very

gentle in the central part of the domes, while at the margins dip varies from

30°-40°.

Sandstones of CDM show beautiful interference ripple marks along with

micro ripples and cross-bedding. At certain places calcite veins has been

developed along the cracks of sandstones.

Belemnites are by far the abundant in CDM along with other fossils such

as, bivalves, brachiopoda (Rhynchonellid) and ammonoids. Fossils are' found

from intraformational conglomerate as well as from the shale-siltstone

intercalations. Some unidentifiable plant remains also found from shales.

Along the partings of shale-siltstone abundant bioturbation is preserved. Few

indistinct trace fossils are also recorded from the thick sandstone, which is

quarried. Different varieties include Arenicolites, Biformites, Calycraterion,

Didymaulichnus, Diplocraterion, Fustiglyphus, Glockeria, Gyrolithes,

lmponoglyphus, Lockeia, Megagrapton, Monocraterion, Ophiomorpha,

Palaeophycus, Phycodes, Phymatoderma, Stellascolites, Taenidium,

Teichichnus, Thalassinoides etc.

According to Spath (1924, 1933) Pascoe (1959), Rajnath (1932, 1942),

Krishnan (1968), the CDM is assigned to Middle Callovian age based on fossil

content.

2.2.3 Samtiya Dungar Member (SDM): The type section is exposed in Samtiya Dungar at 23° 09' 49" N latitude

and 69° 30' 58" E longitude, from which the name has been given as "Samtiya

Dungar Member". It is 3.75 km away from the Samatra village in southeast

44

direction. Rocks of SDM are also exposed in Samtiya Dungar block, Chadwa

Dungar block, Bharasar dome and Wala-Khawas area ofBharapar block. It has

covered wide tract in Samtiya Dungar anticline and Chadwa Dungar anticline,

while it forms small patches at Bharasar dome and Wala-Khawas area. The

total thickness of the SDM is approximately 36m.

SDM is overall arenaceous and composed of medium to coarse grained,

hard, red-ferruginous sandstone. It is characterized by the presence of rounded

to sub-rounded cobbles and boulders (diameter varies from 5 em to 2 m) of

sandstones enclosed within the matrix of sandstone (Plate 1 c). The exposed

boulders occasionally are worshiped by the local people as "Shivlinga"­

representing the symbol of mighty god "Shiva''. In Samtiya Dungar block and

Chadwa Dungar block it occupies wide tract because SDM is exposed at the

centers of this two anticlines. It is found usually as the ridge top. In the central

part of the anticlines, the beds are gently inclined to nearly horizontal at places,

while on the margins dip is as high as 51 o in Chadwa Dungar block. The lower

part of the SDM is exposed at the northern periphery of Samtiya Dungar

anticline. The oldest bed of SDM exposed is yellowish sandstone (2 m thick)

with thin bands of elongated, ferruginous pebbles. Cross-stratified, medium

grained sandstone bed (7 m thick) with ferruginous to calcareous matrix

exposed above first one, in which lower 3.0 m is red-highly ferruginous.

Bioturbation is preserved indistinctly in the sandstones of lower part. This is

followed by 2 m thick shale bed, which is overlain by a prominent sandstone

bed with rounded to sub-rounded cobbles and boulders of sandstones.

Thickness of this bed varies from place to place. It forms top of the ridge at

most of the locations. At places sandstone becomes gritty. In Bharasar dome

SDM is somewhat thin than the type section and not quarried like the sandstone

ofCDM.

One of the peculiarities of SDM is the presence of sandstone with

rounded to sub-rounded cobbles and boulders, which are texturally and

lithologically slightly different than the host rock. As proposed by Bhatt, 1996,

45

the fonnation of boulders can be attributed to any one of the following cause or

combinations:

• Erosion of underlying sandstone in some nearby area possibly under

sub- aerial arid conditions, later on resulting products being entrapped in

this litho unit.

• These boulders might be remnants of some totally washed out sandstone

bed, which during some exceptionally strong stonn event rolled and

entrapped in this bed.

• Could have produced due to early diagenesis.

• These objects may be the products of localized precipitation of mineral

matter- mostly carbonate.

• May be resulted within the depositional basin due to large scale

reworking and surging under exceptionally high energy conditions.

• May be caused due to centralized cementation in the pores of sediment

about a nucleus or centre, known as 'Kugelsandstein" (Fuhrmann,

1968).

• These may be sand balls, similar in origin to armored mud balls (Bell,

1940) and reported in various conditions, here may be beach (Kugler

and Saunders, 1959).

Stratigraphically the lower boundary of SDM can be fixed with cross­

stratified sandstones with indistinct bioturbation lying above the shales of

CDM. At the junction plane, load casts of sandstones are developed in lower

shales. The upper boundary is fixed on the top of the unfossiliferous, cross­

stratified sandstones, which are overlain by highly fossiliferous, gritty

sandstones ofPiludi Lake Member.

The sedimentary structures such as cross-bedding, herringbone structure,

ripple marks, interference ripples etc. are common in SDM. In the upper part

folding is frequently found in fonn of symmetrical anticlines and synclines.

Minor faults are also found trending in almost north-south direction. In Samtiya

Dungar block, one interesting feature found is a basic-doleritic sill which is

penetrated within the sandstones of SDM. The sill also covers large tract along 46

with SDM in the Samtiya Dungar block. Godpar dyke, Dahisara dyke, as well

as other igneous intrusions is protruding SDM along with other members of

Jumara Formation.

Bivalves, brachiopods and plant fossils are observed in the lower part of

SDM. Compare to CDM fossil content is very less. Trace fossils are not

common but in the lower part some structures found such as, Biformites,

Chondrites, Dip/ocraterion, Monocraterion, Ophiomorpha, Palaeophycus,

Taenidium, Teichichnus, Tha/assinoides, Rivulrites (pseudo trace fossil).

Middle callovian age can be assigned to the SDM following Pascoe

(1959), Krishnan (1968), Rajnath (1932, 1942), etc.

2.2.4 Piludi Lake Member (PLM): The name has been given from the type section which is exposed near

Piludi Lake, on southern flank of Bharasar dome. The coordinates of the

section are 23° 09' 55" N latitude and 69° 33' 37" E longitude. It is 3.38 km

due south of Bharasar village. PLM is also exposed in the other parts of the

study area, such as - Chadwa Dungar block, Samtiya Dungar block, Prag Sar

block, Wandhaya block and Wala-Khawas area of Bharapar block. The total

thickness of PLM is approximately 54 m. Thickness varies at different sections.

Shale is dominant in PLM with thin bands of limestones, siltstones and

intraformational conglomerates. Sandstone beds are somewhat thicker varies

from 0.6 to 5 m in thickness. In the lower part of PLM sandstones are common,

in the middle part - shale with thin intercalations of limestones and in the upper

part shale is dominant. At few places in the upper part along with sandstone

thin bands of limestone and intraformational conglomerate are exposed.

In Bharasar dome, the rocks of PLM are exposed typically. In the lower

part of PLM, mainly sandstones are exposed. These sandstones are hard,

ferruginous, cross-stratified and highly fossiliferous. Fossils are of belemnites,

brachiopods-mainly large Rhynconella and ammonoids. At places it is gritty

also. At least four fossiliferous sandstone bands intercalated with shales are

exposed. In the middle part of PLM shales - yellowish and greenish are

47

------------ -------

exposed with thin bands of fine grained, grayish, cherty limestone. In the upper

part of PLM mainly shales are forming the low grounds before the prominent

ridge of Dhosa Oolite. Shales exposed along the streams are yellowish to

greenish and gypseous. At few places 1.5 m thick gypsum bands are exposed,

as found near Samatra village i.e. in Prag Sar block. Red-ferruginous bands are

also common along with gypseous shales. These red bands are also highly

fossiliferous containing belemnites, bivalves and brachiopods. In the upper part

of PLM at certain places such as Prag Sar block as well as northern flank of

Samtiya Dungar block and near Kandawari Wadi, yellowish calcareous to red­

ferruginous sandstone is exposed, which is also fossiliferous consisting

bivalves, belemnites, brachiopods and ammonoids fossils. In Bharasar dome

particularly southwest of Piludi Lake, in the upper part of PLM along with

shale, siltstone and intraformational conglomerate bands are exposed on the

lower ground. In the conglomerate pebbles are clayey in nature with yellowish

and reddish-ferruginous in colour. Matrix is siliceous with coarser grain size.

Belemnites are abundant in this conglomerate. This intraformational polymictic

conglomerate which possibly marks a major stormy event can be seen

developed over the fossiliferous beds (Bhatt, 1996). The top part of PLM is

very well exposed at northern flank of Samtiya Dungar anticline near small

weir. Here along with shale-sandstone intercalations, gritty bioclastic

conglomerate-highly ferruginous and fossiliferous and conglomerate with silty

matrix and abundant bivalves forming the topmost part of PLM. This

conglomerate indicates sub-aerial erosional event and an unconformable

junction with the younger Dhosa Oolite Member. Here nearer to the Dahisara

dyke sandstones having minute fossils of vertebrates - probably teeth and

vertebrae of fish enclosed in hard, ferruginous, coarse grained sandstones. Near

Kandawari Wadi of Chadwa Dungar block, topmost part of PLM is exposed in

form of at least two bands of hard, ferruginous sandstone. Mega ripples are

found on the surface of sandstone along with bivalves and vertical burrows. At

the top red-ferruginous conglomerate bed is exposed with Thalassinoides.

Throughout the member claret-dark red to brownish coloured ferruginous

48

nodules or concretions occur at well defined levels. According to Fursich et al.

(1992) the concretions are interpreted as of early diagenetic origin during

trangressive low sediment influx phases, within rhythmic transgressive­

regressive cycles.

Stratigraphically the lower boundary of the PLM can be fixed by cross­

stratified, calcareous gritty sandstones which are lying conformably over the

topmost beds of SDM. This boundary is sharp and nondepositional. Both the

sides of the boundary hard sandstones are exposed, but it is distinguishable

because in SDM, sandstones are un-fossiliferous. While in PLM, sandstones

are highly fossiliferous and gritty. The uppermost boundary is fixed by the a

hard 2 - 4 m thick sandstone bed containing numerous Thalassinoides and

gritty to pebbly inverse graded top part, which is the top most band of PLM and

underlying the shales of Dhosa Oolite Member. This topmost sandstone bed of

PLM is equivalent to the ridge sandstone or China wall sandstone of Biswas

(1977).

Sedimentary structures like cross-stratification, ripple marks as well as

mega ripples, herringbone structure are mainly found in the hard sandstones.

Bioclastic red ferruginous conglomerate indicate the unconformable junction

with younger Dhosa Oolite Member. Normal graded bedding and inverse

grading in gritty sandstone is also common. Folding is also found at certain

places mainly in sandstones. Many minor faults are found affecting the PLM.

Along with other members of Jumara Formation PLM is also traversed by

north-south trending major faults, which are described earlier.

Bivalves and brachiopods - mainly larger Rhynconellids are abundant

everywhere in PLM. Other fossils found at certain locations only are

belemnites, ammonoids, vertebrate remains etc. Trace fossils are not abundant

in PLM compared to other members of J umara Formation. At most of the

places structures are indistinctly preserved. Trace fossils include Arenicolites,

Chondrites, Lockeia, Monocraterion, Ophiomorpha, Palaeophycus, Taenidium

and Thalassinoides.

49

Upper Callovian age can be assigned to PLM following to Pascoe

( 1959). According to Pandey and Dave (1993) unconformable junction

between the PLM and Dhosa Oolite Member represents unconformity between

Callovian and Oxfordian. As per these authors, the standard ammonite zone of

Kachchh equivalent to the Member is P. athleta zone of Upper Callovian.

2.2.5 Dhosa Oolite Member (DOM): The name of the member is derived from the topmost bands of Jumara

Formation popularly known as Dhosa Oolites. These are the distinct marker

horizons in the Mesozoic sequence throughout the Kachchh mainland

separating Jumara Formation from Jhuran Formation. According to surface

distribution it is more prominently developed than the PLM even though the

thickness is restricted to few meters only. In the study area typically it is

exposed at Samtiya Dungar block and Chadwa Dungar block. It is also exposed

in other parts of the area like Bharasar Dome block, Prag Sar block, Wandhaya

block, near Shiv-Parasnath temple at Wala-Khawas on Bhuj-Mandvi road and

near Bhata talav on Bhuj-Mundra road. The cumulative thickness of the DOM

generally tends to be around 18 m. Thickness varies at different locations.

DOM mainly comprises of Dhosa Oolite and shale. There are alternate

bands of shale and Dhosa Oolite. Dhosa Oolite is the most consistent

lithological feature of Jumara Formation. It is the fossil rich oolitic limestone,

often sandy and nodular in appearance. The oolites are 2 to 4 mm in size and

yellowish to grayish-green and brownish in colour found enclosed in muddy

matrix. At places angular quartz grains are seen embedded in the matrix along

with the ooliths. There are some variations in lithology from section to section.

Usually the topmost band is conglomeratic and 3 to 4 bands of Dhosa Oolite

found alternating with shales. Often the rock appears as mixed complex pattern

of more than one lithology. The mixing of the lithologies is ascribed to the

burrowing activity of organisms. The large broken blocks of the rock suggest

collapse of lithified burrow systems - mainly of Thalassinoides giving a

conglomeratic look to the rock (Plate 1 d). It contains reworked rounded to

50

elongated pebbles. Majority of these pebbles are bored and/or encrusted by

bivalves and/or brachiopods. Largest measured dimension of one of these

boulders is 80 em x 60 em x 25 em, while dimension of the smallest pebble is

2 em x 3 em. Some of the boulders contain ammonoid or echinoderm fossils in

their core part. These boulders are mixed with fossiliferous lag deposits

indicating high energy conditions (Bhatt, 1996). At many places on surfaces

dissolution effects and crust development is seen. At most of the places calcite

veins are found within Dhosa Oolite along with crystals of nailheadspar.

Usually 3 to 4 bands of Dhosa Oolite are found at different sections in the

study area, but behind the Shiv-Parasnath temple, near Wala-Khawas on Bhuj­

Mandvi road, 5 bands and to the north of Prag Sar, 6 bands of Dhosa Oolite

occur.

Lower part of the member is argillaceous along with the marl bands as

found near Samatra -Northern flank of Samtiya Dungar anticline. In the upper

part different bands of Dhosa Oolite found alternating with shales. Shales are

mainly yellowish to grayish in colour and gypseous and glauconitic at certain

places. Shales are usually weathered out while Dhosa Oolite cropping out as

prominent ridge. Shale beds are usually 0.5 to 10 m in thickness while Dhosa

Oolite ranges from 0.15 to 0.5 m. Pandey and Dave (1993) have included about

50 m of shale immediately underlying the Dhosa Oolite in the Oxfordian on the

basis of benthonic foraminifer studies. As to Singh ( 1989), this stage represents

transgressive condensed horizon at the time of lower Oxfordian followed by a

hiatus during Middle and Upper Oxfordian.

Stratigraphically, the DOM overlies the PLM and underlies the

Kandawari Wadi Member of Jhuran Formation. The lower boundary can be

fixed by the yellowish to grayish shale, which are underlying as well as

alternating with oolitic limestone bands and lying above the sandstone of PLM.

The topmost boundary of DOM can be fixed by a thick bioclastic

intraformational conglomerate and ferruginous crust at or near its top. Reddish

brown ferruginous crust has been formed on the intraformational autoclastic

conglomerate. The PLM and DOM discussed as separate member, even though

51

their depositional conditions seems to be similar. Soft sediment characters are

similar in both the members but different hard and prominent beds of PLM are

conglomeratic with a mixture of ferruginous and calcareous material as matrix.

This suggests high energy to stormy conditions with low rate of net sediment

supply. While in DOM such beds are mainly calcareous and only ferruginous

material found is in form of ooids. Further coarser - rudaceous to arenaceous

material is absent, which in general suggests low energy condition and low rate

of net sediment supply (Bhatt, 1996).

This is the topmost member of the Jumara Formation. It exhibits on its

top, a prominent disconformity and a large time lapse evident by conglomerate

and mineral crust. This is not only structural but biogenic content of DOM and

immediate overlying rocks also points out same general thing (Agrawal, 1957;

Fursich et al., 1992).

The rocks of DOM lacks in any distinct physical structures like cross­

bedding, ripple marks etc. But it is affected by faulting, folding and penetrated

by igneous intrusions like the other members of Jumara Formation. Dhosa

Oolite band is displaced along the Godpar dyke and Dahisara dyke. Near

Samatra village, laccolith - basic intrusion is exposed, on the periphery of

which Dhosa Oolite band is typically found. Near the Wandhaya village, Dhosa

Oolite band is found folded in to anticlines and synclines, which is mapped on

large scale. Dip of the Dhosa Oolite band is usually more than 30° except few

places where it is horizontal, but at places it is almost vertical.

Dhosa Oolite unit is very rich in fossils, especially ammonoids, along

with brachiopods, bivalves - Oysters and belemnites. Other fossils like

nautiloids, gastropods and fossil wood is also commonly found. Common

bivalves of the Dhosa Oolite are Pleurotomaria, Lopha, Pecten, Trigonia,

Modiola, Inoceramus, Pinna, Astarte, etc. Many species of brachiopod -

Rhynconella and Terebratula are also present (Singh, 1989). Shells are

frequently bored and encrusted and occasionally covered with a thin

ferruginous crust. The fossils of Dhosa Oolite are often corroded, sometimes

showing limonitic crust (Spath, 1933 ). All the thin sections of the Dhosa Oolite

52

invariably show presence of foraminifera and few also depicts presence of

ostracods. Among the trace fossils, Zoophycos and Thalassinoides are

abundant. Other recorded is mainly Rhizocorallium.

Oxfordian age is assigned to DOM, based on biostratigraphic evidences

as per Spath ( 1933 ), Rajnath (1932, 1942), Pascoe (1959), Krishnan (1968) etc.

As per Fursich et al. (1992), it represents the sediments of Middle Oxfordian

Plicatilis zone.

2.3 Jhuran Formation

Jhuran Formation has been named after its type section exposed along

the stream passing close to the ruined village of Jhuran. The lower and upper

limits of the Formation are very well defined in this section. In Charwar Range,

the rocks of Jhuran Formation show more uniform lithologic characteristics.

According to lithostratigraphy (Biswas, 1977) it has been sub-divided into four

members - Lower, Middle, Upper and Katesar. The Charwar Hill Section can

be considered as a para-stratotype for the Formation which also represents the

typical Lower, Middle and the lower part of the Upper Members (Biswas,

1993). In the southern strip of Mainland, rocks of Jhuran Formation extend

along the Katrol Hill Fault from the Nana Dongar Hill on the west to Nigal on

the east. The older formation, i.e. Jumara Formation occurs as inliers within

this Formation at the cores of the closed structures. As discussed earlier, the

lower boundary of Jhuran Formation with Jumara Formation is distinctly

marked on the top Dhosa Oolite band. The upper boundary with Bhuj

Formation is disconformable to overlapping. The marine sandstones of the

Jhuran Formation grade upward into marginal marine sandstones of the Bhuj

Formation. Jhuran sandstones are calcareous~ which are overlain by rhythmic

sequences of ironstone and lateritic bands of the marginal marine Bhuj

sandstones. The paralic facies and the physical and biological characteristics of

the sediments of different members tend to indicate that the environment

shifted from sub-littoral to supra-littoral and finally into continental deposition

53

of the overlying formation (Biswas, 1977). The age of the Jhuran Formation

can be fixed as Kimmeridgian to Lower Neocomian from the mega fossils and

the palaeobotanical evidences. In the revised time-stratigraphic scale (Royal

Dutch Shell Group, 1958), Argovian is placed as a separate stage above the

Oxfordian and below the Kimmeridgian. Hence the time range of the Jhuran

Formation is, therefore, stated as Argovian to Neocomian (Lower Cretaceous)

(Biswas, 1993 ).

Rocks of Jhuran Formation are exposed around following localities:

south and southwest of Wandhaya village, near Gurukul Dongar, Ajapar, Prag

Sar, Pad Sar, Rathi Dungar, Wagrai Dungar, south of Kandawari Wadi, near

Jamora lake, Sir Edmund lake, south ofShiv-parasnath temple at Wala-Khawas

on Bhuj - Mandvi road, near Sanatorium, south of Bhata Talav on Bhuj -

Mundra road and near Tapka Devi Mandir. Overall thickness of the formation

is approximately 280 m. Based on the major lithological changes, distinct

contacts and unconformable junctions, Jhuran Formation has been divided into

three members in ascending order as follows:

(1) Kandawari Wadi Member

(2) Rathi Dungar Memebr

(3) Sir Edmund Lake Member

The formation is predominantly argillaceous in the lower and middle

parts and arenaceous in the upper part. The contacts between the members are

gradational and inter-tongue with each other which make it difficult to place a

boundary accurately between any two members in the field. In the study area

the rocks of Lower, Middle and Upper members of Jhuran Formation are

exposed, but there are no outcrops of the youngest Katesar member of Jhuran

Formation. It comprises a thick sequence of alternating beds of sandstone and

shale. The rocks of Jhuran Formation shows gentle dip towards southern side,

but at times there are some variations in strike and dip of the strata. Faulting

and igneous intrusions are again common in Jhuran Formation similar to the

Jumara Formation.

54

2.3.1 Kandawari Wadi Member (KWM): The name has been given from the section exposed adjacent to

Kandawari Wadi. Although there are many good sections of this member ot

Jhuran Formation, but here these rocks are very well exposed. The coordinates

are 23° 09' 0.01" N latitude and 69° 31' 29.62" E longitude. It is 710 m due

west of Kandawari Wadi. Rocks of KWM are also exposed in Chadwa Dungar

block, Bharasar Dome block, Prag Sar block, Wandhaya block, near Shiv­

parasnath temple at Wala-Khawas on Bhuj- Mandvi road and near Bhata talav

on Bhuj- Mundra road. Overall thickness of the KWM is approximately 40 m.

Thickness of the Member varies from place to place.

K WM is defined by ferruginous sandy shales occasionally grey in

colour and gypseous in nature. These bands alternating with shale is lying

above the Dhosa Oolite Member of Jumara Formation unconformably. These

ferruginous sandy shale partings are famous as Katrol ammonite beds. This is

followed by alternate sequence of shale, siltstone and sandstone.

The lowermost part of KWM is very well exposed around Kandawari

Wadi as well as S of Wandhaya village. Towards west of Kandawari Wadi,

above Dhosa Oolite there are at least 13 ferruginous bands alternating with

shales. Number of these bands varies at different locations from 5 to 18.

Maximum 18 such bands exposed at Wala-Khawas on Bhuj - Mandvi road.

Ferruginous bands are sandy to silty and 5 to 10 em in thickness. These bands

are having ammonites enclosed in large red coloured pebbles. Near Phat Sar

lake cobble sized rounded and red-ferruginous concretions are found enclosed

in shale-siltstone intercalations. Burrowing activity, fossil wood and box work

is common in these bands. Mud drape - thin encrustation of ferruginous

material indicates local break in sedimentation. In these mud drapes, cracks are

developed and later on filled up by fine grained material during sub-aerial

exposure of bed. Alternate with these bands, 5 to 15 em thick yellowish shales

are present - indicating fluctuating conditions of depositional environment.

Thickness of these bands near Kandawari Wadi is 3m, while it is 10m at south

of Wandhaya village. Near Kandawari Wadi, above these bands alternate

55

sequence of shale and sandstone is exposed which is somewhat thicker in

eastern part in Chadwa Dungar block. Shales are yellowish and grayish in

colour and at one place shows cross-stratification. Sandstones are medium to

coarse grained and yellowish to red-ferruginous in colour. The topmost band of

KWM is highly ferruginous coarse grained fossiliferous sandstone,

occasionally conglomeratic and felspathic, which is found in form of pockets.

Overall thickness in this part ranges from 20-30 m, while south of Wandhaya

village it is up to 40 m. South of Wandhaya, above the ferruginous sandy shale

partings there are numerous partings of micaceous siltstone and shale, which

are yellowish to grayish. It is about 15 m in thickness. Which is then followed

by shale-sandstone intercalations as found near Kandawari Wadi. In contrast to

other areas at south of Wandhaya village, the strike of the beds is N38°W­

S380E with dip of 13° due S52°W. Everywhere the topmost band is ferruginous

gritty sandstone, which is exposed in form of small patches - pockets within

shale sequence indicating marginal-marine condition of deposition. The shale

bands are grayish and gypseous, which also indicates high rate of evaporation.

Stratigraphically the lower boundary of the KWM is very well marked

by the thin intercalations of ferruginous bands and shales, which are lying on

the top of Dhosa Oolite beds -a marker horizon for the entire Kachchh

Mainland. On the top beds of Jumara Formation i.e. bioclastic intraformational

conglomerate with reddish brown ferruginous crust, the basal rocks of Jhuran

Formation were deposited unconformably. The upper boundary of KWM can

be fixed by ferruginous sandstone beds, which is overlain by shales of Rathi

Dungar Member.

Various sedimentary structures found preserved in K WM. Box work,

cross-stratification, parting lineation, load cast, linguoid ripple marks and mega

ripples are commonly found. Folding and faulting is also common which

disturbed the strata particularly in the lower part. Locally monocline structure

is recognised in shale as exposed near Wala-Khawas.

Ammonites are very common in KWM, particularly in the lower part

and that is why these bands are famous as Katrol ammonite bands. Near

56

Wandhaya, these bands contain large sized ammonites. Among other fossils,

belemnites and fossil wood are common. Burrowing activity is also common.

The trace fossils found in the KWM are Cochlichnus, Didymaulichnus,

Margaritichnus, Palaeophycus, Protovirgularia, Taenidium, Teichichnus and

Trusheimichnus.

The "Jhuran Belemnite Beds" were thought to be the only representative

of Lower Kimmeridgian by Spath (Pascoe, 1959, p. 1148) on the basis of the

ammonites collected from these beds. On the evidence of the age of the "Jhuran

Belemnite Marl", the lower limit of the Jhuran Formation can be fixed as

Lower Kimmeridgian (Biswas, 1993 ).

2.3.2 Rathi Dungar Member (ROM): The rocks overlying KWM are typically exposed at Rathi Dungar and in

surrounding area from which the name has been given to this member as Rathi

Dungar Member. The coordinates are 23° 08' 23.02" N latitude and 69° 30'

50.40" E longitude. It is 1.34 km due southeast of Phat Sar and 5.31 km north

of Dahisara village. Rocks of RDM are also exposed near Wandhaya lake,

almost 5 km away from Samatra on Samatra-Wadasar road, near Prag Sar, in

Chadwa Dungar Block, Bharasar Dome block, approximately 10.5 km away

from Bhuj on Bhuj-Mandvi road and about 8.5 km away from Bhuj on Bhuj­

Mundra road. The cumulative thickness of the member is 190m.

RDM is represented by a thick shale sequence. These shales are

alternating with thin bands of calcareous sandstones. Thin red-ferruginous

partings and nodular bands are also common.

The shales are dark grey to black, yellowish and grayish at places. It is

gypseous, micaceous and laminated. Alternate with these shales there are thin

bands of micaceous siltstones, fine grained calcareous sandstones and

flagstones. The same kind of sequence also exposed in the other parts of the

study area. In the lower and upper part of the sequence shale is thick while in

the middle part calcareous sandstone layers are prominent. Towards eastern

part of the study area, the top of RDM is arenaceous, while towards western

57

part it is argillaceous. This may be due to the basement high which exists in the

eastern part. Nearer to high the basin is shallow and towards west it becomes

deeper. These arenaceous bands are mainly gritty- calcareous sandstones with

red to pink ferruginous tint at places. In the shale sequence thin bands of red

ferruginous concretionary layers are common. Siltstones are yellowish to

grayish in colour and micaceous in nature. Sandstones are calcareous to

ferruginous in nature with fine to medium grain size. It is hard and yellowish to

reddish in colour. Locally red-ferruginous pebbly band found exposed in

arenaceous matrix. Elephant skin surfaces and honey comb structures are

typically found exposed on the surfaces of this calcareous sandstone due to

weathering action, which mark differential diagenesis. Due south of the

Kandawari Wadi the rocks strikes E-W with dip due S, while in the west and

east of it strike is NW-SE with dip due SW and NE-SW with dip due SE

respectively, so overall Jhuran Formation forms arcuate shaped larger half cut

dome structure.

Stratigraphically the lower limit of the RDM can be fixed by the shales

of RDM, which are overlying the sandstones of KWM. This boundary with

underlying KWM is distinct at certain places. Distinct angular unconformity is

found in northeast part Bharasar dome and conglomerate bed found at east of

Wandhaya village forms unconformity between KWM and RDM locally. This

conglomerate found in patches along unconformity is polymictic and

intraformational in nature. It contains large pebbles of mudstone enclosed in

gritty matrix- paraconglomerate. In general, top part of KWM is arenaceous

represented by gritty sandstone and lower part of overlying RDM is

argillaceous. The upper boundary of RDM is also distinct. Angular

unconformity is seen at south of Wala-Khawas on Bhuj-Mandvi road. Locally

ferruginous layers are also seen on the top part of RDM, which indicates break

in deposition as found towards north of Jam ora lake.

Different sedimentary structures encountered m the field are cross­

stratification, interference and linguoid ripple marks (Plate 2a), load cast, scour

and fill structure, parting lineation, box work on the surface of ferruginous

58

·~ - \. . ... , .. -. -.

··-·. f . ,.

. .

..... . ·_SJ·'~' .. . .f.:-: , ~ ... "" .. · .

---· -· ---~·-: .·~:· . . . . b

... ·. . . - . .. ·: .- ... -· .• -= ... ~ ........... ;. •• .. - ,!f> ••• :.~ ... • • .....:,:._, -.. ---..,!.'..£::-- . - - y

•:. -..--·.- . -~ - .:--' ~. - ... :- . ..... ·-~-~;. • . . . -~ ··~·· r.· .. ~~:. . . .:..:-- . . ·: ... . '•' ./ . .tr~·~· .. ',,,-, .. ·.-.~-...... , ... ..-. · ... ,~L.;

' •

0

•tl .. ; y .. I ' o , "'... .--. .. ~ . • . ~ ~ • .. ..:. ";~ -- ,,_ .. ·.. """" ._. • . ,.. •• .• ·1

--- . -~~~-! ... ~~· · ... ~ _., , .. ..,;,: ,_~ ........ ·~·~' llflll'.- . .., ' .. _ : ....... .i. ~.~ ~ r ... :..,.. • • • ,. - . .; -- • -~ .. - ~~ .,,..... -· .J ,... , lt . , - ··'· 7• ~ . -~ .--•. ~ .. ,..~~--.. ·~.· -· .;.~ .f'·~""' ~ -:-··;,;· .~·· .:::.. ... -· . .. . - . ·..~ ~-- a- ~-· ··':" -~., ..;_,. • ,~ ... •* 4"""': . . ; .... ~ ..., • . _; -~ .... ..~ .. 4 , ,. ;. '..tit:.·-·"-;;~. -_. :·r. ·:.. · ""-~· · .. ·; -~ .. • .·"' .. -•• · ·.- :~ ... ... ~ • • A .... • •• ~. ' .. • -~ ·"" ' A . ~ .· ·-· • t ' •. ...,.- ·- •. . , • ..,. ....... - ~

....-:. .- ~ ;_ • . .I ·.~. , .. I .,;1 4 ...... :.. .....~: : • .

... • . .,... /. - .• f • ..,, ~ ....... ._.. . ~ ilf:~ _4fC __ #_.· • · , .• • . _ I # '. . -~·~ ·-- .. '1._ ·. "";. Ill' ...:;:;,.-tr. , • .. .:.. .# ... .-q • ... ~- . -~

~' ;: -- . . • .r ~--· .... _ ·~:-~-:;:.-. ~ .. ·· -· • ..... 0 ·- .. .

~~-~· --.... .

-~ ····~··· ~ ,_ ...,, ;:. . . . . ~.-... !'-'

.. oe".

(a) Linguoid ripple marks on the surface of sandstone, Rathi Dungar Member of Jhuran Formation, northwest of Sir Edmund lake dam site.

(b) Intraformational fossiliferous conglomerate bed exposed northwest of Sir Edmund lake dam site.

(c) Slump structure found near Sir Edmund Lake dam site.

(d) Highly bioturbated sandstone, Rukmavati Member ofBhuj Formation, Godpar stream.

(e) Structures produced due to differential erosion by wind action in sandstone of Rukmavati Member, Bhuj Formation, near Godpar stream.

59

partings, and wedge shaped sandstone layers. All these features indicated near

shore zone of deposition. Folding and faulting are also commonly observed.

Among the fossils different varieties of bivalves - trigonia, oysters etc.

along with gastropoda, belemnites, fossil wood and leaf impressions are

commonly found in RDM. Bioturbation is distinct at certain layers and

varieties of biogenic structures are found preserved. They include Arenicolites,

Didymaulichnus, Dolopichnus, Gyrochorte, Monocraterion, Palaeophycus,

Phycosiphon, Rhizocorallium, Sublorenzinia, Taenidium, Teichichnus,

Thalassinoides etc.

Portlandian age can be assigned to RDM according to the existing data

as proposed by Biswas (1993).

2.3.3 Sir Edmund Lake Member (SELM): The name has been given from the section exposed northwest of Sir

Edmund Lake dam site. The coordinates are 23° 08' 17.00" N latitude and 69°

33' 07.39" E longitude. It is 2.43 km NNE of Godpar village and 980 m of

northwest of Sir Edmund Lake dam. Rocks of SELM also exposed in other

parts of study area, such as near Nabhoi Nani, Nabhoi Moti and Ajapar in

Wandhaya block, almost 1.9 km due northeast of Wadasar on Wadasar­

Samatra road, south of Pad Sar in Prag Sar block and near Jamora lake in

Chadwa Dungar block. The cumulative thickness of the member is 50 m.

This member is predominantly arenaceous. The member consists mainly

of arenites and subordinate amount of argillites. This member starts with a bed

of yellow, massive, current bedded, coarse grained sandstones. It is overlain by

thinly bedded fissile and shaly sandstones with alternations of grey gypseous

shales and micaceous siltstones. The upper part is represented by purple,

massive, coarse grained ferruginous sandstone.

Sandstones are fine to medium grained in size, massive, yellowish to

grayish and reddish-ferruginous in colour. In the lower part sandstones contain

glauconite nodules in it. At places it is cherty and highly jointed. This

sandstone is locally quarried for construction purpose on Bhuj-Mandvi road. It

60

is overlain by shale - siltstone intercalated sequence. Then again towards the

top sandstone dominates with purple-highly ferruginous and coarse grained

nature. Near Ajapar it is hard, rine to medium grained, yellowish to pinkish and

felspathic. In the middle part of the member shale - siltstone intercalations are

found having shales as dominant unit; which are fine grained, yellowish,

grayish and blackish-carbonaceous, at few places. In between shale siltstone

sequence fine grained to silty red-ferruginous bands are common. Shales are

finely laminated, while siltstones are yellowish and micaceous. An

intraformational, polymictic, paraconglomerate layer (Plate 2b) exposed at

various places viz. along the stream - northwest of Sir Edmund lake as well as

south of Rathi Dungar. It contains angular to sub-rounded pebbles of clays.

Pebbles are yellowish to red-ferruginous in colour. At south of Rathi Dungar,

matrix is coarse grained, ferruginous and sandy, while it is fine to medium

grained and siliceous to calcareous at Sir Edmund Lake. Here it contains

abundant belemnites guard as bioclast.

Stratigraphically the lower boundary of the SELM with RDM is sharp,

which is found in form ofunconformablejunction at south ofWala-Khawas on

Bhuj-Mandvi road. Lithologically the top part of RDM is argillaceous, while

lower part of SELM is arenaceous. Further north of Jam ora Lake, a ferruginous

band is exposed between RDM and SELM, which indicates depositional break.

The upper boundary of SELM with Godpar Member is the boundary between

the Jhuran and Bhuj Formation. Lithologically the top part of SELM is

arenaceous, while in the lower part of Godpar Member rhythmic alternations of

ferruginous layers are present. Angular as well as overlapping relations are

visible at Jamora Lake and Sir Edmund Lake.

Various sedimentary structures found preserved in the rocks of SELM

are cross-stratification, load cast, ripple marks with mega ripples, slump

structure, channel structure etc. Sandstones of lower part of member on Mandvi

road shows water escape structure preserved in form of small sand volcanoes.

Folding and faulting is also commonly found.

61

Bivalves, belemnites, leaf imprints are most common among the fossils.

In the sandstones of upper part indistinctly preserved large sized ammonites

found, where suture lines are clearly visible. Biogenic structures are less, which

includes Didymaulichnus, Gyrochorte and Oldhamia.

Lower Neocomian age can be assigned to the SELM as per the existing

lithological data and fossil assemblage as proposed by Biswas (1993).

2.4 Bhuj Formation

The name of the formation has been given from its type locality around

the city of Bhuj, where these rocks are very well exposed. It is the youngest

Mesozoic Formation of the Mainland Kachchh, represented by marginal marine

rocks. This formation is defined by the marine beds of the Jhuran Formation

below and the Deccan Trap lava flows above. Rocks of Bhuj Formation are

exposed extensively in the Mainland Kachchh and almost occupying about

3/4th of total area of the Mesozoic outcrop. The Rukmavati river section of

Charwar hills, which is a part of the study area, exposes a complete and very

typical section from its base to its top below the Deccan Trap. This section can

be considered as the type section as described by Biswas (1993). As to him the

formation is divided into two informal members, lower and upper in the eastern

and central mainland. Again the thickness of the formation is more with the

development of younger rocks towards west than east. Being composed chiefly

of soft friable sandstones, the formation is easily weathered out forming the

low lying sandy plains. These are good aquifers, so the low lying plains are

highly cultivated. In fact, it is one of the key features of the formation that after

barren hard exposures of sandstones of Jhuran Formation, the highly cultivated

plains indicates the starting of Bhuj Formation. In the lower part of the

formation, the presence of hard ironstone and laterite bands forming low

cuestas. So these are forming residual hills standing out within the low lying

plains. As discussed earlier the lower boundary of Bhuj Formation with Jhuran

Formation is disconformable to overlapping. This disconformity exists between

sandstones of Jhuran Formation and rhythmic alternation of ferruginous bands

62

and shales of Bhuj Formation. The upper boundary is very sharply defined

below the Deccan Trap lava flows. These lava flows rests on the eroded

undulating surface of Bhuj Formation, which is indicating long exposure to

erosion for the formation. It is concluded from the lithology, absence of fauna

and richness of flora, sedimentary structures, patterns of current roses and

marine tongues in the down basin direction, that the sediments represent deltaic

deposits with distal part (delta front) towards the west and the proximal part

(fluvial) to the east in the direction of the land (Biswas, 1977). The age of the

Bhuj Formation can be given from Neocomian to at least Santonian i.e. Lower

Cretaceous.

The rocks of the formation are exposed in form of two patches. One in

the north, which is bordered in south by Katrol Hill Fault, extends in east-west

direction and lying southwest of Bhuj town. Another east-west trending plains

bordered in south by Deccan Trap range, which is lying south of Charwar

range. Rocks of Bhuj Formation are exposed around following localities: Near

Jamthara, Ludva, along Rukmavati Nadi and Hatawaki Chhello, near Wadasar,

Vingdia, Rampar Vekra, Sarli, Dahisara, Godpar, Meghpar, Naranpar, on Bhuj­

Mandvi road, south of Sanatorium, near Kirgiriya Dungar and Bharapar.

Overall thickness ofBhuj Formation is approximately 357m. Based on distinct

contacts, the Bhuj Formation has been divided into two members in ascending

order as follows:

(1) Godpar Member

(2) Rukmavati Member

As a whole the formation is arenaceous. It consists of sandstones of

different types with thin layers of sandy shales. Sandstones are usually soft,

friable and white to pale brown in colour. Few thin bands of quartzitic

sandstones, gritty sandstones, ironstone and laterite are common. At places

carbonaceous shale with typical flora found. Glauconite is also found from

some oolites, which suggests slow sedimentation rate. Faults and dykes, which

occupy these faults, are also common in Bhuj Formation like the other

formations of Mesozoic sequence.

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2.4.1 Godpar Member (GM): The typical section from which the name has been given is exposed just

north of Uodpar village. The coordinates of the section are 23° 07' 21.76" N

latitude and 69° 32' 48.24" E longitude. It is 690 m due NNE of Godpar

village. Another beautiful section exposed just south of Sir Edmund Lake

which is nearer from the type section. Rocks of GM are also exposed north of

Jamthara, near Wadasar, Vingdia, along Hatawaki Chhello and Rukmavati

Nadi, around the bifurcation of Mandvi and Naranpar on Bhuj-Mandvi road,

around Sanatorium and north ofKirgiriya Dungar from the southern belt. In the

northern belt the member is exposed west of Bhuj town, Kodki and Kanpar.

Overall thickness of the member is approximately 77 m.

The member is characterized by cyclic repetition of ferruginous or

lateritic bands, shales and sandstones. The thickness of the sandstone increases,

while thickness of the shales, siltstones and ferruginous bands decreases and

completely vanish in the upper part of the sequence.

The sandstones exposed in different parts of the study area are

yellowish, reddish-ferruginous, fine to coarse grained, soft, friable, well sorted

and intercalated with shale and siltstone in lower part, while towards top it is

thick, coarse grained to gritty and cross-stratified. Along the Ajapar stream top

part is gritty to conglomeratic with wave ripples. In the lower part along the

partings of shale - siltstone, bioturbation is abundant which is found at Sir

Edmund Lake, near Godpar, along Ajapar stream and Wadasar stream. Shales

are yellowish, pinkish and black-carbonaceous intercalated with ferruginous

bands. Ferruginous bands are characterized by hematitic or lateritic nature with

spongy or nodular weathering. At places glauconitic band is also encountered

along these partings, as found at Jamthara- along Rukmavati Nadi and Ajapar

stream. Siltstones are gray to white and calcareous in nature.

Stratigraphically the lower boundary of GM with Jhuran Formation is

sharp and distinct. Lithologically the lowermost beds of GM are rhythmic

alternation of ferruginous bands and shales, which are lying above the

sandstones of SELM. The relation is parallel disconformable junction to

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overlapping sequence. The upper boundary can be fixed by cross-bedded

sandstones, which are overlain by highly bioturbated ferruginous sandstone of

Rukmavati Member.

Along Rukmavati Nadi, numerous sedimentary structures are beautifully

preserved such as horizontal stratification, cross-stratification, slump structure­

seismites (Plate 2c ), channel structure etc. These structures are also common in

other parts of the study area along with other structures like trough cross­

stratification, hummocky cross-stratification, ripple marks, interference ripple

marks with development of hummock structure, load cast, inverse grading, air

trap structure and box work on the surface of fine grained ferruginous band.

Along the stream of Wadasar, small shear zone trending N40°E-S40°W with

the development of numerous fractures and slight disturbance exists. Along the

same stream, parallel to its length one sandstone dyke is projected, which

intrudes the GM sequence. Along with major faults minor faults are also

common which displaces the strata vertically 5-7 inches as found on Bhuj­

Mandvi road. Spheroidal weathering is common in the doleritic dykes

protruding these sandstones.

Faunal content is very less in GM. Only one fossil specimen of Trigonia

found from Ajapar stream. Bivalve casts are found from Sir Edmund Lake and

along the Wadasar stream. Fossil wood encountered from north of God par. It is

rich in fossil flora, which containing several plant species allied to Upper

Gondwana flora, found from carbonaceous shale beds exposed along Ajapar

stream and north of Godpar. Common forms reported earlier are species of

Ptylophyllum, Williamsonia, Brachyphyllum, Pecopteris, Aurocarites,

Taeneopteris, Cladophlebis, Equisatum, Elatocladus etc (Biswas, 1977).

Bioturbation - trace fossils abundantly preserved in the lower part of GM,

while in the upper part sandstones having very less and indistinct bioturbation.

It includes Chondrites, Cochlichnus, Didymaulichnus, Gyrochorte,

Monocraterion, Oldhamia, Ophiomorpha, Palaeophycus,

Parahaentzscheliana, Phoebichnus, Rhizocorallium, Skolithos, Taenidium and

Trichichnus.

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The micro I macrospores from the Ghuneri and Trumbow coal beds

(Singh et al., 1963) indicate that the Ghuneri and lower (GM) members are

equivalent and correlatable with Wealden Formation of England. Roy (1967)

from leaf impressions from the lower member came to similar conclusion. This

indicates a Neocomian age, i.e. Berriasian-Hauterivian for GM (Biswas, 1977).

2.4.2 Rukmavati Member (RM):

Rukmavati section is the type section for entire Bhuj Formation, where

rocks of Lower and Upper members are exposed typically as described by

Biswas, (1977). Along the Rukmavati Nadi, near Jamthara- the rocks of Upper

Bhuj Formation are typically exposed, from which the member name is given

as Rukmavati Member. The coordinates of the section are 23 o 06' 26.51" N

latitude and 69° 25' 58.92" E longitude. It is 2.5 km due ENE of Jamthara

village. Another typical section is also exposed around Dahisara, which is 19.5

km S of Bhuj on Bhuj-Mandvi road. Rocks of RM are also exposed near

Ludva, Jamthara, Rampar Vekra, Sarli, Meghpar, Naranpar and Bharapar from

the southern belt. In the northern belt, the rocks of RM exposed at south of

Bhuj town, on way to Mundra up to 5 km from Bhuj, south ofLalan College on

Bhuj-Mandvi road, Deshalpar, Samatra, Nangiari, Bharasar, Mankuwa,

Sukhpar, Mirjapar and Madhapar. The cumulative thickness of the member is

280m.

RM is represented by buff and pink coloured medium to coarse grained,

poorly sorted, friable, massive, current bedded, felspathic sandstones. At places

it is gritty and micaceous. Near Dahisara it is quarried also as a building stone.

At certain places, the sandstones become conglomeratic containing sub-angular

to sub-rounded pebbles of quartz. It is found in form of thin bands and lenses of

conglomerate. In the lower part intercalations of shale-siltstone beds are

common along with ferruginous bands at regular intervals. Shales are yellowish

brown, grayish, red-ferruginous and black-carbonaceous having plant fossils in

it. Yellowish to red, micaceous siltstones are also alternating these beds. Like

the GM, in RM also there occurs a rhythm in the sedimentation. Here it is

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indicated by the repeated occurrences of kaolinitic shale, claystone and

ferruginous band alternations at regular intervals of massive coarse felspathic

sandstones. The felspathic cement is sometimes replaced by silica to form

quartzites. Such quartzites are commonly capping the massive sandstones. This

probably originated from the induration of the sandstone by the Deccan Trap

lava flows, which overlies the sandstones at once and now eroded away.

Stratigraphically, the lower boundary of the RM with underlying GM is

distinct. It can be defined by the lowermost beds of RM, which are rhythmic

sequences of highly bioturbated ferruginous sandstones. These sandstones are

having abundant bioturbation and ferruginous in nature (Plate 2d), which might

be developed during the sub-aerial exposure of the area. The upper boundary of

RM is unconformable. It is also the topmost part of Mesozoic sedimentary

sequence. A zone of weathered sandstone lying beneath the Deccan Trap lava

flows indicate long exposure to erosion before it being covered up by lava

flows.

Rocks of RM are horizontal to sub-horizontal with abundant

sedimentary structures. Near Bharasar it shows E-W strike with dip 15° due S.

Tabular cross-stratification, trough cross-stratification, channel structure,

convolute bedding, slump structure, flame structure, honey comb structure,

ripple marks, interference ripple marks, wave ripples, inverse grading, parting

lineation are some of the physical sedimentary structures preserved at many

places of the study area. Structures produced due to differential erosion of wind

action are also seen in the same area (Plate 2e ). Plant rootlets in the rocks

support terrestrial conditions in the uppermost part of the sequence. Faulting

and basic-doleritic intrusions are common similar to other formations of

Mesozoic sequence.

The member is devoid of any fossil fauna, but it is rich in fossil flora

containing several plant beds in the carbonaceous shales and sandstones. Fossil

wood and plant debris beautifully preserved in highly ferruginous gritty

sandstone of RM along the railway cutting south of Gurukul, on Bhuj­

Nakhtrana road. Trace fossils are abundant in the lowermost bed of RM, while

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towards upper part bioturbation is scarce and indistinct. It comprises

Balanoglossites, Diplocraterion, Monocraterion, Pholeus and Skolithos.

The plant beds occurring are considered to be younger than the Jabalpur

series and basal Cretaceous in age (Pascoe, 1959, p.994). Mathur et al. (1970)

on palynological evidences fixed the upper limit as Santonian.

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