1
CHAPTER 1
INTRODUCTION
1.1
GENERAL
Karnataka state is the home of the well-known ancient Dharwar group
of rocks and is a classical region for the study of Precambrian Geology. A great
variety of rocks is found in Precambrian terrains, and each continent differs
from another in this regard. The Precambrian rocks of Australia, Africa,
Siberia, S. China, W, Mongolia, E. Greenland, Canada, Iran, Namibia,
Newfoundland, Morocco, Scandinavia, USA and India (lesser Himalayas) and
other parts of the world show the same range in variety and abundance. They
are represented by all kinds of sedimentary rocks, extensive lava flows, and
some still relatively undeformed, unmetamorphosed and uninvaded by great
mass of granitic rocks.
The exposed area of the earth’s land surface is 8-9%. Precambrian
rocks underlie all other rocks of the continents. They occur beneath a great
blanket of flat or deformed sedimentary and other rocks, which are near the
surface, covered by a thin veneer of strata or unconsolidated material. Mainly,
they occur in two principal types of geologic settings - shields and mountain
cores. In the Asian continent, the Precambrian occurs in the Siberian shield,
which includes the Angaran or Aldan and the Anbar shields. These rocks are
found in abundance in the cores of many mountain ranges of the central axis.
2
Peninsular India is also one of the shield areas. The geological history of
Karnataka state is largely confined to the two oldest eras - the Archean and
Proterozoic. Archean, from the Greek ‘arkhaios’ = “ancient” denotes the era
from 3.9-2.5 Ga. Proterozoic is derived from the Greek ‘proteros’ meaning
“former, anterior, or fore in place, time, order or rank.” The term Proterozoic is
synonymous with Algonkian (USA), which is widely used for late Precambrian
time in the two-fold subdivision of the Precambrian. The major part of the rocks
of Karnataka, therefore, is Archean in age, going back to the very dawn of
geological history. At the end of this long period of quiescence, the northern
part of Karnataka, lying within the limits of the present day Dharwar, Belgaum,
Bijapur, Bidar and Gulburga districts was depressed below sea level, creating
an extensive basin of deposition. In this basin, sediments were deposited which
are recognized as the Kaladgi and Bhima of Proterozoic age, named after the
town of Kaladgi in Bijapur district, and the valley of the river Bhima
respectively, where rocks of these groups are typically well developed. The
Kaladgi sediments are separated from the underlying schistose and granitic
rocks of Archean age by a distinct unconformity - ’the Great Eparchean
Unconformity'.
On Indian the stratigraphical scale, the Precambrian rocks are called
Purana formations. The Purana formations overlying the Archean gneisses are
basins of Cuddapah and Vindhyan rocks. A few isolated patches of Purana
rocks do occur along the Godavari, Krishna and Bhima valleys of Andhra
Pradesh and northern Karnataka state, south India. Geologically, Karnataka
state is comprised of four major divisions, and the rocks rest on 3400 Ma old
gneisses. The first division includes early to middle Archean - Sargur group,
having several unclassified association of supracrustal rocks. The second
division is middle Archean, 2900-3000 Ma old peninsular gneisses, constituting
3
older granite, gneiss, migmatite complex and granitoids. The third division rests
unconformably on these peninsular gneisses, and belongs to late Archean to
early Proterozoic. The fourth division includes middle to late Proterozoic
sedimentary rocks of Kaladgi and Bhima Groups, and is exposed in the
northern parts of Karnataka, partly covered by Mesozoic to early Tertiary
Deccan basalts.
At the end of the Precambrian era, the Proterozoic (late Precambrian)
sediments were well developed in the Bhima basin, which commences in the
extreme NE comer of the Kaladgi basin with sub-metamorphic rocks, differing
considerably in petrological character from the Kaladgi Group and resembling
very closely, in many respects, the Kumool Super Group (Andhra Pradesh).
The younger of the two sub-metamorphic series occupies large area on the
eastern side of Peninsular India. The Kaladgi and Bhima sediments are believed
to extend further north, but their northerly extension lies buried under a thick
cover of the Deccan Traps of a much younger age, with the result that they are
seen at present occurring as a fringe beneath the trap cover (Figure 1.1).
1.2
PROTEROZOIC ERA (2.5 billion To 544 Ma ago)
The Precambrian represents the first 4 billion years of the earth’s
history (approx. 85%). Precambrian rocks constitute the bulk of continental
crustal rocks, mostly obscured by a relatively thin veneer of Phanerozoic
sedimentary, igneous, and metamorphic rocks. These "rafts" of Precambrian
igneous/metamorphic rocks are called the continental 'cratons'. The exposed
areas are called the 'shields'. These shields are only partially exposed on the
continents. These limited outcrop areas form the basis for our knowledge of the
Precambrian earth.
4
KARNATAKA
Geology
N
4
(Based on the Geological Map of Mysore (1915) by W.F. Smeeth and the
Geological Map of Karnataka, Swam! Nath et aL 1981 with modification)
SCALE
40
60
MAHARASHTRA
ANDHRA PRADESH
INDEX
Tertiary to Quaternary
Deccan Trap
Bhima
Kaladgl
Younger Granites
Granulltes
Dhanvar Schist Belt
(Chitradurga Group)
Dharwar Schist Belt
(Bababudan Group)
Gold-Bearing Schist Belts
(Kolar Type)
Gnelssic Complex
Ancient Supracrustals
(SargurType)
ARABIANSEA
TAMIL NADU
KERALA
Figure 1.1
Geological
map
of
Karnataka
Vaidyanathan, GSI, 1994)
(Radhakrishna
and
Kms.
5
The period of earth's history that began 2.5 billion years ago and
ended 544 million years ago is known as the Proterozoic. Many of the
geological events in the history of the earth and life occurred during the
Proterozoic - stable continents. First abundant fossils of living organisms,
bacteria, (1.8 billion years ago), eukaryotic cells are reported in literatures.
With the beginning of the middle Proterozoic marks the first evidence of
oxygen build-up in the atmosphere. This global phenomenon spelled doom for
many bacterial groups, but made possible the explosion of eukaryotic forms.
1.2.1
Evolution of the Precambrian Atmosphere
The climate during the Precambrian was intimately linked to secular
changes in atmospheric composition, and played a significant role in basin
evolution as it controlled the rates of weathering and denudation. It also
strongly influenced the sea level during global glaciations (Dehler et al 2001,
Ojakangas et al 2001a, b). The elevation of a continent above MSL (Wise 1972,
1974) indicates the interaction of sea level changes, continental crustal growth
rates and denudation rates (Eriksson 1999).
According to Scopf (1999), by about 3.9 Ga, there would have been a
decrease in surface heat influx and the oceans would have formed due to
condensation of steam atmosphere (Kasting 1993). The remaining atmosphere
was probably dominated by CO2, CO and N2. Later, the reduction of C02 and
the production of 02 by photosynthetic activity led to aerobic conditions that
have been recorded around 2Ga. The surface temperature in the Precambrian
was always high (Eriksson et al 1998) and the overall variability of temperature
was rather small; global mean surface temperature was ~ 5°C higher than
present. BIF formed before 1.85Ga, with minor exceptions (Kasting 1991,
Trendall 2001) and pyrite (detrital) deposits, Uraninite (unstable in oxidizing
6
environments) are restricted to pre-2Ga sequences (Condie 1997). Thereafter
subaerial red beds, completely absent before ~ 2Ga, formed indicating
significant increase in atmosphere O2 levels (Rye and Holland 1998). Multiple
global glaciations occurred in the Neoproterozoic, when rapid chemical changes
seem to have affected the atmosphere (Dehler et al 2001).
Many Neoproterozoic marine carbonates showing evidence for colder
climates and widespread glacial deposits and alternated with warm and moist
climates (Eriksson et al 1998).
1.2.2
Glaciation
Precambrian glaciations reflect the interplay of atmospheric, tectonic,
oceanic, astronomic and biologic processes, and the widespread distribution of
glacial deposits records global events. Erosion, transportation and deposition
processes in certain Precambrian environments may have differed markedly
relative to modem settings. The use of glacial deposits as distinctive markers
for intracontinental correlation of Precambrian sequences has had a long history
(Fairchild and Hambrey 1995). Glacial sequences have been proven valuable
for
the
intercontinental
correlations
required
for
reconstruction
of
Neoproterozoic supercontinents. Further, Eriksson et al (1998) discussed in
detail about Precambrian glaciations with detail data from worldwide
formations.
Except the north Atlantic region, all Neoproterozoic successions show
lithostratigraphic evidence for only two distinct Neoproterozoic ice ages from
worldwide (Kennedy et al 1998). But recent studies have been raised the
possibility that there may have been more than four ice ages during the later
Neoproterozoic.
This is mainly by negative excursions in the 813C record,
7
which suggest four or five ice ages during the Neoproterozoic (Kaufman et al
1997, Jacobsen and Kaufman 1999) at approximately 740, 720, 590 and 575
Ma.
Since there is no >2 glacial intervals are observed in most
successions, the larger number has been doubted as possibly an artifact of
stratigraphic miscorrelation (Kennedy et al 1998) and/or the way that glacial
intervals are counted. Although Neoproterozoic glaciation was clearly extensive
(Hoffman et al 1998a, 1998b), the interpretation of as many as four events
implies that during any given ice age, non-glacial facies would have
accumulated over a significant portion of the planet. There are four discrete
Neoproterozoic ice ages bracketed, extreme positive to negative shifts in the
813C of seawater (Kaufman and Knoll 1995). The Varangerian and the Sturtian
ice ages were marked by a steep climb in seawater 8 C from negative values
back to very high 813C values (Kaufman et al 1993, Derry et al 1992). The
worldwide occurrence of Neoproterozoic glacial intervals, their association
with marine carbon isotopic excursions, and paleomagnetic evidence for lowlatitude glaciation all suggest that these deposits record global climatic events
and provide evidence of earth’s most extreme ice ages (Kirschvink 1992,
Hoffman et al 1998a, Kennedy et al 1998). Recently, the snowball earth model
of global glaciation, with the ocean virtually covered by sea ice but as a thin
and patchy continental ice cover, was proposed to explain Neoproterozoic
glaciation (Kirschvink 1992, Hoffman et al 1998a). Chemostratigraphy seems
to resolve the question of how many late-Precambrian icehouse conditions are
of global significance. Though some have speculated on as many as 5 or 6
occurrences of glaciogenic rocks, only two match with isotopic signals, one
(Sturtian) around 700 Ma and one around 600 Ma (Marinoan). Both have
associated negative 813C excursions in carbonates to the level of mantle carbon,
8
which suggest that life was reduced to a minimum by 'Snowball Earth'
conditions.
1.2.3
Precambrian/Cambrian Boundary
The Precambrian/Cambrian (PC/C) boundary was a period of global
extension, with formation of rifts, ocean basins and passive margins. These
major geotectonic events affected ocean circulation, upwelling sites and
nutrients supply, organic burial rate and recycling. All factors affected the
seawater isotope composition (Tucker 1989). This is the significant interval in
the life history, which marked the appearance of new metazoan groups and
development of biomineralization and skeletonization. The PC/C boundary,
initially kept close to the first appearance of shelly fossils (Cowie 1985), was
redefined later at the emergence of the trace fossils (Brasier et al 1994). This
boundary has been traced all over the world Precambrian formations.
1.2.4
Fossil Evidence
The oldest fossils are 3.4 and 3.5 billion year old single-cell,
photosynthetic, prokaryotic, filamentous cyanobacteria (blue-green algae)
found in Western Australia and South Africa. The stromatolites (mounds of
cyanobacterial mats) found so far are about 3.2 b.y. Prokaryotes are all singlecelled organisms that lack membrane-enclosed nucleus and organelles. They
reproduce by simple cell division creating duplicates of the parent genes are not
exchanged/combined from separate parents. Prokaryotes include the kingdoms
Archaebacteria and Eubacteria. Eukaryotes are organisms with membraneenclosed nucleus and organelles (mitochondria, chloroplasts, golgi apparatus,
endoplasmic reticulum etc.). They probably evolved by about 1.6 b.y. The
oldest fossil eukaryotes are acritarchs. These fossils appear very similar to the
9
cyst or resting stage of modem dinoflagelates, which are true algae. Eukaryotes
include the kingdoms protista (protozoans and algae), fungi, plants, and
animals.
Eukaryotes
are
now widely believed to
have
evolved by
endosymbiosis between two or more prokaryotes. Evidence for this is the fact
that mitochondria and chloroplasts both contain their own DNA and RNA,
which strongly suggests that they were once free-living organisms that came to
live inside some host cell. Sexual reproduction evolved among eukaryotes
probably by about 1.1 b.y. Combining genes from two parents greatly increased
the variations in populations rapidly increasing the rate of evolution. The first
clear evidence of metazoans (complex multi-cellular animals) appeared in the
rock record by about 630 - 600 million years ago in the Vendian Period of the
Late Proterozoic as the soft body imprints of the Ediacaran fauna.
1.3
NEOPROTEROZOIC BASINS OF INDIA
1.3.1
Kurnool Group
The Kumool Group of rocks is equal to the Bhima Group of rocks.
The Kumool Group of rocks unconformably overlie the sedimentary rocks of
the Cuddapah Super Group and occupy an aerial extent of 8000 km2 comprising
alternating quartzite, limestone and shale sequences of about 500 m thickness
(Nagaraja Rao et al 1987, Raman and Murthy 1997). The Banganapalli
Quartzite is the lowermost lithological unit of the Kumool Group, which rests
unconformably over the Srisailam Quartzite of the Cuddapah Super Group.
This formation has an impersistent diamondiferous polymictic conglomerate at
the base followed successively by grit, quartzite and shale. The pebbles of the
conglomerate are mostly chert, jasper, quartz and minor amount of feldspar in
an arkose matrix. The quartzite is feldspathic and ferruginous in nature with
occasional occurrence of glauconite. Hardened clasts of shale derived from the
10
underlying Cuddapah formation are noticeable at places in the conglomerate
bed. Sedimentary structures such as “herring bone” cross bedding, ripple marks
and mud cracks are present, indicating shallow marine tidal flat environment of
deposition (Nagaraja Rao et al 1987). Further subsidence due to continued
sedimentation, the limestones of Naiji Formation were deposited in a relative
deeper environment. This formation is 100 to 200 m thick and occurs
extensively through out the basin. At places, the lower unit of Naiji limestone
consists of pink coloured, thin lenticular lenses of gritty ferruginous sandstone.
The middle portion is constituted by thinly bedded, grey coloured massive
limestone. In the upper part, the limestone grades into calcareous and flaggy
variety. Presence of pyrite and minor amount of glauconite is seen in certain
basal horizons, indicating reducing environment of deposition. The Owk shale
Formation is impersistent and overlies the Naiji Formation. A gradational
contact between the Naiji limestone and the purple/buff coloured Owk shale
has been observed. The upper part of Owk shale is siliceous in nature and
contains yellow coloured ochre. A sharp contact has been observed with the
overlying conglomerates of the Panium Formation. Sub-aerial exposure is
evident for these rocks. The limestones of Koilkuntla Formation overlie the
Paniam Quartzite. These limestones are much thinner (15 to 20 m) and more
siliceous as well as flaggy than the Naiji Limestone. They also reflect shallow
marine environment of deposition. The uppermost unit of Kumool Group is the
Nandyal Shale with calcareous intercalations. The limestone associated with
this unit reflects shallow marine condition of deposition. Mud cracks in
Nandyal Shale are indicative of exposure to sub-aerial condition. It appears
from the foregoing that although the entire sediments of the Kumool Group
were deposited in a shallow marine environment, the lower Banganapalli and
Naiji Formations represent relatively deeper depositional environment than the
upper formation following transgressive and regressive cycles.
11
1.3.2
Krol Formation, Lesser Himalaya
The Infra Krol Formation and Krol Group are part of a
Neoproterozoic and Lower Cambrian succession more than 12 km thick,
cropping out in the Lesser Himalaya in a series of doubly plunging synclines
between Solan in the northwest and Nainital, 280 km to the southeast. The
lower half of this succession consists of quartzite, sandstone, argillite, carbonate
rocks and minor mafic volcanic rocks of uncertain age, but younger than 1 Ga,
and possibly rift-related. The upper half of the succession begins at an
unconformable contact with as much as 2 km of diamictite, siltstone and
sandstone of glacial and glacial-marine origin. These rocks are overlain by a
"cap carbonate" no more than a few meters thick (uppermost Blaini), and by up
to 400 m of shale, siltstone and minor sandstone assigned to the Infra Krol
Formation. Carbonate rocks of the overlying Krol Group are overlain, in turn,
by as much as 2,800 m of terrigenous rocks of Cambrian age (Tal Group), with
a distinctive unit of black shale, chert and phosphorite, up to 150 m in thickness
at the base.
These younger Neoproterozoic and Cambrian rocks are interpreted to
represent the inner part of a north-facing passive continental margin (Brookfield
1993), with a rift to post-rift transition tentatively interpreted within or perhaps
at the base of the Blaini. A passive margin setting is inferred on the basis of
scale, the absence of igneous rocks, and comparatively simple regional facies
and thickness trends within the Infra Krol and Krol, with no evidence for the
syndepositional tectonism that might be expected in a foreland basin.
In the High Himalaya to the north, this pattern was interrupted in the
early Ordovician by deformation, metamorphism and granite intrusion that
together signal a change in tectonic habitat (Garzanti et al 1986). In the Lesser
12
Himalaya, the Tal Group is unconformably overlain by a comparatively thin
carapace of Permian and Cretaceous strata. All the rocks were thrust
southwestward
as
a result of the
India-Eurasia collision,
beginning
approximately 55 m.y. ago (Najman and Garzanti 2000). Deformation on the
main boundary thrust, which structurally underlies the Lesser Himalaya, began
prior to 10 Ma, and continues today.
1.4
STUDY AREA
The Bhima Group of rocks is well developed in Bijapur and Gulburga
districts of northern Karnataka and Ranga Reddy district of Andhra Pradesh,
South India. This basin is irregular in outline and possesses a straight boundary
in E-W direction over a distance of nearly 40 km in the southern margin of
central part. The basin extends between long. 76°15’ and 77°30’E and from lat.
16°15’ to 17°35’ N, covering an area of 5,200 km2. Regionally, the Bhima
basin extends in a NE-SW direction simulating a rough ‘Z’ shape. The name
Bhima is after the Bhima River, which rises near Mahabaleswar in the Western
Ghats and crosses the basin in a northwest-southeast direction. The area
exhibits contrasting physiography in relation to the underlying geological
formations. The granitic rocks are sparsely distributed as knolls and tors with
prominent hill ranges appearing at Shrorapur and Shahapur. In general, the
Bhima rocks present a rolling topography with worn out intermittent shale
bands and the altitude varies from 360-540m MSL .The communication
network by both rail and road has enabled Gulburga district in the development
of cement factories: ACC, Shahabad Cement Works, Kit Ply, Raymond
Cements, Rajashree Cements, Vasavdatta Cements etc situated at Shahabad,
Wadi, Jewargi, Sedam, Chitapur, Tandur. The south central broad gauge line
connecting
Gulburga,
(17°20'30”N;
67°50’30E”),
Wadi
(17°31’20”N;
13
76°59’30”E), Shahabad (17°08’30”N; 76°56’E) passes through this area. The
Wadi-Secunderabad broad guage line passes through Malkhaid (17°12’30”N;
77°90’E), Chitapur (17°1’N; 77°5’E) and Sedam (77°18N; 17°11’E). The state
highway road passes through Shahpur and Jewargi. The chief lithological units
of Bhima basin are represented by five formations of two cycles of
sedimentation. They are Rabanpalli Formation, Shahabad Formation, Halkal
Shale Formation, Katamedavarhalli Limestone Formation and Harwal Shale
Formation. Limestone is the major rock type, particularly the Shahabad
Formation occupies 2000 km of the total area of 5200 km (Venkoba Rao
1977) (Figure 1.1). The limestone, sandstone, siltstones, and shale samples
were collected from Bhima basin for geochemical and sedimentological studies.
(Location map - pouch, Figure 1.1a).
1.5
PHYSIOGRAPHY AND DRAINAGE
The area under investigation in Gulburga district can be grouped
physiographically into two regions: (1) hill tracts and (2) alluvial plains. The
hill tracts form an arcuate feature/shape extending through western, northern
and northeastern portions of the region. The hills to the northwest, north and
northeast are mostly of the Deccan traps, usually forming flat-topped
discontinuous plateau; those towards the east and southwest are generally
composed of granitic rocks. The hill regions exhibit an irregularly dissected
topography. The trap hills on the northeastern and eastern side rise to 600 m
above MSL; towards the north, the altitude is around 500 m. The granite hills
occur in isolated patches and knolls. Near Shahapur, the hills attain an elevation
X
X
X
Figure 1.1
X
X
0
:
77
1
3Q
Formation
N
SCALE
O
25Kms
Shaba bad Formation
Rabanpalii Formation
Archean Basemertcompiex
Halkal Shale
25
Hilllllill
I88&&1 Katamedavarhalli
LEGEND
Deccan Traps
Harwal Shale
Geological map of Bhima basin (after Janardhana Rao et al., 1975)
X
\f\
-
14
15
of 600 m, while around Shorapur they are less than 600 m. The alluvial plains
are found mostly along the Bhima and Krishna rivers. A large portion in the
area forms, part of the Doab in between Krishna and Bhima rivers. The Doab is
comprised of a relatively thick capping of alluvial materials, besides, thick
deposits of residual soil/black cotton soil. The maximum thickness of the soil
along the banks of Bhima and Krishna is around 20 m.
The general slope of the study area is in a southeasterly direction,
down to an altitude of about 350 m, around the confluence of Bhima and
Krishna rivers. The plains on the northwestern and western side range in
elevation from 400-450 m. The drainage pattern in Bhima and Krishna basins
varies considerably. It may be generalized that the area exhibits a combination
of trellis and dendritic patterns of drainage. The important perennial feeders of
Bhima are the Bori river joining near Shahabad, the Benithora river, which is a
feeder of the Kagna joining near Malkhaid village, and Kamalti-nadi joining the
Kagna north of Sedam. The Bhima itself, with all its feeders, intimately empties
into the river Krishna at about 2 km to the west of Raichur railway station.
1.6
CLIMATE
The Bhima basin experiencesa warm summer and a comfortable winter.
Humidity is very low and precipitation is relatively less. Of the two monsoons
that prevail in the area, the southwest monsoon is incomparably important and
more constant in its influence on the ground water of the area. The effects of the
northeast monsoon are not greatly felt, as the rainfall accompanying it is much
less in quantity and duration. The winter is of short duration between the
months of December and January, when the temperature decreases an average
27°C. During this period, fine weather prevails with strong and dry easterly
winds. The December is the coldest month in this study area. During this month
16
temperature decreased more around 13 to 15°. The relative humidity is
maximum (~90%) in the months of July and August and minimum (-25%) in
the peak summer months.
In March, the hot season begins and the temperature rises rapidly. The
prevalent wind is a westerly one. During April and May, the heat becomes
intense and in certain areas of Gulbarga district, the temperature rises to more
than 46°C (115°F). This gives rise to local thunderstorms, which are sometimes
accompanied by very heavy rains. Sufficient rain falls all over to impart a much
less burnt up appearance than in March. As the southwest monsoon approaches,
the storms become more frequent and heavy. The monsoon rains effectively
cool the air, and the ploughing of the land for the great crop of Jowari is started.
By the middle of October, the northeast monsoon sets in and brings rain to the
district till the end of the month or even till the middle of November. The great
difference of temperature between the cold nights and hot days renders, it,
however, quite a drying climate to those exposed to its vicissitudes.
1.7
STRATIGRAPHIC NOMENCLATURE
The informal use of stratigraphic terminology in the past has led to
much confusion in the Indian stratigraphy and a necessity for uniformity in the
stratigraphic classification and terminology was felt. Due to this, the code of
stratigraphic nomenclature of India was formulated. After a detailed study of
the different codes, the names of the lithological units of Bhima were modified.
The name ‘series’ is essentially a chronostratigraphic term. Hence, Janardhana
Rao et al (1975) renamed the ‘Bhima Series’ as ‘Bhima Group.’
The first reference to Bhima sediments came from Newbold, who
referred Talikote limestone and Muddebihal sandstone in comparison with
17
Kumool. King (1872) surveyed the basin and named the sediments as Bhima
Series. Later, Foote (1876) recognized the unmetamorphosed shale and
limestone of Bhima Series in parts of Gulburga and Bijapur districts of northern
Karnataka. The Bhima sediments are thus classified into a lower series
consisting of conglomerates, sandstone and shale, and an upper series of
limestone. Later, Mahadevan (1947) revised the classification based on a
detailed survey of Gulburga district during 1935 and 1941. He recognized the
different divisions of Bhima Series against the two-fold division of Foote, and
classified the series into lower, middle and upper divisions. The total thickness
of Bhima Series has been computed by Mahadevan (1947) as 373.38 m, of
which lower Bhima consisting of basal conglomerates, sandstone and shale of
about 106.68 m, middle Bhima series consisting of limestone accounting for
about 167.64 m, and the upper Bhima series made up of local sandstone, shale
and flaggy limestone having a thickness of 99 m. However, it is to be reiterated
that the estimated thickness of sediments has not been accompanied by either
measured sections or by a lithostratigraphic column. Later, Misra et al (1987)
recorded the total thickness of Bhima rocks as 93m-273m. In the present study,
the Bhima basin has been demarcated into western, central and eastern parts for
working convenience.
The stratigraphic classification of Foote (1876) and Mahadevan
(1947) was revised by Janardhana Rao et al (1975) after remapping a large part
of Bhima basin in Gulburga district. They proposed a new nomenclature based
on the concept of formation and modem stratigraphic nomenclature, and
divided the Bhima Group into five units ascribing to two major cycles of
sedimentation. They are Rabanpalli Formation, Shahabad Limestone, Halkal
Formation, Katamadevarhalli Limestone and Harwal Shale. Later Mathur
(1977) restudied the Bhima rocks and modified the nomenclature used by
18
Janardhana Rao et al (1975). The Rabanpalli Formation represents the basal
beds consisting of few extremely thin bands of conglomerates, quartzitic
sandstone and siltstone; while shale are thick formed compare to other rock
types.
Harwal Shale and Halkal Formation are two names that sound very
similar. It is considered that such a close similarity in the same group is also
likely to lead to confusion. Hence, the name Halkal shale is retained and
Harwal shale is replaced by ‘Gogi’ shale after another prominent locality where
this formation is well defined. Misra et al (1987) introduced Sedum and Andola
subgroups in to the classification of Janardhana Rao et al (1975). Kale et al
(1990) regrouped the five formations into two formations in Bhima basin. The
stratigraphical classification proposed by Janardhana Rao et al (1975), Misra et
al (1987), and Malur and Nagendra (1994) has been followed in the present
study (Table 1.1).
The present thesis embodies the detailed studies of geochemistry and
depositional environment of limestones, siltstones, sandstones and shales of
Bhima basin. The study focused on element concentrations, element alteration
process, diagenesis of lithotypes and isotope geochemistry of limestones. The
field data were used to decipher the depositional environment of Bhima basin
and Neoproterozoic events.
1.8
PREVIOUS LITERATURE
1.8.1
Global Scenario
Over the last few decades, Neoproterozoic sedimentary formations
have been investigated intensively for carbon, oxygen, sulphur and strontium
isotope ratios. These studies were motivated by several reasons, among which
19
.fanardhana Ran el al (1975)
Malur and Nagendra (1994)
Misra et al (1987)
Deccan trap with
intratrappean sedimentarics
Harwal-Gogi
Formation
Purple shales
SHALE
Deccan traps
HARWAL
Intratrappean bed
Fissile Red shales
-----Sharp contact ?
Dark grey compact
siliceous limestone
Massive dark grey
and bluish grey
Variegated and
siliceous/Chert
Massive dark grey bluish gre
limestonewith disseminated
pyrite grains
Variegated siliceous bluish
green or pink/pale blue coloi
Blocky, light grey limestone
Slabby and flaggy bluish
grey limestone
Sharp contact ?
Purple shale Grcen/Yellow
shale silt stone
Calcareous purple and
yellowish grey shale
Quartzitic sandstone
Conglomerates and
grits
Granites, Granitoids and
gneisses
with/ without Dharwars
Quartzitic sandstone with
Ripple mark and
Cross lamination
Quartzitic conglomerate with
chert pebbles
Conglomerates with pebbles of
gneissic, Quartz and pink
feldspars
/
Pink granites
Orthoquartzitic
sandstone
and Conglomerate
Slabby and flaggy
RABANPALLI SHALE
Sedam subgroup
Blocky,light grey
to bluish grey
RABANPALLI FORMATION
Greenish yellow and
purple shale with
siltstone and sandstone
or conglomerate'grit at
the bottom
Grey or buff coloured
fissile shale
k
I Inconfnrmiti
ity
Flaggy dark grey bluish grey
argillaceous limestone
K.URKUNTA LIMESTONE
Massive dark grey
and bluish grey
limestone
Variegated and siliceous
limestone with various
colour shades chert bands
in upper horizon
Flaggy and slabby
limestone
Fissile Shale member
Orthoquartzite Chert
Pebble Conglomerate
Paraunconjbrmitv
Flaggy,dark grey
and argillaceous
Flaggy grey argillaceous
limestone
Slabby to blocky,light
grey to bluish grey '
limestone
HALKAL SHALE
it Sharp contact 7 aaa
HALFCAL Fm.
Greenish yellow to
bu(T coloured snalcs
with local Quartzitic
sandstone and
conglomerate
Andola subgroup
Well bedded and flaggy
dark grey limes'onc
yAAAAAAA/
Granites,Gneisses
and Dharwars
Table 1.1 Lithostratigraphy of Bhima Basin
20
deciphering the composition of ancient seawater and the search for regional
stratigraphic correlations were of great importance. Researchers have created a
substantial database, leading to the reconstruction of temporal trends in the
carbon and strontium isotopic composition of Neoproterzoic seawater.
The pioneer researchers, Magaritz et al (1986) in Siberian platform,
Tucker (1986a) from Southern Morocco, Aharon et al (1987) from Lesser
Himalaya, Lambert et al (1987) in Yangtze Platform, Kirschvink et al (1991)
from Siberia, Morocco and S. China, from Central Siberia, Corsetti and
Kaufman (1994) from Eastern California and West Nevada, Knoll et al (1995b)
from Northwest Siberia, Kaufman et al (1996) from north Siberia, Kimura et al
(1997) from northern Iran, Shen et al (1998) from Yangtze platform and Bartley
et al (1998) from northwest Siberian platform have discussed about PC/C
boundary problem in the well preserved Precambrian - Neoproterozoic
sequences on a global level. Further, Kaufman et al 1997 compiled the data
from global carbonate successions about PC/C boundary. Santos et al (2000)
reported Meso-Neoproterozoic boundary from limestone deposits of Bambui
and Paranoa Groups, of Central Brazil. Bartley et al (2001) have discussed
global events across the Mesoproterozoic-Neoproterozoic boundary by C and
Sr isotopic evidence from Siberia.
Kaufman and Knoll (1995) studied the variation of C-isotopic
composition of seawater during Neoproterozoic and gave the average curve for
C and Sr isotope concentrations by stratigraphic and biogeochemical
implications. They compared different country’s successions C isotopic
variations and classified four intervals in the Neoproterozoic formations with
stratigraphic and biogeochemical evidences. Further, Knoll (2000) discussed
about Neoproterozoic time in an excellent paper. Knoll and Walter 1992,
21
Kaufman and Knoll 1995, Hofmann et al 1998, Jacobsen and Kaufman 1999
have compiled C and Sr isotope data from Neoproterozoic carbonate sequences
and discussed glaciation, Ediacaran assemblages and seawater isotopic
variations.
Recently, the temporal isotopic trends of Neoproterozoic seawater
have been applied for age determination and correlation of Neoproterozoic
carbonate sequences of the Una Group, Irece Basin, Brazil (Misi and Veizer
1998), and for indirect age determination of nonfossiliferous, medium to highgrade marbles in the Norwegian Caledonides (Meleznik et al 1997).
Subsequently, sequence and biostratigraphic studies have also been
discussed in detail by many authors with C isotope and biogeochemistry. Blick
et al (1995) gave an excellent interpretation method for sequence stratigraphy in
Neoproterozoic earth history. Besides, many authors studied biostratigraphy in
Neoproterozoic formations (Jenkins 1995, Sergeev et al 1997). Haines (2000)
reported problematic fossils in late Neoproterozoic sediments from Wonoka
Formation, Southern Australia. Samuelsson and Butterfield (2001) reported
stratigraphic and paleobiological significances of Neoproterozoic fossils from
Franklin Mountains, northwestern Canada. Jacobsen and Kaufman (1999)
discussed the Sr, C and O isotopic evolution of Neoproterozoic seawater, and
their study revealed detailed first order records of isotopic variations ( Sr/ Sr,
5 C and 5 O) in seawater through the late Neoproterozoic Era, during which
several discrete global ice ages (snowball glaciations) occurred (VI, V2, SI,
S2) and the first macroscopic animals evolved. These data were obtained from
well preserved marine limestones from Siberia, Namibia, Canada, Svalbard and
East Greenland. Jiedong et al (1999) reported evidences for oxygenation of
Neoproterozic seawater using C, Sr isotopes and Ce anomalies. Shen (2002)
22
studied C-isotope variations and paleoceanographic changes during the late
Neoproterozoic on the Yangtze Platform, from China.
Further,
researchers have discussed Neoproterozoic tectonism,
orogeny (Kuzmichev et al 2001), supercontinents (Condie et al 2001),
economic mineral deposits, depositional environmental conditions, dating of
carbonate sedimentation using C and Sr isotope chemistry (Melezhik et al
2001)
and
provenance,
paleo-weathering
Neoproterozoic age formations.
for
siliciclastic
rocks
of
Besides, literatures have recorded on
geochemistry of carbonates (Banner, Veizer references given in the Chapter 3),
sandstones and shales (Cullers, McLennan, Taylor, Elderfield, Schidlowshki,
Condie, Cox etc. references given the Chapter IV).
1.8.2
Indian Scenario
In India stable and radiogenic isotope geochemistry of Proterozoic
sediments has been well documented by number of authors. Gururaja et al
(1998) traced the PC/C boundary in the Cuddapah basin. Subsequently, Dasari
Rao (1989) studied the isotopic variations in limestones from Kumool
sediments in Cuddapah basin. Mazumdar et al (1999) studied REE and stable
isotope geochemistry of early Cambrian chert-phosphorite assemblages from
the Lower Tal Formation of the Krol belt (Lesser Himalaya, India). Patil et al
(2002) have presented C, O and Sr isotope geochemistry of carbonate rocks
from the Kumool Group, southern India. Kumar et al (2002) have reported
carbon, oxygen and strontium isotope geochemistry of Proterozoic carbonate
rocks of the Vindhyan Basin, central India. Recently, Ray et al (2003) discussed
age, diagenesis, correlations and global events in carbonate sequences from the
Vindhyan Super Group with help of C, O, Sr and Pb isotope study. Islam et al
23
(2002) have discussed source rock assessment for Neoproterozoic Nagthat
siliciclastics of NW Kumaun Lesser Himalaya.
1.8.3
Previous Literature of the Study Area
A perusal of previous literature on Bhima basin shows that not many
publications exist pertaining to geochemistry of Bhima carbonates, economic
resources evaluation and industrial applications. A review of published
literature shows that many geoscientists have contributed to stratigraphy,
structures, palynology, exploration of uranium minerals and hydrogeological
aspects.
Foote (1876) was the first develop to the geology of Bhima basin in
his memoir on “South Maharatta country.” He gave the name Bhima series,
after the Bhima River. He proposed the bipartite classification of Bhima series
and described the general lithology. Later, Mahadevan (1947) studied the
Puranas and Archeans of South India and reclassified the Bhima rocks and
proposed the tripartite classification in his paper “Re-examination of some
aspects of Puranas and Archeans of South India.” He studied the lithology in
detail and computed the thickness of Bhima series as about 373.6 m; he also
reported two dolerite dykes cutting through the Bhima series.
Sinha (1971) studied in detail the ground water conditions in the
saline areas of Gulburga district. In his view, the horizontal bedding planes of
Bhima limestone and shale play a prominent role in ground water potentiality,
especially when the pervious and impervious layers intervene.
Later, Janardhana Rao et al (1975) studied the lithounits of Bhima
basin in detail and reclassified the rocks into five formations, and renamed the
24
Bhima series as Bhima Group in their paper “Reclassification of the rocks of
Bhima basin, Gulburga district, Mysore State.” Subsequently, Venkata Rao
(1977) dealt with the chief lithological units of the basin in detail and he
estimated the limestones to constitute over 2000 Km of the total area of 5200
■j
Km . The general chemistry of carbonates and their variation with depth was
also studied by him. He estimated the cement grade limestone reserves to be of
the order of 1500 MT.
This was followed by the work of Mathur (1977) on “Some aspects of
the stratigraphy and limestone resources of the Bhima Group.” He changed the
names of the lithounits following the recent code of stratigraphic nomenclature.
He has also published a note on the occurrence of glauconite in Bhima Group.
Akthar (1977) discussed the depositional environment of the clastic
sequence in the Bhima basin. On the basis of an integrated study of bedding
types, primary structures, texture and composition, he concluded that the Bhima
sediments are of marine origin.
Jayaprakash and Murthy (1979) recorded the development of pressure
solution structures in limestone with a detailed study of the characteristics of
stylolites in different units of limestone.
Later, Peshwa et al (1983) studied the Lower Palaeozoic Bhima
sediments and associated Archean rocks by using Remote sensing technique.
This helped to delineate the major stratigraphic units, regional fractures and
faults. The aerial photo interpretation enabled detailed lithostratigraphic
mapping of Precambrian of Bhima Group.
25
This was followed by geological investigations by Mudholkar and
Kale (1984) in the Rabanpalli area using aerial photographs on 1:60,000 scale.
They classified Rabanpalli Shale Formation into four members and proposed
the lithostratigraphical classification of this unit, in addition to recording faults
and intrusions. Krishna Rao et al (1984) contributed on “Tectonic history of
parts of Bhima basin and its influence on ground water conditions.” They
inferred variations in ground water potentiality between the tectonic and nontectonic regions of both Archean and Bhimas, besides, recording second order
shears and thrust faults, and inferred the age of the tectonic cycle as postBhima. Jayaprakash (1985) first reported the occurrence of Barytes in Bhima
basin, which suggests a synsedimentary origin for the shale unit.
Later, Malur and Nagendra (1989) studied in detail the macrostylolitic
structures of Bhima basin, and discussed the relationship between lithology and
stylolites. They also classified the macrostylolites, besides reporting new types
of solution structures. Misra et al (1987) classified the Bhima rocks into two
sub-groups, five formations and thirteen discernible members. Malur and
Nagendra (1992) reported a detailed study of microstylolites in the carbonates
and described new patterns based on the geometrical and bedding plane
relation. The presence of residual matter as capping along the stylolites was
also discussed.
Earlier, Malur and Nagendra (1988) had carried out a detailed study
of clay minerals from Bhima argillites and inferred illite is the dominant clay
mineral. Based on the EC and pH determinations, the prevalence of an acid
environment during the period of deposition of these argillites was suggested.
Sathyanarayan et al (1987) discussed the stable isotope geochemistry of Bhima
26
Group and inferred the genetic relationship primarily to the hypersaline
environment.
Malur and Nagendra (1994) recorded the lithostratigraphical column
and lithological contacts between formations and depositional environment.
Kale and Peshwa (1995) published a book on Bhima basin covering
sedimentation, structure and age of the Bhima group and also suggested field
traverses for understanding the geology of the basin.
After Sathyanarayan et al (1987), Kumar et al (1999) reported about
chronostratigraphic implications of carbon and oxygen isotopic compositions of
the Proterozoic Bhima carbonates, and inferred the depositional age of Bhima
sediments to be Post-Varanger, Terminal Proterozoic. Jayaprakash et al (1999)
classified the Shahabad Formation in to five members and described its
importance in cement industries. He has computed the thickness of the
limestone horizons in the proposed five members.
Dhanaraju et al (2002) have reported uranium mineralization in the
Neoproterozoic Bhima basin around Gogi and Ukinal area by ore petrography
and mineral chemistry.
Senthil Kumar and Srinivasan (2002) have reported the fertility of
Late
Archaean
basement
granite
in
the
vicinity
of U-mineralized
Neoproterozoic Bhima basin, Peninsular India. Recently, Nagendra and
Nagarajan (2003) have reported geochemical aspects of Shahabad Formation
and its depositional environment.
A perusal of previous literature on Bhima basin shows that there has
not been much emphasis on geochemistry (major, trace and REE) of Bhima
27
carbonates and siliciclastic rocks. However, evaluation of the economic
resources and industrial applications of limestones for the study area have been
given much importance. Hence, this research works encompasses the following
objectives:
1.9
OBJECTIVES
1.
To study the diagenetic paths and effects of different litho-units
(from early diagenesis to burial).
2.
To understand the geochemical behaviour, mobility of major,
trace and rare earth elements.
3.
To understand the depositional environment of limestones and
siliciclastic rocks.
4. To understand the tectonic setting, provenance and paleoweathering of siliciclastic rocks.
5.
To evaluate the isotopic concentration and burial rate of organic
carbon.
6.
1.10
To understand the Neoproterozoic events in the Bhima basin.
METHODOLOGY
To reach the goal of the above objectives the following methodologies
have been used in this study. Fieldwork, literature collection and laboratory
studies form the main components of the research. Detailed fieldwork and
mapping was carried out in Gulbarga and Bijapur districts covering the five
formations of the Bhima Group for period of five months. Field data such as
lithological
characters,
thickness,
litho-contacts
textural
relations,
28
macrosedimentary structures altitudes etc. were recorded. Integrated the field
data with laboratory results to achieve the objectives*
v
The Rabanpalli Formation consists of sandstones with well
preserved current bedding, ripple marks, shales of different colours, thickness,
fissility and quartzites, which are well exposed in sections along the fringes of
the basin. A major E-W fault was traced along the Gogi-Domahalli Zone. The
conglomerate horizon was studied in detail at the Gogi ridge. The pressure
solution structures in the limestones of Shahabad Formation were recorded
from exposures and quarry sections. Representative limestone samples with
various colors, sandstone and shale samples were collected from outcrops and
quarry sections at regular intervals for geochemical studies. Macrostylolites,
joints, faults and burrow structures were recorded in this formation. The Halkal
shale, Katamadevarhalli limestone and Harwal shale formations were studied in
outcrop sections and the field data were documented.
1.10.1
Petrography
The rock thin sections were prepared by using standard procedure for
petrological studies, such as diagenetic signatures, microstructures and cement
relationship. One hundred thin sections were prepared to study the petrography.
Stains of the thin sections were made to know the mineralogy and cement types.
Many thin sections were subjected to Alizarin Red - S stains to confirm the
presence or absence of dolomite and calcite and Potassium ferri-cyanide to
confirm the presence of absence of ferroan/nonferroan carbonate rocks.
Friedman’s (1959) organic stain specific for calcite and Katz and Friedman’s
(1965) combined organic and inorganic stain specific for iron rich calcite have
been adopted to identify the mineralogical variation across the basin.
29
1.10.2
Geochemistry
Selected samples were grained and sieved through 230 mesh ASTM
which were analyzed for major, trace and Rare Earth Elements (REE). The
major trace and some REE were analyzed for this study using Inductive
Coupled Plasma Atomic Emission Spectrometer (ICP-AES) (Jobin-Yvon
JY138 Ultrace) at the Department of Geochemistry, Ecole des Mines de Saint
Etienne, France. The samples were prepared by dissolution (in HN03 + HF),
and silicon was lost during fuming off the excess HF. Silica was thus not
determined in ICP-AES. ICP-AES allows accurate determination of low
amounts of compatible elements, including 'major' elements (Mg, Ti) down to
<0.01%. The analysis of silica carried out by other method, the setting in
solution of the samples for the ICP is carried out mainly by acid attack (HfHNO3-HCI). Si02 Nb, Zr, and Th were analyzed by XRF method on pressed
pellets only for computation of absorption effects on the trace elements. The
vertical litho-section samples were analyzed for major elements using XRF
method.
Bulk samples were ground and sieved through a 200 mesh (about
0.074 mm pore size) nylon sieve for chemical analysis. Powdered sediment
splits of 0.2 g were digested with 4 ml HN03 and 1 ml of HC104 for 24 h in a
tightly closed Teflon vessel on a hot plate at less than 150°C, heated to dryness,
and then digested with a mixture of 4 ml of HF and 1 ml of HC104. Later, the
solution was evaporated to dryness, and extracted with 10 ml of 1% HN03.
Meanwhile, separate sample aliquots were leached with 2M HC1 plus 0.5M
HlN03 for 24 h under 25° C to extract the leachable fraction. The digested
samples were measured for rare earth elements by ICPMS (Plasma QUAD 3).
The geochemical standard SPL - 29 was used for this study.
30
The following method was used for bulk rock analysis to assess the
quality of the limestones. Samples were analyzed (bulk rock analysis) after
Shapiro (1975) for major oxides using rapid analytical techniques. 50 mg, in
case of silicate samples, and 250 mg for carbonate samples were accurately
weighed. These samples were fused with NaOH in a nickel crucible and
solution A was prepared for Si02 and A1203 determination. Solution B was
prepared by digesting 500 mg of samples with (HF+HC1+HN03) acid mixture
to estimate Na20, K20, Fe203, CaO, MgO, P2Os and MnO. Total iron, silica,
alumina and P205 were determined using a spectrophotometer (Spectronic 20).
Calcium and magnesium were determined by titration method using EDTA
with screened calcite and O-Cresolpthalein complexon indicator. The amounts
of sodium and potassium were estimated using a flame photometer. Insoluble
residue were determined the following method for this study. 1 g powdered
sample taken and 10ml of 6 N HC1 was added which heated until the C02
effervescence stopped. The suspension was then cooled for about an hour, and
was then poured through a 0.45 pm filter. The solid material trapped in the filter
was washed with distilled water, and then was dried at 80° C for 2 hours.
Following cooling the resulting insoluble residue was weighed.
1.10.3
Isotope Study
Representative limestone samples were used for stable isotopic
studies. C and O isotope analyses were carried out at the stable isotope
laboratory (LABISE) of the Department of Geology, Federal University of
Pernambuco (UFPE), Brazil. C02 gas was extracted from powdered carbonates
in a high-vacuum line after reaction with 100% orthophosphoric acid at 25° C
for one day (three days were allowed, when dolomite was present). The C02
released after cryogenic cleaning was analyzed in a double inlet, triple collector
°\
p^
31
SIRA II mass spectrometer and the results are reported in 8 notation (%o, PDB
scale). The uncertainites of the isotope measurements were 0.1%o for C, and 0.2
%o
for O, based on multiple analyses of an internal laboratory standard (BSC).
Representative samples were selected based on Mn/Sr ratio and C and
O isotope values to analyze for Sr isotope study. Limestone samples were
leached in IN ammonium acetate prior to acid digestion. Sr was separated in
2.5 M HC1 using Bio-Rad AG50W X8 200-400 mesh cation exchange resin.
Total procedure blank for Sr samples prepared using this method was < 200 pg.
For mass spectrometry, Sr samples were loaded on to single Ta filaments with 1
N phosphoric acid. Sr samples were analyzed on a VG Sector 54-30 multiple
collector mass spectrometer. A 87Sr intensity of IV (1 x 10~11 A) ± 10% was
maintained and the 87Sr/86Sr ratio was corrected for mass fractionation using
87Sr/86Sr = 0.1194 and an exponential law. The VG Sector 54-30 mass
spectrometer was operated in the peak-jumping mode with data collected as 15
blocks of 10 ratios.
For this instrument, NIST SRM987 gave a value of
0.710260 ±11(1 SD, n = 17) during the analysis.
80®B83