Geological Studies of the Sedimentary Structures of the ...Cuddapah Basin, Andhra Pradesh, South India Harish Vijay G, Srinivasa Gowd S*, Maheswararao R, Pradeep Kumar B & Ravi Kumar

Geological Studies of the Sedimentary Structures of the Cuddapah Basin, Andhra Pradesh, South India

Harish Vijay G, Srinivasa Gowd S*, Maheswararao R, Pradeep Kumar B & Ravi Kumar P

Dept. of Geology, Yogi Vemana University, Kadapa-516005, Andhra Pradesh, India.

*Corresponding author: [email protected]

ABSTRACT There are umpteen varieties of sedimentary structures in the Cuddapah Basin, especially best

seen in the western part of the basin. They can be classified following the classification of sedimentary

structures by Petti john (1975). Though most of the sedimentary structures are easily identifiable a few

are slightly difficult to explain. Sedimentary structures are very useful in paleo current analysis and

interpretation of siliciclastic shallow marine environment. These interesting sedimentary structures such

as parallel bedding, cross bedding, ripples, and mud cracks as well as synaeresis cracks, are best studied

in the field. They are formed by a variety of sedimentary processes, including fluid flow, sediment-

gravity flow, soft-sediment deformation and biogenic activity. Gulcheru Formation has evidence of

interaction of microbial communities with clastic sedimentation during Paleoproterozoic time. Because

of high porosity-permeability of siliciclastic of Gulcheru Formation, paleontologists do not expect many

fossils preserved in such rocks and thus they have been overlooked. Microbially induced sedimentary

structures (MISS) are highlighted in the Gulcheru Formation. They are indicative of shallow marine

environment. Gulcheru Formation shows alluvial fan to shallow marine shelf environments within a

limited thickness of about ~ 110m, which indicates an alluvial plain coast where alluvial deposits are

modified by wave forces.

INTRODUCTION

In contrary to the voluminous studies on tectonics and sedimentary geochemistry no studies on

primary sedimentary structures has been carried out which contribute significantly for understanding

depositional environment. This paper describes the important primary sedimentary structures observed

in the Gulcheru quartzite around south-western margin of the Cuddapah basin with a special emphasis

on microbial mat related features to highlight additional observations on MISS that has not been

described earlier.

SEDIMENTARY STRUCTURES OF THE AREA

Sedimentary structures in the area are grouped into three broad categories: microbial mat related

structures, stratification structures (different types of cross beddings) and bed forms (ripples),

beddingplane markings (mud cracks and synaeresis cracks).

GEOLOGICAL SETTING

The crescent-shaped Cuddapah basin is an intracratonic basin located on the eastern margin of

the Dharwar craton in the Indian shield (Fig. 1). The Cuddapah basin consists of sedimentary and

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associated volcanic rocks, about 12 km thick, ranging in age from late Paleoproterozoic to

Neoproterozoic (Bhaskar Rao et al., 1995; Ramam and Murty, 1997; Zachariah et al., 1999). The

sediments unconformably overlie the basement, consisting of peninsular gneiss and granite with

remnants of greenstone belts. The Cuddapah Supergroup is composed dominantly of argillaceous and

arenaceous sequences with subordinate calcareous sediments deposited in peritidal complex with

shallow marine carbonate shelf and beach. A detailed description of stratigraphy, structure, igneous

activities, mineral potentiality and basin evolution is given by Nagaraja Rao et al. (1987). In the northern

part of the basin, the lower sequence of the Gulcheru Formation is represented by conglomerate and

arkose, but in the southern half it is dominantly represented by quartzite.

Fig. 1. Geological map of the Cuddapah basin showing the sub-basins (after Nagaraja Rao et al., 1987).

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PAPAGHNI GROUP

Gulcheru Quartzite

The main primary structures noticed in the Gulcheru Quartzite are (1) current bedding (2) mud

cracks (3) ripple marks and (4) occasional pit and mount structure. The secondary structures are (5)

Liesegang rings and (6) ring like structure due to leaching.

Current bedding: The Gulcheru Quartzite exhibits both planer and trough type of current bedding. The

current direction in general is from SW in the southern and NW in the northern part of the unit. The

tangential cross bedding is seen well in the Parnapalle area (Fig.2).

Mudcracks: Mud cracks are best observed in the siliceous shales of Gulcheru Quartzite. Mud cracks are

filled generally with the same material in which they occur. In the Gulcheru Quartzite the filled-in-

material is siliceous. Some of the mud cracks are filled with the same material and some are empty

without any filling. The top of the filled-in material is either convex or flat. Well-developed mud cracks

generally show the development of cracks of several orders – first, second and third. Thus, on a single

surface, cracks and polygons of different magnitude are present (Reineck and Singh, 1973). Mudcracks

of primary, secondary and tertiary order are noticed in the Gulcheru siliceous shales in Gulcherughat

section (Fig. 3).

Ripple marks: The quartzite and siliceous shale show more ripples than any other lithological unit. The

ripple marks observed are mainly wave ripples or symmetrical ripples with curved crests. The majority

of the ripples observed are aqueous oscillatory having R.I. of 6 cm. A few of them have R.I. of 12-32

cm. Further, there is interference ripples in which the crests of one set ripples lie in line with troughs of

another set. These are the resultant of the superimposed ripple pattern (Pettijohn1975) and are known as

‘tadpole nest’. Two sets of ripple marks occurring at right angles are observed east of Maddimadugu, in

the Gulcheru Quartzite horizon. These are wave ripples produced by two equally strong wave directions.

In the Kadiri-ghat section (old) variety of ripples with different wave length and amplitude are observed.

In the same bed ripple of different pattern can be seen (Fig. 4a, 4b, 4c).

Fig.2. Cross-bedding in Gulcheru horizon. Fig.3. Mud Cracks in Gulcheru horizon

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Fig 4a. Fig 4b. Fig 4c.

Fig.4a, 4b, 4c. Ripple Marks in Gulcheru Quartzite

Pit and mound structures: The top horizon of Gulcheru Quartzite in the area southwest of .2341

exhibits an interesting feature, which resembles pit and mound structure. They are elevated mound like

structures with a vesicle at its centre. The structures are shallow extending very little into the rock. The

diameter of the mound-like structure varies from a few mm to 1 cm or even more. Pits are also

associated with mounds. These features noticed in the Gulcheru Quartzite reflect all the characters of pit

and mound like structure described by Shrock (1948) except that they are mostly seen in the mudshales

of high viscosity according to Shrock. Radial cracks described by Shrock are absent in the structures

observed in the Gulcheru Quartzite.

Liesegang Rings (Ring like structure): Gulcheru Quartzite exhibits this structure in the area west of

.546. The diameter of the rings varies from 0.5 cm to 2 cm’s. These rings are made up of ferruginous

material and alternate with quartzite (Fig.5). Sometimes two or more rings coalesce with each other,

thereby giving rise to composite ring-like structure. On the weathered surface these stand out as rounded

pebbles.

Ring like structures due to leaching: The Gulcheru Quartzite of Gandi area exhibits circular patterns, the

margin of which is marked by ferruginous material. At places ‘nuclei’ like feature are also noticed at the

center of the ring. On the weathered surface of Quartzite, these stand out as nodules.

Vempalle Formation:

The main sedimentary structures are stromatolites and stylolites. Chert associated with dolomite gives

rise to various shapes which are difficult to describe.

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Stromatolites: Stromatolites are the organic structures noticed in the dolomites and cherts of the

formation. King (ibid) was the first to describe these structures. Later,Srinivasa Rao (1949) described

these from the Rayalacheruvu area, Prasad and Verma (1967) described a new species of Collenia

Rajurkarai, from near Lingala. Viswanathiah and Aswathanarayana Rao (1967) described some species

of Collenia and Cryptozoonfrom Mutssukota. Sarma and Nageswara Rao (1969) described the

stromatolites in general. Palaeontology division of the Southern Region, Geological Survey of India had

taken up the study of the stromatolites of Vempalle Formation on a project basis.

The Stromatolites of Vempalle Formation belong mainly to Collenia Cryptozoon species (Fig.6).

Geometrically the Stromatolites can be classified as LLH-C and SSH type (Logan 1953). The main

localities where the Stromatolites can be best studied are south and south west of Pulivendula,

Bhumayagaripalle road section, north-east of Vempalle, Rayalacheruvu, the road section of Nayanipalle,

Mutssukota and near Kolhapur.

Stylolites: Stylolites are noticed in the dolomite of Vempalle Formation. Geometrically, the stylolites

can be classified as (1) Simple primitive wave like type, (2) Sutured type, (3) Sharp peak type, (4)

Seismogram type (Fig. 7) (Park & Scot 1968) and genetically these represent (5) inter connected and (6)

horizontal stylolites. Mega stylolites, mainly up-peak type is also noticed south west of Pulivendula.

Chitravati Group:

Pulivendula Quartzite:

This unit exhibit oscillatory transverse ripples and a few current ripples. Simple plain type of current

bedding is commonly noticed.

Tadipatri Formation:

The shale unit of the Tadipatri Formation exhibit sedimentary structures of comparatively deeper water

facies, which are detailed below:

Flute casts: These are noticed on the sole of shale of the Tadipatri Formation. They range in size from a

few mm to a few cms. Flutes of elongate, deltoid, distorted and over-lapping type are noticed in the area

north of Mallela.

Groove and Striation casts: (Tool marks): These are observed on the sole of siliceous shale of Tadipatri

Formation. These are generally formed in the underlying shale before it is consolidated. Straight running

nature for greater length and uniformity of height are the characters of these. These tool marks are well

developed in the Mallela Ghat sections (Fig.8)

Flame Structure: The siliceous shale of Tadipatri Formation exhibits flame structure, which can be used

to recognize top and bottom of beds. This structure is best noticed in the Mallela ghat section.

Accretionary structures:

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Concretions: These are common in the limestone and shale horizon of Tadipatri Formation. The

concretions in the Tadipatri limestone are siliceous and of various shapes. These are best noticed in the

Mallela Ghat section. Disc like concretions associated with shale, at all stratigraphic levels is the

characteristic feature of the Tadipatri Formation.

Fig.5.Liesegang Rings in Gulcheru Quartzite Fig.6. Stromatolites in Vempalle Formation

Fig.7.Stylolites in Vempalle Formation Fig.8. Groove and Striation Casts in Tadipatri Formation

Branched Stromatolites: These are observed in the dolomites of Tadipatri Formation on the way to

Velpula. (Fig. 9)

Gandikota Quartzite

The primary sedimentary structures noticed in the Gandikota Quartzite are:

Current Bedding: The simple plain type of current bedding is very common in this unit; occasionally

trough type of cross-bedding is also observed. Herringbone cross bedding is noticed in the Gandikota

Fort area (Fig.10)

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Ripple-marks: The quartzite exhibits oscillatory transverse ripples with curved crests. These are well

developed in the Muddanur-Jammalamadugu road section. It also reflects interference pattern that

appears to be slightly difficult to explain (Fig.11)

Mud cracks: Polygonal mud cracks are noticed in shale-quartzite sequence of Gandikota.

Concretionary structures: Disc like concretionary structures are also noticed in the intercalated shale

sequence in the Malliyam Bhavi area (Fig.12). The secondary structures are not well developed, except

the seismogram type of stylolite in the quartzite.

Fig.9. Stromatolites in Tadipatri Formation Fig.10. Herringbone Ripples in Gandikota Quartzite Formation Fig.11. Interference Ripples in Gandikota Quartzite Fig.12. Concretionary Structure in Tadipatri Formation Nallamalai Group:

Bairenkonda Quartzite

The main sedimentary structures are oscillatory ripples and planer cross-bedding which is conspicuously

noticed; the latter is used on the eastern most Velikonda quartzite to recognize top and bottom. The cross

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bedding and current bedding structures are preserved at several places. An attempt to understand to

current direction from a few reading has not lead to logical conclusions.

Cumbum Formation

Biogenic forms: The petrographic examination of cherty dolomite and chert from Varikunta area has

revealed the possible biogenic forms, mostly represented by micro-stromatolites of laterally-linked

hemispheroidal and oncholitic type. These oolitic and pellety structures at first glance appear to be

deformed oolites, but the shapes and structures are too complicated, varied and typical to belong to true

oolites however deformed the latter may be. These relict shapes and structures are suggestive of the

presence of micro-fossils. The forms related to these “pseudo-oolites” range from spherical, ovoid, bean-

shaped, pelletyetc; some of those with a partly preserved leaf-like structure resemble stromatolites.

Some are with coats or concentric lamellae built around near-square or rectangular pieces of intraclastic

fragments. The central part or the nucleus mineralogically made up of either chamosite or chert or,

rarely, the intraclastic rock fragment. Thus, the nucleus is generally a rock or mineral granule while in

some cases it could have been a hollow region later filled (or replaced) by chert or carbonates. The

chamosite granule of the nucleus itself occasionally contains tiny dolomite euhedra in the central part of

the whole structure. This, for instance, could happen when the parent material of the dolomite euhedra

had been an aragonite-bearing microfossil which was preferentially dolomitized.

The alternate laminae constituting the coat of these structures are represented by alternate layers of a

very fine-grained carbonate and an indefinite, dusty, sometimes spongy material impregnated with

probable carbonaceous (or ferruginous) dust. It is suggested that the dusty or spongy layers of the cortex

represent biogenic filament proper (algal or bacterial), while the fine-grained carbonate could be a

biomicrite. The formation and/or preservation of chert in a carbonate milieu itself could have been

possible due to the protective shell of the algal origin. The possibility of the micro-crystalline chert of

the interior part of these pseudo-oolites (oncholites) in itself representing the silica secreted by an

organic agency is not ruled out. Not frequently such cherty structures are impregnated with carbon dust,

while the same is absent in the overall cherty matrix in which these cherty oolites are embedded. This

feature is also suggestive of biogenic origin of such structures.

The pellet-shaped bodies are even more strongly suggestive of biogenic origin. These are also in a

variety of irregular, crescent, and curved shapes besides being cylindrical with tapering ends. Their

length generally exceeds ten times their width. A dusty trail along the axis of some of these simulates a

septum. Similar structures found in “Cheyair limestone” are of algal origin, (Srinivasa Rao 1949).

The first record of these possible biogenic structures from Nallamalai Group formations is given by

Mehdi (1978). The probability of structures of biogenic origin is also confirmed by Birbal Sahni

Institute of Palaeobotany.

The other sedimentary structures noticed are ripple marks and cross-bedding occurring in the

inetercalated quartzite and siliceous shale sequence.

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Nagari Quartzite

The Nagari Quartzite exhibits a variety of sedimentary structures such as ripple marks, mudcracks, cross

bedding, mammilary fractures etc.

Ripple marks: Ripple marks from the upper beds of Nagari horizon in the Kalahasti ridge were recorded

by Murthy (1954). Major ripple is noticed in the quartzite of Sanipai area (Mehdi, Nagaraja Rao, 1969).

Wave ripples with curved crests with an average wavelength of 6 cm and an amplitude of 1 cm are

recorded in the Tirumala hills (Nagaraja Rao, 1970). The ripple index ranging from 8 to 20 confirms

their aqueous origin. Interference ripples in which the crest of one set lie in line with the trough of

another set are noticed in the area east Maddimadugu. These are also due to superimposed ripple

patterns.

Mudcracks: These are noticed in the intercalated shale and quartzite. Incompletely developed

mudcracks are seen in the Nagari Quartzite, near a tank 12r south of Apparajupalle. These are

curvilinear with tapering ends and resemble worm trails. Filled-in mudcracks showing rectangular

pattern are also noticed in the siliceous shale interbedded with quartzite northwest of 228.

Cross-bedding: Murthy (1954) recorded fine current bedding in quartzite in the Kalahasti ridge. Profuse

current bedding in quartzite is seen in hillock north east of Thantipandal. Mehdi et. al. (1969) have

noticed small to mega-scale planer current bedding in the Seshachalam ranges east of Sanipai, Nagaraja

Rao (1972) observed simple and trough type of current bedding in the Nagari Quartzite in the Palakonda

hill ranges.

Mammilary fractures: Mammillary fractures resulting due to breaking of quartzite in a typical pattern to

expose a structure that resembles mammillary glands in all its characters is noticed in Nagari Quartzite

in the area east of Maddimadugu recorded by Nagaraja Rao (1972). The fineness of the quartzite and the

tendency to break in a radial concave pattern may be the reasons for the development of mammilary

fractures (Fig 13). These have resemblance to Manroe structures.

Fig.13.Mammilary Fracture in Nagari Quartzite

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Other Structures: Sole marks, flute casts and load casts are also found besides the above mentioned

features, in the Nagari horizon in the area south of Apparajupalle. The load casts are highly irregular and

variable in shape. The size of the flute casts ranges from 1-8 cm in length

Pullampet Formation:

Slump structures: Slump structures and Septaria, are the main sedimentary structures. The cherty

dolomite unit located east of Rajampet exhibit varied structures because of the presence of chert which

are difficult of describe.

Other Sedimentary Structures of the Cuddapah Basin

PALAEOCURRENT ANALYSIS

The dip direction of cross-bed fore sets; the asymmetry and orientation of the crests of current

ripples are directional data obtained from sedimentary structures. Because the fore set laminae in cross

Fig.14. Ichino Fossils in Gulcheru horizon Fig.15. Oolites in Vempalle Formation

Fig.16. Concretion in Vempalle Shale Fig.17. Contemporaneous deformation in

Vempalle Formation

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beds are generated by avalanching on the down current (lee) side of ripples, the fore sets dip in the down

current direction. However, due to the lack of three-dimensional outcrops strike and true dip directions

of the fore set laminae was not possible to determine. Thus only current ripples have been used for

palaeocurrent analysis. The orientation of directional sedimentary structures has been determined in the

field with a Brunton compass by taking measurements from as many different outcrops in plan and

individual beds as possible and practical. The orientation of directional structures determined from the

Gulcheru Formation shows considerable scatter. Therefore, these directional data have been treated

statistically in a manner to reveal primary and secondary directional trends. At places the cross-bed fore

sets in sandy deposits of marine tidal channels display two opposing dip directions owing to formation

of cross-beds during both incoming and outgoing tides. This type of opposing flow is referred to as

bidirectional. The paleocurrent flow is showing three modes in the study area. However, out of three

prominent directions of flow as revealed by the directional data easterly direction is dominant and

represents regional paleocurrent directions. Apart from this, local paleocurrent directions also have

environmental significance. Features from lower part of the Gulcheru Formation indicate a unimodal

current direction related to alluvial fan setting. The symmetric wave ripples also show alternate N-S and

E-W crest line orientations at places. The uppermost part of the Gulcheru quartzite is indicative of tidal-

flat origin. Therefore, a transgressive sequence can be seen with in Gulcheru Formation.

CONCLUSION

These structures are the best indicators in any deposit of processes operating in the depositional

environment because they formed where they are presently found. Hence, they provide powerful tools

for assessing the influence of processes that could not be observed because the processes operate

infrequently and/or in remote sites (e.g., current patterns and concretions forming below the sediment-

water interface), or because they operate at a rate unsuited to direct observation (either too rapidly or too

slowly). Within about 110 m thickness of Gulcheru Formation in the study area, the environmental

condition ranges from alluvial fan to shallow marine shelf with a transgressive sequence. It represents a

setting of an overall coastal zone with relatively short shore faces where the foothill and tidal plane land

is very close to shore line. The detritus was carried to the sea along small straight stream channels over

short distance. Therefore, the Gulcheru Formation represents an alluvial plain coast where alluvial

deposits are modified by wave forces. Interpretations from sedimentary structures range from formative

process through way-up determination in deformed rock sequences, to determining paleo current

directions and/or paleo slopes, to indicators of the presence and activities of organisms at or shortly after

deposition, and to environmental recognition.

References

Bhaskar Rao, Y.J., Pantulu, G.V.C., Damodara Reddy, V. and Gopalan, V. (1995) Time of early sedimentation

and volcanism in the Proterozoic Cuddapah Basin, South India: evidence from the Rb–Sr age of

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Logan, B.W., Rezac, R, Ginsburg, RN., (1964). Classification and environmental significance of algal

stromatolites. Journal of Geology, pp 68-83.

Mehdi, S.H., Nagaraja Rao, B.K., (1969). Geology of Rajampet area, Cuddapah District, Unpublished Report,

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Documents

Geological Studies of the Sedimentary Structures of the ...Cuddapah Basin, Andhra Pradesh, South India Harish Vijay G, Srinivasa Gowd S*, Maheswararao R, Pradeep Kumar B & Ravi Kumar