IAPRS & SIS, Vol.34, Part 7, “Resource and Environmental Monitoring", Hyderabad, India, 2002
colour composite geocoded images of IRS-IA/IB on
1:50,000 scale were also interpreted for a elaborate
study. Various structural features namely lineaments,
faults, folds and shear zones are identified based on different
image characteristics as observed on satellite images.
5. GEOLOGY
The Pranhita-Godavari basin displays a record of terrestrial,
marine, and paralic deposits. Further, this basin preserves a
geological record of sedimentation of Permian, Triassic,
Jurassic, and Lower Cretaceous periods covering the entire
span of Gondwana period in Peninsular India. In this linear
belt, the Lower Gondwana (Talchir, Barakar, Barren Measures,
Kamthi) sediments are exposed along both the margins, while
the upper Gondwana (Maleri, Kota, Chikiala) formations cover
the axial portions. On the south-eastern extremity in the
Chintalapudi area, the Kamthi beds are preserved and further
south the coastal upper Gondwana sediments occur as a linear
belt running sub-parallel to the coast. Rao et.al (1996) inferred
the possible extension of discontinuous coal-bearing Barakar
formation along its strike direction at different places and
showed as a continuous linear formation. Several authors
(Ramanamurthy, 1987; Lakshminarayana et. al. 1992; Kasturi
Dasgupta, 1993) discussed the revised stratigraphic succession
of the Pranhita-Godavari valley.
6. Structural Framework
The northern part of the basin, ie., from the north of
Kothagudem, it is found to be more structurally disturbed with
many number of faults/lineaments than that of southern part. In
the southern part of the basin, which mainly comprises coastal
Gondwana formations, the number of inferred faults/lineaments
are less. This may be due to alluvial cover over these
formations. There are master faults trending NNW demarcating
the boundary between the entire lithological formations
namely, a) Pakhal and Kota b) Pakhal and Chikiala, c)
Precambrian and Kota, and d) Precambrian and Maleri in the
eastern part of the basin. In addition, many faults cut across the
formation boundaries and transverse to the trend of the
individual formations.
The Pakhal formation in the north of Yellandu and east of
Mailaram high are highly folded. In the south-eastern part of
the basin, two major continuous shear zones are identified.
The western shear zone is recognized occurring between
Mailavaram in the south and Donkarayi in the north running
along NE-SW direction. This shear zone seems to be folded
near Kukunuru and appears like a meandering of a river. This
shear zone in the northern half lies at the contact between the
high grade rocks (granulites) of the Eastern ghats and the low
grade rocks (amphibolites) of the Bastar craton (Chetty and
Murhy, 1994) This shear zone is considered as pre-Gondwana
feature which has been reactivated after the deposition of
Gondwana sediments. The other shear zone which is nearly
parallel or sub-parallel to the earlier one runs through
Precambrian formation. This shear zone starts from Donkarayi
in the north and abruptly terminates near Kannapuram because
of the Godavari graben structure. In the south-western part of
the basin, a major shear zone running along NW-SE direction
passing through Khammam, Madhira, Mahabubabad is
distinctly seen. This shear zone converges with the other shear
zone near Vijayawada. Almost parallel to this in the west, a
big lineament is also inferred which runs through Precambrian.
Both these features are considered as pre-Gondwana type.
7. FREQUENCY ANALYSIS
7.1 Procedure
The lineament and tectonic maps were subjected to analysis by
applying the integrated deformation model. The study of sum
total ruptural deformation of an area in hard rocks is named as
integrated deformation model. Initially, the map was
superimposed by a 2 cm X 2cm grid dividing the area into
several equally spaced squares of SkmX5km. The directions of
the lineaments, faults, and shear zones falling in each of the
squares were measured. By doing so, major lineaments, faults
and shear zones running over longer distances are counted more
than once as they fall in more than one unit area. Thus, proper
weightage was provided for such major structures during
frequency analysis. The directions along which major sets of
these structural features are aligned are grouped as lineaments,
faults, and shear zones. All the three structures are combined
and represented as single fracture frequency diagram to get a
comprehensive view. Similar diagrams are constructed for each
lithological formation of Gondwana group and their adjacent
formations (Figure-1). The structural trends based on the
frequency analysis of the individual formations are given as
follows.
7.2 PRECAMBRIAN
From the combined fracture frequency, it is observed that the
majority of the fractures are along NW-SE and NE-SW
directions and very few are in NS and EW directions. Among
these directions, the major trend is in NW-SE direction.
7.3 SULLAVAI AND PAKHAL
In Sullavai and Pakhal groups, faults and lineaments are lying
in NW direction followed by EW direction. Among these
directions, NW-SE direction is predominant, in which majority
is in N 25°-35° W. These lineaments and faults coincide with
master faults demarcating the boundary between Gondwana
formation and their adjacent Archaean crystallines.
7.4 LOWER GONDWANA FORMATION
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In Talchir formation the predominant direction is EW that is
mainly due to lineaments. The distribution of these features is
noticed equally in NW and NE directions. The trend in the NW
direction is slightly higher.
In Barakar formation most of these features are trending in NE
direction with a maximum number in N 159-25? E. These
features are also observed considerably in E-W direction while
very few are observed in NW direction.
In Barren measure formation majority of these features are
appearing in EW direction. The trend in the NNE-SSW
direction is also observed prominently (Figure-1).
In Kamthi formation, major direction of the fractures is in NE-
SW, with a maximum number trending in N 35?-45? E followed
by NW-SE and EW directions.
7.5 UPPER GONDWANA FORMATION
In Maleri formation, when the trends of the lineaments and
faults are combined and more or less equal distribution of
