Chapter 4 Structure

Chapter 4 STRUCTURE OF THE PROJECT AREA

CHAPTER # 4

STRUCTURE OF THE PROJECT

AREA

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Chapter 4

Structure of the Project Area

4.1 Introduction:

Geologically the Khanpur area forms eastern part of Hazara Basin (Chaudhary et

al., 1998 and Ahsan and Chaudhary, 2008). To the north it is bounded by Nathiagali

Thrust (NGT) and Main Boundary Thrust (MBT) is situated to the south of the area that

separates it from the Potwar Plateau (PT). Earlier workers such as (Ghazanfar et al., 1990

and Ghazanfar, 1993) designated Khanpur Area as well as the remaining Hazara in

Attock Hazara Fold and Thrust Belt (AHFTB). In a study (Ghazanfar et al., 1990)

described Kozagali Synclinorium Complex that comprised of Tertiary Formations. Later

on (Latif et al., 1995) described Dor and Harrow Troughs as the two main structural

features of the area. Prior to this (Latif, 1970) described four zones on the basis of

stratigraphic variations as Northern Crystalline and Metamorphic Zone, the Slate or

Abbotabad Zone, the Nummulitic Zone and Upper Tertiary Zone from north to south.

The general trend of the faults and folds axis in Khanpur area is similar to

remaining Hazara Basin i.e. NE-SW. The faults of the area are either fore-thrust i.e.

following the general trend of major faults or back-thrusts i.e. dipping opposite to the

major faults. The structure of the project area is complex and consists of various

anticlines, synclines, antiformal synclines, overturned folds, fault propagational folds and

reverse faults either over-thrusts or back-thrusts. The detail of the observed structures is

given below.

4.2 MAJOR FOLDS:

The major folds of the project area are:

1. Sinjala Anticline

2. Khoi Kamman-1 Antiformal Syncline

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3. Khoi Kamman-1 Syncline

4. Khoi Kamman Overturned Fold

5. Najaf Pur Syncline

4.2.1 Sinjala Anticline:

Sinjala Anticline is located to the south west of Sinjala Village indicated by the

occurrence of Hangu Formation in the core and flanked by Lockhart Formation. Lockart

Limestone and Patala Formation are present on the north-western limb and south-eastern

limbs respectively. The trend of the fold axis is NE-SW. The north-western limb has the

faulted contact with Kawagarh Formation and the south-eastern limb has the faulted

contact with the Samana Suk Formation. It is the result of lateral compression. Due to the

fault in the south-eastern limb, the Patala Formation forms the associated drag fold that

was observed in the field and thus due to incompetent lithology of Patala Formation. On

the basis of interlimb angle the fold is classified as an isoclinal fold.

4.2.2 Khoi Kamman-1 Antiformal Syncline:

The locality of the antiformal syncline is the north of Khoi Kamman Village. This

fold is situated in the folding of Lockart Limestone and Patala Formation. Patala

Formation is present in the core of the antiformal syncline and Lockart Limestone is

present on its flanks. The trend of the fold axis is NE-SW. The north-western limb has the

faulted contact with Samana Suk Formation and the south-eastern limb has the

conformable contact with Patala Formation. On the basis of interlimb angle the fold is

classified as open fold.

In an anticline the beds young away from the core while in a syncline the beds

young toward the core. In both cases the younging direction points (or faces) upward, so

we call these structures upward facing folds. Sometimes the oldest bed lies at the top and

the youngest bed at the bottom as we observed in the project area. When we generate the

same geometry of antiforms and synforms, the younging direction is opposite to what we

had before. In the present antiform, the beds young toward the core i.e.. towards the

younger Patala Formation that dips towards the older Lockart Limestone whereas in the

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synform the beds young away from the core. Both cases are downward facing folds, and

an antiform with this younging characteristic is therefore called a downward-facing

antiform or antiformal syncline and similarly downward-facing synform or synformal

anticline. The project area has the antiformal synclinal structures.

Here some secondary process has inverted the normal stratigraphic sequence

otherwise it is the violation of Law of Superposition. These folded structures are typically

found in areas containing an early generation of regional folds with horizontal axial

surfaces i.e. recumbent folds. These are quite common in Himalayas or other collisional

mountain belts. Subsequent folding of these early structures generates a series of upward

and downward-facing folds. e.g next to Khoi Khamman-1 antiformal syncline there is

Khoi Kamman-1 Syncline in the southern direction. The fold axis follows the general

trend of collisional mountain belts structures (Ben A. Van Der Pluijm and Stephan

Markshak, 2004, Earth Structures, 2nd Edition).

4.2.3 Khoi Kamman-1 Syncline:

The locality of the syncline is the north of Khoi Kamman Village. It formed by

the folding of Margala Hill Limestone and Patala Formation. Margala Hill Limestone is

present in the core of the syncline and Patala Formation is present on its flanks. The trend

of the fold axis is NE-SW. The north-western limb has the conformable contact with

Lockart Limestone and the south-eastern limb has the conformable contact with the

Margala Hill Limestone which forms antiformal syncline. On the basis of interlimb angle

the fold is classified as a tight fold.

4.2.4 Khoi Kamman Overturned Fold:

The locality of the overturned fold is Khoi Kamman Village. It formed by the

folding of Cretaceous, Eocene and Paleocene age rocks. Lumshiwal Formation is present

in the core of the overturned fold. Patala Formation and Kawagarh Formation are present

on the north-western limb and south-eastern limbs respectively. The overturned limb of

the fold has the formation of Cretaceous, Eocene and Paleocene age. The trend of the fold

axis is NE-SW. The north-western limb has the conformable contact with Margala Hill

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Limestone and the south-eastern limb has the unconformable contact with the Lockart

Limestone. On the basis of interlimb angle the fold is classified as mashroom type fold

that have the negative interlimb angle.

4.2.5 Najaf Pur Antiformal Syncline:

The locality of the syncline is Najaf Pur Town. This fold is indicated by the

folding of Lockart Limestone and Patala Formation. Patala Formation is present in the

core of the syncline and Lockart Limestone is present on its flanks. The trend of the fold

axis is NE-SW. The north-western limb has the faulted contact with the formation of

Cretaceous, Eocene and Paleocene age and the south-eastern limb has also faulted contact

with Margala Hill Limestone. On the basis of interlimb angle the fold is classified as

isoclinal fold.

4.3 MAJOR FAULTS:

The major faults of the project area are:

1. Sanjala-1 Thrust

2. Sanjala-2 Thrust

3. Sanjala-3 Fault

4. Najaf Pur-1 Thrust

5. Najaf Pur-2 Thrust

6. Dhunian-1 Thrust

7. Dhunian-2 Fault

8. Dhunian-3 Fault

4.3.1 Sanjala-1 Thrust:

The locality of the Sanjala-1 thrust is the north of Kharala Village. It is an NE-SW

trending fault. The Cretaceous age Kawagharh Formation moves up relative to Lockart

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Limestone near the cross section line AA`. It is a fore-thrust in nature that dips at angle of

43D NW.

4.3.2 Sanjala-2 Thrust:

The locality of the Sanjala-2 fault is Kharala Village. It is an NE-SW trending

fault. It brings Samana Suk Formation in direct contact with Patala Formation near the

cross section line AA`. It is back-thrust in nature and dips at angle of 35 SE.

4.3.3 Sanjala-3 Fault:

The locality of the Sanjala-3 fault is south Kharala Village. It is an NE-SW

trending fault. It brings Samana Suk Formation in direct contact with Lockart Limestone

near the cross section line AA`. It is a reverse fault in nature that dips at angle of 80 NW.

Kharala-2 and Kharala-3 faults are the result of popup structure. It is a

compressional structure which is developed when folding is not enough to solve volume

problems. In areas where incompetent rocks are affected by compressional tectonic

regimes, when folding is not enough to shorten the overburden, additional shortening

(pop-up structures) is developed in the crest of anticline structures to accommodate the

sediments to new volume conditions. So fore and back-thrusts form as the result of pop-

up structures.

4.3.4 Najaf Pur-1 Thrust:

The locality of the Najaf Pur-1 fault is Najaf Pur Village. It is an NE-SW trending

fault. It brings the Cretaceous, Paleocene and Eocene rocks in direct contact with Lockart

Limestone near the cross section line AA`. It is fore-thrust in nature and dips at angle of

41 NW.

4.3.5 Najaf Pur-2 Thrust:

The locality of the Najaf Pur-2 fault is Najaf Pur Village. It is an NE-SW trending

fault. It brings Lockart Limestone in direct contact with Margala Hill Limestone near the

cross section line AA`. It is fore-thrust in nature and dips at angle of 40 NW.

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4.3.6 Dhunian-1 Thrust:

The locality of the Dhunian-1 fault is Dhunian Village. It is an NW-SE trending

fault. It brings Lockart Limestone in direct contact with Margalah Hill Limestone near

the cross section line AA`. It is a back-thrust in nature that dips at angle of 41 SW.

4.3.7 Dhunian-2 Fault:

The locality of the Dhunian-2 fault is Dhunian Village. It is an NW-SE trending

fault. It brings Lockart Limestone in direct contact with Margalah Hill Limestone near

the cross section line AA`. It is a foreland dipping rever se fault in nature that dips at

angle of 50 SW.

4.3.8 Dhunian-3 Fault:

The locality of the Dhunian-3 fault is south of Dhunian Village. It is an NW-SE

trending fault. It brings Margalah Hill Limestone in direct contact with Lockart

Limestone near the cross section line AA`. It is a foreland dipping reverse fault in nature

that dips at angle of 50 SW.

All the series of Dhunian faults are the result of duplex structures. It is foreland

dipping duplex. It is imbricate structure in which the slip on individual horses is greater

than the length of the horse. Here the rock units of Paleocene and Eocene age between

these faults are the horses and the overlying roof thrust is missing in this area. When this

occurs, the successive uplifts of the roof thrust and previously formed horses occur

behind the early formed and forward transported horses. This rearward uplift changes the

dip sense of the imbricate faults and the overall dips of their continued strata and the

imbricate structures thus forms the foreland dipping duplex. So the Dhunian Faults are

out of sequence thrusts. This results basically due to the movement of fault blocks over

irregularly oriented ramps and flats geometry which sets up folds in the moving block

and so Najafpur-2 fault is the frontal ramp i.e. perpendicular to the overthrust

transportation (John G. Ramsey, 1987, Modern Structural geology, vol. 2).

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Chapter 4 Structure

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