Compiled BY:
Jawad Bas hir (T hu nder ). Ma lik Shadi. O mer is haq. 1
A DAY TRIP TO KHEWRA GORGE: Bahria university Islamabad campus (Earth environmental department) arrange a field trip of one day for Bs-5 on April 16th 2009.The field trip is related to the subject of GOP (geology of Pakistan). The objective for that field trip is to study and observe the lithology, depositional condition, sedimentary structures, rock types, contacts and fossils of that area. Another purpose of that trip is to get the students familiar with some unique characteristics of Khewra salt mine in Pakistan. The Khewra Gorge is situated at about 165 km away from capital of Pakistan (Islamabad).
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TABLE OF CONTENTS: Chapter 1 Introduction to Field Trip
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Chapter 2 Salt Range Formation
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Chapter 3 Jhelum Group
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Chapter 4 Khewra Salt Mine
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Chapter 5 Conclusion
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1) INTRODUCTION TO FIELD TRIP 1.1. OBJECTIVE: The primarily objective of our field trip is to enhanced our knowledge and to strong our grip on GOP subject, specially to concentrate on geology of Khewra group. To study the structures, lithology, depositional environments, rock types and economical importance of different formations.
1.2. LOCATION: The planned area which we have visited is about 165 kilometers from Islamabad. It is located 33º 46΄ North and 73º 8΄ East.
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1.3. DATE AND TIME OF ARRIVAL We have visited Khewra gorge on 16th of April 2009 and the time of arrival at extraction point is 10:15 am.
1.4.Accessibility The area is easily accessible and we went there through university bus and it took about 3 hrs to reach the desired location as it is about 165 kilometers from Islamabad. The journey was pleasant and smooth, because we went by motorway. The field which we visited was unsteady; rocky and it was along the saline water channel among the mountains
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1.5. CLIMATIC CONDITIONS: The climate is hot and arid with very little precipitation. The sand and rocks show signs of heavy rain falls about 1 to 3 days ago.
2. SALT RANGE FORMATION (PRE-CAMBRIAN ROCK SEQUENCE) 2.1.
History
The basement rocks of Indian shield are overlain by an unmetamorphosed sequence of Salt, marl, gypsum and dolomite which was earlier designated as “Saline Series” by Wynne (1870, 1878). The formation has been since renamed after the Salt Range by Asrarullah (1967) and its type locality is Khewra Gorge in the Eastern Salt Range. The Salt Range Formation is widely distributed in Salt Range, between Jogi Tilla in the east and Kalabagh in the northwest. 2.2.Lithology The lower part of the formation comprises beds of marl and gypsum with bituminous shales and dolomites. The base of the formation is not exposed. The middle part of the formation contains an alteration of gypsum, dolomite, shale, siltstone with oil-shale layers. The top of the Formation is formed by gypsum layer containing high-grade-oil-shale or a layer of highly altered volcanic rock known as Khewra Trap. 2.3. Thickness
The thickness of the Salt Range Formation is more than 800 m at type locality (base not exposed). In the Kohat-Potwar region the thickness locally exceeds 2,000 m as a result of secondary salt migration and accumulation induced in the decollement* and southward-thrusting of the overlying sedimentary sequence 2.4. Litho-stratigraphic Divisions The Salt Range Formation has been divided into an upper Sahiwal Marl Member, a middle Bhandar Kas Gypsum Member and a lower Billianwala Marl Member (Asrarullah 1962, 1967; Alam and Khan 1982).
2.5.1 Billianwala Salt Marl Member
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It has been named after the Billianwala nala near Khewra and is largely composed of hematitic, dull red, gypsiferous marly beds with thick seams of salt. It is best exposed near Khewra, where it is more than 650 meters thick and the base is not exposed. In the Khewra Salt Mine, salt is excavated from this member. There are three main salt seams, mainly Buggy, Sujowal and Pharwala. These seams are topped by Khallar (impure
Billianwala salt marl member(dull red color with gypsiferous marl beds)
Salt intercalations within Billianwala member
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Open pit mining exposed in Billianwala member
2.5.2Bhandar Kas Gypsum Member This unit is named after the Bhandar Kas nala and overlies the Billianwala Member. It is composed of massive gypsum, dolomite and marl. It is 80 m thick in the Khewra Gorge.,
Red marl beds with gypsum, dolomite beds
2.5.3 Sahiwal Marl Member It is named after the Sahiwal Village near Khewra; this Member overlies the Bhandar Kas Member and is comprised of an upper 3-100 m thick bright red marly unit and a lower unit containing dull red marls. Theses units are easily mapable due to their tonal differences. 8
The upper bright-red marls are exposed throughout the Salt Range. The marls are interlayered with gypsum, clay and thin seams of salt. Higher up in the sequence, thin beds of gypsum, bituminous shales and Khewra Trap are present. The oil shales found in this unit have a kerosene odour and are considered a potential hydrocarbon source.
Red color marls are exposed
Red marls exposed
2.5.4 Khewra Trap (Sahiwal member) The Salt Range Formation contains thin flows of an ultrapotassic rock commonly known as Khewra Trap; the flow occurs in Late Proterozoic or Eocambrian rocks consisting mainly of marly anhydrite, gypsum and oil shales. Since it was first reported by Fleming (1953), the trap has attracted the attention of several geologists because of its highly
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unusual composition, texture and paragenesis. The trap occurs throughout the Salt Range. The petrology of the trap has been presented by Wynne (1878), Martin (1956), Mosebech (1956), Shuaib et al. (1993) and Jan and Faruqi (1995). The trap is purple, reddish brown, orange to buff, rarely dark green rock. The phenocrysts are euhedral to skeletal spinifex, and commonly grown radially. The Khewra Trap is so unique that Mosebech (1956) assigned it a new name Khewrite.
2.5.5 Contacts and Age The upper contact with the Khewra Sandstone appears to be confirmable. Salt range formation is totally devoid of fossils and is considered to be of late proterozoic
In red Sahiwal member of salt range in grey to maroon Khewra
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A small water drainage path also marks contact
2.6. STRUCTURES OBSEREVED IN SALT RANGE FORMATION 2.6.1 Chert nodules
2.6.2 Stalactite
2.6.3 Stalagmite
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2.6.4 Khewraite
3. JEHLUM GROUP (CAMBRIAN ROCK SEQUENCE) The Cambrian sequence in Salt Range is Characterized by dominance of terrigeonous red beds largely composed of red gypseous marl with rock salt at the base; maroon sandstone, dolomite and dolomitic sandstone in the middle; and blood-red shale, flaggy sandstone with salt Pseudomorphs in the upper part. The Cambrian sequence of Salt Range has yielded several fossils. These have been referred to as Redlichia fauna. In Potwar, Salt Range and Trans-Indus Ranges, the Cambrian sequence is collectively known as the Jhelum Group and is comprised of the Khewra Sandstone, Kussak Formation, Jutana Formation and Baghanwala Foramtion. 3.1.Khewra Sandstone 12
It is previously known as the “Purple Sandstone Series” (Waynne 1878), this formation was named “Khewra Group” by Noetling (1984) after the Khewra gorge near Khewra Town. This name has been now formalized as Khewra Sandstone (Fatmi 1973). The Khewra Sandstone overlies the Proterozoic Salt Range Formation without any apparent disconformity. The type locality is the Khewra Gorge in the Eastern Salt Range. The Khewra Sandstone consists mainly of reddish-brown to purple, thick-bedded to massive sandstone with few brown shale intercalations. The sandstone is characteristically cross bedded. It is 150 m thick at type locality in eastern Salt Range, and 80 m in the Khisor Range. Apart from rare trace fossils interpreted as trilobite by Schindewolf and Seilacher (1955), the formation is devoid of fossils.
Khewra Sandstone (maroon) in between Sahiwal Marl member (red)& Kussak Formation(top) The formation was probably deposited in an arid continental environment, possibly under near shore to Aeolian conditions as can be seen from frequency of cross laminations, ripple marks, sun cracks and such surface marks as rain drop prints, worm burrows and fucoid’s impressions.
Sedimentary structures in Khewra: 3.1.1 Fold
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3.1.2 Faults
3.1.3 Ripple Marks:
3.2 Kussak Formation It was first named as “Obolus beds”by Waynne (1878) and later “Neobolus beds” (Waynne 1885), this formation was named ‘Kussak group’ by Noetling (1894). This name has been formalized as Kussak Formation by the Stratigraphic Committee. The Kussak Formation
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rests disconformity over Khewra Sandstone, marked by a widespread, thin conglomerate developed at the base of the Kussak Formation. Type locality is near Fort Kussak in the eastern Salt Range. The Kussak Formation is well exposed in the Salt Range between Jogi Tilla (320 51’ N; 730 27’ E) in the east and Chiddru (320 33’ N; 710 46’ E) in the west. The Formation only consists of grey, silty and sandy, glauconite shale with some sandstone intercalations and few black shale layers. The thickness of the formation is 75 m at type locality, and locally more than 200 m in the southern Punjab plain. The Kussak Formation contains brachiopods and trilobites.. The fauna together with glauconite content indicates a marine depositional environment.
Contact between Khewra and Kussuk formation(Kussuk with light grey color).
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The Kussuk Formation is conformably overlain by Jutana Formation, which is a sandy dolomite. 3.2.1 GLUCONITE:
3.3 SEDIMENTARY FEATURES IN KUSSAK 3.3.1Burrows:
3.3.2 Alternate Bedding:
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3.4 Jutana Formation Previously named “Magnesian Sandstone beds” by Fleming (1853) and “Jutana Stage” by Noetling (1894), respectively overlies the Kussak Formation conformably. Type locality is near the village of Jutana in the eastern Salt Range. The formation has a distribution similar to the Kussak Formation in the Salt and Khisor Ranges as in the eastern and southern Potwar Basins, in the Mianwali Re-entrant and in the Southern Punjab Plain. The Formation has yielded some brachiopods, gastropods and trilobites, among the Redlichia noetlingi and Pseudotheca subrugosa (Teichert 1964), as well as Cruziana sp. (A. Seilcher, pers.commun.). The fossils indicate a late Early Cambrian to early Middle Cambrian age.
juttana formation overlying
3.4.1
STRUCTURES FOUND IN JUTTANA
3.4.2 CROSS BEDDING:
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3.4.3 IRON INCLUSSIONS:
3.4.4 DISSRUPTED BURROWS:
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KHEWRA SALT MINE
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4.1.Discovery of the mine It is said that when Alexander the Great visited sub-continent, coming across the Jhelum and Mianwali region, Khewra Salt Mines were discovered. The discovery of the mines was however was not made by Alexander nor his "allies", but by his horse. It is stated that when Alexander's army stopped here for rest, the horses started licking the stones. One of his soldiers took notice of it and when he tasted the rock stone, it was salty thus leading to the discovery of the mines. 4.2.Production from Khewra Salt Mines Salt has been mined at Khewra since 320 BC, in an underground area of about 110 sq. km. Khewra salt mine has proven reserves of 300 million tons. This reserve could not be consumed in 600 years even at the rate of 5 lakh tons production every day. Current production from the mine is around 3 lakh tons. 4.3.Mining method Room-and-pillar mining is a popular underground method for bedded deposits of potash, rock salt, and talc. Room-and-pillar mining is a means of developing a mine and, at the same time, retaining supports for the roof. With this technique, rooms are developed from large, parallel tunnels driven into the solid salt, and the intervening pillars of Salt are used to support the roof. The percentage of salt recovered from a seam depends on the number and size of protective pillars of salt thought necessary to support the roof safely. 4.4.Shades of Salt Salt is transparent, white, pink, reddish to beef-color red. There are beautiful alternate bands of red and white color salt.
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4.5 Indoor Brine Ponds Inside the mine there are certain chambers filled with saturated brine solution. The salty water seeps through mine walls and roof and collects into these chambers overtime. There are several such waterfilled chambers in the mine but they are very difficult to see in the dark. Only two such ponds have been illuminated for tourism purposes. The approximate density of these ponds is 2.6. 4.6 Khewra Salt Mines, an Attraction for Visitors Khewra Salt Mines is a salt mine in Pakistan, about 160 kilometers from Islamabad and 260 kilometers from Lahore. It attracts up to 40,000 visitors per year and is the second biggest salt mine in the world. Situated at the foothills of the Salt Range, Khewra Salt Mines are the oldest in the salt mining history of the sub-continent.
Chaghi Mountain
Light-House
Salt Wall
Salt mine has been decorated to develop the interest in tourists e.g. Basdshai Mosque and inner decoration lights the decorated bridge, the electric train for the tourists and different salt walls.
SEDIMENTARY STRUCTURES OBSERVED IN KHEWRA GORGE & SALT MINE 20
5.1 Fault Fault is a displacement of rock layers in the Earth's crust in response to stress, accompanied by a break in the continuity of the rocks on each side of the fault line.
5.2 Joints Fault is crack in the crust of the earth along which there has been movement of the rocks on either side of the crack. A crack without movement is called a joint.
5.3 Burrows
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Well preserved burrow
Disrupted burrow
5.4 Fold Fold is a bend formed in a rock layer in response to the stresses produced within the rock
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5.5 Stalactite Conical pillar hanging in cave: A conical hanging pillar in a limestone cave that has gradually built up as a deposit from ground water seeping through the cave's roof.
Stalactite 5.6
Stalagmite Conical pillar rising from cave floor: a conical pillar in a limestone cave that is gradually built upward from the floor as a deposit from ground water seeping through the cave of wall .
5.7 CHERT NODULES Chert is impure granular variety of cryptocrystalline quartz. The stone is similar to flint but is more brittle. It is commonly gray, white, yellow, or brown
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CONCLUSION In the area of our visit sedimentary features are mostly exposed e.g. joints, ripple marks, fault, fold, salt leeching etc. The formations dated from Pre-Cambrian to Cambrian period. In pre-cambrian period Sahiwal Marl, Bhandar Kas Gypsum and Billianwala Salt Marl were members of Salt Range Formation, whereas in Cambrian period Jhelum group includes Baghanwala Formation, Jutana Formation, Kussak Formation and Khewra Sandstone. We also visited the Khewra salt mine, where we observed the indoor Brine Ponds and different shades of salt. Interior embossing of the salt mine increase the interest of the visitors.
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