M. S. Krishnan Salt Tectonics in the Punjab Salt Range

M. S. KRISHNAN

SALT TECTONICS IN THE PUNJAB SALT RANGE, PAKISTAN1

Abstract: Salt deposits occur in two areas in the Upper Jurassic, below the Eocene, and below western Pakistan: one near Kohat west of the Indus the Upper Oligocene. The Saline Series with its as- River, and the other in the Punjab Salt Range be- sociated salt, marl, gypsum, dolomite, and oil-shale tween the Indus and Jhelum rivers (lat. 35° N.; beds is exposed all along the Salt Range. The salt long. 71°-74° E.). The Salt Range is the south-fac- beds attain a maximum thickness of 800 feet. The ing scarp of the Potwar Plateau. The plateau is salt appears massive except where it includes marl formed by a great thickness of sedimentary rocks and gypsum bands which show very complex fold- which have been thrust southeastward between two ing. The Saline Series occupies various stratigraphic wedges of the Indian Peninsula toward Kashmir positions, and its contacts with the other formations and Waziristan. The strata in the Potwar basin are highly disturbed and brecciated, presumably as (whose southern border is the Salt Range) are a result of thrusting. gently folded in the south but progressively more The controversy regarding the age of the Saline intensely folded and faulted in the north. Series, whether Cambrian or Eocene, will probably The Salt Range exposes a good sedimentary suc- not be settled without the aid of new techniques, cession but has a long gap between the Cambrian for the observable geologic features can be used to and the Upper Carboniferous, and short gaps below support either side of the controversy.

The Potwar Plateau, with an average altitude Introduction of 1600 feet, is bounded on the south by the Saline deposits occur in two areas in western Salt Range and on the north by the Kala Chitta Pakistan. The northern occurrence is around Hills which are a short distance north of Rawal- Kohat (lat. 33° 36' N.; long. 71° 29' E.), west pindi (lat. 33° 37' N.; long. 73° 8' E.). It is a of the Indus River, whereas the southern one basin containing Tertiary and Mesozoic strata is along the southern scarp of the Potwar folded along east-west axes and also faulted in Plateau which faces the plains of Mianwali and the same direction. The intensity of folding Shahpur districts east of the Indus River. The gradually increases from south to north. The latter actually continues to the west of the basin narrows toward the west so that it is nar- Indus and turns south, parallel to the Baluchis- rowest between Kalabagh on the Indus River tan Arc. The Punjab Salt Range is located to (at the western end of the Salt Range) and the north of the Jhelum River between lat. Kohat. The basin also narrows somewhat on 32° 15'-33° 0' N. and long. 71° 34'-73° 45' E. the east where it is cut off by a fault along It is arcuate and convex to the south with a which the Jhelum River flows from north to general east-west trend but turns to the north- south. west near the western end and to the northeast In terms of structure, the plateau can be near the eastern end (Figs. 1 and 2). divided into four zones (Fig. 2): (1) Salt The average elevation of the Salt Range Range, (2) Scan syncline, (3) "anticlinal zone," is about 2500 feet, and the highest peak, Mount and (4) "faulted zone." The southernmost zone Sakesar (lat. 32° 32' N.; long. 71° 56' E.), is is the scarp slope of the Salt Range. To its north 4992 feet high. The upper part of the scarp is the Soan syncline, which is fairly wide and is exposes Permian or Eocene limestones or Ter- traversed by the Soan River. The "anticlinal tiary sandstones. The plateau itself has a very zone" farther north shows several east-west- gentle northward slope and is capped by the trending anticlines in which there are a few Murree (Upper Oligocene to Lower Miocene) producing oil fields. The "faulted zone" still and the Siwalik (Upper Miocene to Pleistocene) farther north consists of a series of close-set strata. parallel faults which are nearly vertical or high-

1 Short version of a paper presented at the International Conference on Saline Deposits held in the United States in November 1962

Geological Society of America Bulletin, v. 77, p. 115-122, 4 figs., January 1966 115

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dipping overthrusts whose northern limbs have sometimes overlain by the Saline Series. The been thrust over the southern limbs. This zone stratigraphic succession is given in Table 1. was mistakenly believed to show numerous iso- The Cambrian succession consists of Purple clinal folds. The apparent isoclinal structures Sandstones with a few shale intercalations, over- are actually due to the northern limbs of the lain successively by the Neobolus Shales (with faulted anticlines forming cusps curving over Middle Cambrian brachiopods and trilobites), the southern limbs (Gill, 1951). These faults Magnesian Sandstones, and Salt Pseudomorph were developed at a late stage in the folding of Shales. These beds locally contain some gypsum the region and are believed to be connected and anhydrite. The Purple Sandstones are with shear planes in the basement. The axes of strikingly similar in lithology and other charac- the folds and faults are roughly linear and par- ters to the Upper Vindhyan sandstones exposed at Agra and Bharatpur near Delhi, and may be contemporaneous with them. The Salt Pseudo- morph Shales generally show pseudomorphs of silty material after halite on both sides of al- most every bedding plane. Cambrian strata do not occur in the Kohat area. In the eastern part of the Salt Range, the Saline Series is generally found underlying the Cambrian strata; and the lithology from top to bottom is: (3) "Upper gypsum-dolomite stage"—massive white and gray gypsum with dolomite, oil-shale, and a bed of weathered diabase (Khewra Trap), up to 100 feet I : : : :| Poit Eoe«n« thick I II 111 Eoc.™underlie (2) "Salt marl stage"—bright- or dull-red to purple marl with thick seams of rock salt, Figure 2. Map of the Potwar Plateau show- up to 800 feet thick ing the structural zones (1) "Lower gypsum-dolomite stage"—massive gypsum and variegated red gypsiferous clays, 750-1000 feet thick. allel, but they do show some bending, the folds There are four unconformities in the succes- often terminating at the faults and also coming sion. The oldest and the most prominent, which closer together toward the west. The actual is also characteristic of peninsular India, is the fault zones are generally narrow, only a few gap between the Cambrian and the Upper yards wide, but in some cases they attain a Carboniferous tillite. The next occurs between width of more than 50 yards and are marked by the Lower and Upper Jurassic. The next, below brecciated pieces of sandstone and shale trav- the Lower Eocene, is generally conspicuous as ersed by numerous anastomosing veins of cal- the rocks below are lateritized. The last, within cite. Beyond the "faulted zone" is a belt con- the Upper Eocene, marks an important oro- taining Precambrian rocks, viz., the Attock genic phase. The beds above this gap are the Slates, over which the highly folded Mesozoic brackish-water Murree Sandstones and the rocks are thrust from the north. These folded fresh-water Siwalik Sandstones. The Siwalik Mesozoic rocks constitute the anticlinorium of Sandstones are similar to the Molasse formation the Kala Chitta Hills. of the Alps, and contain a rich mammalian fauna. Stratigraphy The Salt Range exposes a fairly complete Structural Features succession of strata ranging from the Cambrian The structure of the Salt Range and the Pot- to the Tertiary. Precambrian rocks are not ex- war Plateau is controlled by two submerged posed, but a few outcrops are found in the wedges of the Indian Peninsula, one directed Kirana and Sangla hills in the Punjab plains, a toward Kashmir and the Pamir Plateau, and the few miles to the southeast of the Salt Range. other toward Mianwali and Kalabagh on the The oldest beds exposed in the Salt Range are Indus River, where the Salt Range crosses that Cambrian rocks which are often underlain and river. The sedimentary rocks of the Potwar

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basin have been compressed and thrust toward very little space for the rocks to move horizon- the south as an arc between these wedges. It is tally. thought that at and near the apices of these The Mesozoic sedimentary rocks in the Pot- wedges the strata have been held back and war basin have much in common with those of consequently are highly compressed, as can be the same age in western Rajasthan and Kutch, seen clearly in a geological map of western as these were evidently laid down along the

TABLE 1. STRATIGRAPIIIC SUCCESSION IN THE SALT RANGE, PUNJAB Thickness in feet Age Formation Eastern Western

Upper Siwalik Sandstone 400 3000 Lower Pleistocene Middle Siwalik Sandstone 5000 6800 to Lower Siwalik Sandstone 3000 5000 Upper Oligocene {Murree Sandstone 1000 Absent —Unconformity— fKirthar Series Absent Absent Middle Eocene jChharat Beds Absent 200 Middle to Lower /Laki Series 0-400 350-1000 Eocene \Paleocene 0-150 200-1500 —Unconformity— /Lumshiwal Beds Absent 0-75 Cretaceous \Belemnite Shales Absent 0-150 /Baroch Limestone Absent 0-200 Upper Jurassic \Variegated Sandstone Absent 0-500 —Unconformity— Lower Jurassic Kingriali Beds Absent 0-400 Triassic Ceratite Beds Absent 0-400 Permian Productus Beds Absent 0-900 Lavender Clays 0-150 50-200 Lower Permian to Speckled Sandstones 0-450 200-500 Upper Carboniferous [Conularia Beds 0-75 50-75 Upper Carboniferous Tillitc 0-100 0-350 —Unconformity— (Salt Pseudomorph Shales 0-350 0-300 I Magnesian Sandstones 0-250 0-100 Cambrian ] Neobolus Shales 70-150 0-100 [Purple Sandstones 250-450 0-300 — Thrust or sedimentary contact — Eocene or Cambrian (Upper Gypsum-Dolomite Stage 30-200 0-150 (Saline Series) i Salt Marl Stage Up to 800 Variable (Lower Gypsum-Dolomite Stage Up to 800 Variable

Pakistan. The distance over which the sedi- same coast of a marine basin. On the other mentary rocks have been thrust in the southern hand, there are some differences in the lithology part of the Potwar Plateau may be 20-25 miles. and fauna of the Salt Range and the main The effects of compression on the strata in- Tethys basin of the Himalayas. The differences crease markedly toward the north: the broad are accounted for by the fact that the Salt open folds of the Soan syncline give way to the Range-Kutch area of deposition was an arm of anticlines of the oil-bearing region and farther the Tethys basin which extended south of it north, to a series of closely spaced shear planes over a distance of at least 10 degrees of latitude. marked by thrust faults in which the northern Although rock-salt deposits and associated limbs are thrust steeply toward the south. The evaporites occur both in the Salt Range and at movements in the "faulted zone" have been Kohat, there are certain differences (Pinfold, mainly vertical, presumably because there was 1918; 1945). In both there are two series of

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massive gypsum and dolomite beds with inter- broken up and the fragments flattened parallel calated beds of rock salt and marls. A few thin to the contact zone (Middlemiss, 1891). The layers of oil shale are a conspicuous feature of shaly material of the tillites is also disturbed. the gypsum-dolomite beds in both the areas. The salt beds and the associated marls are found The Kohat salt beds are associated with fresh- in various stratigraphic positions in different water fauna, whereas the Salt Range beds do parts of the Salt Range: under the Cambrian, not contain any fossils. The Kohat salt is gen- under the Talchirs, or under some part of the erally gray, with pink salt appearing only rare- Mesozoic or Tertiary strata. In the Bidder ly; the Salt Range salt is overwhelmingly pink, scarp, which is the southern slope of the Jogi with only rare lenses of gray salt. So far as Tilla ridge in the eastern part of the Salt Range known, there are no potassium salts in the (Fig. 3) the salt marl appears under the Cam-

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HORIZONTAL £ VERTICAL Figure 3. Section across the Jogi Tilla ridge northwest of Kanial. T.P.GYP. MARL = thrust plane along gypsiferous marl bed.

Kohat region, whereas thin beds and streaks of brian but apparently overlies the Nummulitic these salts have been found in the Salt Range, limestones along a thrust plane. On the Jogi especially in the middle and eastern parts. In Tilla ridge itself (Fig. 4) several sections are both areas the salt shows lenticularity as well seen in which the Saline Series is present under as various degrees of shearing; the Kohat salt is the Siwalik Sandstones, as indicated by the highly sheared and even schistose and fissile. presence of salt springs under the latter (Wadia, The Salt Range salt is generally massive, with- 1945). In most sections, therefore, there is un- out readily visible structure except where inter- deniable evidence that the Saline Series is thrust calated marl or gypsum bands show compli- into various abnormal positions. cated folding, shattering, and shearing. The Saline Series in the Salt Range occurs Age of the Saline Series mainly at the bottom of the sedimentary suc- The Salt Range and the neighboring regions cession in the eastern and east-central parts of were originally mapped by Wynne (1878), who the range. The contact of the Saline Series with considered the Saline Series to be Cambrian or the beds above is generally very disturbed, in- infra-Cambrian because it was found below the dicating that these beds have over-ridden the Purple Sandstones in many sections. The plas- salt. Where the Purple Sandstones are above ticity of salt and its tendency to be squeezed the salt, they are brecciated at and near the into various positions when under pressure contact; this disturbance may extend 20-30 feet caused some geologists (Holland, 1903; Zuber, into the sandstones and diminishes in intensity 1914; Pascoe, 1920) to think that the Saline away from the contact. The same is the case Series was Eocene and that it was in an abnor- with the tillites, the pebbles of which are often mal position below the Cambrian. Lees (1927),

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Harrison (1930), Lehner (1945), and also Gee has the same appearance as the gypsum associ- (1945), who mapped the Salt Range during the ated with the Saline Series. An investigation of 1930's, supported the view that the Saline the oil shale from the Salt Range as well as oil Series was Cambrian. shale from the Kohat area seemed to indicate The Saline Series as well as some parts of the (Lahiri, 1945) that both are of the same nature stratigraphic succession are repeated near and contain more or less the same constituents. Khewra and Sakesar because of strike faulting. These characteristics, together with the unmis- Evidence of thrusting and disturbance are seen takably "intrusive" nature of salt in many ab- at several places, particularly in the eastern and normal stratigraphic positions, indicate that the middle parts of the Salt Range. salt is of Eocene age but has been thrust into

N N W

^54, *>4ff^ y --«C5 -^<> D,.,ieOSoi , '4/V Cy, W°/?P(JC- '^&i»»&%?°"&s«**

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'^l* HORIZONTAL 5 VERTICAL Figure 4. Section across the Bidder Scarp on the southern slope of the Jogi Tilla ridge. N.L. = nummulitic limestone; T.P. = thrust plane.

Gee (1945) has presented some evidence to various positions during the Himalayan oro- support the view that the contact of the Saline genic movements. Series with the Cambrian or with the tillite is It is doubtful if this controversy concerning normally a sedimentary one. He believes that the age of the Saline Series of the Salt Range, the sections near the Nilawan ravine, Chittidil, whether Cambrian or Eocene, can be settled on and Chhidru do not show any disturbance at the basis of ordinary geologic observations. the contacts. On the other hand, Sahni (1945; There is no doubt that the salt of Kohat, which 1947) and his co-workers found that all the lies to the northwest of the Potwar basin, is of rocks of the Saline Series, including salt, gyp- Eocene age, as the salt beds are closely associ- sum, dolomite, and oil shale contained micro- ated with fossiliferous Eocene rocks. There is, scopic plant fragments of definitely post-Cam- however, no reason why salt beds of two dif- brian age. These were obtained even when ferent ages should not occur in this region. Oc- every precaution was taken to ensure that the currences of two different ages, Cambrian and material came from undisturbed parts of such Eocene, are present in close proximity to each rocks from the interior of fresh mine workings, other in southern Iran according to the geolo- borehole cores, etc. In support of an Eocene age gists of the former Anglo-Iranian Oil Company. for the Saline Series in the Salt Range is the Further detailed studies, using geochemical and fact that, in a few sections in the western part of isotope techniques may contribute to the solu- the Salt Range, limestone containing Eocene tion of this problem. foraminifera passes laterally into gypsum which

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References Cited Gee, E. R., 1945, The age of the Saline Series of the Punjab and of Kohat: Nat. Acad. Sci. India, Proc. v. 14B, p. 269-312 Gill, W. D., 1951, Tectonics of the sub-Himalayan fault zone in the northern Potwar region and in the Kangra district of the Punjab: Geol. Soc. London Quart. Jour., v. 107, p. 396-413 Harrison, J. V., 1930, Geology of some salt-plugs in Laristan: Geol. Soc. London Quart. Jour., v. 86, p. 463-522 Holland, T. H., 1903, General report of the Geological Survey for 1902-03: Calcutta, Govt. India Press, 20 p. Lahiri, A. N., 1945, The occurrence of bitumen in the Punjab Salt Range and Kohat areas and its bearing on the age of the Saline Series: Nat. Acad. Sci. India, Proc. v. 14B, p. 329-334 Lees, G. M., 1927, Salzgletscher in Persien: Mitt. Geol. Gesell. Wien, v. 20, p. 29-36 Lehner, E., 1945, The Persian salt formations: Nat. Acad. Sci. India, Proc. v. 14B, p. 249-258 Middlemiss, C. S., 1891, Notes on the geology of the Salt Range of the Punj ab with a reconsidered theory of the origin and age of the salt marl: Geol. Survey India, Rec. v. 24, p. 19-42 Pascoe, E. H., 1920, Petroleum in the Punjab and North-West Frontier Provinces: Geol. Survey India, Memoir v. 40(3), p. 330-493 Pinfold, E. S., 1918, Notes on structure and stratigraphy in northwest Punjab: Geol. Survey India, Rec. v. 49, p. 137-160 •—•— 1945, The age of the Saline Series of the Punjab Salt Range: Nat. Acad. Sci. India, Proc. v. 14B, p. 239-243 Sahni, B., 1945, Microfossils and problems of Salt Range geology: Nat. Acad. Sci. India, Proc. v. 14B, p. i-xxxii • 1947, Microfossils and the Salt Range thrust: Nat. Acad. Sci. India, Proc. v. 16B, p. i-xlix Wadia, D. N., 1945, A note on the repeated overthrusts of the Cambrian rocks on the Eocene in the northeastern part of the Salt Range: Nat. Acad. Sci. India, Proc. v. 14B, p. 214-221 Wynne, A. B., 1878, On the geology of the Salt Range in the Punjab: Geol. Survey India, Memoir v. 14, p. 1-313 Zuber, R., 1914. Beitrage zur Geologic des Punjabs, Ost-Indien: Wien, Verh. K.-K. Geol. Reichanstalt, Jahrbuch v. 64, p. 327-356

GEOLOGY DEPT., OSMANIA UNIVERSITY, HYDERABAD 7, INDIA (FORMERLY DIRECTOR, GEOLOGICAL SURVEY OF INDIA, CALCUTTA, INDIA) MANUSCRIPT RECEIVED BY THE SOCIETY JANUARY 15, 1965

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