Thrust Geometries And Evolution Of The Eastern North Potwar ...

Indian plates to the north and south, respectively.In northern Pakistan, the Himalayas havefour major tectonic subdivisions (Yeats 6.Lawrence, 1984). These, from north to south, arethe Karakoram Ranges and Hindu Kush Rangesof Gondwana affinity sutured to Eurasia (theTuran Block) in Late Triassic to the middleJurassic time (Sengor, 1979). The Kohistan IslandArc located between the MKT and theMMT was docked with Eurasia in late Cretaceousto early Eocene time (Jan & Asif, 1981;Tahirkheli, 1982; Pudsey, 1986; Searle et al.,1987; Treloare et al., 1989). The low ranges ofSwat, Hazara and Kashmir in Pakistan locatedbetween the MMT and the MBT represent themarginal foreland fold-and-thrust belt in Pakistanequivalent to the sub-Himalaya in India.Zeitler et al. (1982) suggested that the MMTlocked approximately 15 Ma, subsequent to rapiduplift north of the fault between 30 and 15 Ma(Zeitler et al., 1980). Following the cessation ofmovement along the MMT, deformation propagatedsouthward to the MBT. Along MBTunmetamorphosed Mesozoic and Lower Tertiaryrocks are thrust over Neogene molasse strata.The Neogene molasse strata in the footwallof the MBT can be divided into two age groupsbased on its outcrop pattern. Middle to upperMiocene Rawalpindi Group strata is mostly exposedin the NPDZ north of the Soan Syncline.Middle Miocene to Quaternary 'strata is exposedsouth of the Soan Syncline (Figs. 2,3). Thicknessof molasse strata is about 5 km below the SoanSyncline (Lillie et al., 1987; Baker et al., 1988).However, mostly Rawalpindi group strata ofmoderate to steep dips is exposed in a wide zoneof over 20 km north of the Soan Syncline (Fig. 3 ).Apparently this strata is repeated involving platformstrata but not involving Siwaliks. How isoutcrop pattern controlled by tectonics and sedimentation?The problem is considered in thisarticle as an effort to resolve the structure of theNPDZ. The SR/PP south of the MBT representsbroad Himalayan foreland in northern Pakistan.Yeats et al. (1 984) observe that the Siwalik strataof Upper Miocene to Pleistocene age is fullyinvolved in deformation in the Salt Range. TheSalt Range constitutes a narrow zone of localizedstrong folding, faulting and uplift at the mountainfront in contrast to the thrust imbricates ofthe Potwar Plateau. The two structural domainsare separated by the asymmetrical Soan Syncline,the south limb of which is much gentlerthan the north limb. Complex deformation ofthe North Potwar is discussed in this article.STRATIGRAPHYA stratigraphic column based mostly onlithological log in Dhurnal oil field is shown inFigure 4. The Rawalpindi and Siwalik Groupstrata have variable thicknesses from one to theother location (Jaswal, 1990; Pennock et al.,1989). The rationale for thickness calculations isto have a better idea about the estimated stratigraphicthickness for extrapolation of stratigraphyduring construction of geological cross-sections.The oldest formation known to lie on topof the basement is the Eocambrian Salt RangeFormation. The overlying Paleozoic to Eocenestrata is about 105 1 m thick. In Dhurnal the baseof this sequence is marked by pelitic to arenaceousPaleozoic Tobra, Dandot, Warchha, Sardhaiand Amb Formations. This group is disconformablyoverlain by pelitic to calcareous strata ofJurassic to Eocene age. The upper part of stratigraphicsection in the vicinity of Soan synclinecomprises the Miocene Rawalpindi Group(- 2106 m thick) and the Upper Miocene-Pleisdtocene Siwalik Group (- 2881 m thick). TheRawalpindi Group consists ofMurree and Kamlialformations of dominantly pelitic and arenaceousstrata of the Chinji, Nagri, Dhok Pathan andSoan formations (Fig. 4). The Siwalik have beendeposited during the last 13 Ma (Johnson et al.,

Fig. 3. Geological map of the eastern NPDZ. AA' locates the structural cross-section shown in Figure 7.Structures: KMT = Khairi-Murat Thrust, MBT = Main Boundary Thrust, MT = Murat Thrust, SET =Soan Backthrust, SS = Soan Syncline. Strata from younger to older: Ts = Soan Formation, Tdp = DhokPathan Formation, Tn = Nagri Formation, Tc = Chinji Formation, Tk = Kamlial Formation, Tm =Murree Formation, Te = Eocene, E-J = Eocene to Jurassic. Wells: BK = Bokra, G = Golra, K = KhairiMurat, FM = Faisal Mosque, RWP = Rawalpindi. Arrows with numbers show dip of beddings. Otherstructures are similar as shown in Figure 2.1979, 1982). Top of the Murree Formation is erosional products of southward advancing Hidatedat 17 Ma. These strata are non-marine time malayan thrust front. Johnson et al. (1979) sugtransgressive molassic facies that represent the gest that the fluvial and fluvio-deltaicRawalpindi

Conglomerate,sandstone, claystoneClaystone, sandstone 1+450 m600 rnSandstone, shale I 51 8 m--Sandstone, shaleSandstoneShale, sandstone1ShaleDolomite shale ss 234mLimestoneLimestone, ShaleLimestoneSandstone, shaleLimestoneSandstone. shaleShaleSandstone, shaleSandstone, shaleIsiltstoneSandstone.Dolomite, shale, saltIII+I00 rnBiotite schistFig. 4. Stratigraphic column of the NPDZ based on Dhurnal-3 well (after Kamran &Rake, 1987; Jaswal, 1990;Ahmed et al., 1993). Age dating of Siwaliks is based on chronostratigraphy (Johnson et al., 1979; 1982).

Fig. 5. Sequential evolution of the Soan Syncline (from Jadoon &Frisch, 1995). Timing constrains are basedon magnetostratigraphy by Raynolds (1 980), Raynolds and Johnson ( 1985) and Johnson et al. (1 986).a part where a fault is parallel to a stratigraphichorizon and ramps where the fault cuts acrossthe stratigraphic horizon at a high angle. Themovement along a fault may result in bending ofhanging wall over the footwall to produce faultbend(Suppe, 1983), fault-propagation folds(Suppe & Medwedeff, 1984; Suppe & Shaw,1994), and thrust imbricates (Figs. 6,7). In othercases, bedding of hanging wall strata between alower and an upper detachment results in duplexstructures. In duplex geometry, strata above andbelow an upper detachment may be called as roofand duplex sequence, respectively.The roof sequence may propagzite towardsthe foreland or the hinterland (Fig. 7). Whenroof sequence propagates passively towards thehinterland compared to the underlying duplexes,the resultant geometry is called as a passive-roofduplex (Banks & Warburton, 1986). In a passive-roofduplex, the roof sequence remains passivewith respect to the underlying duplex. In thiscase, shortening in the roof sequence may beaccommodated along a se t of passive-backthrusts.The passive-backthrusts ideally evolve from thetip of each duplex in order to accommodatecomparable shortening that occurs due to movementof duplex horses. Thus, evolution of apassive-back thrus t involves tilting and final emergenceof the roof sequence over the duplexes(Fig. 6, 7Dii). Such a similar fault has evolvedbelow the northern limb of the Soan Syncline,herein called as the Soan-backthrust (Figs. 2,3).The Soan-backthrust is one prominent featureof the eastern NPDZ (Fig. 2). Along this

42 krn SHORTENING ' j*O KIL~rnRS 10( fWWJPINDI GROUP-7 BASEMENTECCENEPALEOZOCFig. 6. Step-wise construction of cross-section AA' shown in Figure 3. The cross-section shows thin-skinned features of the eastern NPDZ with a trianglezone geometry and imbricates. Some imbricates show breakback thrusting. 42 krn of shortening is estimated along the section. Text for discussion.

structure, surface dips vary drastically fromnear horizontal along axis of the Soan Synclineto vertical near the passive-backthrust.The backthrust is located near the top ofthe Rawalpindi Group strata and involves90' of rotation and uplift of about 3 km(Jaswal, 1990; Raynolds &I Johnson, 1985).As deformation along the northern limb ofthe Soan Syncline occurred between 2.1 to 1.9Ma, uplift rates of about 15 mmlyr can be calculated.C) Khairi-Murat and Golra ImbricateZone: The Khairi Murat and Golra set of southvergentimbricates are dominant structures betweenthe Soan Syncline and the MBT (Figs. 2,3). They are named after the Khairi MuratRange and the Golra village. Generally lowerto middle Miocene Murree Formation (molasse)of erratic trends is exposed in this zone of over20 km acrossstrike. However, along Khairi Muratand Golra thrust linear outcrop of Eocene strataare extensively exposed. The dips are moderateto vertical and even overturned. Thus, substantialrepetition of strata can be envisaged. Presentlylow relief of the area suggests cessation ofactivity and substantial erosion. Deposition ofalmost horizontal Lei Conglomerate representsend of the tectonic activity. The base of the LeiConglomerate is dated at 1.9 Ma (Raynolds,1980). Since then, erosion and resultant thickcover of alluvium concealed outcrops, particularlyin synclinal areas and footwall of the faults.However, faults can be traced laterally based onstructural trends, along strike ridges, stratigraphy,and steps in topography. Gouge, calciteveins, fault breccia, steps in relief, and springs aretypically related to the faults. Established faultscan be traced laterally in Islamabad due to stepsinroads i.e., Golra fault south of the Faisal Mosque(Fig. 3). The surface exposure of the Khairi MuratFault is prominent due to thrusting of the Eocene(Chorgali) strata over the Murrees. Similar struc-tural and stratigraphic relationship is observed tothe west along the Khairi Murat Fault (Jaswal,1990).North of the Khairi Murat Fault, an extensiveexposure of Murree Formation is exposedalong the Kashmir Highway (Islamabad). Thestructure here is of a broad Bokra syncline(Fig. 3). Along the axis of the syncline shallowdips upto 15' are encountered. A dry hole wasdrilled to a depth of 1939 m on the adjacentBokra anticline (Kamran & Ranki, 1987). Bokraanticline and syncline allow to locate a rampand a flat of a thrust sheet. Towards SW in theKhairi Murat ranges, moderate to steep dippingMurree Formation (Fig. 3) is mapped to be imbricated(Jaswal, 1990). This set of imbricates mayrepresent small bedding-parallel slip and relatedsplays.The south-vergent Golra fault merges intothe MBT towards NE (Fig. 3). Along this faultEocene strata is exposed on the hanging wall ofthe fault. Fault is very well exposed near thePakistan Air Force Mess (PAF) in Islamabad andalong Grand Trunk Road. In Islamabad, PAFMess is constructed over the fault escarpmentand the Pleistocene conglomerate. The faultcan be traced laterally, by the emplacementof Eocene strata against Murree stratalalluviumand the features described above. Hangingwall strata records moderate to steep dips between65O to 80'. North of the Golra fault,another south-verging fault, herein called as ShahAllah Ditea juxtaposes Eocene and Miocenestrata.Both Golra and Shah Allah Ditta faults aresplays of the MBT. They merge eastwards in thelatter. The Margalla Hill Range with Mesozoicand Lower Tertiary strata is located along thehanging wall of the MBT. In the study area, theMBT may consist of several relatively smallerfaults at concurrent positions instead of being a

Fault-Band FoldFault-Propagatlon FoldImbricate ModelDuplex ModelC) Piggy-Back ThrustingID) Kinematically Inadmissible DuplexDi) Kinematically Admissible DuplexDii) Kinematically Admissible DuplexFig. 7. Fold-and-thrust geometries applicable to eastern NPDZ. Text for discussion.

single continuous fault. This hypothesis can betested in future.CONSTRUCTION OF STRUCTURALCROSS-SECTIONA representative structural cross-section hasbeen constructed using concepts of balancedsections (Dahlstrom, 1969; Woodwards et al.,1989; Jadoon, 1992) according to the followingsteps:Assembly and projection of basic dataThe data discussed above was projected on theprofile AA' in Figure 6. The profile is selectedparallel to the direction of tectonic transport forits usefulness to reflect a true picture of subsurfacestructural geometry and calculation of shortening.Generally, direction of tectonic transportremains perpendicular to bedding, fold axes, andcleavages. Subsequently stratigraphy, fold axes,faults, and dips were projected on the profile inFigure 6A.Basement depth and sedimentary thicknessesAfter projection ofbasicdata, it was important tolocate basement with consideration of the maindecollement and any deformation above. Besides,thickness of sedimentary strata was criticalfor structural geometry and balancing purpose.Basement was located on the profile at depth ofabout 6 km along the axis of the Soan Synclineand at about 7 km along the MBT (Fig. 6B) basedon seismic reflection data (Pennock et al., '1989;Jaswal, 1990). The lo dip of basement towardsnorth is based on reflection interpretations (Lillieet al., 1987). Plot of the basemen't provided aspace, above, for extrapolation and interpolationof structures and stratigraphy. Figure 4 based onDhurnal-3 well provides details of Precanibrianto Neogene strata. About 1 km of Eocene toPaleozoic platform and 3776 m of molasse stratawas encountered in the Dhurnal well. Paleozoicto Eocene platform strata does not show muchvariation in thicknesses in the SR/PP (Lillie etal., 1987; Baker, et al., 1988; Pennock et al.,1989).Following basement, an important stepwas to locate the main decollement. Thedecollement is well established in the Eocambr ianevaporites throughout the Salt Range (Lillieet al., 1987; Pennock et al., 1989). It remains inthe same horizon in the eastern NPDZ (Jaswal,1990).Hereon, structures were interpolated andextrapolated using geometrical techniques ofbalanced cross-sections. Line-length balancingand kink method is used for the construction ofcross-section AA' in Figure 6. The resultantcross-section shows thin-skinned features relatedto the Himalayan collision in eastern NPDZ.INTERPRETATIONStructural styleFigure 6C shows some details of the complexstructural geometry in the NPDZ. During presentstage of evolution, most prominent structure betweenthe Soan Syncline and the MBT is atriangle zone and a set of imbricates. A trianglezone is formed by wedging of competent stratabetween a floor and a roof thrust. The roof thrustsin a triangle zone generally show hinterlandvergence (Jones, 1982; Price, 1986) andare termedas passive-backthrusts (Banks & Warburton,1986). As prograde deformation occurs from hinterlandtoward foreland, the most proximal thrustlocated hinterland side of the backthrust reachesthe erosional surface in the regular triangle zones(Fig. 8). Such a similar structural geometry isinterpreted below the northern limb of the SoanSyncline in eastemNPDZ. The basal decollement(floor thrust) and the Soan backthrust (roofthrust) represent the two faults that bound awedge of Rawal~indi and older strata below thenorthern limb of the Soan Syncline (Fig. 6).

Fig. 8. Model of a triangle zone geometry with a core wedge bounded between a floor and a roof (back) thrust.Khairi MuratIMurat faults represent the proximalthrusts located hinterland side of thebackthrust. This interpretation is consistent withseismic reflec tion observations in the Dhumal oilfield (Jaswal, 1990).Figure 6 predicts the presence of a faultbendand a fault-propagation fold in the trianglezone. Along the fault-bend fold the floor thrustmakes a ramp across the competent platform andRawalpindi Group strata and merges in the roofthrust at a depth of about 3 km. About 2.3 kmof displacement along the duplex and theoverlying accommodating fault resulted in about90' clockwise rotation of the roof sequence,exposing the passive-backthrust. The fault-propagationfold shows a slip of about 200 m and anamplitude of 300-400 m. The propagating faultdies out in the core of the fold. So, it does notmerge in the roof thrust. To the west, a similarstructure, the Dhumal pop-up (Fig. 2) is producinghydrocarbons (Jaswal, 1990; Kemal, 1991;Ahmed et al., 1993).The cross-section AA' (Fig. 6) shows thatthe fault-propagation fold under the northernedge of the Soan Syncline is asak cored anticline,recognized as a pop-up within the triangle zone(Jaswal, 1990; Kemal, 199 1). The triangle zoneshave been reported in the frontal portions of theSulaiman and Kirthar ranges of Pakistan (Banks& Warburton, 1986; Humayon et al., 199 1 ; Jadoonet al., 1992), the eastern Rocky Mountain foothillsof Canada (Price, 1981; Jones, 1982; Price,1986) and Magallenes Foreland Fold-and-ThrustBelt, Southern Chile (Alvarez-Marron et al.,1993), and seems to be major structures of themountain fronts.North of the triangle zone, Figure 6 pregdicts the presence of a set of imbricates (duringpresent stage of evolution) which splays off fromthe basal decollemen t. Present structural geomgetry is of piggy-back thrusting. Each splay involvesa displacement of about 6 to 10 m. Ofthese, Khairi Murat and Golra show furtherimbrication near their tips. The secondary splaysmerge in the main thrust at depth of about 2 km.It is probable, that Murat is the main thrustwhereas Khairi Murat represents a splay suggest*ing breakback thrusting along the Khairi Muratand the Golra faults. This is consistent withobservation of Dahlstrom ( 1970) from the Cana.dian Rockies. He suggests that imbrication near.

[he surface may a breakback sequenceunlike a breakforward sequence at depth.However, Jones (1987) consider that the hangingor footwall imbricates (terminology afterButler, 1982) can develop in any order dependingupon when major fault of the sequence hasdeveloped.Thrust geometries and kinematicsThe structural cross-section AA' (Fig. 6C)reflects some characteristic features of the fore-land fold-and-thrust belts. It shows deformationin the sedimentary strata above the decollement.Deformation in the sedimentary strata isdominated by a set of imbricate fan with thrustsheets consisting of platform and RawalpindiGroup (Murrees) strata. Siwalik strata is notobserved in the thrust sheets. It is critical todifferentiate if Siwalik strata was not depositedat the time of thrusting in the NPDZ (Fig. 7C)or if thrusting occurred as duplexes below theSiwalik strata (Fig. 7D). Chronostratigraphiccontrol on the Siwalik strata is available(Johnson et al., 1979; Johnson et al., 1982)that constraints deposition of the Siwaliks(Chinji, Nagri, Dhok Pathan) between13.1-5.1 Ma (Fig. 4). Thus, an imbricatemodel would suggest that deformation in theNPDZ has occurred prior to the 13.1 Ma. However,as Siwalik strata is not involved in theimbrication and as much of deformation in theeastern Potwar Plateau may have occurred after4.5 Ma (Johnson et al., 1986) with major movementalong MBTat 1.8 Ma (Burbank & Raynolds,1988); it is most likely that deformation in theNorth Potwar has occurred after deposition of theSiwalik strata. This would suggest a duplex styleof deformation between a floor and a roof thrustaccording to a duplex model (Fig. 7D). In thismodel, roof thrust can be located in theRawalpindi Group strata. Thus, absence of theSiwalik strata in the NPDZ may be related to thethrust geometries.The duplex geometry in Figure 7D presentsan inadmissible section because it does not showsimilar length of the stratigraphic horizons belowand above the roof thrust. Figure 7Di shows asadmissible geometry by introducing an emergentfault in the roof sequence similar to as suggestedby Treloar et al. (1992). Baig (1995) presents asimilar solution considering Riwat thrust (Fig. 2)as the emergent thrust. However, Jadoon andFrisch (1995) demonstrate that the Riwat thrustis genetically related to a hinterland-vergenttectonic wedge (Fig. 5). Moreover, the Riwatthrust with a displacement of about 5 km cannotaccommodate shortening of duplexes in theFigures 6 and 7Di. Alternately the roof thrustmust show a passive northwards translation(Fig. 7Dii) similar to a passive-backthrust of atriangle zone (Gordy, 1977; Jones, 1982) or apassive-roof duplex geometry (Banks &Warburton, 1986). The triangle zone geometry isbeing increasingly recognized as the forelahdstructure of the several fold-and-thrust belts suchas the Canadian Rockies (Jones, 1982; Price,1986; Lawton et al., 1994); the Andies (Ramos,1989); the Carpathians (Jones, 1982) and theSulaiman lobe ofPakistan (Humayon et al., 199 1;Jadoon et al., 1992; 1994). The backthrusts in thepassive-roof duplex may accommodate comparableshortening in the roof-sequence. This interpretationis consistent with the'presence of aextensive passive-backthrust along northern limbof the Soan Syncline (Jaswal, 1990; Jamshed,1995; Baig, 1995). Backthrusting is also shown insome preliminary sections across the Kala ChittaRange towards west (Qureshi et al., 1994).The presence of basal decollement andtermination of faults in the decollement is aregular features in thin-skinned deformation offold-and-thrust belts (Chapple, 1978; Jones,1987). The NPDZ has a floor and a roof thrust inthe Eocambrian Salt Range Formation andRawalpindi Group strata respectively. Multiple

faults bounded between the floor and roofthrust has stacked a hinterland dipping duplex.During NPDZ evolution, the roof sequenceof Siwalik strata has been uplifted and eroded,probably along multiple backthrusts similarto the Soan-backthrust (Figs. 2,3). Figure 7Diishows the possible structural geometry beforeand after erosion of the roof sequence in theNPDZ.Shortening, timing and rate of deformationBalancing of Figure 6 shows about 42 km horizontalcontraction between the Soan Syncline andthe MBT. The total minimum shortening calculatednear Indus River (western Potwar) is over40 km (McDougall et al., 1993). Thus, ourestimate of shortening from eastern Potwarare closer to that of western Potwar. However,it is in disagreement with Jaswal, (1990) andTreloar et al. (1992) who have calculatedshortening of about 69 km and 80 km, respectively,in the NPDZ. The difference may representerror or lateral variation in the amount ofshortening.Known the shortening and timing of deformation,one can estimate the rate of orogeniccontraction. If 42 km of shortening in theNPDZ has occurred between 4.5 and 1.9 Ma, asdiscussed above, the rate of shortening is 16 mm/yr. This number compares with shortening estimatesof 9-14 mmlyr in the SR/PP (Leather,1987; Baker et al., 1988) and 1-15 rnmlyr in theSub-Himalaya in India (Lyon-Caen & Molnar,1 985).Our shortening estimates of 42 km alongcross-section AA' (Fig. 6) represent orogeniccontraction between the Soan Syncline andthe MBT. An orogenic contraction of 23 km iscalculated by Pennock et al. (1989) along abalanced cross-section in the eastern Salt Range(between thrust kont and the Soan Syncline).Thus, a total shortening of 65 km can be pre-dicted south of the MBT in the eastern SR/PP inPakistan.CONCLUSIONStructural interpretation of the NPDZ shows atriangle zone geometry below the northern limbof the Soan Syncline and a set of imbricatesbelow the footwall of the MBT. The triangle zonegeometry is characterized by a core wedge boundedbetween afloor thrust in the Eocambrian evaporitesand a roof thrust in the Rawalpindi Groupstrata. The floor thrust propagates upsectionfioma depth of about 7 km and merges in the roofthrust at a depth of about 3 km. The roof thrusthas a hinterland vergence similar to backthrustsof the triangle zones in other fold-and-thrustbelts. A fault-bend and a fault-propagation foldoccupy the position of the core wedge in thetriangle zone. These structures may have accumulatedsufficient quantities of hydrocarbons fordrilling.The imbricate set north of the trianglezone consists of thrust sheets of Murree Formation(molass) and older platform sequence, Asdeformation is apparently younger than depositionof most of the molasse strata, absenceof the Siwalik strata in thrust imbricates is attributedto the duplex style of deformation in theNPDZ. Besides, absence of a foreland vergentfault suggests a hinterland-vergence to the roofsequence. This is consistent with the exposedbackthrust and triangle zone geometry to thesouth.Total shortening in the NPDZ is about42 km between 4.5 and 1.9 Ma. This dataprovides a shortening rate of about 16 mmlyr.The 16 mrn/~r shortening estimate in the NPDZis comparable with 9-14 mmhr in the SR/PP(Leather, 1987; Baker et al., 1988) and10-15 mmlyr in the Sub-Himalayas in India (Lyon-Caen & Molnar, 1985). Total

shortening of 65 km can be predicted southof the MBT in northern Pakistan combining42 km in the NPDZ with 23 km south of theSoan syncline in the eastern SR/PP (Pennocket al., 1989).Acknowledgement: The author rhanks theAlexander von Humboldt Stiftung Germanyfor a post doctoral research fellowship (1994-1996) and Prof. Dr. W. Frisch who providedfacilities and stimulating guidance during thepreparation of this manuscript at Tubingen University.Special thanks are extended to Arif Kemal(Oil and Gas Development Corporation), NusratK. Siddique (Pakistan Petroleum Limited), andAkram Bhatti (Geological Survey of Pakistan)for data support. Syed M. Ali, and Riaz Ahmed(Hydrocarbon Development Institute of Pakistan)are gratefully acknowledged for always beingvery open to research and useful discussions.Quaid-i-Azam University is acknowledged forpartial funding throughuniversity Research Fund(196-1997).REFERENCESAbid, I. A., Abbasi, I. A. & Shah, M. T., 1983.Petrology and geochemistry of the Siwaliksandstone and its relationship to the Himalayanorogeny. Geol. Bull. Univ. Peshawar, 17,65-83.Ahmed, S. N., McGann, G. J. & Aizad, T., 1993.Dhurnal oil field, Potwar basin, Pakistan.Pakistan Journal of Petroleum Technology, 2,1-18.Baig, S., 1985. Structural study of the main BoundaryThrust System in northwest Himalaya, Pakistan.Unpubl. M.Phi1. thesis, Quaid-i-Azam University,Islamabad, Pakistan.Baker, D. M., Lillie, R. J., Yeats, R. S., Johnson, G. D.,Yousaf, M. & Zaman, A. S. H., 1988. Developmentof the Himalayan thrust zone: Salt Range,Pakistan. Geology, 16,3-7.Banks, C. J. & Warburton, I., 1986. 'Passive-roofduplex geometry in the frontal structures of theKirthar and Sulaiman mountain belt, Pakistan.Jour. Struct. Geol., 8,229-237.Burbank, D. G. & Raynolds, R. G. H., 1988. Strati.graphic keys to the timing of thrusting in theterrestrial foreland basins: applications to thenorthwest Himalaya, In: Frontiers in Sedimenatary Geology, New Perspective in Basin Analysis(K.L. Kleinspehn, & C. Paola, eds.). Springer-Verlag, 33 1-3 5 1.Burbank, D. W. 6r Beck, R. A*, 1991. Rapid, longtermrates of denudation, Geology, 19,1169-1 172.Burbank, D. W. 6r Beck, R. A., 1991. Models ofaggradation versus progradation in the Himalayanforeland. Geologische Rundschau, 80,623-638.Butler, R. W. H., 1982. The terminology of structuresin thrust belts. Jour. Struct. Geol., 4,239-245.Chapple, W. M., 1978. Mechanics of thin-skinnedfold-and-thrust belts. Geol. Soc. Amer. Bull., 89,1189-1 198.Dahlstrom, C. D. A., 1969. Balanced cross-sections.Canadian Jour. Earth Sci., 6, 743-75 7.Dahlstrom, C. D. A., 1970, Structural geology in theeastern margin of the Canadian Rocky Mountains.Bull. Canadian Petroleum Geology, 18,33 2-406.Gordy, P. L., Frey, F. R. & Norris, D. K., 1977. Geologicalguide for the C. S. P. G. and 1977 Waterton-Glacier Park field conference. Calgery CanadianSoc. Petrol. Geol., 93 pp.Humayon, M., Lillie, R. J. & Lawrence, R. D,, 1991.Structural interpretation of eastern Sulaimanfoldbelt and foredeep, Pakistan. Tectonics, 10,299-324.Jadoon, I. A. K., 1992. Balanced geologicalcross-sections: Concepts, construction, andevaluation. Summer Workshop (July12-14, 1992), Department and NationalCenter of Excellence in Geology, University ofPeshawar, 43 pp.Jadoon, I. A. K., Lawrence, R. D. & Lillie, R. J., 1992.Balanced and retrodeformed geological cross-

section from the frontal Sulaiman Lobe,Pakistan: Duplex development in thickstrata along the western margin of theIndian plate. In: Thrust Tectonics (K.McClay, ed.). Chapman and Hall, London,3 43-3 5 6.Jadoon, I. A. K., Lawrence, R. D. & Lillie, R. J., 1994.Seismic data, geometry, evolution, and shorteningin the active Sulaiman fold-and-thrust belt ofPakistan. Amer. Assoc. Petrol. Geol. Bull., 78,758, 774.Jadoon, I. A. K. & Frisch, W., 1995. Structural variation,uplift rates, and development of aconcealedreservoir below the Riwat fault, Himalayanforeland, Pakistan: Pakistan Jour. Petrol. Technology(in press).Jamshed, S. Q., 1995. Structural interpretation ofnorth eastern Potwar Deformed Zone and theMain Boundary Thrust in Pakistan. Unpubl.M.Phi1. thesis, Quaid-i-AzamUniversity, Islamabad,Pakistan.Jaswal, T., 1990. Structure and evolutionof the Dhurnaloil field, northern Potwar Deformed Zone and theMain Boundary Thrust in Pakistan. Unpubl.M.S. thesis, Oregon State University, Corvallis,Oregon.Jan, M. Q. & Asif, M., 1981. A speculative tectonicmodel for the evolution of NW Himalaya andKarakoram. Geol. Bull. Univ. Peshawar, 14,199-201.Johnson, G. D., Johnson, N. M., Opdyke, N. D. &Tahirkheli, R. A. K., 1979. Magnetic reversalstratigraphy and sedimentary tectonic historyof the Upper Siwalik Group, eastern SaltRange and southwestern Kashmir. In:Geodynarnics of Pakistan (A. Farah & K.A.DeJong, eds.). Geological Survey of Pakistan,Quetta, 149-165.Johnson, G. D., Raynolds, R. G. & Burbank, D. W.,1986. Late Cenozoic tectonics and sedimentationin the northwestern Himalaya Foredeep:Thrust ramping and associated deformationin the Potwar region. In: Foreland basins(P, Allen 65 P. Homewood, eds.). InternationalAssoc. Sedimentalogists. Spec. Publ., 8,273-291.Johnson, N. M., Opdyke, N. D., Johnson, G. D,,Lindsay, E. H. & Tahirkheli, R. A. K,, 1982.Magnetic polarity stratigraphy and ages ofsiwalikGroup rocks of the Potwar Plateau, Pakistan.Palaeogeography, Palaeoclimatology, Palaeoecology,37, 17-42.Jones, P. B., 1982. Oil and gas beneath east-dippingthrust faults in the Alberta Foothills, In: RockyMountain Association of Geologists Guidebook(K. Powers, ed.). 61-74.Jones, P. B., 1987. Quantitative geometry of thrustand-foldbelt structures. Amer. Assoc. Petrol.Geol. Bull. Methods in Exploration Series 6,26 PP.Kamran, M. & Ranki, U., 1987. Pakistan oil data.Hydrocarbon Development Institute of Pakistan.Unpub. report, 128 pp.Keller, H. M., Tahirkheli, R. A. K., Mitra, M. A,,Johnson, G. D., Johnson, N. M. &Opdyke, N. D.,1977. Magnetic polarity stratigraphy of the upperSiwalik deposits, Pabbi Hills, Pakistan. EarthPlanet. Sci. Lett., 36, 187-201.Kemal, A., 199 1. Geology and new trends for petroleumexploration in Pakistan. In: New directionsand strategies for acceleratingpetroleum explorationand production in Pakistan (G. Ahmed, A.Kemal, A.S.H. Zaman, & M. Humayon, eds.).Ministry of Petroleum and Natural Resources,Pakistan, 16-5 7.Khan, M. A., Ahmed, R., Raza, H. A. & Kemal, A.,1986. Geology of petroleum in Kohat-Potwardepression, Pakistan. Amer. Assoc. Petrol. Geol.Bull. 70,396, 414.Lawton, D. C., Spratt, D. A. & Hopkins, J. C., 1994.Tectonic wedging beneath the Rocky Mountainforeland basin, Alberta, Canada. Geology, 22,5 19-522.Leathers, M., 1987. Balanced structural cross-sectionof the western Salt Range and Potwar Plateau:Deformation near the strike-slip terminus ofan overthrust sheet. Unpubl. M.S. thesis,Oregon State University, Corvallis, Oregon,271 pp.Lillie, R. I., Johnson, G. D., Yousaf, M., Zamin,A. S. H. &Yeats,R. S., 1987. Structuraldevelopmentwithin the Himalayan foreland fold-and-

Yeats, R. S. & Lawrence, R. D., 1984. Tectonics of theHimalayan thrust belt in northern Pakistan. In:Marine geology and oceanography of ArabianSea and coastal Pakistan (B. U. Haq & J.D.Millimann, eds.). New York, Van NostrandReinhold, 177-198.Yeats, R. S., Khan, S. H. & Akhtar, M., 1984. LateQuaternary deformation of the Salt Rangeof Pakistan. Geol. Soc. Amer. Bull., 95,958-966.Zeitler, P. K., Tahirkheli, R. A. K., Naeser, C. W,& Johnson, N. M., 1980. Tectonic interpretationof fission-track ages from theLessar Himalayas, northern Pakistan. ESO, 7,359.Zeitler, P. K., Tahirkheli, R. A. K., Naeser, C. W. &Johnson, N. M., 1982. Unroofing history of asuture zone in the Himalaya of Pakistan by meansof fission-track annealing ages. Earth Planet. Sci.Lett., 57, 227-240.