Journal of the Geological Society, London, Vol. 151, 1994, pp. 269-290, 26 figs. Printed in Northern Ireland
Early Cretaceous strata of the Nepal Himalayas: conjugate margins and rift volcanism during Gondwanan breakup
M. R.GIBLING', F. M. GRADSTEIN2,I. L. KRISTIANSEN3, J. NAGY4, M. SARTI' & J. WIEDMANN" 'Department of Earth Sciences, Dalhousie University, Halifax, Nova Scotia, Canada B3H 3.5 2Atlantic Geoscience Centre, Bedford Institute of Oceanography, Dartmouth, Nova Scotia, Canada B2Y 4A2 3Norsk Hydro Research Centre, N-5020, Bergen, Norway 4Department of Geology, University of Oslo, PO Box 1047, Blindern, 0316 Oslo 3, Norway 'Dipartimento di Scienze della Terra, Universita della Calabria, 87030 Castiglione Cosentino Scalo, Italy %stitut fur Geologie und Palaontologie, Sigwartstrasse 10, 7400 Tubingen, Germany
Abstract: Early Cretaceous sandstones, shales and marlstones (Chukh, Tangbe and Muding Forma- tions, at least 625 m thick) crop out north of the Main Central Thrust in central Nepal. They were stronglydeformed during Himalayan collision, with telescoping of facies transitionsas a result of crustalshortening. The sediments show northerly palaeoflow and weredeposited on the steadily subsidingnorthern (Tethyan) margin of Gondwana. Berriasiandeltaic deposits pass upwardinto Valanginian-Albian, storm-dominated shelf deposits and into latest Albian pelagic slope carbonates. An unconformity, probably of Valanginian age, separates the Chukh and Tangbe formations locally, and is overlain by volcanic conglomerates. The Gondwanan marginsuccession matches wellwith that observed on the formerly conjugate margin of NW Australia, which separated from Greater India during the Valanginian to Hauterivian. Volcanicdetritus, where suitable for analysis, showswithin-plate geochemical affinity and reflects Gondwanan fragmentation. Abundant volcanic detritus in Aptian strata may have been derived from extensions of the Rajmahal Traps of northeast India. However, volcanismwas active near central Nepal in the Valanginian and volcanic detritus, possibly far travelled, reached the area during the Berriasian.Early Cretaceous strata1 successions andrelative sea-level changes show a first-order relationship to tectonism associated with Gondwanan break-up. The Gondwanan continent underwent radical change during thelate Mesozoicwhen GreaterIndia, Australia, Africa, Madagascar and Antarctica drifted apart (Powell et al. 1988; Audley-Charles 1988; Fig. 1).Correlation of stratigraphic successions in formerly contiguous but now widely dispersed regions of Gondwana is of considerable geological interest. Mesozoicsuccessions in northernGreater India and northwest Australia show broad similarity (Gradstein et al. 1991; Gradstein & von Rad 1991), but detailed correlation hasbeen hampered because crucial parts of theGreater Indiasuccession are located in theHimalayas where the strata are highly deformed and relatively inaccessible. Early Cretaceouscorrelation ofis special interestbecause northern Greater India and NW Australia were conjugate margins of the developing Indian Ocean during this period (Powell et al. 1988; Ogg et al. 1992). The purpose of this paper is to document more fully the Early Cretaceous (Berriasian to latest Albian) record in the Himalayan (Thakkhola) region of central Nepal, based on recently obtained sedimentological, biostratigraphic (cepha- lopods,foraminifera and palynomorphs) and petrological information. Comparison is drawn with the NW Australian margin, the tectonic history of which is well established from seismic studies and drilling. Fig. 1. Disposition of East Gondwanaland at a time equivalent to Cretaceous strata are present in central Nepal (Bordet et magnetic anomaly MO (about 118 Ma). Modified from fig. 8 of al. 1971),in Kumaon(Gansser 1964), Spiti (Fuchs 1982), Powell et al. (1988). Area of Rajmahal Traps adapted from Kent andthe Zanskar Range of northernIndia (Gaetani et al. (1991). MBT, Main Boundary Thrust; ITSZ, Indus Tsangpo Suture 1986; Garzanti & van Haver 1988), and in the Lesser Zone; K, T, present positions of Kagbeni and Tansen, respectively. Himalayas of Nepal(Sakai 1983, 1989). The tec- Northern edge of Greater India represents postulated Gondwana tonostratigraphicevolution of theseand associated strata margin prior to crustal shortening during Himalayan deformation. 269
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hasbeen discussed by Searle et al. (1987) and Gaetani & Nl DECOMPACTEDCURVESBURIAL (a) IRA
Garzanti (1991). Recentstudies of theThakkhola ..._Average water depth Cretaceous succession by Gradstein et al. (1989a, 1991, -Burial curves for each age point 1992)focused onfaulted and deformed outcrops in the southernpart of theoutcrop belt. In April 1991, the relatively complete but formerly inaccessibleLower Cretaceous section, first documented by Bodenhausen et al. (1964) near Tangbe, was studied. The Cretaceous strata are noteworthy for the abundance of volcanoclastic sediment whichwas thought to reflect ophioliteobduction tothe north of thearea duringthe Himalayan collision (Gansser 1964, p. 244; Bodenhausen et I al. 1964; Bordet et al. 1971) buthas more recentlybeen cl attributed to Gondwanan rifting prior to collision (Gaetani 1111111~1111 RESTORED SEDIMENTATION RATE et al. 1986; Sakai 1989; Gradstein et al. 1989a). The nature and age of the volcanic detritus, as well as its relationship with the extensive Rajmahal Traps of northeast India, are discussed below.
Geological setting of Thakkhola Mesozoic strata The Cambrian to mid-Cretaceous succession of Thakkhola rests on crystalline rocks that were emplaced along the Main Central Thrust of the Himalayan Orogen (Fig. 2). The strata generally dip and become progressively younger northward but are intensively deformed(Bordet et al. 1971). The PERMIAN~TRIASSIC~ JURASSIC I CRETACEOUS I CENOZOIC Mesozoic strataarepreserved in the north-trending AGE (Ma) ThakkholaGraben which probablyformed during a late Fig. 3. Decompacted burial profile (a) and restored sedimentation Cenozoic extensionalphase (Armijo et al. 1986). Latest rates (b) for the Permian to mid-Cretaceous strata of Thakkhola. Jurassic andCretaceous strata are missing fromthe Profile was calculated using the F77 program BURSUB (Stam er al. adjacent,structurally more elevated Dolpo-Karnali and 1987; Gradstein et al. 19896) which calculates the restored Manang regions (Fuchs 1977;Fuchs et al. 1988). The sedimentation, burial and subsidence rates of sedimentary units at ThakkholaSeries, provisionally datedas Mio-Pliocene by (well) sites. Corrections were applied for increased compaction of sedimentary units through time with deeper burial, and for changes Bordet et al. (1971), is apparentlythe youngest pre- in sea-level elevation relative to the Present. The small water depth Quaternary unit in the region. of the sedimentary deposits renders errors in palaeobathymetry The Thakkhola Mesozoicsuccession comprisescoastal, estimates negligible. In the absence of estimates for porosity and open shelf and shelf-to-slope deposits (Gradstein et al. 1991, grain density for different lithologies, use was made of default 1992). A burial profile for theGondwanan margin at (global) values, stored in the program, of porosity with depth for Thakkholaduring this period (Fig. 3) hasbeen updated each lithology. Basement unloading to arrive at tectonic subsidence from a provisional profile (Gradstein et al. 1991) in order to is based on Airy-type of local compensation; no corrections were attempted for flexural loading. Time scale after Kent & Gradstein (1985). Small uplift shown at 100 Ma is an artefact of our lack of data concerning post-Albian history: the basin floor was allowed to rise to sea-level, with final uplift in the Miocene to the present elevation of more than 2 km above sea level. Elevation was probably much greater at times in the Neogene.
provide geotectonica framework for analysis of the Cretaceousstrata. The revised profile, which incorporates refined estimates of formation thickness,age and deposi- tional environment, is based nn almost 20 age-depth points, with greatest uncertainty for the poorly dated Valanginian to Barremian interval. As discussed below, a poorly dated hiatus separates the Chukh and Tangbe formations locally buthas not been identified everywhere.For burial calculations, this time is considered to havebeen depositional. As discussed below, the hiatus may correspond on the NW Australian margin to a local unconformity which hasbeen related to the final separation of Australia from Greater India prior to the late Valanginian (Gradstein et al. 1992;Boyd et al. 1992). However, until theearly Fig. 2. Principal structural elements of the Himalayan Mountains in Hauteriviansedimentation was continuous along the Nepal and vicinity. Location of study area is shown. Modified from western part of theExmouth Plateau, offshore NW Searle et al. (1987). Australia (Gradstein & von Rad 1991).
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Subsidence and accompanying sedimentation was steady subsidence rate caused profoundchanges in sedimentary from Jurassic through mid-Cretaceous times in Thakkhola. facies throughtime; rather, climatic changerelated to Sedimentation generally kept pacewith subsidence, which latitudinal drift was probably of majorimportance may have been largely thermal in origin as deduced from its (Gradstein et al. 1991), as was sea-level fluctuation. relatively constant and slow rate. Decompacted sedimenta- tion rates vary from 1 to 5 cm ka-l, withan average near 2.5 cm ka-.', and terrigenous sedimentation rates were about Late Jurassic and Cretaceous stratigraphy of twice those for carbonates. The continental margin appears Thakkhola to havebeen relatively 'passive', without significant The most completeCretaceous sections knownin inversion. Insufficient sediment was available to fill the basin Thakkholaand the adjoining Mustang region are located at about 150 and 105 Ma, but this lack was compensated by near Chhukgaon and Tangbe (Fig. 4), where Bodenhausen later basinal fill. There is no evidencethat variation in et al. (1964) definedprovisional stratigraphicunits. The
I 83"50' E ALBIAN 28"55' N CHHUKGAON km 5 4UDING FM. limestone,rnarlstone, shale 0 l L- l 1 NEOCOMIAN-ALBIAN
ANGBE FM.
NEOCOMIAN
FM pale sandstone:HUKH pale FM
OXFORDIAN-BERRIASIAN
4UPRA FM. p1shale
- fault 25 L dlpand strtke observed DZONG RIDGE :ontact andcovered
lhmlt of rnapplng .4273
0 vtllage
3914. *F,F-3 ,a 83350' E e 'ig. 4. Outcrop location map of Kagbeni-Muktinath-Tangbe area to show partial distribution of Late Jurassic and Early Cretaceous tratigraphic units.
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sectionshave been inaccessible forsome years to Alternativeformational names have been applied by Westerners. These authors named a lower Chukh Formation several workers to incompleteand deformed strata in the and an upper Tangbe Formation, separated by dark shales Kagbeni, Chyanche and Dzong areas south of the Tangbe which they termed the Saligram Formation and correlated type section (Table 1). In view of the priority of the Tangbe with the well-known Spiti Shale of northern India, of Late type area and the complex nature of thepreserved facies Jurassicage. The shalesnear Tangbe are in fact Early transition (discussedbelow), sections measured in these Cretaceous in age(Bordet et al. 1971): the incorrect southerly outcropareas are attributed to theChukh and correlation was probablydue to anerroneous Middle Tangbe formations.These attributions are supported by Jurassicage assigned to plantfragments in theChukh lithological similarities and supplemented by age indications. Formation, tothe non-exposure of the basal Chukh The section described by Bodenhausen et al. (1964) near Formation near Tangbe, and to the similar appearance of Tangbe (section CHH1, Figs 4 & 5) is considered the type the Jurassic and Cretaceous shales. section of the Chukh and Tangbe formations. Two reference Outcropsnear Jharkot (Fig. 4)show thatthe Chukh sections are alsodescribed: section T4, west of Tangbe, Formationconformably overlies the Spiti Shale, locally whichexposes most of the younger strata of the Tangbe named the Nupra Formation. The Nupra Formation is dated Formation, and section JK1 north of Jharkot, which exposes in this areaas Early-Mid-Oxfordian to Tithonian the contact between the Nupra and Chukh formations. The (Gradstein et al. 1989a, 1991) andrests with amarked Muding Formation was examinedon the DzongRidge hiatuson the Ferruginous Oolite, a 4.7m unit the top of (section D1, Fig. 4), within thetype area indicated by which is earliest Callovian in age. Based on the timescale of Bassoullet & Mouterde (1977). A compositestratigraphic Harland et al. (1990), the hiatus represents perhaps 5 Ma. column for all three formations is shown in Fig. 7 (symbols The stratigraphic usage of Bodenhausen et al. (1964) has used in this and subsequent stratigraphic columns are shown been followed onthe grounds of priority(Table 1) and in Fig. 6). completeness of the section near Tangbe, butthe base of the The measured sections shown on Fig. 4 are named in the TangbeFormation has been lowered to include strata subsequent text according to theirnearest geographic assigned tothe Saligram Formation.Carbonate rocks locality: Tangbe (CHHI, T4); Kagbeni (KAI); Chyanche overlying the Tangbe Formation on the Dzong and Muding (KA3, KA4); Jharkot (JK1); and DzongRidge (Dl; JK4, ridges were termed the Calcaires de Mudingby Bassoullet & with subsections 1 and 3 ascribed to the Tangbe Formation Mouterde (1977) following mapping by Bordet et al. (1971), and subsection 2 to the Chukh Formation). Written logs of but were not noted by Bodenhausen et al. (1964). The term all sectionshave beendeposited with the Society Library Muding Formation is used here for these strata. and the British LibraryDocument Supply Centre, Boston Spa, W. Yorkshire LS23 7BQ, UK, as Supplementary Publi- Table 1. Stratigraphicframework for Late Jurassic and Early cation No. SUP 18085 (39 pages). Cretaceous strata of Thakkhola The ChukhFormation shows relatively little lateral variationin facies within the study area.However, the EODENHAUSEN THIS STUDY ETAL 1969 TangbeFormation shows considerablelateral change in
TINGE - OZOIlG facies at similar stratigraphic levels, especiallyacross fault lines. Faultsand outcrop belts tendto showan E-W MUDING FM NARSING SERIES orientation (Fig. 4) and strata are locally tightly folded and (r25m) overturned. Paleoflow indicators inboth theChukh and Tangbeformations are northerlydirected (Fig. 8). A
TANGBE FM 15Orm)
CHUKH FM +70m) 1 I NUPRA FM SPIT1 SHALE DE SPIT1 (,2Y)rn) (5oom)
The Saligram Formation of Bodenhausen et a/. (1964)was incorrectly correlated bythem with the Spiti Shale; their CheckpostFormation, correlated by some later workers with Cretaceous strata. representsfaulted Triassicstrata near Jomosom.Gradstein et al.(1989a, 1991,1992) named informal,provisional units in theKagbeni to Muktinatharea whichare replaced by thepresent formal terms based on relativelycomplete sections near Tangbe. Garzanti & Pagni Frette(1991) carried outa stratigraphic exploration in the southernThakkhola region and modified thestratigraphic Fig. 5. Type section (CHHI) of Chukh Formation (C) and Tangbe nomenclature of Bassoullet & Mouterde (1977) by splitting the Formation (T) near Tangbe. Dashed line shows formation contact. Grks de Kagbeni into a quartzose sandstone unit (Dangardzong Chukh Formation is 67 m thick in this section. Tangbe Formation is Formation) and an overlying greenish sandstone and shale unit at least 236 m thick, with a section measured to 23 m above base of (KagbeniFormation). However, strata newlyassigned to the the dark sandstone in the cliff at top right. Kagbeni to Chhukgaon DangardzongFormation were previously assigned to the path is visible in the lower part. See Fig. 4 for location and Fig. 7 Chukh Formation (Bodenhausen et a/. 1964). for measured section. Photograph viewed from west.
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LEGEND TANGBE SEDIMENTARY FEATURES CHHl T4
\S/ troughcross-beds ,~..,~,~ planar cross-beds ',v~ cross-beds(geometry uncertain)
~ - asymmetricripple marks
7% ripplecross-lam. symmelrlc ripple marks eoscillatory-flow cross-lam. DZONG S- combined-flowcross-lam. RIDGE hummocky uoss-strat. (HCS)
bF-+form-concordant strat. * CHHl - 162GK 0 DZ - 5A, ~ : planarto low-angle lam. @ D1 -178GK -e' loadcasts diL contortedstrat. FM' MUDINGFM. -0 L swur G * CHHI - 154GK @ .. . erosionalsurtace G -CHHI - t53GKB groove cast G P primarycurrent lineatwn , paleoflow measurement G!- (npflh UP page) am ferrugmousnodule 4 chert nodule
D extrabasmalclasts
A shale(intrabasinal) dasts ~-bedding (generalised)
G glauconite 'O FOSSILS B;- @ ammnites m belemnites A bivalves 0 fish scales a burrows (generalised) spreiten burrows W 0- plant fragments A roots l 0 ostracods
OTHER FEATURES
-F- faun contact JK1 A finingupward unit (begins at A base) warsening upward unit v (ends atv top)
mud -ravel A CHUKH FM. A Fii. 6. Legend for Figures 7,9, 14, 17 and 18.
MU1-5GK @ northward proximal todistal facies trend is inferred from E sedimentological analysis of theTangbe Formation (see below). It is concluded that the outcrop belt represents a facies transitionthat is disjunctand compressed due to crustal shortening. Fig. 7. Composite stratigraphic column for the Chukh, Tangbe and Muding formations, central Nepal. Column includes type section of Chukh Formation the Chukh and Tangbeformations near Tangbe (CHHl),reference The formation consists of fine- to coarse-grained terrigenous sections near Tangbe (T4)and Jharkot (JKl), anda section on the clastics, with prominent pale quartzose sandstone and dark Dzong Ridge (Dl). Location of measured sections shown in Fig. 4. or variegatedshale. Thickness is morethan 70 m in the Legend shown in Fig. 6. Locations of samples mentioned in the text Tangbetype section (Fig. 7) wherethe upper contact is are shown, with an indication of the major type of fossil: C, visible, and morethan 100m in theJharkot reference cephalopods; P, palynomorphs; F, foraminifera. section (Fig. 9) where the formation rests conformably on the Nupra Formation. The Chukh Formation in the Kagbeni lost through faulting in the Kagbeni section. No northward section (Figs 9, 10) is 110 m thick but considerably deformed proximal to distal trend was evident between Kagbeni and and possibly tectonically thickened. The ChukhFormation comprises repeated groups of Tangbe, nor any indication of upward change in sedimentation style within the formation. strata(here termed units) in which sandstoneproportion, Individual units comprise some or all of six facies. In the grain size and bed thickness all increaseupward. The Tangbe section (formation base not seen) commenceswith a most complete units, all six occur in the upward succession described below. coarsening-up unit 22.3 mthick, with pebbles and large wood fragments in the topmost granule-conglomerates and Facies 1. Darkshale intercalated with siltstone to fine-sandstone. coarsesandstones; four overlying units average 11 m in Coarser beds, typically 10-20cm and up to l m thick, have abrupt thickness. Fourteencoarsening-up units atJharkot and bases and tops, and show parallel to low-angle lamination, ripple Kagbeni range from 5-28111 in thickness, with some shale cross-lamination, combined-flow ripples andrare hummocky
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KAG BEN1
CROSS BEDS. A KA1 GYMMETRIC RIPPLES JHARKOT F- JKI GROOVE CASTS, PRIMARY CURRENT E '- I
RIPPLES (CRESTLINES) DZONG (n.. = 11 RIDGE Fig. 8. Palaeoflow data for the Chukh and Tangbe formations.All trough cross-bed measurements were made on bedding surfaces; JK4 (2) vertical faces in which palaeoflow could not be measured precisely indicate generally northerly palaeoflow (12 cases), southerly(1 case), and westerly (1 case).
cross-stratification. Macrofossils in thisfacies are restricted to ammonites in the basal unitat Jharkot,sparse ichnofossils (Palaeophycur and Taedium?), plantfragments, and bivalves observed in one thin section. Facies 2. Scour-based, very fine- to fine-grained sandstone beds cut into shale. Such beds are especially well seen in three coarsening-up units at the top of the Jharkot section (Fig. 9; Column A, Fig. 11). Beds are 50-130 cm thick, show up to 50 cm of basal relief, and are -- , predominantlyplanar-laminated, with ripplecross-laminated caps. Planar-laminatedintervals locallypass laterallyinto convex-up bedsets,several decimetres in thickness,that contain form- concordant,even lamination; some bedsets are capped by ripple cross-lamination. These mounded forms resemble in some respects the dune-plane bed transitions described by Cheel (1990). v Facies 3. Thick (upto 15 m)sheets of fine- tocoarse-grained sandstone. Some sheets are divided by thin shales into strata1 sets 2-3 m thick. Beds are 30-100 cm thick, and their basal surfaces are sure typically planarbut locally showminor erosional relief (Fig. 12). Sandstone sheets in the topmost three units at Jharkot are planar to low-angle laminated(Fig. 13; Column A, Fig. 11) with convex-up mounds.Primary current lineation was notnoted. Ripple cross-laminationand 10-40cm trough cross-beds arecommon at higherlevels. Sparsevertical burrows (Skolirhos?) arepresent locally.In othersections, sandstone sheets appear massive, but locally showplanar lamination, 8-25 cm troughcross-sets, and 20 - ripplecross-lamination. Asymmetric 2D-ripples are present at the p top of several units. Facies 4. Thick (upto 9.3 m)channel-based, medium-coarse- grainedsandstone. Sandstones are trough cross-bedded (Column B, Fig. 11). One unit at Jharkot is capped by a scour-based, 2 m planar cross-set of coarse sandstone (Column A, Fig. 11).
Facies 5. Nodular and ferruginous topmost strata (a few decimetres thick) with asymmetric ripples and (or) a pebbly cap. These strata commonly overlie an erosional surface. Two units are capped by a 0 thin coaly layer with roots. Facies 6. Thin (average 3 m) bedsets that coarsen up from shale to sandstone.These bedsets show siderite nodules, diffuse bioturba- Fig. 9. Measured sections of the Chukh Formation, Kagbeni to tion, and tough, nodular to undulating tops with roots and scattered Muktinath area, including reference section at Jharkot (JK1). See granulesand coarse sand (Column C, Fig. 11). Someshales are Fig. 4 for section locations. Locationsof cephalopod (C) and rooted. palynomorph (P) samples are shown.
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A OPEN SHELF -- v --c&Oiedtop- \, DISTRIBUTARY C 'X CHANNEL '------
SUBAQUEOUS l MOUTHBAR BAY FILL
Fig. 10. Cliff exposure on thewest bank of the Kali Gandaki at Kagbeni (KAl section). See Fig. 9 and 17 for detailed logs of the , ~-1 Chukh and Tangbe formations, respectively.C, Chukh Formation; l T, Tangbe Formation;S, green sandstone unit(17 m) at base of Tangbe Formation; U, = upper sandstone in Tangbe Formation l -2- above 43 m shale (forms scree slope at right). Thicknessof Chukh R l- SUBAQUEOUS Formation and Tangbe Formation up to the base of the upper MOUTH BAR sandstone is 263 m. The Chukh Formation restswith structural discordance on Tangbe shales, and contains numerous dislocations. II reworked top Note the prominent, tabular sandstones that cap coarsening-up units in the Chukh Formation. DISTRIBUTARY CHANNEL Theunits are interpreted asdeltaic progradational PRODELTA bodies(cf. Coleman & Prior 1980). Threevariants with suggested interpretations are shown in Fig. 11. Facies 1 and 2 are interpreted as prodelta deposits reworked by storms, as indicated by thepresence of hummockycross- stratification and combined-flow ripples. The predominance of thick, plane-laminated sandstones in the prodelta facies and in theoverlying mouth bar deposits(Facies 3) is unusual. Closely similardeposits were described by Martinsen (1990) fromthe British Namurian, where thick (up to 15 m) sheets of planar and cross-laminated sandstone are present. Martinsen attributed the planar lamination to Fig. 11. Depositional setting inferred for selected coarsening-up upper regime, density-current flows generated by frequent units of the Chukh Formation (locatedin Fig. 9). A: Jharkot intenseflooding in deltaic distributary systems. Facies 4 is section, 84-99 m interval. B: Kagbeni section, 53-72 m interval. C: interpreted as distributary channel deposits on the basis of Jharkot section, 37-70111 interval.
Fig. 12. Coarsening-up, 15 m unit in the Chukh Formation. Jharkot section,84-99 m position (Fig. 9). Unit rests abruptly on shales, and coarsens up from medium-to coarse-sandstone. Sandstones are planar laminatedbelow with trough cross-sets and ripple cross-lamination above. Unit is capped by a scour-based, planar cross-set2 m thick (p), which is truncated by a SO cm scour-based unit (S). Top ofunit shows no indication of subaerial exposure, and sandstone is overlain by shale. Scale (arrowed) is 1 m long.
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Formation. The shale units are up to 57m thick, black and bioturbated, with tough silty layers up to lOcm thick and minor sandstone beds with ubiquitous plant fragments and glauconite. Sideriteand pyrite concretions are commonin both sandstone and shale. Anoverlying 141 m of dark, fine- to medium-grained sandstone with sparseammonites and abundant vol- canoclastic detritus is present at Tangbe (top of CHHl and in T4). The lower part shows large-scale cross-beds, ripple cross-lamination, bivalves, and bioturbation. The upper part is conspicuouslyglauconitic but locally quartzose, with Trigonia and other bivalve genera. The shells form coquina layers up to 50 cm thick with disarticulated valves typically convex up.Planar lamination, cross-stratification, hum- mocky cross-stratification, bioturbation and plant fragments are common. Fig. 13. Close-up of planar laminated lower part of Fig. 12. Bed On the southern face of the Dzong Ridge (JK4, Figs 14 bases are even to slightly erosional. Hammeris 30 cm long. & 15), faulted outcrops comprisemainly stacked coarsening- up units of shaleand dark, volcanoclastic sandstone with hummocky cross-stratification and wave ripples. The basal scours overlainby unidirectionaltrough and planar bivalves Aucellina, Lima and Cercomya werepresent in cross-beds. Thetops of thesand bodies (Facies 5) show small outcrops below the base of one measured section evidence of subaerial exposure (roots and coaly layers) or, (JK4(3)), and an ammonite was found ex situ. These strata more commonly,show features indicative of wave are considered equivalent to the volcanoclastic sandstone at reworking duringrelative sea-level rise. Thethin, Tangbe. Little detail of the topmost Tangbe sandstones and coarsening-upand rooted bedsets that cap a few units shales on the Dzong Ridge (Dl, c. 170m) was obtained. (Facies 6) are interpreted as interdistributary bay deposits. Fourshale samples were barren of, or yielded sparse, Less probably, they could represent a barred, lagoonal stage palynomorphs,with dinocysts moreabundant than spores in a delta-top transgressional succession (cf. Penland et al. and pollen. Organic material was predominantly inertinitic, 1988). Capping alluvial deposits are lacking. suggestive of high energy or far-travelled material. At Jharkot, the basal deltaic unit is exceptionally thick Thepresence of thick sandstones withhummocky (28m), rests on outer shelf or upper slope deposits (Nupra cross-stratification, waveripples andmarine coquinas Formation)and may representa shelf-margin delta. suggests a storm-influenced,shallow marinesetting. The Younger, thinner units represent shelf-phase deltas. coarsening-up, subaqueousunits maybe associated with delta-lobeprogradation (Dott & Bourgeois 1982; Craft & Tangbe Formation Bridge1987). Theabundance of glauconitesuggests The TangbeFormation consists of darkto greenishgrey frequent episodes of condensation. The frequency of spores, sandstones and siltstones, intercalated with dark grey shale. the scarcity of bisaccates, the large amount of (degraded) A fewpebbly beds are associatedwith the sandstones. plant materialand the scarcity of dinocysts support a Glauconite and volcanoclastic grains are prominent in many nearshore setting. The dinocystassemblage is nearly sandstones. The formation rests conformably on the Chukh monotypic, suggestive of a restricted setting. Formation near Tangbe, but the contact is unconformable Foraminiferalassemblages in the CHHl section are of near Chyanche (section KA4). The formation is at least 500 low diversity and show a strong dominance of agglutinating m thick nearTangbe (Fig. 7) and shows considerable taxa (Fig. 16). The number of species varies from 2 to 12 geographic and stratigraphic variation in depositional style. (mean 6.4). TheTangbe assemblages thus diverge Tangbe shales can be distinguished from the Upper Jurassic significantly fromCretaceous normal-marine shelf as- Nuprashales whichlack glauconiteand silty and sandy semblages and, in accord with observations above, are taken interbeds. to indicate a varied but marked deltaic influence. Reduced oxygen levels were apparentlynot a restricting factor because the shales contain only moderateamounts of Tangbe and Dzong Ridge (CHH1, T4, D1, JK4) organic carbon (Fig. 16). The lowermost sample from the The basal 209 m of the Tangbe Formation near Tangbe(Fig. CHHl section(143) is moderatelydominated by 7) shows7) three thick (upto25 m)sandstone units Ammobaculites followedby Trocharnmina. The overlying intercalated with shale.The sandstones are fine- to samples (148-162) are strongly dominated by Trochammina coarse-grained and variablyglauconitic andquartzose. or contain only this genus. In modern settings, both these Sedimentarystructures include planar lamination, large- generatolerate low salinity conditionsand are common scale trough cross-beds, ripple cross-lamination andrare constituents of estuarine and deltaic assemblages, although gradedbeds, withwave-rippled andbioturbated bed tops they occur also in open-marine settings. A particularly high common.Shale clasts andplant fragments are present degree of deltaic influence is evidenced by sample 148 which locally, scattered in the sandstones or forming discrete contains onlytwo taxa,both belonging to Trochammina, pebbly layers. The tops of the sandstone units are locally with a species dominance of 93%. The sample was collected knobbly and glauconitic butnot rooted. Several coarse- from a sandy and silty shaleat the base of an upwards grained sandstone layers with abundant rounded glauconite coarsening sandstone unit (Fig. 7) and probably represents pellets are present in the lowerpart of theTangbe the beginning of adelta progradation phase. Samples153
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DZONG RIDGE and 154 were taken from the lower part of a thick shale unit with glauconitic,sandy horizons (Fig. 7). The calcareous JK4 (3) fauna1 component is 15% in sample 153 and 12 species are scattered sandstone present in sample 154, featuresthat reflect relativea outcrops (26 m) decrease of deltaic influence in thedepositional area. Sample 153 containsa few glauconitegrains in the 63-500 pmfraction of theforaminiferal preparations, whereas no glauconite was observed in this fraction of other samples. Coarsergrained, glauconite-bearing horizons, attributable to more open marine shelf conditions, were not analysed in this study.
Kugbeni (KA1) The base of theTangbe Formation here is abrupt and apparently coplanar with the underlying Chukh Formation (Fig. 10) but may be astructural contact. The section is divided into four large-scale successions (Fig., 17).
(1) A thick (17 m), multistorey sandstone with pebble lags (S in Fig. 10). Distinctive features include unidirectional cross-beds and A0_. abundant 1 m woody fragments. The unit is interpreted as a fluvial \\\ I or estuarine deposit. Plant fossils from this unit were identified by Bordet et ul. (1971) and Barale et al. (1978). (2) A progradational succession. Two basal coarsening-up units of intercalatedshale andsandstone with hummocky cross- stratification and wave ripples are capped by scour-based, pebbly sandstones with northward-directed trough cross-beds. An overlying TANGBE FM. fining-up unit contains hummocky cross-stratification and unidirec- tional ripples, and a succeeding thick (9.1 m), fining-up sandstone unit shows an abrupt, pebbly base and northward-directed trough cross-beds. The progradational succession concludes with six, sandy units, 3-5m thick, that variously coarsen and fine upward. Roots, plant fragments and thin coaly shales, bioturbation (Pulueophycus), JK4 (1) oscillatory and combined-flow ripples, and hummocky cross- stratification are present. The basal coarsening-up units probably reflect advancing delta lobes, and the capping scour fills and the succeeding fining-up unit are interpreted as subaqueous distributary channel deposits. The deltaic sediments were reworked periodically by storms. The thick fining-up unit is interpreted as a fluvial or estuarine body of the delta top.The six cappingunits, which containevidence for frequent subaerial exposureand wave reworking, are interpeted as the deposits of an interdistributary bay filled with crevasse splay or bayhead delta deposits (coarsening up) '5v and channeldeposits (fining up). These bayfill deposits could be 1
0 OW Fig. 15. South face of Dzong Ridge. Dark strata in mid face are Fig. 14. Tangbe Formation (dark, volcanoclastic sandstone of part of upper Tangbe Formation (T)(Section JK4 (3). 95 m thick, upper part) in faulted sections on Dzong Ridge. See Fig. 4 for Fig. 14). Pale strata (at least 25 m thick) of the Muding Formation section locations. (M) form the ridge crest.
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NUMBER OF DISTRIBUTION OF GENERA RELATIVE LEVEL SPECIES m Trochamminadominant OF TERRESTRIAL TESTS m Agglutinating m Ammobaculites 1 benthic IMPACT (% OF TOTAL TESTS) Calcareous benthic Subordinate benthic m HIGH LOW Planktonic 12345% Planktonic a- 3 ve rall distribution: 3verall m-5 Planomalina 2 Thalmanninella Pseudothalmanninella very IOW - no record g Praeglobotruncana (PX11.6) 10 Hedbergella S I
D
(127 8)
148 (35.5)
143 (16 2)
I Fig. 16. Foraminiferal data for the Tangbe and Muding Formations. Subordinate genera are: 1, Cribrosfomoides; 2, Haplophrugmoides; 3, Recurvoides; 4, Scherochorella; S, Spiroplecfummina; 6, Nodosaria; 7,Asfucolw; 8, Lenticulina. Organic carbon data from Rock Eval analysis by M.G. Fowler (pers. comm. 1992).
~ ------_ INTERDISTRIBUTARY BAY plantmatertal abundant KA1@ - . KA1 KAG BEN1 coaly layers, roots 101W, thin. coarsening- and fining-up units 102w NEARSHORE lzzl 17 waveripplesrare and HCS
OFFSHORE sparse line-sandstone
I------
2 channel fill 9 trough cross-sets (50 cm). N paleoflow erosional base with pebblylag wave-reworked top NEARSHORE coarsening-up units. coarsenlng-up untts below ‘. ’ ‘ F g cappedby cross-bedded scour lllls shale dominated 140 unlts thicken and shale proportion -- / HCS rlpples+ wave .. . bioturbation increases upward ,X I reworked unit tops (progressive deepening) HCS +wave rlpples minor bioturbation slderite nodules In sandstones
multistorey, fining-up channeli valley fill - pebbles In lags andon trough bases 120 1 cross-setstrough (30 cm) Fig. Tangbe Formation at Kagbeni, ,- N paleoflow 17. *“op L? with inferred depositional setting. See
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KA4 CHYANCHE COASTAL I NEARSHORE (RETROGRADATIONAL)
thin, coarsening- and fining-up units KA3
HCS + SCS? + wave ripples + gravel ripples bioturbation common bivalves
no exposure local channelised bases (25.6 m) fining-upto units Fig. 19. Unconformity between the Chukh Formation (C) and basal trough cross-sets (20 cm) 8 m of Tangbe Formation (T) at theChyanche section (KA4, see Fig. 18 for stratigraphic log). Strike and dipof beds changes from 080"/46"N to 096"/56"N across the unconformity. The beds are steeply dipping, but show little indication of structural disturbance. Topmost unit of the Chukh Formation is a pale, cross-stratified sandstone. Basal unit (1) of the Tangbe Formation is a ferruginous, 3 wavy-bedded sandstone with hummocky cross-stratification. Above is a volcanic granule to pebble conglomerate overlain by a fluvial sandstone (2) with large-scale inclined stratification.
part of a transgressive succession (Penland er al. 1988). The progradational unit thus shows successive nearshore, delta front to top, and interdistributary bay deposits. (3) Aretrogradational succession. The succession commences L1 (upto~~m~ong) with six coarsening-upunits with hummocky cross-stratified and gz abundant wave-rippled sandstones. The unitsincrease in thickness and proportion of shaleupward, and are overlain by dark grey shale ~- Y7 coal, roots with sparsesandstone beds (43m). The coarsening-upunits thin, coarsening- and resemble in somerespects thedelta lobe deposits of theChukh Formation (Facies 1, above),and indicatedeposition on a fining-up units nearshore shelf. The thick shales are interpreted as anoffshore shelf -- l 3* sparse bioturbation deposit. A (4) A majorsandstone body. The base of thisthick, dark sandstone (the lower part of the Gr2s de Dzong of Bassoullet & RIVER I ESTUARY Mouterde 1977; Table 1) is apparently conformable, but the strata are so deformed that areliable section couldnot be measured. LL multistorey,fining-up Ammonites (see below) and the bivalve genera Enfoliurn, Panopaea channel/valley fill and Trigonoarca?, are present. The basal unit(8.5 m) is parallel-laminated with shale clasts, plantfragments and a channelised unit bases &L &L wave-rippled cap. Higher units are 3-10 m thick and intercalated pebble conglomerates with shale. They contain tabular layers of fine sandstone, typically trough cross-sets about 40cm thick, that show hummocky cross-stratified sandstone (40 cm) capped by wave-rippled sandstone, overlain in turn by shale (HXM N paleoflow type of Dott & Bourgeois 1982). Sequence bases are abrupt and one plant material sandstone top showed the ichnofossils Gyrochorfe cornosa, Rhizocorallium parallelurn. and Arenicolites (Cruziana ichnofacies: sparse wave ripples Frey 1975). Some layers overlie erosionally based lags, up to 40 cm + HCS thick, of inoceramid bivalve debrisand shale clasts (cf. Dott & Bourgeois 1982; Craft & Bridge 1987). Thetabular layers are locally stacked in groups up to 1.5 mthick, with sandstones amalgamated or separated by thinshales. The layers reflect the passage of major storms, following which trace-makers recolonised the sea floor.
Chyanche (KA3, KA4) The most complete Chyanche section (KA4, Fig. 18), which Fig. 18. Tangbe Formation atChyanche, with inferred depositional formsthe basis of the following description, contains an setting. See Fig. 4 for section locations. unconformable Chukh/Tangbe formation contact (Fig. 19).
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Conglomerates just above the base of the Tangbe Formation containmetamorphic, reworked carbonate and probable Triassic sandstonefragments, indicative of widespread erosion at this level (S. Diirr, pers.comm. 1992). An unconformity capped by thick conglomerates is also reported south of Kagbeni and west of the Kali Gandaki (E. Garzanti, pers. comm. 1992). The base of theTangbe Formation is notseen in section KA3, whichshows reasonable correlation with KA4 (Fig. 18). Three large-scale successions are recognized within the sections (Fig. 18):
(a) A volcanic conglomerate and sandstone succession about 25 m thick, that contains four fining-up units. The initial 2.6m unit is highly ferruginous and contains hummocky cross-stratification. The overlying unit, 7.2 m thick, shows a basal (2.1 m) layer of granule and pebbleconglomerate (8 mm average clast size, 14cm maximum) with a prominent volcanic component. The conglomer- ate is clast-supported with a very fine sand matrix, and clast Fig. 21. Channel fill cut through shallow marine strata in Tangbe long-axes lie parallel to weakly developed stratification. Overlying Formation at Chyanche. Basal strata (at right) are planar-bedded sandstonescontain trough cross-sets. Succeeding units, 8 m and fine sandstones with hummocky cross-stratification. Channel-fill unit 11.5 mthick, show erosional (locally deeply incised) bases and is 2 m thick, cuts down 1 m through underlying strata and contains 20cm cross-sets and abundant woody material. Top surface of fill (not visible) is a planar surface with wave ripples. Section KA4, 78-86 m interval (Fig. 18). Hammer is 30cm long.
unidirectional trough cross-sets and ripple cross-lamination. Indurated, ferruginous layers, broken up and partially incorporated into suprajacent units, along with one volcanic-conglomerate clast, suggest early lithification of some beds. The channelized bases and fining-up nature of the units and the unidirectional flow indicators suggest a fluvial or estuarine setting. The conglomeratefabric is consistent with a stream-flow, rather than a debris-flow, origin. (b) A succession with thin, coarsening- and fining-up units with woody material, roots and coals. The units are broadly similar to the inferred interdistributary bay deposits at Kagbeni (see above). (c) A succession with prominent marine biota. The strata con- tain inweramid shell fragments and a diverse assemblage of ichno- fossils typical of the Cruziana ichnofacies: Thalassinoides sueuicus, Lockeia, Bergaueria langii,Palaeophycus, Rhizocorallium, Arenicolifes,Diplocraferion? and Chondrites. Coarsening-up units are prominent and show wave ripples, probable swaley cross- stratification (Leckie & Walker 1982) and hummocky cross- stratification, the latter including large, regularly spaced hummocks with a complex internalgeometry (Fig. 20). AlOcm granule- conglomerate bed with symmetrical ripples suggests storm activity (gravel ripples are the hydraulic equivalent of hummocky cross-stratification: Leckie 1988). One coarsening-up unit is capped by a @cm planar cross-set with extrabasinal clasts and bivalve and plant fragments. Erosionally based, fining-up units, 2-2.5 m thick, (Fig. 21) show trough cross-stratification, plant material and abundant bioturbation. Their tops are typically reworked, with wave ripples, intense bioturbation and (or) truncation of underlying beds.This topmost succession is interpreted as coastal/nearshore deposits. The coarsening-up units probably represent the fringe of prograding, wave-reworked deltaic or coastal sand bodies. The fining-up units are interpreted as deltaic or tidal-channel deposits in view of their association with bioturbation and wave activity.
Fig. 20. Pinch-and-swell unit, 80 cm thick, in Tangbe Formation at Correlation of sections Chyanche. Unit forms part of gradationally based (to left) unit of fine sandstone 3 m thick (37-40 m interval of Section KA3, Fig. 18). The upper parts of the Tangbe and Kagbeni sections and Swell bases appear scoured, andunit contains multiple sets faulted segments of the Dzong Ridge include thick (140 m at (20-60 cm thick) of inclined strata with internal truncations and Tangbe)dark sandstones that are richin volcanoclastic apparent reversals of flow direction (probably hummocky materialand yieldbivalves andEarly Aptian ammonites cross-stratification). Stratification at topof swells is form- (see below). These strata form the basal part of the Grts de concordant. Pole is 75 cm long. Dzong of Bassoullet & Mouterde (1977), and are considered
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correlativeacross the study area. The underlying, basal succession was observed.Sample JKl-1OlW from the lowermost interval of theTangbe Formation is consideredbroadly sandstone bed of the ChukhFormation yielded Blunfordicerus correlative across the area but shows systematic stratigraphic wullichi (Gray), Pronicerus muzenoti Collignon and Bochiunites sp. and sedimentologicalchanges from south northto cf. buculoides Arnould-Saget (Fig. 22, A, B). From the uppermost (Chyanche to Kagbeni to Tangbe). 5 m of highly concretionary black Nupra shale, sample JKl-102W (1) The intervalthickens northward from Kagbeni yielded Blunfordiceruswullichi (Gray), Pronicerus cf. muzenoti (153 m) to Tangbe (209 m). Collignon, and Bochiunites sp. cf. buculoides Arnould-Saget, and (2)Both the Chyanche and Kagbeni sections show an sampleJKl-103W yielded Spiticerus (Sp.) cf. obliquelobutum upward transitionfrom afluvial/estuarine to a nearshore (Uhlig) (Fig. 22 C)and Huplophyllocerus strigilis (Blanford). setting. The basal volcanoclastic sandstone and conglomer- Sample JKl-lMW, representative of the underlying 15 m of dark, ateat Chyanche is probablycorrelative with the basal deformed Nupra shale, yielded again Blunfordicerus wullichi (Gray) multistorey sandstone at Kag Beni, based on petrographic (Fig. 22 K, L), B. ucuticostu (Uhlig) (Plate1, Figs H, I) and criteria (S. Diirr, pers. comm. 1992). Huplophyllocerus strigilis (Blanford). A similar but less fossiliferous stratigraphic succession is exposed in section MU4, 1 km west of the (3) The presenceat Chyanche of conglomerates,the Muktinath monastery. Sample MU4-1OlW from uppermost Nupra relatively high sandstone:shale ratio and a30 m intervalwith concretions andabout 7m of basal Chukhsandstones yielded an abundant neritic fauna at the top of the section suggest a Blunfordiceruswullichi (Gray), and sample MU4-102W from 20m more proximal setting,although local facies variability of underlying Nupra shale with a basal belemnite breccia yielded cannot be ruled outentirely. These coarse-grained units Belemnopsis ulfuricus (G.Boehm) (Fig. 22 D, E) and B. gerurdi apparently wedge outnorthward towards Tangbe. Shales (Oppel). In section MU5, 1 km northeast of Jharkot near Purang, form a higher proportion of measured sections near Tangbe, sample MU5-1OlW from 20m of upperNupra shale yielded roots and coals are absent, and shallow marine invertebrates Blunfordiceruswullichi (Gray) (Fig. 22 M,N), Spiticerus (Sp.) cf. and trace fossils are much less abundant. plunum (Uhlig) (Fig. 23 C, D), Pronicerus cf. muzenoti Collignon (4) The formation base changes from unconformable to and Huplophyllocerus strigilis (Blanford). These faunas are conformable northward, although the presence of disconfor- considered to represent the equivalent of the ‘Blunfordicerus mities in the Tangbe section cannot be ruled out. assemblage’ of Spiti (Krishna et al. 1982) or the ‘Blunfordicerus- Theseobservations, coupled with thenorthward Huplophylloceras assemblage’ of Wiedmann (in Gradstein et al. paleoflow, suggest a proximal to distal trend northward. The 1992) and to be of Late Tithonian age. Early Cretaceous affinities of relatively abruptchanges in the basal TangbeFormation some specimens (e.g. Bochiunifes, Spiticerus) confirm that the probably reflect tectonic assembly of formerly widely sampled sections are high in the Tithonian. separated facies. The uppermost few decametres of the Nupra shale at Jharkot contain foraminifera indicative of a latest Tithonianage and documented fully by Gradstein et al. (1992). Muding Formation A dinoflagellate cyst assemblage with Kulypteu wisemuniue The Muding Formation is a greenish grey succession of Stover and Helby (Fig. 24, No l), Butioludinium spp. Brideaux and marlstone,sandy marlstone and calcareoussandstone and ?Cyclonephelium spp. Deflandre and Cookson was identified in siltstone, at least 25 m thick, which lies near the top of the sample MU1-5GK from an isolated occurrence of basal Chukh Dzong Ridge (Fig. 15). Premoli Silva et al. (1992) described sandstones overlying Nuprashale near Muktinath (Fig. 4, a 40.2111 section in this area. The foraminiferal assemblage approximate stratigraphic level shown in Fig. 7). This assemblage is indicative of an early Berriasian age based on zonations used in NW obtained during the present study (Fig. 16) comprises nine Australia (Helby et ul. 1987). A Berriasian age is also assigned to planktonic taxa, about five agglutinated and more than eight the upper part of the Chukh Formation at Tangbe which yielded calcareous benthic species, with 4% of benthic tests and a (sample CHHl-140GK, Fig. 7) a spore/pollen assemblage including p1anktonic:benthic ratio of 11.6. The high abundance of Pilosisporites notensis Cookson andDettmann, Microcuchryidites planktonictests suggests an outer shelf toupper slope antarcticus Cookson, Cicutricosisporites spp.and Contignisporites depositional setting. The presence of tubular benthic tests, cooksoniue (Balme) Dettmann (Fig. 24, Nos 5-7). The presence of although in small numbers, is in accordance withsuch a the dinocyst Egmontodiniumtorynum (Cooksonand Eisenack) setting. Dinocysts and calcite-replaced radiolaria were noted Davey (Fig. 24, No 2, 3) in thissample furthersupports a duringthe present study, and calcareousnannofossils, Berriasian age (Helby et al. 1987). Shales from a faulted section of ostracods,calcispheres, echinoids, molluscs, dasycladacean theChukh Formation on the Dzong Ridge (JK4-7MG) yielded algae and siliceous sponge spicules were reported addition- Contignisporifes cooksoniue and Cicutricosisporites spp.. indicative ally by Garzanti & Pagni Frette (1991) and Premoli Silva et of an Early Cretaceous age. al. (1992). These data collectively indicatetopmosta Tithonian to Late Cretaceous and early Palaeogene strata are present Berriasian age for the Chukh Formation. elsewhere in theHimalayas (e.g. Zanskar: Gaetani efal. 1986). Strata of this age may have beendeposited in Tangbe Formation Thakkhola but subsequently removed by erosion. Bordet et al. (1971) reportedEarly Aptian ammonites from the middle part of the formation, and EarlyAptian ammonites were Biostratigraphy collected in situ in1991 from severallocations. An Early Aptian Forbesi Zone (?) age may be indicated by thepresence of Deshuyesites cf. normuni Casey(Fig. 23, H) in sample CHHl-20 Chukh Formation from the upper part of the Tangbe section (Fig. 7). A mid-Lower LatestTithonian cephalopod faunas were found in sectionsJK1, Aptian Deshayesi Zone age is indicated by thepresence of MU4 and MU5 in the Muktinath-Jharkot area (Figs 4, 22 & 23). At Tropueum hillsi (J. de C. Sowerby) (Fig. 23, E) in a loose sample the well-exposed transitional section between the Nupra/Spiti and collected near Chyanche and by Deshuyesites sp. in a loose sample ‘Chukh formations at JK1 (Fig. 9), the following cephalopod collected near section JK4(2)on the Dzong Ridge. A late Early
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AptianBowerbanki Zoneage is confirmed by the presence of degraded plant material. These, however, were not age diagnostic, Dufrenoyia sp. juv. (cf. D. sp. nov.? in Casey 1964, p. 394, pl. 64, andthe duration of the hiatusrepresented by the unconformity fig. 2) (Fig. 23, F) fromthe top of the CHHl section, and between the Chukhand Tangbe formations couldnot be Dufrenoyia mackesoni Casey(Fig. 23, A, B, G) from sample determined.Plant fossils reported by Bordet et al. (1971) and KAl-IOIW just above the measured section at Kagbeni (Fig. 17). Barale et al. (1978) from the basal Tangbe sandstone at Kagbeni Fine-grained strata were sampled for foraminifera at five levels yielded a generalised Early Cretaceous age. of the CHHl section at Tangbe (Figs 7 & 16). The >63 pm fraction Garzanti & Pagni Frette (1991) and Premoli Silva et al. (1992) was used in analysis, and the samples contained assemblages large reported Late Albian planktonic foraminifera from the uppermost enough for quantitative treatment (Fig. 16).The assemblages greensand interval of the Tangbe Formation on the Dzong Ridge. include comparatively large numbers of diagenetically deformed Samples collected during the present study from the same interval tests and previously undescribed taxa, and an extensive use of open on the Dzong Ridge yielded no planktonic foraminifera. nomenclature is currently necessary. SampleCHH1-143 yielded The above analysis shows that the Tangbe Formation contains Cribrostomoides canui Cushman, Haplophragmoides sp., Valanginian, Hauterivian and Lower Aptianstrata, with a Late Ammobaculites aff. gerkei Sharovskaya, Recuruoides cf. excellens Albian agereported for the topmost part of theformation. No Ryggina, Trochammina aff. mugiensis Dain, T. aff. schaimica Barremian or Upper Aptian to Middle Albian fossils have yet been Kisseleva and Lenticulina sp. (Fig. 25, Nos 2-4, 8). Sample identified. The common glauconitic layersindicate frequent CHHI-148 yielded Trochammina mugiensis and T. aff. schaimica. condensation, and hiatuses within the succession cannot be ruled Sample 153 yielded Trochammina ficta Romanova, T. aff. out. mugiensis, Nodosaria sp., Astacolus aleskerouae Romanovaand Astacolus sp. (Fig. 2.5, Nos 5, 6). SampleCHHl-1.54 yielded Scherochorella sp., Haplophragmoides sp., Ammobaculites aff. gerkei,Recurvoides cf. excellens, Spiroplectammina sp., Muding Formation Trochammina aff. composita Bulynnikova, T. aff. mugiensis, T.aff. Analysis of three carbonate-cemented marlstone samples from the schaimica, Lenticulina sp., Astacolus aleskerovae and Astacolus sp. Dzong Ridge shows that planktonic foraminifera are common (Fig. (Fig. 2.5, Nos 1, 7, 9).Sample CHHI-l62 yielded Ammobaculites 16) whereas benthic foraminifera are sparse and poorly preserved. aff. gerkei, Trochammina ficta, T. aff. mugiensis, T. aff. schaimica Foraminiferal tests in amounts adequate for quantitative treatment and Astacolus sp. could not be extracted owing to the strongly cemented nature of the The foraminiferalassemblages have significant affinity with sediment. The benthic fauna1 component includes tubular tests assemblages fromSiberia andother Arctic localities, facilitating similar to Bathysiphon and Rhizammina, and planispiral forms correlation with these regions. The range of Cribrostomoides canui comparable to Ammodiscus and Haplophragmoides. The single terminates in the Berriasian in Spitsbergen (Nagy et al. 1990) and in benthic form determined at the generic level is Lenticulina sp. The the Valanginian in theCanadian Arctic(Souaya 1976). The rather rich planktonic component previously recorded by Gradstein occurrence of thisspecies 16m abovethe base of theTangbe et al. (1989a, 1992) includes Planomalina buxtorji (Gandolfi) (Fig. Formation but its absence from younger samples accords with the 25, Nos 10-12), Thalmanninella appenninica (Renz), T. gandolfii Berriasian age suggestedfor the underlying Chukh Formation (LuterbacherPremoliand Silva), T. brotzeni (Sigal), (above). Trochammina ficta and ASI~CO~USaleskerouae were Pseudothalmanninella ticinensis (Gandolfi)(Fig. 25, Nos 13, 14), reported from Valanginian strata in Siberia by Bulynnikova et al. Praeglobotruncana delrioensis (Plummer), Hedbergella simplex (1990). Four speciesrecorded under open nomenclature from the (Morrow), H. costellata Saint-Marc and H. cf. rhinoceros Coccioni. TangbeFormation (Ammobaculites aff. gerkei, Trochammina aff. The ‘sugary’ preservation of the specimens did not allow Ticinella schaimica, T. aff. mugiensis and Recuruoides cf. excellens) show species to be distinguished, but Premoli Silva et al. (1992) recently generally Valanginian to Hauterivian affinities. Comparative taxa in identified from theDzong Ridge section Ticinella roberti western Siberia show the following ranges,according to (Gandolfi), T. primula (Luterbacher), T. raynaudi Sigal and Bulynnikova et al. (1990): A. gerkei (Late Berriasian to Early Biticinella breggiensis (Gandolfi). The planktonic assemblage Valanginian), and the closely similar A. subasper (Late indicates a latest Albian age (Buxtorfi-Ticinensis and Buxtorfi- Hauterivian); T. schaimica (Hauterivian); T. mugiensis (Early Appenninica Zones: Gradstein et al. 19890, 1991), and is of low- to Hauterivian). R. excellens occurs in theValanginian in Prikaspiya mid-latitude character. Premoli Silva et al. (1992) alsoinferred a (Azbel & Grigjalis 1991). These observations strongly suggest the Late Albian age for these strata. presence of theValanginian and Hauterivianstages in the lower The presence in sample D1-178GK from the Dzong Ridge of a 170m of the Tangbe Formation in the CHHl section.A closer diverse dinocyst assemblage with Litosphaeridium siphoniphorum delineation of the two stages will require further analysis. (Cookson and Eisenack) Davey and Williams, Xenascus ceratioides The upperpart of the Tangbe Formation(sample T4-175GK) (Deflandre)Lentin and Williams, Xiphophoridium alarum yielded poorly preservedspecimens of the dinocyst Dingodinium (Cooksonand Eisenack) Sarjeantand Odontochitina operculata ceruiculum (Fig. 24, No. 4), indicative of a Late Hauterivian to (0.Wetzel)Deflandre and Cookson indicatesa Late Albian to Early Albianage (Helby et al. 1987). Shalesfrom the Chyanche Cenomanian age by comparison with the Australian record (Helby sections yielded spores, bisaccates, poorly preserved dinocysts and et al. 1987).
Fig. 22. Ammonites from the topmost Nupra Formation, Thakkhola, Nepal. Arrows indicate position of last suture line. (A & B) Bochianites sp. cf. baculoides Arnould-Saget. GPIT 1751/1. Dorsal (A) and lateral (B) views. 1/1. Topmost Tithonian,Blanfordiceras-Haplophylloceras assemblage. Nupra Formation, Sample JKl-10IW. (C)Spiticeras (Spiticeras) cf. obliquelobatum (Uhlig). GPIT 1751/2. Lateral view. 1/1. Same age as A,B. Nupra Formation. Sample JKl-103W. (D) Belemnopsis alfuricus (G. Boehm). GPIT 1751/3. Lateral view. 2/3. Topmost Tithonian. Nupra Formation. Sample MU4-102W. (E)Same species. GPIT 1751/4. Lateral view. 2/3. Same age and locality. (F & G) Haplophylloceras strigilis (Blanford). GPIT 1751/5. Ventral (F) and lateral (G) views. l//l. Same age as A,B. Nupra Formation. Sample MU5-IOIW. (H& I) Blanfordiceras acuticosta (Uhlig). GPIT 1751/6. Front (H) and lateral (I) views. 1/1. Same age as A,B. Nupra Formation. Sample JK1-104W. (K & L) Blanfordiceras wallichi (Gray). GPIT 1751/7. Ventral (K) and lateral (L) views. 1/2. Same age and level as H,I. Nupra Formation. Sample MU5-10IW. (M & N) Same species. GPIT 1751/8. Lateral (M) and ventral (N) views. 1/2. Same age. Nupra Formation. Sample MU5-101W.
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Fig. 24. Palynomorphs from the Chukh and Tangbe Formations, Thakkhola,Nepal. Photographs taken underlight microscope. Default magnification is approximately X680. (1) Kafypfeawisemaniae Stover & Helby 1987. Sample contains one specimen from which the presence of an intercalary archeopyle could not be verified. ~340.The total length of the cyst is approximately 220 pm. Chukh Formation,sample MUl-5GK. (2 & 3) Egmonfodinium forynum (Cookson & Eisenack 1960) Davey 1979. Chukh Formation, sample CHHl-140GK. (4) Dingodinium ceruiculum Cookson & Eisenack 1958 emend. Mehrotha & Sarjeant 1984. Upper part: focus at horn; lower part: focus at body. Tangbe Formation, sample T4-175GK. (5) Microcachryidifes antarcticus Cookson 1947. Chukh Formation, sample CHH1-140GK. (6) Confignisporifes cooksoniae(Balme 1957) Dettmann 1963. Chukh Formation, sample CHHl-140GK.(7) Pilosisporites nofensis Cookson & Dettmann 1958. ~430.Chukh Formation, sample CHH1-140GK.
Nature and distribution of volcanic detritus hawaiites. Geochemical analysis indicates that the rocks are The nature of the volcanic detritus has been studiedby Diirr slightly undersaturated alkali basalts of within-plate affinity (1992 and pers. comm. 1993). Volcanic detritus is sparsely (Pearce et al. 1981; Pearce 1982). The presence of rare distributed in the BerriasianChukh Formation atTangbe perlite pebbles points to bimodal volcanism with subordin- and Jharkot, but is abundant in the Valanginian toLate ate rhyolitic or dacitic rocks. Preliminary work indicates no Albian Tangbe Formation. Volcanic pebbles at the base of significant change in the microscopic appearance of volcanic the TangbeFormation at Chyanche show a pilotaxitic grains through the Tangbe Formation. texture, with therare plagioclase phenocrystsmore calcic thangroundmass plagioclase. Rounded, devitrified glass sherds are common, and amygdales up to 2 mm in diameter Cretaceous regional correlation are present in most pebbles. Calculation of Rittmann values Early Cretaceousreconstructions of Gondwana (Powell et (Rittmann 1973) indicatesthat the rocks are olivine al. 1988; Fig. 1) show thatthe mid-Jurassic to
Fig. 23. Ammonites from the topmost Nupra and Tangbe Formations, Thakkhola,Nepal. Arrows indicate position of last suture line. (A)Dufrenoyia mackesoni Casey. GPIT 1751/9. Lateral view. 1/1. Bowerbanki Zone, Transitoria Subzone, late Lower Aptian. Tangbe Formation, top KAl section. Sample KAl-102W. (B)Same species. GPIT 1751/10. Lateral view of latex cast. 1/1. Same age and section. Sample KAl-101W. (C & D) Spificeras (Spificeras)cf. planum (Uhlig). GPIT 1751/11. Ventral (C) and lateral (D) views. 1/1. Topmost Tithonian, Blanfordiceras-Haplophylloceras assemblage. Upper Nupra Formation. Sample MUS-lO1W. (E)Tropaeum hihi (J. de C. Sowerby). GPIT 1751/12. Lateral view of initial living chamber. 1/2. Topof Deshayesi Zone, middle Lower Aptian. Loose, 1 km east of Chyanche, Tangbe Formation. Sample KA3-1OlW. (F) Deshayesites sp. juv. (cf. Dufrenoyia sp. nov.? in Casey 1964). GPIT Ce 1751/13. Lateral view of fragmentary specimen. 2/1. Same age as A. Tangbe Formation.Section CHHl, upper part of section (MS coll.). (G) Dufrenoyia mackesoni Casey. GPIT 1751/14. Lateral view of living chamber. 1.5/1. Same age and place as B. (H) Deshayesites cf. normnni Casey. GPIT 1751/15. Oblique view of fragmentary specimen. 2/1. Forbesi Zone, ?early Lower Aptian. Tangbe Formation. Section CHHl, unit 20 (FG coll.).
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Fig. 25. Foraminifera from Thakkhola, Nepal. Specimens 1-9: Tangbe Formation, Chukh. Specimens 10-14: Muding Formation, Dzong Ridge. (1) Scherochella sp. 1. X230. Sample CHHI-154GK. (2) Ammobaculites aff. gerkei Sharovskaya. ~108.Sample CHHI-143GK. (3 & 4) Trochammina aff. mugiensis Dain & Bulynnikova. X 148 (transmitted light), X 185. Sample CHHI-143GK. (5 & 6) Trocharnrninaficfa Romanova. ~153,X 189. Sample CHHI-153GK. (7 & 8) Trochammina aff. schairnica Kisselova. Sample CHHI-I54GK, ~153.Sample CHHI-143GK. X 166. (9) Asfacolus aleskerouae Romanova. X112. Sample CHHI-154. (10,11& 12) Planornalina buxtorfi (Gandolfi). ~72, x112, x81. Sample DZ-SB. (13 & 14) Pseudofhalmnnninella ticinensis (Gandolfi). ~90,~81. Sample DZ-5B.
mid-Cretaceous was a period of crustal extension and rifting mid-Oxfordian (Fig. 26). The FerruginousOolite and the between Greater India, Australia and Antarctica. Strata of hiatus are presentalong much of theHimalayan Tethyan this age on the Greater India margin are known from widely belt (Krishna 1983; Westermann & Wang 1988; Hallam & separatedand deformed strata. Consequently, the tec- Maynard1987; Garzanti et al. 1989; Gaetani & Garzanti tonostratigraphicevolution of Thakkhola is interpreted 1991). A correspondinghiatus is recognized on the throughcomparison with theconjugate NW Australian Australianmargin whereit is inferred to reflect breakup margin (Fig. 26),for which abundantdata are available north of the Exmouth Plateau (Boyd et al. 1992; Fig. 26). from seismic, drilling andoutcrop studies (Boote & Kirk The oldest ocean crust below the Argo Abyssal Plain north 1989; von Rad et al. 1992; Gradstein et al. 1990; Gradstein of theExmouth Plateau (Fig. 1) is lateOxfordian in age & von Rad 1991;Boyd et al. 1992; von Rad & Bralower (Gradstein et al. 1990; Fig. 26). An early to mid-Callovian 1992). Study of the many seismic lines across the margin has transgressionhas been recognizedglobally (Hallam 1988; enabled regional discontinuities to be mapped and related Haq et al. 1988). confidently to the region’s tectonic history. The deltaic deposits of the Berriasian Chukh Formation The FerruginousOolite/Nupra Formation contact in in Thakkhola correspond to fluvial and deltaic deposits of Thakkholamarks hiatusa from latest Callovian to the Barrow Group on the Australian margin where clastics
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were supplied by widespread uplift of rifted margins (Boote (1991) inferred that progressive deepening resulted from a & Kirk 1989; Hocking et al. 1988; Boyd et al. 1992). Deltaic pulse of ocean crust production (Fig. 26), primarily in the systems in both areas prograded northward. The Australian Pacific Ocean. Theabundance of glauconiteboth in deposits comprise the Barrow Sands of the Exmouth Plateau Thakkhola and Australia suggests a limited detrital supply andthe lower part of theNanutarra Formation and during this transgressive phase. YarraloolaConglomerate of the NWShelf (Fig. 26). The On the Argo Abyssal Plain north of Exmouth Plateau, geometry and area1 extent of individual deltabodies is Berriasian or Valanginian sediments include bentonites (von unknown,and it remainsuncertain whether autogenetic Rad & Thurow 1992). Atthe westernfoot of Exmouth (delta-switching) or allogenetic (eustatic or tectonic) factors Plateau,uppermost Valanginian sediments withvol- controlled their stacking. canoclastic material are interbedded with Fe-rich, tholeiitic The base of the Tangbe Formation in Thakkhola is not basaltic sills (Gradstein et al. 1990), andindicate a dated precisely but a Valanginian age is inferred; the contact Valanginian datefor separation of Greater Indiaand varies from unconformable to conformable northwards. The Australia. basal Tangbe strata near Kagbeni are fluvial deposits that During the latest Albian,deep-water carbonate sedi- pass northwardinto shelf deposits.Younger strata show ments (Muding Formation) appeared in Thakkhola, and are progressive deepening to sandyand muddy nearshore and broadlyage-correlative with the HaycockMar1 andother offshore shelf deposits through to the Late Albian. On the calcareous deposits ofthe Australian margin. Detrital Australian NW Shelf andExmouth Plateau, late a sediment (Gearle Silstone) persisted in more proximal parts Valanginian to early Hauterivian ‘breakup’ unconformity is of the Australian margin until the Late Cretaceous. From present,and overlying strata show a northward, fluvial to paleomagnetic evidence (Klootwijk & Bingham1980; offshore transition from the YaraloolaConglomerate and Powell et al. 1988; Gradstein et al. 1992), Thakkhola lay NanutarraFormation tothe BirdrongSandstone, Mardie south of the tropical belt during the Early Cretaceous but Greensandand Muderong Shale (Fig. 26). The shelf wasmoving northward in Albiantime. The upward deepened progressively. The basalunconformity was transition to carbonates may reflect input from calcareous inferredto represent final breakupbetween Greater India plankton related to a northward drift,, andAustralia along the Gascoyne and Cuvier Rifts south Break-upand oceanic subsidence in theGascoyne and west of the Exmouth Plateau (Boyd et al. 1992). Larson Abyssal Plain at about 130 Ma (Gradstein & von Rad 1991)
OCEAN NW AUSTRALIANNW MARGIN ‘ECTONIC CRUST AGE EVENTS, PRODUCT- ION Ma iXMOUTH - PLATEAU RATE
l00
120
DRIFT OF GT INDIA FROM AUSTRALIA
i Fig. 26. Correlation chart for Early Cretaceous strata of Central Nepal (this study) and the northwest Australian BREAKUP l margin. Columns for Exmouth Plateau 140 S OF and tectonic events from Boyd et al. EXMOUTH PCATEAU (1992). Other Australian margin data from von Rad et al. (1989) and RIFT TO Gradstein et al. (1990). Volcanic rocks FINAL BREAKUP at the base of the Argo column have been dated radiometrically (Gradstein et al. 1990). Ocean crust production rate
BREAKUP from Larson (1991). Timescale from NOF 1 Harland et al. (1990). F.O., Ferruginous 16C 7’,9”,’,”LOW - HlGt - Oolite.
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are not reflected by changes in subsidence and sedimenta- Conclusions tion on the Thakkhola burial profile (Fig. 3). However, this (1) Tethyan strata in Thakkhola, Nepal were deposited apparent lack of correspondence may resultfrom unwar- on thenorthern Gondwana continental marginwhich rantedsmoothing of theage-depth curve forthe subsided steadily from the Jurassic to the mid-Cretaceous. Valanginian-Barremian and Early-Mid-Albian periods, for Three Early Cretaceous formations, at least 625 m thick in which more biostratigraphic data are needed. total,are recognized in relatively completesections near Whereas the Oxfordian-Tithonian ammonites from the Tangbe:the Chukh (Berriasian), Tangbe (Valanginian to Nupra Formation (as well as those from the Spiti Shale) are Albian) and Muding (latest Albian) formations. The strata mainly endemic or regionally restrictedspecies of the rest conformably on theNupra Formation, correlative Indo-Madagascan fauna1 province,those of theEarly regionally with the Spiti Shale. Aptian Tangbe Formation are cosmopolitan species. This is (2) The Early Cretaceous strata, principally sandstones surprising in view of thecontinental slope setting of the and shales, show northward palaeoflow and an upward NupraFormation and the shallow marineto nearshore deepening trend. Deltaic deposits (Chukh Formation) pass setting of the Tangbe Formation, and remains unexplained. up intostorm-dominated shelf deposits with reworked, Volcanic detritus in theThakkhola Early Cretaceous distal deltalobes and glauconitic,condensed horizons strata wasinitially inferredto beof ophiolitic origin and (Tangbe Formation). Pelagic, continental slope marlstones shed from a rising collisional belt tothe north (Gansser (Muding Formation)cap the succession.Fluvial vol- 1964; Bordet et al. 1971). However,more recent studies canoclastic rocks overlie a local unconformity at the base of (Gaetani et al. 1986; Sakai 1989; Gradstein et al. 1989a; the Tangbe Formation. A northward facies transition within Gaetani & Garzanti 1991) have related volcanic detritus in theTangbe Formation is disjunct and compressed dueto the Tangbe Formation and Giumal Sandstone to extensional Himalayan crustal shortening. volcanism associated with Gondwananfragmentation. (3) Volcanoclastic detritus is sparse in theBerriasian Geochemical analysis of Tangbe volcanics indicates a Chukh Formation but abundant in the Tangbe Formation. within-plategeotectonic setting typical of rift volcanism Geochemical analysis of basaltic pebbles (Valanginian?) at (Durr 1992). The northward palaeoflow in both Chukh and the base of theTangbe Formation indicates within-plate Tangbeformations also suggests a volcanic source in the volcanism. The locus of volcanism was probably close to and interior of Gondwana. Minor volcanoclastic detritus is south of the Thakkhola areain view of the coarseness of the present as early as theBerriasian in the basal Chukh detritus, evidence for relative uplift atthis time, and the Formation.The age of the volcanic conglomerateat northward palaeoflow. A thick volcanoclastic sandstone Chyanche is not well constrained but may be Valanginian. (Aptian) in theupper part of theTangbe Formation The association of the volcanic conglomerate with an probably correlates with the Rajmahal Traps of northeast unconformity and the only fluvial deposits identified in the India.The source of theBerriasian and Valanginian EarlyCretaceous strata may reflect a connectionbetween volcanic detritus is not known with certainty. volcanism and uplift. Volcanic detritus is widespread in the (4) The EarlyCretaceous succession corresponds well TangbeFormation through the Aptian and probablyinto with that of the (formerly conjugate) northwest Australian the Albian. margin. LateJurassic to Early Cretaceous rifting and The extensiveRajmahal and related volcanic traps sea-floor spreading in this part of northern Gondwana was (alkali basalts and olivine tholeiites) of northeast India lie followed by late Valanginian to early Hauterivian final southand southeast of Thakkhola(Fig. 1) and show separation of Australia and Greater India. within-plate geochemical affinity (Baksi et al. 1987). (5) Although burialprofiles show thatthe northern Eruption was probablyrelated to the motion of Greater Gondwanan margin subsided steadily through theMesozoic, India over the Crozet hotspot (Curray & Munasinghe 1991) LateJurassic to Early Cretaceous sedimentation patterns and began about 120 Ma (Ar dating: Baksi et al. 1987), in and changes in relative sea-level were influenced primarily theEarly Aptian according to the Harland et al. (1990) by tectonism associated with Gondwananbreak-up. timescale. Volcanic detritus is abundant in the Early Aptian Hiatuses at twolevels reflect stages in thebreak-up. The dark sandstones of the Tangbe Formation, and could have Early Cretaceous unconformity is associated with rift-related been derivedfrom presently unknown extensions of the volcanism, and enormous amounts of volcanic detritus were Rajmahal Traps. However, detrituswas available also in the available until the Albian. An Early Cretaceous deepening Valanginian and locally in the Berriasian, possibly as early trendprobably reflects widespread sea-floor spreading as as 140 Ma. Phonotephrites,trachyandesites and trachytes Gondwana separated. Northward drift of Greater India may cropout near Tansen in the Lesser Himalayas(Fig. l), have influenced sediment type by the mid-Cretaceous. where associated fluvial strata show northerlypalaeoflow (Sakai 1989; Arita et al. 1991). However,these volcanic Wethank the Geological Survey of Nepal and G. Gabert for rocks were probablynot the source of theThakkhola support during our time in Nepal. We are indebted to theSherpa volcanoclastic material because the two groups of material Society, MingmaSherpa and his team of expedition staffand differ geochemically (S.Durr, pers. comm. 1993) and porters who provided excellent logistical assistance, to the people of because the Tansen rocks appear to be too young, based on Thakkhola, and to D. Brown, S. Durr, R. Matsumoto, J. a Rb/Sr biotite-feldspar age of 96.7 f 2.8 Ma (Arita et al. Nazarchuk, J. Ogg and U. von Rad, fellow Lost Ocean Expedition 1991). Kent (1991) inferred from palaeoflow data in eastern 11 members. Wethank two journalreviewers for theirthoughtful Indiathat a long-lived mantleplume beneath eastern comments on an earlier version of the manuscript, and R. Boyd for Gondwana had generatedregional northwesterly drainage helpful discussion. J. MacEachern, S.G. Pemberton and G.M. from Permo-Triassic to early Cretaceous times, and hence Narbonne made provisionalidentifications of trace fossils, B. some volcanic detritus in Thakkhola could have been Tocher assistedwith identification of some dinocysts, andMai distantly derived. Nguyen drafted the diagrams.Financial support toM.R.G. from
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Natural Sciences and Engineering Research Council of Canada and GAETANI,M. & GARLANTI, E.IYYl. Multicyclic history of the northcrn India to J.W. from DeutscheForschungsgemeinschaft is gratefully continental margin (northwcstcrnHimalaya). Bulletin of the American acknowledged. Association of Petroleum Geology, 75, 1427-1446. -, CASNEDI,R.. FOE, E., GARZANII, E.,JADOUL, F.. NICORA, A. & TINTORI.A. 1986. Stratigrdphy of theTcthys Himalaya in Zanskar, References Ladakh - Initial Report. Rivirtu Italiana di Paleontologia e Strutigrafia, 91, 443-478. ARITA, K., SAKAI, H.& KOIDE, Y. 1991. Crctaccous alkaline magmatism in GANSER.A. 1964. Geology of the Himalayas. Wilcy. London. the Ncpalcsc Lcsser Himalayas. Geologie Alpine, Memoirs. 16, 9-10. GARLANTI.E. & PAGNIFRETTE. M. IYYI. Stratigraphic succession of the ARMIJO,R.. TAPPONNIER,P.. MERCIER, J.L. & HANTONG-LIN 1986. 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Rcccivcd 16 July 1992; revised typescript acccptcd 20 July 1993.
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