Some rudists from Khalsi limestone of Indus Formation, Ladakh Himalaya

SOME RUDISTS FROMKHALSILIMESTONEOF INDUS FORMATION,LADAKHHIMALAYA

par N.S. MATHUR* & KLAtJSVOGEL**

ABSTRACT

RI~SUMI~

The paper describes three taxa of rudists, namely Eoradiofires gilgitensis DOUVILL~, ? Horiopleura sp. and cf. Toucasia sp., from the Khalsi limestone of Indus Formation, Ladakh Himalaya exposed 2.5 kms East of Khalsi. The age and affinity of the rudist fauna have also been discussed.

Description de trois Rudistes : Eoradiolites gilgitensis DOtrVlLL~, ? Horiopleura sp. et cf. Toucasia sp., provenant du calcaire de Khalsi (Indus Formation, Ladakh Himalaya) situ6 ~ 2,5 km ~ PEst de Khalsi. L'~ige et l'affinit6 de la faune de rudistes sour discut6es.

KEY-WORDS: APTIANRUDISTS,STRATIGRAPHY,LADAKHHIMALAYA. MOTS-CLI~S: RUDISTESAPTIENS,STRATIGRAPHIE,LADAKHHIMALAYA.

* WadiaInstitute of HimalayanGeology,33 GeneralMahadevSingh Road,Dehra Dun-248001 (India). ** Geologisch-PaliiontologischesInstJtut, derJohann-Wolfgang-GoetheUniversidit,D-6000Frankfurtam Main (WestGermany). Geobios, n ~ 21, fasc. 6

p. 693-707, 2 fig., 1 tabl., 3 pl.

Lyon, d6cembre ]988

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INTRODUCTION Although the occurrence of rudists from Ladakh was noted by Parona as early as in 1928, it is surprising to note that no detailed work has been carried out so far from this region. The present paper describes three taxa of rudists from the Khalsl limestone of Indus Formation, Ladakh llimalaya. The IndusTsangpo suture zone of Ladakh and Tibet extending for about 2500 kms has been postulated as a junction between the Indian plate and the Eurasian plate. This zone has received the attention of

...

a number of geologists both From India and abroad. In recent years, the tectonostratigraphy of the Ladakh Himalaya has been worked out by a number of geoscientists (Srikantia & Bhargava 1978 ; Sdkantia & Razdan 1980 ; Thakur 1981,1987 ; Bassoullet et afii 1981, 1982, 1984 ; Baud et alii 1982 ; Honegger el alii 1982 ; Van Hayer 1984 ; Van llaver et alii 1984 ; Sharma 1987 ; and several others). A geological map of Ladakh and adjoining regions is given in fig. 1.

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SCALE Fig. 1 - Geological map of the Kohlstan and Ladakh regions showing different lithotectonlc units and the southern and northern limits of the Eurasian and Indian Plates. Carte g~ologique des r~gions de Ladakh et du Kohistan montrant diff~rentes unit(~s lithotectoniques el: les limites herd et sud des plaques euraslenne et Indienne. Kohistan : 1 = green schist and amphibolitic belt with local blueschist sfices/ophiolitie melanges and ultramafic complexes ; 2 = Kohistan arc batholith ; 3 = Dir volcanics and volcano-sediments (2 and 3, calc-alkaline magmatic arc) ; 4 = Chalt ;'olcanics, Yasin group rocks and ophiolitic melange ; 5 = Karakoram metamorphics ; 6 = Karakoram plutonic belt. Ladakh : I = Lower Gondwana rocks ; 2 = Dras volcanics, Indus flysch with blueschist slices, ophiolitie melanges and ultramafle complexes ; 3 = Eocene-Oligocene, llemis Conglomerates and Miocene-Plioeene Indus Molasse ; 4 = Ladakh are batholith ; 5 = Khardung volcanics and valcano-sediments (4 and 5, calc-alkaline magmatie arc) ; 6 -- Shyok vok'anics, sedimentary rocks and ophiolitic melange ; 7 = Karakoram metamorphics ; 8 = Karakoram plutonic belt. (Based on Coward etalii 1986 ; Sharma 1987).

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The Indus Formation consists of a thick succession of conglomerats, sandstone and shale with subordinate limestone. The lithostratigraphic succession of this formation has been worked out by Pal & Mathur (1977), Pal et alii (1978), Baud et alii (1982), Thakur & Bagati (1983) and several others. Pal et alii (1978) have recognized five members (A to E in ascending order) in this formation and assigned a Lower Cretaceous to Middle Eocene age to it. The Khalsi limestone belongs to member A of this classification. Member A comprises mainly conglomerate with red and green shale and also grey limestone ; member B-sandstone with subordinate shale ; member C - grey shale with subordinate sandstone, and limestone ; member D - red shale with subordinate sandstone, siltstone and conglomerate ; and member E - conglomerate with subordinate sandstone and shale. Baud et alii (1982) have divided this formation into seven litho-units and correlated them with those of Pal et alii (1978). Three tectono-stratigraphic units have been delineated by Thakur & Bagati (1983) in this formation : (a) conglomerates, sandstone and shale with "Itippttrites" bearing limestone ( = Khalsi rudist bearing limestone) of Cretaceous age, (b) nnmmulitic limestone and shale of Lower and Middle Eocene age, and (c) overlying plant bearing conglomerate and shale. The Indus Formation is bounded by Ladakh batholith representing a magmatic arc in north and ophiolitic melanges and ophiolites considered to be palaeosubduction zone complex in the south. Recently a lot of biostratigraphic works have been carried out on the Indus Formation of Ladakh Himalaya (Shanker et alii 1976; Bassoulletetalii 1982 ; Mathur 1981, 1983 ; Van Hayer

1984 ; Van tlaver et alii 1984 ; Cherchi et Mii 1984). In the Khalsi area, the lowest unit of this formation has yielded a number of taxa of rudists, foraminifera and algae. The following taxa of rudists have been recorded from the Khalsi limestone exposed in two sections SW and E of Khalsi, indicative of an Early Cretaceous (Aptian-Albian) age : L:oradiolites sp. cf. E. gilgitensis DOUVlLLE,Sphaerulites sp. cf. S. cantabricus DOUVILLI~,and Polyeonites sp. (Bassoullet et alii 1982 ; Van-tiaver 1984 ; Vantlaver et alii 1984). From the higher horizons of this formation from sections east of Khalsl (Tar, Alchi, Zanskar Valley, Kundala, Mlru and Chumathang-Nidar), a fairly rich fossil assemblage comprising mainly larger foraminifera has been recorded, indicative of Late Cretaceous (Cenomanian-Maestrichtian) to Middle Eocene (Lutetian) age. The Late Cretaceous taxa recorded from Tar section include Siderolites calcitrapoides LAMARCK,Lepidorbitoides socialis (Lv.~tEmE), while other sections (Zanskar Valley, Kundala, Miru and Chumathang-Nidar) have yielded a rich foraminiferal assemblage indicating a Thanetian to Lutetian age : Miscellanea mlscelta PFENDER,Assilina dandotica DAVIES,A. sp. ex gr. A. davlest var. nammalensis GILL,A. leymeriei (d'ARCHIAC& IIAIME),A. umbltcata DE CIZANCOURT,Operculina sp. cf. O. salsa DAVIES,O. sp. cf. O.jiwani DAVIES,Alveolina globosa LI:~tERIE, A. elliptica DAVIES,Nttmmulites beaumonti d'ARCtIIAC& HAIME,N. sp. ex. gr. N. oblusus (SOWERBY),IV. atacictts LEYMERIE,N. globulus DAVIES,and several others (Shanker et alii 1976 ; Mathur 1983 ;Van Hayer 1984 ; Van IIaver et alti 1984).

PALAEONTOLOGICAI, INVESTIGATIONS ON RUDIST FAUNA IN ADJOINING REGIONS In the present survey some of the palaeontological investigations, particularly on the Cretaceous rudist fauna in the neighbouring regions of Kohistan (Yasin), Afghanistan and Tibet have been reviewed. This review will be helpful in interpreting the stratigraphic position of the Khalsi rudist bearing limestone. Table 1 summarizes the views expressed by various workers on the age of rudist bearing limestones from these regions.

KOHISTAN(YASIN) tlayden (19] 5) reported the occurrence of "ltippuriles" and Orbitolina in crushed limestone and calcareous shale at Yasin (Kohistan). This material was later studied by Douvill6 (1926) who described the following taxa : Orbitolina bulgarica (D~ ilAYES),O. cf. discoidea GRAS,Nerinea coquandiana d'ORntG~' and a few corals besides two new species, namely Horiopleura

haydeni and Praeradtolites gilgitensis, lie assigned an Upper Barremian to Aptian age to this faunal assemblage. Rossi Ronchetti & Farioli Mirelli (1959) described the following taxa from Yasin : Horiopleura haydeni 300VILLI],Praeradiolites gilgitensis DOtrVlLLI~,Adizop~yxis coquandiana (d'ORBIGNY),A. renauxiana (d'ORBIGNY),Nerinea vogtiana DE MORTILLETandM. desioi FARIOLIMIRELLIbesides Rhabdophyllia cf. gracilia DE FROM.and Isastrea cf. regularis DE FROM.On the basis of this assemblage, Desio (1959) assigned a Barremian-Albian age for the Yasin sequence. In 1965, Rossi Ronchetti described from Yasin the following fossils : ltoriopleura haydeni DOUVILLI~,Eoradiolites?gilgitensis (DoINILLI~),Cossmannea (Eunerinea) vogtiana (DE MORTILLET),Adiozoptyxis coquandtana (d'ORmGSY), PlesiopCyxts desioi (FARIOLIMIRELLI)besides two new species, namely Iloriopleura desioi and Plesioptyxis yasinensis, lie assigned to this faunal assemblage an Upper Aptian age which may range into Lower Albian. Ichikawa & Maeda (1965) described from Yasin AdiozopO,xis cf. A.coquandiana (d'ORBIGNY)and

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l CENTRAL WESTERN AFGHANISTAN TIBET

KOHISTAN ( YASIN )

A G E

STAGE

DOUVI_LE' I DESIO j 1926 959

my.

88.5

-

ROSSI RONCHETT; 1965

PUOSEv ] ETAL

L ,.9~

MONTENAET AL

,9B2

YANG ETAL.

1982

LADAKH(KHALSI-TAR} "EWARI ET AL.

VAN-HAVER'BASSOULLET ETAL.

,I ,9ETAL _8 4 '

1979 t

CHERC-I "~-TH~S ETAL

;982

1984

PAPER

TURONIAN 91 .0 CENOMAN~AN

97~,

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F'l I

ALB,AN

r i i i

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i I

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'19.C~ BARRE-

JP

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D

1

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D

Tabl. I -Age of rudist bearing limestones from F.ohistan, Central Afghanistan, Western Tibet and l.adakh regions. Age des rudlstes des maleaires du Kohistan, de l'Mghanistan central, du Tibet oceidental et de la r,~gion de Ladakh.

Horiopleura haydeni DOUVILLI~in addition to three new taxa, namely Plesioptyxis matsushitai, P. huzitai and IIoriopleura haydeni var. Recently Pudsey et aIii (1985) have described the follow~ng fossils from Yasin Group exposed in Mashotan-YasinHasis area : PraeradioIiles gitgitensis DOUVlLLI~,Horiopleura haydeni DOU'ClLLI~,Palorbitolina lentic~daris (BLUMENBACIt), Praeorbitolina cormyi SCtIROEDER,Orbitolina (Mesorbitolina) cf. parva DOUGLASS,O. (m.) texana (RoF~tER) and ? Mayncina sp. They also reported the occurrence of Mimachlamys rob# naldina (d'ORBmNY), Actaeonella sp., lIoriopleura sp. and chondrodonts from the area. They suggested topmost Aptian and/or Lower Albian age to the Yasin Group and also opined that the Yasin fauna is of tethyan "northern shore" characters.

CENTRALAFGH&NISTAN

Philip (in Montenat et alii 1982) described Horiopleura haydeni DOUVlLLI~major n. vat. PHILIP, Eoradiolitesgilgitensis

(DouvI~.L~.)and Sphaemlttes griesbachi (Dou'VILLI~)from Central Afghanistan. Montenat et aHi have also discussed, in brief, the palaeogeography and geodynamics of Afghanistan during Barremlan-Albian lntervaL

TIBET

From the Jaggang Group (Aptian-Cenomaniau) of the Ngari area in we.stem Tibet, Yang et aHi (1982) have described Praeradiolites biconvextts YANG, NIE & WU n. sp., P. ngariensis YANG, NIE & WU n. sp. and Rutonaia bangonghuensis in addition to Praeradiolites hedini DOU'vlLLI~,? Requienia sp. and Toucasia sp. The rudist species Praeradiolites ngariensis has been regarded as synonymous of Eoradiolites gilgitensis (see systematics). These taxa occur in association with Orbitolina and colonial hexacorals.

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LOCALITY,HORIZONAND MATERIAL In the present paper three taxa of rudists represented by Eo. radiolites gilgitensis (DoUVILL~), ? Horiopleura sp. and cf. Toucasia sp. are being described from Khalsi limestone exposed 2.5 km East of Khalsi, Ladakh region (fig. 1). This limestone belongs to lower part of the Indus Formation (Member A of Pal et alii ; Zone I of Mathur 1983). A stratigraphic sequence of the Khalsi area is given figure 2.

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Fig.2 - Stratigraphlesection of the Khalslarea, Ladakh IIImalaya. Coupestrattgraphlque de la r6glon de Khalsi,Ladakh Inmalaya.

LADAI 8ATHO (ALBIA UR EO(

SYSTEMATICS

The classification followed herein for Bivalvia is the one given in Treatise on Invertebrate Paleontology edited by Moore (1969). All the figured specimens have been deposited in the Museum of Wadia Institute of llimalayan Geology under Reg. Nos. WIF/A247-252.

Order HIPPURITOIDEA NEWELL, 1965 Superfamily Hippurilacea GRAY,] 848

OBSERVATIONS: A single ill-preserved specimen was found in the material. The attached valve (AV) is coiled and appears to be carinate and keeled. The maximum diameter of the specimen is 85 ram, the height being 47 mm. The specimen shows some resemblance with Toucasia carinata MATHERONvat. compressa PAQUIERdesGibed by Paquier (1903) from the Urgonian facies of Spain and France in overall shape and size. However, lack of good preserved material prohibits its exact identification

Family Requieniidae Dot/vlLI.I~,1914 Family Caprotinidae GRAY,1848 Genus ToucaMa MIJNIER-CIIALMAS,1873 cf. Toucasta sp. pl. 3, fig. 4 & 5 MATERIAL One specimen : tlolotype Reg. No. WII'/A 247.

GenusHorlopleura MUNIER-CHALMASin DOUVILLI~,1889 ?Hortopleura sp. MATERIAL: 'lXvospecimens. Holotype Reg. No. WIF/A248.

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OBSERVATIONS:

D~C~PTION:

Two ill preserved and fragile specimens are present in the material. One of the specimens (attached valve) was prepared which is elliptical in outline transversally. The maximum lengths of primary and secondary cavities are 30 mm and 20 mm respectively. The specimens have been questionably assigned to the genus Horiopleura belonging to the family Caproti. nidae. The absence of canals in the shell wall of the specimens rules out the possibility of their belonging to the family Caprinidae. In this family both primary and secondary cavities are also present. It may be added that IIoriopleura is a very common genus which has been recorded from the Yasin Group of Kohistan.

Attached valve cylindrical with a well developed ligamental groove. The length of the largest AV (incomplete) is 52 mm. The siphonal bands and longitudinal costae cannot be seen clearly on the specimens as most of the outer shell well is either peeled off or diagenetically dissolved. In some transverse sections, however, traces of longitudinal costae and siphonal bands can be made out. The shell well is calcitic, non-cellular and prismatic (characteristic of the genus Eoradiolites DOOVlLL~,1909), the prisms being separated by straight partitions as described by Philip (in Montenat et alii 1982). The ligamental ridge is typically fork shaped at the inner end as also shown by Pudsey et alii (1985). The outline of the specimens is subellipticaL Due to distortion and breakage some specimens are subtriangular in cross-section or elongated at right angle to the dorsoventral line.

Family Radlolitidae GRAY,1848

The maximum and minimum diameters of the largest specimens are 35 mm and 25 mm respectively. Free valve is slightly concave with fine concentric laminations. A section immediately below this valve shows teeth and myophore apophyses.

Subfamily Radlolitinae GRAY,1848 Genus Eoradtolttes DOUVILLI~,1909

Eoradtolttes gtlgttensts (DOUVILLI~,1926) pl. 1, fig. 1-5 ; pl. 2, fig. 1-5 ; pl. 3, fig. 1-3

1926 - Praeradiolites gilgitensis DOUVILLI~; p. 353, pl. 13, fig. 4 a-b. 1932 -Praeradiolites gilgitensis DotrVlLL~': Kiihn, p. 126. 1939- Eoradiolttes ?gilgitensis (DOUVlLLf,;):Jacob, p. 503. 1958 -Praeradiolites ?gilgilensis DOtlVILL~: Rossi Ronchetti & Farioli Mirelli, pp. 355, 357. 1959 - Praeradiolites gilgitensis DOUWLL~ : Rossl Ronchetti & Farioli Mirelli, pp. 91, 93. 1965 - EoradioBtes ? gilgitensis (DOUVlI,Lf~) : Rossi Ronchetti, pp. 251,252, pl. 39, fig. 1, 2. 1982 - Eoradiolites ? gilgitensis (Dot~VILL~): Philip in MontenatetaHi, p. 118, pl. 1, fig. 3. 1982 - Eoradiolites gilgitensis DOUVltL~.: Pudsey et alii, p. 160161, fig. 5 a-b.

MATERIAL: A number of specimens ; attached valves (AV) : ltypotype Reg. Nos. WlF/A 249-251 ; free valve (FV) : Hypotype Reg. No. WIF/A 252.

OBSERVATIONS: There is a lot of controversy regarding the generic position of this species. It was originally placed under Praoradiolites DOrtJVILLI~,1902. This generic assignment was later followed and/or supported by number of workers (see synonymy). Jacob (1939) doubted this generic placement of the species and transferred it questionably to Eoradiolites DOUVILLI ~:, 1909. Later on Rossi Ronchetti (1965) also supported this generic shift mainly on the basis of surface sculpture and characters of siphonal bands. Philip (in Montenat et alii 1982) transferred this species to Eoradiolites on the basis of wall structure and surface ornamentation. This generic shift was followed by Van Hayer et alii (1984). The present authors also support this generic placement because the wall structure is noncellular, compact and prismatic in contrast to cellular wall structure of Praeradiolites. Secondly in EoradioBtes the siphonal bands are not undulating as in case of Praeradiolites. Pudsey et alii (1985) have discussed the similarity of this species with Praeradiolites ngariensis described by Yang et alii (1982) from Ngari (western Tibet) in size, form and myocardinal arrangement. They have attributed the bulb shaped cross-section of the ligamental ridge of the Tibetan form to the growth of dark calcite in the ligamental cavity. They have suggested that the two taxa may be conspecific.

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DISCUSSION Varying ages from Aptian to Albian have been assigned to the Khalsi limestone on the basis of rudist and/or orbitolinid fauna. In order to reconstruct tectonic history of the crucial Indus suture zone, a more precise age assignment to this important stratlgraphic horizon of the Indus Formation is warranted. Tewari et alii (1970) suggested an Aptian age of this horizon in the Khalsi area on the basis of the following species : Orbitolina pileus FOSSAMANCINI,0. cf. parma FOSSAMANCINI,t). kashmirica SAHNI & SASTPa,and 0. cf. discoidea GRAS.Later on Bassoullet et alii (1982), Van Hayer (1984) and Van Hayer et alii (1984) gave an Aptian-Albian age to this horizon exposed in Khalsi and Tar sections based mainly on Orbitolina (Mesorbitolina) texana DOU6LASS,O. (M.) subconcava LEYMERIE,O. (M.) parva DOtlGtASS, Praeorbitolina sp., Palorbitolina Ienliczdaris (BLUMENBACH), Sphaemlites sp. cf. cantabricus DO0VlLLfi,Polyconites sp. and Eoradiolites sp. cf. gilgitensis DOUVlLLI~.Cherchi et alii (1984) restricted the age of this unit to the lowermost part of Upper Aptian on the basis of Praeorbitolina (Praeorbitolina cormyi $CHROEDER,Praeorbitolina sp.) in association with Orbitolina (Mesorbitolina) parva DOIJ6LASS. From the above survey a broad Aptian-Mbian age can be assigned to the Khalsi limestone based on rudtsts. However, the associated orbitolinid fauna is of great significance in fixing the age of the Khalsi limestone. Schroeder (1975) has given important phylogenetic lineages of Orbitolina. Following Schroeder (1975) the orbitolinid assemblage comprising Praeorbitolina

cormyi, Orbitolina (Mesorbitolina) texana, O. (ill.)parva, and O. (M.) subconcava suggests an Aptian age (possibly extending into Lower Albian) for the Khalsi limestone. The rudtsts were an important component of Tethyan assemblages during Cretaceous. The Khalsi limestone has yielded the following rudist taxa : Eoradiolites gilgitensia; Sphaerulites sp. cf. S. cantabrictts, Polyconites sp., Horiopleura sp. and cf. Tottcasia sp. Out of these Eoradiolites gilgitensis also occurs in Yasin Group of rocks in Kohistan (Pudsey et alii 1985). Praeradiolites ngariensis (a form similar to and probably synonym

of Eoradiolites gilgitemis fide Pudsey et alii 1985) has been described from Aptian-albian strata from Ngari Western TibeO. Sphaerulites griebacbi has been recorded from Central Afghanistan. The rudist genera Eoradiolites, Horiopleura and Toucasia occur in Mediterranean region and also in West Afghanistan (unpublished data of Vogel), Central Afghanistan, NW Pakistan and also in West Tibet. These genera are also distributed in Texas and Mexico. This shows that during Aptian, there was marine connection of Mediterranean region with Afghanistan, NW Pakistan, Ladakh and Tibet. Thakur (1987) has given sequence of events of the various tectonic zones of the Himalaya and has recognized three main stages, viz. (a) pre-collision stage, (b) subduction stage and (c) collision stage in its tectonic evolution. Mong the site of the Indus suture zone, there was development of rift in Triassic time resulting in formation of Indus basin (Thakur 1981 ; Bassoullet et alii 1981). Recent evidences indicate that separation of India from the southern continent and its northward drift in Aptian time initiated the closing of the Indus basin. The subduction of Indian plate under the Eurasian plate resulted in the formation of (a) palaeosubduction complex represented by Shergol ophiolitic melange, the Nindam Formation and Nidar ophiolite, (b) magmatic arc represented by Ladakh magmatic arc including Dras, Shyok and Early Tertiary plutonics of Ladakh, (c) Arc-Trench gap basin represented by Kargil Formation lying unconformably over the granitoids of Ladakh plutonic complex (Ladakh batholith) and the parautochthonus Indus Formation, and (d) Marginal basin (back arc) represented by Shyok and Nubra groups (fide ThaRur 1987). Though the northward drift started in Aptian time, the collision between the two plates took place in post-Ypresian time. This resulted in complete withdrawl of the sea from the region leaving a narrow basin separating the Indian and the Eurasian plates. In this basin, molassic sediments of the Kargil Formation lying unconformably over the Ladakh batholith were deposited.

Acknowledgements One of the authors (Mathur) is grateful to Dr. S.fi.D. Sah, then Director of Wadia Institute of Himalayan Geologyfor providing various facilities and to Deutscher Akademischer Austauschdienst (DAAD)for providing financial support to visit Geologisch-PalfiontologischesInstirut, Franki'urt am Main. He also expresses his thanks to Dr. V.C. Tha-

kur, Director of the Institute and Dr. R.J. Azmi for giving critical comments. The authors express their gratitude to Mr. Gottwarl for preparing the specimens and making polished sections ; and to Mr. Kahl for taking photographs of the rudists.

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REFERENCES BASSOULLETJ.P., COLCHENM., MARCOUXJ. & MASCLEG. (1981) Field evidences for continental rifting in Triassic time in the Ladakh part of the Indus suture zone. In "Geology and Ecological studies of Qinghai - Xizang Plateau" (L~N DONG-SHENGet alii, eds.), Proc. Syrup. Qinghai-Xizang (Tibet) Plateau (Beijing, China). Science Press, Bejing and NewYork, 1 : 579-585. BASSOULLETJ.P., COLCHENM., JUTEAUT., MARCOUXJ., MASCLEG. & REIBEL G. (1982) - Geological studies in the Indus suture zone of Ladakh (Himalayas). In "Contributions to Himalayan Geology" (V.J. GUPTAed.), Hindustan Publishing Corporation, Delhi, 2 : 96-124. BASSOULLBTJ.P., COLCHENM., GILBERTE., MARCOUXJ., MASCLEG., SUTURE E. & VAN HAYERT. (1984) - L'orogen~se Hlmalayienne au Crdtac6. Mdm. Soc. gaol. France, Paris, N.S., 147 : 9-20. BAUD A., ARN R., BUGNONP., CRISINELA., DOLIVOE., ESCHERA., IIAMMERSCHLAGJ.G.,MARTtIALERM., MASSONH., STECKA.& TIECHEJ.C. (1982) - Le contact Gondwana-pdri-Gondwana daBs le Zanskar oriental (Ladakh, Himalaya). Bull. Soc. #ol. France, Paris, (7), 24 : 341-361.

ICtlIKAWAK. & MAEDAY.(1965) - Some Lower Cretaceous molluscan fossils from Yasin, West Pakistan. "Geology of the Karakoram and llindu Kush", Kyoto (Results of the Kyoto Univ. Scientific Expedition to the Karakoram and Hindukush, 1955), 7 : 137-146. JACOB C. (1939) - La vie et l'oeuvre de llenry Douvilld (18461937). Bull. Soc. gaol. France, Paris, (5), 9 : 321-59~. KI~I~NO. (1932) - Rudistae. Fossilium Catalogus I. Animalia, Berlin, pars 54, 200 p. MATHURN.S. (1981) - Biostratigraphy of the Cretaceous-Eocene sequence in the Himalaya in relation to palaeobiogeography. IIimalayan Geology, Dehra Dun, I I : 287-322. MATHURN.S. (1983) -The Indus Formation of the Ladakh Himalaya : its blozonation, correlation and faunal provincialism. In "Geology of Indus Suture Zone of Ladakh" (V.C. THA~R & ILK. SItARMAeds.). Wadia Institute of IHmalayan Geology, Dehra Dun : 127-144. MOORE R.C. ed. (1969) - Treatise on lnvermbrate Paleontology. Geol. Soc. America, N. (Mollusca 6), Vol. 2 (of 3), 952

p. CHERCHIA., GUPTAV.J. & SCHROEDERR. (1984) - Late Aptian calcareous algae and larger foraminifera from Khalsi, Ladakh, India. Bull. Indian Geol. Assoc., Chandigarh, 17, 2 : 145-157. COWARDM.P., WINDLEYB.F., BROUGHTONR., LUFFl.W., PETrERSON M.G., PUOSEYC., REX D. & KHANM.A. (1986) - Collision tectonics in the NW tlimalayas. In "Collision Tectonics" (M.P. COWARD& A.C. RIES eds.). Geol. Soc. London, Spec. Publ., 19 : 203-219. DESlO A. (1959) - Cretaceous beds between Karakorum and ttindu Kush ranges (Central Asia). Riv. Ital. Paleont. Strat., Mllano, 65 : 221-229. DOUVILLI~tt. (1926) - Fossiles rectieillis par ttayden dabs le Kashmir en 1906 et les Pamirs en 1974 :leur description. Rec. GeoL Surv. India, Calcutta, 58, 4 : 349-357. HAYDENII.H. (1915) - Notes on the geology Chitral, Gilgit and the Pamirs. Rec. Geol. Surv. India, Calcutta, 45 : 271335.

MONTENATC., MOULLADEM. & PtIILIPJ. (1982) - Le Crdtac6 infdrieur ~. Orbitolines et Rudistes d'Afghanistan central. Gaol. Madit., Marsellle, 9, 2 : 109-122. PAQUIERM.V. (1903) - Les rudistes urgoniens. Mam. Soc. gaol. France, Palaont., Paris, 29 : 1-46. PAL D. & MATHURN.S. (1977) - Some observations on stratigraphy and structure of Indus Flysch, Ladakh region. Himalayan Geology,Dehra Dun, 7 : 464-478. PAL D., SRIVASTAVARA.K. & MATHURN.S. (1978) - Tectonic framework of the miogeosynclinal sedimentation in Ladakh Himalaya : A critical analysis. Himalayan Geology, Dehra Dun, 8 : 500-523. PARONA C.F. (1928) - Fauna cretaciche del Caracorl~m e degli al-

tipiani tibetani : Result. GeoL Geogr. Spediz. ltal. De Fillippi, (Zk'~ICHELLI,ed.), Bologna, 1913-14, 6 9 113147. PUDSEY C.J., SCIIROEDERR. & SKELTONP.W. (1985) - Cretaceous

IIONEGGERK., DIETRICllV., FRANKW., GANSSERA., THOENI M. & TROMMSDROFFV. (1982) - Magmatism and metamorphism in the Ladakh Himalaya (The Indus-Tsangpo Suture Zone). Earth Planet. Sci. Lett., 60 : 253-292.

(Aptian/Albian) age for Island-Arc Volcanics, Kohistan, N. Pakistan. In "Contribution to llimalayan Geology", (v.J. GUPTAet alii eds.), Hindz~tan Publishing Corporation, Delhi, 3 : 150-168.

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TE-F,VARIB.S., PANDEI.C. & KUMARR. (1970) - Lower Cretaceous fossiliferous limestone from Khalsi, Ladakh. Publ. Centre of Advanced Study in Geology, Chandigarh (Panjab Univ.), 7 : 197-200.

RossI RONCHETrlC. & FARIOLIMIRELLIA. (1958) - Rudiste e Nerlnee nella Cretaceo del Pakistan nord-occidentale. Congr. Geol. Intern. Ciudad de Mexico, Mexico 20e Sess., 7 : 355-360.

TIIAKIJRV.G. (1981) - Regional framework and geodynamic evolution of the Indus-Tsangpo suture zone in Ladakh Himalaya. Trans. Roy. Soc. Edinburgh, Earth Sci., 72 : 89-97.

RossI RONCHETI'IC. & FARIOLIMIRELL1A. (1959) - Rudists and Nerineids of North-West Pakistan. Cretaceous. Riv. ItaL Pal. Strat., Milano, 55, 2 : 91-96.

THAKURV.C. (1987) - Plate tectonic interpretation of the Western llimalaya. In "Deep seated Processes in Collision Zone", (H.E GtlP'I'Aed.). Teclonophysics, Spec. Issue, 1 3 4 : 9 1 102.

SCtlROEDER R. (1975) - General evolutionary trends in Orbitolinas. Rev. F.spanola de Micropaleont., (spec. number) : 117-128. SI-b'~NKERR., PANDttl N., PRAKASilG., TltUssu J.L. & WANGDUSC. (1976) - Recent geological studies in upper Indus valley and the plate tectonics. Misc. Pttbl. Geol. Surv. India, 34 : 41-56. S~tARMAK.K. (1987) - Crustal growth and two stage India - Eurasia Collision in Ladakh. In "Deep seated Processes in Collision Zones", (II.K. GUPTA ed.). Tectonophysics, Spec. Issue, 134 : 17-28. SPdKANTIAS.V. & BHARGAVAO.N. (1978) - Tile Indus tectonic belt of Ladakh Himalaya - its geology, significance and evolution. In "Current Trends in Geology : Tectonic Geology of the Himalaya", (P.S. SA~LANI,ed.). Today and Tomorrows publishers, New Delhi, l : 43-62.

THAKURV.C. & BAGATIT.N. (1983) - Indus Formation arc trench gap sedimentation. In "Geology of Indus suture zone of Ladakh", (V.C. TflAKUR& K.tC StlARMAeds.). Wadia Institute of Himalayan Geology, Dehra Dun 9 9-I9. VAN HAVERT. (1984) - Etude stratigraphique, s6dimentologique et structurale d'un bassin d'avant arc : exemple du bassin de l'Indus, Ladakh, Himalaya. T h e e Universit6 Grenoble, France : 204 p. VAN ItAVERT., BASSOULLETJ.,BLONDEAI.rA. & MASCLEG. (1984) Les s6ries ddtritiques du bassin de l'Indus au Ladakh : nouvelles donn6es stratigraphiques et structurales. Riv. It. Paleont. Strat., Luglio, 90, 1 : 87-102. YANGZ., NIE Z., Wtl S. & LIANGD. (1982) - Cretaceous rudists from Ngari, Xizang (Tibet), Autonomous Region, China and their geologic significance. Acta Geologica Sinica, Peking, 56, 4 : 293-300.

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Manuscrit d6pos6 le 23/09/1987 Manuscrlt d6finitif re~zu le 18/07/1988

PLATE 1

Fig. 1-5 - Eoradtolttes gtlgttensis (Dotn0ttLi).

Fig. I, 3 et 4 (E I ; hypotype WIF/A 249). Fig. 4 : polished section of attached valve showing typical fork-shaped ligamental ridge and subelliptical outline of the shell elongated dorsoventrally. Section polie de la valve fixde montrant le bourrelet ligamentaire typique et le contour subelliptique de la coquille allongde dorsoventralement. Fig. I : enlarged view of the same showing typical ligamental ridge. Vue agrandie du m~me spdcimen. Fig. 3 : same specimen cut slightly above the first showing typical ligamental ridge and subelliptical outline. M~me sp6cimen sectionn6 ldg&rement au-dessus du premier bourrelet ligamentaire typique.

Fig. 2 et 5 - (E4 ; hypotype WlF/A 252). Fig. 2 : transverse section (polished) of attached valve showing longitudinal costae. Section transversale (polie) d'une valve fixde, montrant les cStes longitudiuales. Fig. 5 : enlarged view of the same showing noncellular and prismatic wall structure, rue agrandie de la m~me valve montrant la structure non cellulaire et prismatique.

6eobios n ~ 2 I , fasc. 6

PI. 1 N.S. Mathur & IL Vogel

PLATE 2

Fig. 1 - 5 - Eoradtolttes gtlgttensls (DoUVILLI2).(E3 ; hypotype WlF/A 251).

Fig. 1, 2, 4, 5 : horizontal sections through attached valve with siphonaI bands S and E in 2 and 5 and teeth (in 1) and teeth and myophore apophyses of the free valve in 5 and showing non-cellular prismatic wall structure in 2 as seen toward commissure. Sections horizontales ~. travers la valve fix~e, avec handes siphonales Set E (fig. 2 et 5) ; dents et apopyphes myophores de la valve libre (fig. 5). La fig. 2 montre la structure de la paroi.

Fig. 3 : free valve. Valve libre.

Geobios n ~ 2t, fasc. 6

PI. 2 N.S. Mathur & E Vogel

PLATE 3

Fig. 1-3 - Eomdtolites gtlgttensis (DotrvaLL~).

Fig. 1 et 3 (E2 ; hypotype WIF/A250) : horizontal sections of attached valve exhibiting typical ligamental ridge. Sections horizontales de la valve fixde montrant le bourrelet ligamentaire typique. Fig. 2 : (E2 ; hypotype WIF/A251) : showing noncellular and prismatic wall structure, the prisms being separated by straight partitions. Structure de la paroi prismatique, non cellulaire. Les prismes sont s6par6s par des cloisons rectllignes. Fig./3 : enlarged view of the same showing ligamental ridge. Vue agrandie du mO.mebourrelet ligamentaire.

Fig. 4-5 - el. ToucaMa sp. (T1 ; hypotype WIF/A247).

Geobios n ~ 2 t, fasc. 6

PL !i N.S. Mathur & K, Vogel