The Geology of the Markha-Khurnak Region in Ladakh (India) 403 ©Geol
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ZOBODAT - www.zobodat.at Zoologisch-Botanische Datenbank/Zoological-Botanical Database Digitale Literatur/Digital Literature Zeitschrift/Journal: Jahrbuch der Geologischen Bundesanstalt Jahr/Year: 1985 Band/Volume: 128 Autor(en)/Author(s): Fuchs Gerhard Artikel/Article: The Geology of the Markha-Khurnak Region in Ladakh (India) 403 ©Geol. Bundesanstalt, Wien; download unter www.geologie.ac.at Jb. Geol. B.-A. ISSN 0016-7800 Band 128 I Heft 3 + 4 1__ S_._4_0_3_-_4_3_7 W_i_e_n_,J_s_'n_n_e_r_1_9_8_6__ The Geology of the Markha-Khurnak Region in Ladakh (India) By GERHARD FUCHS') With 28 figures and 5 plates Himalaya India Ladakh Indus Suture Zone Tibetan Zone Tectonics Palaeogeography Content Zusammenfassung, Summary 403 1. Introduction 404 2. The Indus Molasse observations along the Leh - Ganda La route 404 3. The Dras Unit and overlying Ultrabasic Klippes 406 4. The Ophiolitic Melange Zones 410 5. The Lamayuru Unit ~ 416 6. The Metasedimentary Sequence of the Nimaling (Tso Morari) Dome 419 6.1. The Basal Flysch 419 6.2. The Micaschist-Dolomite Series 420 6.3. The Carbonate Series 420 6.4. The Siltite-Quartzite-Limestone Series 421 6.5. The Lamayuru Formation 421 6.6. The Age of the Metasedimentary Succession of the Nimaling Dome : 422 7. The Tibetan (Tethys) Zone of Zanskar 422 7.1. The Zanskar Carbonates 422 7.2. The Upper Dogger 423 7.3. The Giumal Sandstone and Khurnak Formation 423 7.4. The Upper Cretaceous 424 7.5. The Upper Paleocene Limestones 424 8. The Markha-Nimaling Area and the Geology of Ladakh 425 8.1. Stratigraphy and Palaeogeography 425 8.2. Tectonics 431 8.3. Is the Tibetan Zone Allochthonous? - a Discussion 433 Acknowledgements 435 References . 435 Zusammenfassung letztgenannte Einheit ist jedoch meist als einfache Überschie- Meine Expedition 1983 konzentrierte sich auf die Erfor- bung ausgebildet. schung des Gebietes Markha - Nimaling - Khurnak in La- Die 0 ras - Ein h e it endet im Markha-Gebiet zwischen sich dakh. Die Arbeit beschreibt die Iithologischen und strukturellen gabelnden Ophiolitischen Melange-Zonen. Die Dras-Flysch- Einheiten sowie deren wechselseitige Beziehungen. Das wich- Vulkanitserie wurde von Ultrabasit-Massen überfahren, die tigste Ergebnis ist die Tatsache, daß das Z ans kar - Sy n- durch ein olistostromes Konglomerat verbunden sind. Dieser klinorium (Tibet-Zone), die Lamayuru-Einheit und das Horizont signalisiert den Beginn der Deckenbewegungen. Die Ni mal i ng- Tso Mo rari - Kri sta II i n miteinander verbunden Sedimentation setzte auch nach diesem Ereignis fort, aller- sind. Letzteres bildet ein randliches Antiklinorium, in dem die dings als Molasse. Gerölle von Foraminiferenkalken belegen basalen Formationen der Tethys-Schichtfolge aufgeschlossen ein post-ober-paleozänes Alter dieser Chi II i ng - Mol ass e. sind. Deren jüngste Schichten - Kreide und Ober-Paleozän - Sie bildet die jüngsten Schichten der Dras-Einheit. Post-ober- bilden den Kern der im SW benachbarten Khurnak-Synklinale. paleozäne Konglomerate finden sich auch als verquetschte Die Lamayuru-Formation nimmt an der Tethys-Schichtfolge teil Bänder in der Melange Zone. und ist mit den Schelf-Karbonaten im S faziell verzahnt. Somit Die In d u s - Mol ass e (s. I.) grenzt mit tektonischem Kontakt ist die ursprüngliche Faziesverteilung Schelf - Kontinentalab- im N an. Die eozänen marinen Klastischen Basisschichten und hang - Becken in Ost-Ladakh mehr oder weniger erhalten ge- Jurutze-Flysch wurden als gefalteter Komplex von den konti- blieben. Auch innerhalb der Lamayuru-Beckenfazies ist gegen nentalen bunten Molasse-Formationen transgrediert. N eine weitere Abnahme des Karbonatgehalts festzustellen, Schließlich wird die Hypothese von BAUDet al. diskutiert, ob und schließlich ist die Lamayuru-Einheit durch Primärkontakte die Ti bet - Z 0 ne als Deckenpaket dem Zentral-Kristallin tekto- mit der Ophiolitischen Melange der Indus-Suturzone ver- nisch auflagert. Alle Ergebnisse meiner Expedition 1983 und bunden. Die Melange grenzt die Lamayuru-Einheit gegen die andere Beweise sprechen gegen das Allochthonie-Konzept. Indus-Molasse bzw. die Dras-Einheit ab. Die Grenze gegen Summary 0) Author's address:: Univ.-Doz. Dr. GERHARDFUCHS,Geologi- My 1983 expedition concentrated on the Markha-Nimaling- sche Bundesanstalt, Rasumofskygasse 23, A-1031 Wien. Khurnak area in Ladakh. The paper describes the lithologic 403 ©Geol. Bundesanstalt, Wien; download unter www.geologie.ac.at and structural units and their interrelationship. Most important 2. The Indus Molasse-observations result is the coherence of the Zanskar Synclinorium, (Ti- betan Zone), Lamayuru Unit, and Nimaling-Tso Morari along the Leh - Ganda La route Crystalline. The latter forms a marginal anticlinorium ex- posing the basal formations of the Tethys sequence. The On the march to the Markha Valley cursory obser- youngest beds of Cretaceous - Upper Paleocene age form vations were made in the Indus Molasse traversed. In the core of the Khurnak Syncline adjoining in the SW. The La- more detail the area was studied by BAUD et al (1982b) mayuru Formation is a part of the Tethys succession and inter- and BROOKFIELD & ANDREWS-SPEED (1984) to whom I fingers with the shelf carbonates in the S. Thus the original fa- cies pattern shelf - continental slope :- basin is more or less refer. preserved in eastern Zanskar. Also within the Lamayuru basin From Spituk to the Rum Valley the trail crosses wide facies there is further decrease in carbonate content towards talus fans covering old, Iight-coloured lake deposits. the N, and finally it is linked by primary contacts with the The mountains to the S consist of thick-bedded molas- ophiolitic melange of the Indus Suture Zone. The melange se series intensely folded with NNE vergency. Where terminates the Lamayuru Unit against the Indus Molasse re- spectively the Dras Unit. The boundary against the latter unit, the Indus turns to the S and the valley becomes narrow however, is mainly developed as a simple thrust. the trail crosses this tick-bedded sequence: Green- The Dr a sUn it pinches out in the Markha area between bi- grey, mainly fine- to medium-grained sandstones, arko- furcating ophiolitic melanges. The Dras Flysch-Volcanics are ses and conglomerates predominate over the interbed- overridden by ultrabasic masses, which are connected by a ded green slates. BAUD et al. (1982b) termed this series olistostromic conglomerate. This horizon signals the beginning of the nappe movements. After this event sedimentation con- the "flyschoid unit of Nimu-Alchi", whereas BROOKFIELD tinued, but of molasse type. Foraminiferal limestone pebbles & ANDREWS-SPEED (1984) designate the series as "Ni- prove a post-Upper Paleocene age of this Chi II i n g Mol as- mu Grits" (STERNE, 1979). Near the junction of the Rum se, which represents the youngest beds of the Dras Unit. and Indus Valleys the steeply folded molasse becomes Post-Upper Paleocene conglomerates also occur as squeezed richer in argillites. This is the passage from the Nimu bands in the melange zone. Grits into the "Zinchon Molasse" (BROOKFIELD & AN- The Indus Molasse (s. I.) adjoins with tectonic contact. The Eocene marine Basal Clastics and Jurutze Flysch form a DREWS-SPEED, 1984). The sandstones still rather thick folded complex transgressed by continental multicoloured mo- are interbedded with several meters thick, dark grey to lasse formations. green, splintery slates and silty shales. Conglomerates Finally the hypothesis of BAUD et al. is discussed whether are rare. Around the village Zinchon a series of large the Ti bet a n Z 0 n e represents a pile of nappes lying with tec- NE directed folds are observed (PI. 3[3]). tonic contacts on the Central Crystalline. All the results of the 1983 expedition and other evidence are against the allochtho- The gorge N of Rumbok crosses a thick-bedded se- ny concept. ries of green sandstones, conglomeratic arkosic sand- stones, and red, green or dark shales. This Rumbok Molasse (BROOKFIELD & ANDREWS-SPEED, 1984) is 1. Introduction steeply dipping towards the SW in the N and towards NE in the S, the main mass being vertical (PI. 3[3]). In Ladakh W of the Zanskar River my work revealed The molasse formations crossed between the Indus a composite allochthonous mass in the Spongtang re- and Rumbok are younging towards the N, regarding gion; the surrounding series of the Zanskar Synclino- their age it may be only said that they are post-Eocene rium, however, are autochthonous or parautochthonous (probably Oligo-Miocene). The several thousands of (FUCHS, 1977b, 1979, 1982). On the contrary BASSOUL- meters thick succession was deposited in a continental LET et al. (1978, 1980, 1983) take the northern carbon- basin with wide floodplains and braided rivers (BROOK- ate belt of Zanskar as allochthonous, their Zanskar- FIELD & ANDREWS-SPEED, 1984). Shillakong Nappe. BAUD et al. (1982 a,b, 1983, 1984) At Rumbok the scenery changes: The rugged range accept this unit as allochthonous, also in the region E built by the Rumbok Molasse (Multicoloured Molasse, of the Zanskar River, and extend the allochthony to the BAUD et aI., 1982b) is followed by morphologically soft whole of the Tibetan (Tethys) Zone. According to these terrain. First comes a band of soft, reddish rocks about authors the Tibetan Zone consists of a pile of nappes 500-600 m thick, and then soft series weathering in resting tectonically on the Central Crystalline of the light colour, these are the Eocene formations of the Ju- Great Himalayan Range. As this hypothesis is opposed rutze area (Fig. 1). to all my experience of the Tibetan Zone, I extended my The Eocene succession starts with red and yellow, studies to the area from where the allochthony of the very well-sorted, calcareous, felspatic and lithic grey- Tibetan Zone is reported. wackes and sandstones interbedded with sandy shales From Leh I went to the Markha Valley via Ganda La (BROOKFIELD & ANDREWS-SPEED, 1984). According to and investigated the various zones along the Indus Su- these authors mudcracks and the fossils found by DAI- ture.