Cretaceous-Tertiary Carbonate Platform Evolution and the Age of the ...

Cretaceous-Tertiary Carbonate Platform Evolution and the Age of the India-Asia Collision along the Ladakh Himalaya (Northwest India) Owen R. Green, Michael P. Searle, Richard I. Corfield,1 and Richard M. Corfield2 Department of Earth Sciences, Oxford University, Parks Road, Oxford OX1 3PR, United Kingdom (e-mail: [email protected])

ABSTRACT The India-Asia collision resulted in the formation and uplift of the Himalaya and the enhanced uplift of the Tibetan plateau. The transition from marine to continental facies within the Indus–Yarlung Tsangpo suture zone and along the northern margin of the Indian plate provides the most accurate method of dating the closure of the Tethys Ocean separating the Indian and Asian plates. Other indirect methods of dating the collision, such as paleomagnetism, dating the UHP metamorphism along the north margin of India, dating the youngest subduction-related granites along the southern margin of Asia, and dating the postorogenic Indus Molasse Group deposits within the suture zone, cannot provide such a precise or reliable age of collision. Ophiolite obduction onto the Indian passive margin occurred during the latest Cretaceous and predated initial collision of the two continental plates. Unconformities occur beneath the Late Maastrichtian Marpo Formation and beneath the Danian Stumpata Formation on the shelf and beneath the Upper Paleocene Sumda Formation in the suture zone. Stratigraphic and structural data from the Indian plate continental margin in the Ladakh and Zanskar Himalaya, northwest India, suggest that the final marine sediments were shallow marine limestones deposited during planktonic zone P8, corresponding to the Cusian stage of the late Lower Eocene (Ypresian) at 50.5 Ma. A regional unconformity across shelf and suture zones above these rocks marks the beginning of continental red bed deposition (Chulung-la and Nurla formations). The age of the final marine sediments is similar in Waziristan (northwest Pakistan) to the west and the South Tibet region to the east, suggesting that there was no significant diachroneity along the Indus–Yarlung Tsangpo suture zone. South of the Himalaya in the Hazara syntaxis, Pakistan, the youngest marine sediments correspond to nummulite-bearing limestones of the shallow benthic zone SBZ10 and planktonic foraminifera P7 zone (52–51 Ma). The timing of closure of Neo-Tethys between India and Asia corresponds closely to the ending of subduction-related granodiorite-granite magmatism along the Ladakh-Gangdese batholith (southern, Andean-type margin of the Asian plate) and precedes the drastic slowing of the northward drift of India. Continental fluvial-deltaic red beds unconformably overlie all marine sediments, both in the suture zone and along the north Indian plate margin.

Introduction The collision of India with Asia was the most recent of a series of continental plate accretions to the stable Siberian shield since at least Triassic time (Dewey et al. 1989). The India-Asia collision resulted in uplift of the Himalaya (fig. 1), initiation of many of the river systems, and enhanced uplift of the Tibetan plateau. Plate motions (Patriat and Achache 1984; Dewey et al. 1989) and paleomagnetic data (Klootwijk and Pierce 1979; Besse et al.

1984; Besse and Courtillot 1988, 1991; Klootwijk et al. 1992) indicate that India was at equatorial latitudes during the Early Eocene and that since collision, India has moved north, with respect to stable Siberia, by some 2600–3700 km (Rowley 1996, 1998) and has undergone between 20° and 30° of counterclockwise rotation (Patriat and Achache 1984; Dewey et al. 1989). Some earlier attempts at constraining the age of India-Asia collision have used indirect methods, which we believe do not give precise ages. The timing of coesite-bearing eclogites and UHP metamorphism along the northern margin of the Indian plate at Tso Morari, Ladakh (U-Pb zircon age 53:3 ± 0:7 Ma; Leech et al. 2005) has been used to define the minimum age of collision (de Sigoyer

Manuscript received September 24, 2007; accepted March 7, 2008. 1 Present address: BP Amoco Exploration, Farburn Industrial Estate, Dyce, Aberdeen AB21 7PB, United Kingdom. 2 Present address: Department of Earth and Environmental Sciences, Open University, Milton Keynes MK7 6AA, United Kingdom.

[The Journal of Geology, 2008, volume 116, p. 331–353] © 2008 by The University of Chicago. All rights reserved. 0022-1376/0000/11604-0002$15.00 DOI: 10.1086/588831

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Figure 1. Geological sketch map of the Himalaya showing the Indus–Yarlung Tsangpo suture zone and ophiolite complexes. Also shown are the three areas where detailed Tertiary biostratigraphy has been described: Waziristan (Pakistan), Ladakh (India), and Tingri (South Tibet).

et al. 2000; Leech et al. 2005). More precise constraints now come from U-Pb zircon and allanite ages of coesite eclogites in Kaghan, Pakistan, which are 46:4 ± 0:1 Ma (Parrish et al. 2006). However, it is possible that this UHP metamorphism occurred during the latest stage of ophiolite obduction, before continental collision, as in Oman (Searle et al. 2004). Treloar et al. (1989) suggested that collision in the Pakistan sector was earlier than in the India– South Tibet sector, based on 40 Ar=39 Ar∼ cooling ages as old as 50 Ma from the metamorphic rocks of the Pakistan Himalaya. Here, peak metamorphism occurred at or before 50 Ma, and these authors suggested that the minimum age of collision must therefore have been around 60 Ma. In Pakistan, the entire north Indian plate margin sequence of the Ladakh-Zanskar region is missing or has been metamorphosed, so most of the sedimentary record is no longer present. Some authors have suggested that the youngest ages of subduction-related granite magmatism along the southern margin of the Asian plate (Kohistan, Ladakh, and Gangdese granites) date the minimum age of collision. U-Pb zircon ages from gran-

itoids along the Ladakh-Gangdese batholith span 102–49 Ma (Honegger et al. 1982; Schärer et al. 1984; Weinberg and Dunlap 2000). The last major pulse in the Ladakh section of the batholith was the Leh quartz diorite, which has a U-Pb zircon age of 49:8 ± 0:8 Ma (Weinberg and Dunlap 2000). However, there may be a considerable lag time between slab subduction and Andean-type granite generation and actual continental collision, so this method cannot be regarded as accurate. The timing of the ending of the continuous Mesozoic–Early Tertiary marine sedimentation along the Indus suture zone (ISZ) was widely interpreted as reflecting the timing of the start of India-Asia collision (e.g., Garzanti et al. 1987, 1996; Searle et al. 1987, 1988, 1997; Garzanti and van Haver 1988; Rowley 1996, 1998; Zhu et al. 2005). Recently, however, Aitchison et al. (2002, 2003, 2007) and Aitchison and Davis (2004) suggested an Oligocene age of the India-Asia collision based on a Priabonian (end-Eocene; ∼35 Ma) age of a nannofossil assemblage from Zhepure Shan (Wang et al. 2002) and the age of the Gangrinboche conglomerates in southwest Tibet. These authors have

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used poorly defined ages of continental Miocene conglomerates (Kailas-Gangrinboche conglomerates) to constrain the initiation of collision. These thick, well-bedded conglomerates are undoubtedly postcollisional deposits, and they imply high mountains and a source area mainly to the north, but they cannot give a precise age of collision. Similar conglomerates in Ladakh (Indus Molasse Group) unconformably rest on the Ladakh granite along the northern part of the suture zone and therefore must be younger than 49 Ma. Of the clasts in the Indus Group, 80%–90% are granitic or calc-alkaline volcanic rocks derived from the uplifted Asian margin (Ladakh-Gangdese batholith). Some 10%– 20% of the clasts are ophiolitic or chert derived from the underlying suture zone rocks or, less commonly, carbonates derived from the Indian margin to the south (Searle et al. 1987). U-Pb and Lu-Hf isotopic analyses of detrital zircons from the Indus molasse in Ladakh suggest that the lowermost Chogdo Formation was deposited at 60–49 Ma along the southern part of the suture zone (Wu et al. 2007). The Indus Molasse Group and Gangrinboche conglomerates reflect nonmarine deposition in an elongate basin along the suture zone. Rapid deposition of thick conglomerates also reflects uplift and enhanced erosion along the southern margin of Asia during that time. We maintain that the most precise method of dating the closure of Tethys and the start of IndiaAsia collision is stratigraphic, using the age of the indigenous fossils within the youngest marine sediments along the ISZ and along the northern margin of the Indian plate. Rowley (1996, 1998) constrained initiation of collision at ≲52 Ma, and Zhu et al. (2005) refined this to 50.6 Ma based on final marine deposition in South Tibet. In this article, we first describe the geology of the ISZ, the northern margin of the Indian plate, and the Spontang ophiolite in Ladakh (fig. 2), and we then describe in detail several Late Cretaceous–Early Tertiary microfossilrich sections around the Spontang ophiolite on the north Indian continental margin in Zanskar and along the ISZ in Ladakh (fig. 3). We illustrate the diverse nature of the microfossil assemblages, which are dominated by shallow-water, calcareous, larger benthic foraminifera. Larger benthic foraminifera, until recently underutilized, are important tools in both paleoenvironmental reconstructions and biostratigraphical correlations. Typically, they evolve rapidly, are abundant, have species or groups of species that become extinct suddenly, and, when recognized in situ, can provide evidence of water depth. We use biostratigraphic data to determine the timing of ophiolite obduction and the initiation

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of India-Asia collision. We then compare the ages of obduction and collision in Ladakh with ages along the strike of the Himalaya in Pakistan and South Tibet. ISZ, Ladakh The ISZ in Ladakh comprises Permian-Mesozoic slope and proximal basin deep-sea sedimentary rocks (Lamayuru complex), distal equivalents (Karamba complex), Dras volcanic arc and related sedimentary rocks, two ophiolitic mélange zones with uncommon blueschist facies rocks, and the postcollisional Indus Group conglomerates, sandstones, and siltstones (Thakur 1981; Searle 1986; Searle et al. 1987, 1988, 1990; Reuber 1989; Robertson 1998; Robertson and Sharp 1998; Clift et al. 2000, 2002). The rocks of the ISZ show several phases of deformation related to (1) the precollisional Late Cretaceous–Paleocene obduction of the Spontang ophiolite and underlying Tethyan oceanic thrust sheets (e.g., Photang and Lamayuru) from the Tethyan basin southwest onto the northern continental shelf margin of India, (2) the syncollision (Early Eocene) closure of Tethys between India and Asia, and (3) Late Tertiary postcollisional northeast-directed backthrusting and shortening of the Indus molasse basin. Following the closing of Neo-Tethys, the Indus molasse basin formed along the suture zone accumulating the eroded debris from the already uplifted Asian active margin to the north and the rising Himalayan chain to the south. The spatial geometry of the rock units within the Indus basin is illustrated in figure 4. Garzanti et al. (1987, 1996), Garzanti and van Haver (1988), and Searle et al. (1987, 1988, 1990) studied the stratigraphy and structure of the ISZ in the Ladakh Himalaya and constrained the marine to continental transition at 54–50 Ma, based on the youngest marine sediments (nummulitic limestones equivalent to the P8 zone of Early Eocene– middle Ypresian age). A diverse marine assemblage of poorly preserved and highly deformed smaller and larger benthic foraminifera and calcareous algae is present (photomicrographs of fig. 4). Seen in petrographic thin section, the larger benthic foraminifera assemblage comprises a range of oblique fusiform (equatorial) and circular (axial) sections exhibiting some axial thickening and little or no flosculinization (the internal thickening of walls by deposition of secondary calcite); they also have a small megalospheric (proloculus, initial cell) stage and are loosely coiled. These features are characteristic of the Alveolines and can be placed within either the Alveolina (Alveolina) cucumiformis

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Figure 2. Geological map of Ladakh, after Corfield and Searle (2000), showing the Spontang ophiolite and Lamayuru thrust sheets overlying the Zanskar shelf carbonate sequence, showing locations of the four stratigraphic sections described in this article (Kanji, Marling, Singe, and Gongma sections).

Figure 3. Integrated chrono- and biostratigraphic time chart of the Zanskar Indian plate margin and Indus suture zone with data from Waziristan-Kohat (Beck et al. 1995, 1996) and South Tibet (Rowley 1996, 1998; Zhu et al. 2005) for comparison. Planktonic zones include foraminifera (P), calcareous nanoplankton (NP and CP), and larger shallow benthic foraminifera (SBZ). Biozonation references: Berggren and Miller (1988); Berggren et al. (1995); Martini (1971); Burky (1973, 1975); Serra-Kiel et al. (1998). 335

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Figure 4. A, B, Photomicrographs of the typical foraminifera and calcareous algal assemblages of the Nummulitic limestones within Indus suture zone, Ladakh. C, Restored cross section of the Indus Group molasse basin showing the Paleocene Sumda Formation and early Eocene Nummulitic limestones overlain by massive continental conglomerates of the Hemis Formation. Foraminifera illustrated show axial cross sections of Nummulites burdigalensis burdigalensis (a), Alveolina ellipsoidalis (b), and Assilina placentula (c). Scale bar ¼ 1 mm.

group (fusiform type) or the Alveolina (Alveolina) ellipsoidalis group (oval types; White 1992). These miliolid foraminifera have a stratigraphic range of latest Late Paleocene to Early Eocene. Postdepositional deformation of the tests of foraminifera from the ISZ samples prohibits any differentiation between these two groups (fig. 4). Also seen are thick-walled lenticular and discoidal forms with a pronounced alar prolongation, marginal cord, and umbilical boss. These features are evident in vertical and axial sections (fig. 4, a, c), while equatorial sections show thick, straight septa and a thick marginal cord. These features are characteristic of nummulitidae assigned to the assiline group and in

particular Assilina placentula. The thick-walled nummulites (fig. 4, a) are similar to the species Nummulites burdigalensis burdigalensis. The age range of both these taxa is mid-Cusian. Serra-Kiel et al. (1998) have used the biostratigraphic range of A. ellipsoidalis to assist in defining shallow benthic foraminiferal biozones (SBZ, fig. 3). The closest complete reference section to the ISZ is the limestones of the Late Paleocene Ranikot Formation of Nammal Gorge in the Salt Range of Pakistan (Haque 1956). Larger benthic foraminiferal species recorded from the Late Paleocene to Late Eocene limestones of this area in western Pakistan by Davies and Pinfold (1937) and Eames (1951) can

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be assigned to shallow benthic zones (SBZs) ranging from SBZ3 (e.g., Lockhartia haimei) to SBZ18 (e.g., Nummulites beaumonti and Nummulites perforatus). An objective of this article is to recognize the shallow benthic zones within the Tertiary larger benthic foraminiferal assemblages of the Zanskar Tethyan limestones occurring around the Spontang ophiolite and in the ISZ. The limestones of the ISZ contain alveoline benthic foraminifera confirmed from SBZs 5 and 6 and nummulites and assilines from SBZ10.

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chrome spinel, derived from the ophiolite, during the Paleocene (Ding et al. 2005; Kapp et al. 2005). The entire ophiolite and Photang thrust sheets have been rethrust along with the underlying shelf carbonate sequence following the continental collision, such that the Spontang ophiolite now overlies Mesozoic shelf and neoautochthonous Paleogene sedimentary rocks (Searle 1986; Searle et al. 1997; Corfield and Searle 2000). This post-Eocene breakback thrusting placed the Spontang ophiolite over the neoauthochthonous Paleocene-Eocene limestones (Corfield et al. 1999, 2001).

Spontang Ophiolite The Spontang ophiolite, obducted onto the northern passive continental margin of the Indian plate, is the best-preserved ophiolite in the Himalaya (Searle 1986; Searle et al. 1988; Corfield and Searle 2000; Corfield et al. 2001). It contains a complete section of mantle peridotites and crustal gabbros, diorites, plagiogranites, sheeted dykes, and pillow lavas. The Spontang ophiolite comprises middle Jurassic mid-ocean-ridge-basalt-type crust overlain by a Turonian arc sequence of andesites and dacites approximately 500 m thick (Corfield et al. 2001). Using the U-Pb method, Pedersen et al. (2001) dated magmatic zircons from plagiogranites within the crustal sequence of the Spontang ophiolite at 177 ± 1 Ma. Zircons from a dacite-andesite sequence of arc lavas erupted on top of the ophiolite (Spong arc) were dated at 88 ± 5 Ma (Pedersen et al. 2001). The ophiolite formed in a mid-ocean ridge setting within Tethys during the Early-Middle Jurassic, and during the Campanian (Late Cretaceous), a subduction zone must have been initiated that was responsible for the Spong arc andesites and the beginning of obduction of the Spontang ophiolite and its arc sequence above, southward onto the Indian plate margin (Corfield et al. 2001; Pedersen et al. 2001). Backstripping of the Zanskar continental margin sediments has shown that a phase of margin collapse coincided with emplacement of the ophiolite onto the margin during the latest Cretaceous (Corfield et al. 2005). The Spontang ophiolite was originally emplaced onto the Zanskar passive margin during the Late Cretaceous, along with the underlying Photang and Lamayuru thrust sheets (Searle 1986; Corfield et al. 1999). The Photang thrust sheet immediately beneath the ophiolite contains imbricated slices of Permian- to Late-Cretaceous-age sedimentary rocks and alkali volcanics but no Tertiary rocks (Corfield et al. 1999). A major change in depositional environment and provenance occurred at ∼65–55 Ma coinciding with the first appearance of detrital

Himalayan Cenozoic Platform Stratigraphy The Himalayan Late Cretaceous (Maastrichtian) to Early Eocene successions outcrop along three northwest-southeast-trending belts: (1) the Himalayan foothills, (2) the Zanskar Tethyan Zone, and (3) the ISZ (Mathur and Juyal 2000). Although a major unconformity is recognized between the Cretaceous and Tertiary sediments (Srikantia et al. 1978), the sediments of this age in the western Zanskar-Ladakh area have been attributed to the Spanboth Limestone (Fuchs 1982). This formation consists of approximately 300 m of predominantly carbonate sediments exposed along the Spanboth Valley (situated approximately 20 km west of the Spontang ophiolite), with the sequence subdivided into litho- and biostratigraphical units (Gaetani et al. 1980). Three distinct members are recognized within this formation: (1) the Marpo Limestone, (2) the Stumpata quartzarenite, and (3) the Dibling Limestone (Nicora et al. 1987). The lower member (Marpo Limestone) has been correlated to the basal Lingshed Limestone, a distal equivalent in the eastern Zanskar (Fuchs 1982). Within this limestone member, a twofold subdivision is recognized: the lower Singe La limestone and the upper Kesi limestones (Garzanti et al. 1987). Gaetani and Garzanti (1991) and Premoli Silva et al. (1992) undertook detailed sedimentary studies of the entire Permian to Mesozoic and early Tertiary shelf carbonate sequence in Ladakh, while sequences in South Tibet have been studied by Liu and Einsele (1994) and Willems et al. (1996). Our study examines sediments from Late Cretaceous and Tertiary successions in several valley profiles around the Spontang ophiolite in the northern Zanskar ranges (fig. 2). Three of the sections occur to the west and the southwest of the ophiolite complex and are situated at Gongma (fig. 5), Marling (fig. 6), and Singe Chu (fig. 7), while the fourth section at Kanji (fig. 8) is situated toward the northwest of the ophiolite complex. Two other sections,

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Figure 5. Geological stratigraphic section through the Late Cretaceous–Early Tertiary rocks of the Gongma area (see fig. 2 for location), with photomicrographs of characteristic foraminifera. Scale bar ¼ 0:5 mm.

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Figure 6. Geological stratigraphic section through the Late Cretaceous–Early Tertiary rocks of the Marling area (see fig. 2 for location), with photomicrographs of characteristic foraminifera. ML ¼ Marpo Limestone, SQ ¼ Stumpata quartzarenite. Scale bar ¼ 1 mm (MA42); 0.25 mm (MA8, MA9, MA33).

Figure 7. Geological stratigraphic section through the Late Cretaceous–Early Tertiary rocks of the Singe-Chu area (see fig. 2 for location), with photomicrographs of characteristic foraminifera. ML ¼ Marpo Limestone, SQ ¼ Stumpata quartzarenite. Scale bar ¼ 1:5 mm (SC70, SC53); 0.5 mm (SC18, SC29).

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Figure 8. Geological stratigraphic section through the Late Cretaceous–Early Tertiary rocks of the Kanji area (see fig. 2 for location), with photomicrographs of characteristic foraminifera. Scale bar ¼ 0:5 mm.

at Dibling toward the southwest and at Marpo (Spanboth) in the west, have been described by Nicora et al. (1987) and are used to illustrate the more proximal exposures of the carbonate facies. The basal Mesozoic comprises Campanian to Late Maastrichtian sediments of the Kanji La Formation. This is a thick (>1000 m) terrigenous detri-

tal series, dominated by massive poorly bedded dark gray-green marls and mudstones with occasional argillaceous- or calcareous-rich sandstone horizons that frequently contain the trace fossil Zoophycus (Fuchs and Willems 1990). The formation is a typical basin deposit, with an abundant supply of terrigenous material coming from a southern direc-

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tion (Fuchs and Willems 1990). As the terrigenous component of the sediment gradually decreases, a shallowing-upward sequence typical of a carbonate outer shelf environment is recognized (Gaetani et al. 1983, 1986). The carbonate units are as follows. Marpo Limestone. The Upper Maastrichtian carbonate-rich Marpo Limestone is the oldest member of the Spanboth Formation, and it conformably overlies and runs upgrade from the Kangi La Formation (Fuchs and Willems 1990). The type section near the village of Marpo reaches a thickness of >100 m (Fuchs and Willems 1990), thinning to the east (22 m at Kanji and 2–5 m at Singe Chu, Gongma, and Marling; figs. 5–8). Lithologically, this unit comprises a series of mixed arenaceous-calcareous beds, with some thicker quartz-rich layers exposed in the Spanboth Valley and exhibiting current bedding, while carbonate-rich horizons can show evidence of burrowing (Fuchs 1982). A diverse benthic-marine assemblage of molluscs, corals, crinoids, and bryozoa, in addition to foraminifera, has been identified (Fuchs 1982; Gaetani et al. 1983, 1986; Fuchs and Willems 1990). The lower dark gray nodular limestone is characterized by the abundant presence of the larger benthic foraminfera Omphalocyclus macroporus, while the upper pelitic limestones are dominated by Siderolites calcitrapoides. Stumpata Quartzarenite. Immediately overlying the Marpo Limestone is the Stumpata Quartzarenite Member. The type section at the village of Stumpata attains a thickness of 67 m (Nicora et al. 1987), thinning distally to the northwest, east, and south. The lithology is typical of a mature fineto medium-grained pure quartz-arenite, typically colored gray-white on fresh surfaces but characteristically weathering brown. The basal and middle beds of the unit are commonly cross-bedded, which is interpreted as representing deposition within a high-energy beach environment (Nicora et al. 1987; Gaetani and Garzanti 1991). Toward the top of the unit, the calcareous component of the sandstone increases, reflecting an interfingering with the overlying Dibling Limestone in the direction of open marine seas of the carbonate platform (Fuchs and Willems 1990). Dibling Limestone. The upper limestones of the Spanboth Formation are exposed as a continuous cliff-forming horizon all around the southern and western edges of the Spontang ophiolite (Colchen and Reuber 1986; Corfield and Searle 2000). Three locally developed subunits or lithozones are developed in the Zanskar area and described from the base up below.

This basal unit is characterized by a series of dark gray to black thinly bedded limestones, occasionally with horizons of black chert nodules and interbedded with minor gray marls. More distal sections (e.g., Singe Chu) are characterized by an increase in the proportion of interbedded marls and chert nodules. A mixed planktonic and calcareous and agglutinated smaller benthic foraminiferal assemblage dominates this part of the sequence. Members of the family Globorotaliidae dominate the deepwater planktic element of the assemblage, with the most abundant taxa being Planorotalites pseudomenardi, Morozovella aequa, and Morozovella velascoensis. These species indicate a Late Paleocene age for this part of the sequence. A diverse assemblage of nondiagnostic agglutinated and smaller calcareous benthic foraminifera is also evident. These include the agglutinated forms Pseudotextularia sp. and Bigenerina sp. and the calcareous semi-infaunal Nodosariacea Vaginulinopsis sp., along with a number of indeterminate taxa of smaller benthic miliolids. Overlying the nodular limestones is a series of planar bioclastic wackestones. Although these contain a less diverse foraminiferal assemblage, fragmented oblique sections through both Planorotalites sp. and Morozovella sp. are recognizable. The increased argillaceous content within this part of the formation marks a transition from an open marine to a protected shallower-water environment (Nicora et al. 1987). The Singe-la Limestone Formation of distal sections to the southeast in our study area (figs. 1, 10) represent deeper-water shelf environment sedimentation, and the sequence is known as the Transition Series (Garzanti et al. 1987). From proximal sections (e.g., Dibling and Kesi columns of fig. 10), shallow-water, calcareous, larger benthic foraminifera (e.g., Assilina, Daviesina, Operculina, Ranikothalia, Lockharti, and Orbitolites) have been recognized throughout the Dibling Limestone (Nicora et al. 1987). These genera are missing from the distal localities and sections of the Singe Limestone. Kesi Limestone. The upper part of the Dibling Limestone is represented as a dark gray to black wackestone and is remarkably consistent across the Ladakh and Zanskar Range. These horizons contain numerous biogenic fragments of small benthic foraminifera, echinoderm plates, and spines. Packstones and grainstones occur in the upper parts that are dominated by shallow-water, calcareous larger benthic foraminifera, most notably Alveolina and Nummulites. Assemblages containing Assilina, Discocyclina, and Orbitolites are also evident, while rare occurrences of Miscellanea and the earSinge-la Limestone.

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liest Nummulitidae Ranikothalia have also been found in stratigraphically higher beds. The larger benthic foraminifera are frequently found in association with smaller benthic agglutinated forms and the ubiquitous smaller benthic miliolids (e.g., Quinqueloculina sp.). Kong Slates. In distal parts of the shelf, the Kong Slates directly overlie the Kesi Limestone, while in the proximal areas a lateral transition into the Chulung La Slates is observed. Basal beds mark an abrupt transition from shallow marine to clastic marine deposition. Foraminifera-rich, angular to well-rounded limestone clasts ranging in size from several centimeters to >1 m diameter are supported in a shaley matrix. The foraminiferal assemblage of the clasts indicates their derivation from the underlying limestones. These are interbedded with fine-grained turbidite deposits (fine sand to mud-size particles), exhibiting obliquely crosscutting axial planar cleavage, typically well developed in the finer shales. The foraminiferal assemblages are dominated by calcareous larger benthic forms, although a smaller benthic assemblage of agglutinates and miliolids is also present. Larger benthic forms exhibit various degrees of fracturing, corrosion, and deformation, supporting evidence of a reworked origin from the underlying limestones. In samples examined from the Chomo valley, foraminiferal test replacement by partial silicification is evident, reflecting the mobile nature of the silica component present in fine-grained volcanic rock fragments derived from the erosion of the Spontang ophiolite. Species identified from the limestone beds and clasts include Assilina pomeroli, Nummulites burdigalensis burdigalensis, and Assilina placentula (Mathur and Juyal 2000), with first occurrences and ranges from SBZ9 to SBZ10 and age ranges of early to mid-Cuisian (fig. 3). The Kong Slates are the youngest marine deposits found anywhere within the Tethyan Himalaya. Carbonate Platform Evolution. At its most basic, a carbonate platform comprises three geometric elements: a ramp (topographically inclined planes, deepening toward a basin), a shelf (a shallower inclination with a steeply defined slope into the basin), and a bank (steeply defined slopes on both seaward and landward sides; James and Kendall 1992). The distribution and relative position of nine distinct Standard Facies Belts encountered through a traverse across a carbonate platform have been described by Wilson (1974, 1975). Criteria used in defining the facies belts included lithology, bedding and sedimentary structures, grain type and depositional texture, the terrigenous component, and the

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biota present, while secondary criteria, such as sediment body morphology and geographical site and situation coupled with microfabric analyses, aided in refining the facies belts. Utilizing the standard carbonate facies belts described by Wilson (1974, 1975), Hallock and Glenn (1986) outlined a model that predicts the distribution of modern larger benthic foraminifera across a Cenozoic carbonate platform. This illustrates the idealized distribution from a nearshore restricted platform and lagoonal areas containing a mixed assemblage of miliolids, peneroplids, and smaller rotaliines progressing to open platform assemblages of intermediate rotaliines and soritids. Lee slope shelf sands, topographic highs (reefs), and foreslope areas are characterized by diverse assemblages of large, ornate thick-shelled rotaliines and flat soritids. Distal open shelf areas have assemblages dominated by the deeper-water, large flat rotaliines, giving way to planktonics in deep basins. Across the carbonate platform of Ladakh, the relative positions of these assemblages are illustrated in figure 9. The value of planktonics in global biostratigraphic zonation and correlations (rapid evolution, short stratigraphic time ranges, abundance in open marine environments) is well established (Postuma 1971), and they have been successfully used in the correlation of Tertiary rocks from Asia to Europe (Nagappa 1959; Dorreen 1974). The adaptation of larger benthic foraminifera as a biostratigraphical tool was initially established by Hottinger (1960) using Alveolines and was later modified by Schaub (1981) to include the Nummulitidae; it was further refined by Serra-Kiel (1998), who used 406 species to establish 20 shallow benthic subzones. Reconstructing the Paleocene–Eocene Shelf Margin We used the detailed stratigraphic and biostratigraphic data to reconstruct the Indian plate margin during the Paleocene–Eocene (figs. 9, 10). Skeletal wackestones dominate the shelf and platform facies and contain a diverse fauna of abundant molluscs, echinoids, and larger benthic foraminifera (Brookfield and Andrews-Speed 1984). Foraminiferal assemblages indicate a range of open marine carbonate platform and shoal facies of grainstones and packstones and associated subenvironments, with an inner shallow platform dominated by a mixed population of larger and smaller benthic miliolids, while the platform edge and slope faunas are composed of the larger benthic foraminifera (Alveolines and Nummulites). The distal deeper basin areas

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Figure 9. Diagrammatic reconstruction of the Early to Middle Eocene carbonate platform with the relative positions of the foraminiferal biofacies present along the Indian plate margin. KL9b: a ¼ Nummulites sp., b ¼ Orbitolites sp. Scale bar ¼ 1 mm.

contain assemblages dominated by globular planktonic foraminifera (Globorotalids). The biostratigraphic and geographic data can be used to construct an evolutionary model for sedimentation and tectonic evolution of the north Indian plate margin during the Early Paleocene to Middle Eocene time (fig. 11). The Spontang ophiolite and the underlying allochthonous Photang and Lamayuru thrust sheets were emplaced onto the passive margin of India during the Late Cretaceous. Along the outer shelf, a major unconformity occurs above the Kangi-la shales and beneath the Upper Maastrichtian Marpo Formation. Folds and thrusts in the shelf sequence beneath are truncated at this unconformity. A major phase of folding and thrusting occurred along the Zanskar shelf margin before

the deposition of the Paleocene Dibling and Singe formation limestones (Searle 1986; Searle et al. 1988, 1997; Corfield and Searle 2000). Mesozoic shelf carbonates below the Paleocene unconformity show tight to isoclinal folding and a large amount of crustal shortening, whereas the Paleocene limestones above are only gently folded. A major regional unconformity occurs above the Lower Eocene limestones across the entire shelf (Dibling, Kesi, and Kong formations) and in the suture zone (above the Nummulitic limestones). Early Eocene flexural folding resulted in uplift and emergence of the Late Paleocene limestones inboard (southwest) and flexural subsidence of the Singe limestones toward the margin. Renewed southwest-directed thrusting occurred during and

Figure 10.

Stratigraphic compilation of the Ladakh proximal to distal shelf-basin with tentative lithological correlations.

Figure 11. Model of the evolution of the north Indian plate margin from Middle Paleocene to Middle Eocene based on sedimentological constraints from eight measured sections.

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after the Middle Eocene, with thick-skinned thrusts affecting the entire Mesozoic and Paleogene sequence. This resulted in late-stage rethrusting of shelf carbonates over the ophiolite along the Photoksar thrust (Corfield and Searle 2000). Age of Initiation of India-Asia Collision Figure 12 shows a compilation of the stratigraphic, paleontological, and structural data for the Late Cretaceous and Early Tertiary rocks from around the northern margin of the Indian plate. The timing of ophiolite formation and emplacement in Oman is well constrained (see review of data in Searle et al. 2004). Around the Indian plate margin, emplacement ages of the West Pakistan ophiolites from radiometric and stratigraphic data have been proposed by Gnos et al. (1996). Apart from Ladakh, two other areas along the Indian plate margin have been studied in detail, the Waziristan-Khost area of northwest Pakistan (Beck et al. 1995, 1996) and the Gamba and Tingri regions of South Tibet (Willems and Zhang 1993a, 1993b; Rowley 1996, 1998; Willems et al. 1996; Zhu et al. 2005). Along the suture zone in South Tibet, the Yamdrock Mélange, previously thought to be Late Cretaceous, also has radiolarians as young as Late Paleocene (Aitchison et al. 2003; Ding et al. 2005). Aitchison et al. (2003) correlate the Paleocene Liuqu conglomerates with the Yamdrok Mélange. Spectacular continental conglomerates and coarse clastic sediments unconformably overlie all marine sediments, mélanges, and ophiolitic rocks everywhere along the suture zone both in Ladakh and Tibet. Waziristan-Khost. Beck et al. (1995, 1996) proposed an early India-Asia collision from a biostratigraphic analysis of the rocks from the WaziristanKurram district of northwest Pakistan. They proposed two episodes of collision-related thrusting, the first as the accretionary prism and trench rocks were thrust onto the northwest passive margin of India between 65 and 55.5 Ma. Upper Paleocene shallow-marine carbonates and shales were deposited unconformably on top of these rocks. The second episode of thrusting affected all these rocks, and the structures associated with this phase of deformation are unconformably overlapped by upper Lower Eocene limestones dated at 49 Ma. The first episode of thrusting in Waziristan probably corresponds to the phase of thrusting in Ladakh associated with obduction of the Spontang ophiolite onto the Indian passive margin (Searle 1986; Searle et al. 1997; Corfield et al. 2001), although in Waziristan it extends up into the Paleocene. Shallow marine Upper Paleocene–Lower

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Eocene limestones (Hangu and Lockhart formations) overlap the highly folded and thrust shelf carbonates and Khost ophiolites in Waziristan. The earliest Eocene Patala Formation indicates a deepening foredeep as the Kahi Mélange was emplaced (Beck et al. 1995). South Tibet (Gamba and Tingri). The marine to continental transition in the Tethyan Himalaya of South Tibet has been intensively studied in the Zhepure Shan ranges west of the Shekar dzong (New Tingri) and the Gamba region, north of Sikkim. Both these regions are between 60 and 100 km south of the suture zone on the Indian plate and therefore may not exactly indicate the age of suture zone closure. Earlier studies proposed that the age of youngest marine rocks in Tibet was Ilerdian (P6 zone, 53 Ma) in the Gamba or the Khampa dzong regions (Willems and Zhang 1993a, 1993b) and early Lutetian (P10 zone, 47 Ma) in the Tingri section (Willems et al. 1996). On the basis of this dating, Rowley (1996) initially proposed a diachronous closure from late Ypresian in the west (Pakistan, Ladakh) to Lutetian in the east (Tibet and Indo-Burman ranges). Wang et al. (2002) proposed an even later marine-continental transition, based on Middle Lutetian to late Priabonian (47–34 Ma) nannofossils from the Pengqu Formation, also in the Zhepure Shan. Zhu et al. (2005) reexamined the same sections and suggested that most of the fossils were reworked in these fluvial channel and floodplain deposits and do not reflect the age of sedimentation. The youngest marine sediments in this part of the Himalaya are the Upper Danian to Ypresian Zhepure Shan Formation and the overlying Youxia Formation (Zhu et al. 2005). The Zhepure Shan Formation consists of well-bedded Nummulitic limestones equivalent to the Dibling, Singi-la, and Kesi formations in Ladakh. The Youxia Formation consists of green shales and thin-bedded sandstones, with rare limestones deposited on an outer-shelf marine environment. Several agediagnostic planktonic foraminifera all have their last appearance in zone P8 with an age range of 50.8–50.4 Ma (Zhu et al. 2005) on the Berggren et al. (1995) timescale, and this has been interpreted to be the final marine sediments exposed on the Indian shelf. The conformable contact between the Zhepure Shan and Youxia Formations marks the transition from passive margin to foredeep tectonic environment (Zhu et al. 2005). A major disconformity, marked by a paleosol horizon, separates the marine Youxia Formation from the overlying continental red beds of the Shenkeza Formation (Zhu et al. 2005).

Figure 12. Jurassic to Eocene time chart summarizing all age data for ophiolites and associated fossiliferous sediments from Oman, Pakistan, Ladakh, and South Tibet (see text for sources of data).

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We contend that the stratigraphic ages from these localities in Gamba, Tingri, and Zhepure Shan may not date the India-Asia collision at all, because they are located so far south of the suture zone. It is possible that India-Asia collision along the Yarlung Tsangpo suture zone was earlier than 50 Ma (Wan et al. 2002) and that these Lower Eocene marine sediments formed in a Persian (Arabian) Gulf–type tectonic position well inboard of the actual collision zone. Indian Plate Foreland. Along the Lesser Himalaya and Indian foreland, the youngest marine sediments exposed range from early Eocene Nummulitic limestone bands (P7 and SBZ10 zones; 52–51 Ma) in the Hazara syntaxis that overlie the Paleocene shallow marine Patala Formation (Bossart and Ottiger 1989) to mid-Lutetian limestones (P11 and SBZ14; 45 Ma) in the Spiti, Bilaspur, and Dadahur areas (Singh 1980). In the Tansen area of Nepal, Matsumaru and Sakai (1989) have identified Nummulites beaumonti (first occurrence SBZ15, P12; 43 Ma) from the Bhainskati Formation, (Kirthar Series) Middle Eocene. The Nummulitic limestones of the Hazara syntaxis are structurally intercalated with thick clastic red beds (Balakot Formation) that have detrital muscovite ages of 36–40 Ma (Najman et al. 2001), indicating a 10-m.yr. gap between the end of marine sedimentation and the beginning of continental sedimentation on the Indian plate. This could be interpreted as the flexural forebulge migrating southward across the Himalaya during the early postcollision phase of deformation. However, the Hazara region was at least 100 km south of the ISZ, probably more (500 km) after restoration of the folds and thrusts in the Himalaya, and these age data may not be at all relevant to the precise age of India-Asia collision. In Nepal, similar Lower-Middle Eocene shallow marine sediments (Bhainskati Formation) are overlain by continental fluvial deposits of the Lower Miocene Dumri Formation, with a 15–20-m.yr. time gap separating the two (DeCelles et al. 1998). Detrital zircon U-Pb age dating indicates that the first sign of Himalayan provenance also occurs in the middle Eocene (DeCelles et al. 1998). Conclusions 1. A minimum age for the closure of Tethys in the Ladakh-Zanskar Himalaya and the start of India-Asia collision is provided by the final marine incursion of Nummulitic limestones (plankton foraminifera zone P8, shallow benthic zone SBZ10, 50.5 Ma; Cuisian and Ypresian stages of early Eocene) along the ISZ and on the northern part of

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the Indian plate margin. Our data supports the earlier studies of Ladakh by Garzanti et al. (1987, 1996), Searle et al. (1987, 1988), and Garzanti and van Haver (1988). Biostratigraphy from Waziristan (Beck et al. 1995, 1996) and southern Tibet (Zhu et al. 2005) are compatible with an ending of marine sedimentation at this time, showing that there is no evidence for diachroneity of collision, at least from northwest Pakistan to southeast Tibet. 2. The maximum age for the initiation of the India-Asia collision is 56.5–54.9 Ma, the end of the Paleocene Sumda Formation limestone deposition, which marks the ending of continuous marine sedimentation within the Tethyan ISZ. This probably marks the initial connection between Indian passive margin continental crust and Asian active margin crust. Chogdo Formation red beds disconformably overlie Upper Paleocene Alveolina limestones (zone P5) but are unconformably overlain by the final marine incursion, the P7-8/SBZ10 Nummulitic limstones in the suture zone. 3. The marine to continental transition recorded in the stratigraphic record of Gamba, Tingri, and Zhepure Shan in South Tibet and the Hazara syntaxis, Pakistan, do not record an accurate age of India-Asia collision because they are a long way south of the suture zone. By analogy to modern examples (Arabia–Central Iran collision), the age of continental collision along the suture zone (Zagros suture) is older than marine sedimentation hundreds of kilometers inboard (present-day Arabian Gulf). 4. A major phase of southward thrusting of oceanic rocks, ophiolites, and mélanges onto the northern passive margin of India occurred during the Campanian–Lower Maastrichtian in Ladakh and up to Lower Paleocene in Waziristan. This was associated with obduction of ophiolites and ophiolitic mélange onto the depressed Indian margin before the India-Asia collision. Ophiolite emplacement, involving at least 100 km of thrusting, was not an instantaneous event and could have lasted for at least 10–15 m.yr. A significant phase of subsidence is recorded along the north Indian shelf margin during the Campanian–Lower Maastrichtian (Corfield et al. 2005) that extended up into the Danian phase of the Early Paleocene in South Tibet (Rowley 1998). 5. Final northward subduction of Neo-Tethyan oceanic lithosphere beneath the Asian margin before the collision coincides closely with the youngest subduction-related (I-type) granitic magmatism along the south Asian margin in the LadakhGangdese batholith (U-Pb ages spanning 102–

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49 Ma; Honegger et al. 1982; Schärer et al. 1984; Weinberg and Dunlap 2000). 6. Following India-Asia collision, the Indus Molasse Group continental clastic sequence was deposited in an elongated trough along the site of the ISZ. Most of the clasts were derived from the uplifted Asian margin (Ladakh-Gangdese granites and calc-alkaline volcanics). A few clasts are ophiolitic or chert derived from the underlying suture zone rocks, or less commonly, they are carbonates derived from the Indian margin to the south. Sr, Nd, and Pb isotopic analysis of shales from the Indus molasse support the contention that the main sediment source was from the Trans-Himalayan batholith to the north (Clift et al. 2002). Post-India-Asia collision crustal shortening along the Indus molasse basin resulted in Neogene shortening of ~35 km that has been absorbed by isoclinal folding and steep north-vergent backthrusting (Searle et al. 1987, 1988, 1990). 7. The Gangrinboche (Kailas) conglomerates do not record timing of India-Asia collision as claimed by Aitchison et al. (2002, 2003, 2007) and Aitchison and Davis (2004). They simply record that by Oligocene time, the southern margin of Asia was topographically high, and it was shedding debris into the postcollisional molasse basin.

8. Stratigraphy, age, and structure of the Tertiary Indus Molasse Group sediments are remarkably similar along the strike of the ISZ, at least from Ladakh to South Tibet (Kailas and Yarlung Tsangpo suture zone), 1000 km to the east, suggesting an orthogonal, nonoblique India-Asia collision that may have begun initially at the end of the Paleocene (56.5 Ma), with the first disconformable continental clastic sedimentation (Chogdo Formation) above marine limestones. The final closure of Neo-Tethys immediately followed deposition of the youngest marine Nummultic limestones in the suture zone in the Lower Eocene (50.5 Ma). The most robust age for the marine to continental transition along the ISZ, and hence the closing of Tethys in the Himalaya is 50.5 Ma (during the planktonic foraminifera zone P8, shallow benthic zone SBZ10). ACKNOWLEDGMENTS

This work was carried out using Natural Environment Research Council grant NER/K/S/2000/951 to M. P. Searle. We thank Fida Hussein and Lobsang and Namgyal Tsering of Leh for local logistics, D. Sansom for assistance with drafting the figures, and E. Garzanti and D. Rowley for constructive detailed reviews.

REFERENCES CITED

Aitchison, J. C.; Ali, J. R.; and Davis, A. M. 2007. When and where did India and Asia collide? J. Geophys. Res. 12, doi: 10.1029/2006JB004706. Aitchison, J. C.; Badengzhu; Davis, A. M.; Liu, J.; Luo, H.; Malpas, J. G.; McDermid, I. R. C.; Wu, H.; Ziabrev, S. V.; and Zhou, M.-F. 2000. Remnants of a Cretaceous intra-oceanic subduction system within the YarlungZangbo suture (southern Tibet). Earth Planet. Sci. Lett. 183:231–244. Aitchison, J. C., and Davis, A. M. 2004. Evidence for the multiphase nature of the India-Asia collision from the Yarlung Tsangpo suture zone, Tibet. In Malpas, J.; Fletcher, C. J. N.; Ali, J. R.; and Aitchison, J. C., eds. Aspects of the tectonic evolution of China. Geol. Soc. Lond. Spec. Publ. 226:217–233. Aitchison, J. C.; Davis, A. M.; Abrajevitch, A. V.; Ali, J. R.; Badengzhu; Liu, J.; Luo, H.; McDermid, I. R. C.; and Ziabrev, S. V. 2003. Stratigraphic and sedimentological constraints on the age and tectonic evolution of the Neotethyan ophiolites along the Yarlung Tsangpao suture zone, Tibet. In Dilek, Y., and Robinson, P. T., eds. Ophiolites in Earth history. Geol. Soc. Lond. Spec. Publ. 218:147–164. Aitchison, J. C.; Davis, A. M.; Badengzhu; and Luo, H. 2002. New constraints on the India-Asia collision: the Lower Miocene Gangrinboche conglomerates, Yarlung

Tsangpo suture zone, SE Tibet. J. Asian Earth Sci. 21: 253–265. Beck, R. A.; Burbank, D. W.; Sercombe, W. J.; Khan, A. M.; and Lawrence, R. D.1996. Late Cretaceous ophiolite obduction and Paleocene India-Asia collision in the westernmost Himalaya. Geodynam. Acta 9:114–144. Beck, R. A.; Burbank, D. W.; Sercombe, W. J.; Riley, G. W.; Barndt, J. K.; Berry, J. R.; Afzal, J.; et al..1995. Stratigraphic evidence for an early collision between northwest India and Asia. Nature 373:55–58 Berggren, W. A.; Kent, D. V.; Swisher, C. C., III; and Aubry, M. P.1995. A revised Cenozoic geochronology and chronostratigraphy. In Berggren, W. A.; Kent, D. V.; Audry, M. P.; and Hardenbol, J., eds. Geochronology, time scales and global stratigraphic correlation. Soc. Econ. Paleontol. Mineral. Spec. Publ. 54:129–212. Berggren, W. A., and Miller, K. G. 1988. Paleogene tropical planktonic foraminiferal biostratigraphy and magnetobiochronology. Micropaleontology 34:362–380. Besse, J., and Courtillot, V. 1988. Paleogeographic maps of the continents bordering the Indian Ocean since the Early Jurassic. J. Geophys. Res. 93:11,791–11,808. ———. 1991. Revised and synthetic apparent polar wander paths of the African, Eurasian, North American and Indian plates, and true polar wander since 200 Ma. J. Geophys. Res. 96:4029–4050.

Journal of Geology


Besse, J.; Courtillot, V.; Pozzi, J. P.; Westphal, M.; and Zhou, Y. X. 1984. Palaeomagnetic estimates of crustal shortening in the Himalayan thrusts and Zangpo suture. Nature 311:621–626. Blondeau, A.; Bassoullet, J.-P.; Colchen, M.; Han, T. L.; Marcoux, J.; Mascle, G.; and van Haver, T. 1986. Disparitions des formations marines à l'Éocène inférieur en Himalaya. Sci. Terre Mem. 47:103–111. Bossart, P., and Ottiger, R. 1989. Rocks of the Murree formation in northern Pakistan: indicators of a descending foreland basin of late Paleocene to middle Eocene age. Eclogae Geol. Helv. 82:133–165. Brookfield, M. E., and Andrews-Speed, C. P. 1984. Sedimentology, petrography and the tectonic significance of the shelf, flysch and molasse clastic deposits across the Indus Suture Zone, Ladakh, NW India. Sediment. Geol. 40:249–286. Burky, D. 1973. Low-latitude coccolith biostratigraphic zonation. Initial Rep. Deep-Sea Drill. Proj. 15:685–703. ———. 1975. Coccolith and silicoflagellate stratigraphy, northwestern Pacific Ocean. Deep Sea Drilling Project leg 32. Initial Rep. Deep-Sea Drill. Proj. 32:677–701. Clift, P. D.; Carter, A.; Krol, M.; and Kirby, E. 2002. Constraints on India-Eurasia collision in the Arabian Sea region taken from the Indus Group, Ladakh Himalaya, India. In Clift, P. D.; Kroon, D.; Gaedicke, C.; and Craig, J., eds. The tectonic and climatic evolution of the Arabian Sea region. Geol. Soc. Lond. Spec. Publ. 195:97–116. Clift, P. D.; Degnan, P. J.; Hannigan, R.; and Blusztajn, J. 2000. Sedimentary and geochemical evolution of the Dras forearc basin, Indus suture, Ladakh Himalaya, India. Geol Soc. Am. Bull. 112:450–466. Colchen, M., and Reuber, I. 1986. Les mélanges ophiolitiques du Zanskar, Himalaya du Ladakh. C. R. Acad. Sci. Ser. D 303:719–724. Corfield, R. I., and Searle, M. P. 2000. Crustal shortening estimates across the north Indian continental margin, Ladakh, NW India. In Khan, M. A.; Treloar, P. J.; Searle, M. P.; and Jan, M. Q., eds. Tectonics of the Nanga Parbat Syntaxis and the western Himalaya. Geol. Soc. Lond. Spec. Publ. 170:395–410. Corfield, R. I.; Searle, M. P.; and Green, O. R. 1999. Photang thrust sheet: an accretionary complex structurally below the Spontang ophiolite constraining timing and tectonic environment of ophiolite obduction, Ladakh Himalaya, NW India. J. Geol. Soc. Lond.156: 1031–1044. Corfield, R. I.; Searle, M. P.; and Pedersen, R. B. 2001. Tectonic setting, origin, and obduction history of the Spontang ophiolite, Ladakh Himalaya, NW India. J. Geol. 109:715–736. Corfield, R. I.; Watts, A. B.; and Searle, M. P. 2005. Subsidence history of north Indian continental margin, Zanskar-Ladakh Himalaya, NW India. J. Geol. Soc. Lond. 162:135–146. Davies, L. M., and Pinfold, E. S. 1937. The Eocene beds of the Punjab Salt Range. Mem. Geol. Surv. India Palaeontol. Indica. NS XXIV, Mem. 1:1–79. Davis, A. M.; Aitchison, J. C.; Badengzhu; and Luo, H.

351

2004. Conglomerates record the tectonic evolution of the Yarlung-Tsangpo suture zone in southern Tibet. In Malpas, J.; Fletcher, C. J. N.; Ali, J. R.; and Aitchison, J. C., eds. Aspects of the tectonic evolution of China. Geol. Soc. Lond. Spec. Publ. 226:235–246. DeCelles, P. G.; Gehrels, G. E.; Quade, L.; and Ojha, T. P. 1998. Eocen–early Miocene foreland basin development and the history of Himalayan thrusting; western and central Nepal. Tectonics 17:741–765. DeMets, C.; Gordon, R.; Argus, D.; and Stein, S. 1990. Current plate motions. Geophys. J. Int. 101:425–478. de Sigoyer, J.; Chavagnac, V.; Blichert-Tift, J.; Villa, I.; Luais, B.; Guillot, S.; Cosca, M.; and Mascle, G. 2000. Dating the Indian continental subduction and collisional thickening in the northwest Himalaya: multichronology of the Tso Morari eclogites. Geology 28: 487–490. Dewey, J. F.; Cande, S.; and Pitman, W. C., III. 1989. Tectonic evolution of the India/Eurasia collision zone. Eclogae Geol. Helv. 82:717–734. Ding, L.; Kapp, P.; and Wan, X. 2005. Paleocene-Eocene record of ophiolite obduction and initial India-Asia collision, south central Tibet. Tectonics 24:TC3001, doi:10.1029/2004TC001729. Dorreen, J. M. 1974. The western Gaj River section, Pakistan, and the Cretaceous-Tertiary boundary. Micropaleontology 20:178–193. Eames, F. E. 1951. A contribution to the study of the Eocene in western Pakistan and western India. D. Discussion of the faunas of certain standard sections, and their bearing on the classification and correlation of the Eocene in western Pakistan and western India. Q. J. Geol. Soc. Lond. 107:173–200. Fuchs, G. 1982. The geology of western Zanskar. Jahrb. Geol. Bundesanst. 125:1–50. Fuchs, G., and Willems, H. 1990. The final stages of sedimentation in the Tethyan Zone of Zanskar and their geodynamic significance (Ladakh-Himalaya). Jahrb. Geol. Bundesanst. 133:259–273. Gaetani, M.; Casnedi, R.; Fois, E.; Garzanti, E.; Nicora, A.; and Tintori, A. 1986. Stratigraphy on the Tethys Himalaya in Zanskar, Ladakh. Riv. Ital. Paleontol. Stratigr. 91:443–478. Gaetani, M., and Garzanti, E. 1991. Multicyclic history of the Northern India continental margin (northwestern Himalaya). Am. Assoc. Petrol. Geol. Bull. 75:1427– 1446. Gaetani, M.; Nicora, A.; and Premoli-Silva, I. 1980. Uppermost Cretaceous and Paleocene in the Zanskar Range (Ladakh-Himalaya). Riv. Ital. Paleontol. Stratigr. 86:127–166. Gaetani, M.; Nicora, A.; Premoli-Silva, I.; Fois, E.; Garzanti, E.; and Tintori, A. 1983. Upper Cretaceous and Paleocene in Zanskar Range (NW Himalaya). Riv. Ital. Paleontol. Stratigr. 89:81–118. Garzanti, E.; Baud, A.; and Mascle, G. 1987. Sedimentary record of the northward flight of India and its collision with Eurasia (Ladakh Himalaya, India). Geodynam. Acta 1:297–312. Garzanti, E.; Critelli, S.; and Ingersoll, R. V. 1996.

352

O. R. GREEN ET AL.

Paleogeographic and paleotectonic evolution of the Himalayan Range as reflected by detrital modes of Tertiary sandstones and modern sands (Indus transect, India and Pakistan). Geol. Soc. Am. Bull. 108: 631–642. Garzanti, E., and van Haver, T. 1988. The Indus clastics: forearc basin sedimentation in the Ladakh Himalaya (India). Sediment. Geol. 59:237–249. Gnos, E.; Immenhauser, A.; and Peters, T. 1996. Late Cretaceous/early Tertiary convergence between the Indian and Arabian plates recorded in ophiolites and related sediments. Tectonophysics 271:1–19. Hallock, P., and Glenn, E. C. 1986. Larger foraminifera: a tool for paleoenvironmental analysis of Cenozoic depositional facies. Palaios 1:55–64. Haque, A. F. M. 1956. The smaller foraminifera of the Ranikot and Laki of the Nammal Gorge, Salt Range. Karachi, Mem. Geol. Surv. Pakistan, 300 p. Honegger, K.; Dietrich, V.; Frank, W.; Gansser, A.; Thoni, M.; and Trommsdorf, V. 1982. Magmatism and metamorphism of the Ladakh Himalayas (the IndusTsangpo suture zone). Earth Planet. Sci. Lett. 60:253– 292. Hottinger, L. 1960. Recherches sur les Alvéolines du Paléocène et d l’Éocène. Mem. Suisses Palentol. 75/76: 1–243. James, N. P., and Kendall, A. C. 1992. Introduction to carbonate and evaporate facies models. In Walker, R. G., and James, N. P., eds. Facies models: response to sea level change. St. Johns, Newfoundland, Geol. Assoc. Can., p. 265–275. Kapp, P.; Yin, A.; Harrison, T. M.; and Ding, L. 2005. Cretaceous-Tertiary shortening, basin development, and volcanism in central Tibet. Geol. Soc. Am. Bull. 117:865–878. Klootwijk, C.; Gee, J.; Peirce, J.; Smith, G.; and McFadden, P. 1992. An early India-Asia contact: paleomagnetic constraints from Ninetyeast Ridge, ODP leg 121. Geology 20:395–398. Klootwijk, C., and Pierce, J. 1979. India’s and Australia’s pole path since the late Mesozoic and the India-Asia collision. Nature 282:605–607. Leech, M. L.; Singh, S.; Jain, A. K.; Klemperer, S. L.; and Manickavasagam, R. M. 2005. The onset of India-Asia continental collision: early, steep subduction required by the timing of UHP metamorphism in the western Himalaya. Earth Planet. Sci. Lett. 234:83–97. Liu, G., and Einsele, G. 1994. Sedimentary history of the Tethyan basin in the Tibetan Himalayas. Geol. Rundsch. 83:32–61. Martini, E. 1971. Standard Tertiary and Quaternary calcareous nannoplankton zonation. In Farinacci, A., ed. Proceedings, Int. Conf. Planktonic Microfossils, 2nd (Roma, 1970) 2:739–785. Mathur, N. S., and Juyal, K. P. 2000. Atlas of Early Palaeogene invertebrate fossils of the Himalayan foothills belt. Monograph Ser. 1. Dehra Dun, Wadia Institute of Himalayan Geology, 257 p. Matsumaru, K., and Sakai, H. 1989. Nummulites and Assilina from Tansen area, Palpa district, the Nepal

lesser Himalayas. Trans. Proc. Palaeontol. Soc. Jpn. NS 154:68–76. Nagappa, Y. 1959. Foraminiferal biostratigraphy of the Cretaceous-Eocene succession in the India-PakistanBurma region. Micropaleontology 5:145–192. Najman, Y.; Pringle, M.; Godin, L.; and Oliver, G. 2001. Dating of the oldest continental sediments from the Himalayan foreland basin. Nature 410:194–197. Nicora, A.; Garzanti, E.; and Fois, E. 1987. Evolution of the Tethys Himalaya continental shelf during Maastrichtian to Paleocene (Zanskar, India). Riv. Ital. Paleontol. Stratigr. 92:439–496. Parrish, R. R.; Gough, S. J.; Searle, M. P.; and Waters, D. J. 2006. Plate velocity exhumation of ultrahigh-pressure eclogites in the Pakistan Himalaya. Geology 34:989– 992. Patriat, P., and Achache, J. 1984. India-Eurasia collision chronology has implications for crustal shortening and driving mechanism of plates. Nature 311:615–621. Pedersen, R. B.; Searle, M. P.; and Corfield, R. I. 2001. U-Pb zircon ages from the Spontang ophiolite, Ladakh Himalaya. J. Geol. Soc. Lond. 158:513–520. Postuma, J. A. 1971. Manual of planktonic foraminifera. Amsterdam, Elsevier, 420 p. Premoli-Silva, I. E.; Garzanti, E.; and Gaetani, M. 1992. Stratigraphy of the Chikkim and Fatu La formations in the Zangla and Zumlung units (Zanskar Range, India) with comparisons to the Thakkhola region (central Nepal): mid-Cretaceous evolution of the Indian passive margin. Riv. Ital. Paleontol. Stratigr. 97:511–564. Reuber, I. 1989. The Dras arc: two successive volcanic events on eroded oceanic crust. Tectonophysics 161: 93–106. Robertson, A. H. F. 1998. Rift-related sedimentation and volcanism of the North Indian plate inferred from a Permo-Triassic exotic block at Lamayuru (Ladakh Himalaya) and regional compressions. J. Asian Earth Sci. 16:159–172. Robertson, A. H. F., and Sharp, I. 1998. Mesozoic deepwater slope/rise sedimentation and volcanism along the north Indian passive margin: evidence from the Karamba Complex, Indus suture zone (western Ladakh Himalaya). J. Asian Earth Sci. 16:195–215. Rowley, D. B. 1996. Age of initiation of collision between India and Asia: a review of stratigraphic data. Earth Planet. Sci. Lett. 145:1–13. ———. 1998. Minimum age of initiation of collision between India and Asia north of Everest based on the subsidence history of the Zhepure mountain section. J. Geol. 106:229–235. Schärer, U.; Hamet, J.; and Allègre, C. J. 1984. The Transhimalaya (Gangdese) plutonism in the Ladakh region; a U-Pb and Rb-Sr study. Earth Planet. Sci. Lett. 67:327–339. Schaub, H. 1981. Nummulites et Assilines de la Téthys paléogène. In Taxinomie, phyogenèse et biostratigraphie. Mem. Suisses Paleontol. Vols. 104–106. Searle, M. P. 1986. Structural evolution and sequence of thrusting in the High Himalayan, Tibetan-Tethys and

Journal of Geology


Indus suture zones of Zanskar and Ladakh, western Himalaya. J. Structural Geol. 8:923–936. ———. 2001. Dating the Indian continental subduction and collisional thickening in the northwest Himalaya: multichronology of the Tso Morari eclogites: comment. Geology 29:191–193. Searle, M. P.; Cooper, D. J.; and Rex, A. J. 1988. Collision tectonics of the Ladakh-Zanskar Himalaya. Philos. Trans. R. Soc. A 326:117–150. Searle, M. P.; Corfield, R. I.; Stephenson, B.; and McCarron, J. 1997. Structure of the North Indian continental margin in the Ladakh-Zanskar Himlayas: implications for the timing of obduction of the Spontang ophiolite, India-Asia collision and deformation events in the Himalaya. Geol. Mag. 134:297–316. Searle, M. P.; Pickering, K. T.; and Cooper, D. J. 1990. Restoration and evolution of the intermontane Indus molasse basin, Ladakh Himalaya, India. Tectonophysics 174:301–314. Searle, M. P.; Warren, C. J.; Waters, D. J.; and Parrish, R. R. 2004. Structural evolution, metamorphism and restoration of the Arabian continental margin, Saih Hatat region, Oman Mountains. J. Struct. Geol. 26:451–473. Searle, M. P.; Windley, B. F.; Coward, M. P.; Cooper, D. J. W.; Rex, A. J.; Rex, D.; Tingdong, L.et al.1987. The closing of Tethys and the tectonics of the Himalayas. Geol. Soc. Am. Bull. 98:678–701. Serra-Kiel, J.; Hottinger, L.; Caus, E.; Drobne, K.; Ferrández, C.; Jauhri, A. K.; Less, G., et al.. 1998. Larger foraminiferal biostratigraphy of the Tethyan Paleocene and Eocene. Bull. Soc. Geol. Fr. 169:281–299. Singh, P. 1980. A note on the palaeogeography of Himalaya during Eocene. Curr. Sci. 49:706–707. Srikantia, S. V.; Ganesan, T. M.; Roa, P. N.; and Tirkey, B. 1978. Geology of Zanskar area, Ladakh Himalaya. Himalayan Geol. 8:1009–1033. Thakur, V. C. 1981. Regional framework and geodynamic evolution of the Indus-Tsangpo suture zone in the Ladakh Himalayas. Trans. R. Soc. Edinb. Earth Sci. 72:89–97. Treloar, P. J.; Broughton, R. D.; Williams, M. P.; Coward, M. P.; and Windley, B. F. 1989. Deformation metamorphism and imbrication of the Indian Plate, south of the

353

Main Mantle Thrust, North Pakistan. J. Metamorph. Geol. 7:111–125. Wan, C.; Li, X.; Hu, X.; and Jansa, L. F. 2002. Latest marine horizon north of Qomolangma (Mt. Everest): implications for closure of Tethys seaway and collision tectonics. Terra Nova 14:114–120. Wang, X. Q.; Jansa, L. F.; and Sarti, M. 2002. Cretaceous and Paleogene boundary strata in southern Tibet and their implication for the India-Eurasia collision. Lethaia 35:131–146. Weinberg, R. F., and Dunlap, W. J. 2000. Growth and deformation of the Ladakh Batholith, northwest Himalayas: implications for timing of continental collision and origin of calc-alkaline batholiths. J. Geol. 108:303–320. White, M. R. 1992. On species identification in the foraminiferal genus Alveolina (Late Palaeocene– Middle Eocene). J. Foram. Res. 22:52–70. Willems, H., and Zhang, B. G. 1993a. Cretaceous and Lower Tertiary sediments of the Tibetan Tethys Himalaya in the area of Gamba (South Tibet, PR China). Ber. FB Geowiss. Univ. Bremen 38:3–27. ———. 1993b. Cretaceous and lower Tertiary sediments of the Tibetan Tethys Himalaya in the area of Tingri (South Tibet, PR China). Ber. FB Geowiss. Univ. Bremen 38:29–47. Willems, H.; Zhou, Z.; Zhang, B.; and Gräfe, K.-U. 1996. Stratigraphy of the upper Cretaceous and Lower Tertiary strata in the Tethyan Himalayas of Tibet (Tingri area, China). Geol. Rundsch. 85:723–754. Wilson, J. L. 1974. Characteristics of carbonate-platform margins. Am. Assoc. Petrol. Geol. Bull. 58: 810–824. ———. 1975. Carbonate facies in geologic history. New York, Springer, 471 p. Wu, F. Y.; Clift, P. D.; and Yang, J. H. 2007. Zircon Hf isotopic constraints on the sources of the Indus Molasse, Ladakh Himalaya, India. Tectonics 26: TC2014, doi:10.1029/2006TC002051. Zhu, B.; Kidd, S. F.; Rowley, D. B.; Currie, B. S.; and Shafique, N. 2005. Age of initiation of the India-Asia collision in the east-central Himalayas. J. Geol. 113: 265–285.