Cambrian Stratigraphy and Depositional History of the Northern Indian Himalaya, Spiti Valley, North-Central India

Cambrian stratigraphy and depositional history of the northern Indian Himalaya, Spiti Valley, north-central India

Paul M. Myrow† Department of Geology, Colorado College, Colorado Springs, Colorado 80903, USA Karl R. Thompson Nigel C. Hughes Department of Earth Sciences, University of California, Riverside, California 92521, USA Timothy S. Paulsen Department of Geology, University of Wisconsin, Oshkosh, Wisconsin 54901, USA Bryan K. Sell Department of Earth Sciences, University of California, Riverside, California 92521, USA Suraj K. Parcha Wadia Institute of Himalayan Geology, Dehra Dun, Uttranchal 248001, India

ABSTRACT facies thicknesses. This paleoenvironmental published stratigraphic or structural evi- reconstruction contradicts previous interpre- dence exists for such an uplift to the south for Recent work on Himalayan tectonics indi- tations of this unit that range from deep-sea either the Greater or the Lesser Himalaya cates that prior to the Cenozoic collision of fl ysch to shallow-marine tidalites. In addi- lithotectonic zones. India and Asia, an enigmatic Cambrian– tion, our paleoenvironmental analysis and Ordovician event may have strongly infl u- paleocurrent data suggest that the upper- Keywords: Cambrian, Parahio Formation, enced the regional geology of the Himalaya. most Lower to Middle Cambrian deposits of India, Tethyan Himalaya, stratigraphy. Stratigraphic and sedimentological analyses the Lesser and Tethyan Himalaya are parts of well-preserved Cambrian deposits are of the same ancient northward-prograd- INTRODUCTION critical for understanding the nature of this ing, fl uvial-deltaic depositional system of the early tectonic event and its infl uence on the paleo-Tethys margin of India. The Himalaya consist of three principal later tectonic evolution of the Himalaya. The An angular unconformity with overlying lithotectonic zones, based on internal stratigra- Parahio Formation, defi ned herein, of the Ordovician conglomeratic rocks has consid- phy and bounding faults, which were activated Parahio Valley, Spiti region, in the Tethyan erable local relief, with meter-scale scours during the Cenozoic collision of India with Asia Himalaya of India, is the best biostratigraph- and a valley fi ll >100 m thick. The scours (Gansser, 1964; LeFort, 1975) (Fig. 1). To the ically resolved section of Cambrian strata in have northeast-southwest orientations, which south, the Lesser Himalaya contains thick Neo- the entire Himalaya. This formation consists parallel both the paleocurrents in the under- proterozoic through upper Lower Cambrian (and of >1350 m of dominantly siliciclastic deltaic lying Parahio Formation as well as published likely younger Cambrian) strata that are uncon- deposits. The formation ranges from upper- paleocurrent readings from the coarse red formably overlain by Permian and younger rocks. most Lower Cambrian (Lungwangmiaoan beds of the overlying Ordovician strata. The central zone, the Greater Himalaya, consists Stage) to middle Middle Cambrian (Hsu- The Cambrian–Ordovician unconformity is of high-grade metamorphic rocks. The northern- chuangian Stage), representing a time span of regional extent, and our recent biostrati- most Tethyan Himalaya contains an extensive of ~5–10 m.y. It contains numerous medium- graphic database indicates that the minimum record of deposition from the Precambrian to scale shoaling cycles that range from storm- hiatus associated with the unconformity in the Eocene. The paleogeographic affi nities of infl uenced offshore deposits to thick trough Spiti is ~15 m.y. Our sedimentological analy- the three zones are the subject of much debate. cross-bedded fl uvial facies. Many thin car- sis and associated paleocurrent data from the Nd isotope and geochronological data have been bonate beds with abundant trilobite fossils Parahio Formation, along with additional used to suggest that the Lesser Himalaya has dis- directly overlie the fl uvial facies and repre- data from units both above and below the tinctly older sedimentary source materials than sent transgressive systems tract deposits. unconformity, indicate that published mod- the Greater Himalaya and the Tethyan Himalaya, The cycles are interpreted to have resulted els portraying foreland basin development at and that the two latter zones together represented from delta-lobe switching, based on a lack of this time with southward-directed thrusting a separate terrane and cover succession, respec- systematic stratigraphic changes in cycle or are problematic. An alternate possibility— tively, that was accreted to India during the early that uplift took place south of the Tethyan Paleozoic (DeCelles et al., 2000). Myrow et al. †E-mail: [email protected]. Himalaya—is also problematic, because no (2003) demonstrated that previously published

GSA Bulletin; March/April 2006; v. 118; no. 3/4; p. 491–510; doi: 10.1130/B25828.1; 15 ﬁ gures.

Lesser Himalayan data were skewed by the al., 1992; Vannay and Grasemann, 1998; Dezes the Spiti region and considered the formation sampling of only older Precambrian strata and et al., 1999; Wyss et al., 1999; Vannay et al., to be of fl ysch origin. An intertidal to tidal-fl at that samples from younger units of similar 2004). The northern boundary of this belt is the environment has been invoked for the upper part depositional age (late Early Cambrian) from the south-dipping Cenozoic Great Counter Thrust, of the section (Bhargava et al., 1982; Bhargava Tethyan Himalaya and the Lesser Himalaya are which marks most of the Indus-Tsangpo suture and Bassi, 1998; Srikantia and Bhargava, 1998, similar to each other and to the protolith of the zone, separating rocks of the Indian and Eur- p. 227), and also for intervals within the lower Greater Himalaya. This eliminated the bulk of asian plates to the south and north, respectively part (Bhargava et al., 1986). evidence for an exotic origin of Greater Hima- (Yin et al., 1999; Yin and Harrison, 2000). The thickness of the Parahio Formation has laya and Tethyan Himalaya rocks. Other tectonic The sections of the Parahio Formation long been debated. Hayden (1904, p. 13) noted models of the early tectonic history of the Hima- described in this study (Fig. 3) are on the south- that in the Parahio Valley “numerous folds laya are based on reconstructions of the northern west limb of the Muth Syncline, 10–15 km west can be seen thus proving that the enormous Indian margin during the Cambrian and Early of the village of Mikkim, on steep slopes on the thickness [of the Parahio Formation] is only Ordovician (Garzanti et al., 1986; Gehrels et north side of the Parahio River, near the confl u- apparent.” He concluded that the entire sec- al., 2003), including an enigmatic tectonic event ence of the Khemangar River and the Debsa tion between the Khemangar River Fault and represented in northern India by a prominent Khad River (Fig. 2). This section was fi rst stud- the Cambrian–Ordovician unconformity is not Cambrian–Ordovician boundary unconformity. ied by Hayden (1904). The uppermost part of more than ~600–900 m thick, but noted that this However, the sedimentological and stratigraphic the section was measured southeast of the vil- estimate was “merely approximate” (Hayden, context of the Cambrian Tethyan sedimentary lage of Thango on the east side of the Sumna 1904, p. 15). Other estimates for the thickness succession, on which such reconstructions rely, River (also known as the Kinlung Nala) just of the entire formation in the Parahio Valley is poorly known. above where it joins the Parahio River. are <400 m (Parcha, 1996; Fig. 2), 1080 m The Cambrian Parahio Formation of the Spiti The base of the Parahio Formation and its (Bhargava and Bassi, 1998), ~2000 m (Fuchs, Valley region of northern India, which lies within contact with the Batal Formation is not exposed 1982), 2700 m (Kumar et al., 1984; Bhargava the Tethyan Himalayan fold-thrust belt that within the area. The units are juxtaposed by the et al., 1986), and 3350 m (Srikantia, 1981). Our formed along the northern Indian passive margin Khemangar River Fault, which is partly covered detailed bed-by-bed measurement of the section during deformation in the Eocene (Searle, 1986; by the river. The fault strikes north-northwest, revealed that structural complications were not Steck et al., 1993; Corfi eld and Searle, 2000; dips steeply to the east, and displays a normal an issue and that a nearly complete measured Wiesmayr and Grasemann, 2002), is particularly sense of stratigraphic offset (Figs. 2, 4). The ori- section was possible. Our section of the Parahio important in this regard. It is a thick and well- entation of the Khemangar River Fault is similar Formation (Fig. 3) is 1352 m thick. An addi- preserved sedimentary Cambrian succession that to a series of north-striking Cenozoic extensional tional ~100–200 m of poorly exposed Parahio has never been subjected to a detailed sedimen- faults ~30 km to the southeast in the Sutlej Val- Formation exists at the base of the section but tary analysis. The formation represents the oldest ley area (Vannay et al., 2004). However, the fault was not measured. The sedimentology of this Tethyan sedimentary rocks with abundant and is also parallel to north-northwest–striking out- interval is directly comparable to that of the rest well-preserved fossils and sedimentary structures. crop-scale strike-slip faults that we measured in of the measured section. Chronostratigraphic data for this section is supe- exposures near the confl uence of the Kheman- Biostratigraphic data help to resolve the dis- rior to that currently available for any other Cam- gar and Debsa Khad Rivers (Fig. 4). crepancy between Hayden’s thickness estimate brian section within the Tethyan Himalaya. We and our own. His trilobite collections are now herein provide the fi rst detailed sedimentological PREVIOUS WORK assigned to 16 species from shale beds (Jell and analysis and depositional history of the Parahio Hughes, 1997). New collections were recov- Formation and discuss the tectonic implications Hayden (1904) performed the fi rst and most ered from some of Hayden’s shale zones, and of its overlying unconformity. comprehensive study of the Parahio Formation for the fi rst time from carbonate beds, and both to date. He established a basic stratigraphy of lithologies contain similar taxa. Data from all GEOLOGIC SETTING OF FIELD AREA this dominantly siliciclastic succession and col- the zones from which we collected are in the lected a Middle Cambrian trilobite fauna from expected stratigraphic order, based on com- The Spiti Valley lies in the Lahual-Spiti dis- several zones within the unit (Reed, 1910; Jell parison with biostratigraphic databases from trict of the state of Himachal Pradesh, northern and Hughes, 1997). His measured section from sections in China. As the order of stratigraphic India. The fi eld area for this study is in the Para- the Parahio River area shows several mixed occurrence of these taxa is similar in both hio River Valley (Figs. 1, 2), a subsidiary val- siliciclastic-carbonate cycles in what he called Hayden’s and our studies, the positions of our ley of the Pin River Valley, which joins the Spiti the Cambrian System. He described upward- collections with respect to height in the section Valley ~40 km southeast of the town of Kaza. coarsening depositional cycles that consist of indicate that Hayden (1904) consistently under- Low-grade Neoproterozoic to Eocene sedimen- a thick lower shale unit and an overlying sand- estimated stratigraphic thickness. tary rocks of the Tethyan Himalayan fold-thrust stone unit that are capped by a thick, orange- Trace fossil assemblages that include ich- belt exposed within the Spiti Valley are bounded weathering dolostone bed. The environments of nogenera attributed to Astropolichnus and Pla- to the south by the high-grade gneisses of the deposition for the Parahio Formation have been giogmus occur below our measured section Greater Himalaya across the Sangla Detach- variably interpreted. Several workers considered within the poorly exposed basal 100–200 m of ment (Vannay and Grasemann, 1998; Wyss the section as a record of an upward transition the Parahio Formation, and were interpreted et al., 1999; Vannay et al., 2004). The Sangla from deeper-water euxinic and fl ysch facies to be Early Cambrian in age (Bhargava et al., Detachment is one of a series of north-dip- to shallow-water deposits with thick, orange- 1982; Bhargava et al., 1986). This is consis- ping, extensional shear zones that are generally weathering dolostone beds (Srikantia, 1981; tent with the age of the oldest trilobites in our referred to as the South Tibetan detachment sys- Bhargava et al., 1982; Srikantia and Bhargava, section. We have no fi rm constraint on the age of tem (Searle, 1986; Herren, 1987; Burchfi el et 1983). Fuchs (1982) also conducted work in the base of the Parahio Formation in the Parahio

492 Geological Society of America Bulletin, March/April 2006 CAMBRIAN STRATIGRAPHY AND DEPOSITIONAL HISTORY IN NORTHERN INDIAN HIMALAYA

77 00‘E 78 00‘ Sub-Himalaya Main Boundary Thrust (MBT) 32 Lesser Himalaya 00‘N Sedimentary Series Munsiari Thrust (MT) Lesser Himalaya Crystalline Sequence (paragneiss) Proterozoic granite Main Central Thrust (MCT) Greater Himalayan Sequence (paragneiss) N Cambrian-Ordovician 500 km Granite

25 km Kumaun TIBET Sangla Detachment (SD) Basin Zanskar Suture STDS Tethyan Himalayan 30 Paleozoic-Mesozoic sedimentary rocks

INDIA MCT Tethyan Himalayan GHS Neoproterozoic(?) sedimentary rocks

Figure 1. Regional geology, showing major faults and geologic units of the northwestern Himalaya in India (modiﬁ ed from Vannay and Grasemann, 2001). Box delineates region shown in Figure 2. STDS—South Tibetan detachment system; TH—Tethyan Himalaya; GHS— Greater Himalaya sequence; LH—Lesser Himalaya.

78 00E 78 05

Measured Sections

Khemangar Fault Ordovician Thango Fm. Quaternary 32 Middle Jurassic- Cambrian Parahio Fm. 00N Late Triassic N Late Triassic- Cambrian Batal Fm. Ordovician 2 km Anticline U Fault Syncline D U: Upthrown D: Downthrown

Figure 2. Simpliﬁ ed geologic map of the Tethyan Himalayan fold-thrust belt in the area of the Parahio and Pin Valleys (compiled and modi- ﬁ ed from Fuchs, 1982; Bhargava and Bassi, 1998; Wiesmayr and Grasemann, 2002). Map area shown as boxed region in Figure 1.

Geological Society of America Bulletin, March/April 2006 493 MYROW et al.

1360 Valley but note that the late Tsanglangpuan trilobite Redlichia noetlingi has been recorded in 1300 the adjacent Pin Valley (Reed, 1910; Jell and General Lower Paleozoic Hughes, 1997), and it is likely that the trace fos- Stratigraphy of sils are late Early Cambrian in age. Parahio Valley On the basis of our new collections of trilo- 1200 bites, the Parahio Formation in the Parahio Val- ley ranges from uppermost Lower Cambrian (Lungwangmiaoan Stage) to middle Middle

Fm. Cambrian (Hsuchuangian Stage). The base of

Thango 1100 the formation is almost coeval with the youngest dated Cambrian strata of the Lesser Himalaya, the upper Lower Cambrian of the Tal Group (Hughes et al., 2005). 1000 STRATIGRAPHY

The stratigraphic nomenclature for the oldest 900 sedimentary rocks of the Tethyan Himalaya is confusing (Fig. 5), owing to the paucity of well- described stratigraphic sections and the lack of chronostratigraphic constraints. Revision of the Parahio Formation Parahio 800 lithostratigraphy and chronostratigraphy of the Parahio Valley is a critical ﬁ rst step toward clari- fying regional relationships. Griesbach (1891), following an initial investigation of the geology 700 of the Spiti region, applied the term Haimanta series to a lowermost package of sedimentary rocks above the metamorphic rocks of the Greater Himalaya (Fig. 5). This term was modi- Batal Fm. 600 ﬁ ed by Hayden (1904, p. 14–15), who suggested

fs that all of Griesbach’s (1891) Haimanta series

carb lies below an angular unconformity that is now known to be no younger than Late Ordovician, 500 and he referred to the rocks beneath the unconformity collectively as the Cambrian System (Fig. 5). We concur with Bhargava and Bassi (1998, p. 19) that all sedimentary rocks below Generalized Stratigraphic Section: Parahio Formation Parahio Section: Stratigraphic Generalized 400 the unconformity in the Parahio Valley section should be assigned to the Haimanta Group. This group is also considered to contain sedimentary rocks older than those known in the Parahio Val- 300 ley, such as the Chamba Formation and Manjir Formation in Khasmir (Frank et al., 1995), which are likely Neoproterozoic in age, consistent with radiometric dates on crosscutting granitic intru- 200 sions from the Tethyan Himalaya (Miller et al., 2001). Our use of the term Haimanta Group excludes beds above the unconformity at the top of the Parahio Formation, in contrast to the usage 100 of others (e.g., Srikantia, 1981; Bhargava et al., 1982) but in accordance with recent practice. Pascoe (1959) applied the term Parahio series to Cambrian sedimentary rocks described 0 by Hayden (1904) from the Parahio Valley

st fs

sh (Fig. 5). This unit comprised “grey and green

vfs carb micaceous quartzites and thin-foliated slates Figure 3. Generalized lowermost Paleozoic stratigraphy of the Parahio Valley and strati- and shales, with narrow bands of light grey graphic section of the Parahio Formation, measured in meters. Explanation: sh—shale; dolomite” ( Pascoe, 1959, p. 581) and repeated st—siltstone; vfs—very ﬁ ne sandstone; fs—ﬁ ne sandstone; carb—carbonate. upward-coarsening shale-sandstone cycles with

494 Geological Society of America Bulletin, March/April 2006 CAMBRIAN STRATIGRAPHY AND DEPOSITIONAL HISTORY IN NORTHERN INDIAN HIMALAYA

carbonate caps. Hayden’s Cambrian trilobite- cal description of the Parahio series provides an herein, with its top defi ned here by the uncon- bearing rocks from the Parahio Valley are within accurate description of these beds, and the term formity and its base defi ned by the fi rst occur- this unit, the upper boundary of which was has historical precedence as a lithostratigraphic rence of trace fossil–bearing strata. Rocks of the defi ned by the unconformity. The base of the name. Accordingly, we formally herein desig- underlying Batal Formation are devoid of car- Parahio series was considered conformable with nate Pascoe’s Parahio series as the Parahio For- bonate beds and trace and body fossils, although the underlying red and black slate, with quartz- mation, with the type section described in this an acritarch assigned to Angulopanina has been ite beds assigned by Pascoe (1959) to the upper paper. The Parahio Formation includes the entire recorded from the uppermost part of this forma- part of the Haimanta series. Pascoe’s lithologi- section of the Parahio Valley rocks described tion, according to Kumar et al. (1984).

Cambrian Cambrian Ordovician Batal Formation Parahio Formation Thango Formation Poles to Bedding pi axis (T&P) 318/1

Figure 4. Simplifi ed geologic pi axis (T&P) 127/31 map of the fi eld area in the pi axis (T&P) n = 19 n = 52 141/16 n = 40 Parahio Valley (modifi ed from Bhargava and Bassi, 1998). Structural Map area is shown in Figure 2. Elements Synoptic equal-area plots of structural data measured in the Batal, Parahio, and Thango Formations show little dif- Fold Axes ference in the orientation of Poles to Cleavage Bedding-Cleavage structural data from Cam- Intersection Lineations brian units and the Ordovician Thango Formation. The major fault in the area displays a normal stratigraphic offset and is covered by the Khemangar River. Note that the fault is parallel to outcrop-scale, right- lateral strike-slip faults that we measured in exposures near the confl uence of the Kheman- gar and Debsa Khad Rivers (Fig. 2). The right-lateral faults Parahio are part of a conjugate strike- River slip fault array, but the parallelism of the right-lateral faults and the Khemangar Fault may indicate that faulting included a component of right-lateral strike-slip movement. Left-lateral N

Strike-Slip 1 km Faults

Right-lateral

Geological Society of America Bulletin, March/April 2006 495 MYROW et al.

Recent authors have commonly referred the Griesbach, Hayden, Pascoe, Bhargava Kumar et This paper Parahio Cambrian rocks to the Kunzam La For- (1891) (1904) (1959) et al. (1982) al. (1984) mation (Bhargava et al., 1982; Bhargava et al., 1986; Bhargava and Bassi, 1998; Kumar et al., Parahio Parahio Member 1984; Parcha et al., 2005), a term fi rst published Kunzam Parahio series La by Srikantia (1981) (Fig. 5). The type section Haimanta Cambrian Debsa Formation series System Formation for this formation was named as the Kunzam La Khad Kunzam La Fm. Member FAULT Pass, but this section is considered to be struc- Upper turally complicated and is a poor choice as a Haimanta Batal Batal Batal type section (Bhargava and Bassi, 1998, p. 20). series Formation Formation Formation Although some trace fossils have been recorded from the Cambrian rocks of the Kunzam La sec- Figure 5. Stratigraphic schemes for the Cambrian deposits of the Parahio Valley, including tion (Sudan and Sharma, 2001), no body fossils our proposed revision (this paper). have been described from it, and thus the Kun- zam La section lacks the biostratigraphic constraint of the Parahio Valley section. The upper stone beds at facies transitions with either the base in an intermediate shelf position. How- and lower boundaries of the Kunzam La Forma- silty facies or the sandstone and shale facies ever, the presence of sandstone-fi lled cracks in tion at the type section are also structurally com- (described later). Molds of trilobites, typically a few units is at odds with this interpretation if plex and have not been adequately described. articulated, exist locally within this facies. they are interpreted as desiccation cracks. The The upper part of the Kunzam La Forma- simplest interpretation is that these features tion, which contains prominent orange-weath- Interpretation formed in a low-energy nearshore environment ering dolomite beds, was named the Parahio The general lack of sandstone and the pres- and represent either synaeresis cracks, which Member (Kumar et al., 1984) (Fig. 5). Our new ence of articulated olenimorphic (Fortey and form subaqueously from shrinkage associated discoveries show that carbonate beds occur Owens, 1990) trilobites in this facies indicate with strong osmotic gradients (Astin and Rog- throughout the formation, although the lower a low-energy, marine-shelf environment well ers, 1991), or diastasis cracks, which form as beds are limestone instead of orange-weather- below fair-weather wave base. The depositional a result of compaction (Cowan and James, ing dolomite. Our work in the Zanskar Valley environment was distal from the shoreline, at a 1992). Bedding plane exposures are lacking, (Myrow et al., 2005) indicates that dolomiti- distance beyond which fl ows were capable of so the plan-view geometry of these structures zation of the carbonate beds of the formation transporting sand during tempestite deposition. is unknown. there extended to deeper stratigraphic levels. Most shale facies units occur stratigraphically This variable pattern of dolomitization cannot below interbedded fi ne sandstone and shale Sandstone and Shale Facies be considered a primary feature for lithostrati- deposits, with an upward transition that indi- graphic correlation, and thus we do not subdi- cates a change to more proximal environments. Description vide the newly defi ned Parahio Formation on This facies is composed of very thin to the basis of this feature. Kumar et al. (1984) Silty Facies medium beds of very fi ne to fi ne brown-weath- also defi ned a lower Debsa Khad Member of ering sandstone and grayish-green silty shale the Kunzam La Formation on the basis of trace Description and shaly siltstone (Fig. 6D). Sandstone to silt- fossils, but our results show that trace fossils This facies consists of gray siltstone and silty stone-shale ratios are ~1:1, although sandstone occur throughout the section. Accordingly, we shale with <1–5 cm beds of very fi ne brown content locally reaches 75%. Very fi ne to fi ne also reject this stratigraphic term. weathered sandstone. Siltstone and silty shale sandstone beds range in thickness from 1 to beds range from 3 to 10 cm thick and average 60 cm and average <5 cm in thickness; thicker LITHOFACIES 5 cm. Very fi ne sandstone beds make up 10% to beds are generally widely spaced. Beds tend to 60% of this facies (average, ~35%). They pinch pinch and swell laterally. Sedimentary structures Six lithofacies are defi ned for the Parahio and swell laterally over tens of centimeters and include wave-ripple lamination, hummocky Formation of the Parahio Valley section. Litho- generally contain parallel and wavy lamina- cross-stratifi cation (HCS) (9 cm average thick- facies are arranged into cycles tens of meters tion. Additional sedimentary structures include ness) (Fig. 6C), parallel lamination, parting lin- thick with repeated stratigraphic patterns. The starved symmetrical ripples and, rarely, sand- eation, symmetrical ripples, interference ripples lithofacies are described in order of stratigraphic stone-fi lled vertical cracks. Trace fossils occur (Fig. 6F), ball-and-pillow structures (Fig. 7A), appearance in these cycles. within a few layers in the lower 200 m of our gutter casts (Fig. 7B), and pot casts. Ball-and- measured section and also occur sporadically pillow structures are abundant and occur in beds Dark Shale Facies higher in the section. up to 2 m thick throughout the formation in this facies. A few units of this facies contain spin- Description Interpretation dly and polygonal shrinkage cracks (Fig. 7C). This facies consists of dark-gray to green- Low sandstone to shale ratios suggest quiet Orientations of parting lineation and gutter casts ish-gray shale. Bed thicknesses range from 2 water deposition where mud settled out of suggest a north-northeast or a south-southwest to 10 m and average ~4 m. Thick units of this suspension. Rare symmetrical ripples indicate transport direction (Fig. 8). facies commonly occur directly over carbon- infrequent wave reworking of sand. Facies tran- ate beds throughout the Parahio Formation and sitions with the shale facies and tempestite-rich Interpretation contain minor, discontinuous siltstone laminae sandstone and shale facies (described later) Features such as symmetrical ripples, HCS, (Fig. 6A, B) and centimeter-thick silty sand- indicate deposition below fair-weather wave gutter casts, and pot casts are all common

496 Geological Society of America Bulletin, March/April 2006 CAMBRIAN STRATIGRAPHY AND DEPOSITIONAL HISTORY IN NORTHERN INDIAN HIMALAYA

A B

C D

E F

Figure 6. (A) Close-up of silt-streaked shale at 235.47 m in the section with irregular silty laminae. (B) Silt-streaked shale with even lamination of silty facies at 236.14 m in the section. (C) Close-up of hummocky cross-stratiﬁ cation (HCS) at 492.09 m in the section. (D) Sandstone and shale facies at 601 m in the section. Note HCS sandstone beds with hummocky tops. Lower sandstone bed capped with rounded symmetrical ripples. (E) Amalgamated HCS facies at 5.4 m. Brunton compass on top of staff for scale. (F) Bed- ding planes in sandstone and shale facies, showing abundant ripples with multiple crest-line orientations at 479.03 m in the section. Pencil for scale in A–D is 14 cm long; the tip is 2 cm long.

Geological Society of America Bulletin, March/April 2006 497 MYROW et al.

A C

Figure 7. (A) Ball-and-pillow structures at 156.26 m in the section. Such structures are common throughout the formation. Hammer for scale. (B) Oblique view of partly exhumed gutter cast (next to pencil) at 491.49 m in the section; 14-cm-long pencil for scale. (C) Shrinkage cracks at 290.62 m in the section.

storm-generated sedimentary features (Myrow, tions in ancient shallow-water deposits com- thickness of ~30 cm. Beds generally pinch and 1992a, 1992b). HCS is produced during high- monly refl ect shoreline orientation caused by swell laterally, and are locally separated by energy, storm-generated multidirectional and wave refraction (Potter and Pettijohn, 1977; cf. centimeter-scale shale beds. Individual hum- oscillatory currents (Arnott and Southard, 1990; Myrow, 1992b). The gutter cast and parting lin- mocks range in spacing from 1 to nearly 4 m Dumas et al., 2005). Interbedding of fi ne sand- eation data are also parallel to paleocurrent data in length. This facies is interbedded with the stone and shale indicates deposition in an inner from inferred fl uvial deposits (described later), sandstone and shale facies in some areas. Both shelf setting below fair-weather wave base. Gut- thus indicating fl ow offshore toward the north- symmetric and asymmetric forms of HCS ter casts refl ect movement of sand via small- northeast. This is similar to other studies that occur within this facies. scale channels and are interpreted to form as a document offshore-directed, storm-generated result of the unidirectional component of storm fl ow (Leckie and Krystinik, 1989) and devel- Interpretation currents that erode the substrate, leaving small opment of gutter casts as a result of shoreline The abundance of HCS indicates deposition channel-like structures that are commonly fi lled bypass of sand (Myrow, 1992b). along a storm-dominated shoreline (Leckie and by lag or fi ne sand from the shoreface (Myrow, Walker, 1982; Dott and Bourgeois, 1982; and 1992a). Pot casts are infi llings of erosional fea- Amalgamated Hummocky Cross-Stratifi ed others). The absence of intervening shale beds tures that form as a result of vertical vortices (HCS) Sandstone Facies refl ects deposition within the shoreface where within storm-generated fl ows (Myrow, 1992a). mud is removed by fair-weather processes and Gutter cast and parting lineation orientations Description amalgamation of sand beds results from storm are north-northeast–south-southwest, indicating This facies consists of amalgamated beds of deposition. Deposition of thick beds of HCS consistent orientations of fl ow during erosive gray, fi ne-grained HCS sandstone (Fig. 6E). accompanied reworking of the shoreface and and depositional stages of storm fl ows. Wave- The sandstone is reddish gray to steel blue on elimination of stratifi cation generated dur- ripple, crest-line orientations are bimodal, with weathered surfaces and gray on fresh surfaces. ing fair-weather conditions. The existence of the strongest mode oriented west-northwest– Beds range in thickness from tens of centime- this facies stratigraphically above the sand- east-southeast. Wave-ripple crest-line orienta- ters to upward of a meter, with an average bed stone and shale facies refl ects shoaling from

498 Geological Society of America Bulletin, March/April 2006 CAMBRIAN STRATIGRAPHY AND DEPOSITIONAL HISTORY IN NORTHERN INDIAN HIMALAYA

nearshore and transition zone environments dolosiltite (Fig. 9E). Bed thicknesses range the Parahio Formation. The long axis directions into shoreface settings. from 23 cm to 12.8 m, with an average thick- of parting lineations (Fig. 8A) and gutter casts ness of ~4 m. Internal sedimentary structures are south-southwest–north-northeast. Wave Trough Cross-Bedded Sandstone Facies and biogenic structures are absent except ripples (Fig. 8B) display scattered orientations, where phosphatic brachiopods are concentrated but the strongest mode is essentially perpendic- Description along individual laminae. Diagenetic nodules ular to the other features, namely, west-north- This facies consists of large-scale, trough cross- of orange-weathering dolostone occur locally west–east-southeast. Large-scale sets of trough bedded, gray-green fi ne sandstone (Fig. 9A, B) within underlying sandstone units. cross-beds of the trough cross-bedded sand- that is light gray to white on weathered surfaces. In general, beds of the carbonate facies rest stone facies indicate a unimodal northeastward Bed thicknesses range from 15 to 120 cm, with stratigraphically above trough cross-bedded transport (Fig. 8C). This is consistent with the an average of 54 cm. Units of this facies range facies of presumed fl uvial origin, and, in a few reconstructed position of these Tethyan depos- up to 30 m thick. The bases of these units show places, shoreface deposits of amalgamated HCS its along the northern margin of India at that small-scale cutout of underlying beds laterally in sandstone. These beds in turn are overlain by the time. The largest mode in the wave-ripple data, the section. Decimeter-scale, parallel-laminated dark shale or silty facies. perpendicular to the trough cross-bed sets, sandstone beds locally separate trough cross-bed could represent refraction of waves parallel to sets. This facies generally overlies the amalgam- Interpretation the inferred paleoshoreline, although the data ated HCS facies and underlies the limestone The presence of minor carbonate units within are sparse and somewhat scattered. The scatter facies (described later) and/or shale facies. Paleo- the dominantly siliciclastic Parahio Formation in the data is not unusual for shoreline depos- current readings suggest north-northeastward suggests intermittent decreases in supply of its, because variable coastal winds and shallow fl ow (Fig. 8). terrigenous siliciclastic sediment. Trilobite and depths lead to variable oscillatory water move- brachiopod fossils indicate deposition under ments (Weimer et al., 1982). Interpretation marine conditions. Micritic beds accumulated The paleocurrent readings do not account for The thick beds of trough cross-bedded fi ne in lower energy conditions, whereas the bio- oroclinal bending of the Himalaya and coun- sandstone record the migration of three-dimen- clastic grainstone beds were reworked by ocean terclockwise rotation of India during Cenozoic sional dunes in high-energy depositional systems waves and currents. The homogeneous nature orogenesis, which resulted in a relative move- (Harms et al., 1982). The scale of the cross-bed- of the orange-weathering dolosiltite suggests a ment between India and its northern continen- ding, unimodal paleocurrents, lack of body or shallow-marine environment of uniform energy. tal margin (Klootwijk et al., 1985; Schill et trace fossils, and facies transitions indicate depo- Transitions from underlying trough cross-bed- al., 2001, 2002). Paleomagnetic studies of the sition in a riverine environment (Potter and Petti- ded sandstone to limestone indicate that marine Pin Valley, ~10–15 km south and east of our john, 1977; Walker and Cant, 1984). Stratigraphic fl ooding surfaces (Van Wagoner et al., 1988) study area (Schill et al., 2001), suggest a pos- transitions with underlying shoreface deposits separate these facies. sible 20°–35° clockwise vertical axis rotation of indicate shoaling to nonmarine environments rocks with respect to India. Trial rotations of our associated with progradation of the shoreline. PALEOCURRENTS paleocurrent data, using 20° and 35°, produce nearly due north mean paleocurrent directions, Carbonate Facies Paleocurrent readings were measured from which are an even better fi t with the idea that the parting lineation, trough cross-beds, symmetri- Tethyan Himalaya records the northern margin Description cal wave ripples, and gutter casts throughout of India during the Cambrian. This facies consists of limestone and dolostone beds, many of which serve as marker beds within the formation. The limestone consists of greenish-gray carbonate mudstone to coarse ACB grainstone with abundant trilobites, phosphatic linguliformid brachiopods, and sponge spicules in grainstone. Limestone beds range in thickness from 3 cm to 1.86 m, with an average thickness of ~60 cm. The limestone is thinly laminated (millimeter scale) and is pink to rusty orange on 37 14 25 weathered surfaces. Some of the thinner beds are discontinuous over tens of meters. Thin- bedded homogeneous fi ne-crystalline limestone beds occur below grainstone throughout the section (e.g., 78.7 m). Much of the coarse and fi ne grainstone is thinly interbedded. Limestone beds are partially dolomitized and silicifi ed locally Parting Lineations Wave Ripple Trough Cross-bed Crest-line (Fig. 9C, F). Some beds contain abundant intra- Paleocurrent Orientations Orientations clasts at their base and locally contain thin lag deposits on their upper bedding contacts. Figure 8. Equal-area paleocurrent rose diagrams of the Parahio Formation (north at top). Orange-weathering dolostone beds occur in Parting-lineation orientations and wave-ripple crest-line orientations were taken from the the uppermost 200 m of the formation (Fig. 9D). sandstone and shale facies. Cross-bed orientations were taken from the trough cross-bedded They consist of extremely well-sorted, massive sandstone facies.

Geological Society of America Bulletin, March/April 2006 499 MYROW et al.

A B

C D

E F

Figure 9. Trough cross-bedded facies and carbonate facies. (A) Compound trough cross-bedding at 57.3 m in the section. Pencil (top left) for scale. (B) Large-scale trough cross-bedding with sets up to 1.5 m thick at 760.5 m in the section. Hammer for scale (circled). (C) Partly silici- ﬁ ed limestone bed, showing nodular weathering pattern at 765.14 m in the section. (D) Thick (12.8 m) orange dolosiltite bed at 1242.4 m in the section. (E) Close-up of D, showing well-sorted, homogeneous orange dolosiltite. (F) Nodular gray limestone unit, 1.3 m thick, with abundant chert nodules at 779.35 m. Pencil for scale is 14 cm long.

500 Geological Society of America Bulletin, March/April 2006 CAMBRIAN STRATIGRAPHY AND DEPOSITIONAL HISTORY IN NORTHERN INDIAN HIMALAYA

PALEOENVIRONMENTAL SYNTHESIS et al. (1982, 1986), Bhargava and Bassi (1998, p. (Figs. 11B, 12). The latter type of cycle ends 146), and Parcha et al. (2005) all argued that the with the amalgamated HCS facies (Fig. 12) or The foregoing sedimentological analysis indi- Parahio Formation records overall shallowing with thick, bioturbated sandstone beds, both of cates that the dominantly siliciclastic strata of the from a euxinic basin toward a tidally dominated which are of shoreface origin (Fig. 11A). In a Parahio Formation range from offshore-marine nearshore setting. few cycles, the trough cross-bedded sandstone to trough cross-bedded fl uvial deposits. Over- We fi nd no sedimentological evidence for facies directly overlies the sandstone and shale all, the strata are relatively fi ne grained, ranging deposition in an oxygen-stratifi ed basin, e.g., facies. from shale to fi ne sandstone, with a few scattered biofacies patterns of anaerobic or dysaerobic medium sandstone beds. The presence of thick, environments (Byers, 1977; Myrow and Land- Interpretation of Cycles well-developed deposits of the fl uvial trough ing, 1992), let alone evidence for a long-term cross-bedded sandstone facies indicates a strong euxinic basin. In addition, trilobite taxa that The succession of lithofacies in a cycle is infl uence of fl uvial processes and earmarks these occur in the shallow-water limestone beds are interpreted to record upward shoaling along a strata as deltaic deposits. The fl uvial deposits are identical to those in overlying dark shale facies, prograding storm-dominated shoreline (Fig. 13). also relatively fi ne grained and reasonably well suggesting normal-marine settings for both Complete cycles record changes from offshore- sorted, indicating low local stream gradients and paleoenvironments (i.e., similarly well-oxygen- marine environments to fl uvial settings, although a position relatively distal to sediment sources ated conditions). Fuchs (1987) and Garzanti et incomplete cycles begin in nearshore facies or during the Cambrian in this region. However, the al. (1986) both consider time-equivalent strata end in shoreface deposits, the latter being due general character of the section indicates that riv- exposed in the Zanskar Valley to the north- to renewed transgression before shoaling culmi- ers deposited large volumes of sediment on the northwest to represent tidal fl at, coastal sand, nated in deposition above sea level. The upper shoreline and inner shelf on the ancient northern and peritidal carbonate deposits. Our sedimen- cycle boundaries represent marine fl ooding sur- passive margin of India. tological analysis, as well as our work on the faces. The marine parts of the shallowing cycles Extensive ball-and-pillow features occur Zanskar strata (Myrow et al., 2006), reveals record progradation of a storm-dominated throughout these deposits in several facies. These little evidence for tidal processes in these depos- shoreline with upward increases in tempestite features represent gravitational synsedimentary its, such as diagnostic sedimentary structures bed thickness and decreasing shale content. deformation during sediment accumulation. (e.g., herringbone cross-bedding, reactivation In these cycles, the transitions from fl uvial This kind of deformation results from partial surfaces) or facies successions. cross-bedded sandstone to carbonate facies are liquefaction caused by high pore-fl uid pressures interpreted as marine fl ooding surfaces and and unstable packing (Seed, 1968). Such con- SEDIMENTARY CYCLES subsequent deposition in shallow-marine envi- ditions are common in environments with rapid ronments that were essentially fl ooded coastal sediment accumulation rates, particularly in The strata of the Parahio Formation range plains (Fig. 13). Fully marine conditions are sup- deltas with abundant silt to very fi ne sand. The from storm-infl uenced shelf deposits to thick, ported by the presence of trilobite and brachio- thickness of Middle Cambrian strata in the Para- trough cross-bedded fl uvial facies, many of pod fossils, as well as trace fossils. Beds of the hio Formation indicates high sediment accumu- which are arranged in medium-scale, upward- carbonate facies are sharply overlain by deep- lation rates, which supports our interpretations coarsening shoaling cycles (Fig. 10A). The water shelf deposits of the dark shale facies, the of deltaic deposition. Trilobite biostratigraphic cycles range from 2.5 m to 61 m thick and differ transition representing another fl ooding surface. data indicate that most of the ~1350-m-thick slightly in facies sequences from cycle to cycle. The fl ooding surface at the top of the carbonate measured section is of early and middle Middle An idealized cycle begins with sand-starved represents deepening to the point of shutdown of Cambrian age. On the basis of recent geochro- deposits of the dark shale facies (Fig. 10B, C) carbonate production, as was the case with some nological work (Landing et al., 1998; Davidek and grades upward sequentially into the silty ancient carbonate platforms (Schlager, 1981). et al., 1998), the entire Middle Cambrian was facies, sandstone and shale facies, amalgamated The carbonate facies are thus essentially thin ~10 m.y. in duration. A conservative accumu- HCS facies, and fi nally the trough cross-bed- transgressive deposits. The rest of these cycles, lation rate estimate has been calculated on the ded sandstone facies. Within the cycles, beds from the base or slightly above the base of the basis of (1) the assumption that the lower and of sandstone become thicker and increasingly dark shale facies to the top of the cycles, formed middle parts of the Middle Cambrian were 7 m.y. more abundant upward until all shale is miss- during shoreline progradation (Fig. 13A). Given in duration, (2) an estimate of ~50% shale and ing in the amalgamated HCS facies. The trough the deltaic setting of these strata, and the fact 50% sandstone for the formation, and (3) com- cross-bedded sandstone facies generally overlies that the cycles do not form regular stacking pat- paction estimates of 50% for shale and 15% the amalgamated HCS facies across an erosional terns (i.e., progradationally or retrogradationally for sandstone with >5 km burial (Houseknecht, surface. Carbonate-rich sandstone or beds of the stacked parasequences; Lehrmann and Gold- 1971; Bond and Kominz, 1984). The estimate of carbonate facies overlie the trough cross-bedded hammer, 1999), we interpret the cyclicity to be sediment accumulation rate is 30.4 cm/1000 yr, sandstone facies and are succeeded by another mostly autocyclic, driven by changes in sediment similar to time-averaged accumulation rates in unit of the dark shale facies (Fig. 11A). input associated with switching of delta lobes. deltaic settings (Stanley and Hait, 2000). The Many of these shoaling cycles are incom- Changes in eustasy and subsidence may have interpretation of the Parahio Formation as a plete. Some lack the dark shale facies and played roles in the development of these cycles, storm-infl uenced deltaic succession contradicts instead commence with the silty facies, the but it is not possible to determine their relative previous paleoenvironmental interpretations. sandstone and shale facies, or shoreface depos- infl uence. The few places where fl uvial depos- Srikantia (1981) and Fuchs (1982) considered its (Fig. 11B). One cycle commences with amal- its rest directly on inner shelf deposits of the the succession to be dominated by fl ysch depos- gamated HCS sandstone deposits. Other cycles sandstone and shale facies may point to forced its. Similarly, Parcha (2005) suggested that the are abbreviated at their tops, and the carbonate regression (Posamentier et al., 1992) and rapid Parahio Formation accumulated in an outer facies is absent, or both the trough cross-bedded seaward shift of environments. Avulsion and detrital belt setting. Srikantia (1981), Bhargava sandstone facies and carbonate facies are absent deltaic lobe shifting would have been enhanced

Geological Society of America Bulletin, March/April 2006 501 MYROW et al.

B C

Figure 10. (A) Two well-developed cycles in the upper part of the Parahio Formation. Lower cycle rests on an orange dolostone bed (at top of an underlying cycle) in lower left of photo. Lower cycle begins at 1166.7 m in the section, is 61 m thick, and is capped with an 18-m-thick unit of amalgamated HCS sandstone. Overlying cycle begins at 1227.9 m in the section, is 29.6 m thick, and is capped with a 12.8-m-thick bed of orange dolostone. Sharp upper contact of second cycle is overlain by shale, marking the base of a third cycle. (B) Base of 30-m-thick cycle at 1097.92 m in the section. Note shale (left center) and an upward increase in sandstone thickness and abundance. (C) Base of 18.6 m cycle at 1258.77 m in the section. Note the top of a carbonate bed in the upper left and a dark shale directly above. Note an upward increase in sandstone bed thickness and abundance. Hammer for scale.

502 Geological Society of America Bulletin, March/April 2006 CAMBRIAN STRATIGRAPHY AND DEPOSITIONAL HISTORY IN NORTHERN INDIAN HIMALAYA

A B

345 365

AS Sl

Shoaling Figure 11. (A) Parts of two 895 shoaling cycles from 879.09 to TCS Shoreface with abundant soft- sediment deformation features 899.72 m in the section. Amal- Sh gamated HCS shoreface depos- FS its of the lower cycle, overlain by bioturbated upper shoreface or foreshore deposits and then Fluvial (Minor Shoreface) 360 340 limestone. The base of the lime- ISS stone is a marine ﬂ ooding surface, and the top another ﬂ ooding surface. (B) Parts of three

Shoaling shoaling cycles between 326.59 and 366.42 m in the section. The lower cycle has very thick 890

TCS amalgamated shoreface depos-

Fluvial its overlain by trough cross-

Shelf to Shoreface bedded facies of fl uvial origin. Shoaling Possible foreshore deposits at Sl Shoaling the top are bracketed by fl ooding surfaces, and the base of 355 335 the next cycle begins in lower shoreface deposits directly above the limestone. FS— fl ooding surface; sh—shale; Sh vfs—very fi ne sandstone; fs— AS fi ne sandstone; mic—micrite; 885 FS grnst—grainstone; Lithofacies: LS AS FS SH—dark shale; SI—siltstone; ISS—interbedded sandstone Shoreface Shoreface and shale; BS—bioturbated BS sandstone; AS—amalgamated

Foreshore LS Shoreface/ sandstone; TCS—trough cross- FS 350 Fore- bedded sandstone. 330 AS shore FS?

Shoaling TCS Shoreface 880 Fluvial Shoaling Sl fs fs fs sh sh sh vfs vfs vfs mic grnst grnst

Geological Society of America Bulletin, March/April 2006 503 MYROW et al.

by regional subsidence resulting from sediment loading within the deltaic setting, which would have been caused by high sediment accumulation rates (Coleman, 1988). This subsidence would have enhanced any thermal subsidence 1125 to increase accommodation space. Following avulsion events that shifted sediment supply to 1105 adjacent parts of the shoreline, local production of accommodation space would have been rapid. This would have resulted in deepening through

ISS the zone of carbonate production, which may

Nearshore have been generally narrow in this deltaic set- AS ting, and in deposition of relatively thin, transgressive carbonate deposits.

Shoreface One stratigraphic pattern of note is the presence of thicker (orange-weathering dolostone) carbonate beds in the upper part of the Parahio For- mation. These carbonate beds are more extensive 1120 and continuous than the thinner limestone beds in the lower Parahio. Similar dolostone beds also 1100 Sl occur in the upper part of the Parahio Formation in the Zanskar Valley to the northwest. Unfortu- nately, our biostratigraphic information does not Shelf allow us to determine whether individual dolo- Sh stone beds are continuous between the Zanskar Sand-Starved FS and Spiti regions. In Zanskar, the Parahio Forma- Shore- tion is overlain by the Thidsi Member of the AS face Shoaling Karsha Formation (Myrow et al., 2006), which is composed of >150 m of orange-weathering dolostone (Gaetani et al., 1986). The region- ally extensive Cambrian–Ordovician unconfor- 1115 mity (see following discussion) cuts downsec- tion between Zanskar and the Spiti Valley, so 1095 the Thidsi Member and even younger strata are ISS absent in Spiti. The upper Parahio Formation thus records a transition from siliciclastic- to carbon- Nearshore

Shoaling Shoaling ate-dominated strata, representing a long-term

ISS decrease in supply of terrigenous detritus, and to some degree this transition might represent the Nearshore signal of part of a third- (1–2 m.y.) or second- order (up to 15 m.y.) depositional sequence (Vail Sh et al., 1977). Shelf Sand- Starved 1110 CAMBRIAN–ORDOVICIAN UNCONFORMITY 1090 The unconformity between the Cambrian Parahio Formation and the overlying Thango Formation is poorly understood, but it has important implications for the early tectonic history of the Himalaya. The age of the unconformity is in part constrained by trilobites from fs fs the basal part of the Takche Formation, which sh sh vfs vfs overlies the Thango Formation and which is no Figure 12. Two shoaling cycles from 1087.67 to 1127.92 m in the section. Note thick ball- older than Middle Ordovician and no younger and-pillow zones of probable shoreface origin at the top of the second cycle. See Figure 11 than latest Ordovician (Patterson, 2004; R.A. caption for explanation of abbreviations. Fortey, 2004, personal commun.). Trace fossils from the Thango Formation (Bhargava and Bassi, 1998) are consistent with this estimate, because they also suggest an Ordovician age.

504 Geological Society of America Bulletin, March/April 2006 CAMBRIAN STRATIGRAPHY AND DEPOSITIONAL HISTORY IN NORTHERN INDIAN HIMALAYA

The Cambrian–Ordovician unconformity in the Prograding Shoreline Parahio Valley is a low-angle truncation surface A (Fig. 14A). Small-scale relief at the base of the cobble conglomerate of the Thango Forma- tion consists of large decimeter- to meter-scale elongate scours (Fig. 14C, D). These scours are generally oriented northeast-southwest. South- east of the confl uence of the Parahio and Sumna Rivers, at one of Hayden’s (1904) sections, the N unconformity shows considerable local relief. Boulder conglomerate in the Thango makes up an incised valley fi ll that cuts nearly verti- Initial Transgression: cally through hundreds of meters of upper Para- Deposition of hio deposits (Fig. 14B, E–G). The valley fi ll B carbonate includes large meter-scale boulders of dolostone derived from thick dolostone beds that are cut out by the unconformity (Fig. 14F). A Cambrian–Ordovician unconformity occurs along the length of the Himalaya west of Nepal, although in western Kashmir, Lower Ordovi- cian rocks rest without angular discordance on Upper Cambrian rocks (Reed, 1934; Jell, 1986). In the Peshawar Basin of Pakistan, north of the Late-Stage Panjal-Khairabad Fault, the Ordovician Misra Transgression: Banda Quartzite unconformably overlies the Deposition of poorly dated Tanawai Formation (Pogue et al., C siliciclastic mud 1992), which is presumably of Cambrian age. In the Zanskar Basin the unconformity caps latest Middle Cambrian deposits (Gaetani et al., 1986; Jell and Hughes, 1997). In the Kumaon Himalaya (LeFort, 1975), adjacent to the western border of Nepal, the Ralam Conglomerate overlies the Martoli Group, from which Early Cambrian trilobites have been collected several hundred meters below the unconformity (Kacker and Srivastava, 1996). These relation- Figure 13. Block diagrams illustrating development of large-scale cycles within the Parahio ships suggest uplift and differential erosion of Formation. North arrow for orientation. (A) Progradation of a deltaic shoreline. (B) During sedimentary successions (Hayden, 1904) along initial transgression, sediment supply is reduced and carbonate deposition begins in shallow the length of the orogen. The event is roughly water. (C) Continued transgression results in deposition of siliciclastic mud. correlative with the timing of late Pan-African granitoid emplacement and associated fold- thrust deformation and high-grade metamorphism (Garzanti et al., 1986). Granite intrusions of this age with high 87Sr/86Sr isotopic ratios (Wiesmayr and Grasemann, 2002; Gehrels et to-the-northeast reverse movement. The fault is occur throughout the Himalaya (LeFort et al., al., 2003). However, such structures are diffi cult truncated by the Cambrian–Ordovician contact. 1986), but their tectonic signifi cance is a sub- to document, owing in part to the dominance of However, local evidence for shearing along this ject of debate. Gehrels et al. (2003) suggest that Cenozoic deformation and high-grade metamor- contact suggests that interpretation of the fold the intrusions were associated with a major fold phism. Normal faulting and minor folding have and fault as Cambrian in age is at best dubious. and thrust belt that developed within the Teth- been related to Cambrian–Ordovician deforma- Approximately 10 m south of the area shown yan Himalaya during the Late Cambrian and tion south of the Parahio Valley in the Pin Valley in Figure 15A, the contact is accessible and is Ordovician. Other authors relate the granites to (Wiesmayr and Grasemann, 2002). However, marked by a 40-cm-thick shear zone with evi- extensional, rather than contractional, tectonics the fold and unconformity surface reported dence of anomalously high strain in comparison (Miller et al., 2001). by Hayden (1904) were never given a modern to rocks directly above and below (Fig. 15B). In the Parahio Valley, the Cambrian–Ordovi- structural analysis. The shear zone contains a strong, northeast-dip- cian contact (Fig. 14A) shows truncation of a fold Our analysis shows that the axis of the fold in ping foliation, the defl ection of which suggests in the underlying Parahio Formation (Fig. 15A; Figure 15A plunges 14° to the east-southeast and top-to-the-southwest thrusting. This interpreta- plate 6 in Hayden, 1904). Structures that formed that bedding is offset by a fault with a throw of tion is substantiated by mesoscopic fault sur- during the Cambrian–Ordovician deformation ~5 m. This fault strikes east-west and dips 70° to faces spaced 6–30 cm apart that locally crosscut episode are important in the debate over the tec- the south. The fault surface contains quartz slip foliation within the shear zone. These faults are tonic signifi cance of the related unconformity fi bers with steps that indicate left-oblique, top- inclined at a low angle to the trace of the shear

Geological Society of America Bulletin, March/April 2006 505 MYROW et al.

B A Ordovician Thango Fm. Thick Cambrian–Ordovician Valley Unconformity Fill Ordovician Cambrian Parahio Fm. Parahio Formation

C D

506 Geological Society of America Bulletin, March/April 2006 CAMBRIAN STRATIGRAPHY AND DEPOSITIONAL HISTORY IN NORTHERN INDIAN HIMALAYA

Figure 14. Cambrian–Ordovician unconformity. (A) View of the upper Parahio Forma tion above the Sumna River. Note cutout of orange dolostone beds below the sub-Ordovician unconformity (white dashed lines) and thick valley fi ll on left. (B) View of the upper Parahio Formation in the foreground and conglomeratic Ordovician valley fi ll in the background at left at the same stratigraphic level. (C) Close- up of oriented meter-scale scours along the unconformity at the base of Ordovician deposits. (D) Irregular unconformity at the base of the Ordovician, including oriented scours as shown in C. (E) Close-up of the unconformity at the base of thick valley fi ll, with sandstone and shale of the Parahio Formation at the base and coarse conglomerate of the Thango Formation above. (F) Close-up of coarse, thick valley fi ll with large boulders of orange dolostone that were cut out below the Cambrian–Ordovician unconformity. (G) Thick Ordovician valley fi ll. Photo shows >100 m of conglomeratic strata.

zone, and defl ection of the foliation by the faults, To further evaluate whether Cambrian rocks tion of fold axes in the area (Fig. 4). Disjunctive along with stepped quartz slip fi bers on their sur- contain evidence for pre-Ordovician deforma- slaty to spaced cleavage occurs within all strati- faces, suggests that they represent riedel shears tion, we also examined and compared structures graphic units in the study area and varies from related to top-to-the-southwest thrusting. Inter- above and below the Cambrian–Ordovician being axial planar to slightly fanning around pretation of the contact as a thrust also serves unconformity. Folds occur locally within all of folds. Cleavage strikes northwest-southeast, to explain the stair-step shape of the contact the stratigraphic units within the study area and and cleavage-bedding intersection lineations in profi le as it cuts upsection to the southwest are upright to inclined, cylindrical (Fig. 4), and plunge ~20° to the southeast (Fig. 4), similar in the footwall (Fig. 15A; plate 6 in Hayden, have amplitudes and wavelengths that range to the orientation of the pi axes and fold axes. 1904); this resembles a footwall ramp-on-fl at from a few meters to a kilometer. Bedding-par- A comparison of structures between Cambrian geometry that is commonly displayed by thrust allel slip surfaces occur on the limbs of folds, and Ordovician stratigraphic units reveals little faults (Boyer and Elliot, 1982). The southwest- and these contain quartz and epidote slip fi bers difference in orientation between fold axes, directed sense of movement along the surface is with steps, indicating that folds formed pre- cleavage, and cleavage-bedding intersection consistent with the direction of thrusting for the dominantly by fl exural slip. We did not observe lineations (Fig. 4). Thus, we conclude that no region (Wiesmayr and Grasemann, 2002) and refolded folds indicative of polyphase deforma- clear evidence exists that the Cambrian rocks with minor out-of-the-syncline thrusting related tion. Bedding poles defi ne great-circle girdles have been deformed in a separate phase of to the folding of the Devonian Muth Formation that have horizontal or shallow, southeast- thrust-related folding and faulting during the to the north in Parahio Valley (Fig. 4). plunging pi axes (Fig. 4), similar to the orienta- Cambrian–Ordovician interval.

Ordovician NE Thango Formation SW N (Conglomerate) S

Ordovician Cambrian-Ordovician Thango Formation Unconformity (Conglomerate)

Riedel Shear Fold and left-oblique reverse fault Cambrian Parahio foliation Formation Cambrian- A ~10 m Ordovician Figure 15. (A) Close-up of the Cambrian–Ordovician unconformity at the base Contact of thick valley ﬁ ll. Note that the Parahio Formation has been folded and offset Cambrian- by a fault ~5 m. The fold and fault are apparently truncated by the Cambrian– Ordovician contact. (B) Further close-up of the Cambrian–Ordovician contact Parahio as viewed to the southeast. Note that the contact is marked by a 40-cm-thick Formation shear zone that contains a well-developed foliation and brittle riedel shears. Evi- dence for shear along this contact indicates that the fold shown in A is likely not Cambrian. B

Geological Society of America Bulletin, March/April 2006 507 MYROW et al.

DISCUSSION (Vannay and Grasemann, 2001). The recent metamorphism and deformation as recorded in top-to-the-north displacement along the South the Greater Himalaya. As outlined earlier, the paleoenvironments and Tibetan detachment system is estimated to be a A southern uplift is also problematic in that no depositional history of the Parahio Formation minimum of 35 km in both Nepal (Burchfi el et well-developed Cambrian-age structural fabrics have been radically reinterpreted as recording a al., 1992; Hodges, 2000) and Zanskar (Dezes et are preserved in strata from either the Tethyan series of progradational cycles of a storm-domi- al., 1999). The displacement magnitude of the Himalaya or the Lesser Himalaya. In addition, nated shoreline. Thin limestone beds represent earlier south-directed phase of thrust movement clasts in the Ordovician molasse of Spiti are transgressive systems tract deposits, which were along the South Tibetan detachment system is coarse (boulder size) and of local origin, so they shown in this study to contain abundant trilobite also unclear. Detailed lithofacies analysis of the provide no evidence of long distance transport. fossils. New collections from these beds allow upper Tal Group is needed as a test of the link Ultimately, detailed integrative analyses will be for detailed correlation of this important section between Lesser Himalaya and Tethyan Hima- required along the length of the Himalaya to with those elsewhere in the Himalaya and glob- laya ancient environments, although the simi- decipher, even to the fi rst order, the nature of ally, as well as to defi ne the duration of deposi- larities in detrital zircon age spectra (Myrow et this enigmatic Cambrian–Ordovician event. tion of the formation and the hiatus of the over- al., 2003) and paleocurrents are strong evidence lying Cambrian–Ordovician unconformity. for contiguous depositional systems of the same CONCLUSIONS The results of this study have bearing on the northern Indian margin, with no evidence for an continued debate concerning the early deposi- intervening landmass separating the two regions The Parahio Formation of the Spiti region tional and tectonic history of the Himalaya. Part (cf. Saxena, 1971; Bhargava and Bassi, 1998). represents the northern margin of India during of the debate concerns the relationship between Our structural and stratigraphic analysis indi- the Cambrian. Facies analysis and northeast- the three lithotectonic zones of the Himalaya— cates that although the unconformity in the Spiti directed paleocurrents in this >1350-m-thick the Lesser Himalaya, the Greater Himalaya, Valley is generally a low-relief surface, consid- succession indicate that these strata record and the Tethyan Himalaya. Paleocurrent data, erable local relief of several hundred meters is prograding river- and storm-infl uenced deltaic particularly those from the fl uvial trough cross- represented by a thick valley fi ll. The duration deposits. This is in striking contrast to previous bedded facies of the Parahio Formation, show of the hiatus in the Spiti Valley was a minimum paleoenvironmental interpretations that ranged a parallelism to those of the uppermost Lower of 15 m.y. and possibly as much as 20–30 m.y. from a deep-water fl ysch setting to a tidally dom- Cambrian Tal Group of the Lesser Himalaya (Myrow et al., 2006). A variety of data, includ- inated shoreline (Srikantia, 1981; Fuchs, 1982). (Ganesan, 1975), namely, with transport to the ing the spatial extent of the unconformity, the These strata contain well-defi ned decameter- north-northeast. Myrow et al. (2003) suggested difference in the level of erosion along the scale cycles that record high sediment accumu- that the uppermost Member E of the Tal, which length of the Himalaya, and evidence for early lation rates and likely resulted from delta-lobe consists of more than 1000 m of unfossilifer- structural deformation in the adjacent Pin Val- switching, based on a lack of systematic strati- ous cross-bedded sandstone, is generally age ley, all indicate that the Cambrian–Ordovician graphic changes in cycle or facies thicknesses. equivalent to the Parahio and is of possible unconformity had a tectonic, as opposed to a Trilobite-bearing limestone beds represent thin fl uvial origin. However, Hughes et al. (2005) purely eustatic, origin. transgressive systems tract deposits developed suggested a revised lithostratigraphic correla- The unconformity and bounding strata in over marine fl ooding surfaces. The fauna indi- tion in which the carbonate of Member D of Zanskar were considered by Garzanti et al. cate that the formation ranges from uppermost the upper part of the Tal Group equates to the (1986) to have recorded development of a deep- Lower Cambrian (Lungwangmiaoan Stage) late Middle Cambrian Karsha Formation of water foreland basin and adjacent subduction to middle Middle Cambrian (Hsuchuangian Zanskar. In this case the Parahio Formation complex. Gehrels et al. (2003) extended this Stage). Paleocurrent data from the Parahio For- would be correlative with Member C of the Tal model to include southward-directed thrusting mation indicate northward fl ow, and, combined Group, a 300-m-thick unfossiliferous cross- and development of coarse molasse wedges with geochemical and geochronological data bedded sandstone also likely of fl uvial origin. shed from north to south. Our paleocurrent for these strata, they suggest continuity of depo- Member B of the Tal Group is nearly contem- data from Spiti and additional data from Zans- sitional systems between the Lesser Himalaya poraneous (±1–2 m.y.) with the earliest dated kar (Myrow et al., 2006) indicate fl ow toward and the Tethyan Himalaya in the Cambrian. beds in the Parahio Forma tion. the north during the Cambrian. Paleocurrents A prominent Cambrian–Ordovician uncon- According to this model, the upper Tal is the taken from Ordovician molasse deposits of formity at the top of the Parahio Formation is record of Lesser Himalaya rivers that fed the northern India also indicate transport to the marked by irregular meter-scale scours and a deltaic Tethyan Himalaya environments of the north and northeast (Garzanti et al., 1986; valley-fi ll succession >100 m thick. The meter- Parahio along the northern Indian margin. It is Bagati et al., 1991), parallel to the orienta- scale scours are oriented northeast-southwest, diffi cult to evaluate the original distance between tion of the meter-scale scours along the Cam- parallel to the inferred north- and northeast- these two zones because of uncertainties in the brian–Ordovician unconformity described ear- directed transport of sediment, as measured Cenozoic displacement along two faults: (1) the lier. These are inconsistent with the models of from paleocurrents in the overlying Ordovician Main Central Thrust, with top-to-the-south foreland basin development as just described deposits. The unconformity is of regional extent thrusting; and (2) the South Tibetan detachment (see also Myrow et al., 2006). Given the north- and, within northern India, shows progressive system, with top-to-the-north extensional move- ward-directed Ordovician paleocurrents, it is downcutting from Zanskar in the north-north- ment along with an older phase of top-to-the- possible that uplift may have taken place south west toward the Spiti Valley. Based on our tri- south thrusting. The Main Central Thrust is esti- of the present position of the South Tibetan lobite data, the minimum hiatus associated with mated to have a displacement of 150–200 km detachment system to provide a source of sedi- the unconformity in Spiti is 15 m.y. or more (Schelling and Arita, 1991; Schelling, ment for Ordovician strata, but features that The nature of this Cambrian–Ordovician 1992); southwest of our study area the displace- would clarify the nature of this purported uplift boundary unconformity remains an enigma. ment is estimated as a minimum of 100 km are obscured owing to Cenozoic high-grade Stratigraphic and sedimentological data from

508 Geological Society of America Bulletin, March/April 2006 CAMBRIAN STRATIGRAPHY AND DEPOSITIONAL HISTORY IN NORTHERN INDIAN HIMALAYA

Bulletin, v. 100, p. 999–1015, doi: 10.1130/0016- India): Geology, v. 15, p. 409–413, doi: 10.1130/0091- the Parahio Formation and overlying units from 7606(1988)100<0999:DCAPIT>2.3.CO;2. 7613(1987)15<409:ZSZNEW>2.0.CO;2. both the Spiti and Zanskar Valleys are not con- Corfi eld, R.I., and Searle, M.P., 2000, Crustal shortening Hodges, K.V., 2000, Tectonics of the Himalaya and south- sistent with published models of foreland basin estimates across the north Indian continental margin, ern Tibet from two perspectives: Geological Society of Ladakh, NW India, in Khan, M.A., et al., eds., Tec- America Bulletin, v. 112, p. 324–350, doi: 10.1130/0016- development with southward-directed thrusting. tonics of the Nanga Parbat Syntaxis and the Western 7606(2000)112<0324:TOTHAS>2.3.CO;2. The possibility exists that uplift took place south Himalaya: Geological Society [London] Special Pub- Houseknecht, D.W., 1971, Assessing the relative importance lication 170, p. 395–410. of compaction processes and cementation to reduction of the present southern limit of the Tethyan Cowan, C.A., and James, M.P., 1992, Diastasis cracks: of porosity in sandstones: American Association of Himalaya, namely, the South Tibetan detach- Mechanically generated synaeresis-like cracks in Petroleum Geologists Bulletin, v. 55, p. 633–642. ment system, but there is no published evidence Upper Cambrian shallow water oolite and ribbon car- Hughes, N.C., Peng, S.-C., Bhargava, O.N., Ahulwalia, bonates: Sedimentology, v. 39, p. 1101–1118. A.D., Walia, S., Myrow, P.M., and Parcha, S.K., 2005, for such an uplift in either the Greater or Lesser Davidek, K., Landing, E., Bowring, S.A., Westrop, S.R., Early Tsanglangpuan (late early Cambrian) trilobites Himalaya lithotectonic zones to the south. Rushton, A.W.A., and Adrain, J.M., 1998, New from the Nigali Dhar syncline and the Cambrian bio- uppermost Cambrian U-Pb date for Avalonian Wales stratigraphy of the Tal Group, Lesser Himalaya, India: ACKNOWLEDGMENTS and age of the Cambrian–Ordovician boundary: Geo- Geological Magazine, v. 142, p. 57–80, doi: 10.1017/ logical Magazine, v. 135, p. 303–309, doi: 10.1017/ S0016756804000366. S0016756898008711. Jell, P.A., 1986, An early Late Cambrian trilobite faunule from We thank O.N. Bhargava, L.R.M. Cocks, R.A. DeCelles, P.G., Gehrels, G.E., Quade, J., Lareau, B.N., Kashmir: Geological Magazine, v. 123, p. 487–492. Fortey, C.H. Holland, A.R. Palmer, and J.E. Taylor and Spurlin, M.S., 2000, Tectonic implications of Jell, P.A., and Hughes, N.C., 1997, Himalayan Cambrian trilo- for discussion. We extend particular thanks to Eric U-Pb zircon ages of the Himalayan orogenic belt in bites: Special Papers in Palaeontology, v. 58, p. 1–113. Draganits for discussions of the Tethyan stratigra- Nepal: Science, v. 288, p. 497–499, doi: 10.1126/sci- Kacker, A.K., and Srivastava, M.C., 1996, Redlichia from phy. Associate Editors Ron Law and Robert Rain- ence.288.5465.497. Milam Formation of Martoli Group, Kumaon Himalaya, bird, and reviewers An Yin, Laurent Godin, and an Dezes, P.J., Vannay, J.C., Steck, A., Bussy, F., and Cosca, M., India—Systematics and signifi cance: Proceedings of anonymous reviewer, provided helpful reviews. Field 1999, Synorogenic extension: Quantitative constraints Symposium on Recent Advances in Geological Studies on the age and displacement of the Zanskar shear of Northwest Himalaya and the Foredeep: Geological support was provided through the Wadia Institute of zone (NW-Himalaya): Geological Society of America Survey of India Special Publication 21, p. 291–293. Himalayan Geology. Our Himalayan research is sup- Bulletin, v. 111, p. 364–374, doi: 10.1130/0016- Klootwijk, C.T., Conaghan, P.J., and Powell, C.McA., 1985, ported by U.S. National Science Foundation grants 7606(1999)111<0364:SEQCOT>2.3.CO;2. The Himalayan Arc: Large-scale continental subduc- EAR-9980426 to N.C.H. and EAR-9980376 to Dott, R.H., Jr., and Bourgeois, J., 1982, Hummocky stratifi - tion, oroclinal bending and back-arc spreading: Earth P.M.M., and by National Geographic Society grant cation: Signifi cance of its variable bedding sequences: and Planetary Science Letters, v. 75, p. 167–183, doi: NGS7293-02 to N.C.H. Geological Society of America Bulletin, v. 93, 10.1016/0012-821X(85)90099-8. p. 663–680, doi: 10.1130/0016-7606(1982)93<663: Kumar, G., Raina, B.K., Bhargava, O.N., Maithy, P.K., and REFERENCES CITED HSSOIV>2.0.CO;2. Babu, R., 1984, The Precambrian–Cambrian boundary Dumas, S., Arnott, R.W.C., and Southard, J.B., 2005, Experi- problem and its prospects, northwest Himalaya, India: ments on oscillatory-fl ow and combined-fl ow bed forms: Geological Magazine, v. 121, p. 211–219. Arnott, R.W., and Southard, J.B., 1990, Exploratory fl ow- Implications for interpreting parts of the shallow-marine Landing, E., Bowring, S.A., Davidek, K.L., Westrop, S.R., duct experiments on combined-fl ow bed confi gura- sedimentary record: Journal of Sedimentary Research, Geyer, G., and Heldmaier, W., 1998, Duration of the tions, and some implications for interpreting storm- v. 75, p. 501–513, doi: 10.2110/jsr.2005.039. Early Cambrian: U-Pb ages of volcanic ashes from event stratifi cation: Journal of Sedimentary Petrology, Fortey, R.A., and Owens, R.M., 1990, Trilobites, in McNa- Avalon and Gondwana: Canadian Journal of Earth Sci- v. 60, p. 211–219. mara, K.J., ed., Evolutionary trends: London, Belhaven ences, v. 35, p. 329–338, doi: 10.1139/cjes-35-4-329. Astin, T.R., and Rogers, D.A., 1991, Subaqueous shrinkage Press, p. 121–142. Leckie, D.A., and Krystinik, L.F., 1989, Is there evidence cracks in the Devonian of Scotland reinterpreted: Jour- Frank, W., Grasemann, B., Guntli, P., and Miller, C., 1995, for geostrophic currents preserved in the sedimentary nal of Sedimentary Petrology, v. 61, p. 850–859. Geological map of the Kishtwar, Chamba, and Kulu record of inner to middle-shelf deposits?: Journal of Bagati, T.N., Kumar, R., and Ghosh, S.K., 1991, Regres- region, NW Himalaya, India: Jahrbuch der Geolo- Sedimentary Petrology, v. 59, p. 862–870. sive-transgressive sedimentation in the Ordovician gischen Bundesanstalt Wien, v. 138, p. 299–308. Leckie, D.A., and Walker, R.G., 1982, Storm- and tide-dom- sequence of the Spiti (Tethys) basin, Himachal Pradesh, Fuchs, G., 1982, The geology of Pin Valley in Spiti, Him- inated shorelines in Cretaceous Moosebar—Lower India: Sedimentary Geology, v. 73, p. 171–184, doi: achal Pradesh, India: Jahrbuch der Geologischen Gates interval—Outcrop equivalents of Deep Basin 10.1016/0037-0738(91)90029-D. Bundesanstalt Wien, v. 124, p. 325–359. gas trap in western Canada: American Association of Bhargava, O.N., and Bassi, U.K., 1998, Geology of Spiti- Fuchs, G., 1987, The geology of southern Zanskar Petroleum Geologists Bulletin, v. 66, p. 138–157. Kinnauer Himachal Himalaya: Geological Survey of (Ladakh)—Evidence for the autochthony of the Tethys LeFort, P., 1975, Himalayas: The collided range: Present India Memoir 124, p. 1–210. Zones of the Himalaya: Jahrbuch der Geologischen knowledge of the continental arc: American Journal of Bhargava, O.N., Kumar, G., and Gupta, S.S., 1982, Cam- Bundesanstalt Wien, v. 130, p. 465–491. Science, v. 275-A, p. 1–44. brian trace fossils from the Spiti Valley, Himachal Gaetani, M., Casnedi, R., and Fois, E., Garzanti, El, Jadoul, LeFort, P., Debon, F., Pêcher, A., Sonet, J., and Vidal, P., Himalaya: Journal of the Geological Society of India, F., Nicora, A., and Tintori, A., 1986, Stratigraphy of the 1986, The 500 Ma magmatic event in Alpine southern v. 23, p. 183–191. Tethys Himalaya in Zanskar, Ladakh: Rivista Italiana Asia, a thermal episode at Gondwana scale: Sciences Bhargava, O.N., Bhandari, A.K., and Sharma, R.K., 1986, di Paleontologia e Stratigraphia, v. 48, p. 237–265. de la Terre, v. 47, p. 191–209. Lower Cambrian trace fossils from the Kilung Valley, Ganesan, T.M., 1975, Paleocurrent pattern in the upper Tal Lehrmann, D.J., and Goldhammer, R.K., 1999, Secular Lahaul and Spiti District, Himachal Himalaya: Bulletin rocks of Nigali, Korgai synclines (H.P.) and Mussorie variation in parasequence and facies stacking patterns of the Indian Geologists’ Association, v. 19, p. 66–68. syncline (U.P.): Journal of the Geological Society of of platform carbonates: A guide to application of stack- Bond, G., and Kominz, M.A., 1984, Construction of tectonic India, v. 16, p. 503–507. ing-patterns analysis in strata of diverse ages and set- subsidence curves for the Early Paleozoic miogeocline, Gansser, A., 1964, Geology of the Himalayas: London, tings, in Harris, P.M., et al., eds., Advances in carbon- southern Canadian Rocky Mountains: Implications for Interscience Publishers, 289 p. ate sequence stratigraphy: Application to reservoirs, subsidence mechanisms, age of break up, and crustal Garzanti, E., Casnedi, R., and Jadoul, F., 1986, Sedimentary outcrops and models: SEPM (Society for Sedimentary thinning: Geological Society of America Bulletin, v. 95, evidence of a Cambro-Ordovician orogenic event in the Geology) Special Publication 63, p. 187–225. p. 155–173, doi: 10.1130/0016-7606(1984)95<155: northwestern Himalaya: Sedimentary Geology, v. 48, Miller, C., Tiioni, M., Frank, W., Grasemann, B., Klotzli, U., COTSCF>2.0.CO;2. p. 237–265, doi: 10.1016/0037-0738(86)90032-1. Guntli, P., and Draganitz, E., 2001, The early Palaeo- Boyer, S., and Elliot, D., 1982, Thrust systems: American Gehrels, G.E., DeCelles, P.G., Martin, A., Ojha, T.P., zoic magmatic event in the Northwest Himalaya, India: Association of Petroleum Geologists Bulletin, v. 66, Pinhassi, G., and Upreti, B.N., 2003, Initiation of the Source, tectonic setting and age of emplacement: Geo- p. 1196–1230. Himalayan orogen as an early Paleozoic thin-skinned logical Magazine, v. 138, p. 237–251, doi: 10.1017/ Burchfi el, B.C., Chen, Z., Hodges, K.V., Liu, Y., Royden, thrust belt: GSA Today, v. 13, no. 9, p. 4–9, doi: S0016756801005283. L.H., Deng, C., and Xu, J., 1992, The South Tibetan 10.1130/1052-5173(2003)13<4:IOTHOA>2.0.CO;2. Myrow, P.M., 1992a, Pot and gutter casts from the Chapel Detachment System, Himalayan Orogen: Extension Griesbach, C.L., 1891, Geology of the Central Himalayas: Island Formation, southeast Newfoundland: Journal of contemporaneous with and parallel to shortening in a Geological Survey of India Memoir 23, p. 1–232. Sedimentary Petrology, v. 62, p. 992–1007. collisional mountain belt: Geological Society of Amer- Harms, J.C., Southard, J.B., and Walker, R.G., 1982, Myrow, P.M., 1992b, Bypass-zone tempestite facies model ica Special Paper 269, 44 p. Structures and sequences in clastic rocks: Society of and proximality trends for an ancient muddy shoreline Byers, C.W., 1977, Biofacies patterns in euxinic basins: A Economic Paleontologists and Mineralogists Short and shelf: Journal of Sedimentary Petrology, v. 62, general model, in Cook, H.E., and Enos, P., eds., Deep- Course 9, 249 p. p. 99–115. water carbonate environments: Society of Economic Hayden, H.H., 1904, The geology of Spiti, with parts of Myrow, P.M., and Landing, E., 1992, Mixed siliciclas- Paleontologists and Mineralogists Special Publica- Bashahr and Rupshu: Geological Survey of India tic–carbonate deposition in a lower Cambrian oxygen- tion 25, p. 5–17. Memoir 36, p. 1–129. stratifi ed basin, Chapel Island Formation, southeastern Coleman, J.M., 1988, Dynamic processes and changes in the Herren, E., 1987, Zanskar shear zone: Northeast-south- Newfoundland: Journal of Sedimentary Petrology, Mississippi River delta: Geological Society of America west extension within the Higher Himalayas (Ladakh, v. 62, p. 455–473.

Geological Society of America Bulletin, March/April 2006 509 MYROW et al.

Myrow, P.M., Hughes, N.C., Paulsen, T.S., Williams, I.S., Schill, E., Appel, E., Zeh, O., Singh, V.K., and Gautam, P., tigraphy—Applications to hydrocarbon exploration: Parcha, S.K., Thompson, K.R., Bowring, S.A., 2001, Coupling of late-orogenic tectonics and sec- American Association of Petroleum Geologists Mem- Peng, S.-C., and Ahluwalia, A.D., 2003, Integrated ondary pyrrhotite remanences: Towards a separation oir 26, p. 49–212. tectonostratigraphic reconstruction of the Himalaya of different rotation processes and quantifi cation of Vannay, J.-C., and Grasemann, B., 1998, Himalaya inverted and implications for its tectonic reconstruction: Earth rotational underthrusting in the western Himalaya, metamorphism in the High Himalaya of Kinnaur and Planetary Science Letters, v. 212, p. 433–441, doi: northern India: Tectonophysics, v. 337, p. 1–21, doi: (NW India): Petrography versus thermobarometry: 10.1016/S0012-821X(03)00280-2. 10.1016/S0040-1951(01)00113-5. Schweizerische Mineralogische und Petrographische Myrow, P.M., Snell, K.E., Hughes, N.C., Paulsen, T.S., Schill, E., Crouzet, C., Gautam, P., Singh, V.K., and Appel, Mitteilungen, v. 78, p. 107–132. Heim, N.A., and Parcha, S.K., 2006, Cambrian deposi- E., 2002, Where did rotational shortening occur in the Vannay, J.-C., and Grasemann, B., 2001, Himalaya inverted tional history of the Zanskar Valley region of the Indian Himalayas? Inferences from paleomagnetic remagne- metamorphism and syn-convergence extension as a conse- Himalaya: Tectonic implications: Journal of Sedimen- tizations: Earth and Planetary Science Letters, v. 203, quence of a general shear extrusion: Geological Magazine, tary Research, v. 76 (in press). p. 45–57, doi: 10.1016/S0012-821X(02)00842-7. v. 138, p. 253–276, doi: 10.1017/S0016756801005313. Parcha, S.K., 1996, Cambrian sequences in the Tethyan zone Schlager, W., 1981, The paradox of drowned reefs and Vannay, J.-C., Grasemann, B., Rahn, M., Frank, W., Carter, of Spiti Himalaya and its boundary problems: Newslet- carbonate platforms: Geological Society of America A., Baudraz, V., and Cosca, M., 2004, Miocene to ters on Stratigraphy, v. 34, p. 3–11. Bulletin, v. 92, p. 197–211, doi: 10.1130/0016- Holocene exhumation of metamorphic crustal wedges Parcha, S.K., 2005, Biostratigraphic studies and correlation 7606(1981)92<197:TPODRA>2.0.CO;2. in the NW Himalaya: Evidence for tectonic extrusion of the middle Cambrian successions of northwestern Searle, M.P., 1986, Structural evolution and sequence of coupled to fl uvial erosion: Tectonics, v. 23, p. TC1014, Kashmir Himalaya: Journal of the Geological Society thrusting in the High Himalayan, Tibetan-Tethys and doi: 10.1029/2002TC001429. of India, v. 65, p. 183–196. Indus suture zones of Zanskar and Ladakh, Western Van Wagoner, J.C., Posamentier, H.W., Mitchum, R.M., Vail, Parcha, S.K., Singh, B.P., and Singh, B.P., 2005, Palaeo- Himalaya: Journal of Structural Geology, v. 8, p. 923– P.R., Sarg, J.F., Loutit, T.S., and Hardenbol, J., 1988, ecological signifi cance of ichnofossils from the Early 936, doi: 10.1016/0191-8141(86)90037-4. Overview of the fundamentals of sequence stratigraphy Cambrian succession of the Spiti Valley, Tethys Hima- Seed, H.B., 1968, Landslides during earthquakes due to soil and key defi nitions, in Wilgus, C.K., et al., eds., Sea- laya, India: Current Science, v. 88, p. 158–162. liquefaction: Journal of the American Society of Civil level changes—An integrated approach: Society of Pascoe, E.H., 1959, A manual of the geology of India and Engineering: Soil Mechanics and Foundations Divi- Economic Paleontologists and Mineralogists Special Burma (3rd edition): Calcutta, Geological Survey of sion, v. 94, no. SM5, p. 1053–1122. Publication 42, p. 39–45. India, v. 2, p. 1–1343. Srikantia, S.V., 1981, The lithostratigraphy, sedimentation Walker, R.G., and Cant, D.J., 1984, Sandy fl uvial systems, in Patterson, J.R., 2004, Palaeobiogeography of the Ordovician and structure of Proterozoic–Phanerozoic formations of Walker, R.G., ed., Facies models (2nd edition): Geosci- trilobite Prosopiscus, with a new species from western Spiti basin in the higher Himalaya of Himachal Pradesh, ence Canada Reprint Series 1, p. 71–89. New South Wales: Alcheringa, v. 28, p. 65–76. India, in Sinha, A.K., and Nautiyal, S.P., eds., Contem- Weimer, R.J., Howard, J.D., and Lindsay, D.R., 1982, Tidal Pogue, K.R., Wardlaw, B.R., Harris, A.G., and Hussain, porary geoscientifi c researches in India: Dehra Dun, fl ats and associated tidal channels, in Scholle, P.A., and A., 1992, Paleozoic and Mesozoic stratigraphy of the Sishen Singh Mahendra Pal Singh, v. 1, p. 31–48. Spearing, D., eds., Sandstone depositional environ- Peshawar basin, Pakistan: Correlations and implica- Srikantia, S.V., and Bhargava, O.N., 1983, Geology of the ments: American Association of Petroleum Geologists tions: Geological Society of America Bulletin, v. 104, Palaeozoic sequence of the Kashmir Tethys Himalayan Memoir 31, p. 191–245. p. 915–927, doi: 10.1130/0016-7606(1992)104<0915: basin in the Lidder Valley, Jammu and Kashmir: Journal Wiesmayr, G., and Grasemann, B., 2002, Eohimalayan fold PAMSOT>2.3.CO;2. of the Geological Society of India, v. 24, p. 363–377. and thrust belt: Implications for the geodynamic evo- Posamentier, H.W., Allen, G.P., James, D.P., and Tes- Srikantia, S.V., and Bhargava, O.N., 1998, Geology of Him- lution of the NW-Himalaya, India: Tectonics, v. 21, son, M., 1992, Forced regressions in a sequence achal Pradesh: Bangalore, Geological Society of India, p. 8-1–8-18. stratigraphic framework: Concepts, examples, and 406 p. Wyss, M., Hermann, J., and Steck, A., 1999, Structural and sequences stratigraphic signifi cance: American Stanley, D.J., and Hait, A.K., 2000, Deltas, radiocarbon dat- metamorphic evolution of the northern Himachal Hima- Association of Petroleum Geologists Bulletin, v. 76, ing, and measurements of sediment storage and subsid- laya, NW India (Spiti-eastern Lahul-Parvati valley tra- p. 1687–1709. ence: Geology, v. 28, p. 295–298, doi: 10.1130/0091- verse): Eclogae Geologicae Helvetiae, v. 92, p. 3–44. Potter, P.E., and Pettijohn, F.J., 1977, Paleocurrents and 7613(2000)028<0295:DRDAMO>2.3.CO;2. Yin, A., and Harrison, T.M., 2000, Geologic evolution of basin analysis: Berlin, Springer-Verlag, 425 p. Steck, A., Spring, L., Vannay, J.C., Masson, H., Stutz, E., the Himalayan-Tibetan orogen: Annual Review of Reed, F.R.C., 1910, The Cambrian fossils of Spiti: Palaeon- Bucher, H., Marchant, R., and Tieche, J.C., 1993, Geo- Earth and Planetary Sciences, v. 28, p. 211–280, doi: tologia Indica (15th Ser.), v. 7, p. 1–70. logical transect across the northwestern Himalaya in 10.1146/annurev.earth.28.1.211. Reed, F.R.C., 1934, Cambrian and Ordovician fossils from eastern Ladakh and Lahul (a model for the continental Yin, A., Harrison, T.M., Murphy, M.A., Grove, M., Nie, S., Ryer- Kashmir: Palaeontologia Indica, v. 21, p. 1–38. collision of India and Asia): Eclogae Geologicae Hel- son, F.J., Wang, X., and Chen, Z., 1999, Tertiary deforma- Saxena, M.N., 1971, The crystalline axis of the Himalaya, vetiae, v. 86, p. 219–263. tion history of southeastern and southwestern Tibet during Indian shield and continental drift: Tectonophysics, Sudan, C.S., and Sharma, U.K., 2001, Trace fossil from the the Indo-Asian collision: Geological Society of America v. 12, p. 433–447, doi: 10.1016/0040-1951(71)90044-8. Cambrian rocks of Kunzam La section, Spiti, H.P., Bulletin, v. 111, p. 1644–1664, doi: 10.1130/0016- Schelling, D., 1992, The tectonostratigraphy and struc- India: Journal of the Palaeontological Society of India, 7606(1999)111<1644:TDHOSA>2.3.CO;2. ture of the eastern Nepal Himalaya: Tectonics, v. 11, v. 46, p. 161–171. p. 925–943. Vail, P.R., Mitchum, R.M., Jr., Todd, R.G., Widmier, J.M., MANUSCRIPT RECEIVED BY THE SOCIETY 27 MARCH 2005 Schelling, D., and Arita, K., 1991, Thrust tectonics, crustal Thompson, S., III, Sangree, J.B., Bubb, J.N., and REVISED MANUSCRIPT RECEIVED 1 SEPTEMBER 2005 MANUSCRIPT ACCEPTED 25 OCTOBER 2005 shortening, and the structure of the far-eastern Nepal Hatlelid, W.G., 1977, Seismic stratigraphy and global Himalaya: Tectonics, v. 10, p. 851–862. changes of sea level, in Payton, C.E., ed., Seismic stra- Printed in the USA

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