Refinements in the Upper Permian to Lower Jurassic ... - Springer Link

Facies (2013) 59:915–948 DOI 10.1007/s10347-012-0346-9

ORIGINAL ARTICLE

Refinements in the Upper Permian to Lower Jurassic stratigraphy of Karakorum, Pakistan Maurizio Gaetani • Alda Nicora • Charles Henderson Simonetta Cirilli • Luka Gale • Roberto Rettori • Irene Vuolo • Viorel Atudorei

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Received: 28 March 2012 / Accepted: 7 November 2012 / Published online: 5 December 2012  Springer-Verlag Berlin Heidelberg 2012

Abstract New sampling on critical intervals of the uppermost Permian and Triassic successions of the Northern Karakorum Terrain in the Karakorum Range (Pakistan) has refined the stratigraphy. Two types of successions may be distinguished in the Karakorum Range: a carbonate platform succession, spanning the whole interval from Upper Permian to Upper Triassic, possibly with several gaps; and a basinal succession, deposited from the Middle Permian to Early Carnian (Late Triassic), when the M. Gaetani (&)  A. Nicora  I. Vuolo Dipartimento di Scienze della Terra, Universita` degli Studi di Milano, Milan, Italy e-mail: [email protected] A. Nicora e-mail: [email protected] I. Vuolo e-mail: [email protected] C. Henderson Department of Geoscience, University of Calgary, Calgary, AB T2N 1N4, Canada e-mail: [email protected] S. Cirilli  R. Rettori Dipartimento di Scienze della Terra, Universita´ degli Studi di Perugia, Piazza Universita`, 06123 Perugia, Italy e-mail: [email protected] R. Rettori e-mail: [email protected] L. Gale Department for Palaeontology and Stratigraphy, Geological Survey of Slovenia, Dimicˇeva ulica 14, 1000 Ljubljana, Slovenia e-mail: [email protected] V. Atudorei New Mexico State University, Albuquerque, NM, USA e-mail: [email protected]

carbonate platform prograded into the basin. With the approaching and later docking of the Karakorum Block against the Asian margin closing the Paleo-Tethys, a portion of Karakorum emerged while another part subsided as a fore-deep, receiving clastics from the emerging Cimmerian Range. Molassic sediments filled the basin, whilst shallow-water carbonates transgressed over the emerged carbonate platform sometime between the latest Triassic and the Pliensbachian (Early Jurassic), with Cimmerian deformation occurring to the north. The age control is provided by conodonts, with assemblages of late Wuchiapingian, Changhsingian, Induan (Griesbachian and Dienerian), late Olenekian, early Anisian, late Ladinian, and early Carnian ages, respectively. Some information on the section around the P/T boundary is provided by palynology and isotopic C13 values. The dating of the Norian/Rhaetian platform is provided by foraminifers. Keywords Permian  Triassic  Jurassic  Karakorum  Pakistan  Conodonts  Foraminifers  Palynostratigraphy  Carbon isotopes

Introduction Since 1986, several Italian expeditions worked in the mighty mountains of Karakorum, aiming to unravel the stratigraphy of the Northern Karakorum Terrain (NKT). A number of papers or abstracts include information concerning the Permo/Triassic and/or the Jurassic stratigraphy in the range (Gaetani et al. 1990, 1993, 1995, 1996, 2005). The general evolution of the NKT has been considered in review papers by Gaetani (1997, 2009) and maps with explanatory notes have been produced (Zanchi and Gaetani 1994, 2011).

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Fig. 1 Index maps of studied localities and sections. 1 Sections Wirokhun Saddle, Borom, Kundil II, and Kundil III. 2 Sections Ashtigar 1, 1 bis, and 2. 3 Section Ini Sar. 4 Section Baroghil W. 5 Locality described by Perri et al. (2004)

This paper is concerned with the stratigraphic succession of the uppermost Permian, Triassic, and basal Jurassic in the NKT, introducing refinements of previous interpretations, mostly based on new palaeontological data (Fig. 1). The present paper is based on data gathered during the 1986, 1991, 1992, 1996, 1999, and 2008 expeditions. After the pioneering papers of Hayden (1915) and Desio and Martina (1972), in more recent times (beyond our papers mentioned before) the only studies dealing with this subject are by Perri et al. (2004) on Early Triassic conodonts and by Donnelly (2004), devoted to coal research in Jurassic rocks of the Chapursan Valley.

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Geological setting The NKT consists of a number of thrust sheets stacked with a sense of transport roughly from north to south (Zanchi 1993; Zanchi and Gaetani 1994, 2011; Zanchi and Gritti 1996). They are divided by a major lineament, the ReshunUpper Hunza Fault, running in an west-east direction for at least 200 km (Fig. 2a). To the south of this fault, as ascertained by fossils, the successions contains several gaps, and in a few places the presence of Triassic rocks was demonstrated (Perri et al. 2004; Gaetani et al. 2004). The overall trend is of carbonate sedimentation in prevailing

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Fig. 2 a Palaeogeographic cartoon with platform and basin successions from the Middle Permian to the Triassic. b A synthetic log of platform and basinal successions from Permian to Lower Jurassic (from Zanchi and Gaetani 2011, modified)

shallow waters. No Jurassic rocks have been identified so far by means of fossils in the thrust sheets lying to the south of the Reshun-Upper Hunza Fault. Instead, to the north of this major tectonic partition, two different domains may be recognized. To the west, from Chitral to Karambar Valley, Upper Permian and Triassic rocks consist of shallow-water carbonates, mostly altered into dolostone. Sedimentation gaps are frequent and large palaeokarst cavities occur toward the top of the massive carbonates. Jurassic rocks are present only north of Lashkargaz (Upper Yarkhun Valley). For simplicity we will refer to this domain as the platform succession. To the east, best developed in the Chapursan Valley, deposition since the Middle Permian exhibits significant deepening in the marine environment. The subsequent evolution is more diversified. We name this domain as the basin succession (Fig. 2b). To the north of the Siru Gol, Baroghil, and Chapursan successions are the Wakhan Slates, a slaty metamorphic unit of poorly defined age, which should be at least in part the deeper equivalent of the previous successions (Zanchi and Gaetani 2011).

the Lower Permian was recognized (Gaetani et al. 1995; Angiolini 1996). During the Middle Permian, important extensional-transtensional movements with block faulting and megabreccia landslides occurred and the region was laid down in deeper conditions with cherty limestone toward the top of the Guadalupian (Kundil Formation). Deeper water environments persisted through the Late Permian until the beginning of the Late Triassic (Wirokhun and Borom formations), when shallow-water carbonate sedimentation resumed during the Carnian, forming the peritidal-subtidal platform of the Aghil Formation. By the late Triassic, the Aghil carbonate platform drowned in the Sost Thrust Sheet and was overlain by terrigenous sediments produced by the Cimmerian orogeny developing to the north (Ashtigar and Yashkuk formations) that persisted for most of the Early Jurassic. Marly limestone with coal seams and gypsum intercalations represents large part of the Middle Jurassic (Reshit Formation). The final events in the Late Jurassic and Early Cretaceous are still rather obscure. The refinements we are presenting here concern 1.

the Upper Permian and the Permian–Triassic boundary (PTB), the Lower and Middle Triassic, and the Upper Triassic—lowermost Jurassic successions.

The basin succession

2. 3.

The Permian succession starts with the ubiquitous terrigenous Gircha Formation. Shallow-water carbonate intercalations occurred frequently since the Sakmarian, and prevailed during the Artinskian (Lupghar Formation, Gaetani et al. 1995). A sedimentary gap towards the top of

The first two items were studied in the area between the Borom and the Kundil gullies, west of Sost and Khudabad, the best area west of the Hunza River, where it is possible to study this segment of the succession. The third item is best exposed in the middle-upper Chapursan Valley.

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From Late Permian to Early Triassic In the area of Borom and Kundil gullies, the basinal succession is cropping out in tight folds. Due to the difference in the mechanical behaviour, soft intervals are often affected by minor faults and thrusts. The base of the basinal succession, the Kundil Formation, forms the main ridge crossing from the Kundil to the Borom valley. The general sedimentary succession is as follows, from bottom to top: 1.

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The Kundil Formation. This unit, proposed in Gaetani et al. (1990), consists of cherty limestone (recrystallized wackestone–packstone) in nodular to planar beds, thickening from 10–20 cm in the lower part of the unit to 50–60 cm in the upper part. An imposing sedimentary breccia body may occur in the middle to upper part of the unit. Some thin interlayer of green silt may contain evidence of volcanic ash. A package of thinbedded cherty limestone, about 3.5 m thick, some 43 m below the top of the unit, delivered only a few poorly preserved conodonts. Thickness of the cherty limestone is about 100–120 m, the megabreccia thinning laterally. The Wirokhun Formation. The unit was proposed by Gaetani et al. (1995) and consists of marls and marly limestone (mudstone) in the lower part, gradually passing to planar limestone (mudstone-wackestone) in the upper part. The Borom Formation. The unit was proposed by Gaetani et al. (1990) and consists of dark grey platy limestone, with black chert nodules and bands in the middle and upper part.

The best place we found to study the PTB interval and the lowermost Triassic is the Wirokhun Saddle (Figs. 3, 4, 5). The section of the Wirokhun Saddle was discussed briefly in Gaetani et al. (1995), and in posters during HKT workshops held in Ettal 1999 and in Grenoble 2005. Reconsideration of conodont identifications and resampling of the basal part of the Wirokhun Formation. done in 2008, led to the present interpretation of the section. What initially appeared as minor tectonic disturbance, is now interpreted to be tectonic repetition of the Upper Permian (Lopingian) carbonates. The Wirokhun Saddle section is as follows, from bottom to top and from NE to SW (Figs. 3, 4, 5): Kundil Formation •

Grey cherty limestone in beds 20–50 cm thick, forming the cliff and the wall towards the Chapursan Valley. Thickness is several tens of metres. The topmost layer consists almost only of dark chert. No conodonts were obtained.

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•

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Light grey thin-bedded limestone, poor in chert, with thin shaly partings. Thickness 0.55 m. Conodonts consist of Clarkina abadehensis Kozur, C. hauschkei Kozur, and ramiforms (samples KK113, KK826, KK828). The CAI (Conodont Alteration Index) is 5, corresponding to 300–480 C. Top of Changshingjan (Shen and Mei 2010). 2–4 cm of dark shale followed by 2 cm of ochrecoloured clay, possibly a very altered tuffite.

Wirokhun Formation (reference section of the unit) •

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Grey dark marl, splintery, poorly bedded, alternated with marly limestone in 20–30 beds. The calcareous intercalations are slightly increasing upwards. Thickness 25.2 m. Due to the rather difficult logistics, sampling for conodont has been limited to 2 kg/sample. About 40 % of samples were productive and a good lowermost Triassic succession of Induan (Griesbachian) age was obtained, including the Hindeodus parvus (Kozur & Pjatakova) to Isarcicella isarcica (Huckriede) succession (Fig. 4). The first conodonts were obtained at about 3 m from the base (KG832) and include H. parvus. See Figs. 4 and 5 for details of conodonts, palynomorphs, and chemistry. The CAI is always 5. Fault cutting almost along strike of the beds.

Kundil Formation Contrary to what crops out on the steep slope of the peak NE of the Wirokhun Saddle, where the upper part of the Kundil Formation consists of thick-bedded cherty limestone, here the unit has a thinner bedding and the section continues with: •

Light nodular cherty limestone, thin-bedded, forming packages. Thickness is 1.9 m. The conodont content may be subdivided in two groups. The lowermost samples (KG848 and KG849) contain Iranognathus sosioensis Kozur & Mostler, Clarkina liangshanensis (Wang), C. cf. longicuspidata Mei & Wardlaw, C. orientalis (Barshkov & Koroleva), and ramiforms. The upper samples (KK150 and KK151) contain Clarkina changxingensis (Wang & Wang), C. subcarinata (Sweet), C. liangshanensis (Wang), and C. cf. longicuspidata Mei & Wardlaw. The abundance of Clarkina species is typical of offshore, but relatively warm-water conditions (Mei and Henderson 2001); they often dominate slope environments, but only because they were swimming above them. The occurrence of Iranognathus also suggests warm-water

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Fig. 3 a The tight folds on the southern slope of the Kundil valley with position of Wirokhun, Kundil II, and Kundil III sections. View from the village of Raminji. b Geological map of the upper reaches of Borom gulley, with position on the Borom type-section

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conditions away from the Gondwana margin (Mei et al. 2002). Nodular limestone with sparse nodules of chert and shaly interbedding, progressively less shaly towards the top 2 m. Conodont content (sample KK153): Clarkina bachmanni Kozur. Nodular limestone with well expressed shaly interbedding. Thickness: 2.2 m. Light limestone in 40–60 cm-thick flat beds, cliffforming. Thickness: 7 m. Nodular thin-bedded, grey limestone alternating with thick-bedded light limestone. The base is partly cut by minor faults. Thickness: 5.7 m.

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•

Thick bedded light grey limestone, thickness [4 m. Conodont content (sample KK158): I. sosioensis, C. changxingensis, C. bachmanni Kozur, and C. yini Mei. Fault

Wirokhun Formation • •

Grey planar thin bedded marly limestone and grey dark marls. Thickness: 7 m. Dark splintery shale and marl, forming the depression of the saddle. Poorly exposed. Thickness: 25 m.

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Fig. 4 The reference section of the Wirokhun Formation with conodont occurrences. The base of the section is at 4,414 m with WGS84 coordinates: 36420 06.400 N, 74440 29.400 E

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Fig. 5 Wirokhun section with palynology and d13C ranges. To be noted the large negative excursion of the d 13C value in the lowermost Triassic

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Dark splintery shale with occasional thin bedded limestone. Thickness: 6 m. Because of faults, evaluation of the actual thickness of the Wirokhun Formation is difficult to estimate, but should not exceed 50–60 m.

Borom Formation •

Marly limestone in 10–20 cm thick flat beds, without chert. At the very base Hadrodontina sp., Furnishius sp., Neospathodus dieneri Sweet, Clarkina

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Facies (2013) 59:915–948 b Fig. 6 Late Permian conodonts. Scale bar 2 lm for all pictures.

a, b Clarkina liangshanensis (Wang, 1978), sample KK150, upper and lateral view; c–e Clarkina liangshanensis (Wang, 1978), sample KK150, upper, lower, and lateral view; f–h Clarkina bachmanni Kozur, 2004, sample KK158, upper, lateral, and lower view; i–k Clarkina changxingensis (Wang & Wang, 1981), sample KK 153, upper, lateral, and lower view; l–n Clarkina changxingensis (Wang & Wang, 1981), sample KK 153, upper, lateral, and lower view; o–q Clarkina bachmanni Kozur, 2004, sample KK158, upper, lateral, and lower view; r–t Clarkina bachmanni Kozur, 2004, sample KK158, upper, lateral, and lower view; u–w Clarkina bachmanni Kozur, 2004, sample KK158, upper, lateral, and lower view; x–z Clarkina yini Mei, 1998, sample KK158, upper, lateral, and lower view; aa–ac Clarkina yini Mei, sample KK158, upper, lateral, and lower view; ad, ae Clarkina yini Mei, sample KK158, upper and lateral view; af–ah Clarkina yini Mei, sample KK158, upper, lateral, and lower view

sp., Hindeodus sp. occurs(sample KK163). The CAI is 5. Age Gaetani et al. (1995) referred most of the succession to the latest Permian. Because of the new sampling in its basal part and re-evaluation of the previous conodont identifications, we may now emend the previous age assignments. The Kundil Formation The upper part of the unit contains several conodont assemblages (Figs. 6, 7, 8). The oldest is represented by I. sosioensis, C. liangshanensis, C. orientalis, and ramiforms (samples KG848, KG849). According to Shen and Mei (2010), the two species of Clarkina indicate the late Wuchapingian, being indicative of the last two zones. The next assemblage contains C. changxingensis, C. subcarinata, and ramiforms (samples KK150 to KK153). According to Shen and Mei (2010) C. changxingensis gradually evolves into C. subcarinata and thus these samples should be positioned around the boundary between the two zones, indicating an early to midChanghsingian age. The top of the tectonic slice contains I. sosioensis, C. changxingensis, C. bachmanni, and C. yini (sample KK158). This sample is important because of the co-occurrence of the three species of Clarkina, which occur in separate layers in Iran (Henderson et al. 2008). C. bachmanni is not indicative of a separate zone as indicated by Korte and Kozur (2010), but rather overlaps the upper part of the C. changxingensis Zone and lower part of the C. yini Zone (Shen and Mei 2010), confining this sample to the late Changhsingian. Also the occurrence of I. sosioensis in this bed might be the youngest one so far known. The specimens originally described as C. bachmanni are from the Kuh-e-Ali Bashi section of Iran (Kozur 2004) from 2.7 m below a latest Permian boundary clay.

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The original concept was based on a single illustrated specimen, but Shen and Mei (2010) showed a population concept of this species from topotype material. One of our specimens (Fig. 8f–h) is nearly identical to the holotype and our additional specimens fit the population concept as illustrated by Shen and Mei (2010, fig. 9). Kozur (2005) showed that C. bachmanni occurred immediately above samples of C. subcarinata and therefore attributed an early to mid-Changhsingian age. However, Henderson et al. (2008) clearly showed that this level is very high in the Changhsingian and Shen and Mei (2010) demonstrate that it occurs near the boundary of the C. changxingensis and C. yini zones. This is supported by our material from the Kundil Formation. Iranognathus has not been reported above the lower Changhsingian (Mei et al. 2002), but this is either a fortuitous discovery, in which case this area may have served as a refuge, or the specimens are reworked. The very top of the Kundil Formation, sampled at the beginning of the saddle, contains a few C. abadehensis, C. hauschkei, and ramiforms. These forms occur at the very top of the Permian of the Kuh-e-Ali Bashi and Abadeh sections in Iran, and also, albeit less abundant, in South China (Shen and Mei 2010 and references therein). They are indicative of the last two zones of the Changhsingian. It may be concluded that two different top Permian sections occur at the Wirokhun Saddle. A more proximal one to the east and a more basinal section, thrusted on the previous one, to the west. Permian–Triassic boundary The PTB should coincide with the boundary between the Kundil and Wirokhun formations. A few cm of very altered tuffite mark the boundary and the sharp change in lithology may suggest the presence of a sedimentation hiatus. Wirokhun Formation Most of the Wirokhun Formation is Griesbachian in age. The conodont assemblages may be referred to the early, middle, and late Griesbachian, respectively (Fig. 9). The conodont association from sample KG832 to KK117 indicates an early Griesbachian age and is representative of the Parvus Zone (Perri 1991; Scho¨nlaub 1991; Farabegoli and Perri 1998; Perri and Farabegoli 2003; Nicora and Perri 1999; Yin et al. 2001). Consequently, the succession at the Wirokhun Saddle contains conodonts of the last zone of the Permian and of the first zone of the Triassic. According to the occurrence from sample KG835 of H. parvus (Kozur & Pjatakova), and H. typicalis (Sweet) and in sample KK126 of H. parvus, H. postparvus Kozur,

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Facies (2013) 59:915–948 b Fig. 7 Late Permian conodonts. Scale bar 2 lm for all pictures.

a–c Clarkina orientalis (Barskov & Koroleva, 1970), sample KG 848, upper, lateral, and lower view; d–f Clarkina cf. longicuspidata Mei & Wardlaw, 1994 in Mei et al. (1994), sample KG 848, upper, lateral, and lower view; g–i Clarkina cf. longicuspidata Mei & Wardlaw, 1994 in Mei et al. (1994), sample KG 848, upper, lateral, and lower view; j, k Iranognathus sosioensis Kozur & Mostler, 1996, sample KG 848, upper, and lateral view; l, m Iranognathus sosioensis Kozur & Mostler, 1996, sample KG 848, upper, and lateral view; n–p Clarkina orientalis (Barskov and Koroleva, 1970), sample KG 849, upper, lower, and lateral view; q–s Clarkina cf. longicuspidata Mei & Wardlaw, 1994 in Mei et al. (1994), sample KK 150, upper, lateral, and lower view; t–v Clarkina orientalis (Barskov & Koroleva, 1970), sample KG 849, upper, lateral, and lower view; w–y Clarkina orientalis (Barskov & Koroleva, 1970), sample KG 848, upper, lateral, and lower view

H. typicalis, and C. carinata (Clark) a middle Griesbachian age is recorded. From samples KG840 to KG845 an upper Griesbachian age is supported by the occurrence of H. parvus, H. postparvus, Isarcicella lobata Perri, Is. staschei Dai & Zhang, and Is. isarcica Huckriede (Staschei and Isarcica zones of Perri and Farabegoli 2003). Upwards, many samples were barren. Palynostratigraphy Palynomorphs and palynofacies are affected by high thermal maturity, judging from the dark brown to black colour of organic matter debris. Despite this, some considerations on age are possible based on two productive levels within the Wirokhun Formation. The lowermost portion, at about 2.7 m (KK115) above the putative PTB, yielded a palynological assemblage containing abundant Lundbladispora brevicula, Lundbladispora sp., common Cyclogranisporites sp., rare Calamospora sp., Densipollenites indicus, Dictyotriletes sp., Thymospora ipsviciensis, and Verrucosisporites sp. in association with very few specimens of Grandispora jansonii, Lueckisporites virkkiae, Polypodiisporites mutabilis, and Polypodiisporites sp. The palynological assemblage recorded at about 7 m from the base (KK124) contains L. brevicula, Lundbladispora sp., and Densoisporites nejburgi in association with few Calamospora sp., Dictyotriletes sp., D. indicus, Kraeuselisporites sp., Inaperturopollenites sp., Protohaploxypinus panaki, T. ipsviciensis, Verrucosisporites sp. No significant palynomorphs are present in the next 15 m of the section because the palynofacies is strongly degraded and the terrestrial organic debris is mostly represented by intertinite and subordinate vitrinite palynomacerals. The bisaccate L. virkkiae is regarded as a characteristic Permian marker, although sporadically found, presumably as reworked specimens, in Lower Triassic strata (e.g. Balme 1970; de Jersey and Raine 1990; Mangerud 1994; Gomankov et al. 1998; Song et al. 2000; Gao et al. 2000; Weiss 2001; Wang

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et al. 2004; Dieguez and Barron 2005; Zhang et al. 2007; Jan et al. 2009; Stephenson 2008; Stolle et al. 2011). P. mutabilis has been commonly found in Permian formations from West Pakistan (Balme 1970), South Africa [southern Zambia: Nyambe and Utting (1997) and southwestern Botswana: Modie and Le He´risse´ (2009)], and Tanzania (Weiss 2001). The trilete spore G. jansonii was described and illustrated by Utting et al. (2004) in the Upper Permian of the Sverdrup Basin, Canadian Arctic Archipelago. Gondwanan occurrences of D. indicus, have been recorded in Permian strata from Iraq (Nader et al. 1993), India (Vijaya and Tiwari 1986; Tripathi 1993), Pakistan (Jan et al. 2009), Oman (Stephenson 2008), and in the Upper Permian-Lower Triassic rocks of Central Himalaya (Tiwari et al. 1996). Similarly, the monolete spore T. ipsviciensis is known from Permian and Triassic strata at different palaeolatitudes, from the Barent Sea (Mangerud 1994) to New Zealand (Jeans et al. 2003). Lycopsid spores such as L. brevicula, Lundbladispora sp., and D. nejburgi mark the Early Triassic palynological assemblage reflecting the colonization of herbaceous pioneer vegetation after the end-Permian mass extinction (Ku¨rschner and Herngreen 2010). They have been commonly recorded from not independently and independently dated strata (by ammonoids and/or conodonts) from Early Triassic sections: West Pakistan (Balme 1970), India (Tripathi and Ray 2006 and references therein), China (Ouyang and Utting 1990), Bowen Basin, Australia (de Jersey 1979), northern Italy (Visscher and Brugmann 1988), and the Barents Sea (Mangerud 1994). The co-occurrence of some rare Permian forms and abundant earliest Triassic palynomorphs in the lowermost part of the Wirokhun Formation and the fully Early Triassic assemblage several metres above confirms the position of the PTB in the lowermost part of the unit and allows to ascribe the overlying part of the succession to the Early Triassic. Environment On the whole, the top of the Kundil Formation and the overlying Wirokhun Formation were deposited under deep conditions. The top of the Kundil is chert-free as it was deposited after the radiolarian crisis just before the end-Permian extinction, as is usually the case in low-latitude sections (Kozur and Weems 2011). The sedimentation rate was low, because a mere 55 cm contains conodonts of the last two conodont zones of the Permian (Shen and Mei 2010). According to Korte and Kozur (2010), an additional conodont zone with Clarkina meishanensis and Hindeodus praeparvus should be present at the very top of the Permian; it was not detected here, possibly but not necessarily indicating a gap. The ochrecoloured veneer at the top of the Kundil Formation may represent an altered tuffaceous horizon, similar to tuffs found in other sections from Asia, possibly linked to the

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Facies (2013) 59:915–948 b Fig. 8 Late Permian conodonts. Scale bar 2 lm for all pictures.

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a–c Clarkina hauschkei Kozur, 2004, sample KK112, upper, lateral, and lower view; d–f Clarkina abadehensis Kozur, 2004, sample KK112, upper, lateral, and lower view; g–i Clarkina abadehensis Kozur, 2004, sample KK112, upper, lateral, and lower view; j–l Clarkina orientalis/C. abadehensis Kozur, 2004, sample KG 826, upper, lateral, and lower view; m–o Clarkina abadehensis Kozur, 2004, sample KG 828, upper, lateral, and lower view; p, q Clarkina sp. A, sample KG 124, upper and lateral view. r–t Clarkina sp. A, sample KG 828, upper, lateral, and lower view; u–w Clarkina subcarinata (Sweet, 1973), sample KG 123, upper, lateral, and lower view; x–z Clarkina subcarinata (Sweet, 1973), sample KG123, upper, lateral, and lower view

Siberian Trap effusions (Heydari et al. 2008; Knoll et al. 2007; Korte et al. 2010). If this ‘‘tuffaceous’’ horizon is correlative with bed 25 at Meishan, China (Shen et al. 2011), then the basal part of the Wirokhun Formation may be latest Permian; the first Triassic conodonts do not appear until about 3 m above the formation base. This is comparable to occurrences in the Canadian Arctic where C. meishanensis occurs in the basal shale of the Blind Fiord Formation (Algeo et al. 2012). It should be considered that Karakorum was already far away from Gondwana at that time (Muttoni et al. 2009). Sedimentation rate resumed in

Fig. 9 Griesbachian conodonts. Scale bar 2 lm for all pictures. a–c Hindeodus postparvus Kozur, 1989, sample KG840, upper, lateral, and lower view. d–f Hindeodus parvus (Kozur & Pjatakova, 1975), sample KK117, upper, lateral, and lower view. g–i Hindeodus praeparvus Kozur, 1996, sample KG832, upper, lateral, and lower

view. k–m Isarcicella staeschei Dai & Zhang, 1989, sample KG840, upper, lateral, and lower view. n–q Isarcicella lobata Perri & Farabegoli, 2003, sample KG840, upper, lateral, and lower view. q–s Isarcicella prisca Kozur, 1995, sample KG832, upper, lateral, and lower view

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b Fig. 10 Sections measured in the Borom Formation. The type section

was measured with base at 4,684 m a.s.l. (GPS84 coordinates: 36400 4700 05N, 74440 3200 49E) and top at 4,875 m. The Wirokhun section continues the previous section of the saddle, traversing the slope on the Kundil side. Base of the Kundil II section at 3,630 m (coordinates: 36420 3600 N, 74430 4300 E); Kundil III section, base at 3,480 m (coordinates: 36420 2300 N, 74430 2600 E). GPS coordinates obtained by locating the section on the Google Earth image

the earliest Triassic with a rate that should exceed 20 m/Myr if the Induan stage spans only 1 Myr (Mundil et al. 2010). The shaly and marly deposits are fairly rich in organic matter. More carbonate beds are interlayered, allowing also some isotope measurement. However, the high thermal maturity reduced the fossil preservation as well as the carbonate-poor sediments of the lowermost part of the Triassic, in agreement with many other marine sections (Farabegoli et al. 2007). Hypoxia and hypercapnia may be considered amongst the main factors controlling the PTB interval also in this part of the Palaeo-Tethys (Knoll et al. 2007).

From the Lower Triassic to the Carnian This time interval is represented in the basinal succession by the Borom Formation. This unit was proposed by Gaetani et al. (1990), but never described in detail. The formation, less than 200 m thick, encompasses a time span of about 25 Myrs, therefore with an accumulation rate (not decompacted) hardly reaching 8 m/Myr, testifying to a underfed basin near to starvation. We recognized this unit only in the mountains between the gullies of Borom and Kundil (Fig. 1) where it forms tight folds, like the spectacular fold system on the south side of the Kundil Valley (Fig. 3). We measured four sections (Fig. 10). In the Borom gully, we measured a complete section with base and top, here identified as the type-section; on the Wirokhun Saddle we measured the lower part, immediately above the Wirokhun Formation reference section. We also measured two fragments in the Kundil Valley, the Kundil II and Kundil III sections, the latter containing the topmost part of the unit. Lithostratigraphy of the Borom Formation 1.

2.

The lower boundary is drawn at the onset of thinbedded, planar grey dark limestones. Their appearance is gradual with still significant intercalation of dark slate and mudstone. Thin calcarenitic intercalations may also occur. This part is about 30 m thick. This unit is overlain by a package of thin-bedded dark limestone, often with parallel lamination, with fewer

3.

4.

5.

shaly intercalations, with slumping and thin graded beds (Fig. 10). Thickness about 75 m. The next lithologic unit consists of grey limestone, with planar or nodular surface and with thin bands or lenses of black chert. Thickness about 25 m. The abundance of black chert increases upwards, with planar bedding prevailing in the dark grey limestone. Bed thickness also increases in thickness leading to amalgamated beds up to 10 m-thick in the topmost part. Thickness about 40 m. The upper boundary is marked by the rather sudden appearance of light-coloured, cliff forming, several decametre-thick carbonate breccias, or light-coloured, thick-bedded dolostone. They are assigned to the Aghil Formation.

Throughout the whole section the CAI of conodonts is 5 (Fig. 11). Age Several layers produced conodonts (Figs. 5, 12, 13). Unfortunately, in the Borom section only poor fragments have been obtained. From the Wirokhun section, evidence of a Dienerian (late Induan) age has been obtained based on the conodonts Hadrodontina sp., Furnishius sp., N. dieneri, Clarkina sp., and Hindeodus sp. (sample KK163). Upwards, only ramiforms were obtained. Neospathodus dieneri is indicative of an early Dienerian zone according to Sweet (1970, 1992), and of the fourth zone of the Induan (Zhao et al. 2007, 2008; Tong and Zhao 2011). However, the zone is an interval zone and therefore the range of the species is wider, reaching the top of the Smithian and thus spanning the Induan-Olenekian boundary. Zakharov et al. (2009) proved that N. dieneri may enter the lower part of the Novispathodus waageni Zone, presently used to define the base of the Olenekian. The absence N. waageni might suggest that bed KG163 is still Induan in age. From the Kundil II section, the conodont Triassospathodus homeri (Bender) (sample KN49) suggests a late Olenekian age, due to the absence of Chiosella timorensis (Nogami), which is considered a proxy for the OlenkianAnisian boundary. T. homeri may overlap at the top with C. timorenis (Gaetani et al. 1992; Gradinaru et al. 2007; Krystyn et al. 2007; Yao et al. 2011), but we take in account the absence of C. timorensis in proposing a late Olenekian age. Higher up, the association of Neogondolella regale Mosher and Paragondolella cf. bulgarica (Budurov and Stefanov) (sample KN59) occurs. N. regale is present in the type locality of the Aegean substage (Assereto 1974; Gaetani et al. 1992) and its range seems to be indicative of the earliest Anisian (Aegean) (Nicora 1977; Balini and Nicora 1998; Germani 2000; Balini et al. 2009).

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Fig. 11 a Typical thin bedding of the central part of the Borom Formation. b Cherty limestone of the upper part of the Borom Formation. c, d Daonella (Arzelella) cf. indica Bittner, sample KG151

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Fig. 12 Olenekian and Anisian conodonts. Scale bar 2 lm for all pictures. a–g Triassospathodus homeri (Bender, 1970), sample NK49, a, b lateral and lower view; c, d lower and lateral view; e, f, upper and lateral view; g lower view. h–l Neogondolella regale (Mosher, 1970) sample NK59, upper, lower, and lateral view. m–n Paragondolella

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bulgarica (Budurov & Stefanov, 1965), sample NK59; m lateral view; n lateral view. o–q Paragondolella bulgarica (Budurov & Stefanov, 1965), sample NK59; o, p, lateral and lower view; q lateral view. r–t Paragondolella bulgarica (Budurov & Stefanov, 1965), sample NK59; lateral, upper, and lower view

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Fig. 13 Ladinian and Carnian conodonts. Scale bar 2 lm for all pictures. a–c Budurovignathus diebeli (Kozur & Mostler, 1970) sample KG24; d–f B. diebeli sample KG24: g–i B. mostleri (Kozur, 1972) sample KG24; l–n Paragondolella inclinata (Kovacs, 1983)

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sample KG28; o–q Paragondolella polygnathiformis (Budurov & Stefanov, 1965) sample KG31; r–t Paragondolella polygnathiformis sample KG30; u–z Paragondolella inclinata, sample KG31

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P. bulgarica instead should be younger because it is considered a Bithynian-Pelsonian species (Nicora 1977; Balini and Nicora 1998; Germani 2000; Balini et al. 2009; Kovacs in Velledits et al. 2011). However, it is here identified with some doubt. From the Kundil III section two assemblages have been recovered. The lower (samples KG24, KG27, KG28) consists of Budurovignathus diebeli (Kozur and Mostler), B. mostleri Kozur, Gladigondolella malayensis malayensis Nogami, and Paragondolella inclinata (Kovacs). Budurovignathus diebeli, B. mostleri, and Gl. malayensis are long-ranging species (Kovacs and Kozur 1980; Krystyn 1983; Broglio Loriga et al. 1999; Balini et al. 2000; Orchard 2007, 2010; Orchard and Balini 2007; Mietto et al. 2007), spanning the late Ladinian until the earliest Carnian. P. inclinata, notwithstanding that it is the nam-giving species for the latest zone of the Ladinian, may also range into the earliest Carnian (Orchard 2010 and references therein). The assemblage is referred to the late Ladinian because of the absence of Paragondolella polygnathiformis, whose first occurrence is considered as a proxy for the base of the Carnian.

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The upper assemblage (samples KG30, KG31, KG32, KG33, KG34) contains P. polygnathiformis (Budurov and Stefanov), P. inclinata (Kovacs), and Gladigondolella malayensis malayensis Nogami. The appearance of P. polygnathiformis is considered a proxy for the Ladinian– Carnian boundary (Mietto et al. 2007; Orchard 2010). In the Borom section, one layer (KG151) produced large daonellids referred to Daonella (Arzelella) cf. indica Bittner (Figs. 10, 11). This species is possibly a junior synonym of D. (Arzelella) tyrolensis Mojsisovics (Torti 1999; Schatz 2004). According to Bhargava et al. (2004) and Krystyn et al. (2004), D. indica (= tyrolensis in Spiti, Himalaya), spans most of the Kaga Formation (= former Daonella Shale of Diener 1912) and thus spans most of the Ladinian, but does not occur in the Carnian. The same range is reported for other occurrences of D. tyrolensis (Kittl 1912; Torti 1999). According to Schatz (2004), its range is restricted to the late Ladinian, but not to the latest; therefore the age of the Borom Formation ranges from the late Induan to the early Carnian. Environment We interpret the Borom Formation as deposited on a slope with poorly oxygenated bottom

Fig. 14 Geological map of the surroundings of Ashtigar (3,910 m a.s.l., WGS84 coordinates: N36480 1200 , E74280 50.900 ). Note the unique occurrence of sections not dissected by faults and thrusts between the Asthigar and Reshit E gullies

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Fig. 15 The sections Ashtigar 1 (base: 4,300 m a.s.l., coordinates: N364724.300 , E74280 43.100 ) was measured on the east side of the main gully. The section Ashtigar 1bis was measured by F. Jadoul near to the section Ashtigar 1. The section Ashtigar 2 was measured along the saddle between Ashtigar and E Reshit gullies (base: 4,480 m a.s.l. coordinates: N36470 38.0600 , E74280 58.0200 )

waters. Slumps and graded beds suggest instability linked to a slope, and black colour and parallel faint laminations suggest deposition in a quiet dysoxic environment. The increasing chert content in the late Anisian and Ladinian part would be linked to a renewed abundance of radiolarians that occurs elsewhere in the Tethys seaways at this time (De Wever et al. 2001; Feng et al. 2009). In the

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topmost part, fine carbonate debris may be intermingled in the laminated cherty limestone, eventually passing to brecciated carbonate bodies, probably linked to the fast prograding carbonate banks that form the overlying Aghil Formation. The very low sedimentation rate suggests that the carbonate factories were poorly efficient, and micrite export from the neighbouring carbonate banks was meagre.

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Fig. 16 a Megalodontid limestone, Aghil Formation, Member B, head of the hammer for scale, Ashtigar gully, west side. b Large bivalves, central part of the Aghil Formation. Member B, Astigarh gully, west side. Hammer for scale. c Aghil Formation, Member C, along the ridge where the section Ashtigar 2 has been measured and

the type section of the Ashtigar Formation. d The basal conglomerate of the molassic Yashkuk Formation seals with a gentle angular unconformity the top of the Ashtigar Formation. e Cartoon showing the inferred geometrical relationships at the onset of the Ashtigar Formation

The Triassic–Jurassic boundary and the onset of the Cimmerian orogeny

within the intensely faulted area. In 2008, MG sampled two short sections south of the meadows of Ashtigar. F. Jadoul in 1991 also sampled a section at the same locality and kindly provided the thin-sections (Figs. 14, 15, 16). The stratigraphic succession of interest is, from bottom to top, as follows:

In the gullies south of Reshit–Zodakhun in the upper Chapursan Valley, the best exposures of the Triassic–Jurassic terrigenous units crop out in a kind of a ‘‘mega- boudin’’

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Facies (2013) 59:915–948 b Fig. 17 a Bioclastic grainstone with numerous foraminifera (pre-

dominantly Involutinidae). Aghil Formation, Member B. Ashtigar section, KKJ134. Scale bar 1 mm. b Aulotortus friedli (KristanTollmann, 1962). Aghil Formation, Member B. Ashtigar 1bis section, KKJ134. Scale bar 200 lm. c Miliolechina stellata Zaninetti, Ciarapica, Cirilli & Cadet, 1985. Aghil Formation, Member B, Ashtigar 1bis section, KKJ135. Scale bar 100 lm. d Miliolipora cuvillieri Bro¨nnimann & Zaninetti in Bro¨nnimann et al. (1971) (right) and Miliolipora sp. (left). Arrowheads point at coarse perforations of the wall. Aghil Formation, Member B. Ashtigar 1bis section, KKJ135. Scale bar 200 lm. e Variostoma cochlea Kristan-Tollmann, 1960. Aghil Formation, Member C. Ashtigar 1 section, KG804. Scale bar 500 lm. f Green algae. Aghil Formation, Member C. Ashtigar 1 section, KG806a. Scale bar 1.5 mm. g ?Triadodiscus eomesozoicus (Oberhauser, 1957). Aghil Formation, Member. C. Ashtigar 1 section, KG806a. Scale bar 200 lm. h ?Trocholina crassa Kristan, 1957. Aghil Formation, Member C. Ashtigar 1 section, KG 806a. Scale bar 200 lm. i Palaeolituonella meridionalis (Luperto, 1965). Aghil Formation, Member C. Ashtigar 1 section, KG806b. Scale bar 200 lm. j Earlandia amplimuralis (Pantic´, 1972). Aghil Formation, Member. C. Ashtigar 1 section, KG810. Scale bar 500 lm. k Miliolipora n. sp. Aghil Formation, Member C. Ashtigar 1 section, KG810. Scale bar 200 lm. l Duotaxis metula Kristan, 1957. Aghil Formation, Member C. Ashtigar 1 section, KG811. Scale bar 200 lm. m ?Duotaxis birmanica Zaninetti & Bro¨nnimann in Bro¨nnimann et al., 1975. Aghil Formation, Member C. Ashtigar 1 section, KG812a. Scale bar 200 lm. n Corallite. Aghil Formation, Member C. Ashtigar 1 section, KG812a. Scale bar 1.5 mm

Aghil Formation The name was introduced by Desio (1963), who resumed the term Aghil limestone introduced by Auden (1938) in the Aghil Range, where, however, it was poorly defined. Gaetani et al. (1990) adopted the term for the equivalent carbonate layers in Hunza and Chapursan, preferring the more general spelling of Aghil Formation. Lithostratigraphy. Along the Ashtigar gully, three informal members may be recognized: Member A: Massive heavily recrystallized dolostone, pale grey and brown to somewhat rusty when altered. About 150–200 m thick but disrupted by intense faulting Member B: Grey to dark grey dolostone and dolomitic limestone in 1–3 m-thick beds. Occasionally crowded with large bivalves (Fig. 16a, b). No stromatolitic layers or fenestrae were observed. About 150 m thick The microfacies consists of either bioclastic wackestone or bioclastic-peloidal packstone, well sorted intraclasticbioclastic packstone with large megalodontids (‘‘floatstone’’), and rubbly coarse-grained bioclastic-peloidal packstone. Medium coarse-grained calcarenites are also present. This member probably was mostly deposited under subtidal conditions. Member C: This is a major object of the present study. It starts with 3–5 m of medium-bedded dark grey nodular limestone. The microfacies consists of mudstone, laminated bioclastic wackestone to radiolarian-bearing

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packstone. Framboidal pyrite may be locally abundant. Ostracods, radiolarians, and lagenide foraminifera are rare. This first package is overlain by dark grey limestone (laminated mudstone to radiolarian-bearing wackestone), in thin planar-laminated beds, alternating with dark marls. Ghosts of ammonoids are common. Most bioclasts are pyritized radiolarians and their spines. The laminated limestone is interbedded with allodapic limestones. They consist mostly of calcarenite in the lower part, with thin laminations and gentle erosional surfaces, grading into calcirudite and floatstone. The thickness of beds increases up-section. In the black pebbly floatstone, clasts of shallow-water origin chaotically lie in black hemipelagic calcilutite. Matrix might be dolomitized. These allodapic limestones contain a rich fauna and flora. Overall thickness of the member is around 60 m. Ashtigar Formation Name proposed by Gaetani et al. (1993) with the type section corresponding to upward development of the present Ashtigar 2 section (Gaetani et al. 1993, fig. 3). The unit suddenly starts with dark green shale and siltstone, rarely with very thin arenite. Apparently the contact is not erosional. At about 18 m from the base there occurs a last layer (60 cm) of calcirudite, similar to the equivalent layers of Member C of the Aghil Formation, but yielding also volcanic debris. The unit develops upward monotonously with dominating grey marly shale with interbedded fine-grained turbidites. Thickness is about 110 m. According to Garzanti in Gaetani et al. (1993) the very fine- to lower medium grained sandstones contain common radiolarian chert, chlorite schist, serpentine schist, and basaltic rock fragments. Yashkuk Formation Proposed by Gaetani et al. (1990) and discussed by Gaetani et al. (1993), the formation consists of conglomerate at the base, overlain by greenish-reddish shale, reddish siltstone, and arenite. Total thickness about 150 m. Of interest here is the basal erosional contact, where about 2 m of polymictic conglomerate occurs with well rounded pebbles mostly of carbonate rocks, up to 15 cm in diameter, and rare arenitic pebbles are gradually overlain by coarser arenite, fining upwards. A gentle angular unconformity is present and the underlying Ashtigar shale is mildly folded (Fig. 16d). New paleontological data Chronostratigraphic attribution of the above described lithologic units is based mostly on identifications of benthic

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Facies (2013) 59:915–948 b Fig. 18 a Auloconus permodiscoides (Oberhauser, 1964). Aghil

Formation, Member C. Ashtigar 1 section, KG815a. Scale bar 500 lm. b Ophthalmidium carinatum (Leischner, 1961). Aghil Formation, Member C. Ashtigar 1 section, KG815a. Scale bar 500 lm. c Trocholina crassa Kristan, 1957. Aghil Formation, Member C. Ashtigar 1 section, KG815a. Scale bar 200 lm. d Tubiphytes obscurus Maslov, 1956. Aghil Formation, Member. C. Ashtigar 1 section, KG815bis. Scale bar 500 lm. e Paraophthalmidium carpathicum Samuel & Borza, 1981. Aghil Formation, Member C. Ashtigar 1 section, KG815bis. Scale bar 200 lm. f Aulotortus tumidus (KristanTollmann, 1964) emend. Piller, 1978. Aghil Formation, Member C. Ashtigar 1 section, KG815bis. Scale bar 200 lm. g Thaumatoporella parvovesiculifera (Raineri, 1922). Aghil Formation, Member C. Ashtigar 1 section, KG816. Scale bar 1 mm. h ‘‘Sigmoilina’’ schaeferae Zaninetti, Altiner, Dager & Ducret, 1982. Oblique section. Aghil Formation, Member C. Ashtigar 1 section, KG817. Scale bar 200 lm. i ?Siphovalvulina sp. Aghil Formation, Member C. Ashtigar 1bis section, KKJ144. Scale bar 200 lm. j ‘‘Trochammina’’ almtalensis Koehn-Zaninetti, 1969. Aghil Formation, Member C. Ashtigar 1bis section, KKJ147. Scale bar 200 lm. k Alpinophragmium perforatum Flu¨gel, 1967. Aghil Formation, Member C. Ashtigar 1bis section, KKJ147. Scale bar 1,000 lm. l Duostomina biconvexa KristanTollmann, 1960 and Galeanella tollmanni (Kristan, 1957) (arrowhead). Aghil Formation, Member C. Ashtigar 1bis section, KKJ147. Scale bar 200 lm. m Endotriada sp. Aghil Formation, Member C. Ashtigar 1bis section, KKJ148, Scale bar 200 lm. n, o Lituolidae. Darwaz An Formation. Baroghil area. Scale bar 200 lm

foraminifera found in thin-sections. Some of the most important foraminifera, as well as other biotic components are shown in Figs. 17 and 18. It is important to note, that foraminifera of the Member C of the Aghil Formation and of the Ashtigar Formation were found in clasts only. Without support of fossil groups from autochthonous deposits, there is thus no guarantee that the age is not erroneously attributed to older stages. Yet, we observed no mixed assemblages and thus cannot confirm the presence of ‘‘zombie’’ fossils. Aghil Member B Besides large bivalves, including megalodontids, foraminifera, and the alga ‘‘Thaumatoporella’’ parvovesiculifera (Raineri) are present. Megalodontbearing limestones are especially rich in neomorphically altered involutinids. The total foraminiferal assemblage of the Aghil Member B contains: ‘‘Trochammina’’ alpina Kristan-Tollmann (or large ‘‘T.’’ almtalensis Koehn-Zaninetti), ‘‘Trochammina’’ jaunensis Bro¨nnimann and Page, Earlandia tintinniformis (Misˇik), Aulotortus friedli (Kristan-Tollmann) sensu Piller (1978), Aulotortus sinuosus Weynschenk, ?Angulodiscus communis Kristan, Auloconus permodiscoides (Oberhauser), Agathammina austroalpina Kristan-Tollmann and Tollmann, Miliolipora cuvillieri Bro¨nnimann and Zaninetti, ?Miliolechina stellata Zaninetti, Ciarapica, Cirilli and Cadet, ‘‘Frondicularia woodwardii Howchin’’, ?Meandrospiranella sp., Pilammina sp., Duostominidae, Reophax sp., and lagenids. Aghil Member C Bioclastic and radiolarian wackestones of the lowermost Member C of the Aghil Formation

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contain rare Duostominidae (Variostoma sp.—? V. cochlea Kristan-Tollmann) and encrusting foraminifera (?Calcitornella sp.). Tests are often pyritized, but their outline is also strongly deformed by stylolitization. Allodapic limestone intercalations, in contrast, preserve a variety of platform- and reef-derived components: fragments of corals, hydrozoans, lithified reef clasts, including pieces of corals, sponges and hydrozoans, the microproblematica Bacinella spp. and Tubiphytes obscurus Maslov, green and solenoporacean algae, ‘‘T.’’ parvovesiculifera, gastropod and bivalve fragments, echinoderms, ostracods, and numerous foraminifera. The foraminiferal assemblage consists of Pilammina sulawesiana Martini, Vachard & Zaninetti, ‘‘Trochammina’’ almtalensis, ‘‘Duotaxis’’ birmanica Zaninetti and Bro¨nnimann, Palaeolituonella meridionalis (Luperto), ‘‘Tetrataxis’’ inflata Kristan, ?‘‘Tetrataxis’’ nanus KristanTollmann, ?Endoteba bithynica Vachard, Martini, Rettori and Zaninetti, ?Endotriada tyrrhenica Vachard, Martini, Rettori and Zaninetti, Endotriada sp., Earlandia amplimuralis (Pantic´), Triadodiscus eomesozoicus, Aulotortus sinuosus, Au. friedli, Au. tumidus (Kristan-Tollmann) emend. Piller, Auloconus permodiscoides, Angulodiscus communis, ?Trocholina crassa Kristan, Planiinvoluta carinata Leischner, Hoyenella inconstans (Michalik, Jendreja´kova and Borza), ?Karaburunia rendeli Langer, M. cuvillieri, Agathammina austroalpina, Ophthalmidium carinatum (Leischner), Variostoma helicta Kristan-Tollmann, Duostomina? sp. A cf. Gale et al. (2011), ‘‘F. woodwardii’’, Galeanella sp., ?Ammodiscus/Cornuspira sp., Reophax sp., Paraophthalmidium sp., Duostominidae, and lagenids. Ashtigar Formation We have no biostratigraphic data from the shale and marl at the base of the unit. The level of bioclastic-intraclastic rudstone with reef-derived grains (sample KG824, Ashtigar 2 section) contains a foraminiferal assemblage with ‘‘T.’’ jaunensis, Au. sinuosus, M. cuvillieri, ‘‘Tetrataxis’’ sp., Reophax sp., and Duostominidae. However, all foraminifera are included in clasts. Discussion The evolution from the Member B to Member C of the Aghil Formation points to a deepening of the basin (drowning succession with transition from subtidal to hemipelagic sedimentation), with reduced bottom circulation as testified by the occurrence of pyrite, but still sufficiently oxic to support burrowing organisms. Lamination might also indicate a somewhat oxygenated environment due to weak bottom currents supplying oxygen. A NorianRhaetian assemblage from the Member B, and the cooccurrence of Trocholina crassa (Carnian?—Norian— Rhaetian) and Duotaxis birmanica (Norian—Rhaetian) with Miliolipora cuvillieri (Carnian—Rhaetian) in level

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KG812 of Member C of the Aghil Formation place the formation of the basin into the Norian. The coarsening-upward succession in the upper part of Member C could indicate progradation of the reef-rimmed carbonate platform into the newly formed basin. However, we prefer the model of a drowning margin with normal fault, approaching the convergence zone (Fig. 16e). Sponges, scleractinians, and microproblematica are joined by typical reef-dwelling foraminifera, such as Galeanella tollmanni, Alpinophragmium perforatum, ? Miliolechina stellata, and ‘‘Sigmoilina’’ schaeferae. Other foraminifera, such as Aulotortus sinuousus, A. tumidus, Miliolipora cuvillieri, and Auloconus permodiscoides, are derived from the back-reef area. In contrast to previous interpretations (Gaetani et al. 1993), the present study cannot confirm a Jurassic age for the lower Ashtigar Formation. Instead, Miliolipora cuvillieri and Duostominidae from sample KG824 still suggest a Late Triassic age. Yet, as pointed out above, a

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Jurassic age cannot be excluded, as no foraminifera were found outside clasts. The chert and serpentinite clastics are interpreted as derived from a subduction complex, situated most probably in direction of the present South Pamir (Gaetani et al. 1993). The last allodapic limestone inside the basal Ashtigar Formation might suggest that sediment input from the faulted rim still took place and this was possibly occurring already in the latest Triassic.

The platform succession The exposures of the platform succession are in the area of the Baroghil and Darwaz passes along the continental divide and the Pakistan-Afghanistan border, in the Lashkargaz-Baroghil thrust sheet (Zanchi and Gaetani 2011) (Fig. 19). Two units have been recognized, the Ailak Formation below and the Darwaz An Formation above.

Fig. 19 Geological map of the Baroghil area, with position of the described sections (from Zanchi and Gaetani 2011, simplified)

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Fig. 20 View of the area east of Baroghil with the Darwaz An Lake at the Pakistan–Afghanistan border. The stratigraphic section extends from the Lower Permian (Lashkargaz Formation to the Darwaz An Formation (Lower Jurassic). Roughly, the grey part of the Ailak

Formation is Upper Permian, while the whitish part is Triassic in age. In the distance the Ab-i Wakhan (= Oxus or Amu Darya River) is seen

Ailak Formation

the Triassic are greyer than the upper part, which is mostly stromatolitic and lighter. The heavy dolomitization, especially in the upper part, destroyed most of the microfacies. In the lower part we found with Tubiphytes sp., ostracodes, rare sphinctozoans, ghosts of small foraminifers, and the fusulinids Nankinella and Sphaerulina. Dasycladacean algae (Permocalculus sp.) are also present. Their age is Late Permian (Leven et al. 2007). Upwards, in the prevailing stromatolitic dolostones, no fossils have been found. Only where subtidal wackestone– packstone is not totally dolomitized, ghosts of foraminifers and shelly fragments may be observed. Interesting is the absence of megalodontid remains in the Baroghil/Darwaz area, while they are present in other outcrops of the same unit in Western Karakorum (Zanchi and Gaetani 2011, fig. 50). Of interest is also the section cropping out along the jeep-accessible roadcut south of Shost, pertaining to the Axial Zone, hence lying to the south of the Reshun Fault. There, in grey limestone, the earliest Triassic conodonts have been obtained (Perri et al. 2004). When we mapped the area in 1992 and 1996, the roadcut was not yet finished and sampling along the river resulted in barren samples. Presently, the area is closed to

The Ailak Formation (Gaetani et al. 1996) consists of massive dolostone, which forms the continental divide along the ridge linking the Baroghil and the Darwaz passes. It is chiefly thick-bedded dolostones and calcareous dolostones. The lower part includes grey to lightgrey calcareous dolostone and dolostone with subordinate stromatolitic laminae, arranged in 20–50-cm-thick beds. When not totally transformed into a sucrosic dolostone, it consists of a bioclastic fine to coarse packstone with micritic matrix, occasionally with gastropods, fragments of bivalves, and coated grains. They are overlain by light sucrosic dolostone and calcareous dolostone, in 30–70cm-thick beds, originally mostly packstone, with poorly preserved fragments of bivalves and gastropods. Stromatolitic layers may also occur in this part. The upper part consists of a sucrosic light dolostone, thick-bedded, often with stromatolitic laminae. Internal discontinuities occur within this unit, with evidence of emersion and karst surfaces. The total thickness of the unit is about 500–600 m, of which about 40–50 % should belong to the Triassic. The Permian and possibly the lower part of

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Fig. 21 The type section of the Ailak Formation (coordinates at the base: N36520 1400 , E73260 2800 , 3,930 m a.s.l.; top at N 36520 3800 , E73260 2100 ), and the Baroghil W section (coordinates at the base: N36510 4500 , E73190 0300 , m 4,390 a.s.l.)

foreigners, but this section within easy reach would certainly be of interest. The conodont biofacies suggests a shallow-water environment. The Ailak Formation represents a peritidal carbonate platform, with low subsidence rates and common emersion surfaces. Several subfacies of the carbonate platform should be present, but dolomitization prevents a more detailed analysis (Figs. 20, 21). Of major importance are the karst infillings which crop out on both sides along the Pakistan–Afghan border. We sampled a karst cavity on the west side of an hillock bordering the Baroghil Pass on the east side, below a cairn (Fig. 19). We interpret the infilling as older than the

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arenaceous veneer we observed between the Ailak and Darwaz An formations more eastward. The cavity is up to 100 m deep and 70–80 m wide, with polyphase infillings, including volcanic and metamorphic quartz grains, in an iron-rich matrix (Fig. 22). Darwaz An Formation The Darwaz An Formation (Zanchi and Gaetani 2011) identifies the dark grey limestone occurring just east of the Darwaz An, forming a strip between the top of the Ailak dolostone and the overthrusted Devonian Chilmarabad dolostones (Figs. 20, 23).

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Fig. 22 Microfacies in the karst fillings at the top of Ailak Formation east of the Baroghil Pass (3,940 m a.s.l., N36520 4400 , E73210 2000 ) a Sample CK234, 9 10. Quartz and microcline grains are embedded in a dark matrix, possibly hematitic. b Sample CK237, scale bar 1 mm. Altered carbonate grain with red infillings (below) and sparse grains of quartz, including volcanic quartz, shaly and carbonate fragments; crossed nicols. c Sample CK236, scale bar 0.5 mm. Litharenite. Corroded siliceous shale grain embedded in diagenitic carbonate crystals; crossed nicols. d Sample CK237, scale bar 1 mm.

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Litharenite. Large carbonate grains, rimmed by alteration crust, are embedded in a lithic matrix with volcanic and metamorphic quartz, microcline, and siliceous shale grains; crossed nicols. e Sample CK240, scale bar 1 mm. Litharenite with quartz and carbonatic grains, and with some hematitic embayment. crossed nicols. f Microfacies of the Darwaz An Formation. Basal arenites, sample CK 686, 910, subquartzarenite. The clast population is dominated by quartz grains, mostly metamorphic, and by subordinate microcline feldspars

Lithology At the very base, a few metres of very thin grey-brown subquartzarenites may be present. They are well sorted and may represent the trangressive tract of the new sequence after the emersion, overlain by medium-bedded grey limestone (mudstone to wackestone) with seams of fragmentary bivalves and some layers with turriculate gastropods. The foraminiferal assemblage is basically oligotypic, represented by Amijiella amiji (Henson) (Hauraniidae). The upper part of this unit contains a medium- to thickbedded recrystallized limestone (bioclastic packstone), spectacularly crowded by large to giant bivalves (up to 40 cm in length), including isognomonids and ostreids (Fig. 24). Some of them may be similar to Mytiloperna sp., a form very common in the Lower Jurassic Calcari Grigi Formation of the Southern Alps, NE Italy (identification by R. Posenato, Ferrara) occurring in the Lithiotis facies. Another assemblage is dominated by smaller Liostrea. The preserved thickness is slightly less than 100 m. On the basis of the presence of Amijiella amiji the age of the samples can be referred to the Sinemurian–Bathonian time interval (Bassoullet 1997; Fugagnoli and Broglio Loriga 1998). The assemblages of the Lithiotis-facies along the shores of the Tethys are usually referred to the Pliensbachian.

Fig. 23 The type section of the Darwaz An Formation, measured as continuation of the Ailak section. Base of the section at about 4,090 m asl (N36520 3900 , E73260 2200 )

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Fig. 24 Bivalves from the Darwaz An Formation. a Isognomonid assemblage. b Detail of the isognomonid assemblage. c Giant ostreids; length of the hammer 28 cm. d Liostrea assemblage

Environment The basal sandstones are interpreted as the transgressive tract of the sequence after the emersion and karstification of the dolostones of the Ailak Formation. The high faunal density and low species diversity is typical of restricted environments. A confined lagoon within the wider carbonate platform is represented by the lower mudstone– wackestone, while a more open environment is testified by the bioclastic packstone of the upper part. However, also here, the very high faunal density and low diversity of the bivalve assemblage points to a restricted environment.

Discussion and conclusions The time interval considered in this paper concerns a significant segment of the evolution of the Northern Karakorum Terrain. The drifting of the terrain away from the Gondwana fringe started during the Early Permian (Gaetani 1997; Zanchi and Gaetani 2011).

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A major differentiation occurred during the late Middle Permian, when, in the Chapursan Valley, the succession deepened to basinal conditions, as recorded by the rapid transition to cherty limestones (Kundil Formation), which contain late Middle Permian to Upper Permian conodonts (Gaetani et al. 1995; this paper). Block-faulting is mainly Wordian and Capitanian in age, with rare volcanism. In the Late Permian a peritidal carbonate platform developed in the south and west, facing a deeper basin in the NE (Fig. 2a), which remained deep across the Permo-Triassic boundary and the Triassic until the early Carnian. Within the basin, Wuchiapingian and Changhsingian conodonts revealed the development of a deep water biofacies. The occurrence of Clarkina-dominated conodont faunas throughout this interval suggests that more offshore conditions were prevalent (Mei and Henderson 2001). Discontinuous occurrence of conodonts prevented continuous documentation in the deep-water facies. Noteworthy is the rather starved basin situation in the Middle Triassic and the significant increase of chert in the Ladinian, which is not unusual along the Tethys seaways for this time.

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The recovery of the carbonate platform occurred during the early Carnian, with thick amounts of carbonate breccia. These breccias are locally very thick and allowed the progradation of the carbonate platform across the basinal succession. In the other areas, shallow water carbonate sedimentation continued at a low rate from the Late Permian throughout the whole Triassic, probably with several internal gaps. We refer to this interval most of the massive carbonate units in the North Karakorum Terrain. Local emersions caused karstic phenomena on the carbonate platform. In Chapursan, the peritidal carbonate platform of the Aghil Formation developed in three main steps. First, a peritidal platform, now mostly dolomitized, spread across the area, overlain by more differentiated environments, including a subtidal member with large bivalves, mostly megalodontids, forming crowded beds. The geodynamic evolution during this Permian to latest Triassic cycle is driven by the drifting of the microplate accompanying the progressive opening of the Neo-Tethys ocean and by the northward subduction of the Paleo-Tethys ocean along the Asian margin (Gaetani 1997; Zanchi and Gaetani 2011). However, the evolution of Karakorum during the Permian was not simply controlled by thermal subsidence, because several minor tectonic episodes occurred with local emersion and erosion in the west and basin opening in the east with fault scarps and deposition of submarine megabreccia bodies. Oblique movements dominated by a transtensional regime within the terrain may have caused this complex scenario. Volcanic outpouring that mainly affected the Indian Plate margin of the NeoTethys is unknown or is not important on the Karakorum side. Also, the widespread volcanism quoted in the Permian of the South-East Pamir and Rushan-Pshart Zone (Leven 1967, 1995) is here unknown. By the end of the Triassic, most the Karakorum was close to the southern Eurasian active margin, now exposed in the North Pamir belts (Schwab et al. 2004). Evidence of Karakorum approaching an active margin is the drowning of the topmost part of the Aghil Formation, intermingled with calciruditic bodies originating from the faulted platform rim, of latest Triassic age. Above the drowned carbonate platform, the arenaceous Ashtigar and Yashkuk formations occur (Figs. 15, 16). The quartz–lithic sandstones of the Ashtigar Formation contain clasts of serpentinite schist, basalt, radiolarite, chlorite schist, phyllite, and paragneiss, suggesting erosion of an oceanic subduction complex close to an arc-trench system (Gaetani et al. 1993). The sandstones seem to have been deposited in a narrow trench, bordered by an aggrading ramp. The Jurassic units are unconformably overlain by the molassic red sandstones of the Yashkuk Formation, containing

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sedimentary and metasedimentary clasts, supplied by the erosion of a foreland fold and thrust belt. The base of this unit was dated as Pliensbachian (Gaetani et al. 1993). In the Siru Gol–Baroghil area, in contrast, evidence of the Cimmerian orogeny is meagre. In the Lashkargaz– Baroghil Unit, dark limestones with a quartzarenitic veneer at the base, transgress on the top of the Ailak Formation, which is Triassic in age. The Lower Jurassic Darwaz An Formation contains a few significant foraminifers, but especially large Lithiotis-like and other large bivalves, referred to the Pliensbachian. High-density bivalve assemblages and low diversity testify a rather restricted environment. The thin arenitic veneer at the base of the Jurassic beds suggests that the western area was only marginally reached by the clastics, with mature and well sorted subquartzarenites (Fig. 22). The paleokarst deposits with volcanic fragments and arenitic clasts observed around the Baroghil Pass in the Ailak Formation may be related to emersion of the platform, possibly induced by peripheral bulging of the distal portions of the Karakoram block related to the Cimmerian events. However, both the Baroghil and Chapursan areas fairly strictly bracket the Cimmerian deformation occurring to the north, between the latest Triassic and the Pliensbachian. The sedimentary record of the Cimmerian events registered within the sedimentary cover of the North Karakorum Terrain suggests that it was affected by this important deformational event only marginally. Deep water sedimentation occurred only in limited, possibly faultcontrolled trenches, whilst wider areas especially to the west and to the south emerged or had thin shallow-water marine deposits, due to limited subsidence. Acknowledgments A Nicora, CM Henderson, and I Vuolo worked on the conodonts, S Cirilli on the palynomorphs, R Rettori and L Gale on the foraminifers, and V Atudorei on the isotopes. M Gaetani did the field work in 1986 with the help of A Nicora, and finalized the paper. L Angiolini and L Gaetani helped M Gaetani in the field work in 1991 and 1999. R Posenato tried to recognize large Jurassic bivalves on the basis of pictures. F Jadoul kindly provided the data for the section Ashtigar 1 bis. Italian and European grants to M Gaetani provided the financial support, but no field work would have been possible without the permission of the Pakistan Government, especially by the former Director of the Geoscience Laboratory of the Geological Survey of Pakistan, Dr Hassan Gahuar. All these people are warmly acknowledged. The field activity was organized through the Adventure Pakistan Travel Agency. Their guides and the porters were of invaluable help.

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