the Southeastern Pamir - Springer Link

ISSN 0869-5938, Stratigraphy and Geological Correlation, 2008, Vol. 16, No. 3, pp. 248–256. © Pleiades Publishing, Ltd., 2008. Original Russian Text © O.A. Korchagin, 2008, published in Stratigrafiya. Geologicheskaya Korrelyatsiya, 2008, Vol. 16, No. 3, pp. 26–35.

Foraminifers and Stratigraphy of the Karatash Group (Lower Triassic–Middle Anisian), the Southeastern Pamir O. A. Korchagin Geological Institute, Russian Academy of Sciences, Pyzhevskii per. 7, Moscow, 119017 Russia Received May 16, 2007; in final form, September 13, 2007

Abstract—First data on Middle Triassic foraminifers of the southeastern Pamir are considered. The lower-middle Anisian sediments are reliably recognized within uniform limestone succession of the Karatash Group in the Southeastern Pamir based on found foraminiferal species Meandrospira deformata Salaj, Meandrospira cheni (Ho), Pilamminella ex gr. semiplana (Kochansky-Devide et Pantic), and Endotheba badouxi (Zaninetti et Bronnimann). The lower–middle Anisian Meandrospira deformata Zone is defined and the Karatash Group is subdivided into the Khan (lower) and Yulla (upper) formations. The foraminifers found imply their migration between the western (Alps, Carpathians, Balkans) and eastern (South China platform, Malaysia, Japan) Tethys across the southeastern Pamir region. Characteristic species of the genus Meandrospira recorded in the southeastern Pamirs are described with specifying their taxonomic scope. DOI: 10.1134/S0869593808030027 Key words: Lower Triassic, Anisian, carbonate platforms, biostratigraphy, migration, foraminifers, Pamirs.

INTRODUCTION Triassic carbonate sediments forming thick reefal massifs usually the Carnian–Norian in age play decisive role in geological structure of the southeastern Pamir. They are traceable for 200–250 km from the southeast northwestward being surrounded by belts of carbonate–siliceous and terrigenous sediments. The band of Triassic carbonate rocks was defined as the Central lithotectonic zone, while surrounding belts were united into the Intermediate and Marginal zones (Dronov and Leven, 1960). Subsequently, each of these zones was subdivided into subzones (Atlas of Triassic…, 2001). The Central lithotectonic zone is truncated by faults in the northwest and extends southeastward to western China and Karakorum. In greater part of the southeastern Pamir, the base of the Triassic section is represented by uniform thin-platy black to dark gray limestones of the Karatash Group 50–60 to 100 m thick (Kushlin, 1973). The Karatash Group of the Intermediate zone is subdivided into the Bail’tam, Taldykol, and Zougan formations (Dronov and Luchnikov, 1976). Based on conodonts, the group age in this zone is estimated to be the Induan–early Anisian (Dagys and Dronov, 1989). In the Central lithotectonic zone, the Karatash Group is considered as undivided sequence, age of which is substantiated by correlation with sections from the Intermediate zone. Only occurrence of Anisian brachiopods Mentzelia cf. mentzeli Dunk., Rhynchonella cf. attiliana Bitt., R. sp. and ammonoids Danubites cf. floriani Mojs., and Leiophyllites sp. has been mentioned in the literature (Atlas of Triassic…, 2001). This paper presents information

on foraminifers, one of the orthostratigraphic fossil groups, first found in the Karatash Group. Based on their distribution through the section in the Central lithotectonic zone of the southeastern Pamir, the early–middle Anisian age and stratigraphy of the Karatash Group upper part is substantiated with subdividing the group in two formations. MATERIAL AND METHODS Original materials from thoroughly studied Triassic reference sections in the Central (Khanyulla) and Intermediate (Dzhamantal) lithotectonic zones of the southeastern Pamir served as a basis for this study (figure). The sections were studied in several outcrops. Rock samples were collected from the uniform limestone sequence with intervals of 1.0–1.5 m. Layers up to 1 m thick are characterized either by single samples or by three samples taken from their lower, middle, and upper parts. The traditional procedure was applied to study foraminifers. From 5 to 20 randomly oriented petrographic thin sections were prepared for each sample. Among them, the thin sections crossing the initial chamber and axial parts of foraminiferal tests were selected for study, description, and photographing under the optical binocular microscope MBS-10 and Polam P-112. The classification by Greensmith (1981) was used for carbonate rocks.

248

FORAMINIFERS AND STRATIGRAPHY OF THE KARATASH GROUP

249

2.5 26.0

Foraminiferal zones and zonules

Frondicularia xiphoidea Valvulina azzouzi Ophthalmidium sp.

Endotheba badouxi Haplophragmium sp.

Meandrospira cheni Meandrospira deformata Tolypammina aff. gregaria

Meandrospira immatura

Pilamminella sp. Pseudonodosaria multicamerata

151/3e

Kyrgyz Republic

151/3d 151/3c

151/1-3e

Uzbekistan

33.0

Khan Formation (33.0 m)

Meandrospira deformata Zone

151/18-21

P. ex gr. semiplana – M. immatura M. deformata – M. cheni Pilamminella sp.

151/22-24

151/62 151/60-61 151/58-59 151/56-57 151/54-55 151/52-53 151/50-51 151/47-49 151/45-46 151/43-44 151/41-42 151/39-40 151/38 151/37 151/36 151/35 151/34 151/33 151/32 151/30-31 151/28-29 151/27 151/26 151/25 151/23-24 151/22 151/21 151/20 151/19 151/18 151/14-17 151/12-13 151/10-11 151/8-9 151/6-7 151/4-5

10.0

151/25-35

151/64 151/63

4.0 6.0 7.0 2.5

151/36-62

151/4-10

Induan–Olenekian

Glomospirella sp. 1 152/1

151/63-64

151/11-17

Lower

Lithology

Glomospirella triphonensis Agathamminoides sp. Pilamminella ex gr. semiplana

Thickness, m

15289/1-9

15.0

Foraminiferal species

Bed nos.

Group, formation Chontash Formation (lower part) Yulla Formation (55.5 m)

Stage, substage lower–middle

Middle

T r i a s s i c

Anisian

upper?

Series

System

Section 3. Khanyulla River (mouth and lower reaches)

151/3b

China

Tajikistan

151/3a

Dushanbe Pamirs

1 9 3

151/2 151/1

Afghanistan

1

2

3

4

India

100 km

Distribution of foraminifers in the Khanyulla section and localities of sections mentioned in the text (inset map); lithology: (1) calcisiltites, (2) calcarenites, (3) biospatites, (4) hiatus (some section intervals are shown out of scale); numbers in the map: (1) Dzhamantal, (3) Khanyulla, and (9) Shakhtesai sections (dashed contour outlines reefal massifs).

STRATIGRAPHIC DATA In the Khanyulla section of the Central lithotectonic zone, the Karatash Group is composed of black to dark gray and gray thin- to medium-bedded calcisiltites (in the lower part) and largely calcarenites (in the upper part) up to 100 m thick in total. The group is STRATIGRAPHY AND GEOLOGICAL CORRELATION

divisible into the Khan and Yulla formations. The latter is overlain by massive reefal limestones of the Chontash Formation in the section under consideration and by cherts of the Karakungei Formation in the Shakhtesai section, where the group thickness is reduced to 40–50 m. Vol. 16

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Given below are the bed-by-bed description of the Karatash Group in the Khanyulla section, which contains the most representative assemblage of foraminifers, and characteristics of newly defined formations (Section 3, Outcrop 2, figure). The section is studied along the slope base of the axial crest that separates the Khanyulla and Karakul’ashu river valleys. In this area, light gray yellowish limestones of the Permian are overlain without apparent unconformities by the following units. Karatash Group Khan Formation. The unit is defined for the first time. The formation is named for the Khanyulla River, where it was first described. Stratotype of the formation is located on the right side of the river near its mouth. The formation is recognizable throughout the Central lithotectonic zone from Khanyulla to Shakhtesai being represented universally by thin-bedded (0.01–0.025 m) dark gray to black calcisiltites and subordinate finegrained calcarenites with the H2S odor. The thickness is 20–33 m. In the Intermediate lithotectonic zone, the Khan Formation corresponds to the Bail’tam and Taldykol formations containing conodonts of the early Induan (?) with addition of the Zougan Formation lower part, which is estimated to be the late Olenekian– early Anisian in age. In the Khanyulla stratotype section, the formation is represented by the following sediments: Bed 151/1–151/3e composed of gray to dark gray finegrained thin-bedded (0.01–0.25 m) calcisiltites with siltite matrix, secondary veinlets of white calcite, and H2S odor; rocks are recrystallized and intensely deformed into small folds. The thickness is 33.0 m.

Yulla Formation. The unit is first defined. The formation is named for the Khanyulla River, where it was first described. Stratotype is located on right side of the river near its mouth. The unit 25 to 57 m thick is traceable in the Central lithotectonic zone, where it is composed of medium- to thick-bedded gray to pinkish gray medium- to coarse-grained calcarenites and calcisiltites. The formation is estimated to be the early–middle Anisian in age based on the foraminiferal assemblage consisting of Meandrospira deformata Salaj, Meandrospira cheni (Ho), Meandrospira immatura He, Pilamminella ex gr. semiplana (Kochansky-Devide et Pantic), Pilamminella sp., Glomospirella triphonensis Baud, Zaninetti et Bronnimann, Glomospirella sp. I, Agathamminoides sp., Frondicularia xiphoidea Kristan-Tollmann, Valvulina azzouzi Salaj, Pseudonodosaria multicamerata Kristan-Tollmann, Ophthalmidium sp., Endotheba badouxi (Zaninetti et Bronnimann), and Tolypammina aff. gregaria Wendt. Finds of Anisian brachiopods Mentzelia cf. mentzeli Dunk., Rhynchonella cf. attiliana Bitt., R. sp. and ammonoids Danubites cf. floriani Mojs., Leiophyllites sp. originate likely from this formation. In the Intermediate lithotec-

tonic zone, the Yulla Formation corresponds to the middle and upper parts of the Zougan Formation. In the Khanyulla stratotype section, the formation is of the following structure: Bed 15189/4–15189/10. Calcarenites, light gray to gray and dark gray, medium to thick-bedded, with veinlets (up to 0.5 mm thick) of secondary calcite and detrital grains constituting 50% of the rock volume; siltite matrix is partly recrystallized. The thickness is 4.0 m. Bed 15189/11–15189/17. Calcisiltites, dark gray, medium-bedded, with grains 0.03–0.06 mm across, stylolitic sutures, and fissures filled with secondary calcite. The thickness is 6.0 m. Bed 15189/18–15189/21. Calcarenites, dark gray, finegrained practically lacking matrix and medium-grained with grains 0.2–0.5 mm across (approximately up to 30%), frequently recrystallized, showing veinlets of white calcite and stylolitic sutures. The bed yielded foraminifers Glomospirella sp. I, Glomospirella triphonensis Baud, Zaninetti et Bronnimann, Agathamminoides sp., Pilamminella ex gr. semiplana (Kochansky, Devide et Pantic), Pilamminella sp., Endotheba badouxi (Zaninetti et Bronnimann), and Haplophragmium sp. The thickness is 7.0 m. Bed 15189/22–15189/24. Calcisiltite, dark gray, with grains 0.03–0.06 mm across, medium- to tick-bedded, with abundant stylolitic sutures and fissures filled with secondary calcite. The thickness is 2.5 m. Bed 15189/25–15189/35. Calcarenites, gray to dark gray, coarse-grained with grains approximately 1 mm across (60% of the rock), medium-bedded, with veinlets of secondary crystalline calcite and fine-grained calcarenite matrix; upper part of the bed contains laminae of gray fine-grained calcarenites with rare (1–3%) coal clasts up to 0.1 mm in size. Sediments contain foraminifers Meandrospira immatura He and Ophthalmidium sp. The thickness is 10.0 m. Bed 15189/36–15189/62. Calcarenites, gray to pinkish gray, fine- to medium- and coarse-grained, medium- to thickbedded, with rare veinlets of light calcite. In beds of finegrained calcarenites, grains are 0.1 mm in size and constitute 40–50% of the rock being submerged into similar matrix, while rock fragments in medium-grained calcarenites are up to 0.2 mm across. The upper part of the unit encloses laminae of coarse-grained calcarenite with rounded grains up to 0.3– 0.5 mm in size (20–25% of the rock) and matrix of finegrained calcarenite; rock fragments and matrix are frequently recrystallized. The foraminiferal assemblage includes species Meandrospira deformata Salaj, Meandrospira cheni (Ho), Meandrospira sp., Frondicularia xiphoidea KristanTollmann, Valvulina azzouzi Salaj, Pseudonodosaria multicamerata Kristan-Tollmann, Ophthalmidium sp., and Tolypammina aff. gregaria Wendt. The thickness is 26.0 m. The integral thickness of the Yulla Formation is 55.5 m.

Aktash Group Chontash Formation (lower part). In the Khanyulla section, the formation lower part is represented by following units: Bed 15189/63–15189/64. Biospatite, pinkish gray, medium-bedded, 2.5 m thick. Bed 15289. Biospatite, pinkish gray, thick-bedded, with calcite veinlets (0.5 mm thick) and rounded grains 0.2–0.5 mm in diameter submerged into fine-grained calcarenite matrix; the

STRATIGRAPHY AND GEOLOGICAL CORRELATION

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Stage

Foraminiferal zones and zonules

Intermediate zone Karakungei Formation

Zougan Formation

Taldykol Formation

Central zone Chontash Formation (lower part)

Yulla Formation

Not defined Meandrospira deformata

Aktash Group

Southeastern Pamir

Karatash Group

Anisian Induan Olenekian

Series Middle Lower

Triassic

System

Stratigraphy and correlation of Lower–Middle Triassic sediments in the Central and Intermediate lithotectonic zones of the southeastern Pamirs

Khan Formation

Meandrospira deformata– Meandrospira cheni Meandrospira immatura Pilamminella ex gr. semiplana– Pilamminella sp. Foraminifers are not found

Bail’tam Formation

latter is locally recrystallized into regular calcite crystals. The thickness is 15.0 m.

It should be noted that the lower part of the Chontash Formation is attributed in this work to the Anisian Stage, as it is traditionally accepted (Atlas of Triassic…, 2001). At the same time, there are grounds to suggest the Ladinian age for the interval under consideration. ANALYSIS OF FORAMINIFERAL ASSEMBLAGES In the Karatash Group, foraminifers are irregularly distributed reflecting biofacies peculiarities of the section (figure). They are confined to separate interbeds of light gray to pinkish gray calcarenites of the Yulla Formation. Upward the section, interbeds with foraminifers become more numerous. In the upper part of the Yulla Formation, foraminifers are more diverse and abundant. It is remarkable that most of the foraminiferal tests representing the widespread species M. deformata, Valvulina azzouzi, Endotheba badouxi, Tolypammina cf. gregaria, and others, which have been found in the southeastern Pamir, are similar in size to their counterparts from the western and eastern Tethys. The exceptions are Pilamminella ex gr. semiplana that differs from typical representatives of this taxon in smaller (1.5 times) size and initial whorls more raised over the last planispiral segment and Meandrospira cheni, which is substantially larger than in other regions. The discovered foraminiferal assemblage and host sediments are suggested to be ranked as the Meandrospira deformata assemblage zone. Besides the index species, taxa characteristic of the zone are Meandrospira deformata Salaj, Meandrospira cheni (Ho), Meandrospira immatura He, Pilamminella ex gr. semiSTRATIGRAPHY AND GEOLOGICAL CORRELATION

plana (Kochansky-Devide et Pantic), Pilamminella sp., Glomospirella triphonensis Baud, Zaninetti et Bronnimann, Glomospirella sp., Agathamminoides sp., Frondicularia xiphoidea Kristan-Tollmann, Valvulina azzouzi Salaj, Pseudonodosaria multicamerata Kristan-Tollmann, Ophthalmidium sp., Endotheba badouxi (Zaninetti et Bronnimann), and Tolypammina aff. gregaria Wendt. Despite the fact that the index species Meandrospira deformata is found in the southeastern Pamir only in upper part of the Yulla Formation, the defined assemblage zone includes, in my opinion, also the underlying sediments that contain, as was mentioned, foraminiferal species characteristic of this unit in other regions of the world. Boundaries of the defined zone correspond conditionally to the Yulla Formation boundaries. Compositional differences between foraminiferal assemblages from the lower, middle, and upper parts of the Meandrospira deformata assemblage zone of the southeastern Pamir are used for defining the lowerorder units ranked from the base upward as the Pilamminella ex gr. semiplana–Pilamminella sp., Meandrospira immatura, and Meandrospira deformata– Meandrospira cheni beds or zonules (figure, plate). Boundaries of zonules are conditionally juxtaposed with boundaries of lithological members. Foraminiferal assemblages of the Meandrospira deformata Zone in the western Carpathians and Balkans (Salaj et al., 1983; 1988) are most close to the discovered assemblage in the taxonomic composition and age. Some species found in the southeastern Pamir are known from the Anisian foraminiferal assemblages of the northwestern Caucasus, Szechuan depression of China, Malay Peninsula, and Japan. The assemblage of southeastern Pamir is similar to some extent also to the assemblage characteristic of the Anisian Stage in PakiVol. 16

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stan: some specimens of the latter described as M. pusilla (Zaninetti and Bronnimann, 1975) belong probably to M. deformata and M. immatura. Species of the genus Meandrospira (M. deformata, M. cheni, M. immatura) and Pilamminella ex gr. semiplana occurring among found foraminifers are of the greatest stratigraphic significance. For example, Meandrospira species are index taxa of zonal subdivision in the Lower and lower Middle Triassic sections, and some of them are included into regional zonal scales (Salaj et al., 1983, 1988; Vachard and Fontaine, 1988; Kamoun et al., 2000). Meandrospira deformata has been found in many regions: the Dolomitic Alps (Zaninetti et al., 1994), Carpathians (Salaj and Polak, 1978; Salaj et al., 1983), southern Poland (Gazdzicki et al., 1975), Balkans (Salaj et al., 1988), northwestern Caucasus (Efimova, 1991), Malaysia (Gazdzicki and Smit, 1977), and Japan (Kobayashi et al., 2005). This index species is typical of the lower zone in the Anisian regional scale substantiated for the western Carpathians and Balkans (Salaj et al., 1983, 1988) and corresponding to either the Aegean or the Bithynian regional stages (Salaj et al., 1983). It is also a component of lower horizons in the Pelsonian regional stage (Salaj et al., 1988). In the eastern Tethys, Meandrospira deformata occurring in association with Pilamminella densa and Meandrospira dinarica are confined to the middle–upper Anisian, i.e., to the upper Pelsonian and Illyrian regional stages (Gazdzicki and Smit, 1977; Kobayashi et al., 2005). Meandrospira cheni occurs in both the Lower Triassic and Anisian sediments of the western Tethys (Salaj et al., 1983, 1988) and in undivided Middle Triassic sequences of the eastern Tethys (China; Ho, 1959). In Vietnam, this species is known from the Lower Triassic (?) and Anisian sediments (Martini et al., 1998). M. immatura is described from upper part of the Lower Triassic section in the Yangtze River lower reaches (He, 1988). Pilamminella semiplana (Kochansky-Devide et Pantic), which is similar to specimens from the Southeastern Pamir determined as Pilamminella ex gr. semiplana (Kochansky-Devide et Pantic), was known until recently from the western Tethyan regions (Alps, western Carpathians, Balkans), where it is particularly frequent in the Pelsonian and Illyrian (middle–upper Anisian) sediments (Zaninetti, 1976; Salaj et al., 1983) and occurs also in the lower Anisian interval, for example, in the northwestern Caucasus (Efimova, 1991). Pilamminella sp. (plate, fig. 4) is very close to Pilamminella aff. irregulariformis (Efimova) from the lower part of the Anisian Stage in the northwestern Caucasus (Efimova, 1974, Plate 1, fig. 11). Representatives of genera Haplophragmium, Endotheba, Tolypammina, and Valvulina found in the Meandrospira deformata Zone of the southeastern Pamir are abundant in the Anisian sediments of the western Tethys, precisely in the Meandrospira deformata (lower–lower middle Anisian) and

Meandrospira dinarica (upper middle–upper Anisian) zones. Correspondingly, the Meandrospira deformata Zone of the southeastern Pamir containing representatives of the above genera is correlative with this zone. Consequently, there are grounds to believe that the Meandrospira deformata assemblage zone of the southeastern Pamir corresponds to the synonymous zone of the regional scale used in the western Carpathians and Balkans and spans the Aegean and Bithynian regional stages of the lower Anisian and the lower Pelsonian regional stage of the middle Anisian (Salaj et al., 1983, 1988). Thus, the presented data indicate wide paleogeographic connections of the Pamir basin with western and eastern basins of the Tethys during the early and middle Anisian. Species in common for all the basins were Meandrospira cheni, Meandrospira deformata, and Tolypammina aff. gregaria, whereas Pilamminella ex gr. semiplana and Meandrospira immatura found in the Pamir region are known only from the western and eastern Tethys, respectively. The relatively high diversity of the described assemblage indicates an outburst of foraminiferal biota in the Anisian after the biotic crisis recorded the Permian– Triassic transition (Leven and Korchagin, 2001; Groves and Altiner, 2005). The flourishing was particularly characteristic of the genus Meandrospira. For example, Meandrospira deformata became widespread in the early and middle Anisian from the western (Dolomitic Alps) to the eastern (Japan, Malaysia) margins of the Tethys. The wide dispersal of this species points to extensive transgression and leveling of paleogeographic settings in the Tethyan shelf seas, where water masses could be of elevated salinity, since M. deformata having a peculiar intricately coiled (monstrous) test was tolerant to high salinity (Salaj and Polak, 1978). It is remarkable, however, that in the Tirin and Argandab lithotectonic zones of southern Afghanistan, which are geographically close on the west to the study region, a thick sequence of Anisian limestones contains an impoverished foraminiferal assemblage different from that of the Southeastern Pamir (Farsan et al., 1981). The foraminiferal assemblage of the Meandrospira deformata Zone found in the southeastern Pamir offers opportunity to trace this stratigraphic level eastward to neighboring areas of western China and Karakorum (the Shaksgam basin), where age and correlation of Lower–Middle Triassic sections are also debatable. Inasmuch as representatives of the genus Meandrospira are of a high stratigraphic potential for subdivision and correlation of the Lower and Middle Triassic sediments of the Tethyan realm, it seems reasonable to describe species of this genus first found in the southeastern Pamir.


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2 4 5

1

3

6

7

8 9

12 11

10

13

14

15

P l a t e. Images of foraminifers in thin sections from lower–middle Anisian sediments of the Khanyulla section. All the images are obtained under the light microscope Polam P122 in the transmitted light. (1) Glomospirella triphonensis Baud, Zaninetti et Bronnimann. Sample 151/18; (2) Glomospirella sp. Sample 151/18; (3) Glomospirella sp. I. Sample 151/18; (4) Pilamminella sp. Sample 151/19; (5) Pilamminella ex gr. semiplana (Kochansky-Devide et Pantic). Sample 151/18; (6) Agathamminoides sp. Sample 151/18; (7) Haplophragmium sp. Sample 151/19; (8) Frondicularia xiphoidea Kristan-Tollmann. Sample 151/38; (9) Valvulina azzouzi Salaj. Sample 151/38; (10) Meandrospira deformata Salaj. Sample 151/38; (11) Meandrospira cheni (Ho). Sample 151/38; (12) Pseudonodosaria multicamerata Kristan-Tollmann. Sample 151/38; (13) Meandrospira immatura (He). Sample 151/38; (14) Tolypammina aff. gregaria Wendt. Sample 151/38; (15) Endotheba badouxi (Zaninetti et Bronnimann). Sample 151/19. Bar is 0.1 mm. STRATIGRAPHY AND GEOLOGICAL CORRELATION

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PALEONTOLOGICAL DESCRIPTION SUPERFAMILY CORNUSPIRACEA SCHULTZE, 1854 FAMILY MEANDROSPIRIDAE SAIDOVA, 1981

Meandrospirininae Saidova, 1981: Loeblich and Tappan, 1987, p. 311 (see synonymy) Diagnosis. Test is free. Its initial chamber is followed by coiled tubular undivided chamber, which is either intricately coiled or planispiral, being coiled in the zigzag manner; the wall is calcitic, porcelaneous, imperforate. Generic composition: Meandrospira, Meandrospiranella, Flectospira, Meandrospirella, Bispiranella. Stratigraphic range: Permian (Artinskian)–Upper Cretaceous (lower Cenomanian). Remarks. In this work, the group under consideration is proposed to be ranked as the family Meandrospirinidae. In modern manuals on foraminifers, stratigraphic range of this family is estimated to be wide from the Permian to Holocene. All the genera attributed to the family, except for Meandrospira, become extinct in the Triassic. In my opinion, the upper limit of the family existence should correspond to the early Cenomanian. The opinion is based on peculiar structure of test wall of recent foraminifers usually referred to the genus Meandrospira (Loeblich and Tappan, 1987). Owing to this feature, they were defined not long ago as species of autonomous genus Arenomeandrospira Jones et Wonders, 2000, and attributed to the other family. In this situation, Meandrospira washitensis, the last finds of which are described from the lower Cenomanian (Loeblich and Tappan, 1946), should be considered as the youngest representative of the genus Meandrospira and of family Meandrospiridae correspondingly. Thus, extinction of the large family such as Meandrispiridae in the early Cenomanian is additional evidence in favor of significant and poorly studied biotic crisis at the early–middle Cenomanian boundary time (Korchagin, 2004). Genus Meandrospira Loeblich et Tappan, 1946 Meandrospira Loeblich et Tappan, 1946 (type species Meandrospira washitensis Loeblich et Tappan, 1946): Loeblich and Tappan, 1946, p. 248; 1987, p. 312. Type species: Meandrospira washitensis Loeblich et Tappan, 1946; Lower Cretaceous (Albian). Diagnosis. Test small, its initial chamber is followed by the spiral tubular undivided second chamber, which is coiled, twisting in zigzag manner into planar involute spire with zigzag margins overlapping umbilical areas and distinctly seen only in the last whorl; the wall is calcitic, imperforate, porcelaneous, having terminal simple aperture. Stratigraphic range. Triassic (Induan Stage)– Upper Cretaceous (lower Cenomanian).

Remarks. Triassic species are classed with Meandrospira cheni, M. pusilla (=M. julia), M. flosculiformis, M. deformata, M. insolita, M. karnica, M. dinarica, M. dieneri, and M. immatura. Meandrospira cheni (Ho, 1959) Plate, fig. 11

Trochamminoides cheni Ho, 1959: Ho, 1959, pp. 402–403, 416, Plate VIII, figs. 16–19. Meandrospira cheni (Ho, 1959): Salaj et al., 1983, pp. 99–100, Plate LVI, figs. 1–19 (see synonymy); Zaninetti et al., 1994, Plate 11. Description. Large test is rounded in the cross section. Its initial chamber is spheroid, large; the second tubular chamber is compactly coiled, regularly twisting in two planispiral whorls in the meander-like manner. In the last whorl there are visible 6–7 oval equal ring sections of the tubular chamber; the test contour is rounded, slightly lobulate; wall thick, calcitic, mediumgrained, dark. Comparison. Specimens from the southeastern Pamir are very similar in the number of test whorls, increasing rate and shape of tubular chamber cross sections in the last whorl to the type species from the Anisian sediments of China, in particular to the specimen illustrated by Ho (1959, Plate VIII, fig. 19) and to specimens from the Lower Triassic of the western Carpathians (Salaj et al., 1983, Plate LVI, figs. 1–19), although they differ from the latter in larger test size (0.20–0.35 versus 0.14–0.15 mm) and slightly lesser number of oval–ring sections of the tubular chamber (6–7 versus 7–8). In their size and shape, the described tests are close to the specimen from middle Anisian sediments of the western Carpathians that is referred to M. insolita (Ho) (Salaj et al., 1983, Plate LIV, fig. 9, not Plate LIV, figs. 7–8). At the same time, the last specimen (Salaj et al., 1983, plate LIV, fig. 9) differs from the type representatives of M. insolita (Ho) and other specimens of this species from the western Carpathians illustrated in work by Salaj et al. (1983, Plate LIV, figs. 7–8). Dimensions: large diameter of the holotype (no. 65/167) is 0.22 mm. Locality: southeastern Pamir, Central lithotectonic zone, Yulla Formation, lower–middle Anisian. Material: over 30 specimens from different samples. Geographic distribution and age. Lower Triassic– Anisian in the Carpathians, Alps, Vietnam, Pamirs; undivided Middle Triassic in China. Meandrospira deformata Salaj, 1967 Plate, fig. 10

Meandrospira deformata Salaj, 1967: Zaninetti, 1976, p. 133, Plate 1, figs. 20–22; Salaj and Polak, 1978, pp. 213–215, Plate 1, figs. 1–9, Plate 2, figs. 1–6;


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Salaj et al., 1983, p. 98, Plate LIII, figs. 1–4, Plate LIV, figs. 1–6; Efimova, 1991, Plate 1, fig. 22; Kobayashi et al., 2005, Plate10, figs. 27–28. Meandrospira ? deformata Salaj, 1967: Gazdzicki et al., 1975, p. 290, Plate 7, figs. 9–16. ? “Meandrospira” deformata Salaj, 1967: Zaninetti et al., 1994, Plate 2, fig.13. “Meandrospira” deformata Salaj, 1967: Gazdzicki and Smit, 1977, Plate 4, fig. 6. Description. Large test is oval to round in the cross section. Structure of initial chamber and initial whorls of the tubular chamber have not been observed. In the last whorl, tubular chamber is irregularly coiled, partly characterized by the meander-type coiling. The test contour is even to slightly lobulate; wall dark, granular, calcitic, thick. Comparison. In their shape and size, specimens of Meandrospira deformata from lower–middle Anisian sediments of the southeastern Pamir are similar to the species from the lower Anisian of the western Carpathians illustrated in work by Salaj et al. (1983, Plate LIII, fig. 2). In my opinion, specimens from the Anisian sediments of Pakistan determined as M. pusilla (Zaninetti and Bronnimann, 1975, Plate 34, fig. 10) belong to M. deformata. Dimensions: large diameter of the holotype (no. 65/168) is 0.25 mm. Locality: southeastern Pamir, Central lithotectonic zone, Yulla Formation, lower–middle Anisian. Material: approximately 10 specimens in several samples from the Yulla Formation. Geographic distribution and age: Dolomitic Alps, western Carpathians, southern Poland, Balkans, northwestern Caucasus, southeastern Pamir, Malaysia, Japan, and, probably, Pakistan; lower to lower upper Anisian. Meandrospira immatura He, 1988 Plate, fig. 13

Meandrospira immatura He, 1988: He, 1988, pp. 89, 92, Plate II, figs. 13,14. Description. Small test is trapezoid–rounded in cross section, somewhat irregularly coiled; the second tubular chamber is intricately coiled at the initial stage and almost planispiral beginning from 1.5–2 whorls of the spire; in the last whorl, second chamber is slightly curved, freely planispiral, and the last whorl has only 4–5 cross sections owing to this. The test contour is angular–rounded, even; wall dark, fine-grained, calcitic, recrystallized. Comparison. Specimens from the lower–middle Anisian of the Southeastern Pamir are very close to the type specimen of Meandrospira immatura from the Lower Triassic of China (He, 1988, Plate II, fig. 14). In distinction from other Triassic species of the genus Meandrospira, the studied specimens have lesser numSTRATIGRAPHY AND GEOLOGICAL CORRELATION

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ber of test whorls and sections of the tubular chamber in the last whorl due to almost planispiral but not typical meander coiling mode and the test contour even trapezoid–rounded in the transverse cross section. From M. insolita (Ho, 1959, pp. 7–8, Plate VIII, figs. 11–15) showing peculiar coiling of tubular chamber in the last whorl, M. immatura differs in less number of whorls in the second tubular chamber (1.5–2.0 versus 2.5) and in trapezoid–rounded angular test contour in the transverse section but not rounded lobulate as in M. insolita. In my opinion, the specimen from Anisian sediments of Pakistan attributed to Meandrospira pusilla (Ho) (Zaninetti and Bronnimann, 1975, Plate 34, fig. 15) and specimen from the lower Anisian (Malyi Tkhach Formation) of the northwestern Caucasus determined as M. dinarica (Efimova, 1974, Plate III, fig. 16) are close to M. immatura (He). Dimensions: large diameter of the holotype (no. 65/169) is 0.14 mm. Locality: southeastern Pamir, Central lithotectonic zone, Yulla Formation, lower–middle Anisian. Material: several specimens in two samples from the Yulla Formation. Geographic distribution and age. China (Lower Triassic), southeastern Pamir (lower–middle Anisian), and, probably, Pakistan (Anisian). ACKNOWLEDGMENTS The work was supported by the Russian Foundation for Basic Research, project nos. 05-05-64949 and 0605-65201. Reviewers V. Ya. Vuks and V. A. Zakharov REFERENCES 1. Atlas of Triassic Invertebrates from Pamirs, Ed. by A.Yu. Rozanov and A.A. Shevyrev (Nauka, Moscow, 2001) [in Russian]. 2. A. A. Dagys and V. I. Dronov, “First Conodonts from Triassic Sediments of the Southeastern Pamir,” Dokl. Akad. Nauk SSSR 309, 1469–1471 (1989). 3. V. I. Dronov and E. Ja. Leven, “To Geology of the Southeastern Pamir,” Sov. Geol., No. 11, 21–36 (1960). 4. V. I. Dronov and V. S. Luchnikov, “Triassic System,” in Subdivision of Stratified and Igneous Rocks of Tajikistan (Donish, Dushanbe, 1976), pp. 109–122 [in Russian]. 5. N. A. Efimova, “Triassic Foraminifers of the Northwestern Caucasus and Ciscaucasia,” Vopr. Mikropaleontol., No. 17, 54–82 (1974). 6. N. A. Efimova, “Triassic System,” in Practical Guide on Microfauna of the USSR. Vol. 6. Mesozoic Foraminifers (Nedra, Moscow, 1991), pp. 16–25 [in Russian]. 7. N. M. Farsan, D. Vachard, and C. Montenat, “Bivalves et Foraminiferes de Anisien de Behsud (Trias de l Afghanistan central),” Ann. Soc. Geol. Nord. 101 (2), 65–73 (1981). Vol. 16

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