The carboniferous of the Western Karakoram (Pakistan)

UNCORRECTED PROOF

The carboniferous of the Western Karakoram (Pakistan)

M. Gaetania,*, A. Zanchib, L. Angiolinia, G. Olivinia, D. Sciunnachc, H. Bruntond,A. Nicoraa, R. Mawsone

aDipartimento di Scienze della Terra, Universita di Milano, Via Mangiagalli 34, Milano 20133, ItalybDipartimento dell’Ambiente e del Territorio, Universita di Milano-Bicocca, Piazza della Scienza 4, Milano 20126, Italy

cRegione Lombardia, Struttura Analisi e Informazioni Territoriali, Piazza Duca d’Aosta 4, Milano 20124, ItalydDepartment of Palaeontology, The Natural History Museum, South Kensington, London SW7 5BD, UK

eMacquarie School of Earth Science, Centre for Ecostratigraphy and Paleobiology, North Ride, NSW 2119, Australia

Received 3 December 2002; accepted 13 May 2003

Abstract

The results of the study of the Carboniferous successions in the western part of the Northern Karakoram during three geological

expeditions are summarized here. Rocks of that period are not uniformly preserved in the several thrust sheets forming the Northern

Karakoram. In most of them only the basal part of the Carboniferous, up to the Visean, is preserved, whilst in the Karambar thrust sheet a

more complete section—previously almost unknown—is preserved. Four new lithostratigraphic units, time-constrained by brachiopod and

conodont biostratigraphy, are described, from bottom to top: (1) the Margach Formation: prevailing dark shales with subordinate fine

subarkoses and quartzarenites, up to 300 m thick (mid-Famennian to middle Tournaisian); (2) the Ribat Formation: grey crinoidal limestones

passing upwards to dark marly limestones and marls, at least 300 m thick (middle Tournaisian to Serpukhovian); (3) the Lupsuk Formation:

subarkoses to feldspathic quartzarenites in thick beds, alternating with dark shales and siltstones, up to 400 m thick (Serpukhovian to

uppermost Carboniferous); (4) within the Lupsuk Formation a local member, the Twin Valleys Member, up to 100 m thick, a bioclastic

limestone intercalation of post-Moscovian age, is distinguished. The Carboniferous successions are invariably sealed by the arkoses to

quartzarenites of the Gircha Formation, 133 m above the base of which, in the Karambar area, an Asselian brachiopod fauna was recovered.

The Carboniferous succession is interpreted as recording the evolution of the passive margin of the Northern Karakoram Terrane, from

early rifting stage in the Late Devonian to syn-rift events during the Late Carboniferous. The basal part of the Gircha Formation, of latest

Carboniferous-earliest Permian age, is considered to have been deposited above a break-up unconformity, linked to the early drifting in the

seaway bordering the Karakoram.

In the palaeontological appendix the most significant brachiopod taxa (19 species, one new) are described.

q 2003 Published by Elsevier Ltd.

Keywords: Carboniferous; Palaeo-Mesozoic sedimentary rock; Western Karakoram; Pakistan

1. Introduction

The Karakoram Block consists of four major structural

elements. From south to north they are: the Southern

Metamorphic Belt; the Karakoram Batholith, separated in

the western part of the range by the Metasedimentary

Intermediate Belt; and the Northern Karakoram Terrane,

consisting of crystalline and Palaeo-Mesozoic sedimentary

rocks (Figs. 1 and 2). The absence of a major metamorphic

imprint in the North Karakoram allows us to recognize the

Carboniferous sedimentary successions.

The first reconnaissance expedition to this area failed to

find evidence of Carboniferous rocks (Hayden, 1914; Tipper

in Pascoe, 1924; Talent et al., 1982). In the report of our

1992 expedition (Gaetani et al., 1996) we inferred the

existence of the Lower Carboniferous on the basis of

stratigraphic relationships, but were unable to date the

succession correctly through its palaeontological content.

The first consistent evidence of Carboniferous fossils was

obtained during the 1996 field expedition, especially in the

area around Karambar Lake (Angiolini et al., 1999).

Therefore in the 1999 expedition, additional logging and

sampling was undertaken throughout the area by Zanchi

and Gaetani. Geological field reconnaissance during the

1990s, in the previously almost geologically unknown

1367-9120/03/$ - see front matter q 2003 Published by Elsevier Ltd.

doi:10.1016/S1367-9120(03)00137-8

Journal of Asian Earth Sciences xx (0000) xxx–xxx

www.elsevier.com/locate/jseaes

* Corresponding author.

E-mail address: [email protected] (M. Gaetani).

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UNCORRECTED PROOFWestern Karakoram, was carried out by the following

geologists, with the dates in which they participated:

Angiolini (1992, 1996); Gaetani (1992, 1996, 1999); Nicora

(1992); Olivini (1999); and Zanchi (1996, 1999). Angiolini

studied the Carboniferous brachiopods, Nicora and Mawson

the conodonts, and Sciunnach the sandstone petrography.

The aim of the present paper is to illustrate the general

stratigraphic and tectonic setting of the Carboniferous

successions measured and sampled during three

expeditions (1992, 1996, and 1999). Knowledge of the

Carboniferous is critical to understanding the earlier stages

of rifting and drifting of Cimmerian Blocks away from the

Gondwanan margin.

2. Regional geology

The North Karakoram Terrane, as defined in recent

works (Zanchi and Gaetani, 1994; Gaetani et al., 1996;

Zanchi et al., 2000) consists of a thick and polyphase

stack of thrust sheets which lie to the north of the

Karakoram Batholiths (Le Fort and Gaetani, 1998) (Fig. 3).

In the Chitral region, the Karakoram is separated from the

East Hindu Kush-Wakhan by the Tirich Boundary Zone, a

left lateral shear zone including deformed ultramafic

rocks, completely ignored by most previous authors

(Pudsey et al., 1985; Pudsey, 1986; Searle, 1991).

These rocks record the pre-mid-Cretaceous accretion of

the Karakoram Block to the southern Pamir ranges

(Zanchi et al., 2000). East of the Shah Jinali Pass, the

Tirich Boundary Zone is tectonically elided by NE–SW

left-lateral strike-slip faults, and the Late Palaeozoic

Wakhan and Misgar slates of Wakhan, are directly

stacked above the Karakoram units. Large sheets of

Palaeo-Mesozoic carbonates (Atark and Khan Kun Units,

mostly Permian to Jurassic in age) and poorly known

crystalline complexes including Mesozoic intrusives and

older metamorphic rocks cropping out on the Afghanistan

side (e.g. Qal-a-Ust gneisses) are also included within the

East Hindu Kush-Wakhan.

Fig. 1. Structural index map of the Karakoram and surroundings regions, showing the position of Fig. 2. NP: Nanga-Parbat syntaxis; MMT: Main Mantle

Thrust; NS northern suture; RPZ: Rushan-Pshart zone; WABZ: Wanch-Ak Baital zone.

Fig. 2. General tectonic map of Wakhan and Karakoram.

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UNCORRECTED PROOF

To the west, the southern boundary of the North

Karakoram Terrane is generally tectonic and consists of a

high-angle reverse shear zone with oblique and left-lateral

components, passing to a south-dipping north-vergent thrust

plane in the Chiantar glacier area. Slices of the Cretaceous

batholith are tectonically included within the cover, as well

as deformed metasediments which occur along the main

tectonic boundaries among the intrusive units of the

batholith. Intrusive contacts are locally preserved.

The sedimentary cover of the North Karakoram Terrane

includes several thrust sheets showing complex geometrical

relationships and different directions of tectonic transport

(Figs. 2 and 3). A major subdivision is marked by the Reshun

Fault of Chitral (Pudsey et al., 1985; Zanchi et al., 1997;

Zanchi et al., 2000), which connects to the Upper Hunza

Fault in the east, over a distance exceeding 200 km (Fig. 2).

Its occurrence through the Chiantar glacier area is suggested

by thin slices of the Reshun Formation, which may

interfinger with the Tupop Conglomerate around Chillinji.

South of this fault, tectonic units locally include the pre-

Ordovician crystalline basement and Palaeozoic

sediments, with reduced thickness and poor fossil

content (Axial Unit, Dobargar-Kotalkash metasediments,

Garmuth-Chillinji-Guhjal Units). The one exception is

represented by the Chillinji Unit, where an almost complete

Palaeozoic succession, unconformably covering pre-Ordo-

vician intrusives, is exposed (Fig. 3).

Most of these units were affected by a very low to low

grade metamorphism. The Cretaceous Reshun Formation

occurs locally, with an unconformable boundary above these

units, with a thickness varying from a few tens to hundreds of

metres. The southern margin of these units is intruded by the

Cretaceous to Paleogene plutons of the Karakoram Batholith

(Debon et al., 1987; Debon, 1995; Debon and Khan, 1996;

Debon et al., 1966).

No pre-Ordovician rocks occur north of the Reshun

Fault, where Palaeo-Mesozoic sedimentary successions are

exposed, forming a complex stack of thrust sheets laterally

extending usually a few tens of km (Figs. 2 and 3). Most

of the floor thrusts occur within the Ordovician-?Silurian

slates of the Baroghil Group. West of the Baroghil Pass to

Chitral, up to the longitude of Morich, this thrust system is

tectonically bounded by the Tash Kupruk Unit (Gaetani

et al., 1996), which consists of alkali basalts and

associated marbles.

From the eastern Chitral to the upper reaches of the

Karambar River, thrust sheets consist mostly of Palaeozoic

successions, the youngest sediments being Early Jurassic in

age. On the other hand, along the eastern side of the range,

thrust sheets include rocks not older than Permian or

possibly Upper Carboniferous (Gaetani et al., 1990; Zanchi

and Gaetani, 1994). To the east, Carboniferous fossils have

been found only in the Upper Chapursan Valley between

Buattar and the Chillinji Pass in a small thrust sheet along

the Reshun/Upper Hunza fault system.

The Carboniferous successions have been studied in the

Lasht, Baroghil-Lashkargaz, and Karambar Units, the latter

preserving the most thick and complete sections.

Fig. 3. Structural map of Wakhan and Western-Central Karakoram, from Zanchi et al. (2001). Units in legend are organised from north to south. SJ-P: Shah

Jinali Pass; Ba-P: Baroghil Pass; Ka-P: Karambar Pass; Ch-P: Chillinji Pass.

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UNCORRECTED PROOF

To clarify the regional tectonic setting, a more detailed

description focusing on the tectonic units containing

Carboniferous rocks, follows below.

2.1. The Lasht Unit

The Lasht Unit, which crops out around the village

of Lasht along the Yarkhun valley, mainly consists of

Devonian to Permian, and possibly Mesozoic carbonate to

terrigenous successions (Gaetani et al., 1996). E–W

trending folds and faults make the structural setting very

complex, especially in the west, where the unit is intensively

sliced and repeated tectonically. Several stratigraphic

characters of the tectonic unit, i.e. the occurrence of the

Devonian Chilmarabad and Shogram formations, the

Carboniferous limestones, Permian fusulinid limestones,

very similar those of the Chapursan Group (Hunza valley,

Gaetani et al., 1995; Angiolini, 1966), and red beds of the

Gharil Formation make it comparable to the Baroghil-

Lashkargaz Unit (Gaetani et al., 1996). East of Lasht, the

Lasht Unit is tectonically elided by left-lateral NE–SW

trending strike-slip reverse faults which may represent the

eastern continuation of the Reshun Fault.

2.2. The Baroghil-Lashkargaz Unit

The Baroghil-Lashkargaz Unit occurs in the central part

of the study area around the Baroghil Pass and Lashkargaz.

It consists of an almost complete Ordovician to Jurassic

succession (Gaetani et al., 1996; Talent et al., 1999;

Quintavalle et al., 2000) about 4–5 km thick. It is bounded

to the south by the Axial Unit (Gaetani et al., 1996) through

a complex system of reverse-oblique faults, including

conglomerates of the Reshun Formation and intensively

deformed marble slices. The central-southern part of this

unit is little deformed, showing a continuous sedimentary

succession. On the contrary, its northern boundary is

intensively deformed, showing E–W trending overturned

and recumbent folds and south-vergent thrusts, which

cause intensive shortening and tectonic repetition of the

Lower Permian carbonates. The northwestern boundary

with the Karambar Unit along the Chiantar Glacier is also

very complex.

2.3. The Karambar Unit

The Karambar Unit extends north and east of the

Baroghil-Lashkargaz Unit, between the Chiantar Glacier

and southern Wakhan, also occurring largely to the north of

the Afghanistan border. This unit contains the thickest and

most complete Palaeozoic succession of the Karakoram

Range. It includes at the base Ordovician and ?Silurian

slates and quartzarenites (Vidiakot and Yarkun Formations),

and Devonian carbonates (Vanadil and Chilmarabad

Formations, Early to Middle Devonian in age) which are

not discussed in the present paper.

Above these units follow the ?Givetian-Late Devonian

Shogram Formation and the four lithostratigraphic units of

Carboniferous age, which will be described in Section 3.

The most peculiar stratigraphic feature of the Karambar

Unit is this thick Carboniferous succession which crops out

extensively from the Karambar Lake to Afghanistan and

extends westward to the Ribat Valley area.

The Carboniferous units are conformably covered by the

Early Permian Gircha Formation, which exceeds 1000 m in

thickness. As in other areas the Gircha Formation is

tectonically detached from the older units, this succession

represents a unique complete stratigraphic section across the

Late Palaeozoic in Karakoram. The Gircha Formation is

covered by a thick Permian mainly carbonate succession,

well exposed south of Shuinji.

The southern sector of the Karambar Unit is highly

folded and abruptly cut by the Reshun Fault. The eastern

contact with the Sost-Khora Burt Units still is poorly

defined, due to the inaccessibility of the area and the

intrusion of the Chatteboj granite, which partially masks

the original contacts (Fig. 3). The unit is split by a large

NNE–SSW trending tear fault extending from the Chiantar

Glacier to the east of the Karambar Lake, with a left-lateral

lateral throw of some kilometres. The western and the

northern sectors of the Karambar unit show NNW–SSE to

NW–SE trending west-vergent folds and thrusts, whereas

the eastern part shows E–W south-dipping thrust structures.

Although the Chiantar area displays a very complex

structural setting, the sedimentary succession cropping out

along the Ribat valley is generally poorly deformed and

several stratigraphic logs have been recorded.

3. Lithostratigraphy

3.1. The Karambar Unit

Being the best and most complete succession, the

Karambar Unit will be used as a reference section.

The following lithostratigraphic units have been identified

(Fig. 3):

(6) Gircha Formation (?latest Carboniferous–early Sak-

marian)

(5) Twin Valleys Member (Moscovian-?)

(4) Lupsuk Formation (Serpukhovian–Moscovian)

(3) Ribat Formation (late Tournaisian–Bashkirian)

(2) Margach Formation (mid-Famennian–middle Tour-

naisian)

(1) Shogram Formation (mid-Givetian–mid-Famennian).

3.1.1. The Shogram Formation (Desio, 1966)

This unit, up to 240 m thick, is briefly discussed here as it

forms the base of the Carboniferous succession. The basal

tens of metres consist of conglomerates and arenites, mostly

deposited in a fluvial environment, overlain by alternating

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UNCORRECTED PROOF

fine sandstones and cocquinoid layers, commonly rich in

brachiopods. One distinctive feature is the presence of one

or two grey calcareous horizons of bafflestone, a few tens of

metres thick, packed with colonial corals. This is a

prominent feature in the lansdscape and allows easy

correlations. Upwards, the carbonate content gradually

decreases and the definition of the upper boundary depends

on the quality of the outcrops. Along the Ribat valley

section the boundary with the overlying unit is defined by

the appearance of thick and laterally continuous packages

of dark grey siltstones, with subordinate intercalations of

fine-grained arenites, and negligible calcareous beds.

3.1.2. The Margach Formation (new name)

Between the alternating calcareous/arenaceous rocks of

the Shogram Formation and the crinoidal limestones of the

Ribat Formation, a terrigenous unit, consisting mostly of

dark grey to black siltstones and shales, crops out

extensively. The name originates from the cattle shelter of

Margach on the north side of the valley. Average thickness

exceeds 200 m, but due to the incompetence of the shales,

this unit is often tectonically laminated.

Three lithozones were distinguished in the Ribat section,

which we identify as the type-section of the unit (Figs. 4

and 5). This section was measured along the slope of

the south side of the valley, at an average altitude of

4550–4650 m above sea level, up to a total thickness

of 294 m. From the base upwards:

(a) Dark grey to dark green splintery siltstones intercalated

with thin-bedded arenites, rarely with parallel

laminations; rare intercalations of bioclastic limestones

bearing brachiopods and crinoid fragments, and a

single 0.5 m-thick bed with Receptaculites (an alga

often called ‘sunflower coral’). Thickness 92 m.

(b) Dark grey to black splintery siltstones and slates, with

bioturbated horizons. Rare arenitic intercalations with

dish-and-pillar structures. Thickness 118 m.

(c) Fine- to very fine-grained arenites in beds 20 to

40 cm thick, locally displaying parallel lamination,

dominate in the lower part, whereas coarser

sandstone beds, also displaying microconglomerate

lags and erosional channels, tend to prevail upwards.

Asymmetric ripple marks indicate progradation from

S to N. Bioturbation is more common in the thinner

bedded arenites; hybrid biocalcarenites and biocal-

cirudites are also present. Thickness 84 m.

Fossil content. The Receptaculites (CK1066) is a new

form (Hubmann, personal communication, 2003) of a group

of enigmatic calcareous structures which appeared in the

Early Ordovician and disappeared in the Early Triassic. No

fossils were discovered in the second lithozone. Instead in

the third lithozone a small brachiopod assemblage with

Parallelora aff. subsuavis (Plodowski, 1968), Rhipidomella

sp., and Rhynchopora sp. was collected in samples CK1073,

CK1074, CK1075, CK1077.

Age: Latest Devonian–?early middle Tournaisian.

Environment. The Margach Formation records sedimen-

tation on a muddy shallow marine flat, with significant

terrigenous input under low energy conditions, and largely

sheltered from the waves. No significant emersion was

detected. The third lithozone marks a general increase in

the energy of tractive currents. Erosional channels and

coarser-grained detritus document a general forestepping of

more proximal facies. The fragmentary fossils belongs to

stenohaline organisms. A shoreface environment with no

significant emersion is inferred.

3.1.3. The Ribat Formation (new name)

This unit is established to characterize the grey to dark-

grey limestones and marls that overlie the Margach

Formation in the Karambar and in the Baroghil/Lashkargaz

tectonic units (Fig. 5). A complete section is difficult to

measure, but this unit may be thicker than 300 m. The type

section follows the type section of the Margach Formation

along the slope of the south side of the Ribat valley (hence

the name of the unit), but is interrupted by the moraine of the

Zoe Glacier, 135 m above the formation base. The unit

reappears on the east side of the glacier above the level we

measured, at about 4900–5000 m. We did not climb this

high. An additional section may be measured on the left side

of the Lupsuk Glacier from 5000 m upwards, at the base of

the ridge forming the Pakistan/Afghanistan border. In the

type section, the basal contact is partially covered. The

lowermost part is characterized by hybrid crinoidal lime-

stones, cross-bedded and with topset laminations,

suggesting a transport direction towards the N–NE (in

present coordinates). Fossils are abundant, with crinoid

ossicles and small fragmentary solitary corals. This basal

interval, 15 m thick, is overlain by grey limestones, in beds

20–40 cm thick, often very rich in crinoid ossicles, locally

graded or with parallel lamination. Marly intercalations may

also occur occasionally. This lithology is rather monotonous

along the section measured, with recurrent facies rich in

crinoid ossicles and, locally, also fragmentary Spiriferide

and Productoid (Dictyoclostid) brachiopods. The Ribat

Formation exhibits significant lateral variation. In the

Lupsuk Glacier area (Figs. 4 and 5) the unit forms the

core of an anticline and the lower exposed part consists of

thick-bedded to massive crinoidal limestones, overlain by

well-bedded crinoidal limestones, with sparse Productoid

and Spiriferide brachiopods. In the Triple Junction section,

above the bedded crinoidal limestone, dark marly lime-

stones, alternating locally with chert and marls, are at least

150 m thick (Figs. 4 and 5). In the lower part, the marls are

locally bioclastic with brachiopods, solitary corals and

trilobites. Also in the Twin Valleys section (Figs. 4 and 5)

grey dark marly limestones are prevalent, whereas bioclastic

limestones only form intercalations. Thus, the upper part is

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UNCORRECTED PROOF

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,C

,D

,E

,F

,G

,H

)ar

esh

ow

no

nth

em

ap.

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669

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671

672

UNCORRECTED PROOF

Fig

.5

.S

trat

igra

ph

icco

rrel

atio

ns

of

sect

ion

sm

easu

red

inth

eC

arb

on

ifer

ous

of

the

Kar

amb

arU

nit

,to

pp

edb

yth

eG

irch

aF

orm

atio

n(s

eeF

ig.

4fo

rth

eir

loca

tion

).

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780

781

782

783

784

UNCORRECTED PROOF

more varied, with marls, marly and hybrid limestones, and

calcareous sandstones.

Fossil content. A single sample (CK1081, collected 35 m

above the base) yielded the following conodonts: Gnatho-

dus pseudosemiglaber Thompson and Fellow, 1970,

Gnathodus typicus morph. 2 Cooper, 1939, and Polygnathus

bischoffi Rhodes, Austin and Ziegler, 1969. In the middle

part of the unit (Triple Junction section), where marls are

more frequently intercalated in the limestone beds, the

brachiopods Sajakella sp. and Ectochoristites sp. were

collected in sample KO14, whereas Anthracospirifer sp. and

Permasyrinxinae gen. indet. were identified from sample

KO15, 30 m higher in the succession. In the upper part of

the unit, in several sections (A,E,F,G,H) and in few

localities (CK 588, Lale Ribat 1) (Fig. 4), the following

brachiopods were collected: Buxtonioides sp., Echino-

conchidae gen. indet., Rhipidomella sp., Martiniopsis

grandiformis (Plodowski, 1968), Spirifer cf. subgrandifor-

mis Plodowski, 1968, S. pentagonoides Plodowski, 1968,

S. cf. denis (Beznosova, 1959), Afghanospirifer sp.,

Choristites sp., Gypospirifer sp., Syringothyris sp., and

Composita sp. Details are given in Section 4.

Age: Late Tournaisian–Bashkirian

Environment. The Ribat Formation represents a fully

marine interval, dominated by high productivity of

carbonates, which were transported towards the basin.

Displaced crinoid ossicles and brachiopod shells are

abundant in places, both in the lower part, representing

the transition from shoreface to open shelf environments,

and in the overlying well-bedded, locally graded beds which

represent the deeper parts of the depositional system.

A gradual increase of clay input is recorded from the middle

part upwards. In the Twin Valleys section 10 s of metre-

thick packages of limestone and marls alternate sharply,

indicating a cyclical clay input in a fairly stable carbonate

depositional system.

3.1.4. The Lupsuk Formation (new name)

We introduce this new unit to identify the thick package

(about 400 m) of fine arenites, siltstones, slates, hybrid

calcarenites and thin conglomerates, which are locally

interposed between the limestones and marls of the under-

lying Ribat Formation and the basal quartzarenites of the

overlying Gircha Formation. This unit has so far been

recognized only in the Karambar Tectonic Unit.

We measured a section along the south side of the Ribat

valley at an altitude of 4550–4650 m, from the snout of the

Zoe Glacier towards the east (Figs. 4–6). The lowermost

part was not measured, cropping out at higher altitude on the

east side of the Zoe Glacier. Possibly the best section is on

the left side of the Lupsuk Glacier from 5150 m upwards.

We only cursorily sampled on the west side of the Lupsuk

Glacier, from 5000 m downwards. Therefore we do not

propose a type section for this unit. North of Karambar

Lake, and particularly in the Lupsuk area, the Lupsuk

Formation is notably richer in carbonates with respect to

the area south of the Karambar Pass.

In the Lupsuk Glacier area the unit begins with coarse,

thick-bedded quartzarenites and microconglomerates, with

cross-lamination and foresets dipping to the N. Upwards,

they pass in hybrid sandstones, still with microconglomera-

tic intercalations. This basal part is about 40 m thick. It is

overlain by grey hybrid arenites and arenaceous limestones,

frequently very rich in crinoid ossicles, in 10–30 cm thick

beds, often amalgamated. The thickness of the horizon

reaches 20 m. The upper part of the succession consists of

grey arenaceous limestones very rich in crinoid ossicles,

with parallel lamination, forming amalgamated packages up

to 10 m thick. The thickness of this interval exceeds 100 m.

The unit ends with approximately 30 m of grey–green

siltstones with sulphate nodules.

On the south side of the Ribat Valley, the section is

dominated by medium to fine arenites in the lower part,

more than 150 m thick. By contrast, siltstones with rare

arenitic intercalations dominate the middle and upper parts

(240 m thick). Rare crinoidal limestone intercalations are

interpersed through the section, in beds exceptionally

reaching 2 m in thickness. In addition, fragments of marine

fossils are present throughout the section.

Fossil content. In the basal part of the unit, Spiriferidae

gen. indet., Afghanospirifer sp., and Gypospirifer sp. have

been collected in the Triple Junction section. Also, the

brachiopods Marginovatia sp., Rhynchopora sp., and

Afghanospirifer sp. characterize the middle part of the unit

along the Ribat section.

At the top of the Twin Valleys section and in the

Lashkargaz gulley (Fig. 4) (Angiolini et al., 1999) a

brachiopod assemblage with Densepustula cf. losarensis

Angiolini and Brunton in Garzanti et al., 1998, Dowhatania

sulcata Angiolini and Brunton in Angiolini et al., 1999,

Septacamera dowhatensis (Diener, 1915), Alispirifer cf.

middlemissi (Diener, 1915), and Brachythyris sp. In the

Lupsuk Glacier area, Dowhatania sulcata also occurs in

arenaceous limestones.

Environment. This unit deserves more extensive and

detailed field analysis. The onset of the formation seems

to be characterized by a renewal of erosion, coarser

terrigenous input to the basin and shore-face to fore delta

environments. Upwards, the northern sector seems to be

proximal to banks or ramps relatively unaffected by

terrigenous input, allowing the flourishing of crinoid

‘meadows’, whose ossicles were swept in by the currents

to form a mixed arenaceous/carbonate ramp. Occasionally,

hummocky structures were observed, also suggesting

the existence of shoals. To the south, however, bottom

energy rapidly decreased and only sporadic arenitic or

biocalcarenitic episodes occurred. The whole succession

seems to consist of marine deposits, judging by their sparse,

but invariably marine, fossils. In the south frequent

bioturbation is preserved. The abundance of phosphates

and glauconies in several levels seems to suggest deepening

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890

891

892

893

894

895

896

UNCORRECTED PROOFepisodes with incipient starvation and decrease in terrige-

nous input in a more open shelf environment. This

interpretation also seems to be supported by the reduced

thickness of the unit in the north.

Age: Serpukhovian-latest Carboniferous.

3.1.5. The Twin Valleys Member (new name)

To the east of Karambar Lake, the upper part of the

Lupsuk Formation gives way to a cliff-forming carbonate

unit with sharp lateral variations of thickness, which we

distinguish with the rank of member.

The section in the Twin Valleys was firstly described by

Angiolini et al. (1999, p. 6), who, however, did not

formalize a lithostratigraphic subdivision. The member was

mapped in the Twin Valleys section located just northeast

of the Karambar Lake (3685300000N.–7384503600E.), from

which it derives its name (Figs. 4 and 5).

The Twin Valleys Member comprises 30 to 100 m

of massive bioclastic limestones containing bryozoans,

crinoids, recrystallized brachiopods and corals. This

calcareous unit shows sharp lateral variations in thickness

and is capped by a terrigenous unit, comprising black slates,

sandstones and, more rarely, conglomerates, ascribed to

the Gircha Formation.

Below the Twin Valleys Member, the Lupsuk Formation

consists of 40 m of massive, cross-bedded coarse sand-

stones, bioclastic sandstones and conglomerates, overlain

by 30 m of varicoloured calcareous siltstones with large

Fig. 7. Western side of the Yarkhun valley, near Gharil. The quartzarenitic festooned banks of the Permian Gircha Formation overlie the Visean crinoidal

limestone of the Ribat Formation with a weak angular unconformity.

Fig. 6. The Lupsuk-basal Gircha section along the south side of the Ribat valley. The star show the position of the Asselian fauna (CK 1122).

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1005

1006

1007

1008

UNCORRECTED PROOF

crinoids and fine arenites with intercalations of marly

limestones containing bryozoans, corals and brachiopods.

Environment. The Twin Valleys Member represents a

local enrichment of bioclastic sands, accumulated under

tractive load-carrying current conditions. Continuing

upwards the tendency towards higher bioclastic content

and higher energy, already observed in the Ribat and

Lupsuk Formations in the northern part of the Karambar

thrust sheet, is also seen here.

Age: ?Late Carboniferous, lying above a Moscovian or

Kasimovian brachiopod fauna (Angiolini et al., 1999).

3.1.6. The Gircha Formation (Desio, 1963)

The Gircha Formation is widespread throughout the

Northern Karakoram. In the Karambar area three major

lithozones can be identified. From the base upwards they are:

(A) Alternations of well-bedded grey fine arenites

(arkoses) and dark siltstones, occasionally lighter and

contain thicker arenitic packages, up to 6 m thick. Most

important was the finding on the south side of the Ribat

valley, at 4550 m (Fig. 6), of a 2 m-thick siltstone level,

packed with brachiopods (new species of Bandoproductus,

Kiangsiella sp.; two species of Trigonotreta, Spirelytha

petaliformis (Pavlova, 1973), Punctospirifer afghanus

Termier, Termier, de Lapparent and Marin, 1974 and

large dielasmatids) of Asselian age. Thickness 165 m.

(B) Monotonous grey siltstones and dark grey splintery slates

with rare m-thick arenitic intercalations. The slates are

occasionally bioturbated. The thickness exceeds 360 m. The

western tongue of the Karambar Glacier flowing towards the

Karambar Pass covers the remaining part of the section (Fig. 4).

(C) In the core of the syncline between the western

branches of the Karambar Glacier, a unit of thick-bedded

and lighter arenitic beds crop out, over 100 m thick. They

also crop out on the Pakistan–Afghanistan border to the

N of the small lakes west of the Karambar Pass. Some

of them are fine-grained, moderately to well-sorted

subarkose, containing rare granitoid to hypabyssal-as

well as volcanic-rock fragments, and some intrabasinal

pseudomatrix (Dickinson, 1970).

At the present stage of knowledge, the lower boundary of

the Gircha Formation is rather easily defined in the field

where the base of the Gircha is rich in sandstone layers. In

the Karambar area the position of the boundary, where the

basal part consists of alternating arenites and siltstones,

remains uncertain. The change from hybrid quartzarenites,

commonly barren in lithics, to lithic-bearing arkoses,

subarkoses and quartzarenites, with sharply decreasing

intrabasinal grains, is the most reliable distinctive criterion.

3.2. The Lashkargaz/Baroghil Unit

In this tectonic unit, the Carboniferous succession is

represented only by the lower two formations (Fig. 7).

The Margach Formation outcrops on the ridge between

Baroghil Pass and the Vidiakot gulley (Figs. 3 and 8). There

Fig. 8. Geological map of the Baroghil area, from Zanchi et al. (2001). Location of the map in Fig. 3. The measured stratigraphic section is shown on the map, in

the northwest corner.

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1011

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1101

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1104

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1107

1108

1109

1110

1111

1112

1113

1114

1115

1116

1117

1118

1119

1120

UNCORRECTED PROOF

it is represented by about 100 m of highly cleaved blackish

slates and siltstones. In this section other Carboniferous units

are absent; the Gircha Formation rests with a faulted contact

on the Margach Formation. Elsewhere this unit is absent or

poorly exposed due to tectonics and a subdued topography.

Along the Yarkhun Valley around Gharil (Fig. 7, the

Margach Formation is tectonically reduced and the base

of the Ribat Formation consists of dark laminated marls.

These gradually become more calcareous upwards, with

10–30 cm thick layers of dark grey limestones rich in

crinoid ossicles, reaching a maximum thickness of about

50 m. They are directly overlain by the Gircha Formation,

with a low-angle unconformity. This locality has been

already quoted in Gaetani et al. (1996). Most important is

the finding, about 10 m below the top of the Ribat

Formation along the northern river bank, of conodonts

(sample CK1125). Gnathodus semiglaber Bischoff, 1957,

G. delicatus Branson and Mehl, 1938, G. cuneiformis

Mehl and Thompson, 1947, G. typicus Cooper, 1939;

and Siphonodella lobata Branson and Mehl, 1934

were identified. The specimen of G. cuneiformis is a

young form such as that illustrated by Lane et al. (1980,

pl. 10, fig. 7).

3.3. The Lasht Unit

Carboniferous rocks in the Lasht Unit (Fig. 3) are present,

but because of tectonics they can rarely be measured along

complete sections and identifiable fossils cannot be col-

lected. A section near Rukut (near Lasht), mostly made of the

crinoidal limestones of the Ribat Formation, has already been

illustrated briefly in Gaetani et al. (1996, fig. 12). Another

outcrop, some 50 m thick, with Carboniferous brachiopods

was found along the trail to Siru An (Fig. 9). Here, on

the eastern flank of the floodplain (4100 m) where the Siru

Creek is dammed by the lateral moraine of the Siru Glacier,

dark grey marly limestones in 40–70 cm-thick layers

crop out, with sparse crinoids and few productids

and rhynchonellids (CK1139). Brachiopods (Cubacula sp.

ind., a Dictyoclostinae gen. indet., and a Tolmatchoffini gen.

ind.) identified in this unique calcareous horizon within a

mostly terrigenous succession indicate a Kasimovian age

(Late Carboniferous).

3.4. Buattar

Black marly limestones and bioclastic limestones in the

tectonic slices on the hanging wall of the Upper Hunza fault,

contain few Rhipidomella sp. (Angiolini et al., 1999, p.7).

3.5. The Chillinji Unit

To the south of the Reshun-Upper Hunza Fault (Fig. 2),

possible Carboniferous rocks have been identified only in the

Chillinji Unit. In other areas, the calcareous layers seem to be

absent and we were not able to confirm a Carboniferous age

in this anchimetamorphic terrigenous succession. To the

south of Shost and Lashkargaz, the oldest carbonate rocks are

apparently Permian (Gaetani et al., 1996).

The top of the Baroghil Group (Quintavalle et al., 2000),

overlain by the dolostones of the Chilmarabad Formation,

crops out in the core of the Chillinji anticline (Fig. 10). Then

follow hybrid sandstones and heavily recrystallized coral-

tabulate bafflestones, attributed to the Shogram Formation.

Above this coral horizon, about 80 m offine-grained arenites,

hybrid arenites, siltstones and dark slates follow. Near the

base of this terrigenous unit poorly preserved Schuchertellid

Fig. 9. Lasht Unit. The star indicates the location of the dark marly limestones with brachiopods in the Siru Gol.

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1121

1122

1123

1124

1125

1126

1127

1128

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1139

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1191

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1201

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1203

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1219

1220

1221

1222

1223

1224

1225

1226

1227

1228

1229

1230

1231

1232

UNCORRECTED PROOF

brachiopods were collected and tentatively ascribed to the

Carboniferous (Angiolini et al., 1999).

4. Biostratigraphy

Besides two productive conodont samples, the biostrati-

graphy was based on brachiopods. The brachiopod assem-

blages of the Margach, Ribat and Lupsuk Formations have

been analysed by means of the Unitary Associations method

of Guex (1991), to which the reader is referred for a

comprehensive explanation. Different runs have been

processed with the BioGraph Program and BioGraph Tools

(Savary and Guex, 1991; Savary and Guex, 1999), giving

conflicting results. The data-set was modified by adding or

removing localities and eliminating suspect occurrences or

taxa with very low geofrequency until an optimal result with

minimum contradictions was reached.

A first run based on 28 taxa distributed in 7 sections

(Fig. 5) and 5 localities (Lashkargaz, Lale Ribat, and 3

localities (CK588-590-591, Fig. 4) near the Karambar

Pass, yielded 4 Unitary Associations (UAs) with good

superpositional control but rather low lateral reproducibility

(Fig. 11 for details). A second run was then performed

removing the taxa higher than generic level and the species

with very low geofrequency, which only occur in single

samples (such as Rugosochonetes sp. ind., Sajakella sp.

ind., Buxtonioides sp. ind., Marginovatia sp. ind.,

Fig. 10. Geological map of the Chillinji area, from Zanchi et al. (2001). Location of the map in Fig. 3. The stratigraphic section was measured on the northern

bank of the Karambar River.

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1334

1335

1336

1337

1338

1339

1340

1341

1342

1343

1344

UNCORRECTED PROOF

Marginoproductus ribatensis n. sp., Ectochoristites sp. ind.,

Spirifer cf. denis, S. subgrandiformis, Syringothyris sp. ind.,

and Composita sp. ind.). However, species occurring at

several levels, but in a single section were retained, even if

they have a low geofrequency in the sense of Guex (1991, p.

103). This run, processing a data set of 14 taxa distributed in 6

sections (the Karambar Pass section having been removed)

and 5 localities, yelds 3 UAs (see Fig. 12 for details).

These results, however, do not solve the problems of the

numerous indeterminate relationships between the taxa and

of the correlations of the lower part of the Carboniferous

succession, where only 1 UA has been identified. To

address this issue, we added biostratigraphical data taken

from the Carboniferous succession of Central Afghanistan

(Plodowski, 1968, 1970). These data have been summarized

in a composite section derived from the range charts

published by Plodowski (1970, tab. 1, 2, p. 125–132), taking

into consideration only the genera and species shared with

the Karakoram succession. An optimal result was thus

achieved processing 21 taxa distributed in 8 sections and 5

localities (i.e. the 7 sections and 5 localities from Karakoram

plus the composite section from Central Afghanistan), which

yields five UAs (Fig. 13). The correlation table obtained

by this data-set (Fig. 14) clearly displays the correlation

among the fossiliferous level of the E. Lupsuk section

and the Lale Ribat 1, Karambar CK588, and Karambar

CK590 localities. Only the Karambar Pass section is thus left

undetermined.

Fig. 11. Results of the first run (all the sections of Figs. 4 and 5 localities) showing the composition of the Unitary Associations, the reproducibility matrix, the

reproducibility graph with the superposition of the UAs and the number of contradictions between the maximal cliques. This run yields 4 UAs with good

superpositional control. The number of contradictions between the maximal cliques is 52, but this results from pure indetermination as no forbidden generated

subgraphs occur. The lateral reproducibility of UAs 1 and 2 is very low, the UAs being strictly identified only in the Triple Junction section. Furthermore, UA 1

and UA 2 contain species with unclear relationships and very low geofrequency, as a result of insufficient sampling. UA 1 is characterised by the pair of species

Ectochoristites sp. ind.-Sajakella sp. ind. and UA 2 by the pair Anthracospirifer sp. ind.- Permasyrinxinae gen. indet., which only occur in single samples at the

Triple Junction section. UA 3 and UA 4 are both well defined and have a high reproducibility coefficients of 5 and 4 respectively. UA 3 is characterised by the

pair of taxa Afghanospirifer cf. burgutschensis and Gypospirifer sp. ind. and has been detected in four sections and one locality (CK 591, Karambar Lake). UA

4 records the main change in composition, with the first occurrence of Dowhatania sp. ind., Densepustula cf. losarensis, Septacamera dowhatensis and

Alispirifer cf. middlemissi. However, this UA includes also the assemblage KO25 (Syringothyris sp. ind., Buxtonioides sp. ind. and Echinochonchidae gen.

indet.) which has been found only in the Karambar Pass section and that is completely different from the other assemblage. Its inclusion in UA 4 is probably an

artifact due to the very restricted occurrence of the KO25 assemblage (very low geofrequency).

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Based on the quantitative biostratigraphic analysis of the

brachiopod assemblages, four biozones have been detected,

all separated by barren intervals:

1. The Parallelora aff. subsuavis-Rhipidomella sp.1 Bio-

zone: correponds to UA’ 1 and comprise the index

species and a species of Rhynchopora, which however

ranges up to the third biozone. This biozone occurs only

in the Ribat section, apart from the composite section

from Central Afghanistan.

2. The Spirifer pentagonoides-Martiniopsis grandiformis

Biozone: corresponds to UA’ 2 and 3 in the Ribat

Formation in the East Lupsuk section and at the Lale

Ribat 1, Karambar CK588, and Karambar CK590

localities. It is also recognizable in Central Afghanistan.

In addition to the index species, it includes Margin-

oproductus ribatensis n. sp., Spirifer cf. denis, S.

subgrandiformis, Syringothyris sp. ind., and Composita

sp. ind. and the two species of Rhipidomella.

3. The Afghanospirifer cf. burgutschensis-Gypospirifer sp. ind.

Biozone: also include Rugosochonetes sp. ind., Marginovatia

sp. ind., Choristites sp. ind., Rhipidomella sp. ind. 2,

Syringothyris sp. ind. and Composita sp. ind. This biozone

extends laterally in 4 sections out of 8 in the Karakoram and in

the composite section for Central Afghanistan. The biozone

corresponds to UA’ 4 and mostly characterizes the upper part

of the Ribat Formation, but it also occurs in the Lupsuk

Formation (Ribat section), indicating that it is not ecologically

controlled.

4. The Densepustula cf. losarensis-Septacamera dowhatensis

Biozone: also includes Dowhatania sulcata, Brachythyris sp.

ind., and Alispirifer cf. middlemissi. This biozone (UA’ 5)

occurs in two sections, in the Lupsuk Formation and in its

Twin Valleys Member, and at the Lashkargaz locality.

The correlation of these biozones is shown on the

sections in Fig. 5, which are also independently correlated

by means of lithological markers.

It is important to notice that the biozones and the major

faunal changes (Fig. 15) do not strictly correspond to

lithological changes and are probably not ecologically

controlled. For instance, the Afghanospirifer cf. bur-

gutschensis-Gypospirifer sp. ind. Biozone occurs both at

the top of the Ribat Formation and in the Lupsuk Formation,

Fig. 12. Results of the second run (14 taxa distributed in all the sections of Fig. 4, except for the Karambar Pass section, and 5 localities) showing the

composition of the Unitary Associations, the reproducibility matrix, the reproducibility graph with the superposition of the UAs and the number of

contradictions between the maximal cliques. This run yields 3 UA with good superpositional control and only 8 contradictions resulting from pure

indetermination, as no forbidden generated subgraphs have been detected. The reproducibility of UA 1 is again low, but it is a result of insufficient sampling,

whereas that of UA 3 ðR ¼ 3Þ and especially UA 2 ðR ¼ 5Þ is good. UA 1 is characterised by the pair of species Parallelora aff. subsuavis-Rhipidomella sp.

ind.; UA 2 by Afghanospirifer cf. burgutschensis-Gypospirifer sp. ind. (as UA 3 of the first run) and UA 3 by the pair Densepustula cf. losarensis-Septacamera

dowhatensis (as UA 4 in the first run).

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UNCORRECTED PROOF

and it crosses the boundary between the two formations in the

Triple Junction section (Fig. 5).

5. Chronostratigraphy

We have no age constraints on the lower part of the

Margach Formation, which could be uppermost Devonian:

Receptaculites (CK1066) is a wide-ranging genus

(Hubmann, pers. comm., 2003), and no fossils have

been discovered in the second lithozone. Instead, the

third lithozone is characterized by the Parallelora aff.

subsuavis-Rhipidomella sp. 1 Biozone, which, according to

the distribution of the genera Parallelora and Rhynchopora,

should span the earliest middle Tournaisian. In fact, the

genus Parallelora is late Fammenian–early Tournaisian

and it is followed by a stratigraphic interval devoid of

similar spiriferids before the first appearance of the genus

Spirifer in the middle Tournaisian (Carter, 1992). The

species subsuavis has been reported from Etroeungtian

crinoidal limestones and sandstones of Chuschk-Kol-Tal

(Bukhara-e-Nawar, Central Afghanistan) by Plodowski

(1970). More specifically, the associated Central Afghani-

stan conodonts Polygnathus inornatus, P. symmetricus,

Fig. 13. Results of the last run (21 taxa distributed in all the sections of Figs. 4 and 5 localities and the Central Afghanistan composite section.) showing the

composition of the Unitary Associations, the reproducibility matrix, the reproducibility graph with the superposition of the UAs and the number of

contradictions between the maximal cliques. The number of forbidden generated subgraphs and the list of Z’4 circuits—each with one superpositional

relationship known—are also shown. This run yelds five UAs (here named UA’), with good superpositional control and significant lateral reproducibility,

except for UA’ 3, which could be merged with UA’ 2 as their inter-UA distance is the lowest (0.83; calculated according to Guex, 1991, p. 166–167). The

number of contradictions between the maximal cliques is 8, but they can be solved by adding virtual co-existences, as no forbidden configurations of length 3

and 4 occur, except for 6 circuits of length 4 (Z’4). For instance, the chronological sequence of A. cf. burgutschensis above M. grandiformis and S.

pentagonoides implies that Syringothyris sp. ind. and Rhipidomella sp. 2 should virtually co-exist.

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UNCORRECTED PROOF

Bispathodus spinulicostatus, B. stabilis-listed in Plodowski

(1970, p. 12–13)-indicate the mid-Tournaisian Early

crenulata Zone, according to the range charts of Mawson

and Talent (1999).

The overlying Ribat Formation is well constrained

between the late Tournaisian and the Bashkirian, although

its top is diachronous and does not always reach the

Bashkirian (i.e. in the E. Lupsuk section).

The age of the base of the Ribat Formation is constrained

by the conodont association collected in the Ribat section

(CK1088: Gnathodus pseudosemiglaber Thompson and

Fellow, 1970, Gnathodus typicus morph. 2 Cooper, 1939,

and Polygnathus bischoffi Rhodes, Austin and Ziegler,

1969). Using the ranges given by Lane et al. (1980, p. 121),

the age of this fauna must be the upper half of the

anchoralis-latus Zone as G. pseudosemiglaber makes its

first appearance at the middle of the anchoralis-latus Zone

and Gnathodus typicus morph. 2 disappears at the

anchoralis-latus Zone/texanus Zone boundary. Therefore

the age is Late Tournaisian.

Another conodont sample (CK1125), from the Lashkar-

gaz-Baroghil Unit, contains a conodont assemblage domi-

nated by Gnathodus species. According to the range chart of

Lane et al. (1980), the age of this fauna is from just above

the base of the typicus Zone to the mid anchoralis-latus

Zone, as G. cuneiformis does not appear until just above the

base of the typicus Zone and the highest occurrence of G.

delicatus is mid-anchoralis-latus Zone. Therefore this

sample is also Late Tournaisian in age, but slightly younger

than the previous conodont sample.

In the middle part of the unit (sample KO14–KO15,

Triple Junction section) where marls are more frequently

intercalated in the limestone beds, the brachiopods

Sajakella sp. ind., Anthracospirifer sp. ind., and Ectochor-

istites were collected. They were not considered in the

biostratigraphic analysis above, because of their very low

geofrequency; however, they suggest a probable Serpu-

khovian age for these beds, according to the combined

occurrence of the three genera (the former two spanning

the Serpukhovian–Bashkirian time interval and the latter

the Tournaisian-?‘Namurian’).

In the upper part of the unit, in several measured sections

and isolated localities, the brachiopods of the Afghanospir-

ifer cf. burgutschensis-Gypospirifer sp. ind. Biozone

indicate a Bashkirian age. In fact, the genus Afghanospirifer

occurs in the late Serpukhovian–early Bashkirian of Central

Afghanistan (SW Dasht-e-Nawar); Marginovatia ranges

from the middle Visean to the Bashkirian. The same age

assignment was already suggested by Angiolini et al. (1999).

Other age constraints for the Ribat Formation come

from the E. Lupsuk section, where the Spirifer pentago-

noides-Martiniopsis grandiformis Biozone was sampled

near the top of the formation, indicating a Visean age

according to the distribution of the spiriferid species, which

in Central Afghanistan are associated with Gnathodus

texanus Roundy (Plodowski, 1970). This is confirmed by

the concurrence of the genus Marginoproductus, known

from the Visean of South China. On the other hand, in the

Karambar Pass section (Fig. 5), a low geofrequency

brachiopod assemblage has been collected in the upper-

most part of the formation. This suggests a Bashkirian

Fig. 14. Correlation table of the section and localities processed in the last run (Fig. 13). The numbers refer to the UA’s. Worthy of note is that the fossiliferous

level of the E Lupsuk section can be attributed to the new UA’ 2 (merged with UA’ 3) and correlated to the Lale Ribat 1, Karambar CK588, and Karambar

CK590 localities, whereas only the Karambar Pass section is left undetermined. The relationships of these UA’s with those obtained in the previous run and

displayed in Fig. 12 are as follows: the newly obtained UA’ 1 corresponds to the previous UA1, UA’ 4 corresponds to UA 2 and UA’ 5 corresponds to UA 3,

whereas the newly detected UA’ 2 þ UA’ 3 is an intermediate unitary association between the former UA 1 and UA 2.

Fig. 15. Graphs showing the species diversity and the rates of faunal

turnover calculated from the results of Fig. 13. There is a nearly constant

diversification from UA 1 to UA 3, followed by a reverse trend to UA 4 and

then by a constant rate between diversification and extinctions to UA 5,

which has the maximum inter-UA distance to UA 4 ðd ¼ 2Þ:

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UNCORRECTED PROOF

age based on the co-occurrence of the genera Buxtonioides

and Syringothyris, the latter similar to Syringothyris

sp. 2 described by Plodowski (1970) from the late

Serpukhovian-early Bashkirian of Burgutsch-Tal (13 km

SW Bukhara-e-Nawar, Central Afghanistan).

The Lupsuk Formation in part interfingers with the Ribat

Formation (Fig. 5) and its diachronous base ranges from the

Serpukhovian to the Upper Carboniferous. This formation is

characterized, at its base in the Triple Junction section and

in its lower part in the Ribat section, by the Afghanospirifer

cf. burgutschensis-Gypospirifer sp. ind. Biozone,

suggesting a Bashkirian age for its lower part. However,

its base is probably older (Serpukhovian) in the Ribat and

E. Lupsuk sections.

In the middle part of the unit in the west Lupsuk

section and at its top in the Twin Valleys section-below

the Twin Valleys Member-, the Densepustula cf.

losarensis-Septacamera dowhatensis Biozone indicates a

Moscovian-Kasimovian age (Angiolini et al., 1999).

The age of the Twin Valleys Member is poorly

constrained, but it overlies the Densepustula cf. losaren-

sis-Septacamera dowhatensis Biozone and extends up to the

terrigenous Gircha Formation. This unit should therefore be

of Late Carboniferous age.

The Carboniferous succession is covered by the shales

and quartzose sandstones of the Gircha Formation, includ-

ing a characteristic brachiopod assemblage about 133 m

from its base (Figs. 5 and 6), with Bandoproductus sp.,

Kiangsiella sp., two species of Trigonotreta, Spirelytha

petaliformis (Pavlova, 1973), Punctospirifer afghanus

Termier, Termier, de Lapparent and Marin, 1974 and

large dielasmatids indicating an Asselian age.

6. Sandstone petrography

6.1. Materials and methods

Bulk petrography of sandstones from the Karambar and

Baroghil/Lashkargaz units was analyzed quantitatively

through point-counting of 300 points on standard

25 £ 40 mm thin sections, previously stained with red

alizarine. Detrital modes were recalculated following the

Gazzi–Dickinson method: standard descriptive parametres

are those of Dickinson (1970) ðQ; F; L; C=Q; P=F; V=LÞ and

Zuffa (1980) (NCE, CE, NCI, CI). QFL modes allow

interpretation of sand provenance (Dickinson, 1985),

whereas parametres by Zuffa (1980) are specific for

classifying hybrid arenites and allow correct interpretation

of carbonate and/or intrabasinal grains. Sandstone nomen-

clature relies instead on the widely understood QFR modes

(Folk, 1974).

Grain size and sorting of all samples were semiquantita-

tively evaluated in thin section following the method

described in detail in Sciunnach (1996). A total of 29

samples was analysed, and the results are briefly summarised

in this section (Fig. 16). Unfortunately, most of the sandstone

samples from the Margach type-section were lost in the mail.

6.2. The Margach Formation

Lithozone B ðn ¼ 2Þ: Moderately to well-sorted, fine-

grained subarkoses very rich in detrital mica. Mostly

untwinned plagioclase prevails over K-feldspar ðP=F ¼

0:9Þ; and rock fragments are negligible. White mica and

‘leached’ biotite flakes make up to 5% of rock volume, but

also rutile, opaques, zircon and tourmaline are abundant.

Intrabasinal grains are limited to scarce muddy pseudoma-

trix (Dickinson, 1970).

Lithozone C ðn ¼ 2Þ: Moderately to poorly-sorted, fine to

medium-grained pure quartzarenites and hybrid encrinites.

Quartz is mostly monocrystalline, and only rare plagioclase,

volcanic rock fragments and undetermined ‘dirty’ lithics are

observed. Heavy minerals are limited to the ultrastable

zircon–tourmaline–rutile (ZTR) assemblage and some

opaques. Among bioclasts, echinoderm plates prevail over

brachiopod valves, bryozoans and ostracods.

6.3. The Ribat Formation

Moderately to well-sorted, medium-grained hybrid

quartzarenites and sandy encrinites are found only at the

very base of this limestone-dominated formation ðn ¼ 2Þ:

Polycrystalline quartz slightly increases ðC=Q ¼ 0:030Þ

with respect to the underlying Margach Formation

ðC=Q ¼ 0:015Þ; possibly also as an effect of increased

grain size. A few plagioclase grains, both twinned and

untwinned, were counted; K-feldspar is absent, and rock

fragments are negligible. Oversized phosphate grains

(sandy, bioclastic and pure collophanites following the

classification of Assereto, 1969) are widespread: among

bioclasts, echinoderm plates prevail over brachiopod valves

and spines, as well as minor bryozoan colonies.

6.4. The Lupsuk Formation

Mostly well-sorted subarkoses to feldspathic quartzar-

enites, locally containing plenty of glauconitic pellets and

pseudomatrix (‘subarkosic petrofacies’), alternate with

moderately to very poorly-sorted hybrid quartzarenites,

commonly bioclastic, but also containing traces of phos-

phate (‘hybrid petrofacies’).

Subarkosic petrofacies ðn ¼ 8Þ:Grain size of the analysed

samples ranges from fine to medium. Among feldspars,

twinned plagioclase, chessboard albite and microcline are

abundant at definite stratigraphic intervals; hypabyssal,

volcanic and undetermined rock fragments are also common.

The heavy mineral suites are dominated by the ZTR

assemblage, with minor apatite and opaques. Intrabasinal

grains are limited to a glauconitic interval in the Lupsuk

section, where silicified bryozoans and brachiopod valves,

their endopunctae filled with glaucony, also occur; negligible

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UNCORRECTED PROOF

muddy pseudomatrix and echinoid plates are recorded in the

Ribat section.

Hybrid petrofacies ðn ¼ 7Þ: Grain size of the analysed

samples ranges from very fine to very coarse. Embayed

quartz occurs only concurrent with the maximum

abundance of volcanic lithics, hinting at a volcanic episode

that is documented also by interlayered tuffs; polycrystalline

quartz notably increases with respect to the underlying

units, the C=Q ratio averaging 0.1. Rare feldspar (mostly

untwinned plagioclase and chessboard albite) and granitoid

to volcanic grains occur. Heavy minerals include the ZTR

assemblage, as well as some white mica and sphene. Both

carbonate and non-carbonate intrabasinal grains are

abundant: CI grains document rich faunal assemblages

including echinoderms, brachiopods, pelecypods, gastro-

pods, bryozoans and foraminifers, whereas NCI grains

include phosphate (silty to sandy collophanites after

Assereto, 1969), silty to pure ferricrete chips, oversized

chert (silcrete?) and mudclasts.

6.5. The Gircha Formation

Mostly moderately to well-sorted arkoses, subarkoses

and quartzarenites; grain size of the analysed samples

ðn ¼ 8Þ ranges from very fine ðF ¼ 3:50Þ to coarse

ðF ¼ 0:50Þ: Embayed quartz is abundant only in one

interval, about 40 m above the formational base at Ribat,

where abundant non-carbonate, intrabasinal matrix and

sparse terrigenous to metamorphic lithics are also recorded.

This peculiar interval is thus best ascribed to a ravinement

surface (possibly an Incised Valley Fill?), and quartz

embayments to chemical leaching in soils, rather than to

an episode of volcanic activity. Both twinned and

untwinned plagioclase, K-feldspar and chessboard albite

are common, as are the hypabyssal lithics: granitoid rock

fragments are locally abundant even in medium-grained

sandstones. Volcanic and undetermined ‘dirty’ rock frag-

ments are common, although they account for at maximum

1% of rock volume. Heavy minerals are mostly limited to

the ZTR assemblage; a few apatite and white mica grains

occur in only one sample. Intrabasinal grains are rare and

mostly consist of oversized chert (silcrete?) and muddy

pseudomatrix: only in the Twin Valleys section abundant

bioclasts include echinoderm plates, brachiopod and

pelecypod valves, bryozoan colonies and foraminifer tests.

6.6. Sand provenance and compositional trends

In the studied sample population, correlation of detrital

modes with textural parametres is generally poor; coarser

Fig. 16. QtFL (Dickinson, 1985) and NCE-NCI-CI (Zuffa, 1980) triangular plots for the 29 analysed arenite samples. Textural data (grain size, sorting) are

available upon request.

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UNCORRECTED PROOF

sandstones tend to be more quartzose and finer sandstones

tend to be more feldspathic (Odom et al., 1976), but this

accounts for only 40% of the variations of individual Q; F

parametres and only for one third of their concurrent

variation. Also higher C=Q in coarser sandstones and worse

sorting in CI-rich arenites are obvious characters; however,

the corresponding correlation coefficients are rather low

(around 0.8). Thus, it can be stated that composition of

the analysed Upper Devonian? to Lower Permian sand-

stones provides useful hints for unravelling the tectonic and

magmatic evolution of the Karakoram, because most

petrographic signals have to be interpreted as provenance

signals.

Fine-grained subarkoses, notably enriched in detrital

mica flakes, of the Margach Formation—Lithozone B

(Upper Devonian?) suggest provenance of prevailing first-

cycle detritus from uplifted metamorphic rocks.

The overlying Carboniferous succession (Lithozone C of

the Margach Formation, Ribat and Lupsuk Formations) is

dominated by up to coarse-grained, hybrid quartzarenites

interlayered with shelf limestones and marls. Intrabasinal

grains, both carbonate (bioclasts) and non-carbonate

(phosphorite, glaucony, silcrete, ferricrete), are highly

variable in abundance depending on the depositional setting,

so that subarkoses to pure orthoquartzites alternate with

sandy encrinites. A major sequence boundary corresponds

to a ravine-eroded surface at the top of the Margach

Formation: the only arenite samples from the Ribat

Formation were obtained at its very base, from shelf margin

system tract deposits (just 15 m thick) sharply overlain by

transgressive crinoidal limestones.

In the Lupsuk Formation the hybrid quartzarenite facies

alternates with subarkoses, strongly condensed at Lupsuk,

where they contain abundant glauconite and are considered

as largely Bashkirian in age. At Ribat the subarkoses seem

to span a longer period, Bashkirian to Moscovian, and

contain chessboard albite, volcanic rock fragments and

microcline pointing to a stage of active volcanism coupled

with unroofing of granitoid basement rocks. As a whole,

feeble petrographic signals preserved in both the hybrid

quartzarenites and the interlayered subarkoses actually point

to a major rifting stage, during which portions of the former

passive margin experienced differential drowning and local

sediment starvation. Ongoing syn-rift volcanism and

unroofing of basement rocks exposed on the uplifted rift

shoulder are suggested by small amounts of unstable grains,

but volcanism is also documented by interbedded micro-

lithic spilites.

In all sections, the syn-rift succession is capped by fossil-

poor arkoses to quartzarenites (‘typical’ petrofacies of the

Gircha Formation as described in Gaetani et al., 1995).

Slightly, but steadily increased abundance of K-feldspar and

lithic grains in these sandstones hint at continued unroofing

of a mature rift shoulder, basin inversion and local erosion

of the syn-rift succession.

7. Geodynamic evolution during the Carboniferous:

discussion and conclusions

It is probably too ambitious at this reconnaissance stage of

our field work to construct the geohistory of the Northern

Karakoram. Although a palinspastic restoration of the

analysed thrust sheets has not yet been performed, some

general remarks drawn from our data are noteworthy. The

present curvature of the western part of Karakoram may be

quite recent (Hildebrand et al., 2000), and can be partially

related to NE–SW oriented left-lateral strike-slip faults,

displacing an originally E–W trending belt. These fault

systems are evident along the Yarkhun Valley from Khan

Khun to Lasht. The Lasht Unit shows S-vergent structures as

the Baroghil-Lashkargaz Unit. The Karambar Unit has a

complex structural pattern suggesting westward motion

above the Baroghil-Lashkargaz Unit, and minor northward

motion in its eastern part. The Chillinji Unit and the tectonic

slices along the Upper Hunza Fault show an important

northward translation. This suggests that the Lasht, Baroghil-

Lashkargaz and Karambar Units were probably originally

lying along a transect, oriented approximately E–W in

origin. The Chillinji area was in a more southern position. To

the north of these units, in present geographical coordinates,

additional unknown domains should be present on the

Whakan side. Finally, the Tash Kupruk Unit should have

been located further north. We assume also that the

metasediments of the Axial Unit (Gaetani et al., 1996)

were lying to the south of the previous units. The supposed

development of the Carboniferous rocks along this belt is

summarized in Fig. 17.

It appears that the succession increases in thickness and it

is most complete from south to north in present coordinates.

Apparently no Carboniferous rocks are preserved in the

Axial Zone and the Permian arenites of the Gircha lie

directly above the slates of the Lower Palaeozoic Baroghil

Group (Gaetani et al., 1996). In the Chillinji Zone, about

215 m of dolostones, hybrid arenites and coral bafflestones

(Chilmarabad and Shogram Formations-Devonian) are

interposed between the slates of the Baroghil Group and

the terrigenous succession, which possibly contains also

some Carboniferous sandstones and siltstones. In the Lasht

(besides the single outcrop along the SiruGol

with Upper Carboniferous brachiopods, Fig. 9) and

Baroghil-Lashkargaz thrust sheets only the lowermost part

of the Carboniferous succession is preserved and is

unconformably overlain by the Gircha Formation. The

succession younger than late Tournaisian, if it was ever

deposited, was later eroded. Only in the Karambar thrust

sheet does the succession exceed 1000 m in thickness and

contain also Upper Carboniferous rocks.

We interpret this transect as a part of the continental

margin of the Karakoram Terrane, facing a deeper basin

mostly filled by the Wakhan/Misgar Slates.

The first step in the evolution of the margin could

possibly be traced back to the Devonian, when the peritidal

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UNCORRECTED PROOFplatform of the Chimarabad Formation emerged and was

covered by the conglomerates at the base of the Shogram

Formation. Precise timing has not yet been firmly defined

(mid-Givetian?). The Shogram Formation may reach 180 to

250 m in thickness, with a sedimentation rate (not decom-

pacted) of 11 to 15 m/My. Upwards, terrigenous input

becomes abundant, but is usually fine grained, with intervals

of coarser arenite. Particularly the lithozone B of the

Margach Formation (Late Devonian?), deposited in open

shelf conditions on the passive continental margin, but

seemingly accompanied by block-faulting and relative

tectonic uplift of metamorphic rocks in the source area,

can be related to the onset of rifting, with a sedimentation

rate which may reach 30 m/My. The widespread occurrence

of the transgressive shelf limestones and marls, particularly

rich in crinoidal ossicles, seals this initial rifting event.

The foreset/topset couples observed at the base of the

Ribat Formation point to a northwards aggradation of the

shelf. Also to be noted is the more terrigenous character of

the southern Karambar sections, in comparison to the more

carbonate rich succession to the north. However, these latter

are richer in non-carbonate intrabasinal grains, suggesting

that the terrigenous input reduced northwards and the shelf

was open to deeper water influx and sedimentary

starvation. Instead, subarkoses to pure orthoquartzites

were intermittently laid on the shelf. The sedimentation

rate decreases to around 10 m/My.

The reduced thickness of the Lupsuk Formation around

the Lupsuk glacier, where arenites contain abundant

glauconite, indicates that the previous paleogeographic

position (edge of the shelf?) was still persistent in

Serpukhovian/Bashkirian to Moscovian/Kasimovian times.

To the south, the arenites document active volcanism, also

recorded by interbedded microlithic spilites, coupled with

unroofing of granitoid basement rocks. In addition to the

petrographic evidence, the erosion and gentle tilting of the

Carboniferous succession in the Baroghil-Lashkargaz Unit

and the general trend along the transect, actually point to

a major rifting stage, where rift shoulders were uplifted and

eroded and the unroofing of basement rocks was continuing.

The sedimentation rate slightly increases to 15 m/My.

The generally widespread occurrence of the Gircha

Formation, even if its onset was gradual, seems to

definitively seal the previous syn-rift succession. Therefore,

we propose to draw the break-up unconformity within the

lower part of the Gircha Formation (?latest Carboniferous-

Asselian in age). (Figs. 17 and 18).

Only much more field work will allow a more accurate

interpretation of the rift succession. The major inconsis-

tency in interpreting the Carboniferous succession in term of

rift sequence is the apparently low sedimentation rate, an

unusual character in a rift sequence. We do not exclude the

presence of as yet unidentified gaps.

The data and interpretations of Zanchi et al. (2000) and

of the present paper refine the general geodynamic picture

of Gaetani (1997). The evidence of mantle peridotites

emplaced between the Karakoram and East Hindu Kush and

deformed in pre-Cretaceous times strengthens the general

Fig. 17. Stratigraphic scheme along the transect from the Karambar unit to the Axial metasediments. To be noted the unusual occurrence of Kasimovian

sediments in the Lasht Unit at Siru Gol locality (Fig. 9).

Fig. 18. Cartoon of the geometric relationships below the break-up

unconformity sealed by the Gircha Formation.

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UNCORRECTED PROOF

picture of a block fragmentation along the Northern

Gondwanan margin, with thinned crust and hypothetical

short living oceans between blocks (Leven, 1995).

The geodynamic evolution observed in the North

Karakoram Terrane adds evidence that extensional

movements, starting from the Middle/Late Devonian,

widely involved the Perigondwana fringe from south

East Asia (Metcalfe, 1996 and refs. therein), the Central

Himalaya (Garzanti, 1999 and refs. therein), and the

western Himalaya (Draganits, 2002; Singh, 2002). Should

we interpret the initial spreading of the Palaeo-Tethys

(sensu Metcalfe) amongst Chinese Blocks, propagating to

the west as far as the Karakoram and Himalaya, as

incipient rifting?

The major rift stage recorded by the North Karakoram

successions (Figs. 17 and 18) is in agreement with

subsurface and field evidence from Oman (Al-Belushi

et al., 1996) and from the Himalaya (Vannay, 1993;

Garzanti et al., 1996a; Garzanti and Sciunnach, 1997),

indicating that the Neo-Tethys rifting began as early as the

Early Carboniferous.

Finally, the interpretation of the Gircha Formation as

the unit that blankets the rifted margin within the

lowermost Permian is roughly in agreement with recent

data on the earlier spreading of the Neo-Tethys, from

Oman (Angiolini et al., 2001; Angiolini et al., 2003) to the

Himalaya (Garzanti et al., 1994; Garzanti et al., 1996b;

Garzanti et al., 1999) and SE Asia (Shi and Archbold,

1998) in the Early Permian. In the Karakoram this break-up

unconformity seems to be earlier, possibly because the

terrane was on the northern side of the Neo-Tethys and

already involved in earlier rifting events amongst the

Cimmerian blocks.

In conclusion, the Carboniferous succession records

the passive margin evolution of the Northern Karakoram

Terrane. A first episode of rifting is identified in the mid-

Givetian/Late Devonian, raising the question as to

whether the ocean drifting occurring at that time amongst

the Chinese Blocks (Metcalfe, 1996) was extended as

incipient rifting as far as the Karakoram. The early

rifting episodes continued in the Early Carboniferous,

evolving to the syn-rift stages during the Late Carbon-

iferous. The latest Carboniferous-earliest Permian basal

part of the Gircha Formation is considered to have been

deposited above the break-up unconformity, linked to an

early drifting event in the sea-way bordering the

Karakoram.

Acknowledgements

The 3 expeditions were funded by several grants to

M. Gaetani from the Italian Ministry for Foreign Affairs,

within a cultural agreement with the Government of

Pakistan. We are deeply indebted with Dr H. Gauhar,

Director of the Geological Survey of Pakistan, for

the continuous support to our investigations in the field.

Guides, cooks and porters of the Adventure Tours Pakistan

travel agency substantially helped in carrying out field-

activity in the high mountains.

The paper was Reviewed by A.H.F. Robertson

(Edinburgh) and by C. Winkler-Prins (Leiden). Both and

the Deputy-Editor, A.J. Barber, are deeply thanked for

important improvements to the paper.

Appendix A

The Fig. A1 illustrates the most significant conodont

specimens recovered from the Rabit Formation.

Appendix B

Selected palaeontological descriptions (L. Angiolini,

H. Brunton, G. Olivini)

All the described specimens are housed in the Palaeonto-

logical Museum of the University of Milan, Italy (MPUM

numbers). The systematic study follows the classifications of

Racheboeuf in Williams et al. (2000) for the chonetids, of

Brunton et al. in Williams et al. (2000) for the productids, of

Williams and Harper in Williams et al. (2000) for the orthids,

of Savage (1996) for the rhynchonellids, and of Carter et al.

(1994) for the spiriferids.

Family Rugosochonetidae Muir-Wood, 1962

Subfamily Rugosochonetinae Muir-Wood, 1962

Genus Rugosochonetes Sokolskaya, 1950

Type-species: Orthis hardrensis Phillips, 1841

Rugosochonetes sp. ind.

Material—2 ventral valve internal molds: MPUM9036

(CK1093-1,-2); 1 fragment of ventral valve: MPUM9037

(CK1093-3). Lupsuk Formation, Ribat section, Bashkirian.

Remarks—These slightly convex, finely capillate ventral

valves with no ventral sulcus and internally characterised by

a myophragm and coarse endospines indicates assignment

to Rugosochonetes.

Family Productellidae Schuchert, 1929

Subfamily Plicatiferinae Muir-Wood and Cooper, 1960

Tribe Yakovleviini Waterhouse, 1975

Genus Sajakella Nasikanova in Sarycheva, 1968

Type-species: Sajakella formosa Nasikanova, 1968

Sajakella sp. ind. (Fig. B1(1–2))

Material—1 articulated shell: MPUM9038 (KO14-f); 3

ventral valves: MPUM9039 (KO14 b,d), MPUM9040

(KO14e). Ribat Formation, Triple Junction section. Serpu-

khovian.

Remarks—Four valves characterized by a subovate to

subquadrate outline, a rugose and ribbed visceral disc

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UNCORRECTED PROOF

Fig. A1. Conodonts from the Ribat Formation. Specimens from CK 1089, housed in the Palaeontological Museum of the University of Milano. Scale bar

200 mm. 19/1a,1b, 2 Gnathodus typicus morph. 2 Cooper, 1939; respectively upper and lateral view. 19/3a,3b, 4 Polynatus bischoffi Rhodes, Austin and

Ziegler, 1969, respectively upper and lateral views. 19/5a,5b, 6 Gnathodus pseudosemiglaber Thompson and Fellow, 1970, respectively upper and lateral view.

Specimens from CK1125, housed in the Australian Museum, Sydney with the number prefixed AMF. The scale bar represents 100ıo. 19/7a,7b Gnathodus sp.

cf. G. delicatus Branson and Mehl, 1938. Upper and lateral views of AMF 121957. 19/8, 10 Gnathodus semiglaber Bischoff, 1957. Upper views of AMF

121958 and AMF 121959, respectively. 19/9 Gnathodus delicatus Branson and Mehl, 1938. Upper view of AMF 121960. 19/11 Gnathodus cuneiformis Mehl

and Thompson, 1947. Upper view of AMF 121961. 19/12-15 Gnathodus typicus Cooper, 1939. 12, 13: lateral and upper views of AMF 121962, respectively;

14, 15: lateral and upper views of AMF 121963, respectively. Non-platform elements of Gnathodus: 19/16 a M element; 19/17 a Sc element; 19/18 a ?Sa

element; 19/19 a Sb element.

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UNCORRECTED PROOF

and a finely ribbed trail have been placed in the upper

Visean- Bashkirian genus Sajakella. The ventral valve

shows a median sulcus, deeper anteriorly on the visceral

disc, and spines have been detected only at the cardinal

margin.

Family Productidae Gray, 1840

Subfamily Productinae Gray, 1840

Tribe Productini Gray, 1840

Genus Dowhatania Waterhouse in Waterhouse and

Gupta, 1979

Fig. B1. (All £ 1) (1) Sajakella sp. ind. Specimen MPUM9038 (KO14f). Ventral view of an articulated shell. (2) Sajakella sp. ind. Specimen MPUM9040

(KO14e). Ventral valve. (3) Dowhatania sulcata Angiolini and Brunton in Angiolini et al., 1999. Specimen MPUM9041 (CK1110b). Ventral valve. (4)

Marginoproductus ribatensis n. sp. Specimen MPUM9043 (KO20t), holotype. Ventral valve. (5) Marginoproductus ribatensis n. sp. Specimen MPUM9044

(KO20j). Ventral valve. (6) Marginoproductus ribatensis n. sp. Specimen MPUM9045 (KO20h). Ventral valve. (7) Marginoproductus ribatensis n. sp.

Specimen MPUM9046 (KO20z). Ventral valve. (8–9) Buxtonioides sp. ind. Specimen MPUM9095 (KO25-3g). Lateral and ventral view of a ventral valve.

(10) Marginovatia sp. ind. Specimen MPUM9050 (CK1094-1). Ventral view of an internal mold of an articulated shell. (11) Marginovatia sp. ind. Specimen

MPUM9051 (CK1093-6). Ventral valve. (12) Marginovatia sp. ind. Specimen MPUM9052 (CK1094-2). Dorsal valve external mold. (13) Cubacula sp. ind.

Specimen MPUM9054 (CK1139d). Ventral valve. (14) Rhynchopora sp. ind. Specimen MPUM9059 (CK1074-9). Dorsal valve. (15) Rhipidomella sp.1.

Specimen MPUM9055 (CK1074-2). Ventral valve and fragments. (16) Spirifer pentagonoides Plodowski, 1968. Specimen MPUM9066 (KO20-10). Ventral

valve. (17) Martiniopsis grandiformis (Plodowski, 1968). Specimen MPUM9064 (CK1103c). Ventral valve. (18) Spirifer pentagonoides Plodowski, 1968.

Specimen MPUM9067 (KO20-6). Ventral valve. (19) Spirifer pentagonoides Plodowski, 1968. Specimen MPUM9068 (KO20-16). Partially decorticated

ventral valve showing dental plates. (20) Spirifer pentagonoides Plodowski, 1968. Specimen MPUM9069 (KO20-19). Dorsal valve. (21) Spirifer

pentagonoides Plodowski, 1968. Specimen MPUM9070 (KO20-21). Dorsal valve.

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Type-species: Productus dowhatensis Diener, 1915

Dowhatania sulcata Angiolini and Brunton in Angio-

lini et al., 1999 (Fig. B1(3))

1999 Dowhatania sulcata Angiolini and Brunton in

Angiolini et al., p. 11, pl. 1, figs. 1–10

Material—5 ventral valves: MPUM9041 (CK1110b),

MPUM9042 (CK1109A, CK1110a, c, d). Lupsuk For-

mation, W. Lupsuk section. Moscovian–Kasimovian.

Remarks—Dowhatania sulcata Angiolini and Brunton

in Angiolini et al., 1999 is characterized by its relatively

small size, posteriorly thickened shell, wide and sharp ears,

and deep ventral sulcus.

Tribe Retariini Muir-Wood and Cooper, 1960

Genus Marginoproductus Tan Zhen Xiu, 1986

Type-species: Marginoproductus hunanensis Tan Zhen

Xiu, 1986

Marginoproductus ribatensis n. sp. (Fig. B1(4–7))

Material—20 ventral valves: MPUM9043 (KO20t),

MPUM9044 (KO20j), MPUM9045 (KO20h), MPUM9046

(KO20z), MPUM9047 (KO20KO20c, g, l–n, p–r, s, u–v,

w, x, y, b1, b2, g); 4 dorsal valves: MPUM9048 (KO20d-f,

a). Ribat Formation, Laleribat 1, right topographical side of

Lale Ribat Valley, near the village. Visean.

Holotype: ventral valve, MPUM9043 (KO20t)

Stratum typicum: KO20, Ribat Formation

Locus typicus: locality Lale Ribat 1.

Derivatio nominis: ribatensis from the Ribat Valley.

Diagnosis—Small Marginoproductus with few spines

and fine costae.

Description—Shell concavo-convex, small, with sub-

quadrate outline. Corpus cavity deep. Ears small, well

demarcated from the flanks and angular. Ventral sulcus

absent; flanks parallel. Dorsal valve geniculated with

weakly concave visceral disc. Ornamentation of fine,

regularly spaced costae numbering 10 per 5 mm at 10 mm

from the umbo. Spines present in two symmetrical pairs on

the flanks; 2–3 coarse, erect spines occur at the junction

between the flanks and the ears. Few rugae may occur on

the flanks. Few longitudinal plications may occur anteriorly.

Interior of dorsal valve with traces of a sessile cardinal

process and lateral ridges.

Discussion—The peculiar subquadrate outline both in

posterior and anterior views and the number and

distribution of spines indicate that the KO20 specimens

belongs to the genus Marginoproductus Tan, well

described and figured from the Visean of the Shihtengtze

Formation of Cenral Hunan of South China (Tan, 1986, p.

435, pl. 1, fig. 33–40). Marginoproductus ribatensis n. sp.

differs from the type species by having fewer and smaller

spines, a near absence of rugae, and more numerous and

finer costae.

The specimens described as Tomiproductus elegantulus

(Tolmachev, 1924) from the Upper Tournaisian of the

Geirud Formation of N. Iran (Gaetani, 1968) are close to

the Karakoram species in their outline and the pattern of

ribbing and spines, but have a more marked reticulation

posteriorly on the ventral disc.

Subfamily Buxtoniinae Muir-Wood and Cooper, 1960

Genus Buxtonioides Mendes, 1959

Type-species: Productus amazonicus Katzer, 1903

Buxtonioides sp. ind. (Fig. B1(8–9))

Material-1 articulated shell: MPUM9094 (KO25-3c); 5

ventral valves: MPUM9049 (KO25-1b,-1e,-1f; KO25-2b),

MPUM9095 (KO25-3g). Ribat Formation, Karambar Pass

section. Bashkirian.

Description—Large, plano-convex shell with sub-trape-

zoidal outline and deep corpus cavity. Shell substance thick.

Ventral valve strongly convex with small, but well defined

ears. Ventral sulcus shallow, widening anteriorly, not well

differentiated from the flanks. Ornamentation of numerous,

fine, rounded costellae with angular intercostal furrows.

Irregular longitudinal plications may occur at the anterior

margin. Thin and low rugae are present on the flanks. Spines

irregularly scattered on the ventral valve.

Discussion—These specimens have been placed in the

Bashkirian-Gzhelian genus Buxtonioides based on their

shape and ornamentation.

Family Linoproductidae Stehli, 1954

Subfamily Linoproductinae Stehli, 1954

Genus Marginovatia Gordon and Henry, 1990

Type-species: Productus ovatus var. minor Snider, 1915

Marginovatia sp. ind. (Fig. B1(10–12))

Material—1 internal mold of a articulated shell:

MPUM9050 (CK1094-1); 2 external moulds of ventral

valves: MPUM9053 (CK1093-4,-5); 1 fragment of ventral

valve: MPUM9051 (CK1093-6); 1 dorsal valve external

mould MPUM9052 (CK1094-2). Lupsuk Formation, Ribat

section. Bashkirian.

Description—Large size for this genus (length exceeding

20 mm) with convex, enrolled ventral valve and concave

dorsal valve; outline longitudinally ovate. Ventral valve

ornamented by fine, sinuous costellae numbering 10–11 per

5 mm, with few and low rugae on the flanks, near ears; fine

spines sparse on the ventre. Dorsal valve ornamented by

costellae, rugae and elongated dimples. Interior of dorsal

valve with a submarginal ridge sorrounding the visceral disc.

Discussion—These specimens have been placed in

Marginovatia because of their ovate outline, ornamentation

of few spines and rugae and fine costellae and the internal

thickened ridge enclosing the dorsal visceral disc. Among

the North American species figured by Gordon and Henry

(1990), these specimens most resemble the Lower Pennsyl-

vanian M. aureocollis Gordon and Henry, 1990 by their

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UNCORRECTED PROOF

rugose dorsal ornamentation and the number of costellae,

despite being larger in size.

The genus Marginoproductus Tan, which also occurs in

Karakoram, has a marked subquadrate outline, a different

ornamentation and a high dorsal median septum.

Family Echinoconchidae Stehli, 1954

Subfamily Juresaniinae Muir-Wood and Cooper, 1960

Tribe Juresaniini Muir-Wood and Cooper, 1960

Genus Cubacula Lazarev, 1984

Type-species: Productus subpunctatus Nikitin, 1890

Cubacula sp. ind. (Fig. B1(13))

Material—1 ventral valve: MPUM9054 (CK1139-d).

Dark grey marly limestones at 4100 m of altitude on the

path leading to Siru An. Kasimovian.

Remarks—The species is represented by a single ventral

valve and is recognised by its ventral sulcus and

ornamentation of rugae and both suberect and recumbent

fine spines, regularly arranged in bands.

Family Rhipidomellidae Schuchert, 1913

Subfamily Rhipidomellinae Schuchert, 1913

Genus Rhipidomella Oehlert, 1890

Type-species: Terebratula michelini Leveille, 1835.

Rhipidomella sp. 1 (Fig. B1(15))

Material—4 ventral valves: MPUM9055 (CK1074-2),

MPUM9056 (CK1074-3,-4,-6); 1 dorsal valve: MPUM9057

(CK1074-5); various fragments and external casts of both

valves from the same level. Margach Formation, Ribat

section. Earliest middle Tournaisian.

Remarks—The genus Rhipidomella is here represented

by dorsibiconvex shells with a subcircular outline, orna-

mented by very fine ribs increasing up to 15–18 per 5 mm at

the anterior margin and widely spaced growth lamellae. The

ventral valve interior shows flabellate muscle scars bisected

by a median ridge.

They have been determined as Rhipidomella sp. 1 to

differentiate them from the other Rhipidomella species

(Angiolini et al., 1999, p. 14, pl. 1, fig. 15–17—referred to

as Rhipidomella sp. 2 in the biostratigraphic paragraph)

which comes from higher stratigraphic levels. In fact,

Rhipidomella sp. 1 differs from Rhipidomella sp. 2 in its

more rounded outline, narrower hinge, more numerous ribs

and absence of a sulcus in the dorsal valve.

Rhipidomella sp. 1 resembles the species called R.

michelini (Leveille, 1835) from the middle-upper

Tournaisian of the Murabak Limestone of N. Iran (Gaetani,

1968).

Family Rhynchoporidae Muir-Wood, 1955

Genus Rhynchopora King, 1865

Type-species: Terebratula geinitziana de Verneuil, 1845

Rhynchopora sp. ind. (Fig. B1(14))

Material—1 ventral valve external cast: MPUM9062

(CK1091-1); 5 dorsal valves: MPUM9059 (CK1074-9),

MPUM9060 (CK1074-8), MPUM9063 (CK1091-2,

CK1094-4,-5); 1 dorsal valve external cast: MPUM9061

(CK1074-7); several fragments: CK1073-2, CK1091-3,

CK1094. Margach and Lupsuk Formations, Ribat section.

Early Tournaisian-Bashkirian.

Remarks—The presence of the genus Rhynchopora is

indicated by the occurrence of several biconvex shells with

flaring outlines and with coarse ribs widening anteriorly,

numbering 4 on the fold, 5 on the sulcus and 5 on each flank.

Internally the ventral valve show traces of dental plates

whereas the dorsal valve shows the median septum

supporting the hinge plate.

Family Martiniopsidae Kotlyar and Popeko, 1967

Genus Martiniopsis Waagen, 1883

Type-species: Martiniopsis inflata Etheridge, 1892.

Martiniopsisgrandiformis(Plodowski,1968)(Fig.B1(17))

1968 Eomartiniopsis grandiformis Plodowski, p. 256,

pl. 1, fig. 9

1970 Eomartiniopsis grandiformis-Plodowski, p. 109,

text-fig. 54–56, pl. 8, fig. 5–7

1999 Martiniopsis sp.-Angiolini et al., p. 16, pl. 2, fig. 4–5

Material—1 articulated specimen: MPUM9065

(KO24d); 1 ventral valve: MPUM9064 (CK1103c).

Respectively from the Ribat Formation, E. Lupsuk section

and from scree of the middle part of the Ribat Formation in

the Lupsuk section. Visean.

Description—Biconvex shell with thick shell substance

and relatively wide-hinge. Maximum width around mid-

length. Anterior commissure uniplicate. Complete specimen

with elongate oval outline. Ventral valve convex with sub-

rhomboidal outline. Shell smooth, with narrow median

sulcus. Ornamentation of strong growth lines. Ventral

interior with dental plates. Dorsal interior with crural plates

and cardinal process in the form of a ctenophoridium.

Discussion—These specimens—and those previously

described from the scree of the Ribat Formation near

the Twin Valleys section (samples CK588, CK590 in

Angiolini et al., 1999)—are very close to Eomartiniopsis

grandiformis Plodowski, 1968 from the Goniatites-Stufe of

Burgutsch-Tal (Central Afghanistan) (Plodowski, 1970).

According to the accurate illustrations and description of

Plodowski (1968; 1970, p. 109, fig. 54–55), the species

grandiformis has short but thick crural plates which reach

the floor of the valve, thus differing from the type species of

Eomartiniopsis (E. elongata Sokolskaya, 1941) which has

no dorsal plates (Carter and Poletaev, 1998). Externally, E.

grandiformis is characterised by its large size and a

lamellose micro-ornamentation with sporadic occurrence

of small pits.

The martiniopsid species from Afghanistan is similar to

species of the genus Crassumbo Carter, 1967, which,

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UNCORRECTED PROOF

however, differs by its capillate micro-ornamentation and a

median ridge inside the ventral valve of the juveniles.

Chuiella Chen and Shi, 1999 from the Lower Carboniferous

of NW China (Chen and Shi, 1999) is also similar, but has a

median ridge in the ventral valve interior.

Because of the combination of internal and external

characters the species grandiformis is provisionally trans-

ferred to the genus Martiniopsis, which, however, has

longer dorsal plates and a pustulose micro-ornamentation,

and we do not not exclude the possibility that the Afghan

and Karakoram species may represent a new genus.

Family Spiriferidae King, 1846

Subfamily Spiriferinae King, 1846

Genus Spirifer Sowerby, 1816

Type-species: Conchyliolithus (Anomites) striatus Mar-

tin, 1809

Spirifer pentagonoides Plodowski, 1968 (Figs. B1(16,

18–21) and B3(11–14))

1968 Spirifer pentagonoides Plodowski, p.253, pl. 1, fig. 3

1970 Spirifer pentagonoides-Plodowski, p. 64, text-fig.

32–36, pl. 1,. fig. 11–12, pl. 2, fig. 1–5, pl. 12, fig. 1

Material—1 articulated shell: MPUM9072 (KO20-1); 17

ventral valves: MPUM9066 (KO20-10), MPUM9067

(KO20-6), MPUM9068 (KO20-16), MPUM9071 (KO20-

2,-3,-5,-7,-8,-9,-11,-12,-13,-14,-15,-17,-18,-20); 2 dorsal

valves: MPUM9069 (KO20-19), MPUM9070 (KO20-21).

Ribat Formation, Lale Ribat 1, right topographical side of

Lale Ribat Valley, near the village. Visean.

Description—Biconvex shell, with slightly transverse

subpentagonal outline. Cardinal extremities angular. Ven-

tral interarea concave, high with wide delthyrium. Ventral

sulcus shallow, widening anteriorly, ornamented by 3–4

broad ribs anteriorly. Dorsal fold well defined, anteriorly

elevated forming a broad arch.

Ornamentation of coarse rounded ribs, with narrow

intercostal furrows. Ribs increase in width anteriorly and

number 4 per 5 mm at 10 mm from the umbo and about 2–3

per 5 mm at the anterior margin. Interior of ventral valve

with apical callus, small delthyrial plate and strong, straight

and slightly divergent dental plates.

Discussion—These numerous and reasonably well pre-

served specimens share the specific characters of the Spirifer

pentagonoides Plodowski, 1968 from the Visean Goniatites-

Stufe of Burgutsch-Tal (Central Afghanistan). The species is

characterised by its outline, the coarse ribbing, details of the

dorsal fold and the internal morphology of the ventral valve.

Spirifer subgrandiformis Plodowski, 1968 (Fig. B2(1))

1968 Spirifer subgrandiformis Plodowski, p. 254, pl. 1,

fig. 1

1970 Spirifer subgrandiformis-Plodowski, p. 60, text-

fig. 29–31, pl. 5, fig. 5–8, pl. 6, fig. 1–3.

Material—1 articulated shell: MPUM9073 (KO24a).

Ribat Formation, E. Lupsuk section. Visean.

Description—Large sized (W: 64.9 mm; L: 40.3 mm)

with transverse, subpentagonal outline. Shell substance

thick. Anterior commissure uniplicate; cardinal extremities

alate. Ventral interarea high. Ventral sulcus shallow,

subangular. Dorsal fastigium widening and elevating

anteriorly. Ornamentation of rather coarse, irregularly

bifurcating costae, numbering 6–8 per 10 mm at 10 mm

from the umbo.

Discussion—This specimen is assigned to S. subgran-

diformis because of its dimensions, profile, ornamentation

and shape of the sulcus. S. subgrandiformis has been

found in the Visean Goniatites-Stufe of Central Afghani-

stan. Legrand-Blain (1986) reports Spirifer aff. subgran-

diformis from the early to early late Visean of the

Algerian Sahara.

Spirifer cf. S. denis (Beznosova, 1959) (Fig. B2(2))

Material—1 ventral valve: MPUM 8383 (CK588-2).

Scree of the Ribat Formation near the Twin Valleys section.

Remarks—This convex ventral valve, with a shallow and

narrow sulcus, ornamented by numerous bifurcating, rarely

trifurcating, ribs numbering 10–11 per 10 mm at 15 mm

from the umbo and growth lamellae is close to the

specimens figured as Spirifer denis from the Visean

Goniatites-Stufe of Central Afghanistan (Plodowski, 1970,

p. 75, pl. 2, fig. 6–8).

Genus Ectochoristites Campbell, 1957

Type-species: Ectochoristites wattsi Campbell, 1957

Ectochoristites sp. ind. (Figs. B2(3–4) and B3(7–10))

Material—1 articulated shell: MPUM9074 (KO14a).

Ribat Formation, Triple Junction section. Serpukhovian.

Description—Biconvex, elongated shell (W: 27.4; L:

32.6) with narrow cardinal margin and slightly alate

cardinal extremities. Anterior commissure uniplicate.

Shell substance thick. Ventral umbo incurved over

the interarea. Ventral sulcus deep, ‘V’ shaped. Dorsal

fastigium low. Ornamentation of sparce, rounded costae,

numbering about 4 per 5 mm at the anterior margin of the

dorsal valve and growth lamellae.

Interior of ventral valve with thickened dental plates,

divergent to the valve floor and united to the valve walls by

a callus; dental flanges close medianly up to 6.4 mm from

the umbo, forming an angle with the ventral adminicula

which extend up to 7.2 mm from the umbo.

Discussion—This single specimen is well preserved and

indicates the occurrence of the Tournaisian-?Namurian genus

Ectochoristites in Karakoram. It is characterized by an

elongate outline, rounded costae and divergent dental plates.

A species of Ectochoristites has been reported by Yang

and Fan (1983) from the Visean Eastern Baria Member of

Yungzhu, Xainza County (Central Tibet).

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UNCORRECTED PROOF

Subfamily Prospirinae Carter, 1974

Genus Parallelora Carter, 1974

Type-species: Spirifer marionensis Shumard, 1885

Parallelora aff. subsuavis (Plodowski, 1968)

(Fig. B2(5–6))

Material—4 ventral valves: MPUM9075 (CK1075-1,-2),

MPUM9076 (CK1073-1), MPUM9077 (CK1077-1); 1

dorsal valve: MPUM9058 (CK1074-1). Margach For-

mation, Ribat section. Earliest middle Tournaisian.

Description—Transverse, biconvex with moderately

developed fold and sulcus. Lateral slopes ornamented

by fine rounded costae. Costae seem to bifurcate on the

flanks resulting in more than 17 ribs on each slope at

10 mm from the umbo. Ventral sulcus ornamented by a

median simple costa and 2–3 ribs on each side. Fold

delimited by deep grooves and ornamented by 9 ribs.

Interior of ventral valve with dental plates formed by

thick dental flanges and thin divergent ventral

adminicula.

Fig. B2. (All £ 1) (1) Spirifer subgrandiformis Plodowski, 1968. Specimen MPUM9073 (KO24a). Ventral view of an articulated shell. (2) Spirifer cf. S. denis

(Beznosova, 1959). Specimen MPUM8383 (CK588-2). Ventral valve. (3–4) Ectochoristites sp. ind. Specimen MPUM9074 (KO14a). Ventral and dorsal view

of an articulated shell. (5) Parallelora aff. subsuavis (Plodowski, 1968). Specimen MPUM9075 (CK1075-1). Ventral valve. (6) Parallelora aff. subsuavis

(Plodowski, 1968). Specimen MPUM9058 (CK1074-1). Dorsal valve with a fragment of Rhipidomella sp.1. (7) Afghanospirifer cf. burgutschensis Plodowski,

1968. Specimen MPUM9078 (KO18e). Ventral view of an articulated shell. (8) Anthracospirifer sp. ind. Specimen MPUM9082 (KO15a). Dorsal valve. (9)

Choristites sp. ind. Specimen MPUM9084 (KO23h). Ventral valve. (10) Choristites sp. ind. Specimen MPUM9085 (KO23g). Ventral valve. (11) Syringothyris

sp. ind. Specimen MPUM9093 (KO15b). Partially decorticated dorsal valve. (12) Gypospirifer sp. ind. Specimen MPUM9089 (KO22-2). Ventral view of an

articulated shell. (13–15) Gypospirifer sp. ind. Specimen MPUM9088 (KO22-1). Ventral, dorsal, posterior views of an articulated shell.

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UNCORRECTED PROOF

Discussion—These specimens are very similar to those

described as Spirifer subsuavis Plodowski (1968, p. 253, pl. 1,

fig. 5; 1970, p. 52, pl. 1, fig. 5–10, pl. 11, fig. 2), but they lack

the apical callus and they have longer dental plates and a more

convex ventral valve. The species subsuavis seems to be

characterized by its rectangular ventral interarea, clearly

delineated fold and sulcus, and its moderately numerous

bifurcating costae, features indicative of the late Devonian–

early Tournaisian genus Parallelora Carter, 1974.

Subfamily Sergospiriferinae Carter, Johnson, Gourven-

nec, Hong-Fei 1994

Genus Afghanospirifer Plodowski, 1968

Type-species: Afghanospirifer burgutschensis Plo-

dowski, 1968

Afghanospirifer cf. burgutschensis Plodowski, 1968

(Fig. B2(7))

1999 Afghanospirifer sp.-Angiolini et al., p. 16, pl. 2, fig.

6–7, text-fig. 6a.

Material—2 articulated shells: MPUM9078 (KO18e),

MPUM9079 (KO17a); 2 ventral valves: MPUM9080

(KO23b,f); 3 dorsal valve: MPUM9081 (KO23c,e;

CK1094-3). Ribat and Lupsuk Formations, Triple Junction,

Ribat and Karambar Lake sections. Bashkirian.

Description—Biconvex shell with subrectangular out-

line; dimensions: widths of 34.3 and 38.8 mm; correspond-

ing lengths: 22.8 and 27.3 mm. Cardinal extremities

rounded to slightly pointed. Ventral interarea relatively

high, concave, denticulated. Ventral sulcus shallow. Flanks

ornamented by few, coarse, rounded, bifurcating ribs with

narrow intercostal furrows, numbering 3–4 per 5 mm at

15 mm from the umbo and close growth lamellae. Fold

ornamented by 3–4 ribs.

Discussion—As already pointed out by Angiolini et al.

(1999), based on material from the Twin Valleys section, the

Karakoram specimens attributed to the Serpukhovian-lower

Bashkirian genus Afghanospirifer are not well preserved.

However, based on these new findings, they probably belong

to A. burgutschensis Plodowski, 1968 as no significant

characters differentiate them from the type-species.

Genus Anthracospirifer Lane, 1963

Type-species: Anthracospirifer birdspringensis Lane,

1963

Anthracospirifer sp. ind. (Fig. B2(8))

Material—2 dorsal valves: MPUM9082 (KO15a),

MPUM9083 (CK1101). Ribat Formation, Triple Junction

section and from scree of the Ribat Formation in the Lupsuk

section. Serpukhovian.

Remarks—Two specimens indicate the possible occur-

rence of the Serpukhovian–Bashkirian genus Anthracospir-

ifer. They are dorsal valves with subangular folds

ornamented by a median costa and a pair of bifurcating

lateral ribs; flanks ornamented by coarse, rounded costae

widening anteriorly up to 1.4 mm in width at the anterior

margin with narrow intercostal furrows.

Family Choristitidae Waterhouse, 1968

Subfamily Choristitinae Waterhouse, 1968

Genus Choristites Fischer de Waldheim, 1825

Type-species: Choristites mosquensis Fischer de Wald-

heim, 1825

Choristites sp. ind. (Figs. B2(9–10) and B3(1–6))

1999 Choristites sp.-Angiolini et al., p. 17, pl. 2,

fig. 8–10

Material—1 articulated shell: MPUM9086 (KO16); 4

ventral valves: MPUM9084 (KO23 h), MPUM9085

(KO23 g), MPUM9087 (KO23 l, KO17c). Ribat Formation,

Karambar Lake section and Triple Junction section.

Bashkirian.

Description—Large, biconvex shell with subpentagonal

outline and maximum width at 1/3 the shell length. Interarea

low, concave, trapezoidal and denticulate. Ventral valve

strongly convex especially posteriorly, with incurved umbo

and wide ventral sulcus, deepening anteriorly, ornamented

by a median costa and 3 to 4 ribs on each side. Each ventral

flank ornamented by flat, bifurcating ribs, numbering about

4 per 5 mm at 20 mm and from the umbo. Strong growth

lines also occur.

Interior of ventral valve with slightly divergent dental

plates and elongate oval, depressed muscle field delimited

by rounded ridges.

Discussion—The specimens are similar to Choristites

xainzangensis Yang, 1983 from the middle Carboniferous

Sisuo Formation, Yungzhu, Xainza County (Central Tibet)

(Yang and Fan, 1983), as are those described by Angiolini

et al. (1999) from the Twin Valleys section. They differ by

having a more convex ventral umbo.

Family Trigonotretidae Schuchert, 1893

Subfamily Neospiriferinae Waterhouse, 1968

Genus Gypospirifer Cooper and Grant, 1976

Type-species: Gypospirifer nelsoni Cooper and Grant,

1976.

Gypospirifer sp. ind. (Fig. B2(12–15))

1999 Gypospirifer sp.-Angiolini et al., p. 18, pl. 2, fig.

11–12, text-fig. 6b

Material—3 articulated shells: MPUM9088 (KO22-1),

MPUM9089 (KO22-2), MPUM9090 (KO22-3); 5 ventral

valves: MPUM9091 (KO17e,f,g; KO18f; KO23d). Ribat and

Lupsuk Formations, Triple Junction section, Karambar Lake

section, scree from the Ribat Formation in the Tarsan Valley

near Ribat village. Bashkirian.

Description—Biconvex shells, with transverse semicir-

cular outline; maximum width at the hinge, cardinal

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extremities angular. Ventral interarea wide, denticulate.

Ventral sulcus narrow and shallow. Ornamentation of fine,

rounded, bifurcating ribs, numbering 5–6 per 5 mm at

10 mm from the umbo. Faint traces of ribbing fasciculation

occur posteriorly. Sulcus ornamented by a median rib

bifurcating anteriorly and 2–3 ribs on each side bifurcating

from the costae bordering the sulcus. Interior of ventral

valve with a small delthyrial plate, thin dental flanges, short

adminicula and sub-rhomboidal muscle-field. Interior of

dorsal valve with ctenophoridium.

Discussion—As already stated by Angiolini et al. (1999),

the poor preservation of the Karakoram specimens prevent

an accurate specific assignment. However, the morphologi-

cally nearest species are Gypospirifer guelmounensis

Fig. B3. (1–6) Choristites sp. ind. Specimen MPUM9086 (KO16), serial sections at 4.4, 6.7, 8.0, 9.2, 9.2, 9.8 mm from the umbo. Figs. 1-2 £ 4; figs. 3-4,

6 £ 3; 5 £ 6. 22.7–10 Ectochoristites sp. ind. Specimen MPUM9074 (KO14a), serial sections at 3.6, 5.3, 6.4, 7.2 mm from the umbo. All £ 4. 11–14. Spirifer

pentagonoides Plodowski, 1968. Specimen MPUM9071 (KO20-17), serial sections at 3.5, 5.7, 6.9, 8.1 mm from the umbo. All £ 4.

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Legrand-Blain, 1986 from the Visean-Serpukhovian of the

Algerian Sahara and G. anancites Cooper and Grant, 1976

from the Pennsylvanian-Lower Permian of West Texas.

Family Syringothyridae Frederiks, 1926

Subfamily Syringothyridinae Frederiks, 1926

Genus Syringothyris Winchell, 1863

Type-species: Syringothyris typa Winchell, 1863

Syringothyris sp. ind. (Fig. 21.11)

Material—2 ventral valves: MPUM9092 (KO25c, d).

Ribat Formation; 1 dorsal valve: MPUM9093 (KO25b).

Karambar Pass section. Bashkirian.

Remarks—These specimens show ventral valves with a

high, triangular, slightly concave interarea with an apical

angle of about 1208 and a large delthyrium internally closed

by a delthyrial plate with a syrinx. Ventral sulcus shallow,

diverging at 308. Flanks ornamented by flat-topped costae.

Interior with long diverging dental plates. The partially

decorticated dorsal valve has a large fold and flanks each

ornamented by about 17 flat-topped costa. Internally a long

median myophragm occurs.

They are rather similar to Syringothyris sp. 2 described

by Plodowski (1970, p., pl. 8, fig. 10) from the late

Serpukhovian–early Bashkirian of Burgutsch-Tal (13 km

SW Bukhara-e-Nawar, Central Afghanistan).

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Journal of Sedimentary Petrology 50, 21–29.

SEAES 708—17/12/2003—18:36—RAJA—74521— MODEL 5


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The carboniferous of the Western Karakoram (Pakistan)

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Transcript of The carboniferous of the Western Karakoram (Pakistan)