Unroofing history of Late Paleozoic magmatic arcs within the ''Turan Plate'' (Tuarkyr, Turkmenistan)

Unroofing history of Late Paleozoic magmatic arcs within the

‘‘Turan Plate’’ (Tuarkyr, Turkmenistan)

E. Garzanti a,*, M. Gaetani b

aDipartimento di Scienze Geologiche e Geotecnologie, Universita di Milano-Bicocca, Piazza della Scienza 4, 20126 Milan, ItalybDipartimento di Scienze della Terra, Universita di Milano, Via Mangiagalli 34, 20133 Milan, Italy

Received 15 March 2001; accepted 15 October 2001

Abstract

Stratigraphic, sedimentologic and petrographic data collected on the Kizilkaya sedimentary succession (Western

Turkmenistan) demonstrate that the ‘‘Turan Plate’’ consists in fact of an amalgamation of Late Paleozoic to Triassic

continental microblocks separated by ocean sutures. In the Kizilkaya area, an ophiolitic sequence including pyroxenite, gabbro,

pillow basalt and chert, interpreted as the oceanic crust of a back-arc or intra-arc basin, is tectonically juxtaposed against

volcaniclastic redbeds documenting penecontemporaneous felsic arc magmatism (Amanbulak Group). A collisional event took

place around ?mid-Carboniferous times, when oceanic rocks underwent greenschist– facies metamorphism and a thick

volcaniclastic wedge, with pyroclastic rocks interbedded in the lower part, accumulated (Kizilkaya Formation). The climax of

orogenic activity is testified by arid fanglomerates shed from the rapid unroofing of a continental arc sequence, including

Middle–Upper Devonian back-reef carbonates and cherts, and the underlying metamorphic and granitoid basement rocks

(Yashmu Formation). After a short period of relative quiescence, renewed tectonic activity is indicated by a conglomeratic

sequence documenting erosion of a sedimentary and metasedimentary succession including chert, sandstone, slate and a few

carbonates. A final stage of rhyolitic magmatism took place during rapid unroofing of granitoid basement rocks (Kizildag

Formation). Such a complex sequence of events recorded by the Kizilkaya episutural basin succession documents the stepwise

assemblage of magmatic arcs and continental fragments to form the Turan microblock collage during the Late Paleozoic.

Evolution of detrital modes is compatible with that predicted for juvenile to accreted and unroofed crustal blocks. The

deposition of braidplain lithic arkoses in earliest Triassic time indicates that strong subsidence continued after the end of the

volcanic activity, possibly in retroarc foreland basin settings. The occurrence of transgressive coquinas yielding endemic

ammonoids (Dorikranites) characteristic of the whole Caspian area suggests proximity to the southern margin of the newly

formed Eurasian continent in the late Early Triassic. The Late Triassic Eo-Cimmerian Orogeny caused only mild tilting and

rejuvenation of the underlying succession in the study area. Only at this time were the Turan blocks, a series of Indonesian-type

terranes comprised between the Mashad Paleo-Tethys Suture in the south and the Mangyshlak belt in the north, finally

incorporated into the Eurasian landmass. D 2002 Elsevier Science B.V. All rights reserved.

Keywords: Turan blocks; Oceanic sutures; Volcaniclastic redbeds; Sandstone petrography; Late Paleozoic; Olenekian

0037-0738/02/$ - see front matter D 2002 Elsevier Science B.V. All rights reserved.

PII: S0037 -0738 (01 )00231 -7

* Corresponding author.

E-mail addresses: [email protected] (E. Garzanti), [email protected] (M. Gaetani).

www.elsevier.com/locate/sedgeo

Sedimentary Geology 151 (2002) 67–87

1. Introduction

The Caspian area is of great economic interest due

to the occurrence of numerous giant gas and oil re-

servoirs (e.g., Khain et al., 1991). Geological knowl-

edge is, however, still incomplete, particularly as

regards the pre-Jurassic paleogeographic and paleo-

geodynamic scenario, which is rather poorly con-

strained. Unraveling the earlier stages through which

the area was consolidated and welded to Eurasia will

contribute to the understanding of the extent to which

Paleozoic–early Mesozoic structures have controlled

subsequent sedimentary basin evolution and location

of depocentres (Thomas et al., 1999a). Exposures of

Permo-Triassic rocks are unfortunately limited to

scattered punctiform or narrow linear outcrops includ-

ing the Bolshoe Bogdo in Russia (near Volgograd),

the Gornyi Mangyshlakh and its continuation toward

the Kugusem scarp (Western Kazakhstan), the small

domal structure of Kizilkaya in Tuarkyr (Western

Turkmenistan) and the Aghdarband window in the

Kopet Dagh (Northeastern Iran; Fig. 1).

Geological data on the eastern side of the Caspian

Sea, including Turkmenistan, were collected during

reconnaissance field-work carried out by Soviet au-

thors largely in the 1950s and 1960s (e.g., Luppov,

1957; Gavriliansk, 1965; Likharev, 1966; Volvovsky

et al., 1966). Observations on outcrops were integrated

with numerous geophysical surveys and drillings, but

such wealth of subsurface data has remained classified

and often only summarized in internal reports or Rus-

sian publications with limited circulation. The general

stratigraphic scheme for the Mesozoic was defined

formally in the Samarkand conference (Interdepart-

mental Stratigraphic Commission, 1977). More recent-

ly, reviews based largely on the previously collected

data base (Garetsky et al., 1982; Popkov, 1986;

Zonenshain et al., 1990; Khain et al., 1991; Maksimov,

1992), together with published geological maps (Mir-

sakhanov, 1989; VSEGEI, 1994), have shown that the

area is far more complex than previously held.

1.1. The eastern Caspian geopuzzle

The eastern Caspian area is dominated by two

principal sutures, the northern one representing the

southern front of the Late Paleozoic Altaid Orogen and

the southern one marking the site where Paleo-Tethys

finally closed in the Late Triassic. The geological

framework north of the former (‘‘Altaids’’ of Sengor

and Natal’in, 1996) and south of the latter (‘‘Tethy-

sides’’ of Sengor and Natal’in, 1996) is reasonably

well-constrained. In between lays a large composite

belt (‘‘Intermediate Units’’ of Sengor and Natal’in,

1996), which has been traditionally held to represent

a more or less coherent unit (‘‘Turan Plate’’) stabilized

and accreted to Eurasia during the Late Paleozoic

(Sengor, 1984; Zonenshain et al., 1990; Dercourt et

al., 1993; Stampfli, 1996; Besse et al., 1998; Thomas et

al., 1999a,b). The ‘‘Intermediate Units,’’ however,

appear in fact to comprise a mosaic of microblocks

of various size (including the Karakum Block in the

east and the Karabogaz Block in the west), character-

ized by arc magmatism during Carboniferous to Trias-

sic times and separated by elongated belts of deformed

Paleozoic oceanic rocks seemingly documenting sea-

ways linked to the Turkestan Ocean (Zonenshain et al.,

1990; Kurenkov and Aristov, 1995). Their stratigraphic

features and geological evolution are varied, and their

relative paleogeographic positions are highly contro-

versial. Paleomagnetic data, although few and equivo-

cal, suggest that during the Late Paleozoic to the Early

Triassic at least some of these microblocks may have

lain far to the south with respect to the southern margin

of the East European Craton (Feinberg et al., 1996;

Lemaire et al., 1998a,b).

The northern boundary of the ‘‘Intermediate Units’’

in the eastern Caspian area corresponds to the Man-

gyshlak belt, which includes large volumes of arc

volcaniclastic sediments deposited through Triassic

time in continental to shallow-marine environments

and deformed during the Late Triassic (Gaetani et al.,

1998). This Eo-Cimmerian collisional event, recorded

along the southern margin of the Eastern European

Craton (Nikishin et al., 1996), marks the final incor-

poration of the Turan blocks into Eurasia.

1.2. The key outcrops of Tuarkyr

The Tuarkyr area, in the centre of the ‘‘Intermedi-

ate Units,’’ is critical to understanding the relation-

ships between the Karabogaz to Karakum Blocks and

the Mangyshlak belt to the north and, thus, to unrav-

eling the geological evolution of the Caspian region.

The Upper Paleozoic to Triassic rocks of Kizilkaya

(Tuarkyr; Western Turkmenistan) lie in the middle of

E. Garzanti, M. Gaetani / Sedimentary Geology 151 (2002) 67–8768

the east Caspian steppe, nearly 500 km southeast

of the Mangyshlak belt and nearly 700 km north-

west of the Aghdarband window, representing the

closest outcrops with broadly correlative sedimen-

tary successions (Fig. 1).

The Kizilkaya area was restricted because of a

large uranium mine active until the 1970s, and pub-

lished geological information has remained largely

confidential (e.g., Kalugyn, 1975). Only in recent

years have western geologists had access to the area

to carry out paleomagnetic investigations (Lemaire et

al., 1997, 1998a,b). Petrologic observations on the

Permo-Triassic igneous rocks of the Turkmenbasi

(Krasnovodsk) area, representing the southern margin

Fig. 1. Location map of the Caspian area (A) and geologic sketch map of the Kizilkaya structure (B) (modified after Khurbatov’s map, sheet

K-40-XXXII).

E. Garzanti, M. Gaetani / Sedimentary Geology 151 (2002) 67–87 69

of the Karabogaz High, were also made (Lemaire,

1997). During our 1997 geological expedition to

Tuarkyr, in the framework of the Peri-Tethys Pro-

gramme (Dercourt et al., 2000), we measured a

complete, composite stratigraphic section across the

Kizilkaya structure, and visited the small outcrop of

pillow-lavas near the village of Tuar some 35 km

northwest of Kizilkaya, collecting 138 samples for

paleontological, petrographic and geochemical analy-

sis. Our principal aims were as follows.

(1) To improve the stratigraphic information on the

Upper Paleozoic to Triassic sedimentary succession,

and to integrate it with detailed sedimentological ob-

servations and quantitative petrographic data.

(2) To investigate the geochemical signature of the

associated mafic igneous rocks.

(3) To compare the sedimentary record of Tuarkyr

with that of adjacent basins, with specific reference to

petrologic signatures of terrigenous detritus and tim-

ing of volcaniclastic deposition. In particular, we

wanted to understand whether paleogeographic highs

feeding the Tuarkyr clastics, or the Tuarkyr clastics

themselves, could have represented the source of

detritus for the Mangyshlak trough in Triassic time.

(4) To evaluate the relative incidence of Late Pale-

ozoic versus Late Triassic orogenic events in Tuarkyr,

so as to clarify the paleotectonic and paleogeographic

evolution of the eastern Caspian area. In particular, we

tried and constrain the timing of assembly of the Turan

microblocks and final accretion to the Eurasian land-

mass.

2. The oceanic rocks of Kizilkaya and Tuar

The Kizilkaya structure is a monocline f 17 km

long and 4 km wide, bounded to the northeast by a

major regional fault (Fig. 1). On the southwest side of

the fault, a sedimentary succession dipping mainly

40j–45j west south-west consists of Upper Paleozoic(Amanbulak Group) to Lower Triassic redbeds. Along

the northeast side of the fault, slivers of mafic igneous

rocks and tectonised cherty slates are exposed. These

rocks were first observed in the 1930s by Soviet

geologists, who described an up to 200-m thick cherty

slate unit inferred to be intruded by gabbros near

Kizilkaya and Tuar (Nalivkin and Luppov, 1936, in

Luppov, 1957). All of these structures and rock units

are unconformably overlain by fluvio-deltaic clastics

containing Jurassic floras.

2.1. Mafic igneous rocks

A 100-m thick tectonised sequence including

pyroxenitic cumulates, gabbros, diabases and pillow

lavas mantled by sedimentary chert layers is found in

tectonic contact with the Amanbulak redbeds on the

eastern side of the Yashmu hill. Pillow lavas, locally

associated with chert, also occur at Tuar (Figs. 1 and

4A). In gabbroic rocks, primary clinopyroxene + pla-

gioclase assemblages are partially replaced by greens-

chist–facies assemblages including tremolite, chlorite,

albite. Late-stage sericite, epidote and locally pum-

pellyite are also found. Pillow lavas, consisting of

plagioclase laths set in an altered glassy groundmass,

are spilitized and contain veins and cavities filled by

quartz, chlorite or calcite. Phenocrysts of mafic min-

erals are not preserved. Geochemical analyses of these

largely altered mafic magmatic rocks (Table 1) sug-

gest that they crystallized from low-TiO2, subalkalic,

basaltic to basaltic–andesite magmas (Fig. 2). The

oceanic rocks are undated, although a mid-Paleozoic

age is generally assumed (Mirsakhanov, 1989).

2.2. Dark cherty slates

A small outcrop of anchimetamorphic grey cherty

mudrocks is found in the vicinity of the Kizilkaya

village, where they are invariably in tectonic contact

with the unmetamorphosed and only mildly tilted

Amanbulak redbeds (Luppov, 1957). The dark cherty

slates were generally assigned to the mid-Paleozoic

(Luppov, 1957; Mirsakhanov, 1989; VSEGEI, 1994)

but recently have been reported to contain Early to

mid-Carboniferous radiolaria (Gorelovski, personal

communication, 1997).

3. The Kizilkaya sedimentary succession

The thick continental redbeds of Kizilkaya, largely

of Upper Paleozoic age (Amanbulak Group; ‘‘Aman-

bulak Series’’ of Luppov, 1932, in Luppov, 1957;

Likharev, 1966), are truncated by a major angular

unconformity and covered by Jurassic terrigenous

units. The uppermost part of the sequence, which


consists of grey to red and white clastics, was later

recognized as a separate unit, considered as Early

Triassic in age because it is capped by marine fossil-

iferous strata containing the ammonoid Dorikranites

(Kiparisova and Khurbatov, 1952, in Luppov, 1957).

The Amanbulak Group was subdivided by Khurba-

tov (in Luppov, 1957) into three superposed units: Pa

(sandstones and conglomerates, 300–400-m thick), Pb

(shales, 210–250-m thick) and Pc (conglomerates,

530–600-m thick). Here we retain this tripartion, and

recognize three formations, documenting distinct sedi-

mentary cycles (Fig. 3). The formations are further

subdivided into stratigraphic units, characterized by

specific lithologic, sedimentologic and petrographic

features, and briefly described in ascending order.

The Amanbulak Group is considered to be of ?Late

Carboniferous to Permian age from its stratigraphic

position. The fossil plant Araucarioxylon was found

in the upper part of the unit (middle Pc Unit of

Khurbatov, in Luppov, 1957), where occurrence of

magnetostratigraphic reversals (Lemaire, 1997, p. 57)

would suggest a post-late Wordian age.

3.1. Kizilkaya Formation

This formation (830 m at least), representing the

lower part of the Amanbulak Group, consists of

largely continental redbeds, with intercalated chert

layers and pyroclastic rocks in the lower part. The

term Kizilkaya Fm. was first introduced by Kalugyn

(1975). Four members are distinguished and 24 sand-

stone samples have been analyzed.

3.1.1. Unit KK1

3.1.1.1. Lithology. Largely fine-grained sandstones,

locally displaying current ripples or low-angle oblique

laminations indicating northward sediment transport,

interbedded with dark violet mudrocks increasing

upward in abundance (at least 41 m). Burrowing is

absent. A well-oxygenated, subaerial distal deltaic en-

vironment is suggested.

3.1.1.2. Petrography. Feldspatholithic volcanic are-

nites with quartz phenocrysts and predominance of

Table 1

Chemical analyses of mafic igneous rocks of Kizilkaya and Tuar

Major

and trace

elements

TK 57

pyroxenite

(Kizilkaya)

TK 8

gabbro

(Kizilkaya)

TK 9

gabbro

(Kizilkaya)

TK 10

gabbro

(Kizilkaya)

TK 58

diabase?

(Kizilkaya)

TK 11

pillow lava

(Kizilkaya)

TK138

pillow lava

(Tuar)

SiO2 59.2 50.2 54.7 49.5 50.5 53.2 54.5

TiO2 0.3 0.5 0.4 0.4 0.3 0.9 2.4

Al2O3 10.4 15.4 12.2 13.0 15.7 13.4 12.0

Fe2O3 9.4 7.6 10.3 9.6 11.1 7.3 8.2

MnO 0.3 0.1 0.2 0.1 0.2 0.3 0.1

MgO 6.9 10.7 7.9 7.4 7.8 5.4 2.4

CaO 9.3 9.2 8.2 12.4 7.5 11.1 5.6

Na2O 0.5 2.5 1.9 3.2 0.9 4.5 5.1

K2O 0.0 0.1 0.3 0.1 0.2 0.1 0.1

P2O5 0.0 0.0 0.0 0.1 0.0 0.2 0.2

H2O 3.8 3.5 3.4 4.1 6.5 3.1 9.2

Total 100.2 99.8 99.5 99.9 100.7 99.4 99.9

Zr 18 36 33 22 18 80 95

Sr 24 388 335 112 80 303 391

Rb 1 4 11 3 17 2 5

Ni 220 44 81 53 63 2 188

Ba 19 51 92 18 21 82 66

Th 1 0 0 5 0 4 3

Pb 1 6 4 3 4 7 4

Ce 113 28 24 42 25 12 37

La 0 0 0 0 0 4 0

Note the low content in TiO2, except for the Tuar pillow lava. Sample TK58 is strongly altered and original magmatic texture is not

recognizable.


felsitic to vitric volcanic lithic grains indicate that vol-

canic products were felsic and silica-saturated (mainly

dacites; Table 2). Hypabyssal and granitoid detritus is

negligible; polycrystalline quartz, low-grade metasedi-

mentary grains and muscovite occur however, docu-

menting a minor but significant contribution from

continental basement rocks. Zircon was recorded, as

well as authigenic epidote.

3.1.2. Unit KK2

3.1.2.1. Lithology. Dark violet mudrocks with in-

tercalated thin layers of ochre-weathering, hematitic

silty chert (Fig. 4B), air-fall pyroclastics and up to

fine-grained sandstones yielding chloritic silicate

peloids (33 m). A prodelta to shelf environment

with starvation episodes during transgression is sug-

gested.

3.1.2.2. Petrography. Feldspatholithic volcanic are-

nites as in Unit KK1. Hypabyssal to granitoid detritus

Fig. 2. MnO/TiO2/P2O5 diagram (Mullen, 1983) for pillow basalts,

gabbros and pyroxenites of Tuarkyr. The Kizilkaya samples derived

from low-TiO2 magmas mostly plot in the calc-alkalic arc field

(CAB). The Tuar pillow lava is richer in TiO2. OIT: ocean island

tholeiite; MORB: mid-ocean ridge basalt; IAT: island arc tholeiite;

OIA: ocean island alkalic.

Fig. 3. Composite stratigraphic column for the Upper Paleozoic to

Triassic succession of Kizilkaya (see Fig. 1 for location of measured

sections and logs). In the Yashmu Hill, about 5 km northwest of

Kizilkaya village, gabbros, pillow lavas and chert are in tectonic

contact with the conglomeratic Yashmu Formation. Mid?-Jurassic

clastics unconformably overlie all stratigraphic units exposed in the

Kizilkaya structure (i.e., oceanic rocks, Amanbulak Group, ?basal

Triassic clastics and Dorikranites beds).


(granophyre, perthite) and detrital chert appear. Phyllite

lithic fragments and polycrystalline quartz indicate

minor but persistent contribution from low-grade meta-

morphic rocks. Authigenic kaolinite occurs locally.

3.1.3. Unit KK3

3.1.3.1. Lithology. Reddish to greenish and white

felsic pyroclastic rocks, including welded-tuffs and

surge deposits commonly containing accretionary lap-

illi (41 m).

3.1.3.2. Petrography. Reworked pyroclastics con-

tain, along with volcanic quartz crystals and pumi-

ceous felsitic debris, a few granitoid rock fragments.

At the top of the interval, felsic volcanic lithics with

quartz phenocrysts are associated with microlitic to

fluidal lithic grains derived from intermediate vol-

canic rocks.

3.1.4. Unit KK4

3.1.4.1. Lithology. This 715-m thick member con-

sists of locally conglomeratic (maximum diameter up

to 4 cm) red sandstones alternating with discontinu-

ously exposed red mudrock intervals. Sandstones

commonly display ripple to megaripple lamination

suggesting polymodal (mainly west to northwest)

paleocurrent directions. Scoured bases and cut-and-

fill structures are also frequent. Pyroclastic strata are

locally intercalated in the basal part. Burrows, mud-

cracks, rip-up clasts and reworked caliche nodules

become common in the middle–upper part. A sub-

aerial delta plain environment is suggested.

3.1.4.2. Petrography. Feldspatholithic felsic vol-

canic detritus is associated with subordinate sedimen-

tary rock fragments (radiolarian, spiculitic or non-

fossiliferous chert; siltite to argillite; sporadic sparite

and dolomite). Detrital quartz also increases, along

with supply from deeper-seated continental basement

rocks (quartz-bearing porphyroid, phyllite, quartzite),

associated in the upper part with detritus from gneissic

and granitoid rocks (myrmekite, granophyre, micro-

pegmatite, perthite, microcline). A few lathwork vol-

canic lithic grains derived from mafic lavas occur.

Among the accessory minerals, mostly brown to green

tourmaline and muscovite are common, along with

zircon, apatite and chrome spinel. Detrital spinels with

relatively high Cr content, indicated by a brown to red

color, suggest partially depleted harzburgitic-type

sources. Authigenic Fe-rich epidote is observed occa-

sionally up to the top of the unit.

3.2. Yashmu Formation

This formation (500–600 m), representing the

middle part of the Amanbulak Group, is a fining-

upward megasequence consisting of conglomerates

(Y1), passing upward to sandstones (Y2), and finally

to predominating mudrocks (Y3). These rocks are

assigned to the Yashmu Formation (new name). Four-

teen conglomerate samples and eight sandstone sam-

ples have been analyzed.

3.2.1. Unit Y1

3.2.1.1. Lithology. This very distinct unit consists of

thick-bedded channelized conglomerates rich in angu-

lar carbonate pebbles and cobbles (up to 26 cm in

maximum diameter), intercalated with red sand-

stones—locally displaying west-ward dipping cross-

lamination—and mudrocks. Graded-bedding, planar

lamination or very poor sorting and sparse very angu-

lar pebbles indicate rapid deposition during debris-

flow to flash-flood events in an arid alluvial fan setting

(Fig. 4C and D). Reworked caliche grains are com-

mon. Conglomerates are best exposed in the Yashmu

hill at the northern corner of the Kizilkaya structure,

where both their frequency and overall thickness

decrease southward within few kilometers, from a

maximum of 280 to 153 m. Closely spaced, sinistral,

northeast/southwest-oriented faults cause several

minor displacements of the succession (Fig. 1).

3.2.1.2. Conglomerate petrography. Conglomerate

and microconglomerate beds display an abundance of

sedimentary detritus, including radiolarian and nonfos-

siliferous chert, red sandstone and shallow to marginal

marine carbonate clasts. Carbonate clasts display three

main microfacies: (1) mudstone to sparsely bioclastic

wackestone; (2) bioclastic packstone including bran-

ches of the hydrozoan Amphipora—commonly thickly

coated by envelopes of blue-green algae—green algae

and rare uniserial foraminifers (a typical microfacies of

Devonian back-reef environments); (3) ooidal grain-


stone. Brachiopod associations of Late Silurian (Naliv-

kin and Luppov, 1936, in Luppov, 1957) to Middle–

Late Devonian age (Vistelius et al., 1953, in Luppov,

1957) were reported. Several clasts of fossiliferous

limestone were collected, and studied in detail by Va-

chard, who identified the following genera and species.. Moravamminids (‘‘Pseudo algae’’): Devonoscala

tatarstanica (Antropov, 1959).. Calcispherids: Radiosphaera ponderosa (Reitlin-

ger, 1957).. Parathuramminids: Archaeosphaera sp.; Vicine-

sphaera ex gr. angulata (Antropov, 1950); Salpingo-

thurammina cf. aperturata (Pronina, 1960);Bykovaella

sp.; Suleimanovella suleimanovi (Lipina, 1950); Eovo-

lutina ex gr. elementa (Antropov, 1950); Bisphaera

elegans (Vissarionova, 1950); Irregularina sp.; Cri-

brosphaeroides ex gr. simplex (Reitlinger, 1954); Par-

phia robusta (Maclay, 1965).. True Foraminifera: Paracaligella aff. lobata

(Pronina in Petrova and Pronina, 1980).

These faunal assemblages indicate more or less

restricted back-reef depositional environments, and a

Middle to Late Devonian (probably Frasnian) age

(Vachard, written communication, 1998). Such fossil-

iferous clasts represent the only preserved record of

platform carbonate growth in nearby areas during the

mid-Paleozoic.

3.2.1.3. Sandstone petrography. Sandstone compo-

sition compares with the underlying Kizilkaya red-

beds, with volcanic detritus still predominating over

sedimentary and basement-derived grains (including

Table 2

Petrographic composition of the Kizilkaya sandstones

Stratigraphic

unit

Sample Grain size

(Am)

Quartz

(monoxx)

Quartz

(polyxx)

Plagioclase K-feldspar Chessboard

albite

Volcanic

RF

Hypabyssal

RF

Middle Jurassic TK 6 350 18 3 4 13 0 9 2

TK 1 600 28 15 3 12 1 12 1

Basal Triassic TK 133 160 32 3 11 10 3 18 2

TK 93 850 23 12 1 9 1 21 7

TK 91 1000 32 28 0 13 0 12 2

Amanbulak Kizildag KD3 TK 89 600 14 5 5 4 6 27 3

Fm. Fm. KD3 TK 86 1100 10 6 4 2 9 37 4

KD3 TK 80 1200 11 2 1 3 3 32 4

KD2 TK 73 950 12 2 5 1 13 22 7

KD1 TK 72 500 12 6 7 1 1 20 5

KD1 TK 69 330 15 4 10 2 2 30 4

KD1 TK 62 650 15 8 4 1 1 22 4

Yashmu Y3 TK 61 630 12 2 6 5 7 37 6

Fm. Y2 TK 41 260 21 12 5 1 3 11 2

Y1 TK 30 3000 10 2 2 2 0 16 0

Y1 TK 22 720 17 14 8 3 3 15 2

Kizilkaya KK4 TK 44 220 18 8 8 2 1 10 0

Fm. KK4 TK 130 420 16 6 11 2 2 22 4

KK4 TK 127 280 16 8 19 4 4 28 2

KK4 TK 124 450 21 9 7 1 4 16 5

KK4 TK 113 360 23 8 10 3 3 21 5

KK2 TK 106 200 8 1 14 6 1 26 2

KK1 TK 98 190 13 4 20 6 3 25 0

Twenty-three samples (including the lithic microconglomerate TK30) were point-counted according to both traditional QFR (sandstone

classification after Folk, 1980) and Gazzi–Dickinson QFL methods (e.g., Zuffa, 1985). RF = fine- to coarse-grained rock fragments (traditional

QFR method). NCI = noncarbonate intrabasinal grains (mostly rip-up clasts). Eight primary proportional parameters and secondary ratio

parameters, representing an extension of those originally proposed by Dickinson (1970; Gazzi–Dickinson method), provide a complete

synthesis of framework composition: Q = quartz; F= feldspars, including aplite and granophyre; Lv = volcanic lithics; Lc = carbonate lithics;

Lp = terrigenous lithics; Lch = chert lithics; Lm=metamorphic lithics; Lu = ultramafic serpentine lithics. Qp = fine- to coarse-grained polycrystal-

line quartz, excluding chert; Qv =monocrystalline quartz of possible volcanic origin, showing uniform extinction, embayments or bipyramidal

outlines. P= plagioclase, K=K-feldspars, including albitized grains and chessboard-albite. L= total aphanite lithics; Lvf = felsitic volcanic lithics.


granitoid rock fragments and microcline). Rutile

appears in the dense mineral fraction.

3.2.2. Unit Y2

3.2.2.1. Lithology. Mostly red sandstones and mud-

rocks (70–77 m). Mudcracks are common. Mainly

fine-grained, rippled or intensely burrowed sandstones

largely represent levee to overbank deposits interbed-

ded with floodplain mudrocks, whereas the few inter-

calated pebbly sandstones (maximum diameter 3 cm)

represent the distal toe of the alluvial fan.

3.2.2.2. Petrography. Composition is similar to

member Y1. Sandstones are further enriched in detri-

tal quartz and still contain carbonate lithic fragments.

Granophyre and chessboard-albite grains are com-

mon. Zircon and brown tourmaline are the predom-

inant transparent dense minerals.

3.2.3. Unit Y3

3.2.3.1. Lithology. Dominantly red mudrocks, al-

though a coarsening-upward sequence capped by red

coarse-grained sandstones is intercalated in the mid-

dle/upper part (about 270 m). This poorly exposed

pelitic interval mostly consists of floodplain deposits.

3.2.3.2. Petrography. The rare sandstones show an

abundance of volcanic detritus, from felsic (volcanic

quartz, pumiceous vitric to felsitic lithic grains) and

subordinately from intermediate to mafic products

Plutonic

RF

Carbonate

RF

Terrigenous

RF

Chert Metamorphic

RF

Dense

minerals

NCI Alterites Matrix Cement Authigenic Total

7 0 0 1 3 0 2 7 1 0 33 100.0

5 0 0 1 0 0 9 3 9 1 3 100.0

1 0 0 0 1 1 0 1 7 11 2 100.0

3 0 1 1 8 0 0 1 1 0 15 100.0

1 0 1 0 2 0 0 0 1 0 11 100.0

3 1 1 0 4 0 0 3 1 0 27 100.0

5 0 0 0 4 0 2 3 0 1 17 100.0

6 0 2 0 5 0 0 2 0 0 27 100.0

7 0 11 0 1 0 1 0 6 0 15 100.0

1 4 6 3 5 0 0 2 0 0 29 100.0

2 0 3 1 5 0 1 5 4 3 13 100.0

2 3 2 5 5 0 6 6 1 0 19 100.0

2 1 2 2 1 0 0 9 5 0 5 100.0

1 4 1 1 5 0 11 3 11 0 13 100.0

0 18 6 26 3 0 0 0 2 0 15 100.0

1 7 0 2 2 0 9 0 7 9 6 100.0

0 1 0 2 4 0 9 5 6 0 22 100.0

2 0 2 2 3 0 5 0 3 5 19 100.0

0 0 0 0 1 0 0 0 2 14 3 100.0

5 0 1 4 5 0 4 4 6 3 11 100.0

2 0 0 0 1 0 3 0 2 20 1 100.0

1 0 0 2 1 0 9 12 12 6 3 100.0

0 0 0 0 1 0 0 0 4 25 1 100.0

(continued on next page)


(microlitic to lathwork lithic grains). Hypabyssal and

chessboard-albite grains are also common.

3.3. Kizildag Formation

This formation (686 m), representing the upper part

of the Amanbulak Group, includes abundant pebbly

sandstones to cobble conglomerates, with locally

interlayered boulder megabeds and pyroclastics. The

term Kizildag Fm. was firstly introduced by Kalugyn

(1975). Three members are distinguished and 20

sandstone samples have been analyzed.

3.3.1. Unit KD1

3.3.1.1. Lithology. Pebbly to cobbly (maximum

diameter 13 cm) conglomerates, reddish sandstones

and light red mudrocks (166 m). Tabular cross

lamination and clast imbrication in braided-channel

sandstones and conglomerates with scoured base

point to northward to north-northeast-ward sediment

transport.

3.3.1.2. Petrography. The base of the unit marks a

sharp increase in grain size associated with a distinct

increase in low-grade metamorphic (slate, meta-rhyo-

lite) and sedimentary lithic grains (including green to

black or red chert, clasts of lithofeldspathic volcanic

arenite and subordinate carbonate grains). The P/F

ratio also increases. Volcanic detritus still includes

mainly felsic but also intermediate to mafic lithics.

Carbonate grains are commonly recrystallized or con-

sist of bioclastic packstone yielding Cayeuxia-like

blue-green algae, tiny tubes and rare uniserial fora-

minifers included in lumps; most grains are coated.

Authigenic kaolinite is locally found.

3.3.2. Unit KD2

3.3.2.1. Lithology. Pebbly to cobbly, light grey to

greenish sandstones and red to light grey mudrocks

(309 m). Cross-laminations in braided-channel to

delta-front sandstones point to north-northeast-ward

to northwest-ward sediment transport. Cobbles (com-

monly 12–20 cm in maximum diameter) are mostly

Table 2 (continued )

Stratigraphic

unit

Q F Lv Lc Lp Lch Lm Lu Total Qp/Q Qv/Q P/F K/F Lv/L Lvf /Lv

Middle Jurassic 39 42 17 0 0 1 2 0 100.0 12 17 22 78 88 89

55 24 19 0 0 1 0 0 100.0 35 7 18 76 94 96

Basal Triassic 45 32 23 0 0 0 1 0 100.0 9 6 47 43 97 97

47 23 27 0 1 1 2 0 100.0 35 13 10 83 92 95

71 15 13 0 1 0 0 0 100.0 47 7 0 100 96 96

Amanbulak Kizildag KD3 32 23 38 1 1 0 2 2 100.0 24 35 34 31 87 91

Fm. Fm. KD3 25 22 49 0 0 0 3 0 100.0 35 23 22 14 94 91

KD3 28 19 49 0 3 1 1 0 100.0 18 46 26 52 91 86

KD2 22 31 33 0 13 0 1 0 100.0 15 52 36 9 71 82

KD1 29 15 30 6 9 4 6 0 100.0 33 19 82 14 53 58

KD1 26 21 42 0 4 1 6 0 100.0 21 16 79 12 80 70

KD1 35 11 35 5 2 7 6 0 100.0 36 13 73 13 64 76

Yashmu Y3 18 24 52 1 2 2 0 0 100.0 14 54 35 30 91 74

Fm. Y2 52 16 18 7 0 2 5 0 100.0 36 22 55 20 60 89

Y1 15 4 19 21 8 31 2 0 100.0 14 14 n.d. n.d. 24 n.d.

Y1 45 20 23 9 0 2 1 0 100.0 45 10 61 21 64 88

Kizilkaya KK4 47 24 19 3 1 3 3 0 100.0 32 13 61 29 68 85

Fm. KK4 35 22 35 0 3 2 4 0 100.0 27 20 77 10 80 78

KK4 30 34 36 0 0 0 1 0 100.0 33 6 71 15 98 91

KK4 44 19 26 0 1 5 5 0 100.0 29 28 61 14 73 83

KK4 43 21 35 0 0 0 1 0 100.0 25 10 66 19 98 72

KK2 15 38 43 0 0 2 2 0 100.0 6 19 68 27 92 92

KK1 23 40 35 0 0 0 1 0 100.0 21 9 68 21 96 92


from white ignimbrite to red rhyolite, but also include

sandstone, red to green and black chert, quartzite and

green mafic lava.

3.3.2.2. Petrography. The unit marks a sharp in-

crease in rhyolitic detritus (quartz with uniform extinc-

tion, embayments or bipyramidal outlines, pumiceous

Fig. 4. Volcanic and sedimentary rocks of Tuarkyr. (A) The pillow lava outcrop of Tuar, half-covered by drifting dune sand (Tuar). (B) Thin

chert layers intercalated with mudrocks (Unit KK2). (C) Poorly sorted conglomerate with angular carbonate cobbles deposited by debris flows

in arid fan settings (Unit Y1). (D) Graded layers with angular carbonate pebbles and reworked caliche accumulated during sheet-flood events

(Unit Y1). (E) Decametric slumped megabed (Unit KD3). (F) Festoon cross-lamination in braidplain sandstones (?basal Triassic clastics).

Hammer (A, D, E, F), ruler (B) or coin (C) for scale.


vitric and felsitic lithic grains). Carbonate and meta-

volcanic lithic grains are not found, and both chert and

low-grade metapelite decrease, whereas hypabyssal to

granitoid detritus increases (granophyre to granitoid

grains, perthite, microcline).

3.3.3. Unit KD3

3.3.3.1. Lithology. Light grey to red pebbly sand-

stones to cobble conglomerates interbedded with red

mudrocks (211 m). The base of the unit is marked by a

21.5-m thick cobble conglomerate megabed (with one

boulder over 2 m in maximum diameter; Fig. 4E), over-

lain by red to black pyroclastic rocks. This slumped

megabed suggests gravitational instability, probably

associated with renewed volcanic activity.

3.3.3.2. Petrography. Sedimentary detritus (mainly

sandstone, locally chert) decreases further, whereas

supply from granitoids increases further (sharp de-

crease of the P/F ratio). Volcanic quartz is still abun-

dant. Metamorphic detritus is persistent, including

higher-grade, deeper-seated rocks (phyllite to micas-

chist, paragneiss and orthogneiss).

3.4. ?Basal Triassic clastics and Dorikranites beds

The Mesozoic units overlying the Amanbulak

Group were never given a formational name. The in-

formal term ‘‘Dorikranites beds,’’ introduced herein,

designates the fossiliferous marker horizon found only

locally beneath the Eo-Cimmerian unconformity and

capping the ?basal Triassic clastics.

3.4.1. ?Basal Triassic clastics

The top of the Amanbulak Group is an unconform-

ity which corresponds to a major petrographic and

sedimentologic change and is probably associated with

a significant hiatus which, in absence of chronostrati-

graphic evidence, is generally assumed to roughly cor-

respond with the Permian/Triassic boundary (Luppov,

1957; Kalugyn, 1975). Four sandstone samples have

been analyzed.

3.4.1.1. Lithology. Grey cobble conglomerates with

sharp scoured base, passing upward to amalgamated

braidplain sandstones displaying spectacular large-

scale cross-lamination pointing to mainly west to

northwest, but also north to northeast, sediment trans-

port (Fig. 4F). Cobbles (up to 25 cm in maximum

diameter) consist of white to green and red ignimbrite

and lava, quartzose metamorphic clasts including

meta-conglomerate, and light grey to pink granite.

Grain size progressively decreases upward and, at the

top of the unit, white cross-laminated sandstones are

intercalated within prevailing light red mudrocks. This

unfossiliferous clastic sequence is about 500 m thick.

3.4.1.2. Petrography. Lithic arkoses to feldspathic

volcanic arenites. A sharp increase in detrital quartz

and a decrease in lithic fragments—which mostly

include relatively resistant felsic volcanic types—is

documented with respect to the Amanbulak Group. K-

feldspar becomes dominant among detrital feldspars.

Authigenic kaolinite is widespread.

3.4.2. Dorikranites beds

The Kizilkaya redbed succession is capped by an

over 12-m thick carbonate interval consisting of winn-

owed shelf packstones (‘‘coquinas’’) yielding echino-

derm plates, ammonoids (including Dorikranites sp.)

and pelecypods. The following pelecypod genera and

species were determined by Posenato and Loriga

Broglio (written communication, 1998): Eumorphotis

inaequicostata (Benecke) sensu (Chen, 1976); E. mul-

tiformis (Bittner); E. multiformis reticulata Chen; E.

multiformis rudaecosta (Kiparisova); Promyalina

putiatinensis (Kiparisova); Bakevellia exporrecta

(Lepsius). This transgressive marker layer of late Early

Triassic (Olenekian) age can be traced all around the

Caspian area (Kugusem, Mangyshlak, Bolshoe

Bogdo: von Buch, 1831; Shevyrev, 1968, 1990; Gae-

tani et al., 1998; Kukhtinov and Crasquin-Soleau,

1999).

3.5. Eo-Cimmerian unconformity and Jurassic clastics

The Upper Paleozoic to Lower Triassic succession

of Kizilkaya is truncated by a regional angular uncon-

formity. A very significant time gap, spanning from

the Middle Triassic to the Early Jurassic, is docu-

mented by a red lateritic hardground (0.7–3 m thick)

capping about 20-m thick white kaolinized saprock.

The unconformity is overlain by some hundred

meters of largely flat-lying (mildly tilted to the north-

east only in proximity of the main Kizilkaya fault)


clastic rocks assigned to the upper Lower Jurassic to

Middle Jurassic (Interdepartmental Stratigraphic Com-

mission, 1977).

3.5.1. Lithology

The base of the Jurassic clastics consists of locally

microconglomeratic white sandstones displaying spec-

tacular festoon cross-lamination pointing to north-

northeast-ward sediment transport. Locally interca-

lated are coal seams, carbonaceous grey silty marls,

and very fine-grained sandstones showing hummocky

cross-lamination. A braidplain to paralic depositional

setting is suggested.

3.5.2. Petrography

Coarse-grained lithic arkoses with felsitic volcanic

rock fragments, petrographically indistinguishable

from Triassic sandstones. Recycling of the latter and/

or reactivation of the same source rocks is indicated.

4. Geologic evolution of Tuarkyr

4.1. Sedimentary history

Sedimentology and petrography of the Amanbulak

Group document a complex paleogeographic evolution

during the Late Paleozoic. The transgressive basal part

of the unit (Units KK1 and KK2) consists of deltaic to

marine volcaniclastics derived from a largely undis-

sected, penecontemporaneous magmatic arc source

(Fig. 5; Dickinson, 1985). Detrital modes, dacite-type

character of volcanic detritus, and occurrence of meta-

morphic and hypabyssal to granitoid rock fragments

derived from the wallrocks of the arc suggest a con-

tinental arc setting (e.g., Marsaglia and Ingersoll,

1992). Penecontemporaneous explosive felsic activity

is documented by interbedded pyroclastic deposits

(Unit KK3), followed by continental redbeds contain-

ing a greater variety of grain types (Unit KK4). Oc-

currence of chert, carbonate and quartz-bearing

porphyroid (derived from a slightly metamorphosed

felsic paleovolcanic source) clasts suggests a mixed

collisional belt provenance, still dominated by detritus

from a partly dissected continental volcanic arc (Figs. 5

and 6). Occurrence of Cr-rich chrome spinel suggests

provenance from upper mantle slabs tectonically

emplaced in convergent to strike-slip settings within

the arc-trench system (e.g., Hisada and Arai, 1993).

Clastic petrography, thus, indicates a major paleogeo-

dynamic event, which took place prior to, or contem-

poraneous with, deposition of the Kizilkaya Formation,

around ?mid-Carboniferous times. Petrographic evo-

lution is gradual, suggesting high accumulation rates.

Grain size of sedimentary detritus increases at the

base of the Yashmu Formation, recording the climax

of tectonic activity. Geometry of the conglomerate

body (Unit Y1), rapidly wedging out southward, and

mainly westward paleocurrent directions suggest that

the source area was located to the northeast. Clast

composition points to progressive unroofing of a

sedimentary sequence including chert and mid-Paleo-

zoic platform carbonate (largely Middle to Late Dev-

onian back-reef limestone), along with felsic metavol-

canite, overlying a continental basement including

Fig. 5. Detrital modes of the Tuarkyr sandstones reflect assembly of

continental arcs during the Late Paleozoic and subsequent un-

roofing. Provenance fields (RO= recycled orogen; DA= dissected

arc; TA= transitional arc; CA= undissected continental arc; IOA=

undissected intraoceanic arc; BU= basement uplift) after Dickinson

(1985) and Marsaglia and Ingersoll (1992). Sandstones at the base

of the Kizilkaya Fm. (KK1, KK2) plot in the ‘‘transitional arc’’

provenance field. Next, from the upper Kizilkaya Fm. (KK4) to the

Yashmu (Y) and Kizildag (KD) Fms., detrital modes straddle the

boundary between ‘‘magmatic arc’’ and ‘‘recycled orogen’’ pro-

venance fields. Lithic arkoses of Triassic to Jurassic age plot in the

‘‘dissected arc’’ to ‘‘mixed’’ provenance fields, indicating deeper

erosion into the granitoid roots of the continental arc massif and Eo-

Cimmerian rejuvenation (full explanation in text).


granophyre and microcline-bearing granite (Unit Y2).

After a relatively quiescent stage characterized by

deposition of floodplain mudrocks, prograding clastic

wedges were mostly derived from dacite/rhyodacite

volcanic products (Unit Y3). These source rocks were

possibly co-genetic with the felsic volcanic rocks

exposed in the Turkmenbasi area, which represent a

high-K calc-alkalic series emplaced through thick

continental crust (Lemaire et al., 1997). If this is so,

a Permian emplacement age for the Turkmenbasi lavas,

as suggested by Lemaire (1997, p. 103), would be

confirmed.

The base of the overlying Kizildag Formation (Unit

KD1) documents a change in sediment transport, now

mainly toward the north, and in clastic petrography,

with distinct increase in chert and low-grade meta-

morphic lithic fragments. In the middle–upper part

of the Kizildag Formation, detritus from quartz-bear-

ing ignimbrite sharply increases (Unit KD2). Feld-

spars and granitoid rock fragments also increase at the

expense of sedimentary detritus, testifying to rapid

unroofing during a final stage of rhyolitic volcanism

(Unit KD3).

The supposed base of the Triassic consists of

coarse-grained lithic arkoses indicating a dissected

arc provenance. Sediment was largely derived from

unroofed granitoid rocks, such as those drilled in the

Karakum Block (Gavriliansk, 1965; Volvovsky et al.,

1966) or exposed east of Turkmenbasi (Mirsakhanov,

1989), which may represent the roots of the Turk-

menbasi arc.

Evolution of detrital modes from the Upper Paleo-

zoic to the Jurassic is compatible with that predicted

for juvenile to accreted, unroofed, finally consolidated

and episodically rejuvenated crustal blocks (stages 1 to

4 of Cox and Lowe, 1995). Although the largely

volcaniclastic sandstone suites accumulated in the

Tuarkyr and Mangyshlak episutural basins are broadly

similar in composition (Fig. 6), their sources were

distinct. Continental arc sources in Tuarkyr were in

fact largely unroofed by the close of the Paleozoic and

shed detritus rich in quartz and feldspars during the

Early Triassic, while lithofeldspathic volcanic arenites

were being deposited in Mangyshlak. Recycling of the

Tuarkyr clastics as a source for the Mangyshlak sand-

stones can be ruled out, both because of lithic arkose

composition of Lower Triassic Tuarkyr sandstones and

because of lack of nonvolcanic lithic grains (including

resistant chert) in the Mangyshlak sandstones.

4.2. Climatic changes and latitudinal drift

Climatic indicators (e.g., facies, geometry and

color of continental clastics, occurrence of reworked

caliche, relative abundance of labile lithic fragments)

point to progressively increasing aridity during sed-

imentation of the Kizilkaya Formation, until the

Yashmu fanglomerates (Unit Y1) were deposited in

arid settings. A gradual but steady increase in seasonal

humidity during deposition of the Kizildag Formation

is testified by fluviatile sandstones, more common

light green to grey colors of interbedded floodplain

mudrocks and occurrence of conifer plant fossils.

Unconformable transition to quartz-rich, grey braid-

plain clastics points to subhumid conditions in the

Fig. 6. Detrital modes of Carboniferous to Triassic sandstones from

both Tuarkyr and Mangyshlak are quartz-rich with respect to typical

Circum-Pacific arc suites. They compare better with largely con-

tinental, broadly coeval terrigenous wedges derived from recycling

of volcaniclastic assemblages and accumulated in collisional basins

in Central Asia after the Altaid Orogeny (‘‘collisional successor

basin’’ provenance of Graham et al., 1993; Junggar/Tarim: Carroll et

al., 1995; Noyon Uul: Hendrix et al., 1996), reflecting both con-

vergence and lateral wrenching in back-arc to retroarc foreland

basin settings during continental accretion (Thomas et al., 1999b).

Ideal arkose composition after Dickinson (1985). Provenance fields

as in Fig. 5. Confidence regions (90%, 95%, 99%) around the mean,

calculated according to Weltje (1998), are indicated for the

Amanbulak and Mangyshlak sandstones.


earliest Triassic. These distinct climatic trends are the

result of interplaying factors, including paleolatitudi-

nal drift, paleoclimatic changes, and tectonic events

such as continental collision leading to closure of

oceanic seaways and formation of topographic relief.

All of these factors are not well constrained, and

interpretation of sedimentary data remains tentative.

The stage of pronounced aridity suggested by the

Yashmu fanglomerates (Unit Y1) is particularly sig-

nificant and puzzling, because it took place during the

Late Carboniferous–Early Permian interval, when

Tuarkyr should have lain at low latitudes and not far

from the northwestern shores of subequatorial Paleo-

Tethys. One possible explanation is that the ?mid-

Carboniferous tectonic event caused not only closure

of an adjacent seaway but also formation of signifi-

cant relief and of an effective rain shadow. Progres-

sive increase in humidity in Permian to earliest Tri-

assic time might have resulted from a gradual

peneplation of collided blocks, possibly associated

with a shift of climatic belts at the end of the Gond-

wanan glaciation. Given our limited knowledge of

both paleoposition of Tuarkyr and atmospheric circu-

lation toward the close of the Paleozoic (Crowley,

1994; Francis, 1994), this paleoclimatic problem re-

mains unconstrained.

Recent paleomagnetic studies on the middle–upper

Amanbulak Group (site KC in Lemaire, 1997, roughly

corresponding to our Units Y3 to KD2) suggest

deposition during the mid-Permian, shortly before

the Illawarra magnetic reversal. Unfortunately paleo-

latitudes ranging from 9F 3jN to 12jF 2jN and

even 19jF 7jN have been inferred from the same

site (Lemaire, 1997; Lemaire et al., 1998a,b), leaving

the paleoposition of Tuarkyr poorly constrained. At

that time the Karabogaz and Karakum Blocks are ge-

nerally held to have lain not far from the composite

active northern margin of Paleo-Tethys (Dercourt et

al., 1993; Golonka et al., 1994; Gaetani et al., 2000a,b),

while the Cimmerian blocks (which had detached since

the Early Permian from glaciated Gondwana) were

rapidly drifting northward toward the equator (Gaetani

et al., 1995; Besse et al., 1998).

In the Early Triassic, occurrence of the endemic

genus Dorikranites all around the Caspian area sug-

gests that Tuarkyr lay then not too far from Man-

gyshlak and the northern Caspian region. According

to paleomagnetic data collected by Feinberg et al.

(1996), the paleolatitude of Mangyshlak at that time

was 17F 4jN, but these results also have been

questioned recently (e.g., Besse et al., 1998, p. 86).

Toward the end of the Triassic, Paleo-Tethys finally

closed, and during the Eo-Cimmerian orogeny the

Turan and Peri-Gondwanan blocks all became defin-

itively incorporated into Eurasia (Sengor et al., 1988;

Gaetani et al., 1998).

The thick laterite-type pedogenic profile capping

the pre-Eo-Cimmerian succession documents pro-

longed subaerial exposure in warm humid climates

in Late Triassic to Early Jurassic times. Occurrence of

coal, although less abundant than in Mangyshlak

(Gaetani et al., 1998) or Elburz (Northern Iran;

Assereto, 1966), points to humid subtropical to tem-

perate settings. Increasing humidity may be ascribed

to continuing migration toward northern temperate

latitudes, as indicated by the Laurussia apparent polar

wander path (Van der Voo, 1993). However, scant and

unreliable paleomagnetic data (paleolatitudes ranging

from 26jN to 48jN; Nazarov, 1971) leave even the

Jurassic paleoposition uncertain.

4.3. The oceanic basement of the episutural basin

The sequence of oceanic rocks found from Kizil-

kaya to Tuar along a major fault alignment which pre-

dates the Eo-Cimmerian unconformity, although

strongly tectonized and displaying greenschist–facies

metamorphism, represents a complete section of oce-

anic crust, including cumulates to plutonic, hypabys-

sal, effusive and sedimentary layers. Ultramafic rocks

were not observed in outcrop, but dunites were cored

in nearby localities (Gorelovski, personal communica-

tion, 1997). These ophiolites compare geochemically

with rocks derived from low-TiO2 basaltic magmas

produced in supra-subduction arc settings (e.g., juve-

nile intraoceanic back-arc basins; Serri, 1981), rather

than with mid-ocean ridge tholeiitic suites. Geochem-

ical data and spatial relationships suggest that they

may have represented the deformed oceanic substra-

tum of the Kizilkaya episutural basin.

4.4. Low-grade metamorphism of oceanic rocks

The oceanic rocks of Kizilkaya display greens-

chist–facies metamorphic parageneses. The Amanbu-

lak Group, in contrast, locally contains post-depo-


sitional Fe-rich epidote, indicative of hydrothermal

fluid circulation. Kaolinite is extensively preserved,

increasing in frequency in the upper part of the section

and becoming abundant in Lower Triassic sandstones.

Moreover, well-preserved vegetal matter in the Ki-

zildag Formation displays low thermal maturity (Ci-

rilli, personal communication, 1998). The Amanbulak

Group was not subject to a significant overprint du-

ring the Eo-Cimmerian orogenic event: diagenetic

temperatures, even in the basal part, did not exceed

200 jC.Within ?mid-Paleozoic oceanic rocks, only late

stage growth of very-low grade metamorphic minerals

such as sericite, epidote and pumpellyite may be

ascribed to the Eo-Cimmerian Orogeny. Greens-

chist–facies conditions must have been attained prior

to deposition of the Amanbulak Group, possibly

during the Late Paleozoic (?mid-Carboniferous) oro-

genic episode which caused deformation and mild

metamorphism of the associated dark cherty slates

found in fault contact with the Amanbulak redbeds at

Kizilkaya. Lower greenschist–facies metamorphism

in ?Permian arc-volcanic rocks of the Turkmenbasi

area should instead be ascribed to the Eo-Cimmerian

event, as suggested by K/Ar and Ar/Ar ages between

187 and 229 Ma (Lemaire, 1997, p. 96).

4.5. The Eo-Cimmerian orogeny

In the Late Paleozoic, a series of collision events

accompanied the closure of oceanic seaways lying

north of Paleo-Tethys (e.g., Turkestan Ocean of Zo-

nenshain et al., 1990; Fig. 7) and assembly of the

Turan microblock-collage (‘‘Intermediate Units’’ of

Fig. 7. Tentative Early Carboniferous sketch map showing distinct Turan continental microblocks separated by oceanic seaways linked to the

closing Turkestan Ocean in the north. The spreading centre between the Karabogaz and Karakum Blocks is inferred as formed in supra-

subduction settings related to incipient consumption of Paleo-Tethys in the south. Its original orientation is unknown.


Sengor and Natal’in, 1996). Calc-alkalic to shosho-

nitic volcanism related to the Altaid Orogeny in

Ghissar and south Tien Shan ended in the Middle

Permian (Masumov et al., 1978), and shortly after-

ward rhyolitic activity in Tuarkyr also came to an end.

In the Lower Triassic, Tuarkyr represented the south-

ern gulf of a shallow sea where the endemic am-

monoid Dorikranites dwelled (Fig. 8). Very high

sedimentation rates characterized episutural (arc to

retroarc) basin successions throughout the so called

‘‘Turan Plate,’’ from Aghdarband (volcanic lithic ar-

koses of the Qara Gheitan Fm., followed by the shal-

low-water carbonates of the Sefid Kuh Fm.; Ruttner,

1991; Baud et al., 1991) to Mangyshlak (feldspathic

volcanic arenites of the Otpan Fm. to Tyururpa Group;

Gaetani et al., 1998; Fig. 6). At this time, subduction

of Paleo-Tethys began along the Mashad trench

(Northern Iran), and a new continental arc was formed

close to the Aghdarband area (Baud and Stampfli,

1989).

The Middle to Upper Triassic is not represented in

Tuarkyr, due to nondeposition and/or Eo-Cimmerian

erosion. The Eo-Cimmerian Orogeny, when Iran and

the other Peri-Gondwanan blocks finally joined Eur-

asia along the Paleo-Tethyan Rasht-Mashad Suture

(Alavi, 1991; Eftekharnezhad and Behroozi, 1991),

caused only tilting of the Kizilkaya episutural basin

fill. This event took place before the end of the

Triassic, as indicated by uppermost Triassic strata

overlying the Eo-Cimmerian unconformity from

Kugitangtau (along the eastern Turkmenistan/Uzbeki-

stan boundary; Luppov, 1957) to Aghdarband and

Fig. 8. Olenekian paleogeographic sketch map depicting the ‘‘Turan Plate’’ as the Indonesian-type arc-trench to retroarc foreland basin orogenic

system related to subduction of Paleo-Tethys (here envisaged toward accreting Asia, and not beneath the Cimmerian continent as in Sengor and

Natal’in, 1996). Distribution of the endemic Dorikranites ammonoid fauna and inferred extension of the north Caspian shallow seaway are

shown. Occurrence of a few Tethyan ammonoids in Mangyshlak (Balini et al., 2000) points to westward connections with Tethys north of the

Stavropol High.


Elburz (Northern Iran; Ruttner, 1991; Saidi et al.,

1997).

New stratigraphic data from Tuarkyr confirm that

the so called ‘‘Turan Plate,’’ between the Mashad

Paleo-Tethys Suture in the south and the Eo-Cimmer-

ian Mangyshlak belt in the north, consists of an

originally complex, Indonesian-type mosaic of dis-

tinct continental microblocks and intervening oceanic

sutures. Magmatic arcs and continental fragments of

various size were assembled at successive stages main-

ly during the Late Paleozoic, but were still character-

ized by considerable subsidence at the beginning of

the Mesozoic, until they were finally welded to the

Eurasian landmass during the Late Triassic Eo-Cim-

merian Orogeny.

5. Conclusions

The mid-Paleozoic history of the Karabogaz and

Karakum Blocks is largely unknown. The original

sedimentary successions have long been eroded, and

preserved only as clasts within the Amanbulak terri-

genous wedge. Plutonic to hypabyssal granitoid bodies

found both in the Karakum Block and in the Turk-

menbasi area are generally ascribed to the mid-Paleo-

zoic (Mirsakhanov, 1989; Berkeliev, personal com-

munication, 1997), but geochemical data are lacking

and radiometric ages are old and few (e.g., Late De-

vonian age quoted by Gavriliansk, 1965). Even the

Upper Paleozoic to Lower Triassic stratigraphic record

is preserved only in the Kizilkaya domal structure, and

due to lack of outcrops and limited availability of bore-

hole and seismic data, paleogeographic reconstructions

are inevitably very tentative. Moreover, the original

configuration has been subsequently modified by oro-

genic episodes during the Mesozoic and by intense

strike-slip tectonics during Neogene to recent times

(e.g., Lyberis and Manby, 1999; Thomas et al.,

1999a,b), and we have no information concerning

rotations of crustal blocks.

New sedimentological and petrographic data pre-

sented here allow us to envisage the following major

steps in the geologic evolution of Tuarkyr.

During the Late Silurian to Late Devonian (pre-

Fammenian), platform carbonates, including carbo-

nate banks with abundant Amphipora hydrozoans

and back-reefs with algal-foraminiferal assemblages,

accumulated in a nearby area, on tropical shelves

facing an oceanic seaway lying north of Paleo-Tethys

(Turkestan Ocean).

Convergence and west- to northwest-wards sub-

duction began at the northwestern margin of the

Turkestan Ocean (Zonenshain et al., 1990, pp. 70

and 217), possibly as a response to accelerated spread-

ing of Paleo-Tethys in the south (e.g., Golonka et al.,

1994).

A possibly subduction-related extensional tectonic

regime (e.g., Doglioni, 1994) characterized the over-

riding plate. Rifting in intra-arc or back-arc settings

took place in Tuarkyr around Late Devonian to ear-

liest Carboniferous times (Gorelovski, personal com-

munication, 1997).

During the Early Carboniferous, the Kizilkaya

episutural basin deepened and its bottom was covered

by veneers of cherty sediments, partly interlayered

with pillow basalts.

Around mid-Carboniferous times, closure of Tur-

kestan seaways took place (Solov’eva, 1963; Zonen-

shain et al., 1990; Kurenkov and Aristov, 1995). The

Karabogaz and Karakum continental blocks began to

collide and portions of oceanic crust were subducted

and metamorphosed along the suture zone (marked on

VSEGEI, 1994). Previously emplaced felsic volcanic

rocks also locally underwent low-grade metamorphic

overprint.

Continuing subduction caused explosive dacite-

type volcanism in the Kizilkaya episutural basin,

which was rapidly filled by volcaniclastic redbeds

(Kizilkaya Formation). Chunks of oceanic lithosphere

were exhumed toward the surface during collision

with the Karakum Block.

Collision reached its climax with the closure of

oceanic seaways, probably associated with formation

of significant relief, and caused a marked increase in

aridity roughly around the Carboniferous/Permian

boundary. Detritus was supplied from cannibalized

sedimentary, volcanic and hypabyssal sources (lime-

stone, chert, volcanic arenite, meta-rhyolite and gran-

ophyre clasts) located nearby in the north to northeast

(Yashmu Formation).

After a relatively quiescent stage marked by de-

creasing grain size of terrigenous detritus (Yashmu

Formation, Unit Y3), a new tectonic and volcanic

event is recorded in the overlying conglomeratic

succession (Kizildag Formation, Unit KD1). Detritus


was now derived from sources mainly located in the

south and including volcanic to volcaniclastic, sedi-

mentary and metamorphic rocks (volcanic arenite,

green lava, chert, carbonate and phyllite clasts).

While the source terranes were progressively

eroded to their granitoid backbone, as documented

by sandstones with partly dissected continental-arc

provenance, final explosive episodes of rhyolitic vol-

canism took place (Kizildag Formation, Units KD2

and KD3). Tuffs and liparitic ignimbrites in fact occur

in the Kizilkaya section and were cored both to the

west in the Karabogaz Block (Gorelovski, personal

communication, 1997) and to the east in the central

part of the Karakum Block (Gavriliansk, 1965; Vol-

vovsky et al., 1966). Occurrence of fossil conifers

suggests more humid climates.

A major unconformity at the base of braidplain

lithic arkoses suggests continuing tectonic activity and

erosion of the plutonic roots of the arc massif roughly

around the Permian/Triassic boundary. A further in-

crease in humidity is also indicated.

Rapid subsidence continued into the Early Triassic,

in a complex retroarc foreland-basin setting.

In the upper Olenekian, transgressive marine strata

yielding the endemic ammonoid Dorikranites are

found at Kizilkaya and all around the north Caspian

region, indicating that Tuarkyr lay not too far from the

southern margin of newly formed Eurasia.

Final consolidation of the Turan microblock-col-

lage took place with the Eo-Cimmerian Orogeny,

when the Peri-Gondwanan blocks collided with Eur-

asia. This event only caused mild deformation in

Tuarkyr.

After a prolonged period of erosion and weath-

ering, documented by deeply altered lateritic soil

profiles, sedimentation of lithic arkoses, largely de-

rived from erosion of the remnants of Eo-Cimmerian

anticlines, resumed in the Middle Jurassic.

Evolution of detrital modes from the Upper Pale-

ozoic to the Jurassic is that predicted for juvenile to

accreted, unroofed, finally consolidated and episodi-

cally rejuvenated crustal blocks in arc, retroarc, and

finally intraplate settings. Clastic petrography, thus,

mirrors faithfully the complex, multistep processes

through which continental crust of the several ‘‘Turan

Plate’’ microblocks was generated during the Late

Paleozoic, and finally welded to Eurasia at the close

of the Triassic.

Acknowledgements

This study has been carried out within the Peri-

Tethys Programme. Many hearty thanks to F. Cecca,

V. Kalugyn and driver Tola Polivianij for their friend-

ly assistance in the field. Early Triassic pelecypods

were determined by R. Posenato and C. Loriga

Broglio (Ferrara). Paleozoic algal and foraminiferal

assemblages were determined by D. Vachard (Ville-

neuve d’Ascq). Very useful discussions and exchange

of information in Ashkabad with G. Gorelovski and

T. Berkeleev, and in Europe with M.F. Brunet, M.M.

Lemaire, A. Nikishin, L.E. Ricou, H. van Konijnen-

burg and R.A. Wood are gratefully acknowledged. S.

Poli and G. Weltje provided fundamental help with

chemical analysis of mafic igneous rocks and with

calculation of confidence regions in triangular space.

F. Cordey and S. Cirilli processed samples from chert

(oceanic rocks at Kizilkaya and Tuar; lower Kizil-

kaya Formation) and mudrock layers (Kizildag

Formation) in the vain search for stratigraphically

meaningful radiolaria and pollen. G. Muttoni and L.

Trombino gave advice on paleomagnetic and pedo-

genetic aspects. Drawings by Magda Minoli. The

manuscript has greatly benefited from stimulating

criticism by J.C. Thomas and by careful reviews by

S. Critelli and G. Manby. Financial support from

Peri-Tethys Programme (Paris) and Italian CNR to

M. Gaetani.

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Unroofing history of Late Paleozoic magmatic arcs within the ''Turan Plate'' (Tuarkyr, Turkmenistan)

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