IRitista Italiana di Paleontologia e Stratigrafia

I volur '!'+';-;lpaglne

THE APTIAN STRATIGRAPHY OF SOUTHERN TUARKYR(N\/ TURKMENISTAN, CENTRAL ASIA)

FABRIZIO CE,CCA 1, ANNIE V DHONDT 2 s. TAMARA N. BOGDANOVA3

ReceherJ Marcb 1). 1999:

Key-uords: Ammonoidea, Bivalvia, Biosrratigraphy, Creta-ceous, Aprian, Centrai Asia, Turkmenistan.

Riassunto. Le successioni ammonirifere del Turkrnenistan,quelle del Greater Balkhan e del Tuarkyr in particolare, sono consider-ete di riferimento per l'Aptìano. Sei sezioni relative all'interoallo Bar-remiano sommitale - base dell'Aptiano superiore sono state rilevatenella regione del Tuarkyr nell'ottobre deI 1997. Sono stare raccoltefaune ad ammoniti e bivalvi. I dati ricavati sono confrontati con quelliprovenienti da un'altra sez-ione studiata nel 1959 da una missione russa.

La distribuzione stratigrafica delle faune è disconrinua. Nell'intervallostudiato le faune ad ammoniti sono caratterizzate da bassa diversità,espressa dalla dominanza del genere De sbayesites nell'Aptiano inferioree del genere Epicheloniceras, associaro con il meno Írequente Caspianites, alla base dell'Aptiano superiore. Esistono specie comuni conCaucaso, Inghilterra, Germania, Francia e Svizzera e quindi le fauneriflettono un impoverimento più che un isolamento geografico. IÌe-cluivalenza cronologica della Zona zd Epicheloniceras subnorlosocosta-

raz in Turkmenistan con b Zont ad Epicheloniceras martinioides inuso in Inghilterra è messa in discussione in quanto ilivdrli ed Epiche-/oniceras del Tuarkyr corrispondono alla parte superiore dellaZona a E.martinioides, cioè alla Sottozona a Epicheloniceras buxtorfi. La fauna a

bivalvi è compostx principalmente da pteriidi, Exogyrinae e trigoniidi.

Questi gruppi indicano chiaramente un ambiente rnarino con acque

molto basse ed abbastanza calde, tipico per il Cretaceo inferiore dellaTetide. Gii cterodonti sono rroppo rari per dare ulteriori precisrzionibatimetrichc. Nessuno dei gruppi presenri indica comporramenroinfaunale profondo e tutti sono considerati littorali. La fauna a bivalvipresentx forti affinità con cluella del "Lower Greensand" inglese.

Abstract. The ammonite successions of Turkmemstrn, prrricu-larly those of the Greater Balkhan and Tuarkyr areas, are consideredreferences for the Aptian Stage. Six sect.ions across the uppermost Brr-remian - basal Upper Aptian inter-val were studied in the Tuerkyrdeserr in October 1.997, and amn'ronites and bivalves were collected.Data are compared with those from a section sampled by a Russianteam in 1959. The stratigraphic distribution of the faunas in the sec-

tions is discontinuous, as the fossiliferous levels intercalate wirh rer-rigenous sediments. The ammonite faunas, at least in the intervalssarnpled, show low diversity and are domrnated by the genus

Deshayesites in the lower Aprian and the genus Epicheloniceras, tssoci-ated wrth the less comnonCaspianites, in the basal upper Aprìan. The

dccepted June 2A, 1999

Turkmenisten sections contain species present elso in the Caucasus,England, Germany, France end Switzerland, indicating that the Turk-menian faunas reflecr impoverishement rather than geographic isola-tion. The chronoloeic equivalence between the Turkmenian Eplclreloniceras subnodosctcostatwm Zone nd rhe Epìcheloniceras martinioidesZone in England seems questiénable because the E1>icheloniceras bear-ing beds of the Tuarkl'r correspond to the upper part of the E. martin-ioides Zone, i. e. the Epicheloniceras buxtotfi Subzone. The bivalvefauna consists mainly of pteriids, Exogyrinae oysters and trigoniids.These groups undoubtedly indrcate a very shallow, fairly warm andfully rnarine environrnenr, typical of the Tethyan Lower Cretaceous.The heterodonrs are roo rare to give further bathymetric indicarions.None of the taxa indicate deep burrowing and all are assumed to beveru littoral. The bivalve fauna shows strone affinities wirh thet of the.trngttsn LOwer Irreensand.

Introduction.

During October 1997 one of the authors (F.C.)carried out a survey of the Aptian succession in the south-ern Tuarkyr area (northwestern Turkmenisran, Fig. I ).

The Aptian successions of Turkmenistan werestudied in detail during the '6Os and '7Os by Sovietteams, especially in the Greater Balkhan and in theTuarkyr area. Several publications have been devoted togeologic and stratigrapl-ric rhemes (Resolution of theInterdepartmenral Strarigraphic Commission, Sarnar-kand,1.977; The stratigraphy of the USSR, 1986; Bog-danova & Tovbina 1995; Bogdanova er al., 1989; Preo-brazhensk;2, 1990; Prosorovsky, 1990; Tash[ev & Tovbi-na, 1992) and to ammonite palaeontology (Tovbina,1963; Bogdano\a, 1,971^, b, 1971, 1978, 1979, 1983,1991; Kakabadze et al., 1928).

The last subject is particularly importanr becausethe ammonite succession of Turkmenisran is considereda reference for the Barremian - Aptian boundary. In fact,the \forking Group on Lower Cretaceous Cephalopods

(1) Centre de Sédimentologie et Paléontologie - Université de Provence, UPRESA 6019. 3 placeCedex 03 Fr:rnce. E-mail: cecca@nev'sup.univ-mrs.fr

(2) Departement of Palaeontology, Royal Belgian Institute of Natural Sciences, Vautierstraatdhondt@kbinirsnb.be

(3) All-Russian Geological Insrirure (VSEGEI), Srednyi pr. 74, 1991A6 St.-Petersburg RUSSIA.

Victor Hugo - Case 67 F-11311 Marseilie

29 ll-1000 Brussels BELGIUM. E-mail:

E-mail: vsegei@mail.wplus.net .

378 F. Cecca, A. V Dhondt G T. N. Bogd.anor.,a

Fig. I - Location of the study area, south of Kizilkaya.

(Hoedemaeker 8. Bulot, 1990; Hoedemaeker tr Compa-ny, 1993; Hoedemaeker & Cecca, 1995) retained for thezonation of the Mediterranean area the Deshayesites

tuarkyricus Zone, which was defined in Turkmenisran as

the basal ammonite zone of the Aptian (Bogdanova,197la). The topmost ammonite Zone of the Barremianin Turkmenistan, the Turkmeniceras twrftmenicurn Zone,was proposed as a horizon in the first version of theMediterrane an zonatiorr (Hoedemaeker & Bulot, 1990) .

Bogdanova & Tovbina (1995) and Bogdanova &Lobacheva (1995) proposed the Greater Balkhan area as

the type-region for the selection of the stratotype of theAotìan boundarv.

However, the Vorking Group on rhe Aptian stage(Erba, 1996) did not take into account the Turkmeniansections because, according to the standards normallyrequired for stratotype definitions, no sufficient bios-tratigraphic information was available at the time.Despite the numerous palaeontologic papers onammonites, no detailed stratigraphic logs of the Turk-menian sections were published and no further informa-tion was available, excepr for faunal lists and generallithologic characteristics of the sections. The strati-graphic data reported by Bogdanova (1971a) gave theimpression of a discontinuous distribution of the faunasin the Turkmenian sections.

The expedition in the sourhern Tuarkyr regionwas undertaken to clarify the precise stratigraphic distri-bution of the numerous Turkmenian ammonite speciesand to provide a detailed description of sections.

Geologic setting and localities studied.

The Tuarkyr area is located in NW Tuykmenistan(Fig. 1), east of the Karabogaz Gol. It is characterizedbyan anricline strikins NW-SE with a Permo-Triassic core.A smaller anticline (Fig. 2) with a Jurassic core sur-rounded by Lower Creraceous formations is presentsouth of the periclinal closing of the anticline.

The general stratigraphic features of rhe pre-Apt-ian Lower Cretaceous suciession, as described in theResolution of the Samarkand Congress (Interdeparr-mentai Stratigraphic Commission, 1,977), are from topto Dottom:

interval d) sandstones and siltites with inrercala-tions of shales and limestones containing ammonices(Turbmeniceras, Matheronires) and bivalves; 25-35 m.lJppermost Barremianl

interval c) siltites and shales with intercalatedshelly bioclastic levels. The most common fossils arebivalves (Gen,illia,trigoniids etc.), although ammonitesof the Imerites giraudi Zone (Colchidites gr. colchicus,Imerites faarei, L giraudi) have been reported (Tovbina,1963; Bogdanova, L97La);20-4a m. Upper Barremian;

interval b) calcarenites and intercalated marls andshales, with abundant orbitolinids, bivalves (exogyrineoysters) and brachiopods; 12-50 m. Flauterivian - Bar-remian;

interval a) dolostones and limestones with inrerca-lated shaly levels overlying unconformably Callovianstrata; bivalves (exogyrine oysters) indicative of a shal-iow marine environment are the most common fossils;about 60 m. Hauterivian.

Prosorovsky (1990) included intervals a) and b) inthe Urgonian facies though transitiónal facies to conti-nental deposits occur in the southern Tuarkyr . Intervalsc) and d) form the second Urgonian cycle described byPreobrazhensky (1990) and represent a marine regres-sion pre-dating the major deepening of the basin that led

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The Aptian Stratigraphy of NW Twrkmenistan 379

to the deposition of the Lower Aptian shaly succession(Preobrazhensky, 1990; Prosorovsky, 1990).

It is worth noting that the succession of thesouthern Tuarkyr studied in the present paper shows thecharacteristics that in Prosorovsky's (1990, fig. 2) strati-graphic scheme define his "Cubadag foredeep" morethan rhe "Tuarkyr anteclise", the latter probably refer-ring to the northern Tuarkyr and nor to rhe area studiedin the present paper.

Description of the stratigraphic sections.

Six sections were studied near theGeokdere (Fig. 2, 3):

1 - S\f Mount Bishik, starting 13 km

village of

south ofG eokdere;

2 - NE flank of Mount Bishik, 8 km south oiGeokdere;

3 - Teked;ik 1, located in a crnyon 4.5 km east ofGeokdere;

a - Tekedjik 2, 4 km east norrheast of Geokdere;5 - S Mount Hanbegiiburun, 3.5 km northeast o{

Geokdere;6 - Mount Hanbegiiburun, 3 km norrh norrheasr

of Geokdere.The fossils mentioned in the descriprions of the

sections were collected during the expedition carried outin October 1992.

Another section ("Geokdere"), almost 12 kmnorth northeast of Geokdere, was sampled by one of theauthors (T. N. B.) in 1959 and the most relevan t data arecompared u'ith those obtained from Sections 1-6.

Ve rnust stress that despite the absence of vegeta-tion, the shaly intervals are often covered by relativelythick (0.50 - 1 m) colluvial material. This masks the realsuccession and only the more calcareous, harder, bedsare exposed.

A1l sections are described below from bottom ro top.

Section 1 - This secrion was logged and sampledabout 2 krn S\l of the wesrernmosr edge of the ridgecalled Mount Bishik (Fig. Z). The base of this secrion

1Fig. J) may correspond ro rhe rop of the Urgonirnfarcies sensu Prosorovsky (1990). Older beds crop our inthe canyons located 2-3 km sourh of the southern flankof Mount Bishik.

llnnor Rarromian

Top of the Urgonian facies - Arenaceous lime-stone with orbitolinids and the bivalve Ceratostreontubercultferum (Koch Er Dunker).Layer | - bioclastic calcareous sandstone, capped by a

thin horizon containing numerous internalmolds of bivalves: Cucwllaea sp., Trigoniacarinata Agassiz s.1., ? Àesatrix (Vectorbis)

Fig.2 - Geologic nap of thc srudv arca. Lettcr T indicates theapproximate location of Secrion "Geokderc".

r.,ectensis (Forbes); 1 m- siltstone. 2 m

Layer 2 - thin level wirh ? Ceratostreon;- grey siltstone; rhe brachiopods Belbekella

mubiformis ? (Roemer) and an unidentifiedterebratulid were found O.3O m below thetop. 1.5 m

Layer 3 - laminated sandstone with fragmenrs of mol-I

^ ^^luscs; u.lu nì

- grey siltstone with inrercalarion of numer-ous, ferruginous, hard surfaces; echinoidsreferable to Toxaster cf. retwsus (Lanarck)(sample SWG 3bis) at rhe very base; on top,"Card.ium" aîf. cottaldinwm d'Orbigny and

180 F. Cecca, A. V Dhondt C T. N. Bogdanotta

very abundant specimens of the brachiopodsBelbekella bertheloti (Kilian), Sellithyris sp.;

3.5 m- siltstone. 4.5 m

Layer 4 - thin bivaive-rich level;- siltstone. 1.5 m

Layer 5 - yeliowish sandstone with intercalations ofgrey siltstone znd/or finer poorly cementedsandstone; an oolitic level with fragments ofmolluscs on top; 8 m

- grey shale. 3.5 mLayer 6 - composite level. From the bottom: (6a) layer

of white, micritic nodules (1,5-25 cm longand 5-10 cm thick) dispersed in the shale;(6b) 1 m of shale capped by a hard, ferrugi-nous surface; (6c) 1 m of shale; (6d) Z cmthick bed of a white, micritic limestone; (6e)

0.5 m of shale capped by a thin level with thebivalves Geraillaria alaeformis (J. Sowerby),Geraillella sublanceolata (d'Orbigny), Cer-dtostreon tuberculiferum (Koch & Dunker)and gastropod specimens of Confwsiscalarhodani (Pictet Ec Roux) (identified by V A.Kotkov); 2.80 m thick

- shale. 4 m

Lower Aptian, Deshayesites tuarkyricus Zone.

Layer 7 - bed of hard sandstone 0.30 m thick, overlainby 0.20 m of a bioclastic, oolitic level withfragments of molluscs, echinoids, corals, theammonites Desbayesites antiquus Bogdanovaand Deshayesltes sp. and the bivalve "Iotrigo-nia" abichi (Anthula);

- snale. u.) m.Layer 8 - bed of sandstone, 0.20 m thick, overlain by a

0.20 m thick level with intraclasts, trigoniids,Deshayesites sp.;

- shale (1 m) capped by a hard, ferruginoussurface;

- shale. 1.5 m.

Layer 9 - oolitic sandstone with intraclasts, fragmentsof small bivalves, rhynchonellids, Deshaye-sites cf. antiquus ? Bogdanova; 0.30 m.

- yellowish siltstone. 0.5 m.

Layer 10 - laminated sandstone, pinching out laterally.0.20 m.

Samoling was terminated about 150 m before the""'''r",'b "*" ''foot of the cliff of Mount Bishik due to unfavourable

outcrop conditions and was continued laterally 200 mnorth, just at the base of the slope of the westernmostedge of M. Bishik. srarring from Layer 9.

Layer 9 - oolitic s,àndstone with fragments of bivalves,rhynchonellids; just a few centimetres belowDeshayesites tuarbyricws Bogdanova and thenautiloid Cymatoceras pseudoelegans (d'Or-bigny) were found; 0.20 m.

- yellowish siltstone. 1.80 m.Layer 10 .- sandstone containing oolites and mollusc

1loeDns; u.lu cm.- grey shale. 5 m.

Lower Aptian, Deshayesites u/elssi Zone.

Layer 11, - hard, ferruginous sandstone; 0.15 m.- yellowish silty shale. 1Z m.

Layer 12 - Bed of grey marl, 0.15 cm thick, with abun-dant Deshayeslfes specimens, unidentifiablebivalves, numerous gastropod specimens ofthe genus Nwmmocalcar (identified by M. A.Golovinova) and fragments of echinoidspines, followed by a bed of arenaceous lime-stone, 0.20 cm thick, whose upper surface iscrowded by ammonites: Deshayesitcs afî.deshayesi (Leymerie) , D. luppoai Bogdanova,D.cf.spatbi Casey, D.cf.kiliani Casey,D. cf.eaoloens Luppov;

- grey shales. 2.5 m rhick. c.rpped by a hard.arenaceous, ferruginous bed O.1O m thick;

- grey shafes, r m, capped with a bioturbated,hard, arenaceous surface;

- grey shales. About 2.5-3 m.Layer 13 - 0.30 to O.Z0 m of laminated sandstone form-

. irg globular bodies laterally: this leve1 was

follorved on the flank of the mounrain andcorresponds to Layer 11 of Section 2;

- shale with belemnites and Deshayesites pappiBogdanova on top. 6 m.

Layer 1.4 - Marls with calcareous, glauconite-coatednodules containing rare fragments ofbivalves. This Layer continues in Section 2,

where it has been named L:ryer .t 0.

Section 2 - This section was studied on rhe norrh-western flank of Mount Bishik (Fig. 2,3). lts base cor-responds to the shales at the foot of rhe cliff.

Lower Aptian, Deshayesites welssi Zone.

Layer 76

Layer 15

- limestone bed; 0.20 m.- grey shale. 3 m.- ferruginous sandstone; 0.15 m.- shales and siltstones ìn the upper prrtl Z m.

A specimen ol Deshayesìtes similis Bogdano-va was collected from the talus. but it origr-

F;o 1 - Sr..rio'..hi. l^-s of Sections 1-6. Encircled numbers on the lefr side of the logs correspond to the Lavers discussed in the text, where-'.b.""'."'.b...r''.-."b"es numbers on the right side correspond to sample numbers.

381Tbe Aptian Stratigraphy of N'\X/ Twrkmenistan

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382 F. Cecca, A. V Dhondt & T. N. Bogd.anooa

nared from the interval between the top ofLayer 16 and 4 merres above Layer 15.

Layer 14 - ferruginous sandstone; 0.15 m.tl- snares. J.) m.

Layer 13 - Bed of grey marly limestone; O.1O-0.i5 m.- grey shale; a deshayesitid ammonite was co1-

iected from the talus. 4.5 m.Layer 12 - Bed of grey marly limestone containing rare

f r 1 ' | ^ r ^ ^ a^rragments or Dlvatves; u.tu-u.lu m.- grey shale. 5.5 m.

Layer 1.1 - Globular bodies of sandstone (diameter ofabout 0.5 m) resting upon 0.20 m of a sand-stone bed conraining rare, small bivalves(mainly oysters); this Layer conrinues larer-ally in Section 1, where it was designated as

Layer 13.- grey shale. 6 m.

La1's1 19 - Marl overlain by calcareous, glauconite-coar-ed nodules containing r;rre fragments ofbivalves. This Layer conrinues in Section 1,

where it was named Layer 1,4.

- shale; 3 m.- fine poorly cemenred sandstone. 3 m.

A 41 m thick succession of siltstones and biotur-bated sandstones follows (Fig. 3). Thalassinoides wasobserved in Layer 5 and Layer 4; it is associated withSbolitbos in the siltstone above Layer 4.

U p per Apti an, E p i c he I o n i c e ras s u b n o d o soc ostatu m Zone

Layer 3 - hard, bioturbated (Sl<olithos and Thalassi-noides) sandsrone, tending to form globularbodies; 1 m.

- yellow siltstone. 2 m.Layer 2 - fossil-rich, arenaceous Layer containing

numerous bivalves including,4etostreon latis-simum (Lamarck), Litschkotrigonia ingu-schensis (Renngarten), Pterotrigonia ornata(d'Orbigny), the gasrropod Pleurotomariasp., the nautiloid Cymatoceras psewdoelegans

(d'Orbigny) and rhe amrnonires Epiche-loniceras gr. tschernyscbezai (Sinzow), E, cf.tschernyschezui , E. tscbernyschewi y^r. mlnuta(Sinzow), E. cf. subnodosocostatum (Sin-zow); 0.60 m.

- silty sandsrone. 1 m.Layer 1 - ferruginous, arenaceous concrerions forming

a flat morphology below the top of MountDì'ìDrsnlK; u.) nì.

- shale (not studied) . more than 20 m.

Section 3 - Tekedjik 1 - This section is exposed 4

km easr of Geokdere, in a E-W canyon curting throùghthe northernmosr parr of the Tekedjik ridge (Fig. 2, 3).Its base consists of siltstones and shales cropping out atthe foot of the ridge.

Upper Aptian, Epicheloniceras subnodosocostatum Zone

Layer | - ferruginous srratified sandstone with frag-ments of body chamb ers of Epicheloniceras;0.5 m.

- sandstone. 1 m.Layer 2 - thin, srratified, ferruginous, bioturbated

sandstone with Epicheloniceras tsch-ernyschewi yàr. minuttt (Srnzow) ; O.80 m.

- sandstone; 0.60 m.Layer 3 - stratified ferruginous sandstone wrth Caspi-

anites cf. tuarkyriensis Kakabadze, Eptcheloniceras cf. tsclternyschewt? yar. minuta?(Sinzow). 0.60 m.sandstones and stratified ferruginous sand-stones (Fig. 3). 10 m.

Layer 7 - stratified ferruginous sandstone N,ir.h Epicheloniceras cf . buxtotfi (Jacob) ; Caspianitestuarkyriensis Kakabadze was collected fromthe talus but it probably originated from theoverlying La;'er 8b; 0.5 m.

- sandstone. 3 n'r.

Layer 8 - Composite fossil-rich level. 3 rn. From thebottom:8a, layer of hard sandsrone, containing fr.rg-ments of oysrers and small specimens ofEpicheloniceras, A.7O m, capped by e thinshelly horizon with fragments of smalibival ves l

8b, sandstone with giant, resedirnented andreelaborated (both terms sensu FernandezLopez,1991) an-imonite specimens ol Ept.ch-eloniceras gr. tschernyscheui (Sinzow) whichare concentrated ar the base and E. subno-rlosocostatum var. robusta (Sinzor,); O./O rn.This deposit is discontinuously overlain by.rlenticular bioclastic, bivalve-rich Lryer withGeraillella sublanceolata (d'Orbigny),,4erostreon latissimum (Lamarck), Lttscbbotrrgo-nia inguschersrs (Renngarren), Pterotrigoniaornata (d'Orbigny), Thetis minor (J. de C.Sowerby), "Astarte" learajmanica Prosorov-sky, unidentified pectinids and heterodonts,Belbebella sp. and wood debris; verrical fossilrraces (SÀolltbos ?) are visible in the upperparr;8c, hard, bioturbated sandsrone, with bivalvefragments. 1.60 m.

- sandstone; 1 m.- stratified ferruginous sandstone; 0.5 m.- grey shales, mainly covered by colluvium; 35

m. Under this cover, 6 m above the arena-ceous concretions millirnetric, black-whitemarly alternances overlain by a bed of marlylimestone, O.2O m thick, were observed.

Layer 9 - thrck monospecific coquina with Aetostrec,tnÌatissimum (Lan-iarck); 1.5 m.

- grey to yellowish siltstones. 6 m.

The Aptian Stratigraphy of N\X/ Turkmenistan

Bottom side of a fragmentary specimen oi Epiclteloniceras gr. tscberltjscheul (Sinzorv) showing bivalve encrustations. The arrory indi-cates a juvenile oystcr shell encrusting a broken part of the shell. Specimen MPUM 8274, housed in the Museo di Paleontoloqia of theL.lnn'ersity of Milan.

383

tì;,, I

Layer 10 - thick monospecific coquina with oystershells (not sampled); 0.5 m.

- siltstones (not studied). about 50 m.

Section 4 - Tekediik 2 - This secrion is locatedabout 1 km north of Sectìon 3 (Fig. 2) and it shows a

similar succession. Thus, the same Layer-numbering wasused. The section starts with rhe equivalent of Layer 3 ofSection 3 (Fig. 3).

Upper Aptian, Epicheloniceras subnodosocostatum Zone

Leyer 3 - srratified ferruginous sandsrone with theammonite Epicheloniceras gr. tschernyschezai

(Sinzow). 0.60 m.An 11 m thick succession of sandstones andstratified f erruginous sandstones f o11ows

(Fig. 3).Layer 8 - In this section, this Layer is 2.4 m thick.

From bottom îo top:layer 8a shows the same characteristics as inSection 3;

8b, sands with the same fossil conrenr of Sec-tion 3 plus the bivalves Aetostreon latissimwm(Lamarck) and "Astarte" karajmanicaProsorovsky; 0.60 m.8c, hard, bioturbated sandstone; 0.90 m.

- grey shale. about 30 m.Layer 9 - monospecific coquina wrthAetostreon latissi-

mum (Lamarck); 0.2 m.- fine siltstone. 6 m.

Layer 10 - monospecific coquina with oyster shells. 0.5

Remarks on Layer 8 in Sections 3 and 4.

This composite level is characterized by the pres-ence of gìant Epicheloniceras gr. tschernischerni (Sinzow)resernbling the largest specimens illustrared byNikchitch (191,5\.It must be stressed that the collectionof ammonites from Layer 8 in both Sections 3 and 4 hadto be limìted for practicai reasons. The preservation ofthe specimens from this Layer (and its laterei equiva-lents) is not satisfacrory, because the young whorls arepoorly preserved or absent. The characteristics of theyoung whorls are necessary for species identificarion(Casey, 1960-80) and in the future a Írore detailedpalaeontological study of these giant forms of Epiche-loniceras should be based on larger collections, seekingwith care specimens with better preserved inner whorls.

The faunal content as well as rhe taphonomiccharacteristics, indicate that high energy was required totransport and break the bivalve shells in layer 8a. How-ever, even higher energy is necessary to explain the re-elaboration of the giant (40-45 cm diameter) specimensof Epicheloniceras. The term re-elaboration (or tapho-nomic reworking), meaning the exhumation and dis-

184 F. Cecca, A. V Dhondt G T. N. Bogdanooa

Upper side of rhe same specimen of fig. 4. The arrow indicates both an extcrnal and an internal molcl of two bivalves rcsting on theelaborared upper side of the ammonite internal mo1d.

Fio 5

placernent of previousiy buried preserved elements, isused here according to Fernandez Lopez (1991). Gener-a1ly, these specimens are incomplete with the body-chamber missing. Fragments of body-chambers of spec-

imens that probably reached a diameter of 50-55 cm are

common in layer 8b. Ve observed oysters attached toboth sides of some of these ammonite specimens (Fig. 4,

5\ However the hvnothesis that encrustation occuredduring both the life-cycle (Seilacher, 1960; Donovan,1989) and post-mortem floating of the empty shell maybe excluded since oysters settled also on the corners ofthe broken shell (Fig. a). This observation also excludes

Cope's (1968) hypothesis of encrustation of the under-surface of dead rlmmonites which were resting on thesubstrate.

Due to che weight of such large specimens, theenergy necessary for re-elaboration was very high. Figs.

4 and 5 show these characteristics on a smaller fragmentfrom a specimen of Epicheloniceras cf. tschernyschewi

that we could transport from the fie1d.

The succession of the different taphonomic phas-es can be summarized as follows:

1) accumulation of the fragmented arnmoniteshells on the bottom;

2) bivalves' settlement;3) burying of ammonite shellsl4) compaction and beginning of lithification of

the ammonite's internal moldl

5) re-exhumation and overturning of theammonite shel1s;

6) erosion of the other face followed by encrusra-tion of a second oyster community.

It is worth not;ng that trigoniids are not brokenand the two valves are often connected. Therefore theyare not reworked.

Section 5 - This short section connecrs Section 4and Section 6 and it was logged about 1.5 km south ofthe latter (Fig. 2, 3).

Upper Aptian, Epicheloniceras subnodosocostatum Zone

Layer 7 - reddish, stratified ferruginous sandstone;this Layer was followed for 1.5 km and cor-responds to Layer Z of Section 6; 0.30 m.

- poorly cemented sandstone. 1 m.Layer 8 - hard. ferruginous, bioturbated sandstone

with giant Epicheloniceras spp.;2 m.- poorly cemented sandstone. 12 m.

Layer 9 - monospecific coquina wtth Aetostreon latisst.-

mwm (Lamarck); it is the iateral conrinuationof Layer 9 of section 4; 0.5 m.

- fine, poorly cemented sandstone. 6 m.Layer 10 - oyster coquina (lateral continuation of Layer

f^l0 ol Sectron 4)l 0.5 nr.

- fine, poorly cemented sandstone to siltstone.6m.

Layer 1,1 - hard sandstone. 0.5 m.

The Aptian Stratigraphy of NVt Turkmenistan

Signilicant an'rmonires frorn Section "Geokdere". Deshayesites aff. antiquus Bogdanova, 1983: A) lateral vieq B) frontal view, La].er 9,

specimen 15/9442, xL. Deshayesìtes tuarkTricus Bogdanova, 1983: C) frontal view, D) leteral vieu., La1-er 9, spccìmen 4/9142, xil. Holo-slpe of Turbmeniceras geolederezse Tovbina, 1963: E) lateral view, F) ventral vicw, Leyer ,tr, specimen 7/8293, xL. All spccimens are

housed in the F. N. Chernychev Central Scientific-Research Geological Exploration Museum (CNf GR).

385

Fig. 6

Section 6 - This section was logged 1.5 km northof Section 5 and corresponds to the cliff of Mount Han-begiiburun, whose top is at 283 m (Fig.2). The base ofthe section corresponds to siltstones and shales at the{^^" ^[ "Lo "li{{ iFi" 1)..''- ""' \-'b' "

- sandstone; 0.30 cm.- grey to yellowish shale. 10 m.

Layer 1 - marl overlain by calcareous, glauconitic nod-ules containing some rare fragments of ?

Limaria afÍ. parallela (J. Sowerby), Thetisminor (J. de C. Sowerby) and brachiopods;O.ZO m.A 21 m thick succession of shales and marlswith ferruginous surfaces follows (Fig. 3).

Layer 5 - bed of arenaceous pebbles containing frag-ments of bivalves (trigoniids, pectinaceans)

overlrin by large oystersi 0.20 nr.

- sh.rle. l9 m.

Layer 6 - sandstones with fine debris of mollusc shells,

capped by a hard ground wtth Thalassìnoides;

1m.- yellowish, fine poorly cemented sandstone.

1.7 m.

Layer 7 - reddish, stratified ferruginous sandstonethat was followed for 1.5 km up to Section 5.

0.30 m.

Section "Geokdere" - In 1959 one of the authors(T. N. B.) sampled a section located about 10 km north

of Section 6 (indicated witl-r "T" in Fig. 2), which wascalied "Geokdere". This section provides complementa-ry information because upper Brrremian llrnonitifer-ous beds were discovered. Some significant ammonrtesare reproduced in Fig. 6.

The ammonites Imerites far:rei Rouchadze andImerites giraudi var. multicostata Tovbina were found inLayer 1, a 0.10 m thick bioclastic layer belonging ro theImerites and Colchidltes beds, that can be correiated tothe Imerites girawcli Zone oÍ the Mediterranean zonatron(Hoedemaeker tr Company, 1993).

Layer 1. is overlain by 6.6 m of poorly cementedsandstone.

Layer 4 is also :r 0.20 m thick, bioclastic 1.r1-er inwhich Turbmeniceras geokderense Tovbina (Fig. 6 E, F),T. turkmenicum Tovhina, T. muhicostatum Tovbìna andT rarecctstatun Bogdanova were found. This :rssemblageindicates rhe Turkmeniceras turbmenicum Zone, which is

currently rscribed to the uppernlo\t Barrenrirn (Bog-danova 8e Tovbina, i995), although no direct correla-tions with the Mediterranean areas exist. In {act, Turkmeniceras is reported only in Tr-rrkmenia and Caucasusand is not associated with other taxa that could rr1los.-

correlations.About 22 m o{ poorly cemented sandstone fo11ow,

capped by bioclastic Layer 9,0.40 m thick. It containsDeshayesites tuarkyricus (Fig. 6 C, D), D. taeissiformisBogdanova, D. aff . antiqwws (Fig. 6 A, B) and D. sp. Thisassemblage clearly indicates the Early Aptian D.tuarkyricws Zone.

386 F. Cecca, A. V Dhondt A T. N. Bogdanot,a

It is followedby 5.4 m of silty, poorly cementedsandstone that is overlain by bioclastic Layer 11 whichalso contains ammonites of the D. tuarkyricus Zone: D.tuarkyricus, D. antiquws, D. sp.

Layer 1,1 is overlain by 13 m of sandstone, fol-lowed by 10 m of silty clay,5.5 m of clayey sandstoneand 17 m of clay and silty clay. This in turn is overlain byarenaceous, bioclastic Layer 18 in which ammonites ofthe D. rueissi Zone were found (D. zueissi, D. consobrinus(d'Orbigny) sensu Bogdanova (1983) and D. deshayesi).

This last Layer is overlain by 8 m of siltsone and clayeysiltstone, tentatively ascribed to the D; deshayesi Zone.The marker Layer with calcareous, glauconite coatednodules then occurs( Layer 2A). This marker Layer was

recognized as Layer 14 in Section l,Layer 10 in Section2 and Layer I in Section 6. Interestingly, in the"Geokdere" section the marker Layer is overlain by 4.7m of poorly cemented sandstone vzhich containammonites of the Dwfrenoya furcata Zone at the top:Dufrenoya dwfrenoyi (d'Orbigny), D. fursooae Bogdano-va, Cheloniceras cornuelianum (d'Orbigny) , C. cor-nuelianum yar. pyg?naea Nikchitch, C. seminodosum(Sinzow), C. meyendorfi (d'Orbigny) and Ancylocerasrochi Casey.

The section continues with more than 7A metresof clay, sandstone and siltstone with only two fossilifer-ous bivalve beds. It is worth noting that in this sectionno lateral equivalents of the Epicheloniceras beds (e. g.

Layer 8 in Sections 3 and 4) and coquinaswirhAetostre-on latissimum (Layers 9 and 10 of secrions 3 and 4) exist.

Bivalve fauna.

Bivalve faunas from these regions were studiedpreviously by Bogdanova (1961;1966) and Prosorovsky(in Prosorovsky et al., 1961).

The bivalve faunule studied was poorly preservedwith the heterodont taxa particularly difficult to identi-fy at the species level.

The fauna studied herein consists mainly ofBakevelliidae lGeroillaria alaeformis (J. Sowerby) andGeroillella sublanceolata (d'Orbigny)], of exogyrineoysters lAetostreon latissimum (Lamarck) and Cer-atostreon tuberculiferwm (Koch & Dunker)] and ofTrigoniidae lTrigonia carinata s.L, "Iotrigonia" abichi(Anthula), Litschbotrìgonia ingwschensls (Renngarten)and Pterotrigonia ornata (d'Orbigny)] .

Furtherrnore, one unidentified Cucullaea sp., onelimid [? Limaria aff. parallela (J. Sowerby)], one largeastartid ("Astarte" karajmanica Prosorovsky), one possi-ble mactromyid lThetis minor (J. de C. Sowerby)1, onecardiid ("Carclium" af[. cottaldinwm d'Orbigny) and a

few other heterodonts, mainly unidentified, were found.

Palaeoecological considerations - The taxa identi-fied at species ievel indicate a shallow; fairly warm and

fully marine environmenr, typical for the Tethyan LowerCretaceous (Dhondt & Dieni, 1989; Dhond\1992).

The trigoniids were somerimes found with bothvalves and can be assumed to have been collected in lifeposition. If Stanley's interpretation for such trigoniids(Stanley, 1977; 1978) is f ollowed, they lived in"nearshore habitats of Early Cretaceous Tethyan seas ar

water depths no grearer than 1O - 15 m " (Stan1ey, 1928).Bakevelliid specimens were also found occasional-

ly with both valves. Bakevelliidae were suspension-feed-ers and were assumed to be byssate epifaunal forms(Muster, 1995, p.6, p. 98). Flowever, Musrer, in her dis-cussion of the life position in several bakevelliid genera(1995, p. 98-99) considered Geroillaria alaeformts as

byssally attached to a hard particle in the sedimenr, burwith the umbonal valve partially sunken into the sedi-ment -making the raxon close to being a recliner. For thegenus Geruillella she suggested a mudsticker life posi-tion (see also Fúrsich,1977; Seilacher, 198a); shells ofGervillella swblanceolata would thus have spent most oftheir life sticking in the sedimenr (see also Stanley, 1922,p.187, fig. 19 C).

Exogyrine oysters are epifaunal recliners (cupshaped recliners in Seilacher, 1984) or cemented forms.The iarge Aetostreon latissimum was certainly a recliner,commonly with oyster spar on rhe convex va1ve. Thefairly smal1 Ceratostreon tuberculiferurn can be consid-ered an opportunistic species, las Nanog,ra otrgwla inthe uppermost Jurassic (Fùrsich, 1977)1.

Trigoniids are verv shallow burrowers (Stanley,1978). None of the other taxa known from Tuarkyr indi-cate deep burrowing. Even "Astarte" karajmanica wasprobably a shallow burrower [for recent, smal].er Astartetaxa Stanley (1970) indicates a preference for sand - bothfine and coarse - and a maximum depth of 35 m] .

Most taxa collected from Tuarkyrwere typical forsandy, often fairly coarse substrata.

If we consider the distribution of the fauna, in thebasal Aptian (Section 1, Layers 7 and lO, samples SWG7. l0) and in theLower Aprian lSection 6, L:ryer I, sam-ple H1) only a few taxa were identified because of bothpoor preservacion and low frequency. Definitive conclu-sions are difficult to draw on rhe basis of the relativelysmall faunal sample available. The complete absence oftrigoniids in sample H1 may be considered an indicationthat in this bed ? Limaria af[. parallela and Thetis minorlived in less shallow environments than the faunas frornthe Upper Barremian or Upper Aprian.

. Palaeobiogeographic considerations - Some of thetaxa had a very u.ide tethyan distribution (the bakevelii-ids and the oysters, and two of the trigoniids are foundfrom the west coast of South America to Central Asia,and Gert,illaria alaeformi.r even reached Japan) (Dhondt& Dieni, 1988). Two trigoniids lLitschko*igonia

The Aptian Stratigraphy of NW Turkmenistan 387

Sections 3,4 Section 2 Sections 3,5

Levei 8 Level 2 Level 9

Isle oflfi/iohr

LowerAptian

Section 1

Leve.ls 0-6

UpperBarremian

Section 1

Levels /- Il.

Basal

Aptian

Section 6

Level 1

Lower I 1.."t- (t"

AptianUppe r UpperAptian Aptian

G enti llaria ala eformis

c *" ; t t r, lù r, blll oo r" o I o *I Limaria cf. parallela

Aetastreon latissimwm

ò,1i, i', ii, t ubercu ! iferu m

Trigonia carinata

'?:s"!y 4!!iL its chkotri gon i t i n gu schen s i s

Pterotrigonia ornata

Thetis minor

? Resatrix oectensis

- Comparison between Aptian bivalve faunas from the Isle of Wight and those from Tuarkyr

inguschensis (Renngarten) and Iotrigonia abichi (Anthu-la)l are known from the Caucasus, from Mangyshiakand from Turkmenistan. Litschkotrigonia ingwschensis

has undoubtedly evolved fuorn Qwadratotrigonia nodosa

(J. de C. Sowerby) which has a much wider geographicdistribution. Many taxa are comparable (Table 1) toAptian faunas from the Isle of Vight (Voods 1899 -1913). However, due to intensive collecting over aimosttwo-hundred years, the faunas of the latter locality are

amongst the best known Cretaceous faunas and there-fore diversity of rhe coeval Tuarkyr faunas cannor bejudged with the same criteria. Research in Tuarkyr start-ed relatively recently and both natural and logistic diffi-culties in accessing the outcrops have limited the extentof data collection compared to the Isle of Wight.

Ammonite biostritigraphy.

Due to the natural exposure of the successionalong cuestas devoid of any vegetal cover, we were able

to follow the different stratigraphic Layers and to checkthe correlation between the different sections studied"

The faunas sampled do not have a continuousstratigraphic distribution in the sections but are concen-trated in relatively few fossìliferous beds.

Deshayesites tuarkyricus Zone - The older Layerssampled are located at the base of Section 1. Because noammonites were found, these rocks are assigned to theuppermost Barremian on the basis of the literature. Theentry of the genus Deshayesites, marking the base of theAptian, was recorded in layer 7 wirh the species

Desbayesites antiquus Bogdanova which indic:rres the D.twarleyricus Zone (Bogdanova, 1,971.a, 1979, 1983; Bog-danova 8c Tovbina 1995; Bogdanova & Prosorovsk;., inprint). The marker species was found higher in the sec-tion, in Layer 9, rnd seems to postdate D. antiquus. Asimilar distribution is described by Bogdanova 8e

Prosorovsky (in print) in the section "Utuludzha"(located west of Tuarkyr, in the Greater Balkhan Range)where D. tuarkltricus was f ound in a bioclastic bed locat-ed stratigraphically 5O m above a bed with Deshayesitesoglanlensis Bogdanov;r, D. antiquws and D. aff. antiquus.On the other hand, Bogdanova & Prosorovsky (in print)collected D. antiquus and D, tuarleyricus from the samebed in a section located in southernmost Tuarkyr, in thesouthernmost part of the Tekedjik ridge, arid in Layer 11

of section "Geokdere", whereas D. af{. antiquus and D.tuarkyricus co-occur in Layer 9. It is very difficult todetermine whether or nor D. antiquus really predates D.tuarkyricus. In fact, the ammonite-bearing bioclasticbeds probably correspond to lenses with a restricted 1at-

eral extent which does not allow a fine bed by bed cor-relation.

Deshayeslfes welssi Zone - Deshayesites stmiÌtsBogdanova indicates the beginning of the secondammonite Zone of the Aptian, rhe Deshayesites ueissiZone. This species was found in Section 2, which corre-sponds to the same succe ssion exposed in Section 1 butlocated along the northern flank of Mount Bishik.Though this ammonite was collected from the talus, inthe field it was clear that it must have come from theinterval between the top of Layer 16 and 4 merres above

Layer 15.In Section 1, the bed that contained the speci-

TÎ

+

388 F. Cecca, A. V Dhondt & T. N. Bogdanotta

men of D. similis might be located within the intervalfrom 6 to L2 metres above the bed where D. tuarkyricuswas found. In Layer 12 of Section 1 a rich, althoughpoorly preserved, ammonite fauna was found. Thespecies identified are usually reported both by Casey

(1961) and Bogdanova (1,971a) from the D. rpeissiZone:D. luppor.,i Bogdanova, D. cf . spatbi Casey, D. c[. kilianiCasey, D. cf. eoolvens Lrppov. Flowever, some speci-

mens show morphologic affinities with D. d,eshayesi andwere identified provisionally as D. aff. deshayesi (see pl.1, fig. 6). These specimens rèsemble the ammonitesfrom the D. raeissi Zone illustrated as D. dechyi (Prpp)by Bogdanova (1,977, pl. Z, fig. 1, 2) but subsequentlyascribed rc D. mihhailooae Bogdanova, Kvantaliani &Sharikadze (Bogdanova et aI., 1979). In any case, D.deshayesi is the marker of the third zone of the Aptian.According to Bogdanova (1971a) and Bogdanova trT^,,1-:-^ / loo(\ .L- trO of D. deshayesl is reported fromthe upper part of rhe D. zueissi Zone, though this was

not observed in Kopet Dag and other Transcaspian areas

(Bogdanova, 1978; Tovbina et al., 1985). Unlike in Eng-land (Casey, 1961), in tanscaspia the base of the D.desbayesi Zone is characterized by rhe disappearance ofsome species and not by the FO of the index species. Onthe other hand, the Russian authors correlate the base ofthe tanscaspían D. deshayesi Zone with the lower parrof the same Zone in England (i. e. with the Cheloniceras

parinodum Subzone), though the specific compositionsof the faunal assemblage is different. Thus, the problemof the precise correlation between the Eng[sh and Turk-menian D. deshayesi Zones is not yet resolved because

D. w,eissi is lacking in England. Probably the verticalrange of the English Deshayesites forbesi Zone does notmatch exactly that of the tanscaspian D. zaeissi Zone.

In this connection a deep palaeontologic revision of thespecies D. deshayesi is also recommended.

Deshayeslfes deshayesi Zone - This zone was norrecognized. Fourteen metres above Layer 12 of Section1 the marker Layer with glauconite-coated noduies(Layer 14) occurs. A specimen of D. pappi Bogdanova,indicative of the D. raeissi Zone (Bogdanova, 1971,a;

Bogdanova tr Tovbina, 1995), was found just below thenodular interval. In section "Geokdere", an 8 m thickinterval of unfossiliferous siltstones and clayey silt-stones, underlying the n.rarker Layer, was tentativelyascribed to this zone.

Dufrenoyia furcata Zone - The Layer with glau-conite-coated nodules was recognized in Section 2 (here

named Layer 10), almost 15 km north in Section 6

(Layer 1) and 25 km north of Section 2 in Section"Geokdere" (boundary between Layers 19 and 20). Itmay be used as a 1oca1 marker Layer that probably is

incorporated in the gap mentioned by the Russian

authors (Resolution of the Interdepartamental Strati-graphic Commission, Sarlarkand, 1,977; Bogdanova &Tovbina, 1995) and that probably encompasses theinterval occupied by the D. deshayesites Zone and thelower part of the Dufrenoyia furcata Zone. The latterzone was recognized only in Layer 20 of Section"Geokdere", above the glauconitic marker Layer. How-ever, Bogdanova & Prosorovski (in print) foundammonites of the D. furcataZone within this glauconiticmarker Layer in the southern Tekedjik (southernmostTuarkyr) and the Greater Balkhan.

Epicheloniceras subnodosocostatum Zone - Am-monites of this zone occur in Layer 2 of Section 2. This

PLATE I

Fig. 1 - Deshayesites antiquus Bogdanova, 1983. Tuarkyr, Section 1, Layer 7 , Early Aptian D eshayesites tuarkyricus Zone. Specimen MPUM 82 82,

x1.

Fig.2 - Deshayesites tuarhyricus Bogdanova, 1983. Tuarkyr, Secrron l, Lrver 9, Errly Aptian Deshayesites tuarleyrìcus Zone. Specimen MPUM8289/1, x1. Fragment of the body chamber.

Fig. 3 - Deshayesites cf. spathi Casey, 1964. Tuarkyr, Section 1, Lq'er 12, Early AptianDeshayesites u^eissiZone. Specinen MPUM 8285/1, x1.Fig. 4 - Deshaltesites similis Bogdtnova. Tuarkyr, Section 2, from rn interval between the top of Layer 16 and 4 rnetres rlrove I rver 15, Early

Aptnn Deshayesites.oeissi Zone. Specimen MPUM 8280, x1.

Fig. 5 - Caspianites tuarkyriensis Kakabadze, 1981. Tuarkyr, Section 3, Layer / collected from the talus but probably coming from Layer 8b, Late

Aprian Epicheloniceras subnodosocostatum Zone. Specimen MPUM 8328, x1.

Fig. 6 - Desbayesites aff . deshayesi (Leymerie, 1 84 i ) . Tuarkyr, Section 1, Ltyer \2, Early Aptian D eshayesites ueissi Zone. Specimen MPUM 8293,

x1. Totally septated specimen.

Fìg.7 - Deshayesites pappiBogdanova, i991. Tuarkyr, Section 1, top of La1'er 13, Earll' Ap1i211 Deshayesites ueissiZone. Specirren MPUM 8290,

x1.Fig. 8 - Deshayesites luppooi Bogdanova, 1983. Tuarkyr, Secrion 1, Leyer I2, Eerly Aptian Deshayesites ueissí Zone. Specimen MPUM 8292, x1..

Totrlly septered specimen.

Fig. 9 - Epicheloniceras subnodosocostatum v^r. robusta (Sinzow,1906): 9a r.entral viewi 9b, lateral view. 'Iuarkyr, Section 3, Layer 8b, Late Apt-nn Epicheloniceras swbnodosocostatum zone. Specimen MPUM 8294 xl.

Fig. 10 - Epicheloniceras cf. buxtorfì (Jacob, 1906). Tuarkyr, Section 3, Ltyer 7, Lrte Aptian Epicbeloniceras subnodosocostatum Zone. Specimen

MPUM 8297,xl.

The arrow rndicates the end of rhe phragmocone, where visible.All of the material is housed in the Museo di Paleontolosia of the Universitv of Milar.

l)1. I TLe Ay tiL,t 5rr.trtry"tplty,'f \\\ Trtrk,'tetti,r.tn 339

390 F. Cecca, A. V Dhondt C T. N. Bogdanoz,a

is the first ammoniriferous bed recognized above thernarker Layer with glauconite-coated nodules. FIowever,ammonites of the same zone were found in Sections 3

and 4 below Layer 8, which is the lateral equivalent ofLayer 2 in Section 2; among them a specimen of Epiche-loniceras cf. buxtorfi (Jacob) in Layer Z of Section 3. InEngland this species occurs in the upper parr of theEpicbeloniceras martinioides Zone (the equivalent of theE. subnodosocostatum Zone), rn the Epicheloniceras bux-torfi Subzone (Casey, 1961). Therefore, these Epiche-loniceras - bearing beds correspond to the upper part ofthe English E. martinioides Zone. In the Tuarkyr area at

least, the chronologic equivalence between r.he E. subn-odosocostatwm and the E, martinioìdes Zones (Bogdano-va & Tovbina, 1995) seems to be questionable. Accord-ingly, in the Tuarkyr the genus Caspianites occurs inLayers that are younger than in England, where it disap-pears in the middle of the E, martinioides Zone, ì. e. theEpicheloniceras gracile Subzone (Casey et al., 1998).

Conclusions.

New, detailed, stratigraphic data on rhe verricaldistribution of both ammonire and bivalve faunas were

obtained during the expedition in the southern Tuarkyrthrough bed by bed description of six sections sprnningthe interval from the uppermosr Barremian to the firstammonite-zone of the upper Aptian. The integration ofthese new data with complementary data from section"Geokdere" allows us to improve the knowledge of theAptian stratigraphy of the Tuarkyr.

Both ammonite and bivalve faunas have a scanry,discontinuous distribution within the lithologrc succes-sions. Most of the ammonitiferous beds recognized cor-respond to bioclastic ienses that do not correlate witheach other. The ammonite faunas generally show lowdiversity; only the genus Deshayeslres was found in thelower Aptian whereas Epicheloniceras and Caspianitescharacterize the layers of the basal upper Aptian. How-ever, southwards in both southernmosr Tuarkyr and theGreater Balkhan the faunas :ire slightly more diverse:deshayesitids are always dominant but Phyllopachyceras,P rotetr agonìt e s, P s e ud, o h ap I o c er a s, P s e u rl o s ayn e lla, To xo -ceratoides and Cheloniceras (C.) occur in Lower Aptianstrata. The species Deshayesites spathi and Epiche-loniceras bwxtorfi are reported for the first time fromTurkmenistan.

The range of the Turkmenian E. subnodosocosta-tum zone does not seem to correspond to the entire

PLATE 2

F;ù | - Ft;"1".1^-;----, -tr. tschernyschù (Sinzow, 1906). Tuarkyr, Section 3, Layer 8b, Late Aptran Epicheloniceras subnod.osocostatum Zone.Specimen MPUM 8272/2,x7. Totally septated specimen.

The specirnen is housed in the Museo di Paleontologia of the University of Milan.

PLATE 3

Fig. 1 - Epicheloniceras gr. tscbernyscbmi (Sìnzow, 1906). Tuarkyr, Section 4, Layer 3, Late Aptian Epicheloniceras subnorlosocostatum Zone.Specimen MPUM 8273, x1.. Totally septated specimen.

Fig. 2 - Litscbkotrigonia inguscbensis (Renngarten, 1926): left valve, composite mold. Tuarkyt Section 3, Layer 8b, Late Apttan Eltichelonicerass wbno d.o s o c o statum Z one. Specimen MPUM 83 17 / 1, x 3 / 4.

Fig.3 - "Iotrigonia" abichi (Anthda,1899): right valve. Tuarkyr, Section 1, Layer 7, Early Aptian Deshayesites tuarleyricus Zone. SpecimenMPUM 8309/1,x1.5.

Al1 of the rnaterial is housed in the Museo di Paleontolosia of the Universitv of Milan.

PLATE 4

Fig. 1 - Geruillella sublanceolata (d'Orbigny, 1850): 1a, fragment of right valve; lb, fragment of right valve, inside. Tuarkyr, Section 1, Layer 6,uppermost Barremian. Specimen MPUM 8J07/1, x 1..

Fig.2 - Geruillella sublanceolata (d'Orbigny, ft5A): 2a, fragment of right valve; 2b, fragment of left valve, inside. Tuarkyr, Section 1, Layer 6,uppermost Barremian. Specimen MPUM 8307/2, x 1.

Fig. 3 - Aetostreon latissimwm (Lamarck, 1801): left valve. Tuarkyr, Section 3, Layer 8b, Late Aprian Epicheloniceras subnocLosocostatum Zone.Specimen MPUM 831.5/l,x 1/2.

Fig. 4 - Aetostreon latissimum (Lamarck, 1801): right valve, Tuarkyr, Section 3, Layer 8b, Late Aptian Epicheloniceras subnodosocostatum Zone.Specimen MPUM 831.5/2, x 1/2.

Fig. 5 - Ceratostreon tuberculiferum (Koch & Dunker, 1837); lefr valve; Tuarkyr, Section 1, top of the Urgonian facies (sample SVG 1), UpperBrrremian. Specimen MPUM 8301/1, x 2.

Fig. 6 - "Astarte" learajmanicaProsorovsky, 1961: right valve. Tuarkyr, Section 3, Layer 8b, Lzte Aptian Epicbeloniceras subnodosocostatum Zone.Specimen MPUM 8320, x 1.5.

Fig.7 - Pterotrigonia ornata (d'Orbrgny,1844): right valve; Tuarkyr, Section 2, Layer 2, Late Aptian Epìcheloniceras subnodosocostatum Zone.Specimen MPUM 8326, x 2.5

All of the material is housed in the Museo di Paleontoloeia of the Universitv of Milan.

Pl. 2 The Apti"nt Srr"trigrnplLy of .','l\\/ Turkntcnisrtn 391

F. Cecca, A. \r. Dhondt & Z N. Bogdanot,d

Tbe Aptian Stratigraphy of N\X/ Turkmenistdn 393

394 F. Cecca, A. V Dhondt & T. N. Bogdanoaa

range of the English Epicheloniceras martinioides Zone.At least in the area investigated the faunas indicate onlythe upper part of the latter Zone, i. e. the Epichelonicerasbuxtorfi Subzone.

The bivalve faunas are typrcal of generally shallow;sandy facies. Though affinities with the bivalves of theIsle of Wight are undeniable, thrs Tethyan fauna containsalso elements which are only known from the Caucasus- Mangyshlak - Turkmenistan area. On the other hand,Delanoy et al. 11997) and Cecca et al. (1999), recentlyreported from the La Bédoule area (SE France) numer-ous ammonites previously quoted from Turkmenisranonly, such as Deshayesites antiquus, D, tuarkyricus, andD. luppooi.

Therefore, the Turkmenian biota does not seem rohave been biogeographically isolated from orher areas.

The impoverished character of the ammonite fauna isprobably due to peculiar palaeoenvironmental con-straints such as warer temperature and low depth.

Acknouled,gements .

The expedition in Turknenistan received the financial supporrof the "PTP", Peri-Tethys Program. Many hearty thanks ro M. GaetaniandE. Garzanti (University of Milan), who shared nith F. Cecca theTurkmenian experience, to V Kalugin and the driver Tolia Polir.ranij forfriendly assistance in the field. Franco Paolucci (University of Urbino)produced the drawings. Jean-Jacques Roccabianca (Universrty of Mar-seille) and Vilfried Miseur (Royal Belgian Institute of Natural Sci-ences) took photographs of the ammonires and bivalves, respectively\We are indebted to Philip Hoedenaeker (Naturalis, Leiden) and IginioDieni (Universitv of Padova), who acted as referees, for cnticism andadvices that considerably irnproved the manuscript.

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