On Development of the Aptian Ammonite Zonal Standard for the Mediterranean Region

Céologie Alpine, 1994, Mém. H. S. n° 20, p. 51-59

On development of the Aptian Ammonite zonal standard for the Mediterranean region

by Tamara N. BOGDANOVA* and Stella Z. TOVBINA*

A b s t r a c t . — The paleontological characteristic of the Aptian ammonite zones of the Trans-Caspian area. There are four zones in the Lower Aptian (Bedoulian) - tuarkyricus, weissi, deshayesi and furcata ; two zones in the Middle Aptian (Gargasian) - subnodosocostatum and melchioris, three zones in the Upper Aptian (Clansayesian) - prodromus, nolani and jacobi. The ammonite zonation of the Trans-Caspian area is correlated with those of Caucasus, Europe and the ammonite zonal standard of Mediterranean area. The species-index of the lower zone of the Middle Aptian Colombiceras tobleri is proposed to change to Epicheloniceras subnodosocostatum.

K e y w o r d s . — Trans-Caspian area, Aptian, ammonites, zones.

Extension de la zonation standard d’ammonites de l’Aptien dans la province méditerranéenne

R é s u m é . — Dans la region transcaspienne, les zones d’ammonites de l’Aptien sont caractérisées paléontologiquement. II у a quatre zones dans ľAptien inférieur (Bédoulien) - zones ä tuarkyricus, weissi, deshayesi et furcata, deux zones dans l’Aptien moyen (Gargasien) - zones ä subnodosocostatum et melchioris, et trois zones dans l’Aptien supérieur (Clansayésien) - zones ä prodromus, nolani et jacobi. La zonation d’ammonites de la region transcaspienne est corrélée d’une part avec celles du Caucase de VEurope et d’autre part avec la zonation standard d’ammonites de la province méditerranéenne. Pour la zone inférieure de l’Aptien moyen il est proposé de remplacer ľespéce-index Colombiceras tobleri par Epicheloniceras subnodosocostatum.

M o t s c l é s . — Région transcaspienne, Aptien, Ammonites, Zones.

The Working Group on Cephalopods, acting under were not given any names at a ll; reasons should also be IGCP Project 262 "Tethyan Cretaceous Correlation" in provided for subdivision of certain zones into sub 1990 (Alpes de Haute-Provence, Digne) developed the zones ; parts of some zones taken as horizons (to draft ammonite zonal scale for the Mediterranean become subzones or zones) should be additionally Region [Hoedemaeker and Bulot, 1990] and proposed traced over widen areas. it for discussion. From explanations, given for different Subdivision of the Berriasian, Valanginian, parts of the scheme [Hoedemaeker and Bulot, 1990, Hauterivian and most of the Barremian is based on p. 124-126], it follows that many zones, included in the zonal subdivision in their stratotypes, which is, most draft, need an up-to-date definition and description of likely, accounted for by the fact that stratotypes of these the zonal ammonite assemblage ; the index species of stages have been re-studied by now. For the Albian some zones, adopted as temporary ones, require a stage, zones developed by the English paleontologists grounded substitution ; some stratigraphic intervals for the subboreal region are accepted ; however, these

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Table 1. — Subdivision and correlation of Aptian in the Mediterranean and subboreal regions.

Genlojiie Alpine. 1994, Mémoire H.S. n° 20 T.N. BOGDANOVA and S.Z. TOVBINA 53

zones are also recognized in the Mediterranean Region. relationship : marker horizons, lithological character of Aptian is subdivided into zones developed in Georgia stratons, pattern of facies variability on area. The [Hoedmaeker and Bulot, 1990, p. 126, Comment 17]. developed zonal scheme for the Aptian of the Trans- The reason for introduction of zones of the Georgian Caspian area is the most complete and detailed one for scale in the discussed draft standard for the Aptian was, areas of Eastern and Western Europe (except England), apparently, the fact that stratotype sections of the included in the Tethys paleozoogeographic area, and Aptian in France have not yet been revised, despite the can serve as a basis for the Mediterranean zonal corresponding recommendations of the Lyon standard. Colloqium in 1963. Subdivision of the Aptian adopted Besides, in the Aptian part of the draft Mediter there (tabl. I), does not conform to the modem state of ranean scale, not only subdivision into zones, based on knowledge and subdivision of these deposits in other materials from the Trans-Caspian sections, but also areas of the Mediterranean or adjacent areas. The latter determination of the Barremian/Aptian boundary include western Central Asia (or Trans-Caspian area). stratotype can be recommended. Ammonites of the If we discuss the Aptian zones of the developed zonal genus Turkmeniceras, by now recorded only in this standard, it can be seen that subdivision of its lower region, display an evolutionary transition in time from substage (as regards the number and names of the family Heteroceratidae, which existed in Barremian biostratons) is given totally on the basis of the Trans- time, to the Aptian Deshayesitidae [Bogdanova T.N., Caspian area [Resolution, Samarkand, 1977]. Zones of 1978]. the Middle and Upper Aptian are typical for most regions of Europe. Only the name of the upper zone of Given below is a characteristic of the Aptian zones, the Middle Aptian, Colombiceras tobleri, is taken from earlier repeatedly published for different parts of the the modern Georgian chart, but it is not satisfactory Trans-Caspian area [Bogdanova, 1983 etal.]. (see below). To improve the proposed draft it is necessary to describe zones (type sections, boundaries, characteristic 1 . - L o w e r A p t i a n of ammonite associations and their description) and give their correlation in areas of the Tethys Realm and Lower Aptian deposits in the Trans-Caspian area beyond its limits. The Trans-Caspian region is referred rest conformably on the Upper Barremian and are to the most remote eastern margin of the Mediter represented by rocks, similar to Barremian ones. The ranean, where the Aptian ammonite associations boundary between stages is drawn on the basis of comprise both Mediterranean and subboreal species. paleontological evidence. The authors of the paper are These specific features to a certain extent affected consistently adhering to the viewpoint that the subdivision of the Aptian deposits, which distinguishes Barremian/Aptian boundary the Trans-Caspian area the chart of the Trans-Caspian area from those of should be drawn at the base of the local Tuarkyricus typical Mediterranean areas. However, the same Zone (Deshayesites tuarkyricus [Luppov et a i, 1987]. circumstance makes the Trans-Caspian area a key ) region, through which correlation of charts for different We place the underlying Turkmenicum Zone paleozoogeographic provinces (or areas) is (Turkmeniceras turkmenicum) in the upper part of accomplished (tabl. I). Index species and ammonite the Barremian, correlating it with Beds with associations of Aptian zones in the discussed Mediter Hemihoplites (Matheronites) ridzewski in Northern ranean scale shows certain features in common for Caucasus [Bogdanova, 1971] '. areas in different provinces. Aptian deposits in the Trans-Caspian area are 1.1. Tuarkyricus Zone (Deshayesites tuarkyricus) characterized by excellent exposures, stratigraphic completeness and abundance of diverse fossil groups. Distinguished by Bogdanova [1971, 1983], its The Aptian zones of this large region are characterized stratotype occurs on the northern slope of the Greater by ammonite assemblages, representing evolution Balkhan Ridge, 1-1,5 km west of Utuludzha wells. The stages of three leading families Deshayesitidae , zone is traced over the entire Trans-Caspian area. Parahoplitidae and Douvilleiceratidae, i.e., the same Ammonite assemblage of the zone is represented by families, whose genera and species were also species : Deshayesites tuarkyricus Bogdanova, D. widespread in coeval basins of Europe. At the same oglanlensis Bogdanova, D. consobrinus d'O rbigny, time, the developed stratigraphic scheme is composed D. euglyphus C a s e y , D. weissiformis Bogdanova, D. of biostratons, representing specific geological bodies, antiquus Bogdanova, Pseudohaploceras ramosum whose boundaries are drawn on the basis of a

theoretical assumption of the succession of species 1 It is proposed to introduce the second index Hemihoplites assemblages as a result of the evolutionary process and (Matheronites) ridzewskyi for the unit, placed as T. turkmenicum empirical data on relationship in the sections of horizon in the preliminary zonal chart of the Mediterranean region, as particular teil-zones of species zonal assemblages and it was already done by Kakabadzč [1983]. The areal extent of this species is greater than that of species T. turkm enicum . additional correlated levels determined by this

Géologie Alpine, 1994, Mémoire H.S. n° 20 54 ON DEVELOPMENT OF THE AMMONITE ZONAL STANDARD FOR THE MEDITERRANEAN REGION

Bogdanova. Species D. tuarkyricus occurs over the 1.2. Weissi Zone (Deshayesites weissi) entire Trans-Caspian area, which served as a basis for Its name is taken from A. Koenen’s [ koenen, 1907. choosing this species as a zonal index. Species D. P- 9] and W. Kilian’s [Kilian. 1910. table to p. 287] — " consobrinus and D. euglyph^s, known from publica ŕ —------:------:------\ charts. Range of the tions, are also found in higher Aptian levels ; therefore, modern Trans-Caspian Weissi Zone is, most likely, they cannot be regarded as guide forms of the equal to that o f the German W eissi - Albrechtiaustriae considered zone. However, their presence in a zonal Zone, but it is less than the range o f the French zone. In assemblage may indicate the Aptian age of beds, the Trans-Caspian area, the W eissi Zone occurs containing this assemblage, since the first of the species ubiquitously ; it is not subdivided into subzones. is often recorded in the Lower Aptian of Southeastern Ammonite assemblage of this zone is more diverse as France, South England, Volga area, Caucasus, and compared to that of the Tuarkyricus Zone. In addition other regions, whereas the species D. euglyphus is to Deshayesites, ammonites are represented by genera : characteristic of the Lower Aptian of South England. Phyllopachyceras (baborense C o q u a n d ), Pro- Of certain interest is the species D. antiquus, whose tetragonites (karakaschi D r u z c ic , in fla tu m suture-line has three umbilical lobes, as most Bogdanova), Ancyloceras (rochyi C a sey ), Pseudo- Deshayesites, i.e. ELU]U3 : U2I ; however, lobe U, is h a p lo cera s (m a th ero n i d'Orbigny, ram osum located on the umbilical margin, i.e. similar to Bogdanova), Pseudosaynella (bicurvata M ich elin , Turkmeniceras (early Deshayesitidae ?). This specific fimbriata Im lay), Cheloniceras (seminodosum Sinzow, feature of the structure of suture-line in D. antiquus cornuelianum d'Orbigny). Defined among allows to consider it as one of early representatives of Deshayesites are : D. weissi Neumayr & Uhlig, D. the genus Deshayesites, very similar in the evolutionary planus Casey, D. dechyi Papp, D. normani C asey, D. series to Turkmeniceras ; and the deposits, where it callidiscus C a sey , D.'pygmaeus C a sey , D. topleyi occurs, as the oldest Aptian deposits. Spath, D. kiliani Spath, D. latilobatus S inzow , D. The lower boundary of the zone and, therefore, the consobrinoides Sinzow, D. similis B ogd anova. In the lower boundary of the Aptian is drawn on the basis of upper part of the zone, D. kudijavzevi I. M ich ailova, disappearance of the genera Turkmeniceras and D. consobrinoides S in z o w , D. d ech yi Papp, D. Matheronites and appearance of the above-mentioned levigatus Bogdanova and D. deshayesi L eym erie Deshayesites. appear. The range of the Zone is established from stratigraphic range of two species : D. weisssi and D. In its ammonite assemblage, the considered zone planus. The latter can be regarded as a controlling zonal has no equivalents in the scheme of Aptian subdivision species, since its vertical range is the same, as that of for other regions of the Tethys Realm. However, by its the species D. weissi. Weissi occurs only in Tuarkyr, position in the section, it corresponds to the lower zone Kubadag and Greater Balkhan, whereas planus is also of Aptian in England i.e. Fissicostatus Zone (Pro- widespread in Kopetdag. Generally, Weissi Zone in the deshayesites fissicostatus) and Tenuicostatus Zone Trans-Caspian area can be correlated with Forbesi Zone (Deshayesites (P.) tenuicostatus) in Germany [Kemper, of the English chart or Weissi Zone in Germany. The 1976]. Deshayesites species, assigned to the genus Lower horizons of the Weissi Zone in the Trans- Prodeshay esites, from the evolutionary viewpoint are Caspian area, where D. dechyi is not yet recorded, can, more progressive, than the first Deshayesitidae (genus possibly, correspond to the upper part of Weissi and Turkmeniceras), which is confirmed by subdivision of Albrechti-austriae Zone (D. w eissi and P. albrechti the suture part of their suture-line. The lobe-formula of austriae) of Northern Caucasus. However, such a the species fissicostatus, judging by the figure in R. correlation is arbitary, since it is impossible to Casey's paper [Casey, 1964, p. 354, fig. 125d], is - give a reliable parallelization of the boundary ELU1U3U4 (?) : U2I (with location of U3 lobe on the Barremian/Aptian beds in the considered regions. lateral side) ; i.e. it is the same, as that of Deshayesites, and differs from that of Turkmeniceras. This circumstance makes it possible to correlate the stratons, 1.3. Deshayesi Zone (Deshayesites deshayesi) starting the Lower Aptian in England and Germany, with beds, which have a higher position in the section, The name of the zone is taken from W. Kilian's than beds with early Deshayesitidae of the Trans- chart [Kilian, 191C , table to p. 283] л Caspian area, i.e. with Tuarkyricus Zone (D. The ammonite assemblage is much poorer than that tuarkyricus). Stratigraphic position of this zone, which of the Weissi Zone. This is possibly due to an extensive is lower than that of Weissi Zone (D. weissi), confirms regional erosion of the deposits of this stratoh in the the justified character of this correlation. In the Trans-Caspian area. Its sections, characterized by Caucasus region, Tuarkyricus Zone should, probably, fauna, are traceable only in western parts of the Trans- be correlated with the lower part of the Weissi and Caspian area (Tuarkyr, Greater Balkhan). The Albrechtiaustriae Zone. The difference between the following forms are found here : Phyllopachyceras compared intervals is the absence of Cheloniceratidae baborense C oqu and , D. dechyi Papp, D. levigatus representatives in the Trans-Caspian area. Bogdanova, D. kudrjavzevi I. M ichailova, D.

Céologie Alpine. 1994. Mémoire H.S. n° 20 consobrinoides S in zow , D. deshayesi Leym erie, D. are clearly correlated with each other. When correlating babaschensis Bogdanova, Toxoceratoides royerianus upper Deshayesites beds in England and Trans-Caspian d'Orbigny, Cheloniceras cornuelianum d'O rbigny. area account, should be taken of the following The vertical range of several species is not restricted circumstances : 1) absence in the Trans-Caspian area of only by this zone ; some of the forms "pass" from such species as D. grandis Spath, D. vectensis Spath. Weissi Zone, among them D. deshayesi. Therefore, we and other ammonites, characteristic of the upper are drawing the lower boundary of the Deshayesi Zone Deshayesi Subzone in the English sections ; 2) absence, on the basis of disappearence of D. weissi, D. planus, even in the uppermost beds, among the Trans-Caspian D. topleyi and other Deshayesites, occuring lower. representatives of the species D. deshayesi, of Most ammonites of the Deshayesi Zone in the specimens with distinct features of late mutations of Trans-Caspian area allow placing it under the upper this species ; 3) erosion of the upper beds of Deshayesi Deshayesites Beds of the Lower Aptian of Europe. Zone in the Trans-Caspian area. This enables us to However, correlation with zones of the same name in presume that, generally, the Deshayesi Zone of the other regions is connected with great difficulties, since Trans-Caspian area does not correspond to the entire different workers propose markedly different Deshayesi Zone in England, but only to its lower interpretations of the range of Zones. In a layer-by- Subzone, i.e. Parinodum (Cheloniceras parinodum). layer description of stratotype of the Bedoulian (lower) In view of the above-mentioned specific features of substage of the Aptian Southeastern France (Colloque the species D. deshayesi, its choice as a zonal index sur le Crétacé inférieur, Lyon, septembre 1963 ; 1965) seems to be temporary. At any rate, specimens from the this species was indicated only in its middle part, same locality, where Leymerie's specimen was found, whereas in Resolutions of the Lyon Colloquium of should be studied, or from nearby localities. Besides, 1963, Deshayesi Zone corresponds to the entire the stratigraphic level of this species in the Lower Bedoulian (Colloque sur le Crétacé inférieur, Lyon, Aptian (Bedoulian) type section should be clearly septembre 1963 ; 1965). In the stratigraphic chart of the defined, since data on this section, located in southern Lower Aptian in England [Casey, 1961], which France, should be primarily taken into account, when comprises four zones, it is known from the upper the stratigraphic chart for the Mediterranean Region is Deshayesites Beds. In the Russian Platform, this form developed. is indicated as being characteristic of the lower one of two ammonite horizons, distinguished in the Lower Aptian of the Volga area. In Northern Caucasus, D. 1.4. F urcata Zone (Dufrenoya furcata) deshayesi occurs in the upper Deshayesites beds, distinguished as Deshayesi and Dechyi Zone The striton with the above index was erected by Ch. [Mordvilko, 1960], together with D. kurdrjavzevi and Jacob [?9'o^]. Later, the zone, which has D. furcata as D. consobrinoides. one of its index species, was present in V.P. One of the causes of discrepancy between the Renngarten's chart [Renngarten, 195^Pín West ranges of stratigraphic units of the same name is also Turkmenian sections, deposits with D. furcata rest with different interpretation of the range of species D. erosion on the underlying deposits. deshayesi, which often does not take account its At the boundary of the Deshayesi and Furcata evolution in time. The species D. deshayesi is long- Zones, the ammonoid assemblage changes markedly. lived, which give various mutations in time. R. Casey Representatives of the genus Deshayesites disappear, noted that in the English representatives of D. and the genus Dufrenoya becomes widespread (furcata deshayesi early whorls are characterized by the most Sowerby, subfurcata Kasansky, dufrenoyi d'Orbigny, long-term growth stage and a smooth venter. lurensis K ilia n , sinzovi L uppov, scalata C a sey , Proceeding from the assumption, that in the evolution fursovae Bogdanova, etc.). Another late genus of the process of the genus Deshayesites, costae start to family Deshayesitidae-Burckhardtites is less frequent intersect the venter at increasingly later whorls, R. (palumbes Hamphrey, gregoriensis Hamphrey, imlayi Casey regards this species as an ancestral species of the Hamphrey), which up to now has not been recorded in genus D ufrenoya [Casey, 1964]. In Trans-Caspian Europe. In addition to the above genera Cheloniceras is representatives of this species, a break in costae on the also found in this zone (seminodosum S in z o w , venter of the shell is most often not recorded ; at any cornuelianum d'Orbigny), Toxoceratoides (royerianus rate, this concerns those specimens, which were found in beds together with D. weissi. It is quite likely, that d'Orbigny), A co n ecera s (n iso id es S a r a s in ), they yield the most ancient representatives of the Tropaeum, whose stratigraphic range is wider than a species. In Deshayesi Zone in England, possibly, a zone. younger mutation of the species or a subspecies occurs, Furcata Zone of the Trans-Caspian area is correlated which gave rise to the genus Dufrenoya. Correlation of with Furcata Zone and Subfurcata Zone of Northern the lower boundaries of Deshayesi Zones in Trans- Caucasus and Dagestan. In South England it Caspian area and England is controlled by disappea corresponds to Bowerbanki Zone, which yields almost rance of jnost species of the underlying zones, which the same D ufrenoya and Cheloniceras species. A

Geologic Alpine, 1994, Mémoire H.S. n° 20 56 ON DEVELOPMENT OF THE AMMONITE ZONAL STANDARD FOR THE MEDITERRANEAN REGION

specific feature of the Trans-Caspian sections are single heteromorphic ammonites have a narrow stratigraphic finds of uncoiled shells of the genus Tropaeum. range (are confined only to this zone); among them, the species A. wassiliewskyi can also be regarded as a zonal species for the Trans-Caspian area. Analysis of the species composition of ammonites 2. - Middle Aptian assemblage in the lower part of the Middle Aptian over the extensive territory of southern Eastern and Western The boundary between the lower and middle Europe has shown that this assemblage is extremely substages of Aptian in the Trans-Caspian area, drawn constant both in its species, and generic composition. along the boundary of Furcata Zone and Subnodoso- This circumstance makes easier correlation of the costatum Zone remains not corrrelated with the Subnodosocostatum Zone with the lower unit of the boundary drawn between Bedoulian and Gargasian in Middle Aptian (often having the same name) in the France, where it coincides with the base of beds, considered area. containing Dufrenoya. Possibly, this boundary is drawn at different stratigraphic levels, i.e. the upper part of the Trans-Caspian Furcata Zone corresponds to the lower 2.2. Melchioris Zone (Parahoplites melchioris) part the Gargasian Nisus Zone in France. Boundary with the Lower Aptian deposits in the Trans-Caspian The zone was first distinguished in Mangyshalk by area is drawn on the basis of a distinct succession of A.D. Natsky as Beds with P. melchioris. Later, it was paleontological assemblages. Middle Aptian in the time studied in detail in the Caucasus [Drutschits et al., of predominance of the family Parahoplitidae and 1966 ; Eristavi, 1960 ; Luppov, 1956 ; Mordvilko, 1960 subfamily Colombiceratinae. The first Colombiceratinae and Renngarten, 1951] and was named after the highest appear already in Furcata Zone (Gargasiceras sp. in abundance of the species P. melchioris in these Tuarkyr). deposits. A fossil assemblage in the considered zone differs 2.1. Subnodosocostatum Zone (Epicheloniceras from that of the Subnodosocostatum Zone by subnodosocostatum) appearance of ammonites of the genus Parahoplites (sch m id ti Jacob & Tobler, g ro sso u v re i J a c o b , campichei Pictet & Renevier, melchioris A n th u la , This zone first appeared as an independent unit sjogreni A n t h u la , debilicostatus I. M ichailova, v- (subzone) in Ch. Jacob’s chart [Jacob, 1907] and had multicostatus S in z o w , tra n sita n s S in z o w , sub- two indexes, i.e. subnodosocostatum and buxtorfi. ca m p ich ei S in z o w , irregularis C a s e y , luppovi Zonal ammonite assemblage is extremely rich and Tovbina). Ammonites of the new genus of diverse. Genus Epicheloniceras (which replaced Colombiceratinae, i.e. Protacanthoplites [Tovbina, Cheloniceras in the Early Aptian) is represented by the 1970, 1982] also occur here ; this genus is a link in the species subnodosocostatum S in zow , tschernyschewi lin e a g e Colombiceras-Acanthohoplites. It is S in z o w , J a c o b , K a s a n s k y , b u x to rfi p u ssillu m represented by species P. monilis Tovbina, P. mirus stuckenbergy K asan sk y ; among Parahoplitidae, the Tovbina, P. abichi A n th u la , P. submirus Tovbina, P. genus Colombiceras, which is the second in time, is multinodosus T ovb in a, P. bogdanovae T ovbina, P. widespread (to b leri J a co b , subtobleri K a sa n sk y , quadratus K a san sk y , : P. aff. bigoureti S eu n es, P. ca u ca sica L u p p ov) ; A c o n e c e ra s become more bigoti S eu n es, P. bigoti incivilis Glasunova, etc. abundant : A. nisus d'Orbigny, A. haugi Sarasin. An Ammonites of this genus are predominant in the upper interesting group are heretomorphic ammonites of the part of the Melchioris Zone. In Central, southern part of genera Ammonitoceras (wassiliewskyi Renngarten, Western and Eastern Kopetdag, the upper part of transcaspium S in z o w ), Australiceras (p a w lo w i Melchioris Zone, where representatives of the genus Wassiliewsky), Luppovia (dotshanensis B ogd anova, Parahoplites are not found, and Protacanthoplites are K a k a b a d z e and I. M ichailova, adjiderensis abundant, was distinguished by Tobvina [1982] as Bogdanova, Kakabadze and I. M ichailova). In Monilis Subzone (P. monilis) (the most frequent sections of western regions (Tuarkyr, Greater Balkhan, species). The genus Colombiceras is represented by the Kubadag) Salfeldiella guettardi R aspail, Tetragonites same species, as in the Subnodosocostatum Zone. In depressus R a sp a il, Jauberticeras latericarinatum this connection, attention should be paid to substitution A n th u la occur. of the index species for Tobleri Zone (C. tobleri) in the The species E. subnodosocostatum is known from draft scale of the Mediterranean region [Hoedemaeker the lower zone of the Middle Aptian in Mangyshlak, and Bulot, 1990]. Since in Trans-Caspian area and in Northern Caucasus, Dagestan, Georgia, northern Northern Caucasus species C. tobleri characterizes both Germany and Southeastern France, and some workers zones of the Middle Aptian, it is probably not have chosen it as an index species. E. tschernyschewi reasonable to make it the index species for one of and E. buxtorfi are often found in the considered zone them ; the more so, as among species of other genera, in Mangyshlak, Northern Caucasus, and England. Some particularly such a well known genus as Parahoplites,

Geologic Alpine. 1994, Mémoire H.S. n° 20 the index for the upper zone of the Middle Aptian can Zone), but rather to the lower part of the widespread be chosen. We propose the species P. melchioris, since Nolani Zone. In the zonal chart of the Mediterranean it occurs not only in the Trans-Caspian area, but also in region it corresponds to D. nodosocostatum horizon. Northern Caucasus, Transcaucasus and Germany, where it accompanies the species P. nutfield.ien.sis, 3.2. Nolani Zone (Acanthohoplites nolani) index of one of the Middle Aptian Zones in the Boreal region, which is, most likely, a full equivalent of the Melchioris Zone. In addition to the above ammonites, First appeared as an independent straton in the this zone also contains genera Aconeceras (nisus "Standard of Cretaceous System" [Muller and Schenk. d'Orbigny, h a u g i S a r a s in ) , Sanmartinoceras 1943], and soon afterwards Renngarten provided (a p tia n u m S a r a s in ) , Euphylloceras (velled a e grounds for it, using the material from the Greater M ic h e lin , a p tie n se S a y n , a n th u la i K a s a n s k y ), Caucasus [Renngarten, 1951]. It is traceable throughout Zurcherella (zurcheri Jacob), Tetragonites (depressus the Trans-Caspian area. R aspail, heterosulcatus A n th u la). The assemblage of Trans-Caspian Acanthohoplites of this zone was first described by Sinzow [1908] from sections of Mangyshlak. It is much richer and diverse than that in underlying deposits. In addition to 3. - U pper A ptian Acanthohoplites, there sometimes occur E o douvilleiceras, also indicated in prodromus Zone : E. 3.1. Prodromus Zone (Acanthohoplites prodromus) (E .) b a S iy zic u m I^rmanova and E. (E .) ex. gr. clansayense Jacob./Zonal index species A. nolani is Distinguished by Tovbina [1968]. The section on rather rare in the Trans-Caspian area. The following the southern slope of the Elli-Kaya Ridge in Kopetdag species are more abundant in this region : A. migneni is chosen as a stratotype. Seunes, A. multispinatus A n th u la , A. uhligi A nthula, Most frequent in Prodromus Zone are ammonites of A. trautscholdi Simonovitch, Bacevitch & Sorokin, genera Diadochoceras and Acanthohoplites. Here, the A. subangulicostatus S in zow , A. subrectangulatus Clansayesiarsubgenus Eodouvilleiceras of the genus Sinzow , A. lorioli Sinzow, A. anthulai K asansky, A. Epicheloniceras appears. Several species of the typical com pressus K a sa n sk y , A. elegans Glasunova, A. Clansayesian genus Diadochoceras : nodosocostatum subangulatus Luppov. These species are known from d'Orbigny, causasicum Luppov, aff. hokodsens I. the nolani Zone of Mangyshlak, Northern Caucasus, M ichailova, and local species latiumbonatum Transcaucasus, and Western Europe. Besides the T o v b in a , longispinatum T o v b in a , pseudomulti- widely known species, some parts of the Trans-Caspian spinatum Tovbina in the Trans-Caspian area are area are characterized by local species : A. geokderensis confined to this zone ; but it is on the basis of their T ovbina, A. trapezoidalis Tovbina and A. asiaticus presence that the Prodromus Zone is regarded as a part Tovbina. Phylloceratids and tetragonitids are of Nolani Zone in most areas of Eastern and Western represented by the same species, as in underlying E urope. Acanthohoplites are dominated by local deposits. species : A. prodromus prodromus Tovbina, A. enodis The Trans-Caspian no la n i Zone, most likely, en o d is T o v b in a , A. raricostatus T o v b in a , A. corresponds to the upper part of the zone of the same balchanensis Tovbina ; there are wellknown A. name, extensively traced in Europe, and in the chart for trautscholdi Simonovitch, Bacevitch & Sorokin, Л. the Mediterranean region, to that interval of nolani aschiltaensis Anthula, or affined A. aff. bergeroni Zone, which occurs above D. nodosocostatum horizon. S e u n e s, "A." a ff. b ig o ti Seunes. Among the Clansayesian Epicheloniceras : E. (Eodouvilleiceras) 3.3. Jacobi Zone (Hypacanthoplites jacobi) badkhyzikum U rm an ova, E. (E.) clansayense Jacob should be indicated. In the Trans-Caspian area this zone was Historically, beds taking up the interval between the distinguished by A.D. Natsky2. Then it appeared in the Melchioris and Nolani Zones were distinguished in the chart of the Greater Caucasus [Renngarten, 1951] as Aptian sections of the Trans-Caspian area. In Jacobi-Tscharlokensis Zone (H. jacobi - H. Kopetdag, they were named AschiltaTensis Zone tscharlokensis). And later, for the same region as (Subzone)04. aschilmensis) by analogy with sub Jacobi Zone (H. Jacobi) [Eristavi, 1960]. It is not traced division of the Upper Aptian in Northern Caucasus over the entire Trans-Caspian area. It was subject to [L uppov et a l., 1960]. In Tuarkyr, Beds with erosion in West Turkmenian sections, in Mangyshlak Acanthohoplites ex. gr. uhligi and Diadochoceras and, locally, in Lesser Balkhan. [Bogdanova et al., 1963]. Then S.Z. Tovbina, who studied ammonites of this straton, showed that it did The boundary of the Jacobi Zone with the not correspond to the Caucasian Aschiltaensis Zone (A. underlying deposits is drawn on the basis of aschiltaensis) (this zone, most likely, corresponds in the Trans-Caspian area to the upper part of Melchioris 2 Manuscript of A.D. Natsky 1918 has not been published and is kept Zone and, possibly, to the lowermost part of Prodromus at VSEGEI, St-Petersburg. Géologie Alpine, 1994, Mémoire H.S. n° 20 58 ON DEVELOPMENT OF THE AMMONITE ZONAL STANDARD FOR THE MEDITERRANEAN REGION

replacement of Acanthohoplites by species of the genus 4. - Conclusion Hypacanthoplites. In the boundary beds of Nolani and Jacobi Zones, Acanthohoplites with outlined tubercles 1) The present paper characterizes Aptian zones of on the venter are found, which are, possibly, the Trans-Caspian area, including those, which are transitional to Hypacanthoplites ; however, the comprised into the draft ammonite zonal scale for the tubercles are much less pronounced than in the latter Mediterranean region, i.e. Tuarkyricus, Weissi, genus. Unfortunately, these species have not yet been Deshayesi, Furcata, Subnodosocostatum, Nolani (local adequately studied. The hypacanthoplites assemblage Trans-Caspian Prodromus Zone corresponds in its comprises widely known West European species, on stratigraphic range to D. nodosocostatum Horizon), and which basis the upper zone of the Clansayesian is Jacobi. It is proposed to replace the index species for correlated over an extensive territory : H. ja co b i the Tobleri Zone (C. tobleri). C o l l e t , H. milletianus nodosocostatus F r ite l, H. 2) As mentioned above, type sections of the Aptian sarasini C o lle t, H. spathi D u te r tr e , H. hanoverensis substages in Southeastern France up to now remain C o l l e t . The species H. a sp e r Glasunova, H. unrevised. Data on these sections should, doubtless, be kopetdagensis G la s u n o v a and H. tscharlokensis taken into account, when the Aptian scale for the G la s u n o v a were described by Glasunova from the Mediterranean Region is developed. As is known from considered deposits of Western Kopetdag. Herefrom the earlier published papers, the type sections of the Natsky also described the species H. nolaniformis Bedoulian, Gargasian, and Clansayesian, in case of their most accurate study, cannot, unfortunately, offer Glasunova. The last-mentioned species and H. good prospects as regards the number and preservation tscharlokensis are presently known from the Jacobi of the contained ammonite remains for solving the Zone in the Northern Caucasus. In addition to problem of zonal subdivision of the Aptian, and the Hypacanthoplites, this zone also contains single zonal index species. In this connection, apparently, a Euphylloceras aff. velledae d'Orbigny. problem can be raised of choosing parastratotypes of The constant species assemblage of the Jacobi Zone Aptian substages or of the stage in general. For this and its consistency over an extensive area in southern purpose, sections of the Trans-Caspian area and the and middle Europe justify the introduction of this zone Caucasus, which are stratigraphically complete and into the considered draft. richly characterized by diverse faune, can be used.

References

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Géologie Alpine, 1994, Mémoire H.S. n ' 20