BULLETIN DE L'INSTITUT ROYAL DES SCIENCES NATURELLES DE BELGIQUE SCIENCES DE LA TERRE, 78: 117-147,2008 BULLETIN VAN HET KONINKLIJK BELGISCH INSTITUUT VOOR NATUURWETENSCHAPPEN AARDWETENSCHAPPEN, 78: 117-147, 2008 The upper Albian and lower Cenomanian succession at Kolbay, eastern Mangyshlak (southwest Kazakhstan) by W. James KENNEDY, Christopher KING & David J. WARD Kennedy, W.J., King, C. & Ward, D.J., 2008 — The upper Albian le promontoire de Kolbay au sud-ouest du Kazakhstan. La coupe and lower Cenomanian succession at Kolbay, eastern Mangyshlak est décrite et son interprétation sédimentologique et en termes de (southwest Kazakhstan). /«: Steurbaut, E„ Jagt, J.W.M. & Jagt- stratigraphie séquentielle est proposée. La faune d'ammonites la Yazykova, E.A. (Editors), Annie V. Dhondt Mémorial Volume. plus récente de l'Albien est attribuée à la Zone à Mortoniceras Bulletin de l'Institut royal des Sciences naturelles de Belgique, (Subschloenbachid) perinflatum et comprend Arrhaphoceras (A.) Sciences de la Terre, 78: 117-147, 7 figs, 8 pis, Brussels, October subtetragonum spath, 1928, Callihoplites dorsetensis spath, 31, 2008-ISSN 0374-6291. 1928, Lepthoplites gracilis spath, 1928, Placenticeras kolbajense (Sokolov, 1967) (localité type), Idiohamites dorsetensis Spath, 1939 et Lechites (L.) moreti Breistroffer, 1936. La plus ancienne faune du Cénomanien apparaît 60 mètres plus haut dans la coupe et Abstract peut être attribuée à la partie inférieure de la Sous-zone à Neostlingoceras carcitanense, Zone à Mantelliceras mantelli de la partie inférieure du Cénomanien inférieur. Elle comprend: The Kolbay promontory in southwest Kazakhstan exposes a 90- Placenticeras mediasiaticum Luppov, 1963, Schloenbachia varions metre section of shallow-marine, terrigenous clastic upper upper (j. sowerby, 1817), Mantelliceras saxbii (sharpe, 1857), M. Albian and lower lower Cenomanian sédiments. The section is lymense (spath, 1926b) et Algerites ellipticus (mantell, 1822). described, and a sedimentological and sequence-stratigraphical L'intervalle entre ces deux faunes est dépourvu de macrofossiles are interprétation proposed. The youngest Albian ammonite fauna permettant une datation, mais l'intervalle entre 47,5 et 55,2 m au- is referred to the Mortoniceras (Subschloenbachia) perinflatum dessus de la base de la coupe contient l'assemblage de requins et Zone; it comprises Arrhaphoceras (A.) subtetragonum Spath, de raies d'âge Albien tardif à Cénomanien précoce le plus diversifié 1928, Callihoplites dorsetensis spath, 1928, Lepthoplites gracilis que nous connaissons, aves des dents isolées totalisant plus de vingt- Placenticeras spath, 1928, kolbajense (sokolov, 1967) (type sept espèces. locality), Idiohamites dorsetensis spath, 1939 and Lechites (L.) moreti Breistroffer, 1936. The oldest Cenomanian fauna Mots-clefs: Albien, Cénomanien, ammonites, élasmobranches, comes from metres 60 higher in the section, and can be referred stratigraphie, Kazakhstan. to the lower Neostlingoceras carcitanenese Subzone of the lower lower Cenomanian Mantelliceras mantelli Zone. It comprises Placenticeras mediasiaticum luppov, 1963, Schloenbachia varions (J. sowerby, 1817), Mantelliceras saxbii (sharpe, 1857), Mantelliceras lymense (Spath, 1926b) and Algerites ellipticus Introduction (Mantell, 1822). The interval between these two faunas lacks age-diagnostic macrofossils, but the section between 47.5 and 55.2 metres above the base of the sequence has yielded the most diverse The Mangyshlak anticlinorium, in southwest shark and ray fauna of late Albian to early Cenomanian age known Kazakhstan, extends for 300 km from the Caspian Sea to us, with isolated teeth representing a total of more than twenty- to the western border of the Ustyurt Plateau, trending seven species. westnorthwest-eastsoutheast (Fig. 1). It comprises Keywords: Albian, Cenomanian, ammonites, elasmobranchs, gently folded Mesozoic and Paleogene sédiments, stratigraphy, Kazakhstan overlain unconformably by near-horizontal Neogene strata which form the surface of the Ustyurt Plateau and a number of outliers further west. Marine mid- Résumé Cretaceous rocks are extensively exposed in the Mangyshlak anticlinorium; their régional stratigraphy Une coupe de 90 mètres de sédiments marins peu profonds, élastiques and corrélation were analysed through the study of et terrigènes, datés de la partie supérieure de l'Albien supérieur et seven key sections by MARCINOWSKI et al. (1996). de la partie inférieure du Cénomanien inférieur est exposée dans 118 W. James KENNEDY, Christopher KING & David J. WARD 51° 52° 53° 54° 55° Marcinowski et Kazakhstan al., 1996) and at Kolbay, described here, the upper Albian and lower Cenomanian are relatively expanded, in comparison to sections further Turkmenistan west (Marcinowski et al, 1996, fig. 14). The upper i Shakh- * _ i, Vf, • Albian succession is more than 120 métrés thick, (Bogota • Koksyrtau ^ 44° the lower Cenomanian around 45 métrés. Detailed Sulukapy ^ Caspian ? Kolbay lithostratigraphic corrélation within this interval was AKTAU not carried out by Marcinowski et al. (1996), who Azhirektoy# concentrated on the biostratigraphy of the sequence. • Besakty UZEN The Kolbay section Fig. 1 - Location of the Kolbay section and other sections in the Mangyshlak anticlinorium mentioned in the The section studied text. Inset map: Az. - Azerbaijan. (co-ordinates: 43° 41 46.3" N, 53° 58 E 52.0" E) is near the eastern end ofthe Mangyshlak anticlinorium, on a westward-projecting promontory of Gale et al. (1999) studied the biostratigraphy and the escarpment bordering the Ustyurt Plateau (Fig. 1). sequence stratigraphy of the Cenomanian sucession Here, approximately 90 m of mid-Cretaceous (upper in three of these, namely at Koksyrtau, Shakh-Bogota Albian and lower Cenomanian) sédiments are exposed and Sulukapy. in the western Mangyshlak anticlinorium (Figs 2, 3), overlain unconformably by Neogene (Fig. 1). limestones of the Ustyurt Plateau. Underlying Albian No formai lithostratigraphic nomenclature exists and overlying younger Cenomanian and Turonian for the Cretaceous successions in this area. The upper sédiments are exposed nearby, but were not examined Albian and lower Cenomanian are represented in the during the present study. The Kolbay section was eastern Mangyshlak anticlinorium mainly by non- not studied by marcinowski et al. (1996), but is calcareous fine sands and sandy clays. Macrofossils approximately 20 km northeast of their Azhirektoy occur mainly in a few thin phosphatic beds and in layers section, and approximately 50 km northnortheast of of calcareous concrétions. their Besakty section (Fig. 1). In the eastern part of the Mangyshlak anticlinorium, At Kolbay, the dominant lithologies are silty and in the Besakty and Azhirektoy sections (studied by sandy clays and silty to fine sands, interbedded on Schloenbachiàjûiàd shark teem The Kolbay section, viewed from the south. The height of the escarpment is approximately 90 métrés (photograph by Tatiana Malyshkina, Institute of Geology, Ekaterinburg). Upper Albian-lower Cenomanian of Kolbay, eastern Mangyshlak 119 90-p Fig. 3 - Stratigraphy of the (g) exogyrids common Kolbay section; numbers v p rare Placenliceras refer to fossil levels described in the text. Thickness is in metres. Znirs-ü-O-iXjn I—| Schloenbachia common I 7 | C-fr trigoiliids{'Schloenbachia bed') 70 - trigoniids Ophiomorpha 60 - omission — ÜTLn^vy-vSrLJ surface érosion surface ÜTJv-U-V'-lOxL m aAA shark teeth 50 - Ophiomorpha aAa s x bivalves Ophiomorpha ammonites m o exogyrids glauconite 40- calcareous O O concrétions ironstone interlayered sand & clay 30 - ----- sandstone laniinated & cross-stratified sand 2o - yi fine sand "gÇ3'~(fe51 PU 0) abundant ammonites — — - |—| y—^ and small bivalves silty sand pPlacenticeras bed') sandy clayey silt ^2/ Placenticeras m_N crushed silty clay with thin 'ê^~o"oA silt/sand partings silty clay a metric to decametric scale (Fig. 3). Contacts are account, they are located in the section in terms of generally sharp and are often burrowed omission height above the base of the section, in metres. surfaces. Between 44.5 m and 62.4 m above the base, Level 1 (4.0 m): A thin layer of hummocky cross- there are several units of laminated and cross-stratified stratified sand with large tabular calcareous sandstone sand with Ophiomorpha burrow Systems. The entire concrétions. There is a concentration of crushed section is decalcified, except for concrétion levels; Placenticeras at the base. molluscs occur Level 2 only in a few thin beds. (14.0-15.0 m): the 'Placenticeras bed' - large subspherical silty limestone concrétions in glauconitic sandy silt. These are frequently packed with well- Macrofauna preserved ammonites (predominantly Placenticeras), small bivalves (mostly Aucellina) and some gastropods. Macrofossils have been recorded from eight levels, here The ammonites often retain their aragonitic shell, but designated horizons 1 to 8 (Fig. 3). In the following are frequently fragmentary (although not abraded) and 120 W. James KENNEDY, Christopher KING & David J. WARD randomly oriented. The specimens of Placenticeras 4. Bioturbated silty clay and clayey silt. These may be comprise a wide range of ontogenetic stages and deeper marine neritic sédiments, but the absence of morphologies. macrofauna limits interprétation; Level 3 (44.55-45.15 m): tabular calcareous sandstone 5. Mollusc-rich units. Most of the units with molluscs with dispersed fine phosphate. Common exogyrid have features indicative of slow and/or interrupted