Problems on the Middle Oxfordian biostratigraphy of Western Siberia

• Autorzy: Podobina V. , Polkovnikova E. , Tatyanin G.
• Konferencja: International Congress on the Jurassic System (7 ; 06-18.09.2006 ; Kraków, Poland]
• Języki publikacji: EN

Abstrakty

EN

The knowledge of biostratigraphy of the Middle Oxfordian part of the section of the Verkhnevasyuganskiy Subhorizon although quite good is insufficient for solving all the problems of dating, detailed correlation, and identification of sandy beds of the substantial oil-and-gas bearing deposits complex in the new borehole sections. Another cluster of problems includes the detailed subdivision of two Middle Oxfordian ammonite zones (a-zones) of Western Siberia and their correlation with the coeval Plicatilis Zone of the Submediterranean zonal scheme. At present, two a-zones are distinguished in the Middle Oxfordian of Western Siberia: the lower zone with the Cardioceras densiplicatum and the upper zone with Cardioceras tenuiserratum. Two parts are distinguished in the Cardioceras densiplicatum Zone corresponding to the Cardioceras vertebrale and Cardioceras maltonense subzones. The upper zone is not subdivided, and it is based on the appearance of ammonites of the subgenus Cawtoniceras. Foraminifera are of exceptional biostratigraphical importance when the material from cores is considered where ammonoid finds are generally rare. The Middle Oxfordian sedimentary complex of Western Siberia contains foraminiferal assemblages of two f-zones: Ammodiscus thomsi-Tolypammina svetlanae and Trochammina oxfordiana. The former includes several isochronous beds recognized in different areas of the region. In the circum-polar Urals, L. G. Dain distinguished beds with Ammodiscus thomsi, Tolypammina svetlanae. In western areas, V. I. Levina distinguished beds with Ammodiscus cheradospira (=Ammodiscus aff. pseudoinfimus (=Ammodiscus thomsi) and Eomarssonella paraconica. In the southern area, V. F. Kozyreva recognized beds with Ammodiscus ex gr. pseudoinfimus (=Ammodiscus thomsi) and Trochammina oxfordiana. In the central and southern districts, beds with Trochammina oxfordiana and with Glomospirella galinae were established by G. M. Tatyanin. The geographical range of the Ammodiscus thomsi-Tolypammina svetlanae Zone covers: Western Siberia, the Preuralian, Yamal-Tyumen, Kazym-Konda, Froly-Tambey, Pur-Vasyugan facies districts (the Danilovskoye, Abalak, Vasyugan, Maurynya formations). In the Yenisey-Khatanga depression N. V. Sharovskaya distinguished beds with Trochammina oxfordiana, Lenticulina memorabilissima, now this is the Trochammina oxfordiana Zone (its top correspond to the Ammodiscus thomsi - Tolypammina svetlanae Zone). The range of the Trochammina oxfordiana Zone covers: Western Siberia, the Khatanga and Taz-Kheta facies districts, Central Siberia, the Paksa facies district (Sigovoe Formation). The analysis on the available findings of the Middle Oxfordian ammonites in the south-east of Western Siberia may offer a key to reconciling the combined macro- and microfauna finds with the ammonite scale, and refining the lower and upper boundaries of the Middle Oxfordian foraminiferal associations. This could make possible tracing and comparing the changes in the systematic composition of the foraminiferal assemblages within two Middle Oxfordian ammonite zones which include the sections of the oil-and-gas bearing horizons.

Słowa kluczowe

EN

biostratigraphy; Middle Oxfordian; Western Siberia; ammonites; foraminifera; zones; beds

• Wydawca: Państwowy Instytut Geologiczny - Państwowy Instytut Badawczy
• Czasopismo: Volumina Jurassica
• Rocznik: 2006
• Tom: Vol. 4, no. 1
• Strony: 206--207

Twórcy

autor

Podobina V.

autor

Polkovnikova E.

autor

Tatyanin G.

• Tomsk State University, 36 Lenin ave., Tomsk 634050, Russia,