Geologija 1994, 17 LITHOSTRATIGRAPHY OF

Geologija 1994, 17

LITHOSTRATIGRAPHY OF JURASIC IN LITHUANIA

Algimantas Grigelis

After the Middle and Late Triassic uplifts, continental regime and major stratigraphical gap, the marine basins predominated again in Lithuania and adjacent South Baltic region from Late Middle Jurassic time throughout the Cretaceous and into the Paleogene Sedimentation in these basins completed formation of the Late Permian Lithuanian-Polish (Peribaltic) Syneclise. The south-western most deeply subsident part of the syneclise is affected by the major tectonic lineament, the Tornquist Zone, forming the south-western boundary between the East European Platform and the Central European Plate [6]. In the Lithuanian-Polish Syneclise Jurassic, Cretaceous and Paleogene sedimentary successions are characterized by repeated facies shifts and great diversity in lithologies. They include clastic as well as carbonaceous deposits of continental, lagoonal and marine origin. According to tradition, up to now in the Lithuanian geology the sedimentary sequences of subcontinental genesis of geological systems mentioned above were divided into formations, meanwhile the marine sediments, containing abundant fauna - into biostratigraphical zones. This paper deals with a new stratigraphical concept, where the complete lithostratigraphical subdivision is applied to the whole section [3]. The lithostratigraphical subdivision of the Jurassic in Lithuania is illustrated by sratigraphical chart (Table ). Previous names of these units are used, the newly introduced are marked by an asterisk. The analyses of Jurassic sedimentary sequences show that various conditions of sedimentation in the shelf basin prevailed linked to changes in depth of the basin. Diferences in local environments may often have been caused by interaction between eustasies and synsedimentary tectonic factors. According to the international requirements for stratotype section descriptions, the generalized data about the Jurassic units are given below. Geographical names of stratigraphic units are revised according to the linguistic standarts. In the Kaliningrad Enclave, where after 1945 the new names of settlements have been introduced, the previous old names are also used. References to main works, where this or another unit was separated and described for the first time, are given. The autor is grateful to Prof.Habil.Dr. J.Paškevičius for this critical evaluation of the manuscript, Dr. R. Mertinienė and Dr. P. Šimkevičius - for useful discussion on problems of the Mesozoic stratigraphy. Jurassic In the southern part of the Baltic region, the Jurassic strata are restricted to SW Latvia, Lithuania and Kaliningrad Enclave. The Jurassic rocks gradually increase in thickness towards the south and west a maximum of about 240 m near the Lithuanian-Polish border (Fig 1). Two lithofacies zones may be distinguished though a lithostratigraphical subdivision relevant for both zones is regarded to be valid [1]. Lower and Middle Jurassic No Hettangian or Sinemurian strata are documented from the Baltic area studied. The Pliensbachian and Toarcian Stages are represented by the Jotvingiai Group wich include two formations, viz. the Neringa and the Lava Formations [6, 7]. The Middle Jurassic is represented by the Skalviai Group wich is composed of three formations, viz. the ôsrutis Formation [12], the Liepona Formation [10], and the Papilė Formation [2]. The Lower and Middle Jurassic Jotvingiai and Skalviai Groups are composed of subcontinental terrigenous, sometimes coal-bearing sediments, devoid of carboniferous content. The Liepona and Papilė

Formations represent marine ingressions and have yielded foraminifers and remains of a macrofauna [2]. In the end of the Middle Jurassic, from Mid- Callovian time, marine transgressions into a shelf basin formed the formations described below. Papartinė Formation The name of this formation is derived from the village Papartinė, situated near the town of Papilė on the eastern side of River Venta in NW Lithuania. The stratotype of the formation is located to Papilė (outcrop No.1, in front of the railway station) and the parastratotype in Papartinė [2]. In the Papilė stratotype section (Fig. 2), the Papartinė Formation rests upon the Papilė Formation (Lower Callovian). Between the two formations a stratigraphical gap has been observed. The formation consists of greyish and brownish polymictic, fine-grained sands and sandstones measuring 6.20-6.25 m in thickness [4]. The Papartinė Formation has been dated to Middle - Late Callovian with the aid of ammonites and foraminifers [2, 9]. It is ascribed to the Kosmoceras jason, Erymnoceras coronatum, and the Kosmoceras ornatum ammonite zones (Middle Callovian to early Late Callovian) [9]. In terms of foraminiferal zones, the formation corresponds to the Lenticulina cultratiformis and Lenticulina paracultrata Zones [2]. In the stratotype section the formation in question is overlain by black clays of the Skinija Formation. In the parastratotype section of the Papartinė Formation, at present not accesible, the upper part of formation is composed of oolitic marls and inequigranular sands not exceeding 1.5 m in thickness. Ammonite finds indicate the Kosmoceras ornatum Zone (early Late Callovian age). In the Papartinė outcrop, the lower and upper limits of the formation have not been defined. The most complete sections of the Papartinė Formation are to be found in western Lithuania, in the Žemaitija Depression. In the Vilkyčiai and Šarkuva boreholes within this depression the Papartinė Formation is represented by yellow grey sands, oolitic sandstones and limestones reaching a thickness of 13 m [3]. Some sections of the formation related to local structures, have been interpreted as condensed deposits not more than 0.50.8 m of thick. Foraminiferal studies [2, 4] indicate the presence of the Lenticulina paracultrata Zone in the upper part of the Papartinė Formation. This part is composed of sandy deposits in the Papilė area. Westwards, deeper into the basin, greyish brown clays occur, referred to the Skinija Formation. Thus, the upper boundary of the Papartinė Formation is obviously diachronous (non coeval). Skinija Formation The stratotype section of the Skinija Formation is a core drill section of the Vilkyčiai-18 well in western Lithuania. Another section, documented by drilling, has been chosen as parastratotype, viz. Šarkuva (Lesnoye 50), Kurishe Nehrung in the Kaliningrad Enclave. The formation is named after the Skinija Rivulet, an eastern tributary to River Minija [8]. In the Vilkyčiai stratotype section (Fig. 3), depth interval 117.1-159.2 m, the Skinija Formation rests upon the Papartinė Formation and is overlain by the Ąžuolija Formation. The sequence seems to be stratigraphically complete and consists of homogeneous black shalls containing carbonaceous concretions. The equivalent Šarkuva section, the parastratotype, is found at a depth of 280.9-335.0 m, in Lesnoye - 50. Throughout the Lithuanian-Polish Basin the Skinija Formation consists of clays, silts and siltstones. In the lower part of the formation, referred to the Lenticulina paracultrata Zone (lower Upper Callovian), the formation is composed of greyish and brownish clays, whereas the upper part is characterized by grey to blakish clays, occassionally rich in Astarte shells. This part corresponds to the Lenticulina tumida Zone (upper Upper Callovian) [2]. The most complete section in the Skinija Formation have been found in the Žemaitija and Nivensk Depressions. Foraminiferal studies [2] indicate that the Skinija Formation should be referred to the Upper Callovian, in term of foraminiferal zones to the Lenticulina paracultrata and Lenticulina tumida Zones [2]. Ammonites are rare but may occur, L.Rotkytė (1987) has recorded Quenstedtoceras leachi (Sow.) in the upper part (Bed S1) of the Papilė outcrop No. 2 (to be found in the Jurakalnis gorge). In the Vilkyčiai-18 and Žadeikiai-27 boreholes,

Eboraciceras coronatum (Eichw.), Quenstedtoceras cf. lamberti (Sow.) and Q. henrici Douv. have been obtained [2, 9]. This is charasteristic of the Quenstedtoceras lamberti Zone. The lower boundary of the Skinija Formation is diachronous, as mentioned before, the upper one is in several sites marked by a break in the sedimentation. Above follows oolitic sandstones in the base of the Ažuolija Formation. In the Papilė area the thickness of the Skinija Formation is just about 2 m; in SW Lithuania, however, the formation may reach thickness around 55 m. In local structures of Central Lithuania and the Suvalkai area of SW Lithuania, the Skinija Formation is missing. Here, the Ąžuolija Formation rests directly uppon the Papartinė Formation. Upper Jurassic Ąžuolija Formation This Formation is named after the Ąžuolija village in Western Lithuania. A cored sequence in the Liudvigsortas (Ladushkin-55) borehole, in the Kalinigrad Enclave has been chosen as type stratum, whereas the parastratotype is a sequence of rock strata in the Ąžuolija-20 borehole. In the Liudvigsortas stratotype, 369.8 - 448.9 m interval of drilling (Fig. 4), the Ąžuolija Formation overlies the Skinija Formation and is in turn overlain by the Tarava Formation. Between the first two formations, a distinct break in the sedimentation has been observed. From a stratigraphical point of view the stratotype lacks hiatus and is composed of clayey and marly, fairly homogeneous deposits. At the base of the stratotype a sequence of oolitic clayey sandstone occurs, measuring 0.9 m in thickness. In general, the lower part of the stratotype consists of detrial, clayish limestones, 25 m in thickness, with abundant spongian spiculae, whereas the upper part (57 m thick) is composed of marls and silts interbedded. In the parastratotype, the 159.0-206.2 m interval of drilling in Üýuolija-20 silty sediments are prevailing. In the Baltic Basin the Ąžuolija Forfmation, represented by grey micaceous, carbonaceous silts, clays and marls, has a more restricted distribution than Skinija Formation. In some borehole sequences, viz. in Vilkyčiai-18, Simnas-3 and Kalvarija-2, the organogenic detritic marls and limestones are found in 5-8 m thick bioherms. Foraminiferal data indicate a Middle Oxfordian age of the reef-like structures [2]. Foraminiferal as well as ammonite finds indicate an Oxfordian age of the Ąžuolija Formation [2, 9]. It seems as if the formation is fairly complete, and the ammonite fauna has made the following biostratigraphical subdivision possible (Rotkytė 1987 ): Lower Oxfordian - Vertumniceras mariae, Cardioceras cordatum zones [=Ophthtalmidium sagittum - Lenticulina brueckmani foramininifer Zone], Middle Oxfordian - Cardioceras densiplicatum, Cardioceras tenuiserratum zones [=Ophthalmidium strumosum - Lenticulina brestica foraminifer Zone], Upper Oxfordian - Amoeboceras glosense, Amoeboceras serratum, Amoeboceras regulare, Amoeboceras rosenkrantzi zones [=Lenticulina quenstedti foraminifer Zone]. The lower boundary of the Ąžuolija Formation is characterized by the shift from black clays of the Skinija Formation the basal oolitic sandstone followed by grey marly clays. The upper boundary of the Ąžuolija Formation is less distinct; the grey marly clays gradually turn into siltstones of the Tarava Formation. The Ąžuolija Formation is the result of the most comprehensive marine transgression into the Baltic Basin. The thickness of the formation may reach 85 m. Tarava Formation As a stratotype has been chosen the 351.0-427.4 m interval of drilling in the Miulhauzenas (Gvardeiskoye-57) borehole in the Kaliningrad region. Its name originates from the little town of Tarava (present name: Vladimirov), wich is situated in the ancient Notanga Land, not far away from the Miulhauzenas village in the south-western part of the Kaliningrad Enclave [8]. In the Miulhauzenas stratotype section (Fig. 5), the Tarava Formation is composed of grey siltstones and argillites with interbeds of dark grey clay. It rests on the Ąžuolija Formation and is overlain by the Girdava Formation. The boundary between the siltstones of the Tarava Formation and the marls of the Ąžuolija Formation is gradual. The upper boundary of the Tarava Formation to the Girdava Formation is characterized by a transition

from sandy siltstone to clayey silt. In some other sections of the Tarava Formation also clayish sandstones, marls and biogenic limestones with spongian spiculae have been found [2]. Foraminiferal and ammonite faunas of the Tarava Formation indicate a Kimmeridgian age [2, 9]. A subdivision into substage and zones has been made. Strata wich have yielded rare ammonites from Amolboceras kitchini Zone indicate an Early Kimmeridgian age. In the Upper Kimmeridgian a more prolific ammonite fauna has been obtained showing the presence of the Aulacostephanus mutabilis, Aulacostephanus eudoxus and Aulacostephanus autissiodorensis Zones [9]. A prolific foraminiferal fauna has been found in the Tarava Formation on wich the Lenticulina prussica - Lenticulina kuznetsovae Zone (Lower Kimmeridgian) and the Lenticulina illustris - Lenticulina daiva Zone (Upper Kimmeridgian) are established [2]. In the Baltic Basin the Tarava Formation was formed at the beginning of a Late Jurassic regression. Girdava Formation From the same borehole as the Tarava Formation, the stratotype section of the Girdava Formation has been chosen, including the 328.0-351.0 m interval of drilling. The Girdava Formation forms the uppermost part of the Jurassic succession in the Baltic region. Its name is given from a little town Girdava (at present officially named Zheleznodorozhniy), located to the ancient Barta Land in the southern part of Kaliningrad Enclave [8, 11]. The stratotype (Fig. 5) consists of 23 m of grey marls, clays and silt, succeeding the Tarava Formation. The upper boundary of the formation is erosional in the type section. With a great stratigraphical gap the Girdava Formation is overlain by greenish glauconitic sands of Albian age (Jiesia Formation), thus indicating that the major part of the Lower Cretaceous is missing [2]. Based on foraminiferal analysis, e. g. by finds of Marginulina striatocostata, the Girdava Formation is referred to Lower Volgian [2]. Ammonites are few in the Girdava Formation. To be mentioned are Pectinatites boidini and Pavlovia hypophantica indicating the presence of Lower and Middle Volgian [2, 9]. According to the Jurassic chronostratigraphy, the equivalent of the Lower and Middle Volgian, as the regional stage of the East European Platform, could be the Lower Tithonian. Consequently, the Girdava Formation is attributed to this substage [7]. References

1. Grigelis, A. (Ed.). 1982: Geology of the Soviet Baltic Republics. 340 pp. 2. Grigelis, A. 1985: Jurassic zonal stratigraphy of the Baltic area according to Foraminifers. 131 pp. 3. Grigelis, A. 1993: Lithostratigraphy and geological development of the Jurassic - Palaeogene basins of Lithuania. Abstracts of the Second Baltic Stratigraphical Conference, May 9-14, 1993. Vilnius. P.19. 4. Grigelis, A. 1991: Papilė Jurassic outcrops. In: Geological excursion Guidebook. Vilnius. P. 67-70. 5. Grigelis, A. , Ignatavičius, V. , Saladžius, V. 1971: Lietuvos geologinių ir hidrogeologinių žemėlapių stratigrafinės schemos ir legenda / Stratigraphical charts and legend of geological and hydrogeological maps of Lithuania. Lietuvos geologijos institutas, Vilnius. 225 pp. 6. Grigelis, A., Kadūnas, V. (compilers). 1994: Lietuvos geologija / Geology of Lithuania. Vilnius: Science and Encyclopaedia. 447 pp. 7. Grigelis, A., Suveizdis, P.1993: Catalogue of Permian-Palaeogene stratotypes of the East Baltic area. Vilnius. 28 pp. 8. Pėteraitis, V., 1992: Mažoji Lietuva ir Tvanksta / Lithuania Minor and Tvanksta. Vilnius: Science and Encyclopaedia. 456 pp. 9. Rotkytė, L. 1987: Upper Jurassic ammonites and zonal stratigraphy of the Baltic area. Vilnius: Mokslas. 119 pp. 10. Stirpeika, A. 1968: New data on the Late Permian and Early Mesozoic continental deposits of Pajavonys Kybartai area (South-West Lithuania). Geologijos institutas, Vilnius. P.13-15.

11. Šilas, V., Sambora, H. 1990: Mažosios Lietuvos kultūros pėdsakai Kaliningrado srityje / Tracks of the Lithuania Minor culture in Kaliningrad District. Vilnius: Mintis. 427 pp. 12. Šimkevičius, P. 1973: X-ray analysis of clay fraction of the Lower - Upper (Lower Callovian) Jurassic and adjacent Triassic and Middle Callovian deposits of the South Baltic region. Lietuvos aukštųjų mokyklų darbai. Geologija, geografija, 10. P. 263-267.

Algimantas Grigelis Lithuanian Institute of Geology, Ševčenkos 13, 2600 Vilnius / Lithuania Received 28March, 1994