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Some 36 oilfields, all producing from Middle Cambrian (Deimena Group) sandstones, are located in the central Baltic Basin in an area covering onshore Lithuania and Kaliningrad (Russia) and the adjacent offshore. This paper presents new data on the composition of crude oils from fields in this area and reviews the reservoir properties of the Deimena Group sandstones. Twenty-one crude oil samples from fields in Lithuania and Kaliningrad were analysed by standard techniques including GC and GC-MS. The oils had densities of 790.5 to 870.0 kg/m3, and had low asphaltene ( 200°C) ranged from 12–34%. The saturated hydrocarbon content was 35.3 to 77.8%, and the ratio of saturate to aromatic hydrocarbons was 2.1–5.2, indicating long-distance migration or high thermal maturities. GC analyses of saturate fractions indicated a composition dominated by n-alkanes with a maximum at C13–C15 and reduced abundance in the C20–C35 range. The analysed crude oil samples are characterized by relatively low concentrations of steranes and triterpanes. Biomarker data indicated an algal origin for the precursor organic matter and a clastic-dominated source rock. Sterane isomerization ratios imply that the oils are in general relatively mature. Exceptions are samples from the Juzno Olempijskoye and Deiminskoye fields, Kaliningrad, which were early mature. Oil from well Gondinga-l (Lithuania) was lightly fractionally evaporated and has a relatively higher density, higher viscosity, higher asphaltene content and lower content of saturated fractions. Stable carbon isotope ratios of crude oils and saturated and aromatic fractions were analysed. Whole oils showed little carbon isotope variation, but there were significant differences in δ13C ratios for saturated and aromatic fractions. The geochemical data show differences in oil sourcing and indicate the possible existence of different kitchen areas in the Kaliningrad region. Vertical and lateral variations in Deimena Group reservoir properties are controlled by variations in quartz cementation. In fields in western Lithuania, sandstone porosity ranges from 0.7 to 20% and permeability from 20 mD to 300 mD; in fields onshore Kaliningrad, porosity is up to 34% and gas permeability up to 4.8 D. Wide variations in porosity and permeability occur at a field scale.

Petroleum potential is associated with Silurian reefal and carbonate build-ups in southern and central Lithuania where non-structural traps (reef-associated, lithologic-stratigraphic and combined) have been identified in intervals of Late Wenlock, Late Ludlow and Early Pridoli ages. Three oilfields (Kudirka, Siaures Bliudziai and Lapgiriai) have so far been discovered in this area. In addition, oil flows have been reported at wells in the Bebirva, Saukenai, Bliudziai and Pavasaris accumulations. Reefal build-ups and patch reefs dated as belonging to the Minija Regional Stage of the Early Pridoli, up to 88 m thick, are considered to be the most prospective for hydrocarbons, and all the discoveries so far made occur in this stratigraphic interval. New geochemical data indicate the presence of excellent Llandovery, Wenlock and Ludlow source rocks, composed of dark grey and black clayey marlstones and shales. Recent studies of the composition and maturation of Silurian source rocks indicate the predominance of sapropelic organic matter, present in higher amounts than in Cambrian and Ordovician source rocks. The maturity of Silurian source rocks increases from immature in eastern Lithuania to early oil-phase in the centre and north, to peak oil generation in the west. Geochemical analyses of Silurian crude oils show that they are un- or only weakly biodegraded, in spite of their early emplacement (in the Palaeozoic) and the relatively low reservoir temperatures (40-50°C). The results of these geochemical studies of the Silurian source rocks and oils, incorporated with available geological data, were used to predict the hydrocarbon potential of the Silurian succession in Lithuania. The succession is estimated to have generated as much as 5.8 B tons of hydrocarbons. Previous studies indicate that 100 million tons may have accumulated in patch reefs assigned to the Minija Regional Stage. Estimated oil in-place at the known oilfields totals about 1.77 million tons.

The late Mid Devonian Eday Marl Formation from the Orcadian Basin, Scotland is a terrestrial equivalent of the marine Devonian Taghanic Crisis. The Eday Marl from Orkney contains a high-resolution archive of climatic change controlled by the relative strength of the seasonal insolation. This includes several distinct and discrete episodes of basin flooding as demonstrated by the deposition of lacustrine laminites, bedded evaporites, marginal sheet flood sands and marine influenced bioturbated sheet sands. These flooding events are intercalated with intense and sustained episodes of aridity indicating that insolation was relatively weak and the monsoon climate was ineffective at drawing in seasonal rainfall. Recognition of these basin flooding events has enabled the definition of three new units (the Wha Taing, Roeberry and Berstane members). The Eday Marl Formation can be correlated offshore and also recognised within marginal facies as an aeolian intercalation. An environmental, hydrological and climatic interpretation is given for the different events recognised in the Eday Marl. This sequence of events, when combined with the palynological age dates, enables a detailed correlation to be made with the marine Tully Formation of New York State. This suggests that regressions forced by climatic aridity are significant for understanding the deposition of the shallow water carbonates of the Tully Formation, in what is otherwise, a clastic depositional system. Comparison with the pelagic marine record shows that the latter, as yet, gives only limited resolution of the Taghanic Crisis. Recognising the Taghanic as a rapid alternation of cool arid and relatively hotter pluvial events provides a unifying explanation for the associated collapse in the terrestrial vegetation and the parallel faunal changes in the marine realm.

M. WILDE-PIORKO1, W.H. GEISSLER2, J. PLOMEROVA3, M. GRAD1, V. BABUSKA3, E. BRUCKL4, J. CYZIENE5, W. CZUBA6, R. ENGLAND7, E. GACZYŃSKI6, R. GAZDOVA13, S. GREGERSEN8, A. GUTERCH6, W. HANKA9, E. HEGEDŰS10, B. HEUER9, P. JEDLICKA3, J. LAZAUSKIENE5,17, G. RANDY KELLER11, R. KIND9, K. KLINGE12, P. KOLINSKY13, K. KOMMINAHO14, E. KOZLOVSKAYA15, F. KRUGER16, T. LARSEN8, M. MAJDAŃSKI6, J. MALEK13, G. MOTUZA17, O. NOVOTNÝ13, R. PIETRASIAK6, TH. PLENEFISCH12, B. RŮŽEK3, S. SLIAUPA5, P. ŚRODA6, M. ŚWIECZAK6, T. TIIRA14, P. VOSS8 AND P. WIEJACZ6

P061 GENETIC FEATURES OF ANHYDRITE DOMES WESTERN LITHUANIA 1 S. SLIAUPA 1 R. SLIAUPIENE 1 J. LAZAUSKIENE 2 I. GROTEK 3 V. SIDOROV 2 and L. KORABLIOVA 2 1 Institute of Geology Sevcenkos 13 LT-2600 Vilnius Lithuania 2 Geological Survey of Lithuania 3 Institute of Geology Warszawa Summary Anhydrites dominate the Zechstein succession of the southern half of the western Lithuania which is one of most prospective areas for oil exploration related to underlying Cambrian reservoir. The top of the anhydrite layer is highly undulating while the base is nearly horizontal. It makes seismic interpretation difficult to map small-scale Cambrian