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During the Eocene-Oligocene transition (EOT), a major palaeoenvironmental change took place in the Paratethys Sea of central Eurasia. Restricted connectivity and increased stratification resulted in wide-spread deposition of organic-rich sediments which nowadays make up important hydrocarbon source rocks. The North Alpine Foreland Basin (NAFB) was a major gateway of the Paratethys Sea to the open ocean during the Eocene, but the age of closure of this gateway is still uncertain. The Ammer section in southern Germany documents the shallowing of this connection and subsequent disappearance of marine environments in the NAFB, as reflected in its sedimentary succession of turbidites to marls (Deutenhausen to Tonmergel beds), via coastal sediments (Baustein beds) to continental conglomerates (Weißach beds). Here, we apply organic geochemistry and date the lithological transitions in the Ammer section using integrated stratigraphy, including magnetostratigraphy and biostratigraphy. Nannoplankton and dinocyst results can be reconciled when dinoflagellate species Wetzeliella symmetrica is of late Eocene age. Our magnetostratigraphy then records C13r-C13n-C12r and allows calculation of sediment accumulation rates and estimation of ages of lithological transitions. We show that the shallowing from turbiditic slope deposits (Deutenhausen beds) to shelf sediments (Tonmergel beds) coincides with the Eocene-Oligocene boundary at 33.9 Ma. The transition to continental sediments is dated at ca. 33.15 Ma, significantly older than suggested by previous studies. We conclude that the transition from marine to continental sediments drastically reduced the marine connection through the western part of the NAFB and influenced the oxygen conditions of the Paratethys Sea.

Hydrocarbons in ore minerals of the deposit and in authigenic quartzes of the Lienzer Dolomiten were characterised by their organic-chemical composition. Microthermometric data and the molecular composition of the hydrocarbons indicate a hyperthermal event of migrating condensate-like hydrocarbons in the Middle Cretaceous to Early Tertiary. The hydrocarbons possibly played an important role as reducing agents in second stage sulphide precipitation., Hydrocarbons in ore minerals of the deposit and in authigenic quartzes of the Lienzer Dolomiten were characterised by their organic-chemical composition. Microthermometric data and the molecular composition of the hydrocarbons indicate a hyperthermal event of migrating condensate-like hydrocarbons in the Middle Cretaceous to Early Tertiary. The hydrocarbons possibly played an important role as reducing agents in second stage sulphide precipitation.

The Carboniferous basin hosts about 130 seams, each with a thickness of more than 0.45 m, containing proven reserves of around 60 000 000 000 tonnes. Seams currently mined are 0.6-2.5 m thick and 2001 production was 83 400 000 t in the Ukrainian and 6 500 000 t in the Russian part of the basin. Ash yields and sulphur contents are usually very high, at 12-18% ash and 2.5-3.5% S, but vary significantly according to peat facies. The mines are among the most gassy in the world, average methane content of the coal being 14.7 m3/t but many seams having a significantly higher content. This high content presents a severe mine safety problem but also represents a high potential for coalbed methane projects. Coal and gas outbursts constitute another major hazard that accounts for many fatalities., The Carboniferous basin hosts about 130 seams, each with a thickness of more than 0.45 m, containing proven reserves of around 60 000 000 000 tonnes. Seams currently mined are 0.6-2.5 m thick and 2001 production was 83 400 000 t in the Ukrainian and 6 500 000 t in the Russian part of the basin. Ash yields and sulphur contents are usually very high, at 12-18% ash and 2.5-3.5% S, but vary significantly according to peat facies. The mines are among the most gassy in the world, average methane content of the coal being 14.7 m3/t but many seams having a significantly higher content. This high content presents a severe mine safety problem but also represents a high potential for coalbed methane projects. Coal and gas outbursts constitute another major hazard that accounts for many fatalities.

Two different hydrocarbon systems have been recognised in the basin, a Mesozoic/lower Oligocene oil and thermal gas system and an Oligocene/Miocene biogenic gas system. Compilation and analysis of hydrocarbon industry data shows that the distribution of gas deposits is a result of complex processes which have affected gas generation, migration and alteration. Relatively dry gas in Mesozoic and Eocene reservoirs in the northeast part of the area originated at least partly from anoxic biodegradation of oil. Bacterial gas in reservoir rocks with an Oligocene/Miocene age contains significant contributions from thermogenic gas, and locally liquid hydrocarbons, indicating migration of thermogenic hydrocarbons into shallower horizons and mixing of the two hydrocarbon systems. A number of questions remain in relation to the origin of the gas, and future research will include isotopic investigations of methane, higher hydrocarbons and CO2, mineralogical, geochemical and isotopic studies of pore space cements and studies of the salinity, geochemistry and isotopic characteristics of reservoir fluids., Two different hydrocarbon systems have been recognised in the basin, a Mesozoic/lower Oligocene oil and thermal gas system and an Oligocene/Miocene biogenic gas system. Compilation and analysis of hydrocarbon industry data shows that the distribution of gas deposits is a result of complex processes which have affected gas generation, migration and alteration. Relatively dry gas in Mesozoic and Eocene reservoirs in the northeast part of the area originated at least partly from anoxic biodegradation of oil. Bacterial gas in reservoir rocks with an Oligocene/Miocene age contains significant contributions from thermogenic gas, and locally liquid hydrocarbons, indicating migration of thermogenic hydrocarbons into shallower horizons and mixing of the two hydrocarbon systems. A number of questions remain in relation to the origin of the gas, and future research will include isotopic investigations of methane, higher hydrocarbons and CO2, mineralogical, geochemical and isotopic studies of pore space cements and studies of the salinity, geochemistry and isotopic characteristics of reservoir fluids.

A small area of high coalification in Tertiary sediments between the Penninic windows of Rechnitz and Bernstein indicates a very localised heat source. The fluid inclusion studies show that the mineralisation was precipitated from aqueous solutions of low salinity at minimum temperatures of 210 degrees C. As the deposit was formed at shallow depth pressures were less than 1 kbar. This limits maximum temperatures to 280 degrees C. These results confirm earlier epithermal models of the deposit related to Miocene andesitic magmatism in the region., A small area of high coalification in Tertiary sediments between the Penninic windows of Rechnitz and Bernstein indicates a very localised heat source. The fluid inclusion studies show that the mineralisation was precipitated from aqueous solutions of low salinity at minimum temperatures of 210 degrees C. As the deposit was formed at shallow depth pressures were less than 1 kbar. This limits maximum temperatures to 280 degrees C. These results confirm earlier epithermal models of the deposit related to Miocene andesitic magmatism in the region.