Hydrocarbon and aqueous inclusions in minerals: a review of analyses and interpretations for Paleozoic rocks in Poland

Two decades of microthermometric studies of fluid inclusions within cements of Paleozoic sedimentary rocks in Poland are reviewed. The inclusions contain palaeofluids of variable composition: aqueous, brine, and hydrocarbon. They may be primary and/or secondary in origin and have one, two or more phases. They display visual fluorescence in blue, sometimes yellow to red (oil) or dull blue (one phase, methane) colours, or do not fluoresce at all. Based on the fluorescence characteristics in ultraviolet light, the inclusions' hydrocarbons infill character may be estimated. The homogenization temperatures, which correspond to the minimum estimate of the trapping temperatures in the minerals, show variability in respect to the geological history of the area studied. They point to different geological stages in relation to the basin's burial evolution. Microthermometric analyses enable wider interpretation due to the combination of studies of both hydrocarbon and aqueous inclusions. The presence of oil and/or gas in inclusions is proof of the occurrence and/or migration of oil and gas in the rocks of a region.