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1 Pol ish Geo log i cal In sti tute -Na tional Geo log i cal In sti tute, Rakowiecka 4, 00-975 Warszawa, Po land Jarmo³owicz-Szulc, K., Koz³owska, A., 2016. Tem per a ture and iso to pic re la tions in car bon ate min er als in the Mid dle Ju rassic si der it ic rocks of cen tral and south ern Po land. Geo log i cal Quar terly, 60 (4): 881-892, doi: 10.7306/gq.1323The pres ent study as sesses the physico-chem i cal char ac ter of the flu ids re spon si ble for the gen e sis of car bon ate min er als in the Mid dle Ju ras sic si der it ic rocks at the north east ern mar gin of the Holy Cross Mts. and in the Czêstochowa re gion. These rocks oc cur at pres ent at depths be tween 30 and 600 m. Fluid in clu sion and iso to pic anal y ses have been per formed in the car bon ate min er als from si der it ic sand stones, clayey siderites and si der it ic coquinas. Sid er ite is the main car bon ate min eral of the si der it ic rocks. Cal cite and an ker ite are also pres ent. The sid er ite is rep re sented by two va ri et ies, Mg-rich sid er ite (sideroplesite, less com monly -pistomesite) and sid er ite. Two gen er a tions of sid er ite have been dis tin guished -an early and a late one. The early sid er ite was formed at tem per a tures of about 20°C in the zone of mi cro bi o log i cal methanogenesis from ma rine wa ters with some in flu ence of me te oric wa ters (d 18 O from -7.84 to -1.92‰ VSMOW). The late sid er ite crys tallized at tem per a tures of about 62-110°C from pore wa ters en riched in 18 O (d 18 O >0‰ VSMOW) as com pared with the iso topic com po si tion of the wa ters re spon si ble for the early sid er ite gen er a tion. The con ducted fluid in clu sion anal y ses point to for ma tion of the ce ments from com plex flu ids of brine and car bon di ox ide char ac ter, with den si ties slightly ex ceed ing 1 g/cm 3 and sa lini ties vary ing from 10.5 to 16.9 wt.% NaCl eq. and from 6.4 to 14.0 wt.% NaCl eq. in the Holy Cross Mts. and in the Czêstochowa re gion, re spec tively. The ho mog e ni za tion tem per a tures lie in the in ter vals of 62-110°C and 60-97°C, re spectively and rep re sent el e vated val ues com pared with data from the Pol ish Low lands. Apart from burial, other heat sources must have been im por tant for the lithogenesis of the Mid dle Ju ras sic de pos its.Key words: fluid in clu sions, iso topes, car bon ate min er als, si der it ic rocks, Mid dle Ju ras sic.

Characteristics and results of microthermometric studies of fluid inclusions which occur in the cements of sedimentary rocks of various ages (from Cambrian through Permian to Paleogene) and filled with hydrocarbons (HCFI) are presented. The inclusions are primary and secondary in origin. They display one or two phases and fluorescence in white-blue (oil) or dull blue (methane) colours, sometimes yellow or red. Based on the fluorescence colour in the ultraviolet light a character of hydrocarbons that fill these inclusions and migrate in the rocks of the region can be estimated. The inclusions are filled with palaeofluids of different compositions. The homogenization temperatures, which correspond to the minimum estimation of the trapping temperatures in minerals, show variability with respect to the geological history of the study area. The hydrocarbon inclusions are often accompanied by brine inclusions. Wider interpretation of all microthermometric analyses was enabled due to the combination of studies on hydrocarbon and aqueous inclusions. The presence of hydrocarbons in inclusions is a proof of their occurrence and/or migration in the rocks of the regions studied.

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Fluid inclusions were studied in rocks from different wells from the Barnówko–Mostno–Buszewo (BMB), the largest oil field in Poland and from the Lubiatów field. Sampling was performed at depths between about 3120–3220 m and 3221–3256 m, respectively. Different minerals (dolomite, calcite, anhydrite, quartz) reveal the presence of aqueous (AQFI) and hydrocarbon (HCFI) inclusions, the differentiation of which was checked by UV fluorescence and microthermometry. Inclusions occur in different abundances and are of variable character. The microthermometric studies of fluid inclusions resulted in the determination of temperatures of eutectic melting, ice melting, and homogenization. Based on the results obtained, three types of inclusions have been found. Two-phase non-fluorescent inclusions (AQFI) contain brines of differentiated salinity (from about 6 to 10 and from about 17 to 22 wt% NaCl equivalent). Two-phase fluorescent inclusions (HCFI 1) contain light mature oil of paraffin character. The oil is characterized by API gravity of about 41–42 degrees. Small one-phase non-fluorescent inclusions (HCFI 2) that homogenize in deep freezing contain methane with admixtures. The abundance of inclusions varies, depending on the mineral or well. They have been discussed in the context of hydrocarbon migration and accumulation.