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.