O badaniach izotopowych diagenetycznego illitu z piaskowców czerwonego spągowca Wielkopolski i Pomorza Zachodniego

Abstract

Isotopic investigations of diagenetic illite of Rotliegend sandstones from the Wielkopolska and Western Pomerania regions.A b s t r a c t. Diagenetic illite tends to crystallize most often as fibres and it forms net-like textures reducing filtration abilities of sandstones. Rocks containing this type of illite show a very low permeability or may even be impermeable. K-Ar datings of crystallization of these fibres define the time when permeability was reduced and duration of the post-depositional period when the deposits were permeable for pore fluids, including gaseous and liquid hydrocarbons. Clay fractions <0.2 μm and <0.3 μm were isolated from 12 samples of the Rotliegend sandstones fromWestern Poland in order to define the K-Ar age of illite. The results of investigations show that this age from the fraction <0.2 μm falls between 187.1 and 113.6 Ma (tab. 1), that covers a long period since early Jurassic to late Cretaceous. The determination of δ18O in illite (15.1–15.9‰SMOW), performed in East Kilbride laboratory, and calculations of hypothetic temperatures of illite crystallization (125–173°C) show that it crystallized from pore waters of marine origin and with δ18O values ranging from 4.3 to 7.5‰SMOW, which probably infiltrated from evaporitic Zechstein deposits.