Diagenetic history of Lower Palaeozoic sediments in Pomerania (northern Poland), traced across the Teisseyre-Tornquist tectonic zone using mixed-layer illite-smectite

Mixed-layer illite-smectite From Lower Palaeozoic sedimentary rocks, on bot h sides of the Teisseyre-Tornquist tectonic zone (TTZ) in northern Poland, was studied by X-ray diffreaction and dated by K-Ar means. The percentage of smectite layers in illite-smectite (%S) indicates maximum palaeotemperatures of 125-135 degreesC at the surface of Lower Palaeozoic rocks on the craton (NE of TTZ), and 110 to less than or equal to 180 degre esC in different tectonic blocks to the SW of TTZ (area of Caledonian conso lidation). The vertical changes in the %S indicate that the maximum palaeot emperatures were reached before Permian time on the craton. and before Jura ssic, Triassic, Permian or Carboniferous periods but after the beginning of Devonian time in the Caledonian tons. The K-Ar ages of bentonites indicate that the maximum palaeotemperatures were reached by 370-390 Ma or even sli ghtly earlier (Middle-late Devonian). A maximum of 3-6 km of Silurian-Devon ian cover on the craton and in the TTZ is suggested by the data.