DOJRZAŁOŚĆ TERMICZNA UTWORÓW DEWONU, KARBONU I TRIASU MASYWU MAŁOPOLSKIEGO NA PODSTAWIE WSKAŹNIKA CAI (COLOUR ALTERATION INDEX)

Abstract

THERMAL MATURITY OF DEVONIAN , CARBONI FEROUS AND TRIASSIC ROCKS IN THE CENTRAL PART OF THE MAŁOPOLSKA MASSIF FROM CONODONT COLOUR ALTERATION INDEXAbstract. A paleothermal study of Devonian, Carboniferous and Triassic carbonate rocks was carried out in eight boreholes from the central part of the Małopolska Massif by using data on thermal alteration of organic matter contained in conodonts. The maturity of organic matter expressed as the CAI (Colour Alteration Index) values was used to calculate palaeotemperatures that affected the conodont-bearing rocks. In the Węgrzynów IG 1 borehole, the CAI values for the Upper Givetian, Frasnian, Famennian and Lower Carboniferous rocks range from 3 (Givetian) to 2 (Lower Carboniferous). It suggests heating of rocks (at temperatures from 60 to 110°C) in the area of high palaeogeothermal gradient, close to the Variscan front. In the Upper Devonian sequence of the Pągów IG 1 borehole, the CAI value of 4.5 proves heating of rock at a temperature exceeding 230°C as a result of higher heat flow near a fault zone. The low CAI values (1‒1.5) of Triassic rocks provide the evidence for heating of rocks in the range of 50 to 90°C. The relatively low maturity of organic matter in the Triassic rocks indicates that the Devonian and Carboniferous sediments must have reached their thermal maturity in the Late Carboniferous prior to the Variscan orogeny. The signs of crude oil and natural gas observed in the Devonian and Carboniferous rocks in the central part of the Małopolska Massif attest their potential for hydrocarbon exploration.