THERMAL ALTERATION OF SEDIMENTARY ORGANIC-MATTER BY A BASALT INTRUSIVE (KIMMERIDGIAN SHALES, MILNE LAND, EAST GREENLAND)

The heat effect from a basalt dyke is found to alter the composition of saturated and aromatic hydrocarbons in the surrounding immature shales up to a distance of about half the thickness of the dyke. Severe loss of organic matter is observed in the contact zone. The indigenous, thermally unaffected source material is dominated by isoprenoids and polycyclic alkanes among the saturated hydrocarbons. n-Alkanes are very minor contributors. Maturation of the immature kerogen by heat from the dyke or during laboratory pyrolysis releases considerable amounts of n-alkanes. Increasing thermal alteration is accompanied by diminishing abundance of biogenic polycyclic alkanes. © 1979.