Origin of prist-1-ene and prist-2-ene in kerogen pyrolysates

The principal isoprenoid hydrocarbons in flash pyrolysates from immature ke rogens are prist-1-ene and, to a lesser extent, prist-2-ene. The precise or igin of these compounds is still a matter of debate. Chemical degradation e xperiments performed on a sulfur-rich kerogen in this study show that at le ast two precursors can generate pristenes during pyrolysis of sulfur-rich k erogens: ether-bound precursors, probably tocopherols, and a sulfur-bound p recursor. From pyrolysis experiments performed on mixtures of isolated kero gens with different clay minerals, it is concluded that prist-2-ene is like ly formed by the double-bond isomerization of prist-1-ene. This isomerizati on of prist-1-ene into prist-2-ene depends on the amount of protons availab le for the formation of the intermediate carbonium ion. These protons can b e derived from acidified aluminosilicates (e.g, the clay minerals montmoril lonite or kaolinite) in the rock or from inorganic acids (e.g. HI, HCl). Th e degree of isomerization depends on the amount of protons available relati ve to the total organic carbon content. (C) 2001 Elsevier Science B.V. All rights reserved.