Simulated maturation experiments inv-olving sediments of different source environments give quantitative and kinetic information about generation of petroleum and natural gas. Starting material, temperature, and heating time all play critical roles in determining quantity and type of reaction products. Samples from recent peaty lacustrine and algal mat lagoonal deposits were heated separately in closed systems for 1 to 15,000 hours at temperatures ranging from 35 to 550°C. Reaction products were monitored for both quantity and isotope data. Low molecular weight volatile compounds (C₁-C₅₊, H₂, CO₂) and petroleum-range (C₁₅₊) hydrocarbons were products.

Petroleum product formation occurs in three stages. A premature stage is characterized by production of volatile hydrocarbons and carbon dioxide but little change in C₁₅₊ components. The volatile products are a result of kerogen and humic rearrangements and display marked kinetic isotope effects. In the mature stage, the original biologically related C₁₅₊ hydrocarbon fraction is diluted by catagenetically derived products. Methane formed in this stage is derived from C₁₅₊ components and is characterized by stable carbon isotopes 15 ppt lighter than the starting material. A postmature stage displays C₂-C₅₊ and CO₂ reduction, forming isotopically heavy methane.

Temperature affected the rate of product formation but not the kinetic order governing the reaction or the ultimate production potential for petroleum-like hydrocarbons. Organic source affected both rate of hydrocarbon formation and specific intermediary products of thermal alteration. Peaty organic matter matures more quickly than algal material given the same thermal stress.

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