PETROLEUM
mixing with sediments and being buried under anoxic conditions. As further layers
settled to the sea or lake bed, intense heat and pressure built up in the lower regions.
This process caused the organic matter to change, first into a waxy material known as
kerogen, which is found in various oil shales around the world, and then with more heat
into liquid and gaseous hydrocarbons via a process known as catagenesis. Formation of
petroleum occurs from hydrocarbon pyrolysis in a variety of mainly endothermic
reactions at high temperature and/or pressure.
There were certain warm nutrient-rich environments such as the Gulf of Mexico and the
ancient Tethys Sea where the large amounts of organic material falling to the ocean floor
exceeded the rate at which it could decompose. This resulted in large masses of organic
material being buried under subsequent deposits such as shale formed from mud. This
massive organic deposit later became heated and transformed under pressure into oil.
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