1908 Amer. Jrnl. Sci. 176 45 In a fully represented petrogenic cycle at a batholithic area..the oldest intrusion should be a rock of gabbroid (basaltic) composition.

1947 A. Knopf Pirsson's Rocks & Rock Minerals (ed. 3) vi. 144 A period in which a genetically related series of igneous rocks was formed is called a petrogenic epoch, and as this concept is more definite than ‘petrographic province’, it is supplanting the older idea.

2000 Volcanol. & Seismol. 21 641 The chemical and mineralogical compositions of the rocks had been influenced by various petrogenic processes: fractionation, magma mixing, and the addition of potassium by transmagmatic fluids.

1976 B. B. Bernard et al. in Earth & Planetary Sci. Lett. 31 48/1 The gas can originate from the microbial decomposition of organic matter in anoxic environments at temperatures below 50°C (biogenic gas), and it can be produced by thermocatalytic processes acting on organic matter at higher temperatures (petrogenic gas).

1985 Marine Environmental Res. 15 165 Close to the Beryl platform, where diesel-washed drill cuttings have been dumped, there was an accumulation of petrogenic hydrocarbons in the sediment.

1989 Nature 23 Feb. 724/1 Both markers decreased more rapidly with depth relative to another anthropogenic indicator, the unresolved complex mixture of hydrocarbons (UCM) attributable to petrogenic sources.

2001 Environmental Sci. & Technol. 35 471 The dominant sources of the petrogenic hydrocarbon background..are eroding Tertiary shales and residues of natural oil seepage.