Changes

==Oxidation reduction zones==

==Oxidation reduction zones==

Bacteria and other microbes play a profound role in the oxidation of migrating hydrocarbons. Their activities are directly or indirectly responsible for many of the diverse surface manifestations of petroleum seepage. These activities, coupled with long-term migration of hydrocarbons, lead to the development of near-surface oxidation-reduction zones that favor the formation of this variety of hydrocarbon-induced chemical and mineralogical changes. This seep-induced alteration is highly complex, and its varied surface expressions have led to the development of an equally varied number of geochemical exploration techniques. Some detect hydrocarbons directly in surface and seafloor samples, others detect seep-related microbial activity, and still others measure the secondary effects of hydrocarbon-induced alteration.<ref name=ch18r39>Schumacher, D., 1996, [http://archives.datapages.com/data/specpubs/memoir66/06/0071.htm Hydrocarbon-induced alteration of soils and sediments], in Schumacher, D., Abrams, M., A., eds., Hydrocarbon Migration and Its Near-Surface Expression: [http://store.aapg.org/detail.aspx?id=75 AAPG Memoir 66], p. 71–89.</ref><ref name=ch18r37>Saunders, D., F., Burson, K., R., Brown, J., J., Thompson, C., K., 1999, [http://archives.datapages.com/data/bulletns/1999/01jan/0170/0170.htm Model for hydrocarbon microseepage and related near-surface alterations]: AAPG Bulletin, vol. 83, p. 170–185.</ref> [[:file:surface-geochemical-exploration-for-petroleum_fig18-3.png|Figure 1]] shows a generalized model of hydrocarbon microseepage and hydrocarbon-induced effects on soils and sediments.

Bacteria and other microbes play a profound role in the oxidation of migrating hydrocarbons. Their activities are directly or indirectly responsible for many of the diverse surface manifestations of petroleum seepage. These activities, coupled with long-term migration of hydrocarbons, lead to the development of near-surface oxidation-reduction zones that favor the formation of this variety of hydrocarbon-induced chemical and mineralogical changes. This seep-induced alteration is highly complex, and its varied surface expressions have led to the development of an equally varied number of geochemical exploration techniques. Some detect hydrocarbons directly in surface and seafloor samples, others detect seep-related microbial activity, and still others measure the secondary effects of hydrocarbon-induced alteration.<ref name=ch18r39>Schumacher, D., 1996, [http://archives.datapages.com/data/specpubs/memoir66/06/0071.htm Hydrocarbon-induced alteration of soils and sediments], in Schumacher, D., Abrams, M., A., eds., Hydrocarbon Migration and Its Near-Surface Expression: [http://store.aapg.org/detail.aspx?id=75 AAPG Memoir 66], p. 71–89.</ref><ref name=ch18r37>Saunders, D., F., Burson, K., R., Brown, J., J., Thompson, C., K., 1999, [http://archives.datapages.com/data/bulletns/1999/01jan/0170/0170.htm Model for hydrocarbon microseepage and related near-surface alterations]: AAPG Bulletin, vol. 83, p. 170–185.</ref> [[:file:surface-geochemical-exploration-for-petroleum_fig18-3.png|Figure 1]] shows a generalized model of hydrocarbon microseepage and hydrocarbon-induced effects on soils and sediments.