Introduction To Geochemistry

Geochemistry is the science that uses the tools and principles of chemistry to explain the mechanisms behind major geological systems such as the Earth's crust and its oceans.

Some subsets of geochemistry are:

  1. Isotope geochemistry involves the determination of the relative and absolute concentrations of the elements and their isotopes in the earth and on earth's surface.
  2. Examination of the distribution and movements of elements in different parts of the earth (crust, mantle, hydrosphere etc.) and in minerals with the goal to determine the underlying system of distribution and movement.
  3. Cosmochemistry includes the analysis of the distribution of elements and their isotopes in the cosmos.
  4. Biogeochemistry is the field of study focusing on the effect of life on the chemistry of the earth.
  5. Organic geochemistry involves the study of the role of processes and compounds that are derived from living or once-living organisms.
  6. Aqueous geochemistry studies the role of various elements in watersheds, including copper, sulfur, mercury, and how elemental fluxes are exchanged through atmospheric-terrestrial-aquatic interactions.
  7. Regional, environmental and exploration geochemistry includes applications to environmental, hydrological and mineral exploration studies.

Petroleum originates from a small fraction of the organic matter deposited in sedimentary environments. Out of the average “source rock”, 99% is mineral matter and 1% organic matter. Of this organic matter, 90% is kerogen and 10% bitumens. This organic matter is usually a combination of marine- and terrestrially-derived organic (plant) and zooplankton (animal), which constitutes more than 95% of the life in the oceans. Terrestrial organisms are mainly wind-blown spores and pollen, along with some woody debris from rivers and swamps.

All living matter is composed of four main constituents, lipids, proteins, carbohydrates and lignins.

Lipids These cover all organism-produced substances that are practically insoluble in water. This encompasses fatty substances such as vegetable oil, waxes and animal fats. Lipids are structurally very similar to the non-aromatic NSO compounds. Lipids are one of the main sources for petroleum.

Proteins These are high-order polymers made from individual amino acids, and account for most of the nitrogen and sulfur compounds in organisms. Therefore, most nitrogen and sulfur containing compounds found in petroleum are derived from proteins.

This is a collective name for individual sugars and their polymers. The name is derived from the formula Cn(H2O)n, which suggests hydrated carbons. Carbohydrates are not important sources for petroleum.

Lignins These are widespread in plants and are characterized by their aromatic (phenolic) structures. They are high molecular weight structures (polyphenols). The aromatic content of petroleum is derived from this group.

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