Geoscience Reference
In-Depth Information
8
Biogeochemistry
The purpose of this Chapter is a short review of how biological processes affect the
geochemical pathways that would prevail in the absence of life and how they con-
tribute to the production of specific components that can occasionally form the bulk
of some biological material such as oil. Expertise in biogeochemistry requires a strong
background in biology and biochemistry and also some understanding of how biomass
interacts as a whole with the mineral world. Background is well beyond the scope
of the present book and we will hence try to restrict ourselves to the simplest of
concepts.
8.1 The geological record
Oxidized rocks, limestones, cherts, and phosphates contain the biological materials with
the most spectacular contribution to the geological record. Modern limestones are largely
formed by the accumulation of carbonate tests of foraminifera and unicellular algae such
as coccolithophores. Diatom frustules contribute massive amounts of silica to sediments
at the bottom of the Southern oceans. The gigantic phosphorites of Africa represent fossil
hard parts (teeth and bones) or their remobilization by diagenetic fluids: they are mined
to produce fertilizers for agriculture. On the sea floor, these three types of rocks are often
associated with each other in areas rich in nutrients, continental platforms, wind-driven
upwellings of deep seawater such as next to the coasts of Morocco and Peru and the older
seawater from the Southern oceans.
 
 
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