towards lower latitudes. This is the thermal conveyor
belt transporting heat to higher latitudes and it keeps
the deep ocean water oxidising. In areas near the
equator where the prevailing winds are from the
east, the surface water is driven away from the western coasts of the continents. This generates a strong
upwelling of nutrient-rich water from the bottom of
the sea which sustains especially high levels of
primary organic production (Fig. 1.3). The best
examples of this are the coast of Chile and off West
Africa.
Through photosynthesis, low energy carbon dioxide and water are transformed into high energy
carbohydrates (e.g. glucose):
CO 2 þ H 2 O ! CH 2 O organic matter
ð
Þ þ O 2
The production of organic matter is not limited by
carbon dioxide or water, but by nutrient availability.
Phosphorus (P) and nitrogen (N) are the most important nutrients, though the supply of iron can also be
limiting for alga production. It is this process of photosynthesis, which started 4 billion years ago, that has
built up an atmosphere rich in oxygen while
accumulating reduced carbon in sedimentary rocks as
oil, gas and coal. Most of the carbon is nevertheless
finely divided within sedimentary rocks, for example
shales and limestones, in concentrations too low to
generate significant oil and gas.
Energy stored by photosynthesis can be used directly
by organisms for respiration. This is the opposite process, breaking carbohydrates down into carbon dioxide
and water again, so that the organisms gain energy.
Solar energy
173 000
Transformed
to heat directly
81 000
40 000
Wind, waves
370
Evaporation
Oxidation,
Photosynthesis
Reflected
shortwave radiation
40
40 000
52 000
0.01–0.001%
of organic
production
preserved
in sedimentary rocks
as kerogen, coal,
oil and gas.
Tidal energy
Crystal
heat
flux
Numbers in (10
12 w)
Longwave radiation
Hot springs
32
0.3
3
Fig. 1.1 Transformation of solar energy to fossil fuels by
photosynthesis. Only a small fraction of the solar energy is
used for photosynthesis and most of the produced organic matter
is oxidised. As a result very little organic matter is buried and
stored in sedimentary rocks and very little of this is concentrated
enough to become a potential source rock
1 Introduction to Petroleum Geology
5
belt transporting heat to higher latitudes and it keeps
the deep ocean water oxidising. In areas near the
equator where the prevailing winds are from the
east, the surface water is driven away from the western coasts of the continents. This generates a strong
upwelling of nutrient-rich water from the bottom of
the sea which sustains especially high levels of
primary organic production (Fig. 1.3). The best
examples of this are the coast of Chile and off West
Africa.
Through photosynthesis, low energy carbon dioxide and water are transformed into high energy
carbohydrates (e.g. glucose):
CO 2 þ H 2 O ! CH 2 O organic matter
ð
Þ þ O 2
The production of organic matter is not limited by
carbon dioxide or water, but by nutrient availability.
Phosphorus (P) and nitrogen (N) are the most important nutrients, though the supply of iron can also be
limiting for alga production. It is this process of photosynthesis, which started 4 billion years ago, that has
built up an atmosphere rich in oxygen while
accumulating reduced carbon in sedimentary rocks as
oil, gas and coal. Most of the carbon is nevertheless
finely divided within sedimentary rocks, for example
shales and limestones, in concentrations too low to
generate significant oil and gas.
Energy stored by photosynthesis can be used directly
by organisms for respiration. This is the opposite process, breaking carbohydrates down into carbon dioxide
and water again, so that the organisms gain energy.
Solar energy
173 000
Transformed
to heat directly
81 000
40 000
Wind, waves
370
Evaporation
Oxidation,
Photosynthesis
Reflected
shortwave radiation
40
40 000
52 000
0.01–0.001%
of organic
production
preserved
in sedimentary rocks
as kerogen, coal,
oil and gas.
Tidal energy
Crystal
heat
flux
Numbers in (10
12 w)
Longwave radiation
Hot springs
32
0.3
3
Fig. 1.1 Transformation of solar energy to fossil fuels by
photosynthesis. Only a small fraction of the solar energy is
used for photosynthesis and most of the produced organic matter
is oxidised. As a result very little organic matter is buried and
stored in sedimentary rocks and very little of this is concentrated
enough to become a potential source rock
1 Introduction to Petroleum Geology
5