vi
Peter Stilte and Graham Shields
into the ocean basins either in dissolved form or associated with the suspended
load. Knowledge of these transport mechanisms allows us to establish mass
balances for the oceans. Isotope studies help us also to reconstruct chemical
exchange processes between the suspended load, river water and river basin
sediments as well as determining the origin of toxic elements. Isotope
geochemistry comes into its own when used to identify the sources of
contamination in river water and to trace the transport routes of unwelcome
chemical substances.
Chapter 4 concerns the application of various isotopic systems to the
investigation of our heavily polluted biosphere. It is designed especially to
encourage environmental researchers to explore the application of isotope
geochemistry to their studies. Problems of source, mobility and exchange
characteristics of heavy metals in contaminated soils and natural water bodies are
discussed here.
Chapters 5, 6 and 7 are all concerned with the marine environment. The oceans
represent the most important sedimentary environment. River loads end up here
and authigenic minerals (e.g. phosphates, carbonates, clay minerals, FeMn-ore
bodies) are formed here. Knowledge of the isotopic composition of oceans today
and in the past is of the greatest importance not only for understanding the
processes of exchange between sediments and seawater and during diagenesis but
also for the reconstruction of the paieo-environment. Residence times of elements
in seawater are explained in Sect. 5.3. Elements with long residence times
(relative to the ocean mixing time) can be used for high resolution
chemostratigraphy (e.g. Sr) whereas those with short residence times can be used
to trace ocean currents and reconstruct ocean circulation patterns in the past (e.g.
Nd, Pb, Ce, O). As well as looking in detail at the application of the Rb-Sr and the
Sm-Nd systems to stratigraphy and paleoceanography, this chapter introduces tess
intensely researched isotope systems such as the U-Th-Pb, Re-Os and La-Ce
systems and their potential for future marine research.
While chapter 5 concentrates on seawater and authigenic mineral isotope
geochemistry, chapter 6 deals more especially with detrital and authigenic clay
minerals in marine sediments for dating and for constraining mechanisms of
exchange during deposition and diagenesis. The Rb-Sr and K-A.r isotope systems
of clay-rich rocks are explored here. Special attention is paid to the formation and
dating potential of glauconite.
Chapter 7 concerns the behaviour of the Sm-Nd isotope system in marine
sediments during diagenesis. Chemical and isotopic exchange mechanisms
leading to Nd isotopic homogenization between authigenic clay minerals in
phosphate-rich, detrital sediments and bituminous shales are discussed.
Knowledge of these mechanisms is of great importance, not only for the
reconstruction of diagenetic evolution in a sedimentary basin, but also for dating
these diagenetic processes. However, as was shown recently, knowledge of the
Sm-Nd isotopic system can also be important for petroleum exploration, since
Peter Stilte and Graham Shields
into the ocean basins either in dissolved form or associated with the suspended
load. Knowledge of these transport mechanisms allows us to establish mass
balances for the oceans. Isotope studies help us also to reconstruct chemical
exchange processes between the suspended load, river water and river basin
sediments as well as determining the origin of toxic elements. Isotope
geochemistry comes into its own when used to identify the sources of
contamination in river water and to trace the transport routes of unwelcome
chemical substances.
Chapter 4 concerns the application of various isotopic systems to the
investigation of our heavily polluted biosphere. It is designed especially to
encourage environmental researchers to explore the application of isotope
geochemistry to their studies. Problems of source, mobility and exchange
characteristics of heavy metals in contaminated soils and natural water bodies are
discussed here.
Chapters 5, 6 and 7 are all concerned with the marine environment. The oceans
represent the most important sedimentary environment. River loads end up here
and authigenic minerals (e.g. phosphates, carbonates, clay minerals, FeMn-ore
bodies) are formed here. Knowledge of the isotopic composition of oceans today
and in the past is of the greatest importance not only for understanding the
processes of exchange between sediments and seawater and during diagenesis but
also for the reconstruction of the paieo-environment. Residence times of elements
in seawater are explained in Sect. 5.3. Elements with long residence times
(relative to the ocean mixing time) can be used for high resolution
chemostratigraphy (e.g. Sr) whereas those with short residence times can be used
to trace ocean currents and reconstruct ocean circulation patterns in the past (e.g.
Nd, Pb, Ce, O). As well as looking in detail at the application of the Rb-Sr and the
Sm-Nd systems to stratigraphy and paleoceanography, this chapter introduces tess
intensely researched isotope systems such as the U-Th-Pb, Re-Os and La-Ce
systems and their potential for future marine research.
While chapter 5 concentrates on seawater and authigenic mineral isotope
geochemistry, chapter 6 deals more especially with detrital and authigenic clay
minerals in marine sediments for dating and for constraining mechanisms of
exchange during deposition and diagenesis. The Rb-Sr and K-A.r isotope systems
of clay-rich rocks are explored here. Special attention is paid to the formation and
dating potential of glauconite.
Chapter 7 concerns the behaviour of the Sm-Nd isotope system in marine
sediments during diagenesis. Chemical and isotopic exchange mechanisms
leading to Nd isotopic homogenization between authigenic clay minerals in
phosphate-rich, detrital sediments and bituminous shales are discussed.
Knowledge of these mechanisms is of great importance, not only for the
reconstruction of diagenetic evolution in a sedimentary basin, but also for dating
these diagenetic processes. However, as was shown recently, knowledge of the
Sm-Nd isotopic system can also be important for petroleum exploration, since