Big Chemical Encyclopedia

Chemical substances, components, reactions, process design ...

Articles Figures Tables About

Weathering continental

Most of the Mn(IV) oxide minerals listed in table 8.3 occur in weathered continental rocks, and often constitute important manganese ore deposits. However, several of the minerals, notably todorokite, bimessite, vemadite and, perhaps, buserite and asbolane, are major constituents of seafloor hydrothermal crusts near spreading centres and in manganese nodule deposits. [Pg.346]

Table 3 Incongruent release of isotopes from strongly mechanically weathered continental rocks ... Table 3 Incongruent release of isotopes from strongly mechanically weathered continental rocks ...
In the marine environment, the numerous radionuclides can be classified into three broad categories based on their production or origin (1) those derived from the weathering of continental rocks, the primordial radionuclides, (2) those formed from cosmic radiation, the cosmogenic radionuclides, and (3) those artificially introduced into nature, the anthropogenic or transient radionuclides and tracers. The primordial radionuclides (e.g. Th, and U) were... [Pg.33]

Thorinm-232 is the only non-radiogenic thorium isotope of the U/Th decay series. Thorinm-232 enters the ocean by continental weathering and is mostly in the particulate form. Early measurements of Th were by alpha-spectrometry and required large volume samples ca. 1000 T). Not only did this make sample collection difficult, but the signal-to-noise ratio was often low and uncertain. With the development of a neutron activation analysis " and amass spectrometry method " the quality of the data greatly improved, and the required volume for mass spectrometry was reduced to less than a liter. Surface ocean waters typically have elevated concentrations of dissolved and particulate 17,3 7,62... [Pg.46]

Many important erosion-related phenomena are episodic and infrequent, such as flash floods, landslides, and glaciations, while others such as orogenesis and soil formation involve time scales that exceed those of major climate fluctuations. In either case, the time scale of human existence is too short to make adequate observations. Consequently, it is difficult to directly estimate the rates or characterize the effects of such phenomena on erosion products. The key to understanding weathering and erosion, on a continental scale, is to decipher the relationship between landforms, the processes that produce them, and the chemistry and discharge of river-borne materials. [Pg.206]

It has been argued that phosphorus limits oceanic productivity on the million year time scale (Broecker, 1971). The reason is that essentially all phosphorus in the ocean is introduced by rivers and thus ultimately from the weathering of continental rocks. This flux is, in effect. [Pg.249]

Changes in seawater ( " U/ U) with time are most likely to be induced by changes in the riverine input and may therefore provide information about past continental weathering. In particular, riverine is thought to be increased by physical... [Pg.499]

This review highlights the important potential of U-series disequilibria in understanding the continental alteration and related mass transfers. The recent analytical developments, including TIMS and MC ICP MS techniques, for measuring small amounts of U, Th and Ra in geologic samples, offer today new possibilities and new perspectives for analysing U-series disequilibria in weathering profiles and river waters, and could lead to new and, as yet, unanticipated advances in the field of continental alteration. [Pg.568]


See other pages where Weathering continental is mentioned: [Pg.340]    [Pg.4452]    [Pg.106]    [Pg.194]    [Pg.572]    [Pg.98]    [Pg.340]    [Pg.4452]    [Pg.106]    [Pg.194]    [Pg.572]    [Pg.98]    [Pg.214]    [Pg.187]    [Pg.14]    [Pg.14]    [Pg.34]    [Pg.128]    [Pg.190]    [Pg.195]    [Pg.198]    [Pg.198]    [Pg.207]    [Pg.216]    [Pg.222]    [Pg.222]    [Pg.223]    [Pg.223]    [Pg.224]    [Pg.272]    [Pg.373]    [Pg.401]    [Pg.428]    [Pg.460]    [Pg.127]    [Pg.452]    [Pg.19]    [Pg.459]    [Pg.494]    [Pg.565]    [Pg.566]    [Pg.575]    [Pg.577]    [Pg.584]    [Pg.584]    [Pg.598]    [Pg.23]    [Pg.42]    [Pg.43]   
See also in sourсe #XX -- [ Pg.80 , Pg.86 , Pg.87 , Pg.258 , Pg.270 , Pg.275 ]




SEARCH



Continental

© 2024 chempedia.info