Weathering sediments

Canada Labrador 578 lake sediments Weathering of geologic materials <0.5-126 McConnell (1999)... 

Lake Brompton Quebec, Canada sediments Weathering of geologic materials mining 12 Belzile, Lecomte and Tessier (1989)... 

The rates in Table 7.4 and the soil composition data in Table 7.2 can be combined to calculate the residence time, or turnover rate, of ions in soils. Residence time is the total soil content divided by the loss rate and is the inverse of the weathering rate. The soil s sodium content is approximately 0.4%, or 50 000 kg ha-1 m-1. The sodium loss of 300 mol ha-1 m-1, or 7 kg ha-1 m-1, indicates that sodium s residence time is about 7000 years in the surface meter of soils. This estimate disregards atmospheric sodium input to the soil and also disregards the contribirtion of sediment weathering to the sodium losses in Table 7.4. If sediment weathering contributes half the sodium content of the world s rivers, sodium s residence time in soils is on the average about 15 000 years. 

Geochemical studies of Y are very useful for an improved knowledge regarding the conditions of sedimentation, weathering... 

Characterization of in situ sediments, weathered formation, and engineered fills are further described below. 

Weathering and transportation is followed by the sedimentation of material. The depositional environment can be defined as an area with a typical set of physical, chemical and biological processes which result in a specific type of rock. The characteristics of the resulting sediment package are dependent on the intensity and duration of these processes. The physical, chemical, biological and geomorphic variables... 

Sources. Iron ore deposits were formed by many different processes, eg, weathering, sedimentation, hydrothermal, and chemical. Iron ores occur in igneous, metamorphic, and sedimentary deposits. Normally, as-mined iron ore contains 25 to 68% iron. 

During chemical weathering, rocks and primary minerals become transformed to solutes and sods, and eventually to sediments and sedimentary... 

Owing to the stability of the uranyl carbonate complex, uranium is universally present in seawater at an average concentration of ca. 3.2/rgL with a daughter/parent activity ratio U) of 1.14. " In particulate matter and bottom sediments that are roughly 1 x 10 " years old, the ratio should approach unity (secular equilibrium). The principal source of dissolved uranium to the ocean is from physicochemical weathering on the continents and subsequent transport by rivers. Potentially significant oceanic U sinks include anoxic basins, organic rich sediments, phosphorites and oceanic basalts, metalliferous sediments, carbonate sediments, and saltwater marshes. " ... 

Overall, weathering controls the chemistry of material that is transported into the sediment and that which stays behind in the soil. As an example, consider a general weathering reaction for an aluminosilicate (Stumm and Morgan, 1995) ... 

A fundamental distinction among landscapes is whether the net sediment flux (the total load carried by the river) is limited by the ability of erosional processes to carry sediment (transport-limited environments) or the availability of erodible material (weathering-limited environments). In general, soil-mantled landscapes can... 

Note that this estimate of the annual O2 loss to weathering processes is approximately equal to the estimated annual production of oxygen estimated above. Hence, the weathering of rocks and burial of organic carbon in sediments during their formation are important processes for the oxygen content of the atmosphere. 

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