Profile Alterations

Davis RB. 1974. Tubificids alter profiles of redox and pH in profundal lake sediment. Limnology and Oceanography 19 342-346. 

Figure 13. Simulation of the genesis of a roll-type uranium deposit and of the weathering of a pyrite-rich sandstone. Twenty boxes model at logi = —1 with Vx = 10, In the upper part we present an instant view of the alteration profile with neoformed minerals. Numbers in brackets correspond to the molar percentage of the neoformed minerals vs. total neoformed minerals in each box. In the lower part we present the major physicochemical parameters PE, pH, and [O2] (mol/1) in the percolating water in the above boxes. The scale is the same in the upper part and the lower part. IPW = initial percolating water.

Figure 14. Time evolution of the composition of the percolating water in the downstream part of the alteration profile of a pyrite-rich sandstone. = 10. The concentration of the dissolved species are given in mol/kg and the quantities of neoformed minerals are given in mol as a function of the parameter of advancement of the reaction t All data are represented as the logarithm of the molality (log m) vs. log. XU(a) corresponds to [U/Fe] = 5 X 10 (molar ratio) leached within the sandstone. U(l)) corresponds to the maximum possible dissolved uranium concentration. All the curves are direct Benson plots from the computer.

The manner in which ferricrete alteration profiles evolve differs from laterite weathering profiles in a number of ways a genetic distinction between laterite and ferricrete is adopted here (Figure 3.1). 

Figure 3.1 Schematic diagram showing the laterite-ferricrete genetic relationship, and the natural continuum between the autochthonous (i.e. in situ weathering profiles) and allochthonous end-members. Bidar and MQ (Merces Quarry) are two laterite weathering profiles from India, and PB (Palika Ba) is a fer-ricrete alteration profile from the Gambia (see section 3.3.2).

The division into laterite and ferricrete used in this chapter represents a useful process-based distinction, but the practicality of determining whether mineral components of a profile are allochthonous or autochthonous is problematic because many lateritic weathering profiles are subsequently modified by the introduction of allochthonous materials. Conversely, once formed, ferricretes can be subject to weathering processes in situ and evolve toward more lateritic-type profiles. Nevertheless, the distinction between dominantly autochthonous weathering profiles or allochthonous alteration profiles is an important one because it places constraints upon the processes operating during duricrust evolution, and also upon contemporaneous climatic and geomorphological conditions. 

In contrast to lateritic weathering profiles, ferricrete alteration profiles incorporate materials non-indigenous to the immediate locality of duricrust... 

Figure 3.8 Examples from the ferricrete alteration profile observed at outcrop at Palika Ba (13°28 N, 15°14 W), near the Gambia River, Gambia, West Africa. (A) Nodules of ferricrete developing within Quaternary alluvial sands and silts deposited by the Gambia River. Nodules consist of predominantly goethite with minor haematite (sample PG4 in Table 3.3). (B) Massive iron-cemented ferricrete horizon displaying characteristic tubes (i.e vermiform structure sample PG2 in Table 3.3). Importantly, the iron cement is entirely due to the introduction of allochthonous iron into the pore spaces of the sediment.

The mineralogy of ferricrete alteration profiles can be complex and varied because of the incorporation of mechanically derived materials and the retained importance of host rock composition after the formation of secondary minerals. In general, ferricrete profiles do not display the progression of alteration minerals observed in laterites. Where ferricretes are formed by mechanical accumulation, they can lie disconformably above unaltered bedrock (Bowden, 1987, 1997). In these instances, the ferricrete mineral assemblage will be inherited, in part, from the derived materials, and in part from later cementation processes that involve remobilised iron and alumina deposited as neo-formed oxyhydroxides. In such examples, determining the sequence of mineralogical transformations becomes exceptionally difficult. 

Chemical variations within ferricrete alteration profiles... 

Table 3.3 Geochemical analyses (by XRF) of the ferricrete alteration profile exposed at Palika Ba, Gambia, West Africa, (see figs 3.4C and 3.8)...

Examples from the ferricrete alteration profile observed at outcrop at Palika Ba, near the Gambia River,... 

Geochemical analyses of the ferricrete alteration profile exposed at Palika Ba, Gambia, West Africa. 

Hu D, Cao K, Peterson-Wakeman R, Wang R. Altered profile of gene expression in rat hearts induced by chronic nicotine consumption. Biochem Biophys Res Commun 2002 297(4) 729-36. 

In the following section we will apply the fluid-rock ratio Equations (56) and (57) to these infiltration-reaction curves by inserting values from the calculated continuum mechanics profiles into these equations. The idea is, that each calculated value represents a sample collected from a one-dimensional hydrothermal alteration profile. 

Raisanen SR, Alatalo SL, Ylipahkala H, Halleen JM, Cassady AI, Hume DA, Vaananen HK. 2005. Macrophages overexpressing tartrate-resistant acid phosphatase show altered profile of free radical production and enhanced capacity of bacterial killing. Biochem Biophys Res Commun 331 120-126. 

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