Biotic weathering

ScHWARTZMAN, D. McMenamin, M. 1993. A much warmer Earth surface for most of geologic time Implications to biotic weathering. Chemical Geology, 107, 221-223. 

The alterations in chemical composition of naturally weathered spilled oils are generally resulted from the combined effects of abiotic and biotic weathering, as Figure 27.8 and Figure 27.9 shows. The transformations of oil hydrocarbons by biodegradation are likely to occur stepwise, producing alcohols, phenols, aldehydes, and carboxylic acids in sequence. 

Toxic As concentrations in groundwater and to lesser extent in surface water mostly result from physical or chemical abiotic and biotic weathering of primary or secondary As-containing minerals. Therefore, aquifers with elevated levels of groundwater As derived from natural sources can be classified according to the origin of the As and the mobilization mechanism into the water ... 

Saprophytic, dark pigmented fungi such as Alternaria spp. can infect a wide range of plant species, especially tissues that are exposed to other biotic or abiotic stressors and older and senescing plant tissues. Also, wet weather conditions favour attack by Alternaria spp. Inoculum of Alternaria and potentially production of altemariol is further enhanced when cereal straw and stubble is left on the soil surface and not sufficiently incorporated into the soil after harvest (direct seeding and minimum tillage systems). 

An ore is a metal-bearing mineral that is valuable enough to be mined. Ore formation is primarily due to temperature and pressure effects (e.g., magmatic concentration, deposition upon cooling, evaporation, hydrothermal processes), weathering and transport phenomena (e.g., sedimentation, metamorphism, mechanical concentration, residual concentration), and chemical processes (e.g., abiotic and biotic oxidations, and reductions). These effects, phenomena and processes are illustrated in Figures 5.2-5.4. 

Schwartzman D. W. and VolkT. (1989) Biotic enhancement of weathering and the habitabihty of Earth. Nature 340, 457 0. 

SCHWARTZMAN, D. VoLK, T. 1991. Biotic enhancement of weathering and surface temperatures on earth since the origin of life. Paleogeography, Paleoclimatology, Paleoecology, 90, 357—371. 

The polygenetic model of rock varnish formation combines biotic enhancement of Mn with abiotic processes (Dorn, 1998). It builds on the mineralogy research of Potter and Rossman (1979a,b,c) and studies of bacteria fossil remains within varnish layers (Dorn and Meek, 1995 Krinsley et al., 1995 Dorn, 1998 Krinsley, 1998). In brief, weathered remains of Mn-rich bacterial casts (Figure 8.6) cement weathered clay minerals to rock surfaces. 

Any successful model of varnish formation, however, must also explain additional issues associated with varnish chemistry. First, iron is enhanced slightly in varnish over crustal and adjacent soil concentrations. Although most of the iron derives from the clay minerals, some is biotically enhanced (see Figure 8.7 and Dorn and Oberlander, 1982 Adams et al., 1992 Sterflinger et al., 1999) as the nanometre-scale Fe seen in the bacterial casts (Krinsley, 1998) is also found reworked into the weathered remnants of clay minerals seen in HRTEM imagery. Considerable HRTEM work, however, is needed to better document processes of minor iron enhancement. 

Cronan, C. S. 1985. Chemical weathering and solution chemistry in acid forest soils Differential influence of soil type, biotic processes and H" deposition. In The... 

Cronan, C. S. (1985), Chemical Weathering and Solution Chemistry in Acid Forest Soils Differential Influence of Soil Type, Biotic Processes, and H +, in J. I. Drever, Ed., The Chemistry of Weathering, Reidel, Dordrecht, Netherlands, pp. 175-196. 

Figure 7. Rate and weathering of polluting oil in estuarine and marine waters showing various abiotic and biotic processes (Kennish, 1999).

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