Hornblende etching and quartz/feldspar ratios as weathering and soil development indicators in some Michigan soils

Weathering can be used as a highly effective relative age indicator. One such application involves etching of hornblende grains in soils. Etching increases with time (duration) and decreases with depth in soils and surficial sediments. Other variables, related to intensity of weathering and soil formation, are generally held as constant as possible so as to only minimally influence the time-etching relationship. Our study focuses on one of the variables usually held constant—climate—by examining hornblende etching and quartz/feldspar ratios in soils of similar age but varying degrees of development due to climatic factors. We examined the assumption that the degree of etching varies as a function of soil development, even in soils of similar age. The Spodosols we studied form a climate-mediated development sequence on a 13,000-yr-old outwash plain in Michigan. Their pedogenic development was compared to weathering-related data from the same soils. In general, soils data paralleled weathering data. Hornblende etching was most pronounced in the A and E horizons, and decreased rapidly with depth. Quartz/feldspar ratios showed similar but more variable trends. In the two most weakly developed soils, the Q/F ratio was nearly constant with depth, implying that this ratio may not be as effective a measure as are etching data for minimally weathered soils. Our data indicate that hornblende etching should not be used as a stand-alone relative age indicator, especially in young soils and in contexts where the degree of pedogenic variability on the geomorphic surface is large.     

边坡稳定性分析的无条分法

基于滑面应力修正技术并取整个滑体为受力体,实现了对滑体的整体极限平衡分析。同时,利用Green公式将有关域积分转化为边界积分,而无需再对滑体进行条分。该方法数值特性好,亦可方便地将二维的成果向三维推广,从而实现满足全部6个平衡条件的三维严格极限平衡法。本文是二维部分的成果。     

Splint coals of the Central Appalachians: Petrographic and geochemical facies of the Peach Orchard No. 3 split coal bed,southern Magoffin County,Kentucky

The Bolsovian (Middle Pennsylvanian) Peach Orchard coal bed is one of the splint coals of the Central Appalachians. Splint coal is a name for the dull, inertinite-rich lithologies typical of coals of the region. The No. 3 Split was sampled at five locations in Magoffin County, Kentucky and analyzed for petrography and major and minor elements. The No. 3 Split coals contain semifusinite-rich lithologies, up to 48% (mineral-free basis) in one case. The nature of the semifusinite varies with position in the coal bed, containing more mineral matter of detrital origin in the uppermost durain. The maceral assemblage of these terminal durains is dominated by detrital fusinite and semifusinite, suggesting reworking of the maceral assemblage coincident with the deposition of the detrital minerals. However, a durain in the middle of the coal bed, while lithologically similar to the uppermost durains, has a degraded, macrinite-rich, texture. The inertinite macerals in the middle durain have less distinct edges than semifusinites in the uppermost terminal durains, suggesting degradation as a possible path to inertinite formation. The uppermost durain has higher ash and semifusinite contents at the eastern sites than at the western sites. The difference in the microscopic petrology indicates that megascopic petrology alone can be a deceptive indicator of depositional environments and that close attention must be paid to the individual macerals and their implications for the depositional setting, especially within the inertinite group.     

Balance of S in a constructed wetland built to treat acid mine drainage, Idaho Springs, Colorado, U.S.A.

The wetland constructed at the Big Five Tunnel in Idaho Springs, Colorado was designed to remove, passively, heavy metals from acid mine drainage. In optimizing the design of such a wetland, an improved understanding of the chemical processes operating there was required, particularly SO₄²⁻ reduction and sulfide precipitation. For this purpose, field and laboratory data were collected to study the balance of S in the system. Field data collected included water analyses of the mine drainage and wetland effluents and measurements of H₂S gas emissions from the wetland. The concentration of sulfide in the wetland effluent ranged from 10⁻⁴ to 10⁻³ mol/l. The average rates of H₂S emission from the surface of the substrate were 150 nmol/cm²/d in the summer and 0.17 and 0.35 nmol/cm²/d in the winter. This maximum estimated loss of sulfide was not significant in reducing the amount of sulfide available for precipitation with metals. Sequential extraction experiments for S on wetland substrates showed that acid volatile sulfides (AVS) increased with time in the wetland substrate. A serum bottle experiment was conducted to study the S balance in the Big Five wetland by quantitatively measuring the amount of S in different phases as microbial SO₄²⁻ reduction progressed. The increase in AVS reasonably balanced the decrease in SO₄²⁻ concentration in the experiment, suggesting that the decrease in SO₄²⁻ concentration represented the amount of SO₄²⁻ reduced and that nearly all of the sulfide produced was precipitated as AVS. Sulfide precipitation was determined to be the primary metal removal process in the wetland system and amorphous FeS is the primary iron sulfide formed in the substrate.