Soil genesis and mineralogy across a volcanic lithosequence

Abstract

Lithology is a principle state factor of soil formation, interacting with climate, organisms, topography and time to define pedogenesis. A lithosequence of extrusive igneous lithologies (rhyolite obsidian, dacite, andesite and basalt) was identified in the Clear Lake Volcanic Field in the Coast Range of northern California to determine the effects of lithology on pedogenesis, clay mineralogy and soil physiochemical properties. Based on regional landscape erosion rates (0.2-0.5 mm yr −1 ), the soil residence times for the investigated pedons (~150 cm deep) were of the order of 3000 to 7500 years indicating that the soils developed under the relatively stable Holocene mesic/xeric climate regime. Soils from all lithologies developed to a similar Xeralf taxonomy with remarkably consistent physiochemical properties. Although total (Fe t ) and dithionite-citrate extractable (Fe d ) iron concentrations diverged across lithologies, the degree of weathering as assessed by the Fe d /Fe t ratio was similar across the lithosequence. In spite of large differences in silica content of the parent materials, the clay mineralogical assemblage of all lithologies was dominated by kaolin minerals (kaolinite and/or halloysite). All pedons displayed an increase in halloysite and the degree of halloysite hydration with increasing depth, except the basalt pedon, which was dominated by kaolinite with only trace halloysite. We attribute this lack of halloysite in the basalt pedon to the lower silica activities associated with this silica-poor lithology. There was a lack of nanocrystalline minerals across all lithologies as inferred from selective dissolution. The dominance of crystalline materials is a function of the xeric soil moisture regime whereby summer soil profile desiccation promotes dehydration and crystallization of metastable nanocrystalline precursors. Further, the pronounced summer dry period results in dehydration of halloysite (1.0 nm) to halloysite (0.7 nm; also referred to as meta halloysite in some literature), together with transformation to kaolinite, in the upper soil profile. In spite of the relatively young soil residence times of these soils (Holocene age), the effects of lithology persisted only in differences in Fe oxide concentrations (Fe d ), as well as a lack of significant halloysite in basalt pedons. The overwhelming effect of climate in these highly weatherable parent materials narrowed the trajectory of pedogenesis, resulting in soils from contrasting lithologies converging on kaolin mineralogy, a lack of nanocrystalline constituents, and similar soil physiochemical properties.

Durable Terrestrial Bedrock Predicts Submarine Canyon Formation

“…In addition to promoting bedrock incision, catchment lithology may also influence canyon occurrence in other ways. For example, the strong negative correlation between volcanic bedrock proportion and canyon occurrence (Figure ) may result from the tendency for volcanic rocks to weather to fine‐grained clay minerals (Wilson et al, ). The resulting fine‐grained sediment could inhibit submarine erosion by increasing the cohesivity of the seafloor (Winterwerp et al, ), and slow settling velocities make fine‐grained sediment more prone to exit the littoral cell and be deposited on the shelf before it can reach canyon heads (Harris & Wiberg, ; Perg et al, ).…”

Defining and Managing for Healthy Vineyard Soils, Intersections With the Concept of Terroir

“…In these instances, compost application can be a favorable management strategy to relieve P deficiency, due to the combined beneficial effect of applied SOM and applied P. Management of P deficiency in winegrapes is largely driven by the terroir of the soil, as influenced by pedogensis. For example, weathered soils derived from low P lithologies, such as granite, may be P deficient, but also have low P fixation capacities, and hence would respond well to P applications (Wilson et al, 2016(Wilson et al, , 2017. Conversely, P deficient soils with high P sorption capacities, such as volcanic ash soils, will require higher applications of compost to overcome the P fixation capacity.…”

Arable soil formation and erosion: a hillslope-based cosmogenic-nuclide study in the United Kingdom

“…We suggest that faster formation rates at RFF and CW may be explained by the fact that the specific varieties of sandstone at these study sites are generally more susceptible to weathering than those within the sandstone-based inventory, of which the dominant form is the greywacke, characterised by a hard, fine-grained argillaceous matrix, with greater resistance to weathering (Cummins et al, 1962). Although there has been substantial work on the susceptibilities of major geological rock types to weathering (Stockmann et al, 2014;Wilson et al, 2017), we do not know of any study which seeks to identify whether the susceptibility of specific varieties of sandstone have an influence on soil formation rates.…”