Geology topics

Tiffany Yesavage

Publications and source records attributed to Tiffany Yesavage.

4 recordsLinked to original sources

USGS2019

Comment on “Particle fluxes in groundwater change subsurface rock chemistry over geologic time”

Over the last decade, studies at the Shale Hills Critical Zone Observatory (Shale Hills) have greatly expanded knowledge of weathering in previously understudied, shale-mantled terrains, as well as Earth's Critical Zone as a whole. Among the many discoveries made was the importance of redistribution and losses of micron-sized particles during development of shale-derived soils. A geochemical fingerprint of this process for Al and Fe was illustrated quantitatively by Jin et al. (2010). Subsequent papers, too numerous to list in a Comment, built upon this new recognition by evaluating the spatial and temporal aspects element mobilization. Recently, Kim et al. (2018) examined the composition of suspended, generally micron-sized particles in the Shale Hills stream, along with the dissolved load, across seasons and ranges of discharge. One prominent conclusion from Kim et al. (2018) is that Zr is essentially immobile at Shale Hills. Such a broad conclusion is in direct contradiction with one from Bern and Yesavage (2018) that Zr has been mobilized from soils at Shale Hills, and the losses relative to soil parent material are significant (median 41%). The point is important, because assuming Zr immobility is necessary to index gains and losses of other elements using the open-chemical-system transport function ( τ ). Both papers draw upon patterns and calculations using elemental concentration data from Shale Hills and attempt to construct conceptual frameworks to explain the results. Here, the argument is made that the understanding of substantial Zr mobility from soils at Shale Hills described by Bern and Yesavage (2018) is more accurate. Additionally, issues with adaptations of the standard τ equations used in Kim et al. (2018) and some previous papers are also addressed.

Pennsylvania↗

USGS2018

Dual-phase mass balance modeling of small mineral particle losses from sedimentary rock-derived soils

Losses of small mineral particles can be a significant physical process that affects the elemental composition of soils derived from sedimentary rocks. Shales, in particular, contain abundant clay-sized minerals that can be mobilized by simple disaggregation, and solutional weathering is limited because the parent rock is composed primarily of recalcitrant minerals previously subjected to continental weathering. Here, the dual-phase mass balance model is employed to quantify losses of small mineral particles as water dispersible colloids (WDCs) from three previously studied soil profiles along a hill slope at the Susquehanna Shale Hills Critical Zone Observatory (SSHO). WDCs were isolated from soil in the laboratory to determine their mineralogical and elemental compositions. Clay minerals dominated WDCs, including illite, vermiculite, and chlorite inherited from the parent shale, along with neoformed kaolinite. Quartz present in bulk soil was generally excluded from WDCs. Elements of low solubility and/or bound in recalcitrant forms, like Rb in illite, were employed in tracer ratios in the dual-phase model. Aluminum, Ga, and Rb were enriched in WDCs, and Zr and Hf were partially excluded. Six different combinations of elements into tracer ratios (Al/Zr, Ga/Zr, Rb/Zr, Al/Hf, Ga/Hf, Rb/Hf) each yielded similar model results. Mass losses of WDCs were large, ranging from − 68 ± 7% to − 15 ± 5% relative to soil parent material in different parts of the profiles. Mass losses via solution were smaller, ranging from − 7 ± 2% to a gain of 6 ± 1% in part of one profile. Losses of WDCs account for > 90% of total mass loss, surpassing chemical dissolution, and therefore dominate the weathering portion of denudation at SSHO. Zirconium concentrations were 97–158 ppm in the generally ≤ 1 μm WDCs, suggesting colloidal, Zr-bearing phases. Model-quantified losses of Zr via WDCs were large, with a median loss of 41% relative to parent material. Such losses indicate systematic underestimates of weathering by traditional mass balance that uses Zr as an index element. Losses of Ca, Mg, and K via WDCs exceeded losses via solution, countering assumptions of base cation losses primarily via mineral dissolution. The results illustrate a geochemical fingerprint of physical weathering and the ability of the dual-phase model to quantify that weathering process.

Chemical Geology↗

USGS2017

Ion-adsorption REEs in regolith of the Liberty Hill pluton, South Carolina, USA: An effect of hydrothermal alteration

Ion-adsorbed rare earth element (REE) deposits supply the majority of world heavy REE production and substantial light REE production, but relatively little is known of their occurrence outside Southeast Asia. We examined the distribution and forms of REEs on a North American pluton located in the highly weathered and slowly eroding South Carolina Piedmont. The Hercynian Liberty Hill pluton experiences a modern climate that includes ~ 1500 mm annual rainfall and a mean annual temperature of 17 °C. The pluton is medium- to coarse-grained biotite-amphibole granite with minor biotite granite facies. REE-bearing phases are diverse and include monazite, zircon, titanite, allanite, apatite and bastnäsite. Weathered profiles were sampled up to 7 m-deep across the ~ 400 km 2 pluton. In one profile, ion-adsorbed REEs plus yttrium (REE + Y) ranged up to 581 mg/kg and accounted for up to 77% of total REE + Y in saprolite. In other profiles, ion-adsorbed REE + Y ranged 12–194 mg/kg and only accounted for 3–37% of totals. The profile most enriched in ion-adsorbed REEs was located along the mapped boundary of two granite facies and contained trioctahedral smectite in the saprolite, evidence suggestive of hydrothermal alteration of biotite at that location. Post-emplacement deuteric alteration can generate easily weathered REE phases, particularly fluorocarbonates. In the case of Liberty Hill, hydrothermal alteration may have converted less soluble to more soluble REE minerals. Additionally, regolith P content was inversely correlated with the fraction ion-adsorbed REEs, and weathering related secondary REE-phosphates were found in some regolith profiles. Both patterns illustrate how low P content aids in the accumulation of ion-adsorbed REEs. The localized occurrence at Liberty Hill sheds light on conditions and processes that generate ion-adsorbed REEs.

South Carolina↗

USGS2017

Iron isotope systematics of shale-derived soils as potentially influenced by small mineral particle loss

Loss of small mineral particles from soil has been suggested as a process that can produce net isotopic fractionation in the remaining soil. We extracted water dispersible colloids (WDCs) from bulk soil collected at the Susquehanna/Shale Hills Critical Zone Observatory (SSHO) and measured their Fe isotopic composition for comparison to published data from the site. The goal was to explain soil δ56Fe values that become lighter as Fe is lost from soil. The range of δ56Fe values for WDCs was 0.22 to 0.59 ‰, barely intersecting the value of ~0.8 ± 0.3‰ predicted by mass balance for particulate Fe loss by a previous study. The WDCs extracted likely represent a mixture of unfractionated Fe inherited from shale minerals and secondary Fe fractionated by weathering zone processes. Thus, although the WDC compositions do not confirm small mineral particle losses as causing overall Fe isotope fractionation in SSHO soils, they are compatible with that interpretation.

Conference Paper↗