Modeling the shortening history of a fault tip fold using structural and geomorphic records of deformation

We present a methodology to derive the growth history of a fault tip fold above a basal detachment. Our approach is based on modeling the stratigraphic and geomorphic records of deformation, as well as the finite structure of the fold constrained from seismic profiles. We parameterize the spatial deformation pattern using a simple formulation of the displacement field derived from sandbox experiments. Assuming a stationary spatial pattern of deformation, we simulate the gradual warping and uplift of stratigraphic and geomorphic markers, which provides an estimate of the cumulative amounts of shortening they have recorded. This approach allows modeling of isolated terraces or growth strata. We apply this method to the study of two fault tip folds in the Tien Shan, the Yakeng and Anjihai anticlines, documenting their deformation history over the past 6–7 Myr. We show that the modern shortening rates can be estimated from the width of the fold topography provided that the sedimentation rate is known, yielding respective rates of 2.15 and 1.12 mm/yr across Yakeng and Anjihai, consistent with the deformation recorded by fluvial and alluvial terraces. This study demonstrates that the shortening rates across both folds accelerated significantly since the onset of folding. It also illustrates the usefulness of a simple geometric folding model and highlights the importance of considering local interactions between tectonic deformation, sedimentation, and erosion

The clumped isotope geothermometer in soil and paleosol carbonate

We studied both modern soils and buried paleosols in order to understand the relationship of temperature estimated from clumped isotopes in carbonates (T°C_(clumped)) to actual surface and burial temperatures. Carbonates from modern soils in a broad range of climates were sampled from Arizona, Nevada, Tibet, and India. T°C_(clumped) obtained from these soils shows that soil carbonate only forms in the very warmest months of the year, largely in the afternoon, and probably in response to intense soil dewatering. The highest T°C_(clumped) obtained from modern soil carbonate are <40°C On average, T°C_(clumped) significantly exceeds mean annual temperature by 10-15°C due to (1) summertime bias in soil carbonate formation, and (2) sensible heating of soil. Secondary controls on T°C_(clumped) are site aspect, but especially soil depth and shading

Full propagation of analytical uncertainties in Δ47 measurements

International audienceClumped-isotope measurements in CO 2 and carbonates (Δ 47) present a number of technical challenges and require correcting for various sources of analytical non-linearity. For now we lack a formal description of the analytical errors associated with these correction steps, which are not accounted for in most data processing methods currently in use. Here we formulate a quantitative description of Δ 47 error propagation, fully taking into account standardization errors and their properties. We describe various standardization strategies, along with the assumptions they rely on, in the context of this model, and propose a new, "pooled" standardization approach designed to yield more robust/accurate corrections. User-friendly online resources and an open-source Python library are also provided to facilitate the use of these error models. Among other uses, the mathematical framework described here may be helpful to improve standardization protocols (e.g., anchor/unknown ratios) and inform future efforts to define community reference materials

How I Learned to Stop Worrying and Embrace Isotopic Disequilibrium in Carbonate Minerals

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Direct, Precise Measurements of Isotopologue Abundance Ratios in CO 2 Using Molecular Absorption Spectroscopy: Application to Δ 17 O

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