# Can we calculate the value of Rock-Eval parameters for the 0-50 layer from the measured values on the layers 0-30 and 30-50 cm?

Eva Kanari, Pierre Barré, Lauric Cecillon, Laure Soucémarianadin, Nicolas Bouton, Florence Savignac, François Baudin

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Eva Kanari, Pierre Barré, Lauric Cecillon, Laure Soucémarianadin, Nicolas Bouton, et al. Can we calculate the value of Rock-Eval parameters for the 0-50 layer from the measured values on the layers 0-30 and 30-50 cm?. EGU General Assembly 2019, Apr 2019, Vienna, Austria. . hal-03981214

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Submitted on 9 Feb 2023

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# Can we calculate the value of Rock-Eval parameters for the 0–50 layer from the measured values on the layers 0–30 and 30–50 cm?

Kanari E.<fnref n="1" />,<fnref n="2" />, Barré P.<fnref n="1" />, Cécillon L.<fnref n="1" />,<fnref n="3" />, Soucémarianadin L.N.<fnref n="1" />, Bouton N.<fnref n="4" />, Savignac F.<fnref n="2" />, Baudin F.<fnref n="2" />

<figure><img src="image_2.png" /></figure>

Photography
encouraged

## CONTEXT

* Currently various soil sampling depths, different across studies.

* Organic Carbon (OC) content of a soil profile calculated as the sum of comprising horizons.

* Rock-Eval (RE), a valuable method to investigate soil organic carbon (SOC) stock and stability (Gregorich et al., 2015; Barré et al., 2016; Soucémarianadin et al., 2018).

## OBJECTIVE

Examine application of additivity to RE parameters from two soil horizons

## MATERIALS

natural soils · 10 forest sites · various soil types

<figure><img src="image_3.png" /></figure>

## LITERATURE

Barré, P. et al. (2016). *Biogeochemistry*, **130**(1), 1-12.
Gregorich, E.G. et al. (2015). Soil Biol. Biochem. **91**, 182-191.
Soucémarianadin, L.N. et al. (2018). Soil Biol. Biochem. **117**,
108-116.

## METHOD

20 initial samples · 70 mixtures

· RE6 analysis

obtained thermograms

· RE6 parameters **measured**

<figure><img src="image_4.png" /></figure>

<figure><img src="image_5.png" /></figure>

<figure><img src="image_6.png" /></figure>

Modified after
Saenger et al. 2013

$$ \Sigma \text{ grey areas} = \text{Total Organic Carbon; TOC (wt\%)} $$

Calculation of **theoretical** values for the four classical RE6 parameters based on integration of surfaces of the added signals

<figure><img src="image_7.png" /></figure>

## RESULTS

Spearman correlation coefficient $ρ$ and $p$-value

<figure><img src="image_8.png" /></figure>

Comparison of Rock-Eval parameters
$x \rightarrow$ theoretical values calculated for each mixture based on end-member signals and mixing ratio
$y \rightarrow$ measured in two soil horizons and in composed mixtures

<figure><img src="image_9.png" /><figcaption>Hydrogen Index (mg HC/g C)</figcaption></figure>

## DISCUSSION

* Values of RE parameters measured on composite samples were in good agreement with theoretical values – calculation on added signal of end-members.

* This is particularly the case for the following parameters: $TOC_{RE6}$, PC and $OI_{RE6}$.

* For HI the relationship between measured and calculated values is unsatisfactory.

* Highest deviation was observed for sites with a heterogeneous vertical clay content profile.

* Retention of hydrocarbons by clay minerals could explain this observation.

## CONCLUSIONS

* In temperate soils, most of the classical RE parameters of a soil profile can be calculated as a sum of its horizons.

* This implies that the comparison of results from studies using different sampling strategies is possible.

* Moreover, the natural mineral effect in temperate soils is negligible during RE analysis.

## Further information

Please contact:
eva.kanari@sorbonne-universite.fr

<footnote n="1">¹ENS, Geol Lab, CNRS ENS, UMR 8538, 75005 Paris, FR</footnote>

<footnote n="2">²SU-Univ. Paris 06, ISTeP, 75005 Paris, FR</footnote>

<footnote n="3">³UGA, Irstea, UR LESSEM, 38402 St-Martin-d'Hères, FR,</footnote>

<footnote n="4">⁴Vinci Technologies, 92022 Nanterre, FR</footnote>