Quantifying the magnitude and timing of Holocene soil erosion events on parent materials of known age using in-situ cosmogenic C-14 and Be-10 depth-profiles

Fülöp, Réka-Hajnalka (2012) Quantifying the magnitude and timing of Holocene soil erosion events on parent materials of known age using in-situ cosmogenic C-14 and Be-10 depth-profiles. PhD thesis, University of Glasgow.

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Abstract

Conventional methods for the determination of past soil erosion provide only average rates of
erosion of the sediment's source areas and are unable to determine the rate of at-a-site soil loss.
This study addresses this issue by exploring the extent to which in situ cosmogenic Be-10 and C-14
depth-profiles can be used to quantify the magnitude and timing of site-specific soil erosion events
on soils of known age. The study focuses on two sites located on end moraines of the Loch Lomond
Readvance (LLR) in Scotland: Wester Cameron and Inchie Farm, both near Glasgow. The LLR is
well documented and several LLR moraine radiocarbon ages exist in the literature allowing for the
placement of a first order age constraint on soil/till emplacement. In addition, the site at Wester
Cameron is in the proximity of Croftamie, a well-studied LLR type-locality. The site near Wester
Cameron does not show any visible signs of soil disturbance and so this has been selected in order
to test (1) whether a cosmogenic nuclide depth profile in a sediment body of Holocene age can be
reconstructed, and (2) whether in situ Be-10, C-14 and Al-26 yield concordant results. Field evidence
suggests that the site at Inchie Farm has undergone soil erosion and so this was selected so as to
explore whether the technique can also be applied to determine the broad timing of soil loss.
The results of the cosmogenic Be-10, C-14 and Al-26 analyses in the Wester Cameron site samples
confirm that the cosmogenic nuclide depth-profile to be expected from a sediment body of Holocene
age can be reconstructed. Moreover, the agreement between the total cosmogenic Be-10 inventories
in the erratics and the Wester Cameron soil/till samples indicate that there has been no erosion at
the sample site since the deposition of the till/moraine. Further, the Wester Cameron depth profiles
show minimal signs of homogenisation, as a result of bioturbation, and minimal cosmogenic nuclide
inheritance from previous exposure periods. The results of the cosmogenic Be-10 and C-14 analyses
in the Inchie Farm site samples show a clear departure from the zero-erosion cosmogenic nuclide
depth profiles suggesting that the soil/till at this site has undergone erosion since its stabilisation.
The LLR moraine at the Inchie Farm site is characterised by the presence of a sharp break in
slope, suggesting that the missing soil material was removed instantaneously by an erosion event
rather than slowly by continuous erosion. The results of a Monte-Carlo type analysis carried out
to constrain the magnitude and timing of this erosion event suggest that the event was relatively
recent and relatively shallow, resulting in the removal of ca. 20-50 cm of soil less than 1500 years
BP.
The results of sensitivity analyses show that the predicted magnitude and timing of the Inchie
Farm erosion event are highly sensitive to the assumptions that are made about the background
rate of continuous soil erosion at the site and also about the stabilisation age of the till. The
results further indicate that the density of the sedimentary deposit will also affect the magnitude
and timing of the predicted erosion event. All three parameters can be independently determined
a priori and so despite the method presented in this study being sensitive to variations in these
parameters, they do not impede future applications of the method to other localities. The results
of the sensitivity analyses further show that the predicted erosion event magnitude and timing is
very sensitive to the in situ cosmogenic C-14 production rate used and to the assumptions that are
made about the contribution of muons to the total production of this cosmogenic nuclide. Thus,
advances in this regard need to be made for the method presented in this thesis to be applicable
with confidence to scenarios similar to the one presented here.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Keywords: soil erosion, cosmogenic nuclide depth-profiles, cosmogenic in situ C-14, carbon-14, beryllium-10
Subjects: Q Science > QE Geology
Colleges/Schools: College of Science and Engineering > School of Geographical and Earth Sciences
Supervisor's Name: Bishop, Prof Paul and Fabel, Dr. Derek and Cook, Dr. T. Gordon and Everest, Dr D. Jeremy
Date of Award: 2012
Depositing User: Miss Reka-Hajnalka Fülöp
Unique ID: glathesis:2012-3358
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 14 May 2012
Last Modified: 28 Apr 2016 15:47
URI: http://theses.gla.ac.uk/id/eprint/3358

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