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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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
Funder's Name: UNSPECIFIED
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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