A new CT scan methodology to characterize a small aggregation gravel clast contained in a soft sediment matrix

Laurent Fouinat,Xavier Montet,Pierre Sabatier,Jérôme Poulenard,Jean-Louis Reyss,Fabien Arnaud

doi:10.5194/esurf-5-199-2017

Abstract

Abstract. Over the past decades, X-ray computed tomography (CT) has been increasingly applied in the geosciences community. CT scanning is a rapid, non-destructive method allowing the assessment of relative density of clasts in natural archives samples. This study focuses on the use of this method to explore instantaneous deposits as major contributors to sedimentation of high-elevation lakes in the Alps, such as the Lake Lauvitel system (western French Alps). This lake is located within a very steep valley prone to episodic flooding and features gullies ending in the lake. This variety of erosion processes leads to deposition of sedimentary layers with distinct clastic properties. We identified 18 turbidites and 15 layers of poorly sorted fine sediment associated with the presence of gravels since AD 1880. These deposits are respectively interpreted as being induced by flood and wet avalanche. This constitutes a valuable record from a region where few historical records exist. This CT scan approach is suitable for instantaneous deposit identification to reconstruct past evolution and may be applicable to a wider variety of sedimentary archives alongside existing approaches.

Highlights

At their introduction to the field around 50 years ago, X-ray radiographs were initially used to explore the internal structure of sediment cores (Bouma, 1964; Baker and Friedman, 1969) in order to optimize the opening process or even explore bioturbation structures in the sediment (Howard, 1968)
We propose a complementary method to grain size analysis to better characterize these coarse grains in a simpler, faster and non-destructive way based on the use of computed tomography (CT) scanning
Facies 1 (F1) is silty-clay, dark-brown, finely laminated layer. It is interbedded by two other facies that are almost always associated with each other: facies 2 (F2) is a normally graded bed from coarse sand to silt, sometimes with an erosive base; this facies is always associated with a thin white clay-rich layer, facies 3 (F3), on the top

Summary

Introduction

At their introduction to the field around 50 years ago, X-ray radiographs were initially used to explore the internal structure of sediment cores (Bouma, 1964; Baker and Friedman, 1969) in order to optimize the opening process or even explore bioturbation structures in the sediment (Howard, 1968). Improvements in CT scanning allowed exploration of complex sedimentary structures through 3-D reconstructions, leading to improvement compared to classic 2-D imaging (Pirlet et al, 2010; Bendle et al, 2015). Image analysis of the 3-D numerical model can be used to obtain quantitative information about selected constituents as well as volumetric information (Bolte and Cordelieres, 2006). This type of methodology was recently used to identify and quantify gypsum formation in marine sediments (Pirlet et al, 2010) as well as different sediment clast deposition in a glacio-lacustrine varved context (Bendle et al, 2015)

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Conclusion