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Quarterly Journal of Engineering Geology and Hydrogeology
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Quarterly Journal of Engineering Geology and Hydrogeology; 2007; v. 40; issue.2; p. 187-192;
DOI: 10.1144/1470-9236/06-043
© 2007 Geological Society of London

Discussion

Discussion of ‘Methodology to identify badly weathering limestone using geochemistry: case study on theLower Globigerina Limestone of the Maltese Islands’ byJ. Cassar & A.J. Vella Quarterly Journal of Engineering Geology and Hydrogeology, 36, 85–96

P.A. Gatt1, J. Cassar2 & A.J. Vella3

1 Department of Civil Engineering, University of Malta, Msida, Malta (e-mail: mepcons@hotmail.com)
2 Institute for Masonry and Construction Research, University of Malta, Msida, MSD06, Malta (e-mail: joann.cassar@um.edu.mt)
3 Department of Chemistry, University of Malta, Msida MSD06, Malta (e-mail: alfred.j.vella@um.edu.mt)

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   Introduction
 
P.A. Gatt writes: The Authors offer an interesting perspective on the weathering of limestone dimension stone used for masonry in Malta, also studied by Fitzner et al. (1997) and Gatt (2007). They conclude that a single parameter, namely the difference in marginal non-carbonate content, can be used to predict the durability to weathering in the pelagic sediments of the Lower Member of the Globigerina Limestone Formation, even in freshly cut stone that does not present visual differences. A geochemical approach is used to distinguish between a problematic stone characterized by strong differential weathering with rapid loss of volume, locally known in Malta as ‘soll’ (Fig. 1), from a limestone that weathers more uniformly, known locally as ‘franka’, which is the preferred dimension stone for masonry buildings. The purpose of this discussion is to compare the stratigraphy sampled by the Authors with other works and to focus on the hypothesis linking non-carbonate content to weathering in the Globigerina Limestone Formation.


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  		Fig. 1 Weathered surface of ‘soll’ type of stone used as masonry in exterior boundary wall (locality: Valletta, Malta) showing differential weathering between burrows and matrix.

 

   Stratigraphy
 
The Authors describe the general stratigraphy as follows: ‘the Islands and submerged platform are characterised by Mesozoic sediments’. This is inconsistent with published works (e.g. Pedley 1978) that have always considered the limestone of the Maltese Islands (apart from very limited Quaternary sediments) to be exclusively of a mid- to Late Tertiary age. The limestone samples studied by the Authors . . . [Full Text of this Article]