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Cataclastic Faulting and Cementation Interplay in Shallow Porous Sandstones - Insight from a Groundwater Context
- Publisher: European Association of Geoscientists & Engineers
- Source: Conference Proceedings, Fourth International Conference on Fault and Top Seals, Sep 2015, cp-462-00018
- ISBN: 978-94-6282-164-4
Abstract
The understanding of the interplay between fault zone cataclasis and cementation is important since both processes can reduce the permeability of faults in porous sandstones significantly. The case of fault cementation in high-porosity sandstone reservoirs at shallow depth (<2 km; T° <80° C) has almost never been investigated. The macro- and microscopic analysis of a fault zone in the porous Cenomanian quartz arenite sands of Provence (France) shows that silica diagenesis occurs in the most intensely deformed cataclastic parts of the fault zone. This fault zone contains clusters of shear bands and 19 to 48% of its thickness is occupied by low-porosity silicified cataclastic structures. The analysis of the alteration profile around the fault zone reveals the presence of groundwater silcretes in the form of tabular, tightly silicified sandstone bodies. Cold-cathodoluminescence microscopy analyses of the silica cements (of the fault and the silcrete) tend to confirm the groundwater origin of the silica cements from diagenetic processes. This study therefore shows that silica cementation can occur in a fault zone in a shallow context of groundwater silcrete. Consequently, its sealing capacity could be acquired potentially early in the burial history of a sandstone reservoir.