Stress state inversion in the Eastern Paris Basin, France: insight into long term rheologies and bedrock-cover (de)coupling.

@inproceedings{GunzburgerGM2012,
 abstract = { This paper presents an interpretation of the present stress state in the eastern Paris sedimentary Basin (France) based on considerations that regard the long-term limestone rheology. A comprehensive stress profile was acquired in this region, and it was determined that the minimum horizontal stress in an argillite layer is much larger than that in the under- and overlying, stiffer limestone layers, while the major horizontal stress seems almost insensitive to lithology.
In a previous study, the genesis of this intriguing stress state was modelled by considering the limestone to be elastic. However, the calculation implied the use of unrealistic mechanical characteristics for this rock (extremely low long-term elastic modulus and Poisson's ratio). From the study, it was concluded that some dissipative, viscous process of unknown origin might be at work in the limestone. Herein, we propose that the deformation micromechanism that is responsible for this time-dependent behaviour is pressure solution creep (PSC). We show that this hypothesis is mechanically realistic by adapting an existing model of PSC, which is based on the description of mass transfer within grain-to-grain contacts (dissolution, diffusion and precipitation). We deduce a set of long-term rheological characteristics for the limestone and use them in the numerical model of the stress genesis in the Paris Basin. The results show that PSC is a possible explanation for the present stresses and total strains in this region. The fact that limestone should be considered as visco-elastic over geological time scales (with a viscosity ranging between 1017 and 1021 Pa.s), and not as purely elastic, is at the core of this work. Although it is probably ubiquitous in nature, PSC is notoriously difficult to assess in the laboratory. Thus, our effort of coupling small-scale processes in a quantitative manner to large-scale deformation and in-situ measurements provides a useful tool for gaining insight into the role of PSC in the long-term behaviour of carbonated rocks and its effect on sedimentary basin evolution. },
 author = { Gunzburger, Yann },
 booktitle = { Proc. 32nd Gocad Meeting, Nancy },
 title = { Stress state inversion in the Eastern Paris Basin, France: insight into long term rheologies and bedrock-cover (de)coupling. },
 year = { 2012 }
}