Mesoscale Fractures as Palaeostress Indicators: A Case Study from Cauvery Basin

This paper presents the results of field studies, and palaeostress analyses of the mesoscale fractures and veins in Cauvery basin. It shows that different sedimentary sequences (119 - 64 Ma) are cut by tensile structures that belong to two successive phases of post-Palaeocene brittle tectonics: (i) an early phase during which bedding parallel fractures and veins were developed due to horizontally directed maximum compression and vertical extension, and (ii) a late phase of hydraulic fracturing in a tectonic regime of vertically directed maximum compression. Dynamic analyses imply triaxial and axial compression deviatoric states of palaeostress during first and second phases of fracturing, respectively. Very high pore-fluid pressure and low differential stress, during the second phase of fracturing, resulted into hydraulic brecciation as a consequence of simultaneous extension in different orientations. We suggest that the development of the mesoscale extensional (mode I) fractures in Cauvery basin is due to reactivation of large-scale normal faults in the basement rocks.