3D seismic study of complex intra-salt deformation: An example from the Upper Permian Zechstein 3 stringer, western Dutch offshore

Abstract

Most of the information on subsurface evaporitic structures comes from 3D seismic data. However, this data only provide limited information about the internal structure of the evaporites, which is known from salt mines and salt diapir outcrops. Brittle intra-salt layers (carbonate, anhydrite, clay) of at least 10 m thickness form good reflectors in evaporites, but the structure and dynamics of such ‘stringers’ in the salt movement are poorly understood. In this study, we investigate the intra-salt Zechstein 3 (Z3) stringer from 3D seismic data in an area offshore the Netherlands. Observations show complex deformation including boudinage, folding and stacking. Reflections from thin and steep stringer parts are strongly reduced, and we present different structural models and tests of these. We compare our observations to structural models from salt mines and analogue/numerical models of intra-salt deformation. A smoothed representation of the upper surface of the stringer fragments follows the shape of Top Salt, but smaller-scale stringer geometries strongly differ from this and imply boudinage. The imaged disharmonic patterns of constrictional folds provide evidence for the complexity of the intra-salt, in agreement with observations in salt mines. This may be explained by interaction of the layered salt rheology, complex three-dimensional salt flow, different phases and styles of basement tectonics and movement of the overburden.

Enigmatic structures within salt walls of the Santos Basin—Part 1: Geometry and kinematics from 3D seismic reflection and well data

“…1A) (Jackson et al, 1990); and (iv) thick salt is typically acoustically transparent on seismic reflection data, and internal stratigraphic markers that record strain are typically poorly imaged. However, there are notable exceptions, which we discuss in Section 1.1 (Cobbold et al, 1995;Van Gent et al, 2011;Strozyk et al, 2012;Fiduk and Rowan, 2012;Jackson et al, 2014).…”

“…These data yield an excellent, hitherto underused opportunity to gain a three-dimensional understanding of the internal structure of entire salt structures and, by inference, their kinematics. For example, by using data from the Groningen Basin and Cleaver Bank High, offshore Netherlands, Van Gent et al (2011) and Strozyk et al (2012) mapped the detailed geometry of a highly reflective, thin (40e50 m) layer of claystone-carbonate-anhydrite encased in large (>15 km long), halite-dominated salt diapirs, pillows, and anticlines. They documented a range of shortening (in the form of noncylindrical buckle folds) and extensional (boudins) structures within and adjacent to salt anticlines, which they interpreted as forming due to non-plane strain during highly heterogeneous salt flow.…”

Heterogeneity of folding in Zechstein (Upper Permian) salt deposits in the Kłodawa Salt Structure, central Poland

“…This in di cates that flow and fold ing of salt beds, in fact, be gins long be fore the ini ti a tion of salt pil low or diapir ini ti ation and that prob a bly only a min ute in cli na tion of beds trig gers salt flow. Also re cently, grav ity-driven slid ing, flow and fold ing of stratiform beds have been well-doc u mented by seis mic data in salt basins lo cated on con ti nen tal slopes (Davison et al, 2012;Fiduk and Ro wan, 2012;Fort and Brun, 2012;Adam and Krezsek, 2012;Quirk et al, 2012;Strozyk et al, 2012). These data show that in clined salt beds flow down wards in re sponse to grav ity and sed i ment load ing and that the grav ity-driven slid ing and flow leads to de for ma tion of the evaporite se quence as well as an in crease in its total thick ness down the slope, prior to diapirism.…”

The effect of salt in dilatant faults on rates and magnitudes of induced seismicity – first results building on the geological setting of the Groningen Rotliegend reservoirs

“…r ab , where f d ab is the force on particle 'a' due to the dashpot interaction with a particle 'b', r ab is the current distance between the particles, d ab is a measure of the size of the interaction, v ab is the relative velocity of the particles and A is a material constant representing a microscopic viscosity (eqn 3 in Abe & Urai, 2012).…”