Geometry of half‐grabens containing a mid‐level viscous décollement

Abstract

In this work, we explore by means of analogue models how different basin‐bounding fault geometries and thickness of a viscous layer within the otherwise brittle pre‐rift sequence influence the deformation and sedimentary patterns of basins related to extension. The experimental device consists of a rigid wooden basement in the footwall to simulate a listric fault. The hangingwall consists of a sequence of pre‐rift deposits, including the shallow interlayered viscous layer, and a syn‐rift sequence deposited at constant intervals during extension. Two different geometries exist of listric normal faults, dip at 30 and 60° at surface. This imposes different geometries in the hangingwall anticlines and their associated sedimentary basins. A strong contrast exists between models with and without a viscous layer. With a viscous décollement, areas near the main basement fault show a wide normal drag and the hangingwall basin is gently synclinal, with dips in the fault side progressively shallowing upwards. A secondary roll‐over structure appears in some of the models. Other structures are: (1) reverse faults dipping steeply towards the main fault, (2) antithetic faults in the footwall, appearing only in models with the 30° dipping fault and silicone‐level thicknesses of 1 and 1.5 cm and (3) listric normal faults linked to the termination of the detachment level opposite to the main fault, with significant thickness changes in the syn‐tectonic units. The experiments demonstrate the importance of detachment level in conditioning the geometry of extensional sedimentary basins and the possibility of syncline basin geometries associated with a main basement fault. Comparison with several basins with half‐graben geometries containing a mid‐level décollement supports the experimental results and constrains their interpretation.

The role of salt layers in the hangingwall deformation of kinked-planar extensional faults: Insights from 3D analogue models and comparison with the Parentis Basin

“…Most of these works have determined that the presence of silicone leads to the formation of extensional forced folds above active normal planar faults (Jackson and Vendeville, 1994;Vendeville and Jackson, 1992;Withjack and Callaway, 2000) (Fig. 1C and 1D) and inhibits the upward propagation of synthetic and antithetic faults developed in the sub-silicone hangingwall accommodation zones (Durcanin, 2009;Soto et al, 2007). In addition to this, it is common that the development of faults and diapirs in the brittle overburden results from the polymer lateral flow (Dooley et al, 2004(Dooley et al, , 2005 (Fig.…”

“…They have also established the main parameters controlling the deformation style of the supra-silicone materials during basement-involved extension. These include: 1) the geometry of the basement faults; 2) the thickness of the viscous layer; 3) the thickness and the strength of the overburden; 4) the amount of slip along the basin bounding faults, and 5) the ratio between rates of sedimentation and extension (Jackson and Vendeville, 1994;Soto et al, 2007;Vendeville and Jackson, 1992;Withjack and Callaway, 2000). Tectonophysics 636 (2014) [338][339][340][341][342][343][344][345][346][347][348][349][350] However, almost all of these previous works only have dealt with a constant thickness pre-kinematic silicone layer extending over the entire model or hangingwall block.…”

Probable palaeogeographic influences of the Lower Cretaceous Iberian rifting phase in the Eastern Cameros Basin (Spain) on dinosaur trackway orientations

“…Two major models vie to explain the tectonic rift-basin nature of the Cameros Basin: model 1 involves an extensional-ramp basin formed over a roughly south-dipping ramp in a deep subhorizontal extensional fault located in the basement Guimerà et al, 1995), while model 2 involves a half-graben basin over a shallow detachment level (Soto et al, 2007) (Type 1 of Withjack et al (2002)). In fact, both theories agree with a synclinal basin developed over the hanging-wall trough, with no high footwall scarp.…”

Tectonic inversion of salt-detached ramp-syncline basins as illustrated by analog modeling and kinematic restoration

“…The dry sand was chosen to simulate the brittle deformation of upper crustal sedimentary rocks (Horsfield, 1977;McClay, 1990), and the PDMS polymer was used as our salt analog (Weijermars, 1986), as in most analog modeling studies Nalpas and Brun, 1993;Vendeville et al, 1995;Withjack and Callaway, 2000;Dooley et al, 2005;Soto et al, 2007;Ferrer et al, 2014Ferrer et al, , 2016. Silica sand has a Mohr-Coulomb behavior at moderate values of normal stress, and its mechanical properties were measured using a ring shear tester at the Fault Dynamics Research Group Laboratory.…”

“…For example, Roure et al (1992) and McClay (1990) use a prekinematic sand pack (an analog of brittle materials in nature) over a rigid wooden footwall block and a plastic sheet (used to reproduce the fault geometry and fault motion) to study the formation of ramp synclines. Soto et al (2007) and Ferrer et al (2014) follow the previous technique, and they use different fault geometries -listric, ramp-flat listric, planar, and kinked -but they also tested the role of a shallow Figure 1. Conceptual models of (a) a ramp syncline developed in a salt-free extensional tectonic system, modified from McClay (1990), (b) a minibasin developed in a a salt tectonic system, and (c) a salt-detached ramp-syncline basin developed in an extensional salt tectonic system, modified from Ferrer et al (2016).…”