On the Theory of Growth Faulting*: A Geomechanical Delta Model Based on Gravity Sliding

Abstract

A geomechanical delta model is presented that explains and permits quantitative reproduction of the main features associated with growth faulting. The model is based on a soil‐plasticity analysis of gravity sliding of overpressured clays and silts on very gentle delta slopes. In this analysis, the packets involved in gravity sliding —called ‘units’—are well quantified. The delta body may behave as a stack of such units (‘multi‐unit’ delta model), which can behave differently depending on such parameters as sedimentation rates, changes in lithology and compactional behaviour. Two prominent and essentially different structural expressions of the model are discussed: (a) the regularly spaced growth‐fault pattern, without recognisable toe regions; (b) the complete slide structure with a well‐developed toe region. The shapes of the roll‐over structures (particularly the positions of the crests), the thickening of the layers near the growth faults, antithetic faulting and horsetailing of growth faults can be derived from the model without the need to invoke any deeper seated mechanism in the substratum. The basic assumptions of this geomechanical model are supported by observations in Ireland and examples from literature. It may contribute to the reconstruction of the hydrocarbon migration history in a delta by accounting for the synsedimentary development of stresses and fault structures that may control hydrocarbon migration. Recently, geomechanical aspects came in focus again for the assessment of seismic amplitude anomalies in the search for hydrocarbons (Crans and Berkhout, 1979).

High-resolution record of tectonic and sedimentary processes in growth strata

“…1a) originate at crustal scale due to long-term plate movements and at smaller scales in relation with the spreading of a sedimentary cover on a dé collement layer (e.g. Edwards, 1976;Price, 1977;Coleman and Prior, 1978;Crans et al, 1980;White et al, 1986;Jackson and White, 1989;Childs et al, 1993;Doglioni et al, 1998;Dawers and Underhill, 2000;Morley et al, 2000;Back et al, 2006).…”

“…Dula, 1991;Childs et al, 1993;Hardy and McClay, 1999;Vendeville, 2005) and (3) the topography of the basement (regional and local slope) (e.g. Crans et al, 1980;Koyi, 1991;Koyi et al, 1993;Mauduit et al, 1997;Loncke et al, 2006). At higher frequencies of thousands to hundreds of thousand years the interactions between fault evolution and sedimentary process still remains less understood partly because, at these time scales, it is difficult to assess one independently of the other.…”

Reappraisal of gravity instability conditions for offshore wedges: consequences for fluid overpressures in the Niger Delta

“…Crans et al (1980) proposed an exact, analytical solution based on the slip line theory to capture listric faults for frictional, overpressured materials considering an inclined layer. Their approach applies to the extensional and compressive domains.…”

“…It applies to the extensional upslope (active) and to the compressive downslope (passive) domains but does not propose any connection between the two. The extent of the intermediate region can also be estimated following the same argument of Crans et al (1980), for an inclined layer, as presented by Mourgues et al (2009).…”

“…It applies to the extensional upslope (active) and to the compressive downslope (passive) domains but does not propose any connection between the two. The extent of the intermediate region can also be estimated following the same argument of Crans et al (1980), for an inclined layer, as presented by Mourgues et al (2009).There has been some applications of the CCW theory to fluid-saturated wedges Suppe 2007Suppe , 2014 on the Niger Delta frontal compressive region, assuming a frictional behaviour of the sediments and the detachment. It was found that the pore-fluid pressure within the detachment is 90 per cent of the lithostatic pressure (Hubbert-Rubey fluid-pressure ratio λ ∼ 0.9).…”