Changes

==Shale smear factor==

==Shale smear factor==

Lindsay et al.<ref name=Lindsay>Lindsay, N. G., F. C. Murphy, J. J. Walsh, and J. Watterson, 1993, Outcrop studies of shale smear on fault surfaces: International Association of Sedimentologists Special Publication 15,  p. 113-123.</ref> described outcrop studies of shale smears in a Carboniferous fluvio-deltaic sequence. In contrast to the sequence described by Weber et al. (1978), these rocks were lithified at the time of faulting (burial depth about 2 km). Lindsay et al. (1993) recognized three types of shale smear: shear, abrasion, and injection.

Lindsay et al.<ref name=Lindsay>Lindsay, N. G., F. C. Murphy, J. J. Walsh, and J. Watterson, 1993, Outcrop studies of shale smear on fault surfaces: International Association of Sedimentologists Special Publication 15,  p. 113-123.</ref> described outcrop studies of shale smears in a Carboniferous fluvio-deltaic sequence. In contrast to the sequence described by Weber et al.,<ref name=Weber /> these rocks were lithified at the time of faulting (burial depth about 2 km). Lindsay et al.<ref name=Lindsay /> recognized three types of shale smear: shear, abrasion, and injection.

[[File:Shale Smear Factor Fig1.png|thumb|300px|{{figure number|1}}Field example of clay smears separating sandstones from Frechen lignite mines, Germany (Modified from Weber et al., 1978). Note tapering of clay (black) away from the source bed and the compound nature of the clay smear in the fault zone. (No scale on original figure.)]]

[[File:Shale Smear Factor Fig1.png|thumb|300px|{{figure number|1}}Field example of clay smears separating sandstones from Frechen lignite mines, Germany (Modified from Weber et al.<ref name=Weber />). Note tapering of clay (black) away from the source bed and the compound nature of the clay smear in the fault zone. (No scale on original figure.)]]

(1) Shear smears are analogous to those described by Weber et al.<ref name=Weber>Weber, K. J., G. Mandl, W. F. Pilaar, F. Lehner, and R. G. Precious, 1978, The role of faults in hydrocarbon migration and trapping in Nigerian growth fault structures: Offshore Technology Conference 10, paper OTC 3356, p. 2643-2653.</ref>([[:File:Shale Smear Factor Fig1.png|Figure 1]]). The thicknesses of the smears generally decrease with distance from the source bed, reaching a minimum in the region midway between the hanging-wall and footwall bed terminations.

# Shear smears are analogous to those described by Weber et al.<ref name=Weber>Weber, K. J., G. Mandl, W. F. Pilaar, F. Lehner, and R. G. Precious, 1978, The role of faults in hydrocarbon migration and trapping in Nigerian growth fault structures: Offshore Technology Conference 10, paper OTC 3356, p. 2643-2653.</ref>([[:File:Shale Smear Factor Fig1.png|Figure 1]]). The thicknesses of the smears generally decrease with distance from the source bed, reaching a minimum in the region midway between the hanging-wall and footwall bed terminations.

# Injection smears are a local response to volume changes during faulting. Injection smear thickness is not readily predictable.  

(2) Abrasion smears, which are the commonest type in this lithified sequence, comprise a wafer-thin veneer that is abraded by a sandstone wall-rock as it slips past a shale bed. These smears tend to be thickest when derived from thicker source layers and when the fault throw is small. Larger throws tend to erode the shale veneer.

[[File:Shale-smear-factor-fig2.png|thumb|300px|{{Figure number|2}}Figure 2-Smear factor algorithms for estimating likelihood of clay smear on a fault plane. (a) Clay smear potential (CSP) (Bouvier et al., 1989; Fulljames et al., 1996) given by the square of source-bed thickness divided by smear distance; (b) generalized smear factor, given by source-bed thickness divided by smear distance, with variable exponents; (c) shale smear factor (SSF) (Lindsay et al., 1993) given by fault throw divided by source-bed thickness. Methods (a) and (b) model the distance-tapering of shear-type smears, whereas method (c) models the form of abrasion smears.]]

Lindsay et al.<ref name=Lindsay /> proposed a shale smear factor to constrain the likelihood of shale smear continuity. Based on their observations of abrasion smears in a lithified sequence, they define the shale smear factor (SSF) as (see Figure 2c)

 

Lindsay et al. (1993) proposed a shale smear factor to constrain the likelihood of shale smear continuity. Based on their observations of abrasion smears in a lithified sequence, they define the shale smear factor (SSF) as (see Figure 2c)

SSF = fault throw/shale layer thickness

SSF = fault throw/shale layer thickness

The shale smear factor remains constant between the offset terminations because it does not depend on smear distance (although lateral variations in fault throw would have a corresponding effect on the calculated SSF). SSF thus models the profile of abrasion-type smears. From a study of 80 faults (excluding composite smears), Lindsay et al. (1993) concluded that shale smears may become incomplete for an SSF greater than 7. Smaller values of SSF are more likely to correspond to continuous smears and therefore to a sealing layer on the fault surface. The values of SSF are not additive for compound smears because thin shales give higher SSF and dominate the sum. In such cases, a simple application of SSF values would take the minimum value (most sealing) from the relevant shale beds at that point on the fault.

The shale smear factor remains constant between the offset terminations because it does not depend on smear distance (although lateral variations in fault throw would have a corresponding effect on the calculated SSF). SSF thus models the profile of abrasion-type smears. From a study of 80 faults (excluding composite smears), Lindsay et al. (1993) concluded that shale smears may become incomplete for an SSF greater than 7. Smaller values of SSF are more likely to correspond to continuous smears and therefore to a sealing layer on the fault surface. The values of SSF are not additive for compound smears because thin shales give higher SSF and dominate the sum. In such cases, a simple application of SSF values would take the minimum value (most sealing) from the relevant shale beds at that point on the fault.

==Shale gouge ratio (SGR)==

==Shale gouge ratio (SGR)==