Line 2: |
Line 2: |
| | | |
| ==Shale smear factor== | | ==Shale smear factor== |
| + | <gallery mode=packed heights=300px widths=300px> |
| + | Shale Smear Factor Fig1.png|{{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.) |
| + | 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. |
| + | </gallery> |
| | | |
| 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. | | 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.<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.)]]
| |
| | | |
| # 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. |
| # 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. | | # 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. |
| # Injection smears are a local response to volume changes during faulting. Injection smear thickness is not readily predictable. | | # Injection smears are a local response to volume changes during faulting. Injection smear thickness is not readily predictable. |
− |
| |
− | [[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.<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) |