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| Titel |
3D analysis of deformation bands in unconsolidated Pleistocene sediments |
| VerfasserIn |
David C. Tanner, Christian Brandes |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250038462
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| Zusammenfassung |
| Deformation bands are planar structural elements that occur in porous sandstones, even in the
unconsolidated state (e.g. Aydin, 1978, Fossen et al., 2007). Whereas faults are discrete
surfaces, deformation bands are much thicker, tabular zones of continuous displacement
(Draganits et al. 2005). They have attracted much attention in the past because of their low
permeabilities and their potential impact on fluid flow in sedimentary basins (e.g. Fossen &
Bale, 2007).
We present an outcrop-based study on the 3D geometry and strain of deformation band
faults, which developed in Pleistocene unconsolidated sands in northern Germany.
We digitally photographed a 150 Ã 150 cm square, near-vertical outcrop wall in a
quarry, against an orthogonal scale. Then 15 cm of sand was scraped away and the
procedure repeated. A total of ten sections were procured. The photographs were
interpreted for upper and lower boundaries of the deformation band faults and distinctive
stratigraphic horizons. The sections were then imported into Move2009.1 (Midland
Valley Exploration Ltd, 2009) with the correct orientation and scale. Using the
Move2009.1 software, we analysed the thickness of the deformation band faults,
along-strike displacement of beds along the faults, and the total extension caused by
faulting.
The three-dimensional model is cut by a set of nine major deformation band faults, all
with a normal sense of displacement; one set of six faults strike SE–NW, dipping NE by ca.
50o, the other set of three faults strike NNE–SSW, dipping WSW by ca. 45o. The former
cross-cut the latter, thus their age relationship is shown. In the dip direction the faults are
straight, but slightly arcuate in their strike direction. We identified seven distinct
stratigraphic horizons, from which we were able to analyse along-strike displacement and
total extension due to faulting. The three dimensional model shows that thickness
of the deformation band faults varies elliptically and ranges from zero to 4.5 cm.
Analysis of along-strike fault displacement proves that fault thickness is inversely
proportional to fault displacement. We calculated horizontal extension along three
sections, perpendicular to the strike of the faults. Because fault displacement varies so
much along-strike, extension ranges from 30 to 60%. Clearly the deformation is
unevenly distributed on this scale. Nevertheless, these are very high amounts of
deformation and this has wide implications when upscaled to the whole outcrop or
locality.
Aydin, A., 1978, Small faults formed a deformation bands in sandstone: Pure and Applied
Geophysics 116, 913–930.
Draganits, E., Grasemann, B. & Hager, C., 2005, Conjugate deformation band faults in
the Lower Devonian Muth Formation (Tethyan Zone, NW India): evidence for
pre-Himalayan deformation structures. Geological Magazine 142, 765–781.
Fossen, H. & Bale, A., 2007, Deformation bands and their influence on fluid flow:
Association of American Petroleum Geologists Bulletin 91, 1685–1700.
Fossen, H., Schultz, R.A., Shipton, Z.K. & Mair, K., 2007, Deformation bands in
sandstone: a review: Journal of the Geological Society, 164, 755–769.
Midland Valley Exploration Ltd, 2009, Move2009.1 suite: Glasgow. |
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