TY - JOUR

T1 - Three-dimensional geometry and fabric of shear deformation-bands in unconsolidated Pleistocene sediments

AU - Brandes, Christian

AU - Tanner, David C.

N1 - Funding Information: We would like to thank the owners of the Freden sand pit for permission to enter their property. Financial support by the MWK Niedersachsen ( 11.2-76202-17-7/08 ) is gratefully acknowledged. We would like to thank Claudia Broi for help in the field and preparation of the 3D model and figures. Jens Walter is thanked for helping to carry out grain-size analysis. Jutta Winsemann, Franz Binot and Andreas Mulch are gratefully thanked for discussion. We are grateful to Anita Torabi and two anonymous reviewers for their helpful comments on the manuscript and Haakon Fossen and two anonymous reviewers of earlier transcripts of this paper. Midland Valley Exploration Ltd. is thanked for the use of their software Move 2009.1.

PY - 2012/1/20

Y1 - 2012/1/20

N2 - We present an outcrop-based study on the 3D geometry and fabric of shear deformation-bands that developed in Middle Pleistocene, unconsolidated, glaciolacustrine delta sands in northern Germany. With a three dimensional model of a 3.38. m 3; outcrop we demonstrate deformation band geometries, analysis of band thickness and along-strike juxtaposition maps of beds against the deformation bands. The parallel thicknesses of the shear deformation-bands ranges from 0 to 8. cm, with a mean of 1.5. cm. Analysis of along-strike band displacement of intersecting shear deformation-bands proves the true displacement vector is close to dip-slip movement. The shear deformation-bands compensated a large lateral extension of ca. 10-20%. Though the deformation is unevenly distributed, this is a very high amount of deformation and this has wide implications when upscaled to the whole outcrop or locality. Grain size within the shear deformation-bands is identical to the grain-size distribution of the parent sediment. Conventional Fry analysis of grains in the shear deformation-bands shows strain ratios of 1.4. This, however, is an artifact of bulk grain-shape, since a normalized Fry plot shows strain close to unity. We observe a two-stage calcite overgrowth on the grains of the deformation band (radial sparite followed by micrite). We thus propose grain-boundary sliding (possibly aided by calcite-rich fluids) to be the dominant deformation mechanism. The deformation bands are very likely the product of young basement tectonics and may be related to movements in the crest of a salt anticline. In the study area, the observation of young basement tectonics is a novelty.

AB - We present an outcrop-based study on the 3D geometry and fabric of shear deformation-bands that developed in Middle Pleistocene, unconsolidated, glaciolacustrine delta sands in northern Germany. With a three dimensional model of a 3.38. m 3; outcrop we demonstrate deformation band geometries, analysis of band thickness and along-strike juxtaposition maps of beds against the deformation bands. The parallel thicknesses of the shear deformation-bands ranges from 0 to 8. cm, with a mean of 1.5. cm. Analysis of along-strike band displacement of intersecting shear deformation-bands proves the true displacement vector is close to dip-slip movement. The shear deformation-bands compensated a large lateral extension of ca. 10-20%. Though the deformation is unevenly distributed, this is a very high amount of deformation and this has wide implications when upscaled to the whole outcrop or locality. Grain size within the shear deformation-bands is identical to the grain-size distribution of the parent sediment. Conventional Fry analysis of grains in the shear deformation-bands shows strain ratios of 1.4. This, however, is an artifact of bulk grain-shape, since a normalized Fry plot shows strain close to unity. We observe a two-stage calcite overgrowth on the grains of the deformation band (radial sparite followed by micrite). We thus propose grain-boundary sliding (possibly aided by calcite-rich fluids) to be the dominant deformation mechanism. The deformation bands are very likely the product of young basement tectonics and may be related to movements in the crest of a salt anticline. In the study area, the observation of young basement tectonics is a novelty.

KW - 3d geometry

KW - Deformation band

KW - Leine Valley

KW - Normalized fry-plots

UR - http://www.scopus.com/inward/record.url?scp=84855858379&partnerID=8YFLogxK

U2 - 10.1016/j.tecto.2011.11.012

DO - 10.1016/j.tecto.2011.11.012

M3 - Article

AN - SCOPUS:84855858379

VL - 518-521

SP - 84

EP - 92

JO - TECTONOPHYSICS

JF - TECTONOPHYSICS

SN - 0040-1951

ER -