FABRIC SHAPE AND THE INTERPRETATION OF SEDIMENTARY FABRIC DATA

The concept of fabric shape provides a powerful means of visualizing a nd analyzing data on sedimentary fabric. The shape of a fabric is defi ned in terms of the ratios between eigenvalues S-1, S-2, and S-3, deri ved using the orientation tenser method. A continuum of all possible o rthorhombic fabric shapes can be clearly represented on equilateral te rnary diagrams originally developed for the presentation of particle-s hape data. Two indices are of particular value in scaling these diagra ms: fabric isotropy (I = S-3/S-1) and fabric elongation (E = 1-(S-2/S- 1)). Together, these indices uniquely define the shape of any orthorho mbic fabric, and pro,ide a rational and quantitative basis for reconst ructing depositional and deformational processes. Equilateral ternary diagrams provide a more versatile and powerful basis for analyzing fab ric data than other eigenvalue diagrams now in use. Use of the diagram s in reconstructing processes of sediment transport and deposition is illustrated using fabric data from subglacial tills and a variety of s lope deposits.