DEFORMATION BANDS IN POORLY SORTED, POORLY LITHIFIED AND SHALLOWLY BURIED SANDSTONE ALONG THE SEIYAL FAULT, WESTERN DESERT, EGYPT
Differentially decompacting and backstripping the previously overlying lithologies using a 1-D Airy model allowed a range of burial conditions to be calculated for the Taref Member from the Late Cretaceous to Middle Eocene. The minimum and maximum thicknesses, as well as percentages of the lithologies present in the overlying stratigraphy, were determined through a literature search of local geology reports containing stratigraphic sections. Three unconformities were identified in the stratigraphy, two of which occurred during regional uplift and were therefore erosional.
Through use of the computer program OSX Backstrip v3.2, it is estimated that the Taref Member was buried to a maximum depth of 844 m with an error of +/- 340 m at 49 Ma. This large error range is due to uncertainties about the amount of erosion during formation of unconformities, the variations in porosity of chalk within the section, and the facies changes affecting stratigraphic thickness of the overburden. The estimated maximum burial depth is at the lower end of depths typically quoted for the formation of cataclastic deformation bands in consolidated rock (~1-3 km). The burial curve suggests that the deformation bands likely formed between 49 and 23 Ma, when the sandstone was buried to ~1 km.