Remobilization of sand from consolidated sandstones: evidence from mixed bitumen-sand intrusions

Some sand in intrusive bodies has an origin in the disaggregation of consolidated sandstones. Evidence from the study of mixed bitumen-sand intrusions includes progressive spalling of individual grains from cemented sandstones and individual sand grains with adhering cements. Both physical forces related to rapid fluid movement and chemical dissolution may contribute to the disaggregation process. Rapid fluid flow due to hydrofracturing of an overpressured sequence is responsible for several examples of sand-bearing bitumen veins. As overpressuring is a widespread phenomenon, disaggregation of lithified sandstones may be more prevalent than hitherto appreciated. Sand may be entrapped in bitumen within vein systems cutting kilometres of stratigraphy. Fluid inclusion data from an example at Bentheim, Germany, shows that cementation of sandstone occurred at high temperatures before sand disaggregation and mobilization.