Abstract:

All the dawsonite-bearing sandstones around the world are rich in feldspar, they were reported with the type of debris-feldspar sandstone, feldspathic lithic sandstone and arkose. In order to reveal the relationship between dawsonite and feldspar, a series of analysis methods (polarizing microscope, SEM, CL) are taken to do the research on the petrologic charasteristics of the dawsonite-bearing sandstones in Honggang oil field, Songliao basin. The occurances of dawsonite are included as pore-filling and replacement. While for plagioclase, it is replaced by dawsonite more intenser than K-feldspar. Normally, dawsonite grows into the feldspar along the twin, sometimes even totally replaced the plagioclase, appearing as pseudomorph. The content of dawsonite and feldspar has a negative correlation, and the corrosion of feldspar can provide sodium and aluminium iron for the generation of dawsonite. As the differences in thermodynamic properties, the rate of dissolution for K-feldspar is significant lower than plagioclase, so plagioclase makes more iron contribution for dawsonite generated than k-feldspar.

Key words: dawsonite, feldspar-rich sandstone, sodium iron, aluminium iron, plagioclase