Four diagenetic mechanisms of matrix formation were recognized in graywacke sandstones from the Visingso Group (Upper Proterozoic, southern Sweden). These mechanisms are 1) chemical alteration of detrital silicate minerals, 2) authigenesis (crystallization from pore solutions), 3) pseudoplastic flow of soft argillaceous fragments, forming pseudomatrix, and 4) alteration of pseudomatrix either through fixation or leaching of cations. Compared to the previously published studies dealing with graywacke matrix, the new contribution in the present study is 1) alteration of detrital unstable particles is shown to occur through dissolution and replacement by clay minerals, and 2) the microprobe and X-ray diffraction analyses, scanning electron and petrographic microscopes were used together in the mineralogical and textural investigation.

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