Selective dolomitization of stromatolites occurs in the Boundary Member of the Schooler Creek Formation (Triassic) of British Columbia, Canada. The member is as thick as 34 ft and is a repetitive cyclic sequence of stromatolite-pelmicrite-micrite-pelmicrite-stromatolite.

Interpreted depositional sites are: (1) micrite--local basin center; (2) pelmicrite--nearshore to low intertidal; (3) stromatolite--intertidal; and (4) anhydrite beds--restricted intertidal. Lateral change within the member is slight except for coalescing of units toward the paleoshoreline. Landward, within the major stromatolitic interval, there are tongues of anhydrite; seaward there are tongues of pelmicrite containing composite ooliths.

The stromatolites and beds in contact with them are dolomite with abundant large anhydrite crystals and clots of crystals. The rest of the member is limestone, slightly dolomitic in part, with sparse euhedral anhydrite crystals. The amount of anhydrite and dolomite increases toward the stromatolitic intervals.

Three conclusions are drawn: (1) the association of anhydrite clots and crystals with desiccation features indicates that diagenesis was partly penecontemporaneous with stromatolite formation, (2) dolomite in the beds adjacent to the stromatolitic intervals indicates that some dolomitization occurred after shallow burial of the stromatolite, and (3) selective dolomitization of stromatolitic intervals suggests that these intervals originally had relatively high permeability. Brines from evaporating pans in the landward area refluxed through the permeable zones and dolomitized the stromatolites.

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