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The Middle Devonian of the Stanford Range, British Columbia, is separated into a lower, gray, light gray, and locally red-weathering sandy limestone, dolomite, and sandstone formation laterally equivalent to the Burnais gypsum and an upper fossiliferous brown limestone and dolomite, the Harrogate formation, both of which are described by Belyea and Norford (in press).
The lower formation consists predominantly of cryptograined silty to sandy limestone, dolomite, sandstone, and breccias. Beds 2 inches to 2 feet thick are separated by undulatory surfaces, locally channelled. The carbonates were probably deposited as ooze, some of the dolomite being primary or early diagenetic. Post-depositional changes include micro-brecciation, slump structures, burrowing in plastic carbonate, and desiccation cracks filled by calcite or hematite. Advancing dolomitization is marked by growth of euhedral rhombs, commonly with a nucleus of dusty material, pyrite, or spores. Increase in number and size of rhombs results in a crystalline grain growth mosaic. Pellets, bahamiths, detrital grains, and older fabrics are partly or completely destroyed in the process. Internal cavities and fractures are filled by crystalline (granular) cement and drusy growth. Quartz grains are extensively corroded by carbonate, and late tension cracks are filled by quartz and carbonate. Ostracods and charaphytes are common in some beds. This rock unit, correlative with the Burnais gypsum, is interpreted as the deposit of a shallow water, near-shore environment, periodically exposed, that received drainage from an early Paleozoic terrane of carbonates and clastics.
The overlying Harrogate is dark brown, mostly aphanitic, limestone and finely crystalline dolomite. Post-depositional effects have resulted in development of grain-growth mosaic and drusy growth. Deposition took place in deeper water than the lower unit but subject to wave or current action; lack of oxidation due to abundance of organic growth is suggested as the cause of dark color.
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