BURGESS SHALE-TYPE PRESERVATION OF BOTH NON-MINERALIZING AND SHELLY CAMBRIAN ORGANISMS FROM THE MACKENZIE MOUNTAINS, NORTHWESTERN CANADA

Lower to Middle Cambrian shales of the Mount Cap Formation in the Mack enzie Mountains, northwestern Canada, host a variety of Burgess Shale- type macrofossils, including anomalocarid claws, several taxa of bival ved arthropod, articulated hyolithids, and articulated chancelloriids. Hydrofluoric acid processing has also yielded a broad range of organi c-walled fossils, most of which are derived from forms more typically known as shelly fossils; e.g., trilobites, inarticulate brachiopods, s mall shelly fossils (SSF), hyolithids, and chancelloriids. Organic-wal led hyolithids include conchs, opercula and helens; the proximal artic ulation of the helens is erosive, suggesting that they were formed ''i nstantaneously'' and periodically replaced. Organic-walled chancellori id sclerites exhibit a polygonal surface texture and an inner ''pith'' of dark granular material with distally oriented conoidal divisions; such a pattern is similar to that seen in the fibers of some modern ho rny sponges and points to a poriferan relationship for the chancellori ids. The robust nature but minimal relief of most of these fossils sug gests that primary biomineralization was minimal.