The Wheeler Formation in the Drum Mountains represents the transition between shoal and deeper open-shelf environments. Lithologic evidence suggests continuous deposition and frequent oscillation of lithotopes. The following facies can be recognized: (1) intra-shoal basin with mottled and thin-bedded intrasparites; (2) shoal with trilobite biosparites; (3) deeper open-shelf rhythmite consisting of thin-bedded pelsparite interbedded with fissile calcareous shale or argillaceous partings; and (4) deeper open-shelf shale.

Faunal assemblages and types of fossil preservation further support the interpretation of a transition between shoal and open-shelf environments. Shallower facies are dominated by assemblages of diverse, probably benthic, nonagnostid trilobites, whereas the deeper facies are dominated by pelagic agnostid trilobites. In the shoal facies, trilobites are commonly disarticulated and are found in a sparry matrix, whereas rhythmites of the open-shelf facies commonly contain articulated specimens.

End_of_Article - Last_Page 963------------