Nutrient-triggered bioerosion on a giant carbonate platform masking the postextinction Famennian benthic community

Abstract

The Palliser Formation of western Canada constitutes a giant, tropical carbonate platform of Famennian age. Although now mostly composed of peloids, aggregates, intraclasts, and cortoids, a major proportion of these micritic particles originally consisted of bioclasts, primarily crinoidal, that were obliterated by bioerosion. Analogous to modern tropical environments, microendoliths may have proliferated on this platform during widespread mesotrophic conditions owing to excess nutrients derived from the developing Ellesmerian orogen in the Canadian Arctic. The orogeny was coincident with profound changes in the middle Paleozoic biosphere due to increased pedogenesis accompanying the spread of deep-rooting gymnosperms. This evolutionary event may have resulted in the disturbance of the ecological balance in epicontinental seas by causing enhanced nutrient mobilization and riverine nutrient flux. This precursor to the observed Mesozoic increase in bioerosion hides a bountiful, although low-diversity, skeleton- secreting benthos on the Famennian platform, thereby concealing the extent of the Late Devonian faunal crisis and its recovery.