Lingulide Brachiopods in Western Canadian Triassic Shallow Marine Strata: Implications for the Post-Extinction Recovery of Triassic Infaunal Communities

John-Paul Zonneveld¹, Tyler W. Beatty², and S. George Pemberton^3
1 Geological Survey of Canada, Calgary, AB
² University of Calgary, Calgary, AB
³ University of Alberta, Edmonton, AB

Lingulide brachiopods have been important infaunal constituents of marine and marginal marine depositional systems since the Early Cambrian. Their long span and wide environmental distribution is attributed, at least in part, to their tolerance of adverse environmental conditions including salinity extremes and oxygen deficiency. Their abundance in lower Triassic strata has led to the ideas that lingulides were ‘disaster taxa' (generalists that achieve great abundance and wide environmental and geographic distribution in the aftermath of mass extinctions). The regional distribution of Triassic lingulide shells and lingulide-constructed trace fossils in western Canada shows that this hypothesis is erroneous. Lingulides were important (but not dominant) components of Griesbachian (earliest Triassic) shallow marine successions. Their peak in abundance occurred during the Dienerian and Smithian (medial Early Triassic). They were important but non-dominant members of infaunal communities during the latest Early Triassic and Middle Triassic. Lingulides are ecological opportunists that survived the Permian-Triassic crisis and experienced population expansion several million years after the extinction. Post Permian-Triassic extinction lingulides do not occur in any environment in which they were not represented prior to, and after, the extinction recovery interval. This study clearly shows that the distribution of lingulide shells is a poor proxy for assessing the environmental occurrence of lingulides in ancient successions. Lingulide body fossils and Lingulichnus exhibit distinct but overlapping distributions due to differing preservational constraints on trace and body fossils as well as post-mortem transport of lingulide shells. Both datasets must be considered to accurately assess the original environmental distribution of lingulides.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005