Ichnology of the upper Toad and lower Liard formations, northeastern British Columbia: implications for infaunal recovery after the Permian- Triassic mass extinction
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Abstract
The Middle Triassic upper Toad and lower Liard formations at Williston Lake in northwestern British Columbia contain a suite of highly diverse ichnofossils. The environmental distribution of the ichnofossils is wide, ranging from marine offshore to upper shoreface. Compared with the Lower Triassic ichnofossils in northeastern British Columbia, ichnofossils in the Toad-Liard interval are larger and contain more complicated tiering relationships. Despite this difference, offshore sediments in the Middle Triassic include less diverse ichnofossils with simple tiering relationships. Therefore, except in offshore environments, the bottom water condition in the Middle Triassic was healthy and habitable, unlike the Lower Triassic. Moreover, the Middle Triassic ichnology in the studied interval suggests that marine ichnofacies models are applicable other than offshore ichnofossils. This implies that recovery after the end-Permian extinction was environmentally and faunally incomplete in the Middle Triassic of the study area. Ichnology, therefore, is useful for studies of post-extinction recovery. !