Firmground Zoophycos in the Lower Cretaceous viking formation, Alberta: A distal expression of the Glossifungites ichnofacies

The substrate-controlled Glossifungites ichnofacies is a firmground suite o f trace fossils that commonly demarcates erosional discontinuities in sedim entary successions. The Glossifungites ichnofacies typically is characteriz ed by biogenic structures that are vertical to subvertical, sharp-walled un lined and commonly passively infilled. The structures hitherto have been re stricted to permanent or semi-permanent domiciles, and predominantly to ver tical to subvertical burrows of suspension-feeding organisms. Several cores of the late Albian (Lower Cretaceous) Viking Formation from t he Hamilton Lake Field of Alberta, Canada contain an. atypical Glossifungit es ichnofacies dominated by the foraging, probing and deposit-feeding/ dwel ling structures of firmground Thalassinoides, Rhizocorallium, and Zoophycos . The Thalassinoides are passively infilled with coarse grains of sand and chert granules. Rhizocorallium displays active stages of infill, although t he final, horizontal U-shaped tube is passively filled. The Zoophycos, howe ver, demonstrates active infill manifest by chert granules and coarse sand distributed in the spreite, and this is a departure from the normal express ion of the Glossifungites ichnofacies. The firmground structures subtend from the regional stratigraphic discontin uity BD4, excavated into black, silt and sand-poor offshore and shelf mudst ones. BD4 is interpreted to reflect a transgressively modified sequence bou ndary. Most Zoophycos, Thalassinoides, and Rhizocorallium penetrate no deep er than 3-4 cm below the discontinuity into the underlying mudstones. Where BD4 overlies a sandier substrate, firmground Zoophycos are not present wit hin the suite. The facies directly overlying BD4 consist of fining-upward, pebble-, granul e-, and very coarse-grained sandbearing, thoroughly burrowed muddy sandston es to sandy mudstones, typically 5-25 cm thick. This basal transgressive la g contains Teichichnus, Planolites, Palaeophycus, Diplocraterion, Chondrite s and rare Helminthopsis, and is the source of the coarse-grained material incorporated into the fill of the firmground ichnogenera. The granule beari ng sanely mudstones overlying the transgressive lag contain abundant Teichi chnus, Planolites, Helminthopsis, Anconichnus, Chondrites, and Terebellina, and reflect rapid deepening to proximal offshore conditions. Progressive d eepening is recorded in the accumulation, of distal off- shore and shelf mu dstones of the late Albian Westgate Formation. Although excavation of BD4 occurred above fairweather Leave base, its colon ization occurred under much lower energy conditions. Within distal softgrou nd settings, ichnogenera capable of deeply penetrating muddy substrates are largely restricted to Zoophycos, Thalassinoides, Rhizocorallium, and Chond rites. These ichnogenera constitute forms capable of being excavated, albei t shallowly, within a firm substrate. This is a low energy, distal expressi on of the Glossifungites ichnofacies.