BOUGHT THE WORM FARM: VERMIFORM DIVERSITY AND TAPHONOMY IN THE CAMBRIAN SPENCE SHALE

The Spence Shale Member of the Langston Formation in northern Utah and southern Idaho preserves non-biomineralized fossil assemblages referred to as the Spence Shale Lagerstätte. The biota of this Lagerstätte is dominated by panarthropods, both biomineralized and soft-bodied, but also preserves diverse infaunal organisms including species of scalidophorans, annelids, lobopodians and some problematic vermiform taxa. Historically these taxa have been assumed to come from a single environment, but the Spence Shale Lagerstätte instead encompasses a variety of depositional environments ranging from shallow water carbonates to deep water dark shales, which preserve distinct assemblages of vermiform taxa. Data collected form recent field seasons, museum specimens, sedimentology, ichnology, and geochemistry provide a new view of the benthic communities of the Spence Shale and their preferred environments.

In addition, we analysed specimens from six localities using scanning electron microscopy (SEM) and integrated energy dispersive X-ray spectrometry (EDS), together with comparisons of published data. Taxa are predominantly preserved as a combination of carbonaceous compressions, iron oxide and pyrite replacement, but preservation varies between the shallower more carbonate rich locations in northern Utah and southern Idaho and the deeper water locations in the Wellsville Mountains of Utah. These variations in preservation are also linked to the quality of soft-tissue preservation in the different locations of the Spence Shale. So far, no vermiform specimens have been identified from the deepest water dark shales of the Spence Shale.