MID CAMBRIAN GOGIID MIGRATION BETWEEN THE SOUTH CHINA PLATE AND LAURENTIA BY WAY OF SIBERIA

Gogiids (Eocrinoidea, Blastozoa, Echinodermata) are a significant but irregularly geographically scattered throughout much of the Cambrian especially in upper Stage 4 and Stage 5. They seem to have originated on the deeper shelf and upper slope of the South China Plate (SC) and are scattered globally in similar siliciclastic settings, especially so in western Laurentia (L) (but also e.g., in Prague Basin (PB), or Iberia). South China gogiids are the most numerous and primitive and commonly have polyplated attachment discs, variously platted polyplated stems, thecae and spiral or straight alternatingly biserial brachioles. Many of these characters are shared with Laurentian gogiids but are generally more derived. Migration appears to uni-directional from South China to Laurentia: South Chinese species generally have wider food grooves.>0.5 mm, Laurentian species are narrower <0.5 mm suggesting a more specialized dietary preference and may explain the apparent lack of reverse migration. Between these two widely spaced regions gogiids are known only from the Siligir Formation (Upper Stage 5?) in the Tyung River (tributary of the Lena River) valley in north central Siberia. The material is fragmentary, and its occurrence is highly atypical in that it is found in fore reef to in-reef dolomitized algal limestones of a barrier reef complex. Water depth is estimated to have been no more than 40 meters. This is, hitherto, an unknown environmental setting for gogiids. Attachment discs are significantly smaller than those in South China or Laurentia and disc plating is poorly defined. Attachment appears to be by direct carbonate cementation to a relatively firm carbonate substrate. The attached stems are similar to species like Sinoeocrinus lui (SC) or Gogia palmeri (L). Sprocket-like thecal plates are associated with the stems and are similar to S. lui . The most common remains are holomeric stem fragments are and resemble those of Akadocrinus jani (PB) which are commonly found in deeper water siliciclastics. The Siberian specimens share a shallower, higher energy, carbonate rich environment that is similar to that of some younger upper Cambrian gogiids and gogiid derivatives from other parts of the earth.