The Middle Ordovician Gongwushu Formation

distributed in the Zhuozishan area

Inner Mongolia

consists chiefly of greycoloured thin-bed limestones interbedded with shales in the lower part and thin-bed siltstones in the upper.It also yields abundant trace fossils

some planktonic organism fossils.In terms of its swhmentary characteristics

trace fossil assemblages and the related body fossils

it is suggested that the upper thin-bed siltstones should be sandy contourites

and its sedimentary characteristics are in accordance with the criteria proposed by Hollister and Heezen

Lovell and Stow.The main grain parameters are σ

1

:0.45-0.57;SK

1

:(-) 0.599;K

g

:3.089.Trace fossils which co-exist with the contourites are ichnogenus Helminthopsis and Paleodictyon.Boby fossils which occurred in the formation are graptolites

small thin-shelled brachiopds and deep-coldwater conodents.The sedimentary environment of the formation is belived to be a continental slope with water depth no less than 200-600 metrs during the deposition process.