Deep tiering Planolites isp. in the oolitic limestones of Cambrian Series 3, western Henan, China

Abstract

Planolites isp. is teeming within the oolitic limestone units in the Changhsia Formation of Cambrian Series 3 in western Henan, and its morphology is characterized by a horizontal or low-angle oblique curved cylindrical tube. These burrows occur on a easily migrating sedimentary substrate (oolitic beach), but have no lining walls and are filled with micritic, indicating that the Planolites isp. burrows were formed in a low energy microenvironment under the background of high energy oolitic shoals, where they are not susceptible to turbulent flow. Detailed analysis of the Planolites isp. burrows suggest that the trace makers should be a detritus feeder in deep tieringof sediments. Microscopic observation of ooids and the filling of burrows shows that there are some cyanobacterial filaments in the sediments around the ooids and bit of masticated and partially digested cyanobacterial filamentous fragments within the burrow infilling. indicating the trace makers of Planolites isp. feeds on the cyanobacteriabetween the ooids. The emergence of this kind of deep tiering trace fossils and the unique feeding mode represented by them reveal a more complex survival strategy than that of benthic organisms in the early Cambrian, which provides valuable materials for the study of the evolution of benthic organisms during the Cambrian Explosion.