Fig. 4

Different grades of Thalassinoides bioturbation in the Zhushadong Formation of the Guankou section. a Thalassinoides representing multi-layer colonizers, cross-section view. In the more intensely bioturbated beds, bedding-parallel networks are linked by vertical shafts; b Intense bioturbation in cross section. Penetration of individual burrow shafts is up to 3.7 cm, the bioturbated zone is amalgamated forming up to a 30-cm-thick layer; c Thalassinoides representing mainly horizontally branching burrows. Most burrows form both Y- and T-shaped branchings. Locally, vertical shafts are seen on bedding surfaces; d Thalassinoides boxwork. Most burrows exhibit both Y- and T-shaped branchings, which can be observed both on bedding surfaces and in the cross section. Abbreviations: VS = Vertical shaft; BD = Burrow depth, maximum burrow depth during multi-layer colonization; BT = Thickness of bioturbated zone; YB = Y-shaped branching; TB = T-shaped branching