The Oolitic Types And Associated Trace Fossils From Middle Cambrian, Western Henan

The seven types of oolites can be recognized from Middle Cambrian oolitic limestones of Western Henan on the basis of microfacies analysis.They areconcentric-radial oolite,radial oolite,concentric oolite,radial-concentric oolite dolomitic oolite,crystalloid oolite,minicrystal oolite. Concentric-radial oolite is the dominating type and has the big proportion in all the ooids. It developed in the sedimentary environment of alternation of low and high energy. There are two models on ooid formation:â‘ The model of ooid formation interrelated with stromatolite;â‘¡The model of ooid formation of active stage and stationary stage. The concentric-radial oolites can develope in low energy area between oolite shoals;dolomitic oolites and crystalloid oolites are formed in ridgy areas being leached by fresh water; radial-concentric oolites and concentric oolites are preserved in high energy oolitic shoal of open platform environment;radial oolites only occur in intertidal zone where stromatolite prevails.There are abundant trace fossils Macaronichnus developed in limestone of Middle Cambrian, Western Henan.And they are formed and preserved in oolitic shoal of open platform environment,representing a ichnofabric formed by opportunistic species.Based on the features of opportunistic species and modern polychaetes,the symbiosis of trace fossil Macaronichnus and oolites can be divided into two stages:â‘ The suspending growing stage of larva of Macaronichnus trace makers and oolites;â‘¡Adult Macaronichnus tracemakers feeding in oolitic sediments which deposited as the suitable substrates from the suspending situation.