Sequence boundary and petroleum geology of the Cambrian-Permian strata in the Ordos Basin

In the light of field outcrop profiles,well logs and geophysical data,seven types of sequence boundary in the Cambrian-Permian strata in the Ordos Basin have been distinguished,including unconformity,scoriaceous beds,palaeokarst surface,scour surface,lithology-lithofacies boundary,onlap surface and maximum flooding surface,which may be genetically grouped into four categories: orogeny-associated unconformity,uplifting-associated unconformity,transgressive onlap-associated unconformity and exposure unconformity.These sequence boundaries not only serve as the key of the sequence division but also have important petroleum geological implications.They are interpreted as the responses to the tectonic evolution of the basin,and also as the important geological conditions for the formation of high-quality reservoir spaces and hydrocarbon migration channels.