Extensive occurrence of hiatus in geological record imposes bad effects on the study of chronostratigraphic correlation

organic evolution

catastrophic or episodic depositional layers

and on analysis precise.Hiatus could be classified into syn-depositional and post-depositional ones according to their formation stages

and into micro

small

median

large and giant ones according to their scales.The micro and small hiatus generally formed in syngenetic stages;the large and giant ones resulted from global eustatic movements

paleogeographic and paleoclimatic changes

tectonic activities in epigenetic stage;the median ones formed in both the syngenetic and epigenetic stages.The completeness of a stratigraphic section is defined as the fraction of time intervals of some specified length(t) that left a record.The value of the completeness of any section is less than one but greater than zero.How to determine the completeness of a section is still a unsolved problem.In recent ten years or more

some research workers proposed a number of approaches such as the ratio between long-term and short-term sedimentation rates

the ratio of thicknesses between a section and globle average synchronous deposits

tired trace fossiles and paleomagnetic data methods.These methods have laid down a firm foundation for future work.