PRINCIPLES,METHODOLOGY AND APPLICATION OF MOLECULAR STRATIGRAPHY

As a newly developed subdiscipline of stratigraphy,molecular stratigraphy focuses on a variety of molecular fossils derived from biochemicals including protein,nuclear acids,carbohydrates,lipids and lignin.These organic molecules widely distributed in geological bodies are fingerprints in geological application and can be precisely quantified by using modern techniques such as gas chromatography(GC) and GC-mass spectrometry.They preserve both biological and geological information,which can be revealed by the content,the relative abundance(mainly biomarker ratios),the carbon number distribution and the isotope composition.The application principles are based on known information inherited from biological precursors as well as transformation pathways during diagenesis.Molecular stratigraphy shows a close relationship with biogeochemistry and organic geochemistry,but differs from the conventional stratigraphy such as biostratigraphy,lithostratigraphy and chronostratigraphy in that a molecular stratigraphic unit has not yet been proposed.The unavailable stratigraphic unit prevents the subdivision and correlation of strata using molecular data.We proposed that the molecular stratigraphy unit can be termed as the molecular fossil zone,analogous to a biozone in biostratigraphy.The regional and global correlation could thus be conducted on the basis of the identification of various biological and environmental events using molecular stratigraphy under the control of chronological data.Identical to ecostratigraphy and eventostratigraphy,molecular stratigraphy aims to provide a precise subdivision and correlation of strata under the constraint of chronological data.In this paper,the application of molecular fossils in the subdivision and correlation of the strata is presented,exemplified by the Permian/Triassic boundary strata at Meishan,Zhejiang Province and the Quaternary peat deposits in northern England.