In sequence stratigraphy

boundaries that can be used to define sequences include bottom boundaries

initial marine flooding surface and maximum flooding surface

of which the sediments corresponding to the maximum flooding surface constitute the condensed section.Identification of condensed section is not only the key to understanding of sequence structure

but also critical to analysis of global relative sea level changes during geologic history.Taking the marine Sinian-Middle Triassic in southern China as examples

6 rock formations are recognized in condensed section

including silicalite

black shale

argillaceous rock

biogenic fossil bed

micrite and nodular limestone.Although different types of condensed sections have been deposited in different sedimentary environments

they all have been deposited when the global relative sea level reached the highest position.Their formation time

therefore

corresponds to the optimum development stage of source rocks in southern China.