According to the principles of sequence stratigraphy and sedimentology

we studied the Paleozoic marine deposits in the Lower Yangtze area by using outcrop observation data integrated with drilling and logging data.We identified four types of unconformities through field observation

including uplifting-erosion unconformity

transgressive onlapping unconformity

underwater erosional unconformity and subareal erosional unconformity.In addition

we also identified 4 types of condensed sections

including the Sinian coal layer

the Silurian-Carboniferous Gaolishan Formation shale

thin Ordovician dolomite and thin Carboniferous limestone.According to these boundary marks

11 second-order sequences were recognized and a sequence stratigraphic framework was established in the Lower Yangtze area.According to the lithologies

facies and sedimentary structures defined through field outcrop observation

we established three sedimentary systems for the Paleozoic in the study area

namely continental sedimentary system

transition sedimentary system and ocean sedimentary system.Finally

based on the regional tectonic setting and previous research results

we studied the nature and evolution of basin in the study area.Three sequence stratigraphic models were established

i.e. the Sinian-Late Ordovician

Devonian and Carboniferous stratigraphy model of craton basin

the latest Ordovician-Late Silurian stratigraphy model of foreland basin and the Middle and Late Ordovician

Late Permian-Middle Triassic stratigraphy model of passive margin basin.Their sequence characteristics were summarized.