Sequence stratigraphy of the Late Cambrian strata on the North China platform and the correlation of the sea-level changes with the North America platform

The North China platform appeared as a typical ramp platform during the Late Cambrian. The strata in the northern part of the platform consisting of the Gushan and Changshan Formations are known for the storm calcarenite and biohermal limestone, of which the deep ramp mudstone and marl and shallow ramp grainstone and packstone constitute a number of meter-scale subtidal carbonate cycles. The vertical ordered stacking patterns of these meter-scale cycles within the long-term third-order cycles have reflected that the third-order (sequences) represent, in turn, the sedimentary facies sequences deposited during the deepening and shallowing processes and constrained by the third-order sea-level changes. Four third-order sequences may be identified for the Late Cambrian strata in the study area, in which the tidal-flat dolostones and their circum-tidal flat carbonate meter-scale cycles are well developed in the highstand systems tract. These sequences are characterized by the drowned unconformity as sequence boundary and "deep to shallow ramp facies sequences" consisting of the "condensed sections (?) + highstand systems tract" ("CS(?) + HST") sequences. In the southern part of the North China platform, the sequence boundaries are mostly represented by the exposed hiatal surfaces. The facies sequences comprise the "ramp facies-tidal-flat facies". The strata in the northern and the southern parts are both involved a regular sequence stratigraphic framework. The sequence stratigraphic examination based on the cycles and sequences, and lithofacies and sedimentary facies shows that the meter-scale cycles as the basic units actually may be interpreted as the lithofacies sequences resulted from the "hiatal-aggradational" cyclic mechanisms. The sea-level curves for the Late Cambrian strata on the North China platform may be qualitatively and synthetically constructed on the basis of palaeobathymetric curves for various sections. The similarities and differences of the sea-level curves for both the study area and the North America platform have mirrored that the long-period sea-level changes are controlled by both the global and local changes in the study area.