CARBONIFEROUS SEQUENCE STRATIGRAPHY AND SEA-LEVEL CHANGES IN THE MAJIAOBA DISTRICT,SICHUAN

Based on key boundaries,systems tracts and stacking patterns,in conjunction with regional geological and biostratigraphic data,the Carboniferous carbonate strata in the Majiaoba district,Sichuan are grouped,for the first time,into nine third-order sequences:two in the Yanguan Formation,three in the Datang Formation,two in the Weining Formation and two in the Maping Formation,all of which,in turn,may be subdivided into a number of the fourth- or fifth-order high-frequency sequences or parasequences.The time intervals of individual third-order sequence range between 2 and 11.5 Ma.And the differences of these sequences are attributed to the variations in periods of relative sea-level rises or falls,amplitudes of tectonic subsidence,rates of carbonate production and modes of sediments supply in the study area.