川东南地区长兴组层序充填特征及沉积模式

Sequence Structural Characteristics and Sedimentary Model of Changxing Formation, Southeastern Sichuan Basin

川东南地区长兴组可划分为SQ1和SQ22个三级层序,其均由海侵体系域(TST)和高水位体系域(HST)构成。在长兴组下层序沉积时期,研究区以缓坡型沉积为主,浅缓坡相带内以沉积微晶灰岩为主,HST时期该相带内部分地势高区域则发育部分生物碎屑灰岩、礁灰岩;深缓坡相带内以发育泥灰岩、含泥灰岩等深水沉积物为主。在长兴组上层序沉积时期,研究区发育碳酸盐岩台地沉积,该时期开阔台地相带内以发育微晶灰岩为主,但HST沉积时期局部高地势区域发育一定规模的礁滩体;上层序海侵体系域时期台地边缘相带沉积物以微晶灰岩为主,同时发育一定规模的生物碎屑灰岩,而HST沉积时期以发育生物碎屑灰岩、礁灰岩为主;斜坡相带内以含泥灰岩等深水沉积物为主。TST沉积时期区内沉积物堆积方式以退积为主,而HST沉积时期其堆积方式则转变为以加积和进积为主。

In southeastern Sichuan Basin, the Changxing Formation can be divided into two third- order sequences, SQ1 and SQ2, which are totally composed of transgressive system tract (TST) and highstand system tract (HST). During one deposition of lower sequence, gentle-slope-type deposits occupied in the study area. Most micrite was found in the shallow gentle-slope facies belt; and some bioclastic limestone and reef limestone were developed at the part higher region of facies belt in HST period. Both marl and deep-water sediments with marl were also mainly developed in the deep gentle-slope facies belt. During another deposition of upper sequence, carbonate platform sediments might be found in the study area. Most micrite was developed in the open platform facies belt. However, a certain scale of reef-shoal reservoir body was found at the part higher region in HST peri od. Moreover, most micrite could be developed at platform margin facies belt in TST; simultaneously, some scale of bioclastic limestone could also be seen. In HST period, both bioclastic limestone and reef limestone were found; and some deep-water sediment with marl was found in the slope belt facie. Retrogradation is the main stacking patter in TST period whereas both aggradation and progradation are the key ones in HST period.