川东北前陆盆地须家河组层序-岩相古地理特征

The Upper Triassic Xujiahe Formation in the northeastern Sichuan foreland basin: Sequence-based sedimentary facies and palaeogeography

关键词:  高分辨率层序地层学  岩相古地理  上三叠统  须家河组  前陆盆地  川东北

Key words:  high-resolution sequence stratigraphy  sedimentary facies and palaeogeography  Upper Triassic  Xujiahe Formation  foreland basin  northeastern Sichuan

摘要:

根据控制高分辨率层序的构造和天文因素将川东北前陆盆地晚三叠世须家河期划分为2个超长期、5个长期、18个中期及数十个短期旋回层序,并分析了须家河组超长期层序的岩相古地理特征与演化。在SLSC1超长期旋回时期,米仓山-大巴山构造山系尚处于低幅稳定隆升状态,而龙门山构造山系的逆冲推覆作用较为活跃,川东北前陆盆地属于受龙门山逆冲推覆作用远端效应影响的前陆斜坡,沿米仓山-大巴山前缘地带主要发育辫状河三角洲沉积,而盆地西南部主要发育浅湖沉积。在SLSC2超长期旋回时期,龙门山逆冲推覆进一步增强,同时,米仓山-大巴山开始进入逆冲推覆前的强烈构造隆升阶段,川东北前陆盆地有较大幅度的持续拗陷沉降,在继承SLSC1古地理演化的基础上,形成了以沿龙门山和米仓山-大巴山两逆冲推覆带前缘广泛发育的、以巨厚块状砾岩为特征的大型冲积扇沉积体系。

Abstract:

The Xujiahe Formation sequences consist,in the light of tectonic and astronomic factors controlling high-resolution sequences,of two ultralong-,five long-,eighteen medium-,and many ultra short-period sequence cycles,of which the sedimentary facies and palaeogeography of the ultralong-period sequence cycles are accentuated in this paper.During the deposition of the ultralong-period sequence cycle SLSC1,the steadily uplifting with low amplitudes occurred in the Micangshan-Dabashan tectonic mountain systems,while the thrusting was relatively active in the Longmenshan tectonic mountain systems.Then the northeastern Sichuan foreland basin was on the foreland slope influenced by distal effect of the preceding thrusting event.The braided stream-delta deposits are mostly developed in the Micangshan-Dabashan frontal zone,while the shallow lake deposits appear in the southwestern part of the basin.During the deposition of the ultralong-period sequence cycle SLSC2,the thrusting was further strengthened in the Longmenshan area,whereas the rapid tectonic uplifting occurred in the Micangshan-Dabashan area.The large-scale subsidence took place in the north-eastern Sichuan foreland basin.The alluvial fan depositional systems composed of thick massive conglomerates are well developed along the frontal zones of the Longmenshan and Micangshan-Dabashan thrust zones.