构造及海面波动对四川盆地志留纪生物礁的控制

TECTONIC AND SEALEVEL CHANGE INFLUENCE ON THE SILURIAN REEFS DEVELOPMENT OF NORTH AND SOUTH MARGINS OF SICHUAN BASIN .

通过上扬子板块区各大地构造单元、四川盆地南北缘志留系锶同位素、碳氧同位素分析所显示的海平面变化及其与生物礁发育的关系分析得出：（１）志留纪时，四川盆地南北缘都分别为受上扬子板块内部稳定古隆起（古陆）控制的陆源碎屑—碳酸盐岩缓坡环境，在靠近古陆的地区生物礁发育，而远离古陆时，由于水体逐渐加深，生物礁则不发育；（２）盆地南缘锶同位素从龙马溪组至石牛栏组呈波动式下降，反映出海平面从龙马溪组至石牛栏组总体趋势是逐渐上升，至韩家组，锶同位素值迅速上升，海平面降低；盆地南缘石牛栏组的碳同位素呈波动上升。盆地北缘王家湾组及宁强组的碳同位素也呈逐渐增加的特征。碳同位素演化显示盆地南北缘从龙马溪组至宁强组都处于海进期，而宁强组沉积时达高水位期，以后海平面迅速下降；虽然氧同位素受埋藏成岩作用影响较大，呈较大的负偏移，但其系统变化特征也可间接反映当时的海平面上升过程；生物礁在海进期及高水位期发育，且以在高水位期发育得最好。

According to the tectonic unit characteristics of Upper Yangtze plate and the87Sr/86Sr,C13& 18 O analyses from the Silurian of North & South margins of Sichuan Basin,the following conclusions can be drawn:(1) During the Early Silurian,the North & South margins of the Sichuan Basin were located at the siliciclasticcarbonate ramp environments which were controlled by the inplate old land.Near the old land,reefs developed because of the shallow water,and far away from the old land,reefs undeveloped because of the deep water;(2)At the south margin of the Basin,the87Sr/86Sr value decreased from Longmaxi formation to Shiniulan formation indicating that the sealevel increased gradually.At the bottom of Hanjiadian formation along with the87Sr/86 Sr value increased,the regressive event occurred;(3)At the south margin of the Basin,13 C value in Shiniulan formation increased from bottom to top,and the average value is 1.2 (PDB).At the Basin north margin,the 13 C value increased obviously from Wangjiawan formation to Ningqian formation.The 13 C evolution indicated that the transgressive event occurred from Llandovery to Early Wenlock,and after that the regressive event took place.The systmatic changes of 18 O value induces the similar conclusions,although the 18 O affected by diagenesis;(4) The local sealevel change can be compared with the global transgressiveregressive events in the Early Silurian and all the reefs developed at the transgressive period and high sealevel period.During the high sealevel period,the environment was best for reef development.The topographic characteristies and sealevel changes has strong influence on the reefs development.