黔南独山泥盆纪露头层序地层及海平面变化研究

On Outcrop Sequence Stratigraphy and Sea Level Changes of Devonian in Dushan, South Guizhou

通过独山地区 10余条剖面的追踪调查 ,分析了独山地区泥盆系的层序地层。除河湖相沉积的丹林组外 ,可识别出 31个层序 ,其平均形成时限约 1 2 9Ma ,组成 4个层序组 ;在出露较完整的晚泥盆世中可识别出 195个副层序 ,其平均形成时限约 10 2 6ka。层序相当于Ⅲ级T -R旋回 ,受沉积作用、冰川作用和构造作用等的影响 ,更明显地受全球性海平面变化的控制 ,具有全球性对比的意义。副层序 ,相当于Ⅳ级T -R旋回 ,与米兰科维奇效应相关。通过生物组合、地质事件和层序地层的对比 ,下、中统界线应置于海平面明显下降、并具有古风化层的大河口组之上 ;中、上统界线应置于望城统组第一次最大海泛面 ,其艾菲尔阶 -吉维特阶的界线应置于鸡泡组之下的风化壳 ,受地壳运动影响、发生于P .varcus带早中期的独山抬升可进行全球对比 ;-泥盆石炭系界线应置于Cystophrentis -Pseudouralina间隔带之中的汤粑沟组第一次最大海侵面 ,其弗拉斯阶 -法门阶界线应置于生物绝灭与复苏的尧梭组四方坡段第一个层序界面。

Based on observations of several sections in Dushan, south Guizhou, the Devonian sequences can be divided into 4 sequences sets (or Ⅱorder T-R cycle ) that their time limit is about 1.29 Ma on average, together with the Upper Devonian sequences, which are cropped completely out, can be divided into 195 parasequences (or order Ⅳ T-R cycle) that their time limit is over 102.6 Ka on average. The sequences (or Ⅲ order T-R cycle) may be result from sedimentation, glaciations, tectonic movement, and others, and they are more obvious to be controlled by sea level changes on a globe, so that it is signification on stratigraphic correlation. Milankovitch's effect is considered as a primary factor to result in parasequences (or Ⅳ order T-R cycle). The boundary of lower-middle Devonian may be drawn on between Dahekou and Tunshang formations, where is a distinct nature boundary characterized by old karst and lack of some strata and is the lowest of sea level changes following the transgression from Longdongshui formation. The boundary of Middle-Upper Devonian may be drawn on the largest marine flooding surface in the lower part of the Wangchengpo formation where is upon Stringocphalus disappeared. The Eifelian and Givetian boundary may be draw on the old karst at the top of Tunshang formation. The Dushan uplift affected by crustal movements can correlate with the global sea level drop in the Later-Middle P.varcus zone. The boundary of Devonian and Carboniferous may be drawn near the first transgression in the cystophentis-Pseudouralina interval zone in the lower part of Tangpagou formation. The Frasnian-Famenian boundary may be drawn in the first sequence boundary of the Sifangpo member in the Yaosu formation, what's upon the living thing completely disappeared and below the other living thing appeared again. Minerals formed from Devonian in the area may be interrelated with sea level changes.