塔里木盆地麦盖提斜坡奥陶纪地层划分对比及意义

Ordovician stratigraphic divisions and correlation of Maigaiti slope in Tarim Basin and its significance

以碳同位素值的波动变化与沉积环境、海平面升降及地层界面突变等地质事件相对应为理论依据,开展碳同位素地层研究,建立了各组值域划分标准,解决碳酸盐岩地层缺乏标准生物化石情况下,地层归属难确定的问题。指出奥陶系自下而上碳同位素曲线呈现稳定-上升-正漂移的过程。其中,下统蓬莱坝组—鹰山组δ^(13)C值范围为(-4.2^-0.2)×10^(-3),始终为负值;中统一间房组δ^(13)C值范围为(-0.4~0.6)×10^(-3),以分布在零值附近为特征;上统恰尔巴克组—良里塔格组δ^(13)C值范围(0.7~3.1)×10^(-3),均为正值。在此基础上,开展了巴楚典型露头剖面与麦盖提斜坡井下奥陶系碳同位素地层与岩石地层对比研究,提出麦盖提斜坡中部及东部断洼区发育上奥陶统,除东部断裂带外,普遍残存下奥陶统顶部泥晶灰岩段。

Based on the theory of corresponding relation between carbon isotope value fluctuation with sedimentary environment, sea level eustacy, formation interface mutation, etc, the authors study the stratigraphy by carbon isotopic method, and establish the classification standards for each unit, which solved the difficult problems on determining of the strata without index fossils in carbonate rocks. The Ordovician carbon isotopic curves present a process of stable-rising-positive drift in descending order. The ^13 C values vary from - 4. 2 X 10 3 to - 0. 2 X10 3 in Lower Ordovician Penglaiba Formation and Yingshan Formation, characterized by the values below zero;from -0 . 4 xlO 3 to 0. 6 X 10 3 in Middle Ordovician Yijianfang Formation, characterized by distributed near the zero value, and vary from 0. 7 X 10 3 to 3. 1 X 10 3 in Upper Ordovician Qiaerbake Formation and Lianglitage Formation,featured by the values all above zero. On this basis, with the carbon isotopic standards, the correlation of the Lower Ordovician strata of the typical outcrop profiles in Bachu area with the wells of Margaiti slope was studied.It is confirmed that the Upper Ordovician developed in middle Margaiti slope and the eastern fault depression zone. Except the eastern fault zone, all the areas commonly remain the Micrite Member at the top of the Lower Ordovician