碳酸盐岩中“假纹层构造”的成因分析

GENETIC ANALYSIS OF THE "FALSE LAMINAR STRUCTURE" IN CARBONATE ROCKS

常见于泥微晶碳酸盐岩中的毫米级水平纹层是低能沉积环境特有的相标志。川东北地区长兴组—飞仙关组碳酸盐岩地层无岩芯钻探的岩屑中,通过岩石薄片鉴定发现该层段岩屑样品中,大量岩屑出现纹层构造,甚至水动力条件下不可能形成水平纹层构造的颗粒碳酸盐岩、结晶碳酸盐岩中也有出现,通过对这些现象的薄片鉴定、电子探针及Kα元素面分布等分析手段证实其为非沉积成因、非构造成因的"假纹层构造",研究后将其归因为钻探工艺所使用的钻头(PDC型)。为准确对岩石薄片进行鉴定并提升无岩芯钻井地质剖面的解释质量,针对沉积动力学、构造动力学和制片工艺学都无法解释的"假纹层构造"的成因分析具有十分重要的现实意义。

The millimeter level of laminae that commonly found in muddy microcrystalline carbonate is of unique depositional environment with low marks.The identification of thin sections in the Changxing and Feixianguan Formations in the northeastern Sichuan carbonate rocks shows that in some non-core drilling samples,laminar structures occurred in large number of debris.However,appearance of lamellae is not in accordance with the forming condition of carbonate.Based on the identification of thin sections,combined with the approaches of microprobe and analysis of Kα element surface,it is proposed that the genesis of these ＂false laminar structure＂ is not the sedimentary or tectonic,they were resulted from the process of core drilling with some particular drilling head.This study is of significance both on the interpretation of geological profile of non-drilling cores and on the identification of thin sections.