川东北宣汉黄金口一带中三叠统雷口坡组底界划分

Determination of the bottom boundary of the Middle Triassic Leikoupo Formation in the Huangjinkou area of Xuanhan,Northeast Sichuan

川东北宣汉黄金口一带能源、矿产资源丰富,中三叠统雷口坡组是该区钾、锂资源的赋矿层位之一,也是该区重要的天然气储层。黄金口一带雷口坡组底界多以岩性组合和测井曲线特征来划分,而不是以区域上广泛分布的“绿豆岩”作为其底界划分的标志。笔者在该区的1口钾盐探井中发现绿豆岩,其厚度2~3 cm,镜下鉴定其为富钾长石玻屑凝灰岩。XRD分析表明其主要矿物成分为石英、微斜长石、白云母。通过对岩性组合和测井曲线的对比研究,认为黄金口一带雷口坡组底界应下移,位于原划分的嘉陵江组中。

Abundant energy and mineral resources are widely distributed in the Huangjinkou area of Xuanhan,Northeast Sichuan.The Middle Triassic Leikoupo Formation is one of the host beds of potassium and lithium resources,and also an important natural gas reservoir in the area.The bottom boundary of the Leikoupo Formation in the Huangjinkou area was previously mainly defined by rock association and logging curve characteristics,rather than"mung bean rock"widely distributed in the area as a mark of bottom boundary.The mung bean rock in one of the potash exploration wells in this area was discovered recently with a thickness of about 2~3 cm,which was identified as potash rich feldspar glassy tuff under the microscope.XRD analysis shows that the main mineral components are quartz,microcline and muscovite.The discovery of the mung bean rock makes us reacquaint the correctness of the original bottom boundary of Leikoupo Formation.Based on the comparative study of lithologic association and logging curve,it is considered that the bottom boundary of the Leikoupo Formation in the Huangjingkou area should be moved down to be in the original Jialingjiang Formation.