蓟县铁岭组底部硅质褐铁矿屑砂岩的地质意义

GEOLOGICAL SIGNIFICANCE OF SILICEOUS CEMENTED LIMONITIC SANDSTONE AT THE BOTTOM OF THE TIELING FORMATION IN JIXIAN,TIANJIN

华北蓟县系上部洪水庄组和铁岭组之间长期以来一直被认为是整合接触。近期在蓟县小岭子剖面发现洪水庄组顶部发育铁质风化壳,铁岭组底部有硅质褐铁矿屑砂岩,从而证明洪水庄组与铁岭组之间存在一次强烈的风化剥蚀,二者之间是假整合接触关系。

In the Jixian area, the boundary between the Tieling and Hongshuizhuang Formations of the Jixian System has long been considered as conformable. Recent discoveries of ferricrust at the top of the Hongshuizhuang Formation, and siliceous limonitic sandstone at the bottom of the Tieling Formation at Xiaolingzi in Jixian, Tianjin, however, suggest an event of exposure and strong weathering occurring within the boundary interval between the Tieling and underlying Hongshuizhuang Formations. The contact of these two formations is, therefore, disconformable.