鄂尔多斯盆地中部前石炭纪岩溶古地貌恢复

鄂尔多斯盆地中部以碳酸盐岩为主夹蒸发岩的奥陶系马家沟组,经130余百万年的风化剥蚀及淋滤作用,风化壳古岩溶发育。在认识研究古地质图的基础上,选取马家沟组五段四亚段一小层底部的凝灰岩为标志层,完成了盆地中部前石炭纪岩溶古地貌图。自西向东,研究区可划分为四个岩溶古地貌单元或区块:岩溶高地、岩溶台地(坪)、岩溶盆地、岩溶台地与岩溶沟槽相间区块。岩溶高地地层向西翘倾,岩溶剥蚀面自西向东地层由老到新呈有序分布,西北角有7口井的地层已剥蚀至马五41以下,最西缘陕56井残顶已为马五7地层。岩溶台地是现今马家沟组天然气的主产区,地势相对较低且平缓,并在多个小层发育岩溶溶洞建造岩。

Restoration of Pre-Carboniferous Palaeokarst Landform in Central Ordos Basin

Weathering crust palaeokarst develops in Middle Ordovician Majiagou carbonate rock and some evaporates in central Ordos Basin. On the basis of understanding the palaeo-geologic maps, and choosing the tuff from the first bottom bed of the Sub-member 4 in Majiagou Member 5 as the guide bed, mapping of the Pre-carboniferous palaeokarst landform in central Ordos Basin is finished. The research area can be divided into 4 palaeokarst landform units from west to east: a) karst highland; b) karst platform (level platform); c) karst basin; and d) karst platform and karst grooves. Strata of the karst highland tilt westwards and the eroded karst face shows well-ordered distribution from old to young in geological age from west to east. The karst platform, in which formational rock of karst caves commonly develop within many thin beds, relieves gently and is relatively low and flat in topography and it is now the major production area of gas from Majiagou Formation.