走滑断裂与古岩溶作用耦合关系方面的研究报道较少。本文通过对TH12518走滑断裂在奥陶系一间房组地层内构造样式时空叠加改造特征和不同期岩溶作用的研究,明确不同期次走滑断裂内幕结构与古地貌、古水系间的耦合关系。在TH12518走滑断裂在多期构造活动改造下,一间房组地层构造样式多次差异叠加,形成5种分段类型:Ⅰ型,拉分+平移+拉分段;Ⅱ型,拉分+平移+平移段;Ⅲ型,平移+挤压+拉分段;Ⅳ型,平移+挤压+平移段;Ⅴ型,逆冲推覆改造段。即加里东中期Ⅰ~Ⅲ幕形成平移段和拉分段;加里东晚期形成平移+挤压段、拉分+平移段、逆冲推覆段3种样式;海西早期发生“弯曲效应”,形成平移+挤压+平移段、拉分+平移+平移段、平移+挤压+拉分段、拉分+平移+拉分叠加构造样式。不同期岩溶地貌差异大。加里东中期Ⅰ幕岩溶台地水系欠发育;加里东中期Ⅱ-Ⅲ幕,北部抬升形成岩溶准平原,南部岩溶斜坡区发育近南北向地表水系及暗河;加里东晚期,岩溶斜坡区发育多组水系,沿北东东向断裂新形成北东东向暗河和地表水系。海西早期,岩溶斜坡发育大型曲流河。一间房组地层在不同岩溶期,不同区域不同类型段的岩溶作用不同。加里东中期Ⅰ幕整体发育开发式裸露型岩溶,沿断裂带下渗溶蚀,北北东向断裂拉分段溶蚀较强。加里东中期Ⅱ-Ⅲ幕北部发育开发式裸露型岩溶,南部为半开放式承压型岩溶,拉分段溶蚀进一步增强,Ⅱ幕还发育“下降型”埋藏断控岩溶。加里东晚期发育开发裸露型岩溶、半开放承压岩溶和“下降型”埋藏断控岩溶,北部受岩溶基准面控制,向下在寒武系顶面-白云岩岩性界面岩溶作用受阻。南部不受基准面控制,向下至少溶蚀至寒武系阿瓦塔格组顶面,纵向上岩溶缝洞体分层明显。海西早期,发育半开放式承压型岩溶,除弯曲效应拉分段外,岩溶作用较弱。在空间上存在某一区域储层由某一期或多期关键岩溶期和关键岩溶方式控制决定,如覆盖区加里东中期Ⅱ幕“下降型”埋藏断控岩溶作用是奥陶系一间房组顶面缝洞型储层形成的关键因素。研究成果有助于为滚动开发实践提供地质依据。

The coupling relationship between strike-slip faults and ancient karst processes has not been well studied. This paper examines strike-slip fault TH12518 in the Tahe Oilfield aiming to clarify the coupling relationship between the fault’s internal structure and ancient landform and water systems, by studying the characteristics of spatiotemporal structural superposition and transformation in the Ordovician Yijianfang Formation as well as karst activities during different tectonic phases. TH12518 experienced multistructural superposition under multistage tectonic activities, yielding five structural styles: pull-apart + translational + pull-apart (I); split + translational + translational (II); translational + compressive + pull-apart (III); translational + compressive + translational (IV); reverse thrust + overthrust (V). Stuctural styles I, II mainly occur in the middle Calendonian period, while structural supperposition between various structrual styles (I-V) occurs in the late Caledonian and early Haixi periods, under “bending effect.” There are significant differences in karst landforms between different karst periods. The water systems are underdeveloped during episode I of the middle Caledonian; whilst during episodes II, III the northern part uplifts to form a quasi karst plain while the southern karst slope area develops near N-S trending surface water systems and underground rivers. In the late Caledonian, multiple sets of water systems are developed in the karst slope area, forming a new NE-E trending underground river and surface water system along the fault. And in the early Haixi, large meandering rivers are developed on karst slopes. The karst processes in the Yijianfang Formation differ between different karst periods, regions, and segmentation styles. Episode I of the middle Caledonian develops exposed karst, overall, with infiltration and dissolution along the fault and strong dissolution in the N-NE trending fault segments; episodes II, III develop exposed karst in the north and semi-open overpressure karst in the south; with the segmented dissolution further enhanced, a sinking, buried fault-controlled karst is also developed in episode II. In the late Caledonian, exposed karst, semi-open overpressure karst, and sinking, buried fault-controlled karst are developed. The north, controlled by the karst baseline, exhibits limited downward karst process at the Cambrian top-dolomite interface; the south, not controlled by the reference plane, shows extensive downward dissolution at least to the top of the Cambrian Avatag Formation. Vertically, the karst fissures and caves are clearly layered. Whilst in the early Haixi, semi-open overpressure karst is developed, with weak karstification except for the bending effect and segmentation. This study provides a geological basis for large-scale karst development in the region.