川中地区磨溪区块震旦系顶面古岩溶微地貌及其发育特征

Paleokarst microtopography of the Sinian top and its development characteristics in Moxi area,central Sichuan Basin

针对四川盆地磨溪区块震旦系顶面古岩溶"微地貌"单元划分不系统、研究较为缺乏的问题,综合分析磨溪区块的三维地震资料和钻井资料,论证并选取下寒武统沧浪铺组内部海泛面作为震旦系灯影组的上覆标志面,采用印模法恢复了震旦系顶面的古岩溶地貌。在此基础上,借鉴地貌学的经典坡位分类,结合磨溪区块震旦系顶面古岩溶地貌的发育特征,建立了磨溪区块震旦系顶面古岩溶微地貌的发育模式。优选坡度、剖面曲率、相对高程和长宽比4个参数,厘定各参数定量表征的标准,结合沟谷提取的分析结果,将磨溪区块划分为8类古岩溶微地貌单元,明确了磨溪区块震旦系顶面不同微地貌单元的发育特征,分析了不同微地貌单元中垂向岩溶风化带及溶蚀孔洞层发育程度的差异。研究表明,磨溪区块可划分为陡坡、坡肩、坡脚、残丘、坡顶、坡底、洼地和沟谷8类古岩溶微地貌单元。其中,残丘、洼地、坡顶和坡底在平面上呈低长宽比的似圆状、不规则状;坡肩、陡坡、坡脚和沟谷呈条带状。从坡肩、坡脚到坡底,各微地貌单元中的地表岩溶带和垂直渗流带厚度明显减小,水平潜流带厚度增大。溶蚀孔洞层在水平潜流带中的发育程度大于地表岩溶带和垂直渗流带中的发育程度,且水平潜流带厚度越大的部位其溶蚀孔洞层的累计厚度越大。坡底是有利于溶蚀孔洞层发育的微地貌单元。

Aiming at the problems such as unsystematic division and less research of the paleokarst microtopography units of the Sinian top in Moxi area,Sichuan Basin,this paper analyzes the three-dimensional seismic data and drilling data of Moxi area,demonstrates and selects the marine flooding surface inside the Lower Cambrian Canglangpu Formation as the overlying marker horizon of the Sinian Dengying Formation.The molding method is used to restore the paleokarst topography of the Sinian top.Referring to the classical classification of slope positions in geomorphology,in combination with the development characteristics of paleokarst,this paper builds up a development model for the paleokarst microtopography of the Sinian top in Moxi area.By optimizing 4 parameters of slope,profile curvature,relative elevation and aspect ratio,determining the quantitative characterization standard of each parameter and combining with the analysis results of valley extraction,the Moxi area is divided into 8 types of paleokarst microgeomorphic units,thus making clear the development characteristics of different microgeomorphic units of the Sinian top.Meanwhile,an analysis is conducted on the development degree differences of vertical karst weathering zone and karst cave layer in different microgeomorphic units.The research shows that Moxi area can be divided into 8 types of paleokarst microgeomorphic units:steep slope,slope shoulder,slope toe,monadnock,slope top,slope bottom,hollow and valley.Among them,the monadnock,hollow,slope top and slope bottom are round or irregular with low aspect ratios;slope shoulder,steep slope,slope toe and valley are stripe-shaped.From the slope shoulder,the slope toe to the slope bottom,the thickness of the surface karst zone and vertical seepage zone in each microgeomorphic unit decreases obviously,but the thickness of the horizontal underflow zone increases.The development degree of karst cave layer in the horizontal underflow zone is greater than that in the surface karst zone and vertical seepage zone,and the greater the thickness of the horizontal underflow zone,the greater the cumulative thickness of the karst cave layer.Slope bottom is a microgeomorphic unit that is conducive to the development of karst cave layer.