测井记录中米氏旋回信息提取及其沉积学意义——以济阳坳陷区为例

Feature extraction of Milankovitch cycle in well logs and its sedimentological significance:a case study of Jiyang depression zone

米氏旋回是米兰科维奇效应在地层记录中的表现形式,其代表的时间涵义是进行高分辨率地层划分、对比的有效手段,为了揭示地层中米氏旋回信息保存的差异性,完善地层学尤其是旋回地层学理论,文章依据济阳坳陷38口钻井不同层位地层的自然伽玛测井数据,应用一维连续小波变换模极值法进行了米氏旋回信息提取,并分别计算了岁差、黄赤夹角和偏心率周期在多套地层中的响应厚度及其变化特征.结果表明,研究区多套地层中普遍存在米氏旋回信息.其中早古生代(∈-O)、晚古生代(C-P)和新生代(E-N)地层中岁差旋回层厚度的变化范围分别为3.4～17.1m,8.6～19m和7～11m,其中优势旋回层厚度分别为13,14和10m;黄赤交角旋回层的厚度变化分别为7.2～27.8m,19.5～39.2m和14～26m,其中的优势旋回层厚度分别为27,26和21m;偏心率旋回层的厚度变化分别为20.3～64.6m,37.2～75.1m和40～60m,其中的优势旋回层厚度分别为60,74和51m.中生代(J-K)地层中岁差、黄赤交角和偏心率旋回层厚度变化范围分别为3.2～21.4m,6.2～42.8m和15.4～108.6m,未发现明显的优势旋回层.由此看出,米氏旋回层厚度的变化幅度随地质年代的变老有增大趋势,认为保存在较老地层中的米氏旋回信息因受到后期地质事件的影响稳定性变差;中生代米氏旋回层厚度的变化幅度最大,认为与济阳坳陷中生代时期复杂的构造环境造成的沉积环境分异度高有关.此外,根据优势米氏旋回层的厚度估算了不同时代的地层堆积速率并予以解释.

Milankovitch cycle is the manifestation of Milankovitch effect in the stratigraphic re- cord. Its time property is an effective means to divide and constrast the high-resolution strata.In order to reveal the differences of Milankovitch information preserved among different strati- graphic units, enrich stratigraphic theory, especially cyclostratigraphic theory, Milankovitch features were extracted by means of the Extreme Mode method of one-dimensional Continuous Wavelet Transform from related strata based on the GR well logging data of 38 wells in Jiyang Depression Zone, and the thickness of the cyclothems recognized corresponding to the preces- sion, obliquity and eccentricity was calculated respectively and their fluctuation was also ana- lyzed. The results show that, in the study area, there widely exists Milankovitch information in several stratigraphic intervals. Among them, the thickness of the precession cyclothem va- ries in ranges of 3.4--17.1 m, 8.6--19.0 m and 7-11 m in Early Paleozoic （E-O）, Late Pa- leozoic （C-P） and Cenozoic （E-N） correspondingly. And among them, 13m, 14m and 10m cy- cles are the principal ones; the thickness of the obliquity eyclothem, in the same way, 7.2-- 27.8 m, 19.5--39.2 m and 14--2 6 m, with 27 m, 26 m and 21 m as principal cycles while ec- centricities are 20.3--64.6 m, 37.2--75. lm and 40--60 m, and 60 m, 74 m and 51m being principal ones. The thickness of Milankoviteh cyclothem in Mesozoic varies in ranges of 3.2-- 21.4 m, 6.2--42.8 m and 15.4--108.6 m, corresponding to precession, obliquity, and eccen- tricity respectively, with no obvious principal cycle. A conclusion can be drawn that the fluctu- ation of the thickness of Milankovitch cyclothem tends to strengthen with the aging of the geo- logical intervals from Cenozoic （E-N）, Late Paleozoic （C-P） to Early Paleozoic （E-O）, that is, the stability of Milankovitch cycle information preserved in the older strata is deteriorated more by the following geological events. The strongest fluctuation of the thickness of Milankovitch cyclothem in Mesozoic was probably resulted from the stronger sedimentary environment differentia- tion caused by the active tectonics. Furthermore, the accumulation rate was calculated and explained for different geological intervals in terms of the thickness of principal cyelethom.