涠西南凹陷流沙港组一段天文旋回识别及高频层序划分

Astronomical cycle identification and high frequency sequence division of the 1st Member of Liushagang Formation in Weixinan sag,Beibuwan basin

依据GR测井曲线和岩性变化,使用R软件"astrochron"程序,利用频谱分析、天文调谐等方法对北部湾盆地涠西南凹陷流沙港组一段沉积地层进行了天文旋回识别和高频层序划分。频谱分析结果显示,在频率0～0.1、0.2左右以及0.3～0.4范围能够追踪到405ka长偏心率(E)、123ka短偏心率(e_1)、40ka斜率(O)、23ka(P_1)和19ka(P_2)岁差,表明沉积地层受到天文参数的控制;新生代405ka长偏心率较稳定,以Laskar(2011)长偏心率405ka作为标准,以流一段底部U-Pb锆石年龄作为标准进行天文调谐,并建立了天文年代标尺,结果显示流一段持续时间约为4.8～5.0 Ma;以405ka长偏心率带通滤波曲线与Laskar方案中的405ka偏心率进行比对,分别在Wei-1井和Wei-2井流一段识别出13个完整的中期旋回,由此划分出了13个五级层序。本文研究可为地层高频层序划分及油气勘探精度提高提供思路。

Based on the GR logging curve and the lithological change,“astrochron”program of R software was used to conduct the astronomical cycle identification and the high frequency sequence division on the 1st Member of Liushagang Formation in Weixinan sag through spectrum analysis,astronomical tuning,etc..The results of spectrum analysis show that long eccentricity of 405 ka(E),short eccentricity of 123 ka(e 1),obliquity of 40 ka(O),and precession of 23 ka(P 1)and 19 ka(P 2)can be traced in the frequency ranges of 0~0.1,0.2 or so,and 0.3~0.4,which indicates that the sedimentary strata were controlled by the astronomical parameters.Owing to the long eccentricity of Cenozoic 405 ka is relatively stable,thus selecting the Laskar(2011)long eccentricity of 405 ka as the standard,and taking the U-Pb Zircon age at the bottom of the 1st Member of Liushagang Formation as the standard of astronomical tuning,an astronomical scale was established,and the results show that the duration of the 1st Member of Liushagang Formation is about 4.8~5.0 Ma.By comparing the 405 ka long eccentricity band pass filter curve with the 405 ka eccentricity in the Laskar scheme,13 complete mid-term cycles have been identified in the 1st Member of Liushagang Formation in wells Wei-1 and Wei-2.On this basis,13 fifth-order sequences were divided.This paper can provide ideas for the division of stratigraphic high frequency sequence and the high precision exploration of oil and gas.