阿姆河右岸B区中部卡洛夫-牛津阶高精度层序地层划分及层序发育模式

High-resolution Stratigraphic Division and Formation Model of the Callovian-Oxfordian Sequences in the Central Part of Block B in the Right Bank of Amu Darya Basin,Turkmenistan

土库曼斯坦阿姆河盆地是世界上著名的大型含油气沉积盆地,然而目前盆地内卡洛夫—牛津阶的层序划分和地层对比依然存在争议。基于Vail经典层序地层学及沉积学相关理论,以阿姆河右岸B区29口井的岩心资料及50口井的测井资料为依据,结合地震、薄片、地球化学等手段,开展了阿姆河右岸B区卡洛夫-牛津阶的层序地层研究。将阿姆河右岸B区卡洛夫-牛津阶划分为5个三级层序和15个四级层序,其中卡洛夫阶包括2个三级层序(SQ1和SQ2),牛津阶分为3个三级层序(SQ3-SQ5)。在高精度层序划分的基础上,建立了研究区的层序地层格架,在垂向上,各级层序格架内部高位域生屑砂屑灰岩及礁滩体沉积更为发育;在平面上,根据不同层序沉积几何体和沉积相的分布,明确提出了卡洛夫期和牛津期发育两种不同的碳酸盐岩台地类型的观点:SQ1-SQ2时期(卡洛夫期)研究区应为缓坡型台地,初始具有西高东低的地貌,坡度较缓,沉积速率差别不大,主要发育缓坡台地层序地层模式; SQ3-SQ5时期(牛津期)则演化为镶边台地,研究区沉积速率远小于A区,随着海平面变化形成了差异巨大的西高东低沉积地貌。

The Amu Darya Basin in Turkmenistan is a large petroliferous sedimentary basin,yet its Callovian-Oxfordian stratigraphic division and correlation are still disputed.We analyzed the Callovian-Oxfordian sequences in Block B of the Amu Darya right bank area(based on Vails classic sequence stratigraphy and relevant sedimentology theories),integrating drill core,logging,seismic,thin section petrographic,and geochemical data.We found that the Callovian-Oxfordian sequences can be divided into five 3rd order sequences and 15 4th order sequences.Stratigraphy framework for the study area is newly established based on these high-resolution sequence divisions.Two carbonate platform models were developed:(i)Callovian,the region was likely a ramp platform with topographic highs in the west and lows in the east,and a gradual slope gradient with spatially consistent sedimentation rate;(ii)Oxfordian,the region was likely evolved into a rimmed platform system,with highly disparate sedimentation rates(low in the east)that were sensitive to sea level change,and a starkly different sedimentary landform that was high in the west and low in the east.