苏北盆地海安凹陷古近系阜三段滩坝沉积特征

Sedimentary characteristics of beach-bar in the 3rd member of Paleogene Funing Formation in Hai'an Sag,North Jiangsu Basin

海安凹陷阜三段沉积方面的研究相对欠缺,且存在争议,诸多研究仅局限于次凹,缺乏对整个海安凹陷的系统研究。利用研究区测井、岩心及分析化验资料,在等时地层格架的基础上,结合岩石学、粒度、沉积构造、电性、砂体展布等滩坝识别标志,分析其沉积微相类型、展布规律、形成条件及沉积模式。结果表明,海安凹陷阜三段发育滩坝沉积,多发育于滨浅湖区,粒度累积概率曲线以两跳一悬式最为常见,跳跃次总体呈两段式,沉积构造以反映滨浅湖波浪成因为特征,砂体展布呈卵形或条带状平行于湖岸线分布。滩坝的发育受古物源供给条件、古地貌条件和古风(浪)动力条件的控制。海安凹陷阜三段沉积时期,盛行南风,波浪持续地由南向北传播,在建湖隆起南侧缓坡带形成了较广泛的波浪影响区。在波浪和沿岸流的作用下,高邮凹陷北部的浪控三角洲前缘砂体被再次分配,为海安凹陷滩坝沉积的形成提供了物质基础。

Research on sedimentary environment of the 3rd member of Funing Formation in Hai’an Sag is weak and disput-ed.Most studies are limited to sub-sags,and systematic research on the whole Hai’an Sag is rare.This paper is based on the abundant logging,core,analytical laboratory data and isochronous stratigraphic framework.Combined with the petrolo-gy,grain size analysis,sedimentary structures,electric logging and sand distribution,the identification signs of the beachbars were demonstrated,and the types of sedimentary microfacies,distribution rules,formation conditions and sedimentary model were analyzed.The results show that the 3rd member of Funing Formation in Hai’an Sag is dominated by the beachbar deposits.The beach-bar is common in the shallow lake.The jumping components show two straight lines in the curves of grain-size cumulative probability.The sedimentary structure reflects the wave effect.The distribution of sand body pres-ents oval-like or band-like shape and is parallel to the shoreline distribution.The beach-bar is controlled by multiple fac-tors,which can be summarized as source supply,paleogeomorphology and dynamic conditions of palaeo-wind(wave).Dur-ing the sedimentation of the 3rd member of Funing Formation,the south wind prevailed in Hai’an Sag.Waves continued to propagate from south to north,forming a broad area influenced by wave in the gentle slope on the south side of the Jianhu Uplift.Under the action of waves and coastal currents,the sand bodies of the wave-controlled delta in the northern Gaoyou Sag were redistributed,which provides a material basis for the formation of the beach-bar in Hai’an Sag.