珠江口盆地HA地区古近系文昌组沉积特征

Sedimentary Characteristics of the Paleogene Wenchang Formation in the HA Area, Pearl River Mouth Basin

综合岩心、钻井、测井及地震资料,对珠江口盆地HA古近系文昌组的沉积特征及沉积演化进行了研究。结果表明:HA古近系文昌组可以识别出5个层序界面,划分为4个三级层序,自下而上分别为SQ1、 SQ2、 SQ3和SQ4。其中SQ1主要分布在南部,SQ2和SQ3全区分布,SQ4由于南部构造抬升遭受剥蚀,主要分布在北部H4地区。HA文昌组主要发育辫状河三角洲相、扇三角洲相、近岸水下扇相及滩坝相。文四段时期,惠州凹陷开始裂陷,物源供给较少,靠近XJ30断裂和HZ26断裂主要发育扇三角洲沉积,HA转换带主要发育辫状河三角洲;文三段发育时期,盆地快速断陷,水体加深。HA转换带以大规模的辫状河三角洲沉积为特征,靠近XJ30断裂和HZ26断裂发育扇三角洲沉积,规模相对较小,受波浪不断淘洗,惠州H4地区发育滩坝沉积;文二段发育时期,南部断裂活动进一步加强,处于强烈活动状态,湖平面继续上升,HA转换带辫状河三角洲规模变小,陡坡近岸水下扇、扇三角洲连片发育,规模变大;文昌组文一段时期断裂活动减弱,湖水变浅,物源供应充足,靠近HZ26断裂发育大套扇三角洲,靠近XJ30断裂发育大型浅水三角洲,但后期构造抬升遭受剥蚀,残留的地层厚度较薄。

Based on comprehensive analyses of cores drilling,well logging and seismic data,the stratigraphic characteristics and sedimentary evolution of the Paleogene Wenchang Formation in the HA area of the Pearl River Mouth Basin was analyzed.Results show that five sequence boundaries were identified and four third-order sequences were divided in the study area,including SQ1,SQ2,SQ3 and SQ4.SQ1 was mainly developed in the south,SQ2 and SQ3 were developed in the whole area,and SQ4 was denuded due to the tectonic uplift of the south and it developed mainly in the northern HA4 area.Braided river delta,fan delta,nearshore subaqueous fans and beach-bar facies were developed.The period of SQ1 was the beginning of rift in Huizhou sag,and during this period,sediment supply was not abundant.Fan delta was mainly developed near XJ24 fault and XJ30 fault,and braided river delta was developed in HA transform zone.During the period of SQ2,fault depression became stronger and the water became deeper,and thus braided river delta was developed in large scale in the HA transform zone and fan delta became smaller.Beach-bar facies was developed in the H4 area due to wave washing.During the period of SQ3,fault activities of the south became increasingly stronger,the water became continually deeper,and thus braided river delta was developed in smaller scale,but the nearshore subaqueous fans and fan delta were developed in larger scale.During the period of SQ4,fault activities became weaker,the depth of water became shallower,but sediment supply was abundant.Therefore,large-scale fan delta was developed near to the HZ26 fault,and shallow water delta was distributed in large scale near to the XJ30 fault.Nevertheless,due to the denudation by tectonic uplift,the residual strata was thinner.