苏红图-银根盆地下白垩统层序地层学研究

本文根据沉积、古生物及地震资料对苏红图-银根盆地下白垩统的层序地层学特征进行了研究。把下白垩统划分为１个三级层序和低水位体系域、湖侵体系域、高水位体系域。根据准层序的叠置方式，准层序组有进积型、退积型和加积型，本区下白垩统可以划分９个准层序组，以退积型准层序组最为发育。苏红图-银根盆地早白垩世早期沉积格局曾发生过显著变化，从早到晚先后发育冲积扇、扇三角洲、浅湖和深湖相沉积，并在深湖相暗色页岩中夹有浊流和泥石流沉积，为退积型湖进层序。早白垩世晚期则由滨浅湖相演化为滨湖沼泽和河流相沉积，为进积型湖退层序。本区的湖侵体系域浅湖-深湖相暗色泥、页岩厚度大，有机质丰度高，类型好，是重要的烃源岩。低水位体系域的扇三角洲层序以加积型为特征，即下部为扇三角洲平原，中部为扇三角洲前缘，上部为前扇三角洲。反映了该区处于活动盆地边缘，湖水由浅变深，扇三角洲相应后退，沉降速率大于沉积速率。其中扇三角洲前缘砂体的储集作用不可低估。高水位体系域的滨浅湖滩砂也是重要的油气储集体。而湖侵体系域的深湖相泥、页岩和高水位体系域的滨湖沼泽相泥岩均可作为区域盖层。它们在垂向上构成了有利的生储盖组合。

Sequence Stratigraphy of Lower Cretaceous in Suhongtu Yingen Basin

Based on sedimentary, palaeontological and seismic data, the sequence stratigraphy of the LowerCretaceous in the Suhongtu-Yingen basin has been studied. The Lower Cretaceous is divided into 1 se-quence and lowstand system tract, transgressive system tract as well as highstand system tract. Accord-ing to incumbent style of parasequence, parasequence sets are divided into transgressive style, retrogres-sive style and accretion style. In this region, the lower Cretaceous in divided into 9 parasequence sets, andretrogression parasequence style is developed much better among them. Early period of the Early Creta-ceous has experienced great changes in the Suhongtu-Yingen basin. From Early Cretaceous to Later Cre-taceous, allavial fan, fan delta, shallow lake and deep-lake are developed and turbidity current and debrisflow that belong to lake transgressive stratigraphic sequence of retrogressive style exist in deep-lakemelane mudstone. In late of Early Cretaceous shore-shllow lake has changed into shore-lake swamp andriver that belong to lake retrogressive stratigraphic sequence of transgressive style. In the region, shal-low-deep lake melane mudstone and shale of transgressive system tract that its depth is thick and its or-ganic content is rich and style is good, showing which is important hydrocarbon source rocks. Among fandelta stratigraphic sequence of lowstand system tract, accretion style is more characteristic. In otherwords,its lower part belongs to fan delta plain,its middle belongs to fan delta front and its upper belongsto profan delta. The characteristics reflect that the region might be in the margin of active basin,in whichlake changes from shallow to deep, fan delta retreats with it and rate of subsidence is more rapid thanrate of sedimentation. Reservoir ability of fan delta front is good among them, shore-shallow lake beachsandbody is important gas-oil reservoir body and deep-lake mudstone and shale of transgressive systemtract and shore-lake swampy mudstone of highstand system tract are good cover rock. They have consti-tuted favoruable source-reservoir- cap rocks assemblages.