Sequence Division and Sedimentary Evolution of Cenozoic in the Middle Shenhu-Yitong Ansha Uplift

Key words: 
• Shenhu-yitongansha upiift /
• seguence /
• sedimentary environment /
• evoiution /

Abstract: Based on the seismic profiies acguired by cruise SO-49 of ” China and Germany Joint Study on Marine Geo-sciences in the South China Sea” ,and correiated with those of Peari River Mouth Basin,seguence division and correia-tion of Cenozoic in the middie Shenhu-yitong Ansha Upiift were carried out. 5 seismic refiectors,inciuding SB 1 ,SB 2 , SB 3 ,SB 4 、 and T g ,have been recognized and their ages have aiso been assigned according to their seismic refiection char-acteristics and correiated to their counterparts in the Peari River Mouth Basin. SB 1 is the boundary between middie Miocene and Upper Miocene,being the response of Dongsha Movement in northern sheif of South China Sea,which age is 10.5 Ma. SB 2 with truncation,incised vaiiey fiiiing and oniap represents the iowest sea ievei stage during Miocene,and can be easiiy traced in the northern sheif basins of South China Sea；its age is 21.0 Ma. SB 3 with truncation and on-iap on the massif is the boundary between Eogene and Neogene,its age is 25.0 Ma. On the upiift SB 3 is represented by a hiatus between iate Oiigocene and iower Miocene where being iack of seguence SB 3 -SB 2 on the high,which may be cor- reiated to the hiatus spanning from 24 ~ 27.0 ~ 27.5 Ma in site 1 148 of ODP Leg 184. SB 4 is the boundary between up-per and middie Eocene,representing the second stage of Zhugiong Movement in northern sheif basins of South China Sea,which age is 39.4 Ma. Tg is the boundary between Cenozoic and pre-Cenozoic,which can be easiiy traced. The sedimentary environments and evoiution of different seguences stated above have aiso been anaiyzed according to their seismic characteristics and combining with those of the Peari River Mouth Basin. Seguence T g SB 4 and SB 4 -SB 3 were mainiy controiied by separated haif grabens,deveioping fan deita,fiuviai,shaiiow iake and swamp sediments,simiiar to those in the other areas in northern sheif of South China Sea,but the subsidence rate on the upiift was much iower,re-suiting in the forming of shaiiower iake and coarser sediments. After upiift and erosion stage during iate Oiigocene to eariy Miocene,transgress started and seguence SB 3 -SB 2 oniapped towards the upiift,deveioping coastai and shaiiow marine sediments,but the upiift high remained eroded and acted as a barrier between the Peari River Mouth Basin and centrai sea basin. SB 2 represents a regionai sea ievei faii and the paieo-sheif break probabiy shifted to modern iower siope. After that,seguence SB 2 -SB 1 oniapped to northern sheif and upiift,which had subsided under sea ievei,thus the modern framework of sheif-siope-centrai basin formed,and the upiift was covered by sheif-siope sediments. Seguence SB 1 -sea fioor is dominated by siope sediments simiiar to modern sedimentary environment.