南黄海西部陆架氧同位素3期以来的古沉积环境演化

PALEOENVIRONMENTAL EVOLUTION IN THE WESTERN SHELF OF THE SOUTHERN YELLOW SEA SINCE THE MARINE ISOTOPE STAGE 3

本文选用南黄海西部陆架SYS-0701孔33.30m岩心,通过有孔虫分析,结合粒度变化和过孔浅地震剖面解译,揭示了本区MIS3期以来的古环境演化。MIS3期早期为近岸浅海环境,沉积相为泥质(远端)三角洲前缘和前三角洲沉积,中晚期为滨岸环境,沉积相为砂质(近端)三角洲前缘沉积;MIS2期地层缺失;MIS1期底部为全新世早期海水入侵时留下的潮道充填沉积,中晚期为浅海环境,沉积相是近500年以来形成的老黄河三角洲的水下三角洲沉积。通过研究识别出了全新世小冰期(LIA)中的2个冷期和1个暖期对应沉积,其中孔深7.21—6.29m为LIA第1冷期(1450—1510AD)沉积,期间有孔虫丰度低,典型冷水种Buccella frigida和半咸水低温低盐种El-phidium magellanicum含量均较高;孔深6.29—4.30m为LIA第1暖期(1510—1560AD)沉积,有孔虫丰度大幅度增加呈峰值区,Buccella frigida含量降低,而温带广温种Ammonia maruhasii则有所增加;孔深4.30—1.43m为LIA第2冷期(1560—1690AD)沉积,丰度降低,但属种面貌未很好体现,需要做进一步的研究加以验证。

The Upper 33 meter sediment of Core SYS-0701 taken from the western shelf of the southern Yellow Sea was used to analyze foraminifera. Combined with grain size changes and seismic profile (passing through core SYS-0701) , the paper has revealed the paleoenvironmental evolution of the study area since the Marine Isotope Stage (MIS) 3. The sedimentary environment was coastal shallow water, with a muddy (distal) delta-front and prodelta deposits during the early MIS 3. In the late MIS 3, the environment changed to the offshore water with a sandy (proximal) delta-front deposit. There is no sedimentary record for the MIS 2 in this region. The environment was interpreted as tidal-channel filled by seawater intrusion in early Holocene, while a subaqueous delta deposits of the Old Yellow River delta in a shallow sea was suggested during the last 500 yeas. Through the research we have identified the corresponding deposition of 2 cold stages and 1 warm stage during the Little Ice Age ( LIA ) in Holocene. Depth 7.21—6.29 m which was inferred corresponding to the first cold stage of LIA ( 1 450—1 510AD ), typical cold water species Buccella frigida and low temperature and salt species Elphidium magellanicum are more abundant. Depth 6.29—4.30m should be corresponding to the first warm stage of LIA (1 510—1 560AD ), the foraminiferal abundance increased substantialy with a peak abundance, species Buccella frigida decreased and the extensive-warm water species Ammonia maruhasii increased. Depth 4.30—1.43 m corresponding to the second cold stage of LIA (1 560—1 690AD ), the foraminiferal abundance reduced and the species appearance does not have a good response, which needs further study.