南海北部琼东南盆地渐新世-上新世沟鞭藻指示的沉积环境

OLIGOCENE TO PLIOCENE PALAEOENVIRONMENTAL EVOLUTION BASED ON DINOFLAGELLATE CYSTS FROM THE QIONGDONGNAN BASIN,NORTHERN SOUTH CHINA SEA

通过对南海北部琼东南盆地渐新世—上新世3个钻井剖面412个沟鞭藻样品的系统分析,发现了较丰富的沟鞭藻化石。根据沟鞭藻化石丰度、分异度变化以及特征性的环境指示种,对琼东南盆地渐新世至上新世的沉积环境进行了详细研究。认为研究区从早渐新世早期海水开始入侵,至早渐新世晚期海侵范围进一步扩大,一直持续到晚渐新世;早中新世沟鞭藻化石数量和种类明显出现低谷,发生了一次较为明显的海退;中中新世至晚中新世,沟鞭藻化石较丰富,丰度和分异度增加,海水明显比早中新世沉积时期加深;早上新世早期,指示海侵的化石属种较丰富,反映了温暖浅海的沉积环境;早上新世晚期,指示一种开阔的海洋环境,水体较深;晚上新世早期,沟鞭藻化石属种面貌反映了热带浅海环境,但水体可能比早上新世晚期沉积时要浅;晚上新世晚期,指示海侵的沟鞭藻化石属种达到最繁盛时期,海侵范围进一步扩大。

Abundant dinoflagellate cysts have been found in the Lower Oligocene to Upper Pliocene drilling stratum of the Y-1, Y-2 and Y-3 wells in the Qiongdongnan Basin, northern South China Sea. Based on the diversity, abundance and the morphology of the dinoflagellates, Oligocene to Pliocene sedimentary environment in Qiongdongnan Basin was investegated. Five environmental evolution stages may be recognized. Stage I. Sea water began to invade in early stage of Early Oligocene, and in late Early Oligocene, it maintained a continuous rising of the sea level until the Late Oligocene. Stage II. As the abundance and diversity of dinoflagellates is very low in Early Miocene, it shows that the seawater became shallow in this stage. Stage III. This stage shows a high abundance and diversity of the dinoflagellates, it indicates the rising of the sea level in Middle to Late Miocene. Stage IV. The occurrences of key species which may be the transgression environment indicator, it shows the environment became the neritic sea in early stage of Early Pliocene. And in late Early Pliocene, the sea level continued rising. Stage V. The seawater of early Late Pliocene became shallow again compared with the late Early Pliocene. Based on the highest occurrence of dinoflagellates, it indicates a rising of the sea level, and the expanding of the transgression.