江苏海门王浩钻孔全新世钙质超微化石的环境意义

EVIDENCE OF SEA LEVEL TRANSGRESSION AS INDICATEDBY HOLOCENE CALCAREOUS NANNOFOSSILSFROM WANGHAO HOLES, HAIMEN COUNTY,JIANGSU

初步研究了海门王浩地区ＷＺＫ０１０、ＷＺＫ２１４、ＷＺＫ３００３钻孔中的全新世钙质超微化石组合，优势种Ｇ．ｏｃｅａｎｉｃａ组合中平均占９７％。依据化石的种数、丰度和保存状况，自下而上划分３个亚组合。第Ⅰ亚组合，深度７４４７ｍ，由Ｇ．ｏｃｅａｎｉｃａ，Ｈ．ｃａｒｔｅｒｉｉ，Ｈ．ｗａｌｌｉｃｈｉｉ，Ｓ．ｌａｍｉｎａ，Ｕ．ｓｉｂｏｇａｅ组成，丰度较高，保存较好，代表前三角洲－浅海环境。第Ⅱ亚组合，深度４７—２５ｍ，成分有Ｇ．ｏｃｅａｎｉｃａ，Ｈ．ｃａｒｔｅｒｉｉ，Ｓ．ｌａｍｉｎａ，Ｕ．ｓｉｂｏｇａｅ，丰度低，种数少，保存较差，是三角洲前缘的产物。第Ⅲ亚组合，深度２５—２．０ｍ，种类计有Ｇ．ｃｏｅａｎｉｃａ，Ｅ．ｈｕｘｌｅｙｉ．Ｂ．ｂｉｇｅｌｏｗｉｉ，Ｈ．ｃａｒｔｅｒｉｉ，Ｈ．ｗａｌｉｃｈｉｉ，Ｈ．ｈｙａｌｉｎａ，Ｓ．ｈｉｓｔｒｉｃａ，Ｓ．ｌａｍｉｎａ，Ｕ．ｓｉｂｏｇａｅ，Ｃ．ｌｅｐｔｏｐｏｒｕｓ等，含量较高，种数较多，保存一般，反映海湾一渴湖环境。３个亚组合所在地层的岩胜分别为下部粘土、粉砂，中部粉细砂，上部粘土、粉砂。研究结果证实。

This paper reports the appearance of Holocene calcareous nannofossils in a sedimentcore collected from the Wanghao area of Haimen County,Jiangsu Province,China.Gephyrocapsa oceanica is the predominant species in the core,representing an average of 97% ofthe assemblages in the samples examined. Based on abundance and diversity of the speciesassemblages,the core can be divided into three sections.Section I(74-47m)The predominant calcareous nannofossils species consist ofGephyrocapsa oceanica, Helicosphaera carterii, Helicosphaera wallichii,Syracosphaeralamina,and Umbilicosphaera sibogae. The sediment feature is primarily composed of graygreen clays and clayey silts. This is an indication of predelta--neritic environments.Section I(47-25m)The samples are predominantly composed of four species Gephyrocapsa oceanica, Helicosphaera carterii, Syracosphaera lamina, and Umbilicosphaera sibogae. The abundance of nannofossils was much lower in the section as compared to sectionsfrom other depths. Gephyrocapsa oceanica found in the samples are poorly preserved andmostly in small fragments. The sediment texture is primarily composed of fine sands. Thisis an indication of an intertidal environment at the edge of the delta.Section K (25-2m) There is a high abundance of wei'l-preserved calcareous nannofossils. The sediment is composed of gray green clays and clayey silts. Ten predominant calcareous nannofossil species found in the samples are Gephyrocapsa oceanica, Eml'lianiahuxleyi, Braarudosphaera bigelowii, Helicosphaera carterii, Helicosphaera hyalina,Helicosphaera walll'chii,Syracosphaera lamina, Syracosphaera histrica, Umbilicosphaera sibogae and Calcidiscus leptoporus. These species showed that the area was in bay or lagoonalenvi ronments.The data presented illustrate that the environment in the Wanghao area had undergone major changes in the Holocene from a coastal marine environment to a bay or lagoon.This change corresponds to the transgressive-regressive cycle of sea level changes whichhas dominated the Yangtze River Delta since the postglacial epoch.'