浙江曹娥江下游XYC孔色度特征及其全新世环境记录*

XYC孔位于钱塘江南岸曹娥江下游地区。在对1717个样品的色度、粒度、总有机碳(TOC)测试分析的基础上,重点探讨该钻孔沉积物色度特征及环境意义,并结合年代框架讨论该地区环境变化特征。初步结论如下: (1)钻孔沉积物呈现高亮度、较低黄度和低红度特征,纵向看,①、②层色度波动明显,③层至⑧层下段色度变化稳定,⑧层上段至⑨层色度波动变化再次增强,呈波动—稳定—再波动特征。(2)亮度值与砂含量及TOC含量相关性较好,沉积动力强,砂含量高,亮度值高;TOC含量高,亮度值低。黄度、彩度值与TOC含量呈较好负相关,对气候的状况及海面变化有较好指示意义。(3)色度及其变化过程指示多水或水下沉积环境,并在一定程度上响应该地区海平面变化以及河流相—潮坪相—浅海相—湖沼相的沉积相变化过程: 9690—9107 cal a BP时段,该区以河流沉积为主,水动力变化不稳定,气候偏干,TOC含量较低,亮度高,红黄度低;9107—8613 cal a BP时段,黄度、彩度值降低,气候转湿,半咸水贝类生物及毕克卷转虫为主的底栖有孔虫的出现,表明研究区发生海侵并逐步由低潮坪转为高潮坪环境;8613—7330 cal a BP时段,黄度、彩度值最低,气候更湿润,伴有正常盐度的异地希望虫和少量抱球虫、圆辐虫等浮游有孔虫,海面进一步上升,成为浅海环境;7330—5131 cal a BP时段,黄度、彩度值升高,海面降低,气候变干,研究区转化为湖沼环境,泥炭发育。

Chroma characteristics and its Holocene environmental record of Borehole XYC in the downstream area of Cao'e River,Zhejiang Province

The Borehole XYC is located in the downstream area of the Cao'e River which is in the south bank of the Qiantang River. Based on the analysis of chroma,particle size and total organic carbon(TOC) of 1717 samples,the chromaticity characteristics and environmental significance of the drilling sediments were mainly discussed,and the characteristics of environmental change in the area were documented in combination with a chronological framework. The preliminary conclusions are as follows: (1)The drilling deposits show characteristics of high brightness, low yellowness and low redness. In the vertical direction,the chromaticity fluctuats markedly of Layers ① and ②,and the chroma changes steadly from Layer ③ to lower part of ⑧. However,the fluctuation amplitude of chromaticity changes from the upper part of Layer ⑧ to Layer ⑨ is enhanced again,and it presents the characteristics of fluctuation,stability and re-fluctuation eventually. (2)High brightness values brightness correlates well with sand and TOC content. The stronger the deposition power is,the higher the sand content is and the higher brightness value brightness is;while the higher of the TOC content,the lower of the brightness value. The values of low yellowness,saturation and TOC content have a good negative correlation,and also have a good indication of the humid climate and sea level changes. (3)The chromaticity and its variation process indicates a damp or subaqueous environment,and to some extent,it responds to the sea level change in the area and change process of sedimentary facies between fluvial facies,tidal-flat facies,neritic facies and limnetic facies. During 9690-9107cal a BP,the fluvial deposits were developed,the hydrodynamic changes were unstable,and the climate is dry,the TOC content is low,brightness is high,while the values of yellowness and redness are low. During 9107—8613 cal a BP,the values of yellowness and saturation were reduced,the climate was damp,the brackish water shellfish and benthic foraminifera, mainly including Ammonia beccarii vars., emerged,all of these indicates that transgression occurred in the study area and gradually changed from a low tidal flat to a high tidal environment. During 8932-7330 cal a BP,the values of yellowness and saturation are lowest,the climate was more humid,accompanied by the normal salinity of Elphidium advenum and a small amount of Globigerina spp., Globorotalia spp. and other planktonic foraminifera,the sea further rose into a shallow sea environment. During 8932-7330 cal a BP,the values of yellowness and saturation are increased,the sea level fell and the climate became dry,into the limnetic environment,and the peat was developed.