上新世湖相纹泥及其环境信息与时间标尺记录

纹泥反映了湖相沉积物中特有的沉积韵律，是气候的季节变化和年际变化的产物。山西榆社张村地区上新世晚期的湖心相沉积中发育了极为完好的纹泥剖面。纹泥深浅相间形成清晰的纹理，分别代表夏秋和冬春。一深一浅组成一对，代表一年。纹泥层的单层厚度平均为0．12～0．25mm／条，薄者＜0．1mm／条，厚者可达0．3mm／条。暗色纹泥层的厚度大于浅色纹泥层。暗色纹泥的有机质含量丰富，木本植物孢粉占优势，同时CaO的含量低；浅色纹泥恰好相反。湖相纹泥具有建立高分辨率时间标尺和环境演化序列的特殊优越条件。

LATE PLIOCENE LACUSTRINE VARVES AND ITS ENVIRONMENTAL INFORMATION AND TIME MARK RECORD

Varve, a sort of lacustrine sediments was preduced by seasonal and annual climatic variation. Varve sediments were mainly formed in the central parts and bays of the lakes. The seasonal climatic variation resulted in a series of variations in the lakes, such as the hydrodynamics, physical and chemical characteristics of lake water,the input materials, and the organic composition, etc. These in turn resulted in seasonal variation of the biotic-sedimentation process and the varve deposits were finally formed. In the mean time, the periodical annual variation was also clearly recorded in the varyes. Varyes mirror the climatic changes in temperature and wetness.A well developed varve profile 23.3m in abackness, was discovered in the late Pliocene lacustrine sediments in Zhangcun, Yushe Basin, Shanxi Province. The succession is follows:(1) Two thick layers of silt-fine sand, located in 2 200～2 330 and 1 655 ～1 860cm, counting from the top to bottom, respectively. It presents blocky structure at the bottom and stratified in the middle and upper portions.(2) Five most typical developed varve layers which is located in the layers of 1 860 ～ 2 200, 1 460 ～ 1 655, 1 414 ～ 1 424, 1 392 ～ 1 403, and 1 143 ～ 1 385cm,respectively.Among them, three layers are the back-most with well developed varyes containing fossils of snails, fish, and leaves. The varve deposits in the Zhangcun profile are dark gray, gray green, grayish white, and white colors. The dark colored layers are alternating with light colored ones with distinctive veins, which represents summer-autumn and winter-spring seasons respectively. A pair of varve layers consisting of a dark and a light colored layer represents a year. The mean thickness of a single varve is 0.12- 0.25mm. The thickness of dark layers of the varve are normally thicker than that of the light-colored layers. The structure and composition of the varve layers are fairy complicated. Gypsum occurs between varve layers or went embedded in several layers in the depth of 1 190 ～ 1 530cm, covering a total thickness of about 4 meters. Gypsum are normally needle crystals, growing oppositely from the top and bottom surfaces of the bedding planes. The thickness of a single gypsum layer is 0.5～2cm.(3) Varyes with different thickness total 688cm in thickness located in the layers of 550～1 143 and 340～395cm. Their thickness is variable, 0.2～0.3mm as mean value ranging from 0.5 to less than 0.11mm. Another characteristic is the striking light color of the varyes, which resulting in the indistinct of lamination.(4) Blocky silt-fine sand and marl layers situated in the up-most section of the profile, ranging from 395-510 and 0～340cm, totaled 455cm in thickness.The dark varyes contain abundant organic matter with low CaO content as shown in Tables 1 and 2. Pollen results suggested a conifer-broad leaf mixed forest environment dominated by Picea, Ulmus, Pinus, Abies, Quercus, and Carpinus. On the contrast the light colored varyes contain less organic matter and higher CaO. In their pollen assemblage, herbs, mainly Artemisia predominate.This study has achieved the following results:.(1) The varyes at Zhangcun were generated from seasonal and annual climahc variations. The dark colored layers were deposited in summer and autumn while the light colored ones in winter and spring. This is a characterishc feature of the varyes in monsoon are4 which differs from that in the glacial lakes. A pair of varyes was deposited in a year and therefore can be used for high resoluhon bine mark.(2) Based on visual counhng enhanced with microscopic observahon, the varve layers total 76 720, i. e., 38 360 pairs, represenhng 38 360 years with unavoidable kronor ermrs. The sedimentahon nato is calculated tO be 390ruin / Anllenniurn.(3) The sedimentahon rhytrhln of varyes and the thickness of the dark colored layers may suggest a short Periodical wet Period of 30～40 years and 100- 150 years.(4) The gypsum in the varyes was secondary originated. It was a by-product during the lithogenesis of the varyes. The intervals of gypsum layers are n