In Partial Fulfilment Of Requirements For Admittance Of Philosophy

Nihewan beds" means the Quatemary sediments on the top of the "Red clay" inNihewan basin. The Haojiatai, Xiaochangliang and Donggutuo sections were selectedto study the sequence stratigraphic and the magnetostratigraphic features based on thefiled work in order to compare the sediment characteristics, build the age frame andillustrate the environment meaning of the typical sections.These sections distribute along the NEE direction. The Haojiatai section lies tothe center, and the Dongtutuo section situates on the margin of basin. The sections canbe divided into two third level sequences including some subsequences according tothe characteristics of the sediment grain -size, the magnetic susceptibility and thecarbonate sediment. Fifteen subsequences in the Haojiatai section, eleven's in theXiaochangliang section and nine's in the Donggutuo sections can be identified. Eachsequence and subsequence is constituted by the lacustrine transgressive system andlacustrine regressive system, which means a rising - falling cycle of lake level. Theformer feature is low value in magnectic susceptibility, anisotropic magnitude (P),magnetic lineation (L) and high fraction of fine grain. The later's reverse to it. Thesequence one only developed a little in the Xiaochangliang and the Donggutuosections, because their sediments were formed by the lacustrine expanding process.The magnetostratigraphic investigation on the Haojiatai and the Dongtutuosections were conducted. The characteristic remanent magnetization(ChRM)directions of all samples can be obttained through thermal demagnetization. TheChRM directions have dual polarity chron. One is Brunhes normal polartiy, andanother is Matuyama reverse polarity. Brunhes polarity chron range from 0-28.99mand Matuyama from 28.99-122.3m on the Haojiatai section. Jaramillo subchron isfrom 53.9 to 62.94m, and some normal directions in section bottom may be thebegining of Olduvai subchron. The Donggutuo section aIso have Brunhes(0-17. 16m)and Matuyama polarity chron(l7. 16-44m), Jaramillo subchron exist at 31 .96-39m.Three sections sediment can be corrected by use of the study results of sequencesstratigraphy, magnetostratigraphy and the susceptibility cureve with depth. The twothird level sequences of each section are same period sediment, and the subsequencescan be divided into nine comparing layers. B/M transition and low Jaramillo recordare in same layers. Comparing the fraction curve of 0.2-7.5Pm grain size of theHaOjiatai section with oxygen isotope curve of deep sea sediments corrected byWolfberg applying Milankovitch theory, the results show high value of the fraction isconsistent with odd number stage of isotope index, and Iow value correspond to evennumber stage. Loess susceptibility curve can compare with Weinan loess section's andis parallelism with l-5 isotope stages. The lacustrine correspond to 13-63 isotopestages. The sediments about 400kyr. were absent between the top of lacustrine andloess. The paleoculture age of the Xiaochangliang and the Donggutuo sections isabout l. l - l .2 Myr.The lacustrine suscePtibility value and fine grain fraction are also good proxiesreflecting the environrneot change. Low vaIue of susceptibility and high fraction olfine grain show warm climate, deoxidize environment and lake-level rising; Highsusceptibility and low fine grain fraction imply cold climate, oxidation environmen1and lake-level falling. The sections record fifteen cycles of climate and lake-levelchanging according this rule.The results to comprehensive analysis the sequence stratigraphy and themagnetostratigraphy show that the basin can be divided into fOur evolement stageswithin limited space-time range(the Haojiatai section as an example).Stage one: From the bottom to 76m of section, age from l780 to l200kyr. Stablesubsiding stage;Stage two: From 76m to 64m, age from l200 to l056kyr. The lake water waswidening, and sediments were overl...