| This thesis consists of three separate studies of records of climatic and environmental change in various sedimentary sequences from China.; The first study examines carboxylic acids in recent and ancient hypersaline sediments. The unexpected prevalence of these acids in thermally mature samples from the Qianjiang Fm. is attributed to the preservation of their carbon skeletons under hypersaline depositional conditions, a process that may perhaps be mediated by formation of organo-sulfur compounds.; In the second study, the distributions of long-chain alkenones in lacustrine sediments are, for the first time, used in a systematic assessment of continental climate at a site on the Tibet Plateau, an area critical to global climate. Thus, alkenone unsaturation indices (U{dollar}sbsp{lcub}37{rcub}{lcub}rm K{rcub}{dollar}, U{dollar}sbsp{lcub}38{rcub}{lcub}rm K{rcub}{dollar}) in the {dollar}sp{lcub}14{rcub}{dollar}C-dated sediments provide a quantitative measure of water temperatures that can be integrated with other environmentally sensitive signals, including lake level, lithology, and palynology. These measures provide a record of climatic changes over the last 30 ka. They reflect a warmer, humid period from {dollar}sim{dollar}30 to {dollar}sim{dollar}23 ka B.P. when temperatures were {dollar}sim{dollar}5{dollar}spcirc{dollar}C higher than present; a cool, arid interval from {dollar}sim{dollar}20 to {dollar}sim{dollar}10ka B.P., including cold episodes corresponding to the last glacial maximum ({dollar}sim{dollar}17-18ka B.P.), and the Older and Younger Dryas ({dollar}sim{dollar}14ka, {dollar}sim{dollar}11ka B.P., respectively); rapid climate fluctuations leading to warmer and wetter conditions in the early Holocene ({dollar}sim{dollar}10-7.5ka B.P.); and a warmer and increasingly drier climate for the middle Holocene (7.5-3.5 ka B.P.) and late Holocene (3.5-0ka B.P.) developing into the modern semi-desert environment.; The third study evaluates the distributions and carbon isotopic compositions ({dollar}deltasp{lcub}13{rcub}{dollar}C) of biomarkers in a Permo-Triassic sequence from southern China. The {dollar}deltasp{lcub}13{rcub}{dollar}C values of individual compounds, including n-alkanes and acyclic isoprenoid alkanes, are 5-10{dollar}perthous{dollar} higher in the Permian than in the Triassic strata. The observed molecular and isotopic variations are consistent with the recognized global decrease in marine productivity and the accompanying climatic/environmental changes at the Permo-Triassic boundary. |
