Paleoclimatic Evolution Of The Songliao Basin In The Late Cretaceous

Today warming of the climate system is driven by increases in anthropogenic CO2 emissions, which may force the earth to enter a global greenhouse climate state. The Late Cretaceous is a prototypical example of a past greenhouse period, and therefore paleoclimatic and paleoenvironmental studies of this period provide valuable constraints on future climate predictions. Most records of climate in the Late Cretaceous are derived from marine sediments, and knowledge of terrestrial climate changes is limited due to the fragmentary geological records on continents. The SK-1 Continental Scientific Drilling Project in the Songliao Basin provides a nearly continuous terrestrial record of the Late Cretaceous. In this thesis, we use sedimentary, clay mineralogical and stable isotopic proxies in SK-1 cores to reconstruct paleoclimatic and paleoenvironmental changes of the Songliao Basin in the Late Cretaceous.Sedimentary proxies in SK-1 indicate that the paleolake-level changes were controlled by both tectonic subsidence and paleoclimate, while development of paleosols was primarily influenced by paleoclimate. Clay minerals in SK-1 have three different origins, and sedimentary clays without alteration by diagenesis are controlled by provenance and climate. Isotopic records of paleosol carbonates and compound-specific sedimentary n-alkanes are strongly influenced by temperature and precipitation.Comparing this data with previously published paleoclimatic records in the Songliao Basin, and a global network of paleoclimate records, the proxies in SK-1 indicate that the terrestrial paleoclimate in the Songliao Basin was tightly linked to global climate in the Late Cretaceous. From the late Turonian to early Santonian(~93-84Ma), the earth was in a hot greenhouse state caused by high atmospheric p CO2, and the Songliao Basin climate was warm and semi-humid indicated by high lake level and moderately developed paleosols in the Quantou, Qingshankou and Yaojia Formations. From the late Santonian to the early Campanian(~84-76Ma), the earth cooled gradually as atmospheric p CO2 decreased, and the D of compound-specific n-alkanes in Nenjiang Formation, Units 1 and 2 indicate a relatively depleted D of precipitation, and therefore a cool climate in the Songliao Basin. A prominent D at the upper part of Nenjiang Formation, Unit 1 indicates a sudden change in the lake bottom water sources, and was probably caused by increased runoff from north of the basin bringing cold water from a high-latitude river. From the mid-Campanian to the latest Maastrichtian(~76Ma-66Ma) the earth was characterized by a variable greenhouse climate. Multiple lines of evidence corroborate this fluctuating climate state when the Sifangtai and Mingshui Formations were deposited. A large negative 18-1 pedogenic carbonate nodule in the early Maastrichtian(~70Ma) is interpreted to be the result of decreasing temperature and/or strengthened westerlies during global cooling. At the same time, increases in illite content and the quartz/clay ratio, and decreases in illite chemistry index indicate increasing physical weathering and therefore a more arid climate. The negative 13 C isotopic excursion at ca. 66 Ma and 69 Ma are modeled as higher primary productivity caused by increasing temperature and precipitation in response to a warming climate. Clay mineralogical proxies also indicate increasing chemical weathering and a more humid climate. To summarize, during most periods of high p CO2 in the Late Cretaceous the Songliao Basin climate was warm and humid, which implies that, with increased future anthropogenic CO2 emissions, northeastern China will experience increasing temperature and precipitation.