| Cretaceous is a one of current international hot spot in geological researches. The study on cyclicity of Cretaceous sediments is an effective way to explore the Cretaceous earth surface system, and the cyclostratigraphy just provides a feasible ideas and methods for that. CCSD-SKI ( China Continental Scientific Drilling-SongKe I), a scientific drilling hole with whole coring, had taken the cores from the top of Quantou Fm. (upper Cretaceous) to the bottom of Taikang Fm. (Tertiary) with 96.46% of core recovery. Continuous core of upper Cretaceous provided an unprecedented platform for sediment cyclicity research.The rock core 2485.89m long is the study material of this thesis. Upper Cretaceous lithology section is built up by centimeter-level core description. Kinds of sedimentary microfacies are identified and typical sedimentary sequences are summarized. Meter-scale cycles (a basic genetic stratigraphic unit) are identified based on the explanation of sedimentary microfacies. Metre-scale cycles are classified based on detailed studies of internal characteristics within a metre-scale cycle. Fischer plots of metre-scale cycles show the stacking patterns of meter-scale cycle(sixth-order cycle), fifth-order cycle, fourth-order cycle and third-order cycle, and then cyclostratigraphic framework of upper Cretaceous in Songliao Basin is established. The bottom boundary ages of all members are calculated in three steps.First is taking reliable reference points in the section with the absolute ages from polarity stratigraphy and biostratigraphy as calculation starting points. Second is counting numbers of cycles which have orbit period (precession period or obliquity period) from the bottom boundary of member to starting points. The third is calculating the the duration by calculating the summation of each product of cycle number and corresponding period from starting point to bottom boundary. All boundary ages of member are calculated in this way. Upper Cretaceous chronostratigraphy of Songliao Basin is finally improved. Further calculation includes the time limits of all orders of cycles and the durations of unconformities. The mechanisms of different order cycles also are explained. Sedimentary evolution of Songliao Sag basin are discussed based on seismites in Qingshankou Formation, faults in Mingshui Formation and red beds, as well as sedimentary cyles in whole section of CCSD-SKI.The main progresses are following:1. Identification and classification of rocksTerrigenous clastic rock, intraclast rock and sedimentary pyroclastic rock are three main rock sorts indentified from the core rocks with 2485.89 m in CCSD-SKI. The terrigenous clastic rock is divided into 7 types of rocks after the grain size, including mudstone, siltystone, fine sandstone, medium sandstone, coarse sandstone, fine and medium conglomerate and there are 37 specific lithologies. The intraclast rock includes 3 types of rocks: limestone, dolomite and combustible organic rock, and there are 7 specific lithologies. The sedimentary pyroclastic rock is tuff only.2. Recognition and identification of sedimentary microfaciesLithology, structure, content, rock color and the sequence characteristics are considered in identifying sedimentary microfacies. There are five types of sedimentary environments, including meandering river, delta, lakeshore, shallow lake and semi-deep to deep lake in which 29 kinds of microfacies deveoped. The meandering river develops channel lag, point bar, natural levee, crevasse splay, crevasse channel, flooded plain and flooding lake. The delta develops subaqueous distributary channel, mouth bar, interdistributary bay, distal bar and slump sediment. The lakeshore develops sand beach and mud beach. The shallow lake develops mudstone of still water, turbdite, nearshore bar and tempestite. The semi-deep to deep lake develops mudstone of still water, mud limestone, dolostone, oil shale, volcanic ash, turbidite, slump sediment, temperitite, seismite, ostracoda limestone and sparite carbonate.3. Establishment of microfacies successionThe succession of sedimentary microfacies of CCSD-SKI is established based on completeness of microfacies identification in the whole well. Quantou Formation (from the top of the third member to the fourth member) was dominanted by meandering river facies, and shallow lake and delta just developed at the top of the fourth member of Quantou Formation. Qingshankou Formation was dominated by semi-deep lake and deep lake facies except the top part of the third member which developed the shallow lake facies. Yaojia Formation was dominated by shallow lake and semi-deep lake faices, and delta facies just developed at the bottom of the first member of Yaojia Formation. The first and the second members of Nenjiang Formation were domimated by semi-deep and deep lake facies, the third and the fourth members of Nenjiang Formation were dominated by shallow lake and delta facies, and the fifth member of Nenjiang Formation was dominated by meandering river facies, and delta facies just developed at the bottom of the fifth member of Nenjiang Formation. The lower and the upper parts of Sifangtai Formation were dominated by meandering river facies, and shallow lake facies developed at the middle part. Mingshui Formation was dominated by meandering river facies and the shallow lake facies just developed at the middle and the upper parts. The sedimentary microfacies are different,developed in the same facies but in different formations.4. Identification and classification of meter-scale cyclesThe identification of basic genetic stratigraphic cycle unit is the basis of section cyclstratography research. Each meter-scale cycle represents a forming process of basic stratigraphic unit. Sediments in different sedimentary environments formed their own unique type of meter-scale cycles. Three sorts of meter-scale cycle are classified, which are normal grading, reverse grading and non-grading. The normal grading with fining upward developed in meandering river sediments, lakeshore sediments and upper nearshore bar,indicating a decreasing hydrodynamic energy upward. This sort includes channel lag-point bar, channel lag-point bar-natural levee, point bar-natural levee, point bar-natural levee- flooding lake, crevasse splay- flooding lake, crevasse splay-flooded plain-flooding lake, crevasse splay-flooded plain, flooded plain-flooding lake, crevasse channel-flooded plain, crevasse channel-flooding lake, crevasse channel- crevasse splay-flooded plain, upper nearshore bar, sand beach-mud beach, sand beach and tempestite. The reverse grading with coarsing upward developed in deltac sediments, shallow lake sediments and semi-deep to deep lake sediments,indicating a increasing hydrodynamic energy upward. This sort includes subaqueous interdistributary bay-mouth bar- subaqueous distributary channel, mouth bar- subaqueous distributary channel, subaqueous interdistributary bay-mouth bar, distal bar- mouth bar, mudstone of still water-distal bar, mudstone of still water-sheet sand, mudstone of still water-slump sediment, medium nearshore bar, lower nearshore bar, mudstone of still water-gravity flow channel, mudstone of still water-sandy turbidite, mudstone of still water-ostracoda clast turbidite and mudstone of still water-seismite. Non-grading with no grade changing presents mainly the changes of lithology (mudstone and intraclast rocks) and rock color within a meter-scale cycle. This sort includes marlite-mudstone of still water, recrystalline limestone-mudstone of still water, mudstone of still water-dolomite, oil shale-mudstone of still water, reduction color- oxidation color, strong reduction color- weak reduction color.5. Establishment of upper Cretaceous cyclostratigraphic framework in Songliao BasinFischer plots of meter-scale cycles present the vertical stacking patterns of meter-scale cycles (equivalent to sixth-order cycle). Fifth-order cycle, fourth-order cycle and third-order cycle are identified in turn based on accommodation space changing trend showed by Fischer plots. Fifth-order cycles are defined by vertical stacking of meter-scale cycles, Fourth-order cycles are defined by vertical stacking of fifth-order cycles, third-order cycles are defined by vertical stacking of fourth-order cycles. Each stacking process presents the accommodation space change of increasing at first and then decreasing. Quantou Formation presents seventy-six meter-scale cycles(six-order), twenty-five fifth-order cycles, eight fourth-order cycles and one third-order cycle. Average three or four meter-scale cycles stacked one fifth-order cycle, and average two or three fifth-order cycles stacked one fourth-order cycle. Qingshankou Formation presents five hundred and three metre-scale cycles, one hundred and fifty-five fifth-order cycles, twenty-six fourth-order cycles and three third-order cycles. Average three or four metre-scale cycles stacked one fifth-order cycle, and average five or six fifth-order cycles stacked one fourth-order cycle. Yaojia Formation presents five hundred and fifty-one meter-scale cycles, forty-five fifth-order cycles, ten fourth-order cycles and one complete and two incomplete third-order cycles. Average three or four metre-scale cycles stacked one fifth-order cycle, and, average four or five fifth-order cycles stacked one fourth-order cycle. Nenjiang Formation presents six hundred and thirty metre-scale cycles, one hundred and fifty-two fifth-order cycles, forty fourth-order cycles and five third-order cycles. Average three to five metre-scale cycles stacked one fifth-order cycle, average three or four fifth-order cycles stacked one fourth-order cycle. Sifangtai Formation presents one hundred and seventy-four metre-scale cycles, forty-three fifth-order cycles, thirteen fourth-order cycles and two third-order cycles. Average three or four metre-scale cycles stacked one fifth-order cycle, and average three or four fifth-order cycles stacked one fourth-order cycle. Mingshui Formation presents three hundred and sixty-one meter-scale cycles, one hundred and nine fifth-order cycles, twenty-nine fourth-order cycles and one complete and two incomplete third-order cycles. Average three or four metre-scale cycles stacked one fifth-order cycle, and average three or four fifth-order cycles stacked one fourth-order cycle.6. The improvement of late Cretaceous chronostratigraphy framework in Songliao BasinCalculating geological age in high resolution is an important advantage of cyclostratigraphy, just as it is used in International Stratigraphic Chart (2004). Meter-scale cycles with main precession period in meandering river sediments and fifth-order cycles with main obliquity period are used used in calculating cyclostratigraphic age of CCSD-SKI. The final calculated result is basically consistent with polarity stratigraphy, biostratigraphy and U-Pb ages. The chronostratigraphy framework of upper Cretaceous Songliao Basin is improved based on cyclostratigraphic age. The bottom boundary ages of each member and the duration of unconformity are provided. The bottom boundary age of Qingshankou Formation is 92.04Ma, the bottom boundary age of Yaojia Formation is 85.97Ma, the bottom boundary age of Nenjiang Formation is 84.21Ma, the bottom boundary age of Sifangtai Formation is 75.36Ma, the bottom boundary age of Mingshui Formation is 70.63Ma, and the top boundary age of Mingshui Formation is 64.32Ma. The duration of the unconformity developed at the top of Nenjiang Formation is 1.1 Ma and that developed at the top of Sifangtai Formation is 1.2Ma.7. Time limits of cyclesEach cycle in cyclostratigraphy framework has it's own time limit of cycle. The time limit of cycle is closely related to main controlling factors of cycle forming, but sedimentary records of main controlling factors are differential in different sedimentary environments. The time limits of cycles in CCSD-SKI are as follows.The meter-scale cycles in delta and lake environment have semi-precession period of 8.1~12.29ka, the meter-scale cycles in meandering river environment have precession period of 22.28~22.50ka. The fifth-order cycles in lake and delta environment have obliquity period of 39.03~39.59ka, the fifth-order cycles in meandering river have periods within short eccentricity of 72.5~92.2ka. The fourth-order cycles have eccentricity period of 149~275.38ka. The third-order cycles have a minimum period of 1.10Ma and a maximum period of 3.42Ma.8. Forming mechanisms of cyclesThe forming mechanisms of meter-scale cycles and higher-order cycles are determined based on detailed explainations of autocyclic factors of meter-scale cycle, stacking patterns of cycles and time limits of cycles. The results are as follows: the forming mechanism of normal-grading and reverse-grading meter-scale cycles (excluding event sediments induced meter-scale cycles) was a process of autocycle controlled by allocycle, the forming mechanism of event sediments induced meter-scale cycles was a process of autocycle induced by allocyclic factors, the forming mechanism of non-grading meter-scale cycles was a process of allocycle. The forming process of fifth-order cycles was controlled by obliquity and superposition effect of obliquity period and short eccentricity period. The forming process of fourth-order cycles was controlled by superposition effect of short period and eccentricity period. The forming process of third-order cycles was mainly controlled by basin tectonic activities, followed by external source input, climate change and earth orbit system factors which may controlled the external source input and climate change.9. New understandings of sedimentary evolution of Songliao sag basin based on CCSD-SKISeismites developed in Qingshankou Formation are evidence of Sunwu-Shuangliao transcrustal fault activities. Transcrustal fault activities and associated volcanic activities show that basin extension occurred at the strong subsidence stage of sag basin. Expansion of the lake area and the development of extensional faults in the lower and middle part of Sifangtai Formation, the first member and parts of second member of Mingshui Formation, indicate that extension also occurred at the shrinkage stage of sag basin. Cyclic development is a significant characteristics of upper Cretaceous red beds in Songliao Basin. The studies of relations between rock colors and palaeoclimate show that the red beds developed in high temperature and arid environment or medium temperature and semiarid environment. In addition, red beds corresponding to low accommodation and sedimentary records of Milankovitch cycle (orbital cycle) in whole well indicate climate played an important role at the sedimentary evolution stage of Songliao sag basin.
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