Cyclostratigraphy Of Mesozoic And Cenozoic And Implications For Hydrocarbon Exploration

Cyclostratigraphy is the subdiscipline of stratigraphy that deals with the identification,characterization, correlation, and interpretation of cyclic variations in the stratigraphic recordand, in particular, with their application in geochronology by improving the accuracy andresolution of time-stratigraphic frameworks. Since the recognition of ‘Milankovitch’ orbitalforcing as the ‘pacemaker of the ice ages’, cyclostratigraphy has attracted more and moreattentions from geoscientists and stratigraphers because it can considerably enhance bothrelative and absolute age controls at a resolution of10-100Ka, better understanding of thesedimentology, quantification of rates and duration of sedimentary, climatic, andpaleontological processes, as well as possibilities for correlation within and beyond the basin.During the past two decades, there have been many efforts to construct an accurate geologicaltimescale based on astronomical tuning of climatic response records to astronomical solutions.This provides a better accuracy than the conventional timescales which are often based onlinear interpolation between biozones and/or geomagnetic reversals and/or radiometricallydated calibration points. But in China, only few people focus on this discipline, with even nosystematic introduction of cyclostratigraphy in Chinese. In this dissertation, we introduce thefundamental conceptions, development history, research methods, and research status ofcyclostratigraphy in detail, and then undertake cyclostratigraphic research on several differentgeological times in the Huizhou Depression and the Meishan Section.Several formations of Tertiary in the Pearl River Mouth Basin of South China Seaconsist of deltaic siliciclastic and neritic shelf carbonate rhythmic alternations. To improve thestratigraphic resolutions for hydrocarbon prospecting and exploration in the basin, this study undertakes spectral analysis of high-resolution natural gamma-ray well-logging record todetermine the dominant frequency components and test whether Milankovitch orbital signalsare registered in the rhythmic successions. Because the high-frequency cyclostratigraphyrelies on the conventional timescales based on biostratigraphy, magnetostratigraphy, and/orradio dating, we use planktonic foraminifera, calcareous nannofossil, dinoflagellates, andspore-pollen to construct micropaleontology stratigraphic framework to providebiochronological constraints. Within biochronological constraint, a high-resolutionastronomical timescale was constructed through astronomical tuning of the naturalgamma-ray well-logging record to the most recent astronomically calculated variation ofearth’s orbit. The astronomically tuned timescale can be used to calculate astronomical agesfor geological events and bioevents recognized throughout the period. The differentsedimentary completeness, sedimentary duration, and types of sediment of the researchinterval determine that the sedimentary rate can not be obtained by the same method.Therefore, spectral analysis, sliding windows spectral analysis, high-density sliding windowsspectral analysis and phase relationship correlation methods were advanced to obtain thesedimentary rate in different research intervals.As the Global Stratotype Section and Point for the Permian-Triassic boundary (PTB), thebiostratigraphy, chronostratigraphy, event stratigraphy and ecostratigraphy of the intervalfrom the Upper Permian Changhsingian through the PTB to the lower Triassic YinkengFormation at Meishan section have been extensively studied. However, the sequencestratigraphy and cyclostratigraphy of the lower Triassic of this section have received far lessattention even though exposure of the Lower Triassic succession is also spectacular. Thesequence stratigraphic framework has been constructed by the regional sea-level changesinferred from the hatitat type which represents certain ecological geographic environments.As we know, the Permian-Triassic transition resulted in the most devastating biotic crisis inPhanerozoic history and drastically altered the balance of the biosphere and its subsequentevolution. As consequence of the most devastated biotic crisis, the Early Triassic marinefauna fossils appeared very rare worldwide. So, sequence stratigraphic framework constructedon the basis of ecostratigraphic analyses is questionable. Milankovitch signals have beendetected quanlitatively at Chaohu section which is near the Meishan section by previous works. While quantitative tests of Milankovitch climatic signals in Early Triassic marinerecords at Meishan section are lacking. Whether Milankovitch orbital forcing was a majorclimatic driver during this time is essential to understanding the controlling factors anddepositional mechanisms, and the prolonged biotic recovery after the end-permian massextinction. The depauperate nature of marine faunas suggests a rather low bioturbation level,which enables the excellent preservation of very fine rhythmic cyclicity in the Early Triassicsediments. The well-preserved rhythmic sediments are characteristics of the Lower Triassicsuccessions worldwide. Here, we present a case study of the lower Triassic YinkengFormation exposed at Meishan section, with objectives to distinguish different orders ofembedded cycles and employ modified version of Fischer plots to define the third-andhigher-order sea-level changes. Aiming at the lost signals and the existing noise in the resultof spectral analysis, we proposed an algorithm which deals with the depth-time domaintransformation in the last of this part, with advantages that it can take the differentsedimentation rates between different rock types into account during the transformationperiod.According to the recent published papers, most cyclostratigraphic researchs are focus onhow the variations of earth’s orbit affect the climatic system, and the evolution mechanisms ofthe monsoon, glaciations, bioevents, sea-level changes and etc. While the high-resolutionastronomically tuned Time Scale has still not been applied in hydrocarbon exploration. As thealready known cycles hierarchy and duration, in this dissertation, we attempt to probe intohow the high-frequency Milankovitch cycles can be used in the hydrocarbon explorationdomain like the orgin and duration of the third-order sequence in the classic sequencestratigraphy, high-frequency sequence division, the dection of sequence boundary andsedimentary discontinuity, the prediction of favorable sandbodies, and the estimation oferosion thickness.