Integrated Study Of Petrophysical Analysis For Cretaceous Paleoenvironmental Research

The history of our planet proves that its formation dates back several billion years ago.Since its creation,it has been subjected to several geological and climatological events with many evidences preserved in the deep layers of both marine and continental sediments.Studies based solely on the Earth's surface are not sufficient for a better understanding of these changes,and drilling constitutes only one of the best approaches.Scientific Drilling Projects are aimed to probe and obtain continuous and complete sedimentary strata and also to reconstruct paleoenvironment and paleoclimatic evolution history based on biological,geochemical and physical proxies whose study can be useful to decipher past environment changes.Paleoclimate and paleoenvironmental research in both marine and terrestrial milieus provide important two-side views on the past climatic and environmental variations which can help geoscientists better understand the past state of our planet as well as the majors geological events it has undergone,and their marine and continental repercussions.However,such integrated studies are scarce due to the unavailability of high resolution continuous paleoenvironmental proxies.Geophysical well logs represent in-situ,continuous and high-resolution petrophysical and geochemical parameters of well-preserved underground strata ranging from tens to thousands of meters,making well logs important archives of paleoenvironment and paleoclimate.This research work aims to comprehensively integrate and correlate marine and terrestrial paleoenvironmental/paleoclimate changes based on well log data.Besides,the current study characterizes some complex paleoenvironmental phenomena such as oceanic/lacustrine anoxic events,Cretaceous-Paleogene demarcation and their petrophysical responses in both marine and continental environments based on non-stationary analysis methods.The work is achieved by intercorrelating Upper Cretaceous sedimentary records from the Chinese Continental Scientific Drilling Project Songliao Basin and some Marine Scientific Drilling datasets.The main conclusions and understanding of this study are as follows:(1)The physical properties especially gamma ray and resistivity of terrestrial and marine deposits are proven to be sensitive to past environmental variations and correlated well with changes in the geochemical data.These logging signals have proven to be alternative means to infer useful paleoenvironment and paleoclimate details such us climatic fluctuations,marine incursion,sea level variation.Intervals of oceanic and lacustrine anoxic events related to important changes in the carbon cycles,high sea level,low sedimentation amplitude and high organic-rich shale are associated with significant shifts in the petrophysical properties.Gamma-ray and resistivity represent useful alternative means for continental and marine past environments comparison and intercorrelation.(2)The self-similarity of the Coniacian-Santonian oceanic anoxic event(OAE3)and its terrestrial expression(TEOAE3)was explored for the first time through analysis of the scaling behavior of thorium-potassium and thorium-uranium distributions both in marine and continental environments using the multifractal detrended fluctuation analysis(MFDFA).In both marine and terrestrial depositional environments,the OAE3 and TEOAE3 intervals are mainly defined by their multifractality due to longrange correlations.Nevertheless,the OAE3 intervals have different multifractal features in both marine and non-marine systems that are mostly influenced by fluctuations in the clay mineralogy and the paleo-redox conditions,though some similar trends exist.Based on radioisotope elements,valuable hidden paleoenvironment details have been drawn from the multifractal properties indicating that MFDFA is sensitive to shifts in the sedimentation patterns,and so can be a useful analysis method for both marine and terrestrial paleoenvironmental research.(3)It was found out that the transition from Cretaceous to Paleogene is associated with significant changes in the physical properties of the diverse formations.Although the logs responses were not always identical in the various depositional systems;however,the multi-resolution scanning detection methods indicated that the key sequence boundaries in both marine and terrestrial systems can be detected in the logging signals.In the non-marine Songliao Basin,the K-Pg demarcation is found to be located between depth of 335 – 330 m with a higher confidence.Comprehensive analysis of logging data can effectively help in locating major geological events with more precision since the logs are in situ parameters and moreover have high vertical resolution.This study provides significant evidences regarding the sensitivity of petrophysical proxies to infer past environment changes as well as the characterization of some major geological events in both marine and terrestrial depositional environments;and therefore strengthens the application of well logs analysis in paleoenvironment and paleoclimate research.