Astronomical time scale of the Turonian constrained by multiple paleoclimate proxies

One of the clocks that record the Earth history is(quasi-) periodic astronomical cycles.These cycles influence the climate that can be ultimately stored in sedimentary rocks.By cracking these(quasi-) periodic sedimentation signals,high resolution astronomical time scale(ATS) can be obtained.Paleoclimate proxies are widely used to extract astronomical cycles.However different proxies may respond differently to astronomical signals and nonastronomical noises including tectonics,diagenesis,and measurement error among others.Astronomical time scale constructed based on a single proxy where its signal-to-noise ratio is low may have uncertainty that is difficult to evaluate but can be revealed by utilizing other proxies.Here,we test eight astronomical age models using two astrochro no logical methods from four paleoclimate proxies(i.e.,color reflection L~* and b~*,natural gamma radiation,and bulk density) from the Turonian to the Coniacian of the Cretaceous Period at the Demerara Rise in the equatorial Atlantic.The two astrochronological methods are time calibration using long eccentricity bandpass filtering(E1 bandpass) and tracking the long eccentricity from evolutive harmonic analysis(tracking EHA).The statistical mean and standard deviation of four age models from the four proxies are calculated to construct one integrated age model with age uncertainty in each method.Results demonstrate that extracting astronomical signals from multiple paleoclimate proxies is a valid method to estimate age model uncertainties.Anchored at the Cenomanian/Turonian boundary with an age of 93.9 ± 0.15 Ma from biostratigraphy,the ages for CC11/CC12(calcareous nannofossil zones),Turonian/Coniacian(CC12/CC13),CC13/CC14,and Coniacian/Santonian boundaries are 91.25±0.20 Ma,89.87±0.20 Ma,86.36±0.33 Ma,and 86.03±0.32 Ma in E1 bandpass method,compared with 91.17±0.36 Ma,89.74±0.38 Ma,86.13±1.31 Ma,and 85.80±1.33 Ma respectively in tracking EHA method.These results are consistent with previous studies within error and provide a reliable estimation of uncertainties of the ages.

Astronomical forcing and sedimentary noise modeling of lake-level changes in the Middle Eocene Chezhen Sag,Bohai Bay Basin,eastern China

The accurate determination of geological age is a key to understanding the history and process of paleolake evolution and oil and gas exploration in continental lake basin.However,improving the accuracy of geological age has always been a difficult scientific problem.A 609-m-thick,continuous lacustrine mudstone and sandstone succession in Chezhen Sag(eastern China)provides an ideal middle Eocene sedimentary record for establishing a high-resolution stratigraphic chronology framework.Based on spectrum analysis and sliding window spectrum analysis of the natural gamma(GR)logging data of well Che 271(C271)in Chezhen Sag,the periods of 405 kyr and 40.1 kyr were filtered by a Gaussian bandpass filter,and a“floating”astrochronological time scale(ATS)was established.The total number of 405 kyr eccentricity cycles were 13.6 and 40.1 kyr obliquity cycles were 138 which recorded from the upper member 4(Es4U)to the member 3(Es3)of the Eocene Shahejie Formation,and the depositional duration was 5.53 Myr.Correlation Coefficient(COCO)analysis and evolutionary Correlation Coefficient(eCoCo)analysis found that the optimal sedimentary rate of different strata.Sedimentary noise simulation revealed the history of paleolake water changes in the Middle Eocene in the Chezhen Sag,according to which four sequences are divided.The study shows that the lake level change of Chezhen Sag in the middle Eocene shows prominent 1.2 Myr cycles and an antiphase well-coupled relationship with obliquity modulation.Finally,we propose a model to explain the relationship between the orbital cycle and lake level change in the continental lake basin.When the obliquity of the earth increases,the middle and high latitudes of the earth will be closer to the sun,the direct sunlight will be higher,and the meridional sunshine will increase,thus accelerating the evaporation process of lake basin water.When the seasonal changes are obvious(maximum period of 1.2 Myr ultra-long obliquity),this effect is more significant.The relative lake level change based on the restoration of high-precision ATS has significant scientific and economic value for understanding the vertical evolution of continental stratigraphic sequences and the formation and distribution of oil and gas resources.

Long-term cycles of the Solar System concealed in the Mesozoic sedimentary basin record

Mounting evidence indicates that the orbital period of the solar system’s movement through the Milky Way has had a controlling effect on processes of the Earth’s system throughout the Phanerozoic.To decipher the response of a given terrestrial basin’s rhythms to galactic dynamics,for the first time,we report long-term cycles recorded in the Mesozoic Ordos Basin(Central China).The astronomical time scale(ATS)was established for each successive sedimentary sequence,and the duration of unconformity episodes was estimated based on the chronological constraints.Using this timescale,time-series analysis of the deposition rate is carried out through the Mesozoic Ordos Basin,which reveals compelling periodicities of 93,33,9,3-5,and 2.4Myr.The radial solar system motions around the galactic centre and plate tectonic cycles act cooperatively to impact the magmatic tempo of the Qinling orogenic belt and the 93-Myr depositional cycle of the Mesozoic Ordos Basin.The Mesozoic 33-Myr cycle is a sedimentary response to the half-period of the solar system’s vertical oscillation about the galactic plane.A rational explanation is that galactic oscillation affects mantle convection,which is responsible for periodic asthenospheric upwelling and ultimately controls the vertical crust oscillation of the Ordos Basin.Mesozoic 9-Myr and the higher-frequency 3-5and 2.4-Myr depositional cycles can be sedimentary responses to the Earth’s orbital eccentricity,which affected the temporal variation in depositional environments in the Ordos Basin.Apart from the galactic-geologic correlations,long-term cycles recorded within a sedimentary basin should also consider the tectonically driven mechanisms at these timescales.This framework provides a new perspective for revealing the astronomical origin of Earth’s rhythms.