The Qiongdongnan Basin,located in the sea between Hainan Island and the Xisha Islands,is a faulted Cenozoic basin on the northern continental margin of the South China Sea.The Changchang Sag,situated in the eastern pa...The Qiongdongnan Basin,located in the sea between Hainan Island and the Xisha Islands,is a faulted Cenozoic basin on the northern continental margin of the South China Sea.The Changchang Sag,situated in the eastern part of the central depressional zone in the deepwater area of the Qiongdongnan Basin,exhibits a near EW-striking morphology and represents an important potential target for oil/gas exploration.However,the age of the interface of the Lingshui Formation remains controversial,which hinders a comprehensive understanding of the tectonic evolution and hydrocarbon accumulation pattern in the Changchang Sag.This study focuses on well A,located in the depositional center of the Changchang Sag,and employs cyclostratigraphic analysis to identify cyclic signals of the Milankovitch cycles recorded in the sedimentary strata.Spectral analysis of natural gamma logging data from this well reveals the presence of 405 kyr long eccentricity cycles,100 kyr short eccentricity cycles,39.3 kyr obliquity cycles,and 20.58 kyr age precession cycles.By employing astronomical tuning,a“floating”astronomical time scale of the Lingshui Formation spanning 5.483 million years(Myr)is established.The top interface of the Oligocene in the International Geological Time Scale 2020(GTS2020),with a geological age of 23.03 Ma,is used as the time anchor to establish a high-precision absolute astronomical age framework for the Lingshui Formation.The results indicate that the bottom interface of the first member of the Lingshui Formation is dated at 23.79 Ma,the bottom interface of the second member is dated at 25.08 Ma,and the bottom interface of the third member is dated at 28.51 Ma.Additionally,the average sedimentation rate during this period is estimated to be 9.261 cm/kyr.Furthermore,paleoclimate and paleoenvironmental reconstructions were carried out through quantitative analysis of spore and pollen assemblages,as well as foraminifera within the Lingshui Formation.These analyses suggest that the deposition of the Lingshui Formation occurred under warm and humid temperate climatic conditions.The results of paleoclimate proxy analysis and comparative fitting analysis of the astronomical time scale confirm that the climate evolution during this period was influenced by astronomical orbital forces,such as eccentricity and precession.展开更多
The study of magnetostratigraphy and cyclostratigraphy in the last two decades has provided a great deal of opportunities to improve the geologic time scale.The Cenozoic and Mesozoic geologic timescale have been well ...The study of magnetostratigraphy and cyclostratigraphy in the last two decades has provided a great deal of opportunities to improve the geologic time scale.The Cenozoic and Mesozoic geologic timescale have been well calibrated(Gradstein et al..2012;Ogg et al,2012;Cohen et al.,2018).However,for the Paleozoic era the uncertainty over boundary ages are still very large.展开更多
The Cyclostratigraphy study is increasingly important in the precise dating of the marine strata,especially in the Tethyan realm.Compared with the Western Tethys,the Cyclostratigraphy study on the Eastern Tethys is re...The Cyclostratigraphy study is increasingly important in the precise dating of the marine strata,especially in the Tethyan realm.Compared with the Western Tethys,the Cyclostratigraphy study on the Eastern Tethys is relatively insufficient.Cretaceous marine sediments are cropped out widely in Southern Tibet,among them the late Cretaceous in the Gongzha section of Tingri area is rather continuous and integral.展开更多
The vertical electrical soundings on the Matam region phosphates deposits are interpreted by inversion. To retrieve lithology from the obtained resistivities, mechanical drilling was performed to compare directly the ...The vertical electrical soundings on the Matam region phosphates deposits are interpreted by inversion. To retrieve lithology from the obtained resistivities, mechanical drilling was performed to compare directly the lithologies and the geoelectrical resistivities. The obtained relation is not simple and is not sufficient to interpret all the VES. This situation motivated the collection of supplementary information from cyclostratigraphy. Geoelectrical and cyclostratigraphic?information is combined using fuzzy logic techniques to build a fuzzy inference system. The obtained results seem to be consistent with the stratigraphy of the investigated region and allow retrieving lithological succession. Further investigations are necessary for more accurate thickness determination.展开更多
Cyclostratigraphic studies enable to reconstruct the geological timescales of many marine formations.However,these investigations are still lacking a precise astronomical tuning in lacustrine environments,particularly...Cyclostratigraphic studies enable to reconstruct the geological timescales of many marine formations.However,these investigations are still lacking a precise astronomical tuning in lacustrine environments,particularly in the Middle Jurassic,due to the paucity of biological traces and the lack of data.In this study,detailed spectral analyses of natural gamma ray(GR)logging data were conducted on the lacustrine Sha-1 member from two wells in the Sichuan Basin,southwestern China.Core data samples were calibrated to test the lithological changes for proceeding with cyclostratigraphic analysis with more confidence.The spectral analysis and evolutionary spectral analysis of the GR logs reveal that the wavelength ratios of the stratigraphic cycles are~20:5:2:1,being consistent with the period ratios of astronomical cycles(long eccentricity,short eccentricity,obliquity,and precession).Correlation coefficient(COCO)analyses were applied to quantitatively measure the fitting of the witnessed sedimentary cycles to astronomical periods and provide a possible sedimentation rate range.The results show that astronomical time scale of the studied interval comprises 58.4-60.6 m cycles,representing the 405 kyr eccentricity cycles,and 14.9-16.6 m cycles,representing the~100 kyr eccentricity cycles.This study reveals a~2.43 Myr duration for the Sha-1 member.Sedimentary noise modeling reveals that long-term million-year period(1.2 Myr)astronomical forcing may have been a significant driver of lake-level changes in the Sichuan Basin.Moreover,high-frequency(405 kyr scale)lake-level variations associated with the mid-term base-level cycles(4th-order sequences)were linked to climato-eustatic changes.This study suggests comparison between parameters of cyclostratigraphic records and sequence stratigraphic base-level cycles in lacustrine sediments.The stratigraphic surfaces of mid-term base-level cycles correspond to minima~405 kyr-long eccentricity cycle curve and high values of DYNOT(dynamic noise after orbital tuning).Integrating cyclostratigraphy with the base-level cycles is,therefore,a vital approach for defining the short-term oscillations of lake-level,and proved to be a useful tool for characterizing thin-bedded lacustrine reservoirs.展开更多
The hierarchically organized laminae,bundles,bundlesets and superbundlesets which correspond to a sub-Milankovitch,obliquity or precession,eccentricity and long eccentricity cyclothems,respectively,have been distingui...The hierarchically organized laminae,bundles,bundlesets and superbundlesets which correspond to a sub-Milankovitch,obliquity or precession,eccentricity and long eccentricity cyclothems,respectively,have been distinguished from the Upper Devonian Fras-nian-Famennian(F-F)transitional carbonate successions deposited in the carbonate-basin and slope facies of Guangxi,South China.The durations of cyclothems are 8000-10000a,16667a or 33333a,100000a and 400000a,respectively.The ratio of eccentricity to precession,eccentricity to obliquity,and long eccentricity to eccentricity is 1:6,1:3 and 1:4 in the Devonian,respectively.Orbital cyclostratigraphical studies show that the durations of the conodont falsio-valis Zone,transitans Zone,punctate Zone,Lower hassi Zone,Upper hassi Zone,jamieae Zone,Lower rhenana Zone,Upper rhenana Zone,linguiformis Zone,Lower triangularis Zone,Middle triangularis Zone and Upper triangularis Zone are 0.4,0.4,0.4,0.3,0.4,0.2,0.8,0.6,0.8,0.3,0.3 and 0.3 Ma from bottom to top,respectively,and the duration of the Frasnian is 4.3 Ma.The conodont is the normal marine organism of the latest mass extinction(the latest linguiformis Zone)and the first recovery(including the whole Lower triangularis and Middle triangularis Zone)in the F-F transition.The conodont mass extinction and recovery lasted 200000-100000a and 0.6 Ma,respectively.We consider that average durations of the fossil zones calculated by reported numerical ages divided by fossil zone numbers within a stage or series or system cannot discovery complications and non-uniformity of evolutionary organisms and environments.展开更多
The Induan sequence in the West Pingdingshan Section, Chaohu, Anhui Province, displays a series of superimposed mudstone/limestone cycles. The lithological character of the cycles, combined with power spectral and wav...The Induan sequence in the West Pingdingshan Section, Chaohu, Anhui Province, displays a series of superimposed mudstone/limestone cycles. The lithological character of the cycles, combined with power spectral and wavelet analysis of magnetic susceptibility readings, reveals 12 short eccentricity and 56 precession Milankovitch cycles - obliquity cycles are not apparent. The uniformity of cycle thicknesses indicates a stable depositional setting making this section ideal to perform various geo-logical studies. Accordingly, the Induan Stage is estimated to have lasted 1.1 Ma, and the depositional rate for this part of the section is about 3.7 cm/ka. This places the Induan-Olenekian boundary in the West Pingdingshan Section at about 251.5 Ma based on an age of 252.6 Ma for the Permian-Triassic boundary.展开更多
Spectral analysis is applied to geochemical data from a deep-water Permian-Triassic Boundary (PTB) section across PTB in Dongpan, Guangxi for high-resolution cyclostratigraphic research. The characteristics of the Mil...Spectral analysis is applied to geochemical data from a deep-water Permian-Triassic Boundary (PTB) section across PTB in Dongpan, Guangxi for high-resolution cyclostratigraphic research. The characteristics of the Milankovitch Cycles have been well recorded in the strata of the Dongpan section. Spectrum on Ce/La records shows especially that the ratios among its three preponderant cycles in the section are 5:2:1, which well displays the phenomenon of the sedimentary cycles driven by orbital force. The Milankovitch theory is further confirmed by the Paleozoic records.展开更多
A continuous terrestrial succession was recovered from the Songke-2(SK-2)borehole in the Songliao Basin,Northeastern China.This borehole provides a unique material for further research on the continental paleoclimate ...A continuous terrestrial succession was recovered from the Songke-2(SK-2)borehole in the Songliao Basin,Northeastern China.This borehole provides a unique material for further research on the continental paleoclimate during Cretaceous greenhouse period,following a series of achievements of the Songke-1(SK-1)core.In this study,thorium(Th)logging data were chosen as a paleoclimate proxy to conduct a detailed cyclostratigraphic analysis.The Th series varies quasi-periodically;power spectra and evolutionary fast Fourier transformation(FFT)analysis reveal significant cycles in the Quantou(K2 q),Qingshankou(K2 qn),Yaojia(K2 y)and Nenjiang(K2 n)formations.The ratio of cycle wavelengths in these stratigraphic units is approximately 20:5:2:1,corresponding to long orbital eccentricity(405 kyr),short orbital eccentricity(100 kyr),obliquity(37 kyr),and precession cycles(22.5 kyr and 18.4 kyr).The durations of the K2 n,K2 y,K2 qn and K2 q are estimated as 6.97,1.83,5.30 and 4.52 Myr,respectively,based on the constructed^18.62 Myr"floating"astronomical time scale(ATS).Comparison of the durations between the SK-1 s and SK-2 boreholes exhibits a slight difference of 0.06 Myr and 0.459 Myr for K2 qn and K2 y.Nevertheless,our ATS of K2 n supports the chronostratigraphic frame constructed by the CA-ID-TIMS data of the SK-1 s borehole.This new"floating"ATS provides precise numerical ages for stratigraphic boundaries,biozones and geological events in the Songliao Basin,and can serve as a basis for correlation of strata and events between marine and terrestrial systems.展开更多
High resolution(939 samples)total organic carbon content(TOC)analyses were conducted on the Shuanghe Section of^152.6 m in the Changning area,Sichuan Basin.The sampling section was divided into two units considering t...High resolution(939 samples)total organic carbon content(TOC)analyses were conducted on the Shuanghe Section of^152.6 m in the Changning area,Sichuan Basin.The sampling section was divided into two units considering the distinct-different deposit environment and sediments accumulation rate.The lower part(Unit 1)and the peer part(Unit 2)with high resolution sample spacing(0.08–0.4 m)enables the identification of the precession cycle in two sedimentary sequences with distinct different sedimentary accumulation rate.MTM Power spectral analyses on untuned TOC series reveals significant peaks exceeding above the 95%confidence level and shows that both Unit 1 and Unit 2 have recorded Milankovitch cycles of 405 kyr long eccentricity,short eccentricity,obliquity and precession.The floating astronomical time scale(ATS)was constructed on the Shuanghe Section in the Early Silurian(~439.673–444.681 Ma),and which was calibrated by 405 kyr long eccentricity cycles.The total duration of the Wufeng and Longmaxi shales is 5.01 Myr.The floating ATS used for estimating the duration of the graptolite zones and each stage in the study interval.Finally,we postulated two models that could verify the linkage between orbital cycle and organic accumulation.To make sure whether productivity or preservation is the main factor that under long eccentricity control,the phase correlation between the obtained filtered signal and the theoretical orbital solution should be made clear in the further research.展开更多
1 Introduction The Sandbian-Katian is a critical period for the transition from"hot-house"in the Lower Ordovician to"ice-house"in the end-Ordovician(Trotter et al.,2008).During this interval,the So...1 Introduction The Sandbian-Katian is a critical period for the transition from"hot-house"in the Lower Ordovician to"ice-house"in the end-Ordovician(Trotter et al.,2008).During this interval,the South China Block was located in the equatorial region(Torsvik and Cocks,2016),with the widespread accumulation of Pagoda and Linhsiang formations(Zhan and Jin,2007).展开更多
Based on field outcrop data,the effects of cyclic change of astronomical orbit and volcanic activity on organic carbon accumulation during the Late Ordovician-Early Silurian in the Upper Yangtze area were studied usin...Based on field outcrop data,the effects of cyclic change of astronomical orbit and volcanic activity on organic carbon accumulation during the Late Ordovician-Early Silurian in the Upper Yangtze area were studied using cyclostratigraphic and geochemical methods.d13 C and chemical index of alteration(CIA)were used to filter the astronomical orbit parameters recorded in sediments.It is found that the climate change driven by orbital cycle controls the fluctuations of sea level at different scales,obliquity forcing climate changes drive thermohaline circulation(THC)of the ocean,and THC-induced bottom currents transport nutrient-laden water from high latitude regions to the surface water of low-latitude area.Hence,THC is the main dynamic mechanism of organic-carbon supply.The marine productivity indexes of Ba/Al and Ni/Al indicate that volcanic activities had limited effect on marine productivity but had great influences on organic carbon preservation efficiency in late Hirnantian(E4).Paleo-ocean redox environmental indicators Th/U,V/Cr and V/(V+Ni)show that there is a significant correlation between volcanism and oxygen content in Paleo-ocean,so it is inferred that volcanisms controlled the organic carbon preservation efficiency by regulating oxygen content in Paleo-ocean,and the difference in volcanism intensity in different areas is an important factor for the differential preservation efficiency of organic carbon.The organic carbon input driven by orbital cycle and the preservation efficiency affected by volcanisms worked together to control the enrichment of organic carbon in the Middle–Upper Yangtze region.展开更多
The Sifangtai and Mingshui formations were continuously cored in the SK-1 n borehole（China Cretaceous Continental Scientific Drilling-SongKe1-the north borehole）.The core is 767.96 m long,and the recovery is 94.7%.T...The Sifangtai and Mingshui formations were continuously cored in the SK-1 n borehole（China Cretaceous Continental Scientific Drilling-SongKe1-the north borehole）.The core is 767.96 m long,and the recovery is 94.7%.The ages of the formations range from middle Campanian to Danian.The sequence and process of lithology-lithofacies and cyclic stratigraphy were described in detail.Eight litho-types compose the Sifangtai Formation,and 15 litho-types compose the Mingshui Formation.Deposition was predominantly in meandering river and lacustrine environments,including 10 microfacies in the Sifangtai Formation and 15 microfacies in the Mingshui Formation.The complete sequence is composed of 535 m-scale cycles（sixth-order cycle）,152 fifth-order cycles,42 fourth-order cycles and five third-order cycles.The centimeter-scale description of the section revealed some previously unknown horizons such as a special type of mudstone,marl,volcanic ash and favorable sand reservoirs in the formations.The new-found evidence is very important for the interpretation of the evolution of the basin,conditions such as lake oxic events,the K/Pg boundary,tectonism in the late sag basin stage,and the reservoir-cap rock assemblages in the shallow stratigraphy.展开更多
Cyclostratigraphy is more and more utilized in high-resolution dating in stratgraphy because of its characteristics of high resolution.It is based on the theory of orbital cycles,which are related to three Earth orbit...Cyclostratigraphy is more and more utilized in high-resolution dating in stratgraphy because of its characteristics of high resolution.It is based on the theory of orbital cycles,which are related to three Earth orbital parameters:eccentricity(e),obliquity(ε),and precession(e~*sinω).They affect the Earth periodically and then this information could be preserved in the sediments to be calibrated.However,in the geological time,the periodicities were changing.展开更多
The Middle Permian extinction event is considered one of the most devastating events of all Phanerozoic biotic crises,yet it is not fully understood and has attracted a lot of controversial comments.This event is foun...The Middle Permian extinction event is considered one of the most devastating events of all Phanerozoic biotic crises,yet it is not fully understood and has attracted a lot of controversial comments.This event is found at the end of the Capitanian carbonate strata in the Ruteh Formation(late Wordian-Capitanian)at the Alborz Mountains in Iran.It is characterized by the decimation of marine organisms,particularly calcareous algae and microproblematic fossils.The current study attempts to interpret the cause of this crisis in the framework of astronomically-forced climatic changes.Based on cyclostratigraphy analysis,the evidence of the Milankovitch cycles,including long eccentricity,short eccentricity,obliquity,and precession are recorded in the Ruteh Formation succession.The establishment of a floating astronomical time scale using the long eccentricity cycles led to an estimation of a duration of 1.6 and 2.43 million years for the Wordian and Capitanian stages,respectively.Integrated facies studies and a sedimentary noise model indicate that the Ruteh Formation is composed of three~1.2 Myr sequences,corresponding to third-order sequences,and ten 405-kyr sequences,corresponding to fourth-to fifth-order sequences.The boundaries of the~1.2 Myr sequences indicate regression in sea level and low sedimentation rate.Considering the paleogeographic situation of the Alborz Mountains,the sedimentation of the Ruteh Formation in the Middle Permian was affected by the Inter-Tropical Convergence Zone and interactions between the ocean and atmosphere during the Pangea assemblage,leading to an increase in temperature.With the sum of these observations,we conclude that factors such as high temperature and a decrease in sedimentation rate created unfavorable conditions for the mentioned biota at the end of the Capitanian.展开更多
Cretaceous strata are widely distributed across China and record a variety of depositional settings. The sedimentary facies consist primarily of terrestrial, marine and interbedded marine-terrestrial deposits, of whic...Cretaceous strata are widely distributed across China and record a variety of depositional settings. The sedimentary facies consist primarily of terrestrial, marine and interbedded marine-terrestrial deposits, of which marine and interbedded facies are relatively limited. Based a thorough review of the subdivisions and correlations of Cretaceous strata in China, we provide an up-to-date integrated chronostratigraphy and geochronologic framework of the Cretaceous system and its deposits in China.Cretaceous marine and interbedded marine-terrestrial sediments occur in southern Tibet, Karakorum, the western Tarim Basin,eastern Heilongjiang and Taiwan. Among these, the Himalayan area has the most complete marine deposits, the foraminiferal and ammonite biozonation of which can be correlated directly to the international standard biozones. Terrestrial deposits in central and western China consist predominantly of red, lacustrine-fluvial, clastic deposits, whereas eastern China, a volcanically active zone, contains clastic rocks in association with intermediate to acidic igneous rocks and features the most complete stratigraphic successions in northern Hebei, western Liaoning and the Songliao Basin. Here, we synthesise multiple stratigraphic concepts and charts from southern Tibet, northern Hebei to western Liaoning and the Songliao Basin to produce a comprehensive chronostratigraphic chart. Marine and terrestrial deposits are integrated, and this aids in the establishment of a comprehensive Cretaceous chronostratigraphy and temporal framework of China. Further research into the Cretaceous of China will likely focus on terrestrial deposits and mutual authentication techniques(e.g., biostratigraphy, chronostratigraphy, magnetostratigraphy and cyclostratigraphy). This study provides a more reliable temporal framework both for studying Cretaceous geological events and exploring mineral resources in China.展开更多
Sedimentological and stratigraphic studies of seven stratigraphic sections of Permian Hongyanchi （HYC） and Quanzijie （QZJ） low-order cycles （LCs） in the Tarlong-Taodonggou half graben and Dalongkou area in Bogda...Sedimentological and stratigraphic studies of seven stratigraphic sections of Permian Hongyanchi （HYC） and Quanzijie （QZJ） low-order cycles （LCs） in the Tarlong-Taodonggou half graben and Dalongkou area in Bogda Mountains, NW China, demonstrate effective approaches and methodology in cyclo- and time-stratigraphic analyses of complex fluviallacustrine deposits in an intracontinental rift setting. A new synchronous stratigraphic unit, the lower QZJ LC is defined. The lower and upper boundaries of this cycle include a regionally correlative disconformity, erosional unconformity, and conformity, across which significant and abrupt changes in palaeoenvironments and tectonic and climatic conditions occurred. The lower boundary is an erosional unconformity and disconformity with a high-relief topography that juxtaposes lacustrine deposits of the underlying HYC LC with the overlying meandering stream deposits of the lower QZJ LC, and was caused by a regional tectonic uplift. The up- per boundary is a disconformity and local erosional unconformity and conformity, juxtaposing stacked paleosols developed on fluvial sediments with overlying fluvial and loessial deposits of the upper QZJ LC. The paleosols indicate landscape stability and a prolonged period of subaerial exposure and minimal deposition and suggest that climatic conditions were semiarid with strong precipitation seasonality in the Tarlong-Taodonggou half graben and subhumid in the Dalongkou area. The fluvial-loessial deposits indicate a renewed tectonic uplift and a change in the atmospheric circulation pattern. The newly-defined lower QZJ LC facilitates accurate palaeogeographic reconstruction in the study area during a period of major tectonic and climatic changes. The interpreted tectonic and climatic conditions provide a critical data point in the mid-latitude east coast of NE Pangea during the Mid-Permian icehouse-hothouse transition. The results demonstrate that a process-response approach is effective in time- stratigraphic analysis of complex fluvial-lacustrine strata in a highly-partitioned rift basin.展开更多
The sedimentary environment of the Upper Triassic in the southeastern Sichuan Basin is obviously controlled by Luzhou paleo-uplift(LPU).However,the influence of paleo-uplift on the sedimentary patterns of the initial ...The sedimentary environment of the Upper Triassic in the southeastern Sichuan Basin is obviously controlled by Luzhou paleo-uplift(LPU).However,the influence of paleo-uplift on the sedimentary patterns of the initial stages of this period in the southeastern Sichuan Basin has not yet been clear,which has plagued oil and gas exploration and development.This study shows that there is a marine sedimentary sequence,which is considered to be the first member of Xujiahe Formation(T_(3)X^(1))in the southeastern Sichuan Basin.The development of LPU resulted in the sedimentary differences between the eastern and western Sichuan Basin recording T_(3)X^(1)and controlled the regional sedimentary pattern.The western part is dominated by marine sediments,but the eastern paleo-uplift area is dominated by continental sedimentation in the early stage of T_(3)X^(1),and it begins to transform into a marine sedimentary environment consistent with the whole basin in the late stage of the period recorded by the Xujiahe Formation.The evidences are as follows:(1)time series:based on the cyclostratigraphy analysis of Xindianzi section and Well D2,in the southeastern Sichuan Basin,the period of sedimentation of the Xujiahe Formation is about 5.9 Ma,which is basically consistent with the Qilixia section,eastern Sichuan basin,where the Xujiahe Formation is widely considered to be relatively complete;(2)distribution and evolution of palaeobiology:based on analysis of abundance evolution of major spore-pollen,many land plant fossils are preserved in the lower part of T_(3)X^(1),indicates the sedimentary environment of continental facies.In the upper part of T_(3)X^(1),the fossil of terrestrial plants decreased,while the fossil of marine and tidal environment appeared,this means that it was affected by the sea water in the late stages of T_(3)X^(1);(3)geochemistry:calculate the salinity of water from element indicates that the uplift area is continental sedimentary environment in the early stage of T_(3)X^(1),while the central and western areas of the basin are marine sedimentary environment.Until the late stage of T_(3)X^(1),the southeast of the basin gradually turns into marine sedimentary environment,consisting with the whole basin;(4)types of kerogen:type III kerogen representing continental facies was developed in the early stage of T_(3)X^(1)in the uplift area,and type II kerogen,representing marine facies,was developed in the late stage;while type II kerogenwas developed in the central and western regions of the basin as a whole in T_(3)X^(1).This study is of great significance for understanding of both stratigraphic division and sedimentary evolution providing theoretical support for the exploration and development of oil and gas.展开更多
We present a detailed magnetostratigraphic and cyclostratigraphic profile through the Riphean(Tonian)Katav Formation in the southern Urals.The study confirms the primary nature of the magnetization in these rocks.The ...We present a detailed magnetostratigraphic and cyclostratigraphic profile through the Riphean(Tonian)Katav Formation in the southern Urals.The study confirms the primary nature of the magnetization in these rocks.The cyclostratigraphic study identified several orbital periods including the 405 ka long eccentricity.This allows us to quantify the reversal frequency in the Katav and our estimates range of 7–12 reversals per million years.Based on our study,we identify an interval of magnetic field reversal hyperactivity in the Neoproterozoic interval.Age estimates for the Katav are contentious and range somewhere between 800 Ma and 900 Ma based on carbonate Pb-Pb ages and stable isotope correlations.The paleomagnetic poles obtained in this study of the Katav(and overlying Inzer)Formation do not fit anywhere on the Baltica apparent polar wander path between 1100 Ma and 900 Ma.Furthermore,they lie 90away from the 900 Ma segment of the path.We tentatively estimate their age to be closer to 800 Ma and perhaps confirm a previously hypothesized pulse of rapid true polar wander between 825 Ma and 790 Ma.展开更多
The Oxfordian （Late Jurassic） carbonate-dominated ptatform outcropping in the Swiss Jura Mountains offers a good biostratigraphic, sequence-stratigraphic, and cyclostratigraphic framework to reconstruct changes in f...The Oxfordian （Late Jurassic） carbonate-dominated ptatform outcropping in the Swiss Jura Mountains offers a good biostratigraphic, sequence-stratigraphic, and cyclostratigraphic framework to reconstruct changes in facies distribution at a time-resolution of 100 ka. It thus allows interpreting the dynamic evolution of this platform in much more detail than conventional palaeogeographic maps permit. As an example, a Middle to Late Oxfordian time slice is presented, spanning an interval of about 1.6 Ma. The study is based on 12 sections logged at cm-scale. The interpreted depositional environments include marginal-marine emerged ;ands, fresh-water lakes, tidal fiats, shallow lagoons, ooid shoals, and coral reefs. Although limestones dominate, marly intervals and dolomites occur sporadically. Major facies shifts are related to m-scale sea-level changes linked to the orbital short eccentricity cycle （100 ka）. The 20-ka precession cycle caused minor facies changes but cannot always be resolved. Synsedimentary tectonics induced additional accommodation changes by creating shallow basins where days accumulated or highs on which shoals or islands formed. Autocyclic processes such as lateral migration of ooid and bioclastic shoals added to the sedimentary record. CEimate changes intervened to control terrestrial run-off and, consequently, siliciclastic and nutrient input. Coral reefs reacted to such input by becoming dominated by microbialites and eventually by being smothered. Concomitant occurrence of siliciclastics anddolomite in certain intervals further suggests that, at times, it was relatively arid in the study area but there was rainfall in more northern latitudes, eroding the Hercynian substrate. These examples from the Swiss Jura demonstrate the highly dynamic and （geologically speaking） rapid evolution of sedimentary systems, in which tectonically controlled basin morphology, orbitally induced climate and sea-level changes, currents, and the ecology of the carbonate-producing organisms interacted to form the observed stratigraphic record. However, the interpretations have to be treated with caution because the km-wide spacing between the studied sections is too large to monitor the smaU-scale facies mosaics as they can be observed on modern platforms and as they certainly also occurred in the past.展开更多
基金supported by the major program of the China National Offshore Oil Corporation(No.2021-KT-YXKY-05)the National Natural Science Foundation of China(No.41472098).
文摘The Qiongdongnan Basin,located in the sea between Hainan Island and the Xisha Islands,is a faulted Cenozoic basin on the northern continental margin of the South China Sea.The Changchang Sag,situated in the eastern part of the central depressional zone in the deepwater area of the Qiongdongnan Basin,exhibits a near EW-striking morphology and represents an important potential target for oil/gas exploration.However,the age of the interface of the Lingshui Formation remains controversial,which hinders a comprehensive understanding of the tectonic evolution and hydrocarbon accumulation pattern in the Changchang Sag.This study focuses on well A,located in the depositional center of the Changchang Sag,and employs cyclostratigraphic analysis to identify cyclic signals of the Milankovitch cycles recorded in the sedimentary strata.Spectral analysis of natural gamma logging data from this well reveals the presence of 405 kyr long eccentricity cycles,100 kyr short eccentricity cycles,39.3 kyr obliquity cycles,and 20.58 kyr age precession cycles.By employing astronomical tuning,a“floating”astronomical time scale of the Lingshui Formation spanning 5.483 million years(Myr)is established.The top interface of the Oligocene in the International Geological Time Scale 2020(GTS2020),with a geological age of 23.03 Ma,is used as the time anchor to establish a high-precision absolute astronomical age framework for the Lingshui Formation.The results indicate that the bottom interface of the first member of the Lingshui Formation is dated at 23.79 Ma,the bottom interface of the second member is dated at 25.08 Ma,and the bottom interface of the third member is dated at 28.51 Ma.Additionally,the average sedimentation rate during this period is estimated to be 9.261 cm/kyr.Furthermore,paleoclimate and paleoenvironmental reconstructions were carried out through quantitative analysis of spore and pollen assemblages,as well as foraminifera within the Lingshui Formation.These analyses suggest that the deposition of the Lingshui Formation occurred under warm and humid temperate climatic conditions.The results of paleoclimate proxy analysis and comparative fitting analysis of the astronomical time scale confirm that the climate evolution during this period was influenced by astronomical orbital forces,such as eccentricity and precession.
基金supported by the Fundamental Research Funds for the Central Universities(Grant No.lzujbky-2017-k27)contributed to IGCP 652.
文摘The study of magnetostratigraphy and cyclostratigraphy in the last two decades has provided a great deal of opportunities to improve the geologic time scale.The Cenozoic and Mesozoic geologic timescale have been well calibrated(Gradstein et al..2012;Ogg et al,2012;Cohen et al.,2018).However,for the Paleozoic era the uncertainty over boundary ages are still very large.
文摘The Cyclostratigraphy study is increasingly important in the precise dating of the marine strata,especially in the Tethyan realm.Compared with the Western Tethys,the Cyclostratigraphy study on the Eastern Tethys is relatively insufficient.Cretaceous marine sediments are cropped out widely in Southern Tibet,among them the late Cretaceous in the Gongzha section of Tingri area is rather continuous and integral.
文摘The vertical electrical soundings on the Matam region phosphates deposits are interpreted by inversion. To retrieve lithology from the obtained resistivities, mechanical drilling was performed to compare directly the lithologies and the geoelectrical resistivities. The obtained relation is not simple and is not sufficient to interpret all the VES. This situation motivated the collection of supplementary information from cyclostratigraphy. Geoelectrical and cyclostratigraphic?information is combined using fuzzy logic techniques to build a fuzzy inference system. The obtained results seem to be consistent with the stratigraphy of the investigated region and allow retrieving lithological succession. Further investigations are necessary for more accurate thickness determination.
基金supported by the National Natural Science Foundation of China(Grant Nos.42072183 and 41902124)the Sichuan Province Outstanding Youth Science and Technology Talents Project(2024NSFJQ 0065)the Sichuan Province International Science and Technology Innovation Cooperation Project(24GJHZ0465)。
文摘Cyclostratigraphic studies enable to reconstruct the geological timescales of many marine formations.However,these investigations are still lacking a precise astronomical tuning in lacustrine environments,particularly in the Middle Jurassic,due to the paucity of biological traces and the lack of data.In this study,detailed spectral analyses of natural gamma ray(GR)logging data were conducted on the lacustrine Sha-1 member from two wells in the Sichuan Basin,southwestern China.Core data samples were calibrated to test the lithological changes for proceeding with cyclostratigraphic analysis with more confidence.The spectral analysis and evolutionary spectral analysis of the GR logs reveal that the wavelength ratios of the stratigraphic cycles are~20:5:2:1,being consistent with the period ratios of astronomical cycles(long eccentricity,short eccentricity,obliquity,and precession).Correlation coefficient(COCO)analyses were applied to quantitatively measure the fitting of the witnessed sedimentary cycles to astronomical periods and provide a possible sedimentation rate range.The results show that astronomical time scale of the studied interval comprises 58.4-60.6 m cycles,representing the 405 kyr eccentricity cycles,and 14.9-16.6 m cycles,representing the~100 kyr eccentricity cycles.This study reveals a~2.43 Myr duration for the Sha-1 member.Sedimentary noise modeling reveals that long-term million-year period(1.2 Myr)astronomical forcing may have been a significant driver of lake-level changes in the Sichuan Basin.Moreover,high-frequency(405 kyr scale)lake-level variations associated with the mid-term base-level cycles(4th-order sequences)were linked to climato-eustatic changes.This study suggests comparison between parameters of cyclostratigraphic records and sequence stratigraphic base-level cycles in lacustrine sediments.The stratigraphic surfaces of mid-term base-level cycles correspond to minima~405 kyr-long eccentricity cycle curve and high values of DYNOT(dynamic noise after orbital tuning).Integrating cyclostratigraphy with the base-level cycles is,therefore,a vital approach for defining the short-term oscillations of lake-level,and proved to be a useful tool for characterizing thin-bedded lacustrine reservoirs.
基金This work was jointly supported by the National Natural Science Foundation of China(Grant Nos.40072041 and 40472020)the Chinese Commission on Stratigrapby and the Climbing Project of Ministry of Science and Technology of China(SSER).
文摘The hierarchically organized laminae,bundles,bundlesets and superbundlesets which correspond to a sub-Milankovitch,obliquity or precession,eccentricity and long eccentricity cyclothems,respectively,have been distinguished from the Upper Devonian Fras-nian-Famennian(F-F)transitional carbonate successions deposited in the carbonate-basin and slope facies of Guangxi,South China.The durations of cyclothems are 8000-10000a,16667a or 33333a,100000a and 400000a,respectively.The ratio of eccentricity to precession,eccentricity to obliquity,and long eccentricity to eccentricity is 1:6,1:3 and 1:4 in the Devonian,respectively.Orbital cyclostratigraphical studies show that the durations of the conodont falsio-valis Zone,transitans Zone,punctate Zone,Lower hassi Zone,Upper hassi Zone,jamieae Zone,Lower rhenana Zone,Upper rhenana Zone,linguiformis Zone,Lower triangularis Zone,Middle triangularis Zone and Upper triangularis Zone are 0.4,0.4,0.4,0.3,0.4,0.2,0.8,0.6,0.8,0.3,0.3 and 0.3 Ma from bottom to top,respectively,and the duration of the Frasnian is 4.3 Ma.The conodont is the normal marine organism of the latest mass extinction(the latest linguiformis Zone)and the first recovery(including the whole Lower triangularis and Middle triangularis Zone)in the F-F transition.The conodont mass extinction and recovery lasted 200000-100000a and 0.6 Ma,respectively.We consider that average durations of the fossil zones calculated by reported numerical ages divided by fossil zone numbers within a stage or series or system cannot discovery complications and non-uniformity of evolutionary organisms and environments.
基金the project of the Ministry of Science and Technology (Grant No. 2006FY120300-11)the National Natural Science Foundation of China (Grant Nos. 40325004, 40621002)the National Basic Research and Development Program (Grant No. 2006CB80640)
文摘The Induan sequence in the West Pingdingshan Section, Chaohu, Anhui Province, displays a series of superimposed mudstone/limestone cycles. The lithological character of the cycles, combined with power spectral and wavelet analysis of magnetic susceptibility readings, reveals 12 short eccentricity and 56 precession Milankovitch cycles - obliquity cycles are not apparent. The uniformity of cycle thicknesses indicates a stable depositional setting making this section ideal to perform various geo-logical studies. Accordingly, the Induan Stage is estimated to have lasted 1.1 Ma, and the depositional rate for this part of the section is about 3.7 cm/ka. This places the Induan-Olenekian boundary in the West Pingdingshan Section at about 251.5 Ma based on an age of 252.6 Ma for the Permian-Triassic boundary.
基金the National Natural Science Foundation of China (Grant No. 40621002)Program for Changjiang Scholar and Innovative Research Team in University (Grant No. 20060491502)
文摘Spectral analysis is applied to geochemical data from a deep-water Permian-Triassic Boundary (PTB) section across PTB in Dongpan, Guangxi for high-resolution cyclostratigraphic research. The characteristics of the Milankovitch Cycles have been well recorded in the strata of the Dongpan section. Spectrum on Ce/La records shows especially that the ratios among its three preponderant cycles in the section are 5:2:1, which well displays the phenomenon of the sedimentary cycles driven by orbital force. The Milankovitch theory is further confirmed by the Paleozoic records.
基金supported by the National Natural Science Foundation of China(41790451,41925010,and 41688103)National Key R&D Program of China(2019YFC0605403)the subject development project of RIPED(yjkt2019-3).
文摘A continuous terrestrial succession was recovered from the Songke-2(SK-2)borehole in the Songliao Basin,Northeastern China.This borehole provides a unique material for further research on the continental paleoclimate during Cretaceous greenhouse period,following a series of achievements of the Songke-1(SK-1)core.In this study,thorium(Th)logging data were chosen as a paleoclimate proxy to conduct a detailed cyclostratigraphic analysis.The Th series varies quasi-periodically;power spectra and evolutionary fast Fourier transformation(FFT)analysis reveal significant cycles in the Quantou(K2 q),Qingshankou(K2 qn),Yaojia(K2 y)and Nenjiang(K2 n)formations.The ratio of cycle wavelengths in these stratigraphic units is approximately 20:5:2:1,corresponding to long orbital eccentricity(405 kyr),short orbital eccentricity(100 kyr),obliquity(37 kyr),and precession cycles(22.5 kyr and 18.4 kyr).The durations of the K2 n,K2 y,K2 qn and K2 q are estimated as 6.97,1.83,5.30 and 4.52 Myr,respectively,based on the constructed^18.62 Myr"floating"astronomical time scale(ATS).Comparison of the durations between the SK-1 s and SK-2 boreholes exhibits a slight difference of 0.06 Myr and 0.459 Myr for K2 qn and K2 y.Nevertheless,our ATS of K2 n supports the chronostratigraphic frame constructed by the CA-ID-TIMS data of the SK-1 s borehole.This new"floating"ATS provides precise numerical ages for stratigraphic boundaries,biozones and geological events in the Songliao Basin,and can serve as a basis for correlation of strata and events between marine and terrestrial systems.
基金supported by the National Natural Science Foundation of China (Grant No. 41802030)National Science and Technology Major Project (Grant Nos. 2017ZX05036-004-006 and 2016ZX05036-003007)
文摘High resolution(939 samples)total organic carbon content(TOC)analyses were conducted on the Shuanghe Section of^152.6 m in the Changning area,Sichuan Basin.The sampling section was divided into two units considering the distinct-different deposit environment and sediments accumulation rate.The lower part(Unit 1)and the peer part(Unit 2)with high resolution sample spacing(0.08–0.4 m)enables the identification of the precession cycle in two sedimentary sequences with distinct different sedimentary accumulation rate.MTM Power spectral analyses on untuned TOC series reveals significant peaks exceeding above the 95%confidence level and shows that both Unit 1 and Unit 2 have recorded Milankovitch cycles of 405 kyr long eccentricity,short eccentricity,obliquity and precession.The floating astronomical time scale(ATS)was constructed on the Shuanghe Section in the Early Silurian(~439.673–444.681 Ma),and which was calibrated by 405 kyr long eccentricity cycles.The total duration of the Wufeng and Longmaxi shales is 5.01 Myr.The floating ATS used for estimating the duration of the graptolite zones and each stage in the study interval.Finally,we postulated two models that could verify the linkage between orbital cycle and organic accumulation.To make sure whether productivity or preservation is the main factor that under long eccentricity control,the phase correlation between the obtained filtered signal and the theoretical orbital solution should be made clear in the further research.
基金granted by the National Science and Technology Major Project of China(Grant No.2017ZX05035002-001)the National Natural Science Foundation of China(Grant Nos.41790451,41725007 and 41688103)IGCP project 653`The Onset of the Great Ordovician Biodiversification Event’.
文摘1 Introduction The Sandbian-Katian is a critical period for the transition from"hot-house"in the Lower Ordovician to"ice-house"in the end-Ordovician(Trotter et al.,2008).During this interval,the South China Block was located in the equatorial region(Torsvik and Cocks,2016),with the widespread accumulation of Pagoda and Linhsiang formations(Zhan and Jin,2007).
基金Supported by the China National Science and Technology Major Project(2017ZX05063002-009)National Natural Science Foundation of China(4177021173,41972120)CNPC-Southwest Petroleum University Innovation Consortium Science and Technology Cooperation Project(2020CX020000)。
文摘Based on field outcrop data,the effects of cyclic change of astronomical orbit and volcanic activity on organic carbon accumulation during the Late Ordovician-Early Silurian in the Upper Yangtze area were studied using cyclostratigraphic and geochemical methods.d13 C and chemical index of alteration(CIA)were used to filter the astronomical orbit parameters recorded in sediments.It is found that the climate change driven by orbital cycle controls the fluctuations of sea level at different scales,obliquity forcing climate changes drive thermohaline circulation(THC)of the ocean,and THC-induced bottom currents transport nutrient-laden water from high latitude regions to the surface water of low-latitude area.Hence,THC is the main dynamic mechanism of organic-carbon supply.The marine productivity indexes of Ba/Al and Ni/Al indicate that volcanic activities had limited effect on marine productivity but had great influences on organic carbon preservation efficiency in late Hirnantian(E4).Paleo-ocean redox environmental indicators Th/U,V/Cr and V/(V+Ni)show that there is a significant correlation between volcanism and oxygen content in Paleo-ocean,so it is inferred that volcanisms controlled the organic carbon preservation efficiency by regulating oxygen content in Paleo-ocean,and the difference in volcanism intensity in different areas is an important factor for the differential preservation efficiency of organic carbon.The organic carbon input driven by orbital cycle and the preservation efficiency affected by volcanisms worked together to control the enrichment of organic carbon in the Middle–Upper Yangtze region.
基金supported by the National Basic Research Program of China(Grant No.2012CB822002)the National Natural Science Foundation of China(Grant No.41202072)the "Key Laboratory of Northeast Asia biological evolution and environment of Ministry of Education" platform base construction project
文摘The Sifangtai and Mingshui formations were continuously cored in the SK-1 n borehole（China Cretaceous Continental Scientific Drilling-SongKe1-the north borehole）.The core is 767.96 m long,and the recovery is 94.7%.The ages of the formations range from middle Campanian to Danian.The sequence and process of lithology-lithofacies and cyclic stratigraphy were described in detail.Eight litho-types compose the Sifangtai Formation,and 15 litho-types compose the Mingshui Formation.Deposition was predominantly in meandering river and lacustrine environments,including 10 microfacies in the Sifangtai Formation and 15 microfacies in the Mingshui Formation.The complete sequence is composed of 535 m-scale cycles（sixth-order cycle）,152 fifth-order cycles,42 fourth-order cycles and five third-order cycles.The centimeter-scale description of the section revealed some previously unknown horizons such as a special type of mudstone,marl,volcanic ash and favorable sand reservoirs in the formations.The new-found evidence is very important for the interpretation of the evolution of the basin,conditions such as lake oxic events,the K/Pg boundary,tectonism in the late sag basin stage,and the reservoir-cap rock assemblages in the shallow stratigraphy.
文摘Cyclostratigraphy is more and more utilized in high-resolution dating in stratgraphy because of its characteristics of high resolution.It is based on the theory of orbital cycles,which are related to three Earth orbital parameters:eccentricity(e),obliquity(ε),and precession(e~*sinω).They affect the Earth periodically and then this information could be preserved in the sediments to be calibrated.However,in the geological time,the periodicities were changing.
基金supported by the Science Foundation of China University of Petroleum(Beijing)(Grant No.2462025YJRC008)Ferdowsi University of Mashhad,Iran(Grant No.3/49271)。
文摘The Middle Permian extinction event is considered one of the most devastating events of all Phanerozoic biotic crises,yet it is not fully understood and has attracted a lot of controversial comments.This event is found at the end of the Capitanian carbonate strata in the Ruteh Formation(late Wordian-Capitanian)at the Alborz Mountains in Iran.It is characterized by the decimation of marine organisms,particularly calcareous algae and microproblematic fossils.The current study attempts to interpret the cause of this crisis in the framework of astronomically-forced climatic changes.Based on cyclostratigraphy analysis,the evidence of the Milankovitch cycles,including long eccentricity,short eccentricity,obliquity,and precession are recorded in the Ruteh Formation succession.The establishment of a floating astronomical time scale using the long eccentricity cycles led to an estimation of a duration of 1.6 and 2.43 million years for the Wordian and Capitanian stages,respectively.Integrated facies studies and a sedimentary noise model indicate that the Ruteh Formation is composed of three~1.2 Myr sequences,corresponding to third-order sequences,and ten 405-kyr sequences,corresponding to fourth-to fifth-order sequences.The boundaries of the~1.2 Myr sequences indicate regression in sea level and low sedimentation rate.Considering the paleogeographic situation of the Alborz Mountains,the sedimentation of the Ruteh Formation in the Middle Permian was affected by the Inter-Tropical Convergence Zone and interactions between the ocean and atmosphere during the Pangea assemblage,leading to an increase in temperature.With the sum of these observations,we conclude that factors such as high temperature and a decrease in sedimentation rate created unfavorable conditions for the mentioned biota at the end of the Capitanian.
基金supported by the National Natural Science Foundation of China (Grant Nos. 41790452, 41688103, 41172037 and 41272030)
文摘Cretaceous strata are widely distributed across China and record a variety of depositional settings. The sedimentary facies consist primarily of terrestrial, marine and interbedded marine-terrestrial deposits, of which marine and interbedded facies are relatively limited. Based a thorough review of the subdivisions and correlations of Cretaceous strata in China, we provide an up-to-date integrated chronostratigraphy and geochronologic framework of the Cretaceous system and its deposits in China.Cretaceous marine and interbedded marine-terrestrial sediments occur in southern Tibet, Karakorum, the western Tarim Basin,eastern Heilongjiang and Taiwan. Among these, the Himalayan area has the most complete marine deposits, the foraminiferal and ammonite biozonation of which can be correlated directly to the international standard biozones. Terrestrial deposits in central and western China consist predominantly of red, lacustrine-fluvial, clastic deposits, whereas eastern China, a volcanically active zone, contains clastic rocks in association with intermediate to acidic igneous rocks and features the most complete stratigraphic successions in northern Hebei, western Liaoning and the Songliao Basin. Here, we synthesise multiple stratigraphic concepts and charts from southern Tibet, northern Hebei to western Liaoning and the Songliao Basin to produce a comprehensive chronostratigraphic chart. Marine and terrestrial deposits are integrated, and this aids in the establishment of a comprehensive Cretaceous chronostratigraphy and temporal framework of China. Further research into the Cretaceous of China will likely focus on terrestrial deposits and mutual authentication techniques(e.g., biostratigraphy, chronostratigraphy, magnetostratigraphy and cyclostratigraphy). This study provides a more reliable temporal framework both for studying Cretaceous geological events and exploring mineral resources in China.
基金supported by four student research grants from Geological Society of America, Ed Picou/GCSSEPM, American Association of Petroleum Geologiststhe Al Spreng Graduate Research Grant from the Geology and Geophysics Program of Missouri University of Science and Technology to Jonathan Obrist-Farnera research grant from University of Missouri Research Board and a research grant (No.2011ZX05008 004 053) from Institute of Geol-ogy and Geophysics of Chinese Academy of Sciences to Wan Yang
文摘Sedimentological and stratigraphic studies of seven stratigraphic sections of Permian Hongyanchi （HYC） and Quanzijie （QZJ） low-order cycles （LCs） in the Tarlong-Taodonggou half graben and Dalongkou area in Bogda Mountains, NW China, demonstrate effective approaches and methodology in cyclo- and time-stratigraphic analyses of complex fluviallacustrine deposits in an intracontinental rift setting. A new synchronous stratigraphic unit, the lower QZJ LC is defined. The lower and upper boundaries of this cycle include a regionally correlative disconformity, erosional unconformity, and conformity, across which significant and abrupt changes in palaeoenvironments and tectonic and climatic conditions occurred. The lower boundary is an erosional unconformity and disconformity with a high-relief topography that juxtaposes lacustrine deposits of the underlying HYC LC with the overlying meandering stream deposits of the lower QZJ LC, and was caused by a regional tectonic uplift. The up- per boundary is a disconformity and local erosional unconformity and conformity, juxtaposing stacked paleosols developed on fluvial sediments with overlying fluvial and loessial deposits of the upper QZJ LC. The paleosols indicate landscape stability and a prolonged period of subaerial exposure and minimal deposition and suggest that climatic conditions were semiarid with strong precipitation seasonality in the Tarlong-Taodonggou half graben and subhumid in the Dalongkou area. The fluvial-loessial deposits indicate a renewed tectonic uplift and a change in the atmospheric circulation pattern. The newly-defined lower QZJ LC facilitates accurate palaeogeographic reconstruction in the study area during a period of major tectonic and climatic changes. The interpreted tectonic and climatic conditions provide a critical data point in the mid-latitude east coast of NE Pangea during the Mid-Permian icehouse-hothouse transition. The results demonstrate that a process-response approach is effective in time- stratigraphic analysis of complex fluvial-lacustrine strata in a highly-partitioned rift basin.
基金supported by science and technology project of PetroChina Zhejiang Oilfield Company(grant numbers:zjyt-2021-kj-008).
文摘The sedimentary environment of the Upper Triassic in the southeastern Sichuan Basin is obviously controlled by Luzhou paleo-uplift(LPU).However,the influence of paleo-uplift on the sedimentary patterns of the initial stages of this period in the southeastern Sichuan Basin has not yet been clear,which has plagued oil and gas exploration and development.This study shows that there is a marine sedimentary sequence,which is considered to be the first member of Xujiahe Formation(T_(3)X^(1))in the southeastern Sichuan Basin.The development of LPU resulted in the sedimentary differences between the eastern and western Sichuan Basin recording T_(3)X^(1)and controlled the regional sedimentary pattern.The western part is dominated by marine sediments,but the eastern paleo-uplift area is dominated by continental sedimentation in the early stage of T_(3)X^(1),and it begins to transform into a marine sedimentary environment consistent with the whole basin in the late stage of the period recorded by the Xujiahe Formation.The evidences are as follows:(1)time series:based on the cyclostratigraphy analysis of Xindianzi section and Well D2,in the southeastern Sichuan Basin,the period of sedimentation of the Xujiahe Formation is about 5.9 Ma,which is basically consistent with the Qilixia section,eastern Sichuan basin,where the Xujiahe Formation is widely considered to be relatively complete;(2)distribution and evolution of palaeobiology:based on analysis of abundance evolution of major spore-pollen,many land plant fossils are preserved in the lower part of T_(3)X^(1),indicates the sedimentary environment of continental facies.In the upper part of T_(3)X^(1),the fossil of terrestrial plants decreased,while the fossil of marine and tidal environment appeared,this means that it was affected by the sea water in the late stages of T_(3)X^(1);(3)geochemistry:calculate the salinity of water from element indicates that the uplift area is continental sedimentary environment in the early stage of T_(3)X^(1),while the central and western areas of the basin are marine sedimentary environment.Until the late stage of T_(3)X^(1),the southeast of the basin gradually turns into marine sedimentary environment,consisting with the whole basin;(4)types of kerogen:type III kerogen representing continental facies was developed in the early stage of T_(3)X^(1)in the uplift area,and type II kerogen,representing marine facies,was developed in the late stage;while type II kerogenwas developed in the central and western regions of the basin as a whole in T_(3)X^(1).This study is of great significance for understanding of both stratigraphic division and sedimentary evolution providing theoretical support for the exploration and development of oil and gas.
基金The work was carried within the framework of the State Assignment of IG UFRC RAS No.FMRS-2022-0013This work was partly funded by the Grant No.20-05-00410 of the Russian Foundation for Basic Research.
文摘We present a detailed magnetostratigraphic and cyclostratigraphic profile through the Riphean(Tonian)Katav Formation in the southern Urals.The study confirms the primary nature of the magnetization in these rocks.The cyclostratigraphic study identified several orbital periods including the 405 ka long eccentricity.This allows us to quantify the reversal frequency in the Katav and our estimates range of 7–12 reversals per million years.Based on our study,we identify an interval of magnetic field reversal hyperactivity in the Neoproterozoic interval.Age estimates for the Katav are contentious and range somewhere between 800 Ma and 900 Ma based on carbonate Pb-Pb ages and stable isotope correlations.The paleomagnetic poles obtained in this study of the Katav(and overlying Inzer)Formation do not fit anywhere on the Baltica apparent polar wander path between 1100 Ma and 900 Ma.Furthermore,they lie 90away from the 900 Ma segment of the path.We tentatively estimate their age to be closer to 800 Ma and perhaps confirm a previously hypothesized pulse of rapid true polar wander between 825 Ma and 790 Ma.
基金the financial support of the Swiss National Science Foundation,which is gratefully acknowledged(Projects No.20 41888,20-43150,20-46625,20-67736,and 20-109214)
文摘The Oxfordian （Late Jurassic） carbonate-dominated ptatform outcropping in the Swiss Jura Mountains offers a good biostratigraphic, sequence-stratigraphic, and cyclostratigraphic framework to reconstruct changes in facies distribution at a time-resolution of 100 ka. It thus allows interpreting the dynamic evolution of this platform in much more detail than conventional palaeogeographic maps permit. As an example, a Middle to Late Oxfordian time slice is presented, spanning an interval of about 1.6 Ma. The study is based on 12 sections logged at cm-scale. The interpreted depositional environments include marginal-marine emerged ;ands, fresh-water lakes, tidal fiats, shallow lagoons, ooid shoals, and coral reefs. Although limestones dominate, marly intervals and dolomites occur sporadically. Major facies shifts are related to m-scale sea-level changes linked to the orbital short eccentricity cycle （100 ka）. The 20-ka precession cycle caused minor facies changes but cannot always be resolved. Synsedimentary tectonics induced additional accommodation changes by creating shallow basins where days accumulated or highs on which shoals or islands formed. Autocyclic processes such as lateral migration of ooid and bioclastic shoals added to the sedimentary record. CEimate changes intervened to control terrestrial run-off and, consequently, siliciclastic and nutrient input. Coral reefs reacted to such input by becoming dominated by microbialites and eventually by being smothered. Concomitant occurrence of siliciclastics anddolomite in certain intervals further suggests that, at times, it was relatively arid in the study area but there was rainfall in more northern latitudes, eroding the Hercynian substrate. These examples from the Swiss Jura demonstrate the highly dynamic and （geologically speaking） rapid evolution of sedimentary systems, in which tectonically controlled basin morphology, orbitally induced climate and sea-level changes, currents, and the ecology of the carbonate-producing organisms interacted to form the observed stratigraphic record. However, the interpretations have to be treated with caution because the km-wide spacing between the studied sections is too large to monitor the smaU-scale facies mosaics as they can be observed on modern platforms and as they certainly also occurred in the past.
