The Cretaceous Koum Basin is a rift-related half-graben in northern Cameroon,which constitutes a portion of the Yola Arm of the Upper Benue Trough.This study presents the first comprehensive dataset combining mineral-...The Cretaceous Koum Basin is a rift-related half-graben in northern Cameroon,which constitutes a portion of the Yola Arm of the Upper Benue Trough.This study presents the first comprehensive dataset combining mineral-ogical,bulk-rock geochemical,and stable C-H-O isotopic data for dark-gray,finegrained mudstones from the basin,providing new insights into its sediment source,paleoenvironment,and geodynamic setting.The mudstones primarily consist of phyllosilicates(~8.6%),feldspars(~30.5%),carbonates(~13.7%),and minor iron oxides(~2.7%),with vermiculite,illite,and kaolinite as the main clay minerals.The presence of analcime,ankerite,and dolomite suggests low-grade metamorphism and/or hydrothermal alteration.Fe_(2)O_(3)/K_(2)O(1.52-6.40)and SiO_(2)/Al_(2)O_(3)(2.97-4.68)ratios classify the mudstones as compositionally immature shales(ICV~1.64)with low-moderate chemical weathering(CIA~56.35;PIA~59.74;R^(3+)/R^(3+)+R^(2+)+M^(+)~0.51).Trace element ratios(Th/Sc~1.70,Zr/Sc~1.33,La/Sc~6.30,La/Th~4.14)indicate an intermediate igneous provenance from a continental crustal source.Paleoenviron-mental proxies suggest deposition in a dynamic basin environment marked by fluctuating redox(C org/P:0.21-178.34)and salinity(Sr/Ba:0.34-3.25;N-values:48-35.92)conditions,ranging from oxic to anoxic and brackish to saline.Major element data(SiO_(2) vs.Al_(2)O_(3)+K_(2)O+Na_(2)O)indicate a semi-arid regime,while Paleoclimatic indicators such as Sr/Cu(1.88-37.47)and C-values(0.12-0.93)suggests alter-nating humid and arid conditions.Notably,stable isotope data,reported here for the first time in the Koum Basin,reveal a predominantly terrestrial,fluvial-deltaic C_(3) plant source for organic carbon(δ^(13)C-25.2‰ to -35.2‰)and complex fluid-rock interactions involving meteoric and magmatic-metamorphic fluids under a warm,equatorial climate(δ^(18)O+3.6‰to +24.9‰,δ^(2)H-104‰ to-50‰).The combined mineralogical,geochemical,and isotopic data point to deposition in a tectonically active continental arc setting,with contributions from ocean island arc and passive margin sources.展开更多
The high-quality laminated source rock organic matter(OM)originated from planktonic algae,and its sedimentation was affected by global climate change significantly in the upper Xiaganchaigou Formation of the western Q...The high-quality laminated source rock organic matter(OM)originated from planktonic algae,and its sedimentation was affected by global climate change significantly in the upper Xiaganchaigou Formation of the western Qaidam Basin.However,coupling research on the paleoenvironment change and OM enrichment during the sedimentation period of the source rock is still lacking.This study from the aspects of sedimentary petrology,geochemistry and paleontology palynology,the paleoenvironment of source rock is restored and the OM enrichment model is established in the study area.Firstly,kerogen maceral identification indicates that the kerogen maceral is mainly composed of Botryococcus,accompanied with amorphous organic matter and plant debris.Secondly,arid climate and relatively active tectonic were observed during the deposition of the source rock.The water column was received felsic source from the continental island arc tectonic background,and has the environmental characteristics of relatively saline,shallow depth,medium low productivity,fast sedimentation rate and anoxic reduction and so on.Lastly,the first-order controlling factors for the OM enrichment are anoxic water conditions and suitable sedimentation rate,and the secondary controlling factor is paleoproductivity.Through the coupling study of paleoclimate,paleoenvironment and OM enrichment,the paleoclimate high frequency alternating evolution was the root cause of sedimentary environment change and OM enrichment of the laminated shale in the Upper Xiaganchaigou Formation.The study on the OM enrichment mechanism of algae in Qaidam provides a good model for understanding the coupling relationship between the algae bloom in the saline lake basins and the environments,and provides important theoretical basis for predicting shale oil“sweet spot”and production well sites arrangement for the continental saline lacustrine basins.展开更多
The extra-peninsular Gondwana Group rocks are exposed in narrow patches within the Lesser Himalayan sequence of the NE-Arunachal Himalayas,India.The bulk of sediments for the sandstones of the Gondwana Group were deri...The extra-peninsular Gondwana Group rocks are exposed in narrow patches within the Lesser Himalayan sequence of the NE-Arunachal Himalayas,India.The bulk of sediments for the sandstones of the Gondwana Group were derived from felsic/acidic to intermediate igneous rocks,with minor mafic input from the upper continental crust(UCC),as supported by various discrimination diagrams based on quantification of detrital minerals coupled with sandstone geochemistry.The inputs from metamorphic sources in subordinate amounts cannot be ruled out,as indicated by quantification of the quartz varieties.These sediments were found to be sourced from the interior part of a craton or shield and recycled platformal sediments which were derived from both passive and active margin settings.The sediments experienced a wide variance in climatic conditions,from arid to humid,suffering low-moderate-inten-sity weathering(CIA:63.43;CIW:86.18;WIP:44.84;PIA:75.37;ICV:2.39;C-value:0.42;PF:0.49;Sr/Cu:9.23 and Rb/Sr:1.68)within the vicinity of the low plains to moderate hills.Additionally,redox-sensitive elements indicate the deposition of sediments under oxygenated or oxygen-rich conditions(U_(au):−2.91;Th/U:7.37;U/Th:0.18;V/Cr:1.71;δU:0.67 and Ce/Ce^(*):0.93).展开更多
The Late Paleozoic marked Earth’s most recent icehouse–greenhouse transition,providing valuable insights into future climate and environmental changes.Although the aridification of the North China Craton(NCC)during ...The Late Paleozoic marked Earth’s most recent icehouse–greenhouse transition,providing valuable insights into future climate and environmental changes.Although the aridification of the North China Craton(NCC)during the Late Paleozoic is well established,its pattern and causes remain unclear.Here,we identify four aridification intervals from the late Gzhelian to Lopingian by analyzing continuous records of elemental climate proxies(MgO/CaO,Sr/Cu),a volcanism proxy(Hg/TOC),and spore–pollen assemblages.Interval I(∼303–295 Ma),during which the NCC was located at low paleolatitudes,was characterized by humid conditions and a predominance of ferns,associated with weak volcanism.Interval II(∼295–286 Ma)was subhumid,with increasing gymnosperm presence,and significant climate fluctuations linked to volcanism.CO_(2) emissions from the Tarim LIP and Panjal Traps drove aridification from the late Asselian to late Artinskian,contributing to the decline of the Late Paleozoic Ice Age.As a result,aridification in the NCC lagged behind that of Pangea.Interval III(∼286–280.98 Ma)marked the transition to subarid conditions and the onset of dominance by gymnosperms,associated with a rapid northward drift of the NCC and an increase in atmosphericρCO_(2).Interval IV(∼259.51–251.902 Ma),separated from the underlying Interval III by a major regional unconformity(∼280.98–259.51),coincided with global aridification and intensified volcanism.These findings highlight the significant influences of both tectonic plate motion and volcanism on the climate evolution of the NCC,with shifts in the dominant controlling factors through time.This study provides new insights into the distinct trajectories of global and regional climate dynamics.展开更多
Elemental concentrations of the siliciclastic sediments from a sedimentary basin provide clues on paleo-weathering,paleoclimate,provenance,and tectonic setting of the basin.Records for Permo-Triassic mass extinction a...Elemental concentrations of the siliciclastic sediments from a sedimentary basin provide clues on paleo-weathering,paleoclimate,provenance,and tectonic setting of the basin.Records for Permo-Triassic mass extinction and climatic fluctuations are commonly traced from the sediments in the Gondwana basins.Nevertheless,our understanding on sedimentation,provenance,and regional tectonics of the Raniganj Basin,a Gondwana basin in the eastern India is poor.Minerals including clay particles and major and trace element concentrations of the siliciclastic sediments from different formations of the Raniganj Basin have been studied to establish the paleo-weathering,paleoclimate,provenance,and tectonic settings of the basin.This study suggests that the Talchir Formation experienced cold and dry climatic conditions at the sediment source area,while the Barakar,Raniganj,and Panchet formations had prevailing semiarid climates.The sources of the siliciclastic sediments are from the felsic rocks of the Chotanagpur Granite Gneissic Complex(CGGC).Further,the geochemical results suggest a rift-like(passive)tectonic setting for the Raniganj Basin,while few samples represent the collision tectonic setting of the basement CGGC,formed due to collision of major Indian blocks during the Paleo-Neoproterozoic time.展开更多
The Ordos Basin was recognized as the earliest terrestrial aquatic ecosystem to recover following Permian-Triassic mass extinction,significantly contributing to organic carbon sequestration during the early Mesozoic e...The Ordos Basin was recognized as the earliest terrestrial aquatic ecosystem to recover following Permian-Triassic mass extinction,significantly contributing to organic carbon sequestration during the early Mesozoic era.Volcanic activity has increased the organic carbon burial capacity of the third submember of Ch7(Ch7_(3))within this basin,although it has both positive and negative effects on organic carbon burial.In this study,we quantitatively characterized the organic carbon burial process by calculating the organic carbon accumulation rate(OCAR)and proposed an optimal sedimentary model influenced by volcanic activity.We conducted time series analysis on gamma ray(GR)data from Ch7_(3) to determine sedimentation rates(SRs) while measuring the density of each sample via hydrostatic methods.By integrating these measurements with the total organic carbon(TOC)content,we established a dynamic OCAR for Ch7_(3)(χ=0.68 g/(cm^(2)·kyr))and estimated that it sequestered 0.27 Tt of organic carbon.Our findings indicate that the OCAR under eunixic conditions(χ=1.02 g/(cm^(2)·kyr))is 2.49 times greater than that under ferruginous conditions(χ=0.41 g/(cm^(2)·kyr)).The geochemical identification fingerprints of volcanism suggest that the top of Ch7_(3) is influenced by volcanoes of appropriate intensity.In this sedimentary model,the dilution of organic matter(OM)by rapidly deposited volcanic ash is relatively low.Additionally,the cumulative effect of chemical weathering intensity due to volcanic activity leads to the input of nutrients from continental sources into the lake basin.This process promotes increased productivity,resulting in a significant increase in the OCAR(χ=0.76 g/(cm^(2)·kyr)).This study provides new insights for dynamically assessing the impact of geological events on the OCAR.展开更多
The environmental magnetic proxies of stalagmites hold significant potential for reconstructing regional hydroclimate changes by revealing the content and grain size of magnetic particles within stalagmites.In this st...The environmental magnetic proxies of stalagmites hold significant potential for reconstructing regional hydroclimate changes by revealing the content and grain size of magnetic particles within stalagmites.In this study,we present the contents and grain sizes of magnetic particles within a stalagmite SZ-1,from Shizhu Cave in southwestern China from 70.4 to 22.3 thousand years ago(ka)during the last glacial period.Specifically,the parameters IRM_(soft),soil-derived magnetic minerals,and ARM/SIRM(anhysteretic remanent magnetization/saturation isothermal remanent magnetization),the ratio of fine magnetic particles to total ferrimagnetic particles preserved in stalagmite SZ-1,indicate the fluctuation of regional precipitation.Obvious half-precessional cycles are evident in these two proxies,indicating that hydroclimatic variations in southwestern China may predominantly arise from the heat and moisture transported from tropical oceans.These variations are likely influenced by shifts in the Intertropical Convergence Zone and fluctuations in the Asian Summer Monsoon.展开更多
The late Carboniferous to early Permian period is renowned for extensive coal formation and frequent paleowildfires.Nonetheless,the nature and distribution of these wildfires varied significantly over time.In an effor...The late Carboniferous to early Permian period is renowned for extensive coal formation and frequent paleowildfires.Nonetheless,the nature and distribution of these wildfires varied significantly over time.In an effort to elucidate the patterns of paleowildfires during the late Paleozoic Ice Age and to probe into the controlling mechanisms of paleowildfires under icehouse conditions,a comprehensive analysis was performed on coal samples from the Taiyuan and Shanxi formations within the Dacheng coalfield of Hebei Province,North China.The dataset was augmented with global inertinite data from the late Carboniferous to early Permian periods and was compared to paleowildfire patterns from the Pliocene to Holocene epochs.The results show that paleowildfires in the Dacheng coalfield of North China transitioned from moderate-scale,low-intensity surface fires to large-scale,relatively high-intensity ground fires.Globally,the distribution of paleowildfires shifted from Euramerica to Gondwana,Cathaysia,and Angara from 300 Ma to 290 Ma,accompanied by a corresponding increase in inertinite content.This spatial and temporal variation in wildfire activity appears to have been strongly influenced by paleoclimate and atmospheric conditions.At 300 Ma,cooler and wetter paleoclimate,coupled with relatively low atmospheric pO_(2) levels,likely contributed to a reduced incidence of paleowildfires.In contrast,at 290 Ma,warmer paleoclimate,higher atmospheric pO_(2) levels,and the flourishing mires in Gondwana,Cathaysia,and Angara were conducive to more intense paleowildfires.This pattern is further supported by the comparison to more recent icehouse periods.Similar to the late Carboniferous–early Permian period,wildfire activity increased from the Pliocene to the Holocene,highlighting the critical role of climatic conditions in driving wildfire proliferation under icehouse conditions.However,the Pleistocene to Holocene wildfires were less intense than those of the late Carboniferous–early Permian,suggesting that atmospheric oxygen concentrations played a key role in modulating the evolution of the fire systems over geological timescales.These findings underscore the complex interplay between climate,atmospheric composition,and vegetation in shaping wildfire dynamics across Earth’s history.展开更多
Evergreen broad-leaved forests(EBLFs) are widely distributed in East Asia and play a vital role in ecosystem stability. The occurrence of these forests in East Asia has been a subject of debate across various discipli...Evergreen broad-leaved forests(EBLFs) are widely distributed in East Asia and play a vital role in ecosystem stability. The occurrence of these forests in East Asia has been a subject of debate across various disciplines. In this study, we explored the occurrence of East Asian EBLFs from a paleobotanical perspective. By collecting plant fossils from four regions in East Asia, we have established the evolutionary history of EBLFs. Through floral similarity analysis and paleoclimatic reconstruction, we have revealed a diverse spatio-temporal pattern for the occurrence of EBLFs in East Asia. The earliest occurrence of EBLFs in southern China can be traced back to the middle Eocene, followed by southwestern China during the late Eocene-early Oligocene. Subsequently, EBLFs emerged in Japan during the early Oligocene and eventually appeared in central-eastern China around the Miocene. Paleoclimate simulation results suggest that the precipitation of wettest quarter(PWet Q, mm) exceeding 600 mm is crucial for the occurrence of EBLFs. Furthermore, the heterogeneous occurrence of EBLFs in East Asia is closely associated with the evolution of the Asian Monsoon. This study provides new insights into the occurrence of EBLFs in East Asia.展开更多
This review compiles studies on paleoceanographic and paleoenvironmental changes in the high-latitude Southern Ocean during the late Quaternary based on Chinese Antarctic Expeditions.Four major findings are summarized...This review compiles studies on paleoceanographic and paleoenvironmental changes in the high-latitude Southern Ocean during the late Quaternary based on Chinese Antarctic Expeditions.Four major findings are summarized as follows.(1)Diatom compositions in sediment record sea surface condition changes in the Bransfield Strait and Cosmonaut Sea,indicating an increase in sea ice cover since the Mid-Holocene for both areas,possibly linked to cold water mass injection from the Weddell Sea ice shelf.(2)Export productivity records from Antarctic marginal seas show a glacial-interglacial variation pattern,with higher and lower productivity during the interglacial and glacial periods,respectively,controlled by both the intensity of Circumpolar Deep Water upwelling and sea ice cover.An overall increase of export productivity from Marine Isotope Stage(MIS)12 to MIS 6 is noticed.(3)Ventilation state of the abyssal Southern Ocean is closely related to global climate change and atmospheric CO_(2) concentrations,with elevated ventilation efficiency during deglacial periods responsible for elevated atmospheric CO_(2) concentrations.(4)Antarctic marine-based ice sheets/glaciers wax and wane in line with global and regional ice volume changes,predominantly subject to oceanic forcing,while land-based ice sheets might only reorganize in specific glacial intervals.Despite significant progress in understanding the role of the Southern Ocean and the Antarctic Ice Sheet within the global climate system,challenges remain in sample collection and research methods.Future studies should aim to collect samples from a broader range of latitudes,ensure higher quality and longer temporal span,resolve dating issues,reconstruct seawater temperature,and focus on reconstructions of Southern Ocean carbon cycling and changes of intermediate to deep water masses.展开更多
In research on the legendary Xia Dynasty of ancient China,the famous archaeological site of Erlitou and its culture are the most debated topics.A key question is whether this ancient culture is truly related to the Xi...In research on the legendary Xia Dynasty of ancient China,the famous archaeological site of Erlitou and its culture are the most debated topics.A key question is whether this ancient culture is truly related to the Xia Dynasty.This study combines traditional literature(Xia Xiao Zheng),archaeological evidence(on alligators),and climate simulation(of autumn rains)to demonstrate that the ancient Chinese phenological calendar,Xia Xiao Zheng,likely originated in the same region as the Erlitou culture.A logical explanation of these findings is that both Xia Xiao Zheng and the Erlitou culture are indeed closely related to the Xia Dynasty.展开更多
Hopane separation and isotope determination were conducted on 11 source rock samples from various sedimentary environments.A schematic diagram of the carbon isotope distributions of hopane across different depositiona...Hopane separation and isotope determination were conducted on 11 source rock samples from various sedimentary environments.A schematic diagram of the carbon isotope distributions of hopane across different depositional environments was constructed.By integrating biomarker and organic petrology evidence,the geological significance of hopane carbon isotopes in oil source correlation and paleoclimate and paleoecology reconstruction was revealed.The results showed that the carbon isotopic compositions of hopanes vary considerably with depositional environment.展开更多
The formation of Danxia landscapes is too slow to be observed in our life time and the paleoclimates in which Danxia landscapes developed are significantly different from the present. Thus, this study adopted experime...The formation of Danxia landscapes is too slow to be observed in our life time and the paleoclimates in which Danxia landscapes developed are significantly different from the present. Thus, this study adopted experimental approaches to examine the lithological and paleoclimatic control on the formation of various landscape morphologies in the Mt. Danxiashan, South China. A total of 122 rock samples were collected from a range of Danxia landscape morphologies such as white spots, small and large through caves, honeycomb caves, horizontal grooves, natural bridges, stone pillars, and squama stones. Analyses of the collected samples were conducted in different kinds of experiments, including uniaxial mechanical strength testing; rock resistance against sulfuric acid erosion, freezing, and thawing; X-ray fluorescence spectrometry（XRF） analysis; inductively coupled plasma mass spectrometry（ICP-MS） analysis; and identification analysis under a polarizing microscope. The results indicated that the formation of the various Danxia landscape morphologies could result from one or more of the following processes： differential erosion due to lithological difference, chemical dissolution and recrystallization, freezing and thawing actions, acid corrosion, weathering, lateral erosion of river flows, and tectonic uplifts. Water erosion in humid monsoon climate and the alternations of intensive freezing and thawing actions in the Quaternary glacial stages and the interglacial stages could have had great influences on the formation of Danxia landscape topographies.展开更多
Through the Pearl River Estuary Wan Qing-sha W2 core AMS 14^C dating of sediments, combining with paleomagnetic test, pollen analysis, and comprehensive comparison with other relevant records, the regional framework o...Through the Pearl River Estuary Wan Qing-sha W2 core AMS 14^C dating of sediments, combining with paleomagnetic test, pollen analysis, and comprehensive comparison with other relevant records, the regional framework of Holocene age was established. Using the combined feature grain size and magnetic susceptibility proxies for the environment, climate change information in the area since about 6 000 cal yr BP was obtained. The result showed the area since the middle Holocene had experienced three stages climate changes of warm and dry - cool and wet temperature and humidity South area of China in the late Holocene climate （especially rainfall） had important changes, corresponding to the Northern Hemisphere solar radiation reducing, air temperature decreasing, Asian monsoon weakening, and it had close ties with activities to strengthen El Nino - Southern Oscillation events.展开更多
The Middle Jurassic palynomorphs from the Yan'an Formation in Dongsheng region of Nei Monggol, consist of 63 species of fossil spores and pollen grains belonging to 34 genera, of which two species were described a...The Middle Jurassic palynomorphs from the Yan'an Formation in Dongsheng region of Nei Monggol, consist of 63 species of fossil spores and pollen grains belonging to 34 genera, of which two species were described as new. Based on statistical analysis of 3 863 specimens identified in 10 samples from Hantaichuan, Nianpanlianggou and Liugou sections, the sporo-pollen assemblage from the Yan'an Formation in Dongsheng region was established, which is generally characterized by the slight dominance of gymnospermous pollen grains (generally attaining proportion of 51%-54%), whereas the pteridophytic spores reach 46%-49% in abundance. In comparison with those of adjacent regions as well as Eurasia and North America, the present sporo-pollen assemblage is regarded to early Middle Jurassic (corresponding to Bajocian Stage) in geological age. According to the climatic conditions reflected by the palynoflora, the paleoclimate in Dongsheng region is suggested to be warm temperate or subtropical warm and humid during the early Middle Jurassic.展开更多
The stability of titanite is sensitive to temperature and partial pressure of CO2.The finding of authigenic titanite grains in weathering regolith formed on Parana basalts,Brazil,under tropical climatic conditions,rev...The stability of titanite is sensitive to temperature and partial pressure of CO2.The finding of authigenic titanite grains in weathering regolith formed on Parana basalts,Brazil,under tropical climatic conditions,reveals the thermodynamically-driven conversion from calcite to titanite at elevated ambient temperatures.Being unusual nowadays,this phase transition provides important implications for the understanding of silicate weathering in earlier geological epochs.Two types of secondary titanites were identified in the weathering profile of the study area.The tiny grains of 10 μm are forming in the microscopic voids in the rock.Also,large fractures filled with Fe-rich clay minerals contain bigger specimens of up to 170μm.The titanites of second type often coexist with chalcedony and barite.No carbonate minerals were found in the weathering profile.Weathering sphene can be discriminated from other titanite types by its strong positive Eu anomaly,increased Al2 O3 content and low content of trace elements.Its specific chemical composition and reactive transport modeling link this secondary mineral with dissolution of plagioclase.The titanite precipitation is controlled by slow diffusion in poorly-aerated,highly-alkaline pore fluids.The subaerial weathering of basaltic rocks provides a significant reservoir for atmospheric CO2.However,the deposition of carbonate minerals is thermodynamically avoided at the stability field of titanite.We demonstrate a complex feedback between CO2 and soil carbonates.The rise in pCO2 triggers the precipitation of calcite in the weathering regolith,but the greenhouse effect increasing the temperature can cease carbonate deposition.Secondary titanites were found in several paleosols and at least a part of them can be of weathering origin.展开更多
A granulometric, mineralogical, morphoscopic and exoscopic study and Rock-Eval analysis carried out on samples taken in the Loango Bay and at Kivesso on the Congolese coast have made it possible to highlight the highl...A granulometric, mineralogical, morphoscopic and exoscopic study and Rock-Eval analysis carried out on samples taken in the Loango Bay and at Kivesso on the Congolese coast have made it possible to highlight the highly erosive character of the well-documented wet phases ca 9000 - 3000 years B.P. and ca 320 B.P. in the sub-region. Supported by carbon-14 dating, total organic carbon analyses highlight two major phases of peat deposit emplacement. The first, ca. 7000 years B.P., corresponds to the beginning of the deposition of the yellow formation in the entire Loango Bay;the second, ca. 320 years B.P., is contemporary with the deposition of peat in the Kivesso sector. The granulometric analysis of the sediments shows that they are essentially sandy-clay and very poor in silt, alternating with beds of silty clay sometimes rich in organic matter. These sands have a predominant mode of 0.200 mm and an average varying between 0.150 and 0.300 mm. They constitute the flood phase of the carrier current. They are associated with a population of mode 0.125 mm sometimes 0.050 mm with an average varying between 0.100 mm and 0.126 mm which corresponds to the settling phase. Morphoscopic examination showed several varieties of quartz that argue for a source of supply close to the depositional sites.展开更多
Based on the palynological data from Well Ta-19-36 and Well Ta-19-37 in the Ta＇nan Sag, and Well Ta-22-1 and Well Ta-21-1 in the Bayin Gobi Sag, a spore-pollen assemblage from the Damoguaihe Formation is named as Cic...Based on the palynological data from Well Ta-19-36 and Well Ta-19-37 in the Ta＇nan Sag, and Well Ta-22-1 and Well Ta-21-1 in the Bayin Gobi Sag, a spore-pollen assemblage from the Damoguaihe Formation is named as Cicatricosisporites minutaestriatus- Aequitriradites spinulosus-Protopinus sp. assemblage in the Tamutsag Basin, Mongolia. The assemblage is characterized by abundant gymnosperm pollen and diverse fern spores, counted 46.35%–65.57% and 34.43%–52.58% in percentage respectively. Among the gymnosperm pollen, Pinuspollenites sp.（2.66%–16.94%）, Protopinus sp.（0–11.38%） and Protopicea sp.（0–10.81%） are dominant; and Alisporites sp., Cerebropollenites sp., Podocarpidites sp., and Abietineaepollenites sp. are common. Some important elements, such as Chasmatosporites sp., Callialasporites prominulus, Parvisaccites sp., Parcisporites sp., Jiaohepollis cf. annulatus, J. bellus, J. verus, Polycingulatisporites sp., Schizaeoisporites certus, Classopollis annulatus are seen. Within the fern spores, Osmundacidites wellamanii（0.85%–4.93%）, Appendicisporites sp.（0–4.45%）, Baculatisporites comaumensis（0.80%–2.87%）, Cicatricosisporites sp.（0.51%–2.66%）, C. minor（0–2.14%）, Foraminisporis asymmetricus（0–2.40%）, Aequitriradites sp.（0– 2.19%） and Cyathidites minor（0–2.13%） are dominant; and some specie of Densoisporites, Cooksonites, Impardecispora, Pilosisporites, Schizaeosprites, Fixisporites, Leptolepidites, Trilobosporites, Kuylisporites, Klukisporites, Hsuisporites, Couperisporites, Maculatisporites are seen. The angiosperm pollen are rare in the assemblage, characterized by Clavatipollenites sp.（0–0.80%） and Songipollis sp.（0–0.27%）. The geological age of the Damoguaihe Formation is assigned to Hauterivian – Barremian of Early Cretaceous according to the palynological data, due to the fact that there existed a lot of diverse spores of the family Schizaeaceae and prosperous gymnosperm saccat pollen which the corpus and sacci are differentiated completely, and the presence of early angiosperm pollen of Clavatipollenites. However, the zircon U-Pb isotopic dating of the volcanic rocks in the Nantun Formation indicated that the overlying strata of the Nantun Formation, i.e. the Damoguaihe Formation must be younger than 127.0±2.0–137.9±1.5 Ma. This is consistent with the palynological data. Furthermore, the vegetation reconstructed on the palynological data of the Damoguaihe Formation is conifer forest with shrubs and grassland, belonging to the semi-humid or humid middle to south subtropical climate. Moreover, three new species, namely Biretisporites punctatus sp. nov., Chasmatosporites reticulates sp. nov. and Concentrisporites contractus sp. nov. are described here.展开更多
The Cretaceous is among the most unusual eras in the geological past. Geoscience communities have been having great concerns with geological phenomena within this period, for example carbonate platforms and black shal...The Cretaceous is among the most unusual eras in the geological past. Geoscience communities have been having great concerns with geological phenomena within this period, for example carbonate platforms and black shales in the Early and Middle Cretaceous respectively, during the last decades. But few people have paid any attention to the set of pelagic redbeds lying on the black shales, not to mention the applications to paleoclimatology and paleoceanography. It is shown by the sedimentary records of redbeds, that they were deposited around the CCD, with both a higher content of iron and much lower concentrations of organic carbon, which implies conditions with a relatively high content of oxygen. Such redbeds occurred in the global oceans, mainly in the Tethyan realm, with different durations of deposition and a climax from the late Santonian to early Campanian. Global cooling and dramatic changes in ocean currents might help to increase the oxygen flux between the atmosphere and ocean, after the large scale organic carbon burial during the Middle Cretaceous, and therefore lead to the oxygenation of deep ocean and so the occurrence of late Cretaceous oceanic redbeds.展开更多
文摘The Cretaceous Koum Basin is a rift-related half-graben in northern Cameroon,which constitutes a portion of the Yola Arm of the Upper Benue Trough.This study presents the first comprehensive dataset combining mineral-ogical,bulk-rock geochemical,and stable C-H-O isotopic data for dark-gray,finegrained mudstones from the basin,providing new insights into its sediment source,paleoenvironment,and geodynamic setting.The mudstones primarily consist of phyllosilicates(~8.6%),feldspars(~30.5%),carbonates(~13.7%),and minor iron oxides(~2.7%),with vermiculite,illite,and kaolinite as the main clay minerals.The presence of analcime,ankerite,and dolomite suggests low-grade metamorphism and/or hydrothermal alteration.Fe_(2)O_(3)/K_(2)O(1.52-6.40)and SiO_(2)/Al_(2)O_(3)(2.97-4.68)ratios classify the mudstones as compositionally immature shales(ICV~1.64)with low-moderate chemical weathering(CIA~56.35;PIA~59.74;R^(3+)/R^(3+)+R^(2+)+M^(+)~0.51).Trace element ratios(Th/Sc~1.70,Zr/Sc~1.33,La/Sc~6.30,La/Th~4.14)indicate an intermediate igneous provenance from a continental crustal source.Paleoenviron-mental proxies suggest deposition in a dynamic basin environment marked by fluctuating redox(C org/P:0.21-178.34)and salinity(Sr/Ba:0.34-3.25;N-values:48-35.92)conditions,ranging from oxic to anoxic and brackish to saline.Major element data(SiO_(2) vs.Al_(2)O_(3)+K_(2)O+Na_(2)O)indicate a semi-arid regime,while Paleoclimatic indicators such as Sr/Cu(1.88-37.47)and C-values(0.12-0.93)suggests alter-nating humid and arid conditions.Notably,stable isotope data,reported here for the first time in the Koum Basin,reveal a predominantly terrestrial,fluvial-deltaic C_(3) plant source for organic carbon(δ^(13)C-25.2‰ to -35.2‰)and complex fluid-rock interactions involving meteoric and magmatic-metamorphic fluids under a warm,equatorial climate(δ^(18)O+3.6‰to +24.9‰,δ^(2)H-104‰ to-50‰).The combined mineralogical,geochemical,and isotopic data point to deposition in a tectonically active continental arc setting,with contributions from ocean island arc and passive margin sources.
基金supported by the Joint Funds of the National Natural Science Foundation of China(No.2024DJ8702)the Science and Technology Research Project of the China National Petroleum Corporation(No.2024DJ87)+1 种基金the National Natural Science Foundation of China(No.42272029)the“Light of West China”Program of the Chinese Academy of Sciences(No.xbzglzb2022025)。
文摘The high-quality laminated source rock organic matter(OM)originated from planktonic algae,and its sedimentation was affected by global climate change significantly in the upper Xiaganchaigou Formation of the western Qaidam Basin.However,coupling research on the paleoenvironment change and OM enrichment during the sedimentation period of the source rock is still lacking.This study from the aspects of sedimentary petrology,geochemistry and paleontology palynology,the paleoenvironment of source rock is restored and the OM enrichment model is established in the study area.Firstly,kerogen maceral identification indicates that the kerogen maceral is mainly composed of Botryococcus,accompanied with amorphous organic matter and plant debris.Secondly,arid climate and relatively active tectonic were observed during the deposition of the source rock.The water column was received felsic source from the continental island arc tectonic background,and has the environmental characteristics of relatively saline,shallow depth,medium low productivity,fast sedimentation rate and anoxic reduction and so on.Lastly,the first-order controlling factors for the OM enrichment are anoxic water conditions and suitable sedimentation rate,and the secondary controlling factor is paleoproductivity.Through the coupling study of paleoclimate,paleoenvironment and OM enrichment,the paleoclimate high frequency alternating evolution was the root cause of sedimentary environment change and OM enrichment of the laminated shale in the Upper Xiaganchaigou Formation.The study on the OM enrichment mechanism of algae in Qaidam provides a good model for understanding the coupling relationship between the algae bloom in the saline lake basins and the environments,and provides important theoretical basis for predicting shale oil“sweet spot”and production well sites arrangement for the continental saline lacustrine basins.
文摘The extra-peninsular Gondwana Group rocks are exposed in narrow patches within the Lesser Himalayan sequence of the NE-Arunachal Himalayas,India.The bulk of sediments for the sandstones of the Gondwana Group were derived from felsic/acidic to intermediate igneous rocks,with minor mafic input from the upper continental crust(UCC),as supported by various discrimination diagrams based on quantification of detrital minerals coupled with sandstone geochemistry.The inputs from metamorphic sources in subordinate amounts cannot be ruled out,as indicated by quantification of the quartz varieties.These sediments were found to be sourced from the interior part of a craton or shield and recycled platformal sediments which were derived from both passive and active margin settings.The sediments experienced a wide variance in climatic conditions,from arid to humid,suffering low-moderate-inten-sity weathering(CIA:63.43;CIW:86.18;WIP:44.84;PIA:75.37;ICV:2.39;C-value:0.42;PF:0.49;Sr/Cu:9.23 and Rb/Sr:1.68)within the vicinity of the low plains to moderate hills.Additionally,redox-sensitive elements indicate the deposition of sediments under oxygenated or oxygen-rich conditions(U_(au):−2.91;Th/U:7.37;U/Th:0.18;V/Cr:1.71;δU:0.67 and Ce/Ce^(*):0.93).
基金financially supported by CNPC Innovation Found(2021DQ02-1003)the Fundamental Research Funds for the Central Universities(Ph.D.Top Innovative Talents Fund of CUMTB)(BBJ2025043).
文摘The Late Paleozoic marked Earth’s most recent icehouse–greenhouse transition,providing valuable insights into future climate and environmental changes.Although the aridification of the North China Craton(NCC)during the Late Paleozoic is well established,its pattern and causes remain unclear.Here,we identify four aridification intervals from the late Gzhelian to Lopingian by analyzing continuous records of elemental climate proxies(MgO/CaO,Sr/Cu),a volcanism proxy(Hg/TOC),and spore–pollen assemblages.Interval I(∼303–295 Ma),during which the NCC was located at low paleolatitudes,was characterized by humid conditions and a predominance of ferns,associated with weak volcanism.Interval II(∼295–286 Ma)was subhumid,with increasing gymnosperm presence,and significant climate fluctuations linked to volcanism.CO_(2) emissions from the Tarim LIP and Panjal Traps drove aridification from the late Asselian to late Artinskian,contributing to the decline of the Late Paleozoic Ice Age.As a result,aridification in the NCC lagged behind that of Pangea.Interval III(∼286–280.98 Ma)marked the transition to subarid conditions and the onset of dominance by gymnosperms,associated with a rapid northward drift of the NCC and an increase in atmosphericρCO_(2).Interval IV(∼259.51–251.902 Ma),separated from the underlying Interval III by a major regional unconformity(∼280.98–259.51),coincided with global aridification and intensified volcanism.These findings highlight the significant influences of both tectonic plate motion and volcanism on the climate evolution of the NCC,with shifts in the dominant controlling factors through time.This study provides new insights into the distinct trajectories of global and regional climate dynamics.
基金funded by SERB-DST,New Delhi,India for Early Career Research(ECR/2016/001100)during 2017 to 2021.
文摘Elemental concentrations of the siliciclastic sediments from a sedimentary basin provide clues on paleo-weathering,paleoclimate,provenance,and tectonic setting of the basin.Records for Permo-Triassic mass extinction and climatic fluctuations are commonly traced from the sediments in the Gondwana basins.Nevertheless,our understanding on sedimentation,provenance,and regional tectonics of the Raniganj Basin,a Gondwana basin in the eastern India is poor.Minerals including clay particles and major and trace element concentrations of the siliciclastic sediments from different formations of the Raniganj Basin have been studied to establish the paleo-weathering,paleoclimate,provenance,and tectonic settings of the basin.This study suggests that the Talchir Formation experienced cold and dry climatic conditions at the sediment source area,while the Barakar,Raniganj,and Panchet formations had prevailing semiarid climates.The sources of the siliciclastic sediments are from the felsic rocks of the Chotanagpur Granite Gneissic Complex(CGGC).Further,the geochemical results suggest a rift-like(passive)tectonic setting for the Raniganj Basin,while few samples represent the collision tectonic setting of the basement CGGC,formed due to collision of major Indian blocks during the Paleo-Neoproterozoic time.
基金supported by the National Natural Science Foundation of China(Grant No.42090025)the National Key R&D Program of China(2023YFF0806200).
文摘The Ordos Basin was recognized as the earliest terrestrial aquatic ecosystem to recover following Permian-Triassic mass extinction,significantly contributing to organic carbon sequestration during the early Mesozoic era.Volcanic activity has increased the organic carbon burial capacity of the third submember of Ch7(Ch7_(3))within this basin,although it has both positive and negative effects on organic carbon burial.In this study,we quantitatively characterized the organic carbon burial process by calculating the organic carbon accumulation rate(OCAR)and proposed an optimal sedimentary model influenced by volcanic activity.We conducted time series analysis on gamma ray(GR)data from Ch7_(3) to determine sedimentation rates(SRs) while measuring the density of each sample via hydrostatic methods.By integrating these measurements with the total organic carbon(TOC)content,we established a dynamic OCAR for Ch7_(3)(χ=0.68 g/(cm^(2)·kyr))and estimated that it sequestered 0.27 Tt of organic carbon.Our findings indicate that the OCAR under eunixic conditions(χ=1.02 g/(cm^(2)·kyr))is 2.49 times greater than that under ferruginous conditions(χ=0.41 g/(cm^(2)·kyr)).The geochemical identification fingerprints of volcanism suggest that the top of Ch7_(3) is influenced by volcanoes of appropriate intensity.In this sedimentary model,the dilution of organic matter(OM)by rapidly deposited volcanic ash is relatively low.Additionally,the cumulative effect of chemical weathering intensity due to volcanic activity leads to the input of nutrients from continental sources into the lake basin.This process promotes increased productivity,resulting in a significant increase in the OCAR(χ=0.76 g/(cm^(2)·kyr)).This study provides new insights for dynamically assessing the impact of geological events on the OCAR.
基金supported by the National Natural Science Foundation of China(Nos.42074071,42274094,42261144739)the Shenzhen Science and Technology Program(No.KQTD20170810111725321)+2 种基金supported by the Taiwan University Core Consortiums Project(No.112L894202)the Higher Education Sprout Project of the Ministry of Education(No.112L901001)the National Science and Technology Council(No.111-2116-M-002-022-MY3)。
文摘The environmental magnetic proxies of stalagmites hold significant potential for reconstructing regional hydroclimate changes by revealing the content and grain size of magnetic particles within stalagmites.In this study,we present the contents and grain sizes of magnetic particles within a stalagmite SZ-1,from Shizhu Cave in southwestern China from 70.4 to 22.3 thousand years ago(ka)during the last glacial period.Specifically,the parameters IRM_(soft),soil-derived magnetic minerals,and ARM/SIRM(anhysteretic remanent magnetization/saturation isothermal remanent magnetization),the ratio of fine magnetic particles to total ferrimagnetic particles preserved in stalagmite SZ-1,indicate the fluctuation of regional precipitation.Obvious half-precessional cycles are evident in these two proxies,indicating that hydroclimatic variations in southwestern China may predominantly arise from the heat and moisture transported from tropical oceans.These variations are likely influenced by shifts in the Intertropical Convergence Zone and fluctuations in the Asian Summer Monsoon.
基金supported by the National Natural Science Foundation of China(Grant No.42302205 and No.42002128)the Fundamental Research Funding Project of Liaoning Education Department(Grant No.LJKMZ20220692)the Open Fund of State Key Laboratory of Coal Resources and Safe Mining(Grant No.SKLCRSM22KFA07 and No.SKLCRSM20KFA02).
文摘The late Carboniferous to early Permian period is renowned for extensive coal formation and frequent paleowildfires.Nonetheless,the nature and distribution of these wildfires varied significantly over time.In an effort to elucidate the patterns of paleowildfires during the late Paleozoic Ice Age and to probe into the controlling mechanisms of paleowildfires under icehouse conditions,a comprehensive analysis was performed on coal samples from the Taiyuan and Shanxi formations within the Dacheng coalfield of Hebei Province,North China.The dataset was augmented with global inertinite data from the late Carboniferous to early Permian periods and was compared to paleowildfire patterns from the Pliocene to Holocene epochs.The results show that paleowildfires in the Dacheng coalfield of North China transitioned from moderate-scale,low-intensity surface fires to large-scale,relatively high-intensity ground fires.Globally,the distribution of paleowildfires shifted from Euramerica to Gondwana,Cathaysia,and Angara from 300 Ma to 290 Ma,accompanied by a corresponding increase in inertinite content.This spatial and temporal variation in wildfire activity appears to have been strongly influenced by paleoclimate and atmospheric conditions.At 300 Ma,cooler and wetter paleoclimate,coupled with relatively low atmospheric pO_(2) levels,likely contributed to a reduced incidence of paleowildfires.In contrast,at 290 Ma,warmer paleoclimate,higher atmospheric pO_(2) levels,and the flourishing mires in Gondwana,Cathaysia,and Angara were conducive to more intense paleowildfires.This pattern is further supported by the comparison to more recent icehouse periods.Similar to the late Carboniferous–early Permian period,wildfire activity increased from the Pliocene to the Holocene,highlighting the critical role of climatic conditions in driving wildfire proliferation under icehouse conditions.However,the Pleistocene to Holocene wildfires were less intense than those of the late Carboniferous–early Permian,suggesting that atmospheric oxygen concentrations played a key role in modulating the evolution of the fire systems over geological timescales.These findings underscore the complex interplay between climate,atmospheric composition,and vegetation in shaping wildfire dynamics across Earth’s history.
基金supported by National Key R&D Program of China(No.2022YFF0800800)National Science Fund for Distinguished Young Scholars(No.32225005)+3 种基金National Natural Science Foundation of China(NSFC)(Nos.42072024,42320104005,42372033)the Young and Middle-aged Academic and Technical Leaders of Yunnan(No.202305AC160051)Basic Research Project of Yunnan Province(No.202401AT070222)the 14th Five-Year Plan of the Xishuangbanna Tropical Botanical Garden,Chinese Academy of Sciences(Nos.XTBG-1450101,E3ZKFF7B).
文摘Evergreen broad-leaved forests(EBLFs) are widely distributed in East Asia and play a vital role in ecosystem stability. The occurrence of these forests in East Asia has been a subject of debate across various disciplines. In this study, we explored the occurrence of East Asian EBLFs from a paleobotanical perspective. By collecting plant fossils from four regions in East Asia, we have established the evolutionary history of EBLFs. Through floral similarity analysis and paleoclimatic reconstruction, we have revealed a diverse spatio-temporal pattern for the occurrence of EBLFs in East Asia. The earliest occurrence of EBLFs in southern China can be traced back to the middle Eocene, followed by southwestern China during the late Eocene-early Oligocene. Subsequently, EBLFs emerged in Japan during the early Oligocene and eventually appeared in central-eastern China around the Miocene. Paleoclimate simulation results suggest that the precipitation of wettest quarter(PWet Q, mm) exceeding 600 mm is crucial for the occurrence of EBLFs. Furthermore, the heterogeneous occurrence of EBLFs in East Asia is closely associated with the evolution of the Asian Monsoon. This study provides new insights into the occurrence of EBLFs in East Asia.
基金The National Natural Science Foundation of China under contract Nos 42030401 and 42276077the Open Foundation of State Key Laboratory of Marine Geology,Tongji University under contract No.MGK202207+1 种基金the Open Foundation Project of the Key Laboratory of Polar Geology and Marine Mineral Resources of Ministry of Education,China University of Geosciences (Beijing),under contract Nos PGMR-2024-102 and PGMR-2023-304the Start-up Foundation of Guangdong Ocean University under contract No.060302032110
文摘This review compiles studies on paleoceanographic and paleoenvironmental changes in the high-latitude Southern Ocean during the late Quaternary based on Chinese Antarctic Expeditions.Four major findings are summarized as follows.(1)Diatom compositions in sediment record sea surface condition changes in the Bransfield Strait and Cosmonaut Sea,indicating an increase in sea ice cover since the Mid-Holocene for both areas,possibly linked to cold water mass injection from the Weddell Sea ice shelf.(2)Export productivity records from Antarctic marginal seas show a glacial-interglacial variation pattern,with higher and lower productivity during the interglacial and glacial periods,respectively,controlled by both the intensity of Circumpolar Deep Water upwelling and sea ice cover.An overall increase of export productivity from Marine Isotope Stage(MIS)12 to MIS 6 is noticed.(3)Ventilation state of the abyssal Southern Ocean is closely related to global climate change and atmospheric CO_(2) concentrations,with elevated ventilation efficiency during deglacial periods responsible for elevated atmospheric CO_(2) concentrations.(4)Antarctic marine-based ice sheets/glaciers wax and wane in line with global and regional ice volume changes,predominantly subject to oceanic forcing,while land-based ice sheets might only reorganize in specific glacial intervals.Despite significant progress in understanding the role of the Southern Ocean and the Antarctic Ice Sheet within the global climate system,challenges remain in sample collection and research methods.Future studies should aim to collect samples from a broader range of latitudes,ensure higher quality and longer temporal span,resolve dating issues,reconstruct seawater temperature,and focus on reconstructions of Southern Ocean carbon cycling and changes of intermediate to deep water masses.
基金National Key Research and Development Program of China,No.2023YFF0804704National Natural Science Foundation of China,No.42130604,No.42105044+1 种基金Major Projects of the Ministry of Education's Key Research Bases of Humanities and Social Sciences,No.22JJD770020Social Scienceof Northwest University,No.21XNFH007。
文摘In research on the legendary Xia Dynasty of ancient China,the famous archaeological site of Erlitou and its culture are the most debated topics.A key question is whether this ancient culture is truly related to the Xia Dynasty.This study combines traditional literature(Xia Xiao Zheng),archaeological evidence(on alligators),and climate simulation(of autumn rains)to demonstrate that the ancient Chinese phenological calendar,Xia Xiao Zheng,likely originated in the same region as the Erlitou culture.A logical explanation of these findings is that both Xia Xiao Zheng and the Erlitou culture are indeed closely related to the Xia Dynasty.
基金funded by the Open Project of State Key Laboratory of Geological Process and Mineral Resources(GPMR−2022−07).
文摘Hopane separation and isotope determination were conducted on 11 source rock samples from various sedimentary environments.A schematic diagram of the carbon isotope distributions of hopane across different depositional environments was constructed.By integrating biomarker and organic petrology evidence,the geological significance of hopane carbon isotopes in oil source correlation and paleoclimate and paleoecology reconstruction was revealed.The results showed that the carbon isotopic compositions of hopanes vary considerably with depositional environment.
基金National Natural Science Foundation of China, No.41371204 No.41171163+6 种基金 No.41401216 National Science and Technology Basic Special Key Project, No.2013FY 11 1900 Foundation of State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, CAS, No.SKLLQG1206 No.SKLLQG1422 National Basic Science Personnel Training Project, No.J1103408 Foundation of Modern Analysis Center, Nanjing University, No.0422171010 Priority Academic Program Development of Jiangsu Higher Education Institutions, No.PAPD,Acknowledgements We appreciate the laboratory and field assistance of KONG Qingyou, LIU Di, YANG Li, WANG Xiaocui, FU Jingcheng, LIANG Guomin, MAO Xiaodong, FAN Dengfeng, LUO Jiehong, WU Huaan, TAN Ming, DAI Huibao, and XIE Zhangzhen.
文摘The formation of Danxia landscapes is too slow to be observed in our life time and the paleoclimates in which Danxia landscapes developed are significantly different from the present. Thus, this study adopted experimental approaches to examine the lithological and paleoclimatic control on the formation of various landscape morphologies in the Mt. Danxiashan, South China. A total of 122 rock samples were collected from a range of Danxia landscape morphologies such as white spots, small and large through caves, honeycomb caves, horizontal grooves, natural bridges, stone pillars, and squama stones. Analyses of the collected samples were conducted in different kinds of experiments, including uniaxial mechanical strength testing; rock resistance against sulfuric acid erosion, freezing, and thawing; X-ray fluorescence spectrometry（XRF） analysis; inductively coupled plasma mass spectrometry（ICP-MS） analysis; and identification analysis under a polarizing microscope. The results indicated that the formation of the various Danxia landscape morphologies could result from one or more of the following processes： differential erosion due to lithological difference, chemical dissolution and recrystallization, freezing and thawing actions, acid corrosion, weathering, lateral erosion of river flows, and tectonic uplifts. Water erosion in humid monsoon climate and the alternations of intensive freezing and thawing actions in the Quaternary glacial stages and the interglacial stages could have had great influences on the formation of Danxia landscape topographies.
文摘Through the Pearl River Estuary Wan Qing-sha W2 core AMS 14^C dating of sediments, combining with paleomagnetic test, pollen analysis, and comprehensive comparison with other relevant records, the regional framework of Holocene age was established. Using the combined feature grain size and magnetic susceptibility proxies for the environment, climate change information in the area since about 6 000 cal yr BP was obtained. The result showed the area since the middle Holocene had experienced three stages climate changes of warm and dry - cool and wet temperature and humidity South area of China in the late Holocene climate （especially rainfall） had important changes, corresponding to the Northern Hemisphere solar radiation reducing, air temperature decreasing, Asian monsoon weakening, and it had close ties with activities to strengthen El Nino - Southern Oscillation events.
文摘The Middle Jurassic palynomorphs from the Yan'an Formation in Dongsheng region of Nei Monggol, consist of 63 species of fossil spores and pollen grains belonging to 34 genera, of which two species were described as new. Based on statistical analysis of 3 863 specimens identified in 10 samples from Hantaichuan, Nianpanlianggou and Liugou sections, the sporo-pollen assemblage from the Yan'an Formation in Dongsheng region was established, which is generally characterized by the slight dominance of gymnospermous pollen grains (generally attaining proportion of 51%-54%), whereas the pteridophytic spores reach 46%-49% in abundance. In comparison with those of adjacent regions as well as Eurasia and North America, the present sporo-pollen assemblage is regarded to early Middle Jurassic (corresponding to Bajocian Stage) in geological age. According to the climatic conditions reflected by the palynoflora, the paleoclimate in Dongsheng region is suggested to be warm temperate or subtropical warm and humid during the early Middle Jurassic.
文摘The stability of titanite is sensitive to temperature and partial pressure of CO2.The finding of authigenic titanite grains in weathering regolith formed on Parana basalts,Brazil,under tropical climatic conditions,reveals the thermodynamically-driven conversion from calcite to titanite at elevated ambient temperatures.Being unusual nowadays,this phase transition provides important implications for the understanding of silicate weathering in earlier geological epochs.Two types of secondary titanites were identified in the weathering profile of the study area.The tiny grains of 10 μm are forming in the microscopic voids in the rock.Also,large fractures filled with Fe-rich clay minerals contain bigger specimens of up to 170μm.The titanites of second type often coexist with chalcedony and barite.No carbonate minerals were found in the weathering profile.Weathering sphene can be discriminated from other titanite types by its strong positive Eu anomaly,increased Al2 O3 content and low content of trace elements.Its specific chemical composition and reactive transport modeling link this secondary mineral with dissolution of plagioclase.The titanite precipitation is controlled by slow diffusion in poorly-aerated,highly-alkaline pore fluids.The subaerial weathering of basaltic rocks provides a significant reservoir for atmospheric CO2.However,the deposition of carbonate minerals is thermodynamically avoided at the stability field of titanite.We demonstrate a complex feedback between CO2 and soil carbonates.The rise in pCO2 triggers the precipitation of calcite in the weathering regolith,but the greenhouse effect increasing the temperature can cease carbonate deposition.Secondary titanites were found in several paleosols and at least a part of them can be of weathering origin.
文摘A granulometric, mineralogical, morphoscopic and exoscopic study and Rock-Eval analysis carried out on samples taken in the Loango Bay and at Kivesso on the Congolese coast have made it possible to highlight the highly erosive character of the well-documented wet phases ca 9000 - 3000 years B.P. and ca 320 B.P. in the sub-region. Supported by carbon-14 dating, total organic carbon analyses highlight two major phases of peat deposit emplacement. The first, ca. 7000 years B.P., corresponds to the beginning of the deposition of the yellow formation in the entire Loango Bay;the second, ca. 320 years B.P., is contemporary with the deposition of peat in the Kivesso sector. The granulometric analysis of the sediments shows that they are essentially sandy-clay and very poor in silt, alternating with beds of silty clay sometimes rich in organic matter. These sands have a predominant mode of 0.200 mm and an average varying between 0.150 and 0.300 mm. They constitute the flood phase of the carrier current. They are associated with a population of mode 0.125 mm sometimes 0.050 mm with an average varying between 0.100 mm and 0.126 mm which corresponds to the settling phase. Morphoscopic examination showed several varieties of quartz that argue for a source of supply close to the depositional sites.
基金support by the National Natural Science Foundation of China (grant no. 31270277)
文摘Based on the palynological data from Well Ta-19-36 and Well Ta-19-37 in the Ta＇nan Sag, and Well Ta-22-1 and Well Ta-21-1 in the Bayin Gobi Sag, a spore-pollen assemblage from the Damoguaihe Formation is named as Cicatricosisporites minutaestriatus- Aequitriradites spinulosus-Protopinus sp. assemblage in the Tamutsag Basin, Mongolia. The assemblage is characterized by abundant gymnosperm pollen and diverse fern spores, counted 46.35%–65.57% and 34.43%–52.58% in percentage respectively. Among the gymnosperm pollen, Pinuspollenites sp.（2.66%–16.94%）, Protopinus sp.（0–11.38%） and Protopicea sp.（0–10.81%） are dominant; and Alisporites sp., Cerebropollenites sp., Podocarpidites sp., and Abietineaepollenites sp. are common. Some important elements, such as Chasmatosporites sp., Callialasporites prominulus, Parvisaccites sp., Parcisporites sp., Jiaohepollis cf. annulatus, J. bellus, J. verus, Polycingulatisporites sp., Schizaeoisporites certus, Classopollis annulatus are seen. Within the fern spores, Osmundacidites wellamanii（0.85%–4.93%）, Appendicisporites sp.（0–4.45%）, Baculatisporites comaumensis（0.80%–2.87%）, Cicatricosisporites sp.（0.51%–2.66%）, C. minor（0–2.14%）, Foraminisporis asymmetricus（0–2.40%）, Aequitriradites sp.（0– 2.19%） and Cyathidites minor（0–2.13%） are dominant; and some specie of Densoisporites, Cooksonites, Impardecispora, Pilosisporites, Schizaeosprites, Fixisporites, Leptolepidites, Trilobosporites, Kuylisporites, Klukisporites, Hsuisporites, Couperisporites, Maculatisporites are seen. The angiosperm pollen are rare in the assemblage, characterized by Clavatipollenites sp.（0–0.80%） and Songipollis sp.（0–0.27%）. The geological age of the Damoguaihe Formation is assigned to Hauterivian – Barremian of Early Cretaceous according to the palynological data, due to the fact that there existed a lot of diverse spores of the family Schizaeaceae and prosperous gymnosperm saccat pollen which the corpus and sacci are differentiated completely, and the presence of early angiosperm pollen of Clavatipollenites. However, the zircon U-Pb isotopic dating of the volcanic rocks in the Nantun Formation indicated that the overlying strata of the Nantun Formation, i.e. the Damoguaihe Formation must be younger than 127.0±2.0–137.9±1.5 Ma. This is consistent with the palynological data. Furthermore, the vegetation reconstructed on the palynological data of the Damoguaihe Formation is conifer forest with shrubs and grassland, belonging to the semi-humid or humid middle to south subtropical climate. Moreover, three new species, namely Biretisporites punctatus sp. nov., Chasmatosporites reticulates sp. nov. and Concentrisporites contractus sp. nov. are described here.
基金The research is jointly supported by the Key Project of the National Natural Science Foundation of China(No.40332020)Prophase Special Research of Vital Projects in the Basic Research of the Ministry of Science and Technology of China(No.2001CCA01 800)International Geological Correlation Program(IGCP463/494).
文摘The Cretaceous is among the most unusual eras in the geological past. Geoscience communities have been having great concerns with geological phenomena within this period, for example carbonate platforms and black shales in the Early and Middle Cretaceous respectively, during the last decades. But few people have paid any attention to the set of pelagic redbeds lying on the black shales, not to mention the applications to paleoclimatology and paleoceanography. It is shown by the sedimentary records of redbeds, that they were deposited around the CCD, with both a higher content of iron and much lower concentrations of organic carbon, which implies conditions with a relatively high content of oxygen. Such redbeds occurred in the global oceans, mainly in the Tethyan realm, with different durations of deposition and a climax from the late Santonian to early Campanian. Global cooling and dramatic changes in ocean currents might help to increase the oxygen flux between the atmosphere and ocean, after the large scale organic carbon burial during the Middle Cretaceous, and therefore lead to the oxygenation of deep ocean and so the occurrence of late Cretaceous oceanic redbeds.
