The Upper Cretaceous Qingshankou Formation black shales,deposited in the late Turonian(LTB shales),are the main source rocks of the Songliao Basin.The origins of organic matter enrichment of the shales is a contentiou...The Upper Cretaceous Qingshankou Formation black shales,deposited in the late Turonian(LTB shales),are the main source rocks of the Songliao Basin.The origins of organic matter enrichment of the shales is a contentious subject fuelling many ongoing debates.This study investigates the genesis of the organic matter-rich shale by using molecular geochemistry.The LTB shales can be divided into three sections.The SectionⅠshales were deposited in saline,stratified and anoxic water conditions,which are related to seawater incursion events.At least three episodic and periodic seawater incursion events were recognized during SectionⅠshale deposition.The SectionⅡshales deposited in brackish to fresh and deep lake-level conditions with high primary productivity,which are related to lake-level transgression.The SectionⅢshales were deposited under fresh and slightly oxidized water conditions,which are related to lake-level regression.Two organic matter enrichment models for the LTB shales are identified,that is,the seawater incursion model and the maximum lake-level transgression sedimentation model,which act on different shale sections,both playing significant roles in the enrichment of organic matter.展开更多
One of the clocks that record the Earth history is(quasi-) periodic astronomical cycles.These cycles influence the climate that can be ultimately stored in sedimentary rocks.By cracking these(quasi-) periodic sediment...One of the clocks that record the Earth history is(quasi-) periodic astronomical cycles.These cycles influence the climate that can be ultimately stored in sedimentary rocks.By cracking these(quasi-) periodic sedimentation signals,high resolution astronomical time scale(ATS) can be obtained.Paleoclimate proxies are widely used to extract astronomical cycles.However different proxies may respond differently to astronomical signals and nonastronomical noises including tectonics,diagenesis,and measurement error among others.Astronomical time scale constructed based on a single proxy where its signal-to-noise ratio is low may have uncertainty that is difficult to evaluate but can be revealed by utilizing other proxies.Here,we test eight astronomical age models using two astrochro no logical methods from four paleoclimate proxies(i.e.,color reflection L~* and b~*,natural gamma radiation,and bulk density) from the Turonian to the Coniacian of the Cretaceous Period at the Demerara Rise in the equatorial Atlantic.The two astrochronological methods are time calibration using long eccentricity bandpass filtering(E1 bandpass) and tracking the long eccentricity from evolutive harmonic analysis(tracking EHA).The statistical mean and standard deviation of four age models from the four proxies are calculated to construct one integrated age model with age uncertainty in each method.Results demonstrate that extracting astronomical signals from multiple paleoclimate proxies is a valid method to estimate age model uncertainties.Anchored at the Cenomanian/Turonian boundary with an age of 93.9 ± 0.15 Ma from biostratigraphy,the ages for CC11/CC12(calcareous nannofossil zones),Turonian/Coniacian(CC12/CC13),CC13/CC14,and Coniacian/Santonian boundaries are 91.25±0.20 Ma,89.87±0.20 Ma,86.36±0.33 Ma,and 86.03±0.32 Ma in E1 bandpass method,compared with 91.17±0.36 Ma,89.74±0.38 Ma,86.13±1.31 Ma,and 85.80±1.33 Ma respectively in tracking EHA method.These results are consistent with previous studies within error and provide a reliable estimation of uncertainties of the ages.展开更多
Data on Late Cenomanian and Early Turonian foraminiferal assemblages in the northern palaeo biogeographical district of the West Siberian province are summarized in the paper. In addition, the section of borehole 1016...Data on Late Cenomanian and Early Turonian foraminiferal assemblages in the northern palaeo biogeographical district of the West Siberian province are summarized in the paper. In addition, the section of borehole 1016 of the Parusovaya area located in the far north of the province is considered. New information on the foraminiferal zones of this stratigraphic level along with the previously known sections of the Tazovskaya, Purpeiskaya, Van-Eganskaya areas provided an opportunity to carry out a correlation of these zones between the West Siberian and the Canadian provinces (Western Canada, Northern Alaska). The West Siberian Late Cenomanian Trochammina wetteri tumida, Verneuilinoides kansasensis and the Early Turonian Gaudryinopsis angustus foraminiferal zones have their analogues as similar zones in the Canadian province. Due to the provided correlation of the micropalaeontological (foraminiferal) zones, their age in the West Siberian province has been clarified. Besides, similarity of the conditions of dwelling within the boundaries of the entire Arctic palaeobiogeographical realm has been observed.展开更多
An attempt has been made to systematically revise the Late Cretaceous （Turonian） bivalves of the Bagh Beds, central India. Altogether, fifteen species have been described here. The two species Nicaniella （N） trigo...An attempt has been made to systematically revise the Late Cretaceous （Turonian） bivalves of the Bagh Beds, central India. Altogether, fifteen species have been described here. The two species Nicaniella （N） trigonoides ＆ Protocardia （P） laticostata, which are earlier known from Late Cretaceous of Tiruchirapalli subbasin, southern India, have been recorded for the first time from Narmada Basin. The other species recorded are： Modiolus typicus, Neithea morrisi, Plicatula batnensis, P. numidica, P. instabilis, Lucina （L.） cf. fallax, Astarte similis, Opis corniformis, Protocardia hillana, P. madagascariense, Cytherea （Callista） lancianata, Trigonocallista spathi and Pholadomya sp.. During course of systematic revision, it has been found that many species described by earlier workers from the Late Cretaceous of Bagh Beds have been found conspecific to already known species from the Cretaceous of different parts of the globe and hence, they have been recorded here as junior synonyms. These species have immense implication in the palaeobiogeography of the region.展开更多
An integrated benthic foraminiferal and organic matter analysis of samples obtained from sedimentary sections exposed in the Mangoule-Bonepoupa area, revealed a very shallow marine paleo-depositional environment for t...An integrated benthic foraminiferal and organic matter analysis of samples obtained from sedimentary sections exposed in the Mangoule-Bonepoupa area, revealed a very shallow marine paleo-depositional environment for the sediments studied, with considerable influx of continental organic matter that were accumulated during the Cenomanian-Turonian age. With reference to the lithostratigraphic profile of the Douala/Kribi-Campo Basin, the age obtained reveals that the sedimentary sections studied belong particularly to the lower section of the Logbadjeck/Mungo River Formation, based on the following benthic foraminifera assemblage: Ammobaculites jessensis, Ammobaculites benuensis, Ammobaculites coprolithiformis, Ammotium cf nkalagum, Ammotium nwalum, Haplophragmoides cf beuchensis, Trochamina taylorana. A particularly very poor palynomorph assemblage was recovered and included no age diagnostic species: Acrostichum aureum, Lycopodiumsporites sp., Fungal spore, Lavigatosporites discordatus, Longapertites sp., Verrucosisporites sp. An organic petrographic analysis performed on these samples revealed Kerogen Type-II and Type-III. The entire data sets obtained from this area is remarkably poor and we suspect poor preservation as the cause viewing the extent of weathering. The paleo-depositional environment of these sediments was suggested both from the foraminifera and palynomorphs present and confirmed from the organic matter types and macrofossil contents. The studied sections are composed generally of dark to dark-gray shale beds. As one of the petroleum producing basins within the Gulf of Guinea in which exploration/exploitation activities are on-going, the current research is aim at providing more data useful in the continuous search for more potential source rocks in this basin.展开更多
The Cenomanian-Turonian oceanic anoxic event (C/T OAE) is developed in southern Tibet. Organic geochemical study of the Cenomanian-Turonian sediments from the Gamba and Tingri areas shows that the mid-Cretaceous black...The Cenomanian-Turonian oceanic anoxic event (C/T OAE) is developed in southern Tibet. Organic geochemical study of the Cenomanian-Turonian sediments from the Gamba and Tingri areas shows that the mid-Cretaceous black shales in southern Tibet are enriched in organic carbon. The molecular analyses of organic matter indicate marine organic matter was derived from algae and bacteria. In the Gamba area, the organic matter is characterized by abundant tricyclic terpanes and pregane, which are predominant in 191 and 217 mass chromatograms, respectively. Pristane/phytane (Pr/Ph) ratios in the C/T OAE sediments are less than 1, demonstrating the domination of phytane. The presence of carotane can be regarded as a special biomarker indicating oxygen depletion in the C/T OAE sediments in the Tethyan Himalayas. In anoxic sediments, β-carotane and γ-carotane are very abundant. The β- and γ-carotane ratios relative to nC 17 in the Cenomanian-Turonian anoxic sediments vary from 32.28～ 42.87 and 5.10～ 11.01.展开更多
Sequence stratigraphic studies consider relative change in sea level(as regulated by eustasy,local tectonics and sediment supply)as the main builder of the stratigraphic record.Eustasy has generally been considered as...Sequence stratigraphic studies consider relative change in sea level(as regulated by eustasy,local tectonics and sediment supply)as the main builder of the stratigraphic record.Eustasy has generally been considered as a consequence of the growth and decay of continental ice sheets that would explain large,rapid changes in sea level,even during periods of relative global climatic warmth.However,such a mechanism has become increasingly difficult to envision during times of extreme global warmth such as the Turonian,when the equator-to-pole temperature gradient was very low and the presence of polar ice seems improbable.This paper investigates the timing and extent of sea level falls during the late Cenomanian through Turonian,especially the largest of those events,sequence boundary KTu4,which occurred during the middle to late Turonian peak of the Cretaceous hot greenhouse climate.We conclude that the amplitude of the widespread third-order sea level fall in the middle Turonian that is centered at^91.8 Ma varies at different locations depending on the influence of dynamic topography on local tectonics and regional climatic conditions.Ice volume variations seem unlikely as a mechanism for controlling sea level at this time.However,this causal factor cannot be ruled out completely since Antarctic highlands(if they existed in the Late Cretaceous)could sequester enough water as ice to cause eustatic falls.To ascertain this requires detailed tomographic imaging of Antarctica,followed by geodynamic modeling,to determine whether high plateaus could have existed to accumulate ephemeral ice sheets.Other mechanisms for sea level change,such as transference between ground water(a small amplitude shorter time scale effect)and the ocean and entrainment and release of water from the mantle to the oceanic reservoir(a potentially large amplitude and longer time scale process),are intriguing and need to be explored further to prove their efficacy at third-order time scales.展开更多
基金funded by a grant from the National Natural Science Foundation of China(Grant Nos.U2244207,42102200)the China Geological Survey Foundation(Grant Nos.DD20230257,DD20242404)。
文摘The Upper Cretaceous Qingshankou Formation black shales,deposited in the late Turonian(LTB shales),are the main source rocks of the Songliao Basin.The origins of organic matter enrichment of the shales is a contentious subject fuelling many ongoing debates.This study investigates the genesis of the organic matter-rich shale by using molecular geochemistry.The LTB shales can be divided into three sections.The SectionⅠshales were deposited in saline,stratified and anoxic water conditions,which are related to seawater incursion events.At least three episodic and periodic seawater incursion events were recognized during SectionⅠshale deposition.The SectionⅡshales deposited in brackish to fresh and deep lake-level conditions with high primary productivity,which are related to lake-level transgression.The SectionⅢshales were deposited under fresh and slightly oxidized water conditions,which are related to lake-level regression.Two organic matter enrichment models for the LTB shales are identified,that is,the seawater incursion model and the maximum lake-level transgression sedimentation model,which act on different shale sections,both playing significant roles in the enrichment of organic matter.
基金.This study was supported by NSF CAREERaward to Stephen R.Meyers (EAR-1151438)partially supported by the NSF Grant with No.1835717
文摘One of the clocks that record the Earth history is(quasi-) periodic astronomical cycles.These cycles influence the climate that can be ultimately stored in sedimentary rocks.By cracking these(quasi-) periodic sedimentation signals,high resolution astronomical time scale(ATS) can be obtained.Paleoclimate proxies are widely used to extract astronomical cycles.However different proxies may respond differently to astronomical signals and nonastronomical noises including tectonics,diagenesis,and measurement error among others.Astronomical time scale constructed based on a single proxy where its signal-to-noise ratio is low may have uncertainty that is difficult to evaluate but can be revealed by utilizing other proxies.Here,we test eight astronomical age models using two astrochro no logical methods from four paleoclimate proxies(i.e.,color reflection L~* and b~*,natural gamma radiation,and bulk density) from the Turonian to the Coniacian of the Cretaceous Period at the Demerara Rise in the equatorial Atlantic.The two astrochronological methods are time calibration using long eccentricity bandpass filtering(E1 bandpass) and tracking the long eccentricity from evolutive harmonic analysis(tracking EHA).The statistical mean and standard deviation of four age models from the four proxies are calculated to construct one integrated age model with age uncertainty in each method.Results demonstrate that extracting astronomical signals from multiple paleoclimate proxies is a valid method to estimate age model uncertainties.Anchored at the Cenomanian/Turonian boundary with an age of 93.9 ± 0.15 Ma from biostratigraphy,the ages for CC11/CC12(calcareous nannofossil zones),Turonian/Coniacian(CC12/CC13),CC13/CC14,and Coniacian/Santonian boundaries are 91.25±0.20 Ma,89.87±0.20 Ma,86.36±0.33 Ma,and 86.03±0.32 Ma in E1 bandpass method,compared with 91.17±0.36 Ma,89.74±0.38 Ma,86.13±1.31 Ma,and 85.80±1.33 Ma respectively in tracking EHA method.These results are consistent with previous studies within error and provide a reliable estimation of uncertainties of the ages.
文摘Data on Late Cenomanian and Early Turonian foraminiferal assemblages in the northern palaeo biogeographical district of the West Siberian province are summarized in the paper. In addition, the section of borehole 1016 of the Parusovaya area located in the far north of the province is considered. New information on the foraminiferal zones of this stratigraphic level along with the previously known sections of the Tazovskaya, Purpeiskaya, Van-Eganskaya areas provided an opportunity to carry out a correlation of these zones between the West Siberian and the Canadian provinces (Western Canada, Northern Alaska). The West Siberian Late Cenomanian Trochammina wetteri tumida, Verneuilinoides kansasensis and the Early Turonian Gaudryinopsis angustus foraminiferal zones have their analogues as similar zones in the Canadian province. Due to the provided correlation of the micropalaeontological (foraminiferal) zones, their age in the West Siberian province has been clarified. Besides, similarity of the conditions of dwelling within the boundaries of the entire Arctic palaeobiogeographical realm has been observed.
文摘An attempt has been made to systematically revise the Late Cretaceous （Turonian） bivalves of the Bagh Beds, central India. Altogether, fifteen species have been described here. The two species Nicaniella （N） trigonoides ＆ Protocardia （P） laticostata, which are earlier known from Late Cretaceous of Tiruchirapalli subbasin, southern India, have been recorded for the first time from Narmada Basin. The other species recorded are： Modiolus typicus, Neithea morrisi, Plicatula batnensis, P. numidica, P. instabilis, Lucina （L.） cf. fallax, Astarte similis, Opis corniformis, Protocardia hillana, P. madagascariense, Cytherea （Callista） lancianata, Trigonocallista spathi and Pholadomya sp.. During course of systematic revision, it has been found that many species described by earlier workers from the Late Cretaceous of Bagh Beds have been found conspecific to already known species from the Cretaceous of different parts of the globe and hence, they have been recorded here as junior synonyms. These species have immense implication in the palaeobiogeography of the region.
文摘An integrated benthic foraminiferal and organic matter analysis of samples obtained from sedimentary sections exposed in the Mangoule-Bonepoupa area, revealed a very shallow marine paleo-depositional environment for the sediments studied, with considerable influx of continental organic matter that were accumulated during the Cenomanian-Turonian age. With reference to the lithostratigraphic profile of the Douala/Kribi-Campo Basin, the age obtained reveals that the sedimentary sections studied belong particularly to the lower section of the Logbadjeck/Mungo River Formation, based on the following benthic foraminifera assemblage: Ammobaculites jessensis, Ammobaculites benuensis, Ammobaculites coprolithiformis, Ammotium cf nkalagum, Ammotium nwalum, Haplophragmoides cf beuchensis, Trochamina taylorana. A particularly very poor palynomorph assemblage was recovered and included no age diagnostic species: Acrostichum aureum, Lycopodiumsporites sp., Fungal spore, Lavigatosporites discordatus, Longapertites sp., Verrucosisporites sp. An organic petrographic analysis performed on these samples revealed Kerogen Type-II and Type-III. The entire data sets obtained from this area is remarkably poor and we suspect poor preservation as the cause viewing the extent of weathering. The paleo-depositional environment of these sediments was suggested both from the foraminifera and palynomorphs present and confirmed from the organic matter types and macrofossil contents. The studied sections are composed generally of dark to dark-gray shale beds. As one of the petroleum producing basins within the Gulf of Guinea in which exploration/exploitation activities are on-going, the current research is aim at providing more data useful in the continuous search for more potential source rocks in this basin.
文摘The Cenomanian-Turonian oceanic anoxic event (C/T OAE) is developed in southern Tibet. Organic geochemical study of the Cenomanian-Turonian sediments from the Gamba and Tingri areas shows that the mid-Cretaceous black shales in southern Tibet are enriched in organic carbon. The molecular analyses of organic matter indicate marine organic matter was derived from algae and bacteria. In the Gamba area, the organic matter is characterized by abundant tricyclic terpanes and pregane, which are predominant in 191 and 217 mass chromatograms, respectively. Pristane/phytane (Pr/Ph) ratios in the C/T OAE sediments are less than 1, demonstrating the domination of phytane. The presence of carotane can be regarded as a special biomarker indicating oxygen depletion in the C/T OAE sediments in the Tethyan Himalayas. In anoxic sediments, β-carotane and γ-carotane are very abundant. The β- and γ-carotane ratios relative to nC 17 in the Cenomanian-Turonian anoxic sediments vary from 32.28～ 42.87 and 5.10～ 11.01.
基金a contribution to IGCP Project 609 "Climate-environmental deteriorations during greenhouse phases:Causes and consequences of short-term Cretaceous sea-level changes "
文摘Sequence stratigraphic studies consider relative change in sea level(as regulated by eustasy,local tectonics and sediment supply)as the main builder of the stratigraphic record.Eustasy has generally been considered as a consequence of the growth and decay of continental ice sheets that would explain large,rapid changes in sea level,even during periods of relative global climatic warmth.However,such a mechanism has become increasingly difficult to envision during times of extreme global warmth such as the Turonian,when the equator-to-pole temperature gradient was very low and the presence of polar ice seems improbable.This paper investigates the timing and extent of sea level falls during the late Cenomanian through Turonian,especially the largest of those events,sequence boundary KTu4,which occurred during the middle to late Turonian peak of the Cretaceous hot greenhouse climate.We conclude that the amplitude of the widespread third-order sea level fall in the middle Turonian that is centered at^91.8 Ma varies at different locations depending on the influence of dynamic topography on local tectonics and regional climatic conditions.Ice volume variations seem unlikely as a mechanism for controlling sea level at this time.However,this causal factor cannot be ruled out completely since Antarctic highlands(if they existed in the Late Cretaceous)could sequester enough water as ice to cause eustatic falls.To ascertain this requires detailed tomographic imaging of Antarctica,followed by geodynamic modeling,to determine whether high plateaus could have existed to accumulate ephemeral ice sheets.Other mechanisms for sea level change,such as transference between ground water(a small amplitude shorter time scale effect)and the ocean and entrainment and release of water from the mantle to the oceanic reservoir(a potentially large amplitude and longer time scale process),are intriguing and need to be explored further to prove their efficacy at third-order time scales.
