Detailed examination of sedimentary cores retrieved from Sugan Lake in the northern Qaidam Basin of northwest China’s Tibetan Plateau reveal that fine laminated beddings form in the sediments where water depth exceed...Detailed examination of sedimentary cores retrieved from Sugan Lake in the northern Qaidam Basin of northwest China’s Tibetan Plateau reveal that fine laminated beddings form in the sediments where water depth exceeds 3 m. Seasonal surface sediments trapped at the bottom of the lake suggest that sediments deposited during summer and autumn are mainly light colored monohydrocalcites, while those deposited in winter are dark organic matter, indicating that varve layers form under modern limnological conditions. Continuous varve sediments comprising four types have accumulated in the upper 5.5 m of Core SG03I from the center of the lake. All types exhibit clear seasonality indicative of annual deposition. Varve counts correspondence with 210Pb dates on recent sediments in the upper core suggest the continuous varves of the upper 5.5 m of the core formed in the late Holocene (2670 a BP). The Sugan Lake varve sequence is the first demonstration of annually laminated sediments re-ported in arid western China.展开更多
Proterozoic （pre-Ediacaran） glaciations occurred under strongly seasonal climates near sea level in low palaeolatitudes. Metre-scale primary sand wedges in Cryogenian periglacial deposits are identical to those acti...Proterozoic （pre-Ediacaran） glaciations occurred under strongly seasonal climates near sea level in low palaeolatitudes. Metre-scale primary sand wedges in Cryogenian periglacial deposits are identical to those actively forming, through the infilling of seasonal （winter） thermal contraction-cracks in perma- frost by windblown sand, in present-day polar regions with a mean monthly air temperature range of 40 ~C and mean annual air temperatures of -20 ~C or lower. Varve-like rhythmites with dropstones in Proterozoic glacial successions are consistent with an active seasonal freeze-thaw cycle. The seasonal （annual） oscillation of sea level recorded by tidal rhythmites in Cryogenian glacial successions indicates a significant seasonal cycle and extensive open seas. Palaeomagnetic data determined directly for Prote- rozoic glacial deposits and closely associated rocks indicate low palaeolatitudes： Cryogenian deposits in South Australia accumulated at 〈10% most other Cryogenian deposits at 〈20~ and Palaeoproterozoic deposits at 〈15~ palaeolatitude. Palaeomagnetic data imply that the Proterozoic geomagnetic field approximated a geocentric axial dipole, hence palaeolatitudes represent geographic latitudes. The Cry- ogenian glacial environment included glacier-flee, continental permafrost regions with ground frozen on a kyr time-scale, aeolian sand-sheets, extensive and long-lived open seas, and an active hydrological cycle. This palaeoenvironment confiicts with the ＇snowball Earth＇ and ＇slushball Earth＇ hypotheses, which cannot accommodate large seasonal changes of temperature near the equator. Consequently, their proponents have attempted to refute the evidence for strong seasonality by introducing Popperian ＇auxiliary assumptions＇. However, non-actualistic arguments that the Cryogenian sand wedges indicate diurnal or weakly seasonal temperature changes are based on misunderstandings of periglacial pro- cesses. Modelling of a strongly seasonal climate for a frozen-over Earth is invalidated by the evidence for persistent open seas and glacier-free continental regions during Cryogenian glaciations, and gives a mean monthly air temperature range of only 〈10 ~C for 〈10~ latitude. By contrast, a strongly seasonal climate in low palaeolatitudes, based on the actualistic interpretation of cryogenic sand wedges and other structures, is consistent with a high obliquity of the ecliptic （〉54°） during Proterozoic low-latitude glaciations, whereby the equator would be cooler than the poles, on average, and global seasonality would be greatly amplified.展开更多
On the basis of observation of thin sections and ^137Cs data, laminations in sediment are interpreted to be varves in Bolterskardet Lake （78°06′ N, 16°01′ E）, Svalbard, the Arctic. Varves appear under a ...On the basis of observation of thin sections and ^137Cs data, laminations in sediment are interpreted to be varves in Bolterskardet Lake （78°06′ N, 16°01′ E）, Svalbard, the Arctic. Varves appear under a petrologic microscope as couplets of dark-silt and light-clay layers. The mechanism of varve formation is surmized as follows： each silt layer is the production of sediment inflow interpreted as mainly derived from snowmelt during summer; each clay layer was deposited in a stillwater environment during an ice-cover period. A light -clay layer provides an important index bed to identify the annual interface. The high accumulation rates, long period of ice cover, and topographically closed basin are probably all critical factors in forming and preserving varves. Varve thickness is known to be controlled mainly by summer temperature. The variation of varve thickness in Lake Bolterskardet can then be used to reconstruct summer temperature. The varve series show that there has been distinct decade-scale variability of summer temperature over the past 150 years. Warm periods occurred in the 1860s, around 1900, the 1930s, 1950s, and 1970s, and in the last 20 years. The varved sediments of Lake Bolterskarde preserve an ideal record for high-resolution paleoclimatic and paleoenvironmental research in this data-sparse area.展开更多
Fine-grained carbonate rocks, which extensively occur in the Eocene strata in the Shulu sag, Bohai Bay Basin, North China, represent an unconventional, fine-grained carbonate reservoir. However, previous studies have ...Fine-grained carbonate rocks, which extensively occur in the Eocene strata in the Shulu sag, Bohai Bay Basin, North China, represent an unconventional, fine-grained carbonate reservoir. However, previous studies have ignored the complexity of the lithofacies components and their formation mechanisms. Fine-grained carbonate rocks are typical reservoirs in which hydrocarbons form and gather. A better understanding of the nature of these rocks is extremely important for evaluating the quality of unconventional, fine-grained carbonate reservoirs. Various lithofacies components were discriminated in this study with a combination of petrographic observations and carbon isotope analyses. These finegrained carbonate rocks comprise terrigenous, biogenic and diagenetic materials. Terrigenous input and biologically induced precipitation are the main sources of the materials in the lake. Five lithofacies were identified based on the observations of sedimentary features（core and thin section） and mineralogical data：（1） varve-like laminated calcilutite,（2） graded laminated calcilutite,（3） interlaminated calcisiltitecalcilutite,（4） massive calcilutite, and（5） massive calcisiltite-calcarenite. Their origins were recorded by various lithofacies components, which are controlled by the interactions of physical, chemical and biological processes. This study indicated that the lithology of the bedrocks was the key factor controlling carbonate accumulation. The tectonics and climate can influence the weathering and types of lithofacies. Primary productivity controlled the precipitation of the endogenic calcite. These factors jointly determined the abundant fine-grained carbonate rocks that have accumulated in the Shulu sag.展开更多
1 Introduction Meromictic Shira Lake is a good represfor detail climate modeling due to its locainformation and annually laminated bottomsediment column of 155 cm in length wahammer corer in the deepest(24 m)central i...1 Introduction Meromictic Shira Lake is a good represfor detail climate modeling due to its locainformation and annually laminated bottomsediment column of 155 cm in length wahammer corer in the deepest(24 m)central in 2009.2 Sample Preparations and Measuring展开更多
1 Introduction Annually laminated(varve)sedimentary deposits are considered as one of the most important archives,since they offer precise temporal information(years)in combination with high time resolutions.Bottom se...1 Introduction Annually laminated(varve)sedimentary deposits are considered as one of the most important archives,since they offer precise temporal information(years)in combination with high time resolutions.Bottom sediments of the lakes contain detailed geochemical information on展开更多
We developed a software performing laminae counting, thickness measurements, spectral and wavelet analysis of laminated sediments embedded signal. We validated the software on varved sediments. Varved laminae are auto...We developed a software performing laminae counting, thickness measurements, spectral and wavelet analysis of laminated sediments embedded signal. We validated the software on varved sediments. Varved laminae are automatically counted using an image analysis classification method based on K-Nearest Neighbors (KNN) algorithm. In a next step, the signal corresponding to varved black laminae thickness variation is retrieved. The obtained signal is a good proxy to study the paleoclimatic constraints controlling sedimentation. Finally, the use of spectral and wavelet analysis methods on the variation of black laminae thickness revealed the existence of frequencies and periods which can be linked to known paleoclimatic events.展开更多
There are many different processes generating soft-sediment deformation. This paper is confined to deformations generated by paleoseismic events in Sweden. The Paleoseismic Catalogue of Sweden includes 66 events. The ...There are many different processes generating soft-sediment deformation. This paper is confined to deformations generated by paleoseismic events in Sweden. The Paleoseismic Catalogue of Sweden includes 66 events. The structural characteristics and driving forces of liquefaction are discussed in details. “Crypto-deformations” refer to a special type of fluidization not affecting the sedimentary bedding itself, but the internal orientation of the ChRM and AMS carrying particles. Extensive turbidites are formed at some events. They constitute useful “marker-varves”. Out of the 66 paleoseismic events, 31 are dated by varves as to a single year (in one case even to the season of a year). Tsunamites are recorded from 19 of the paleoseismic events;some with wave-heights up to 15 - 20 m.展开更多
Lamina structure, a typical feature of shale, has significant implications for hydrocarbon generation, shale oil and gas reservoir evaluation, and palaeoenvironmental studies. In this study, we conducted a high-resolu...Lamina structure, a typical feature of shale, has significant implications for hydrocarbon generation, shale oil and gas reservoir evaluation, and palaeoenvironmental studies. In this study, we conducted a high-resolution astronomical analysis of shale strata from the Kongdian Formation in the Cangdong Sag, Bohai Bay Basin, China, and performed macroscopic and microscopic textural characterization of core samples. The time series analysis of the G108-8 Well indicates that stratigraphic cycles of 113.2–25.3 m, 12.7–7.8 m, 4.7–2.7 m, and 2.3–1.3 m are controlled by long eccentricity, short eccentricity, obliquity, and precession, respectively. The sedimentary accumulation rate (SAR) is estimated to be approximately 20.3 cm/kyr. The core description reveals that Ek2 primarily consists of laminated shale with individual laminae less than 1 cm in thickness. Using a polarizing microscope, the average thickness of a single lamina is approximately 250 μm, with most laminae being less than 400 μm. We constructed a time-depth model for lacustrine laminated sediments and compared it with other ancient lacustrine strata and modern lakes. The sediment accumulation rate of ancient lacustrine strata ranges from 1.3 to 20.3 cm/kyr. The sedimentation rate of shale and the thickness distribution of individual laminae provide evidence for the annual nature of the lamina couplets. Finally, we propose a simplified model to illustrate the sedimentation process, emphasizing the record of laminated sediments in semi-deep to deep facies. Our results contribute to the understanding of lacustrine sedimentary processes, laminated sedimentary records, organic matter enrichment processes, palaeoenvironments, and their potential relationships.展开更多
Characteristics of organic matter content, hydrocarbon generation and expulsion of carbonate rocks are discussed by analysis of organic carbon and pyrolysis. There is a strong inhomogeneity in distribution of organic ...Characteristics of organic matter content, hydrocarbon generation and expulsion of carbonate rocks are discussed by analysis of organic carbon and pyrolysis. There is a strong inhomogeneity in distribution of organic matter in carbonate rocks. The organic matter abundance is higher in stylolites, carbonate varves or marls, while it is the lowest in matrixes (purer carbonate rocks around stylolites). Because of stable thickness and broad area, marls and carbonate varves may become good source rocks. At the same depth, stylolites, carbonate varves and matrixes generate and expel hydrocarbons almost at the same time. Expulsion efficiency of carbonate varve is the highest; that of rnatrixes is the lowest and that of stylolites is between marl’s or carbonate varve’s and matrix’s.展开更多
During the 7-9th century,the Tibetan Empire constituted a superpower between the Tang Empire and Abbasid Caliphate:one that played significant roles in geopolitics in Asia during the Early Medieval Period.The factors ...During the 7-9th century,the Tibetan Empire constituted a superpower between the Tang Empire and Abbasid Caliphate:one that played significant roles in geopolitics in Asia during the Early Medieval Period.The factors which led to the rise and rapid decline of this powerful Empire,the only united historical regime on the Tibetan Plateau(TP),remain unclear.Sub-annual scale precipitation and decadalscale temperature records of the central TP are presented,indicating that the height of this Empire coincided with a two-century long interval of uncharacteristically warm and humid climate.The ameliorated climate enabled the expansion of arable land and increased agricultural production.The close relationship between the precipitation records and historical events implied that the Empire implemented flexible strategies to tackle the effects of climate changes.This has implications for agricultural production in alpine regions including the TP,in the context of current global warming.展开更多
基金the NSFC (National Natural Science Foundation of China)National Innovation Research Team Project (Grant No. 40421101)the NSFC Research Projects (Grant Nos. 40301050 and 40301051)
文摘Detailed examination of sedimentary cores retrieved from Sugan Lake in the northern Qaidam Basin of northwest China’s Tibetan Plateau reveal that fine laminated beddings form in the sediments where water depth exceeds 3 m. Seasonal surface sediments trapped at the bottom of the lake suggest that sediments deposited during summer and autumn are mainly light colored monohydrocalcites, while those deposited in winter are dark organic matter, indicating that varve layers form under modern limnological conditions. Continuous varve sediments comprising four types have accumulated in the upper 5.5 m of Core SG03I from the center of the lake. All types exhibit clear seasonality indicative of annual deposition. Varve counts correspondence with 210Pb dates on recent sediments in the upper core suggest the continuous varves of the upper 5.5 m of the core formed in the late Holocene (2670 a BP). The Sugan Lake varve sequence is the first demonstration of annually laminated sediments re-ported in arid western China.
文摘Proterozoic （pre-Ediacaran） glaciations occurred under strongly seasonal climates near sea level in low palaeolatitudes. Metre-scale primary sand wedges in Cryogenian periglacial deposits are identical to those actively forming, through the infilling of seasonal （winter） thermal contraction-cracks in perma- frost by windblown sand, in present-day polar regions with a mean monthly air temperature range of 40 ~C and mean annual air temperatures of -20 ~C or lower. Varve-like rhythmites with dropstones in Proterozoic glacial successions are consistent with an active seasonal freeze-thaw cycle. The seasonal （annual） oscillation of sea level recorded by tidal rhythmites in Cryogenian glacial successions indicates a significant seasonal cycle and extensive open seas. Palaeomagnetic data determined directly for Prote- rozoic glacial deposits and closely associated rocks indicate low palaeolatitudes： Cryogenian deposits in South Australia accumulated at 〈10% most other Cryogenian deposits at 〈20~ and Palaeoproterozoic deposits at 〈15~ palaeolatitude. Palaeomagnetic data imply that the Proterozoic geomagnetic field approximated a geocentric axial dipole, hence palaeolatitudes represent geographic latitudes. The Cry- ogenian glacial environment included glacier-flee, continental permafrost regions with ground frozen on a kyr time-scale, aeolian sand-sheets, extensive and long-lived open seas, and an active hydrological cycle. This palaeoenvironment confiicts with the ＇snowball Earth＇ and ＇slushball Earth＇ hypotheses, which cannot accommodate large seasonal changes of temperature near the equator. Consequently, their proponents have attempted to refute the evidence for strong seasonality by introducing Popperian ＇auxiliary assumptions＇. However, non-actualistic arguments that the Cryogenian sand wedges indicate diurnal or weakly seasonal temperature changes are based on misunderstandings of periglacial pro- cesses. Modelling of a strongly seasonal climate for a frozen-over Earth is invalidated by the evidence for persistent open seas and glacier-free continental regions during Cryogenian glaciations, and gives a mean monthly air temperature range of only 〈10 ~C for 〈10~ latitude. By contrast, a strongly seasonal climate in low palaeolatitudes, based on the actualistic interpretation of cryogenic sand wedges and other structures, is consistent with a high obliquity of the ecliptic （〉54°） during Proterozoic low-latitude glaciations, whereby the equator would be cooler than the poles, on average, and global seasonality would be greatly amplified.
基金supported by the National Natural Science Foundation of China(Grant Nos.40472092,40352001)the Scientific Expedition Associationand the Yilite-Mulin Group,China.
文摘On the basis of observation of thin sections and ^137Cs data, laminations in sediment are interpreted to be varves in Bolterskardet Lake （78°06′ N, 16°01′ E）, Svalbard, the Arctic. Varves appear under a petrologic microscope as couplets of dark-silt and light-clay layers. The mechanism of varve formation is surmized as follows： each silt layer is the production of sediment inflow interpreted as mainly derived from snowmelt during summer; each clay layer was deposited in a stillwater environment during an ice-cover period. A light -clay layer provides an important index bed to identify the annual interface. The high accumulation rates, long period of ice cover, and topographically closed basin are probably all critical factors in forming and preserving varves. Varve thickness is known to be controlled mainly by summer temperature. The variation of varve thickness in Lake Bolterskardet can then be used to reconstruct summer temperature. The varve series show that there has been distinct decade-scale variability of summer temperature over the past 150 years. Warm periods occurred in the 1860s, around 1900, the 1930s, 1950s, and 1970s, and in the last 20 years. The varved sediments of Lake Bolterskarde preserve an ideal record for high-resolution paleoclimatic and paleoenvironmental research in this data-sparse area.
基金provided by the National Major Research Program for Science and Technology of China (No. 2017ZX05009-002)the National Natural Science Fund (No. 41772090)
文摘Fine-grained carbonate rocks, which extensively occur in the Eocene strata in the Shulu sag, Bohai Bay Basin, North China, represent an unconventional, fine-grained carbonate reservoir. However, previous studies have ignored the complexity of the lithofacies components and their formation mechanisms. Fine-grained carbonate rocks are typical reservoirs in which hydrocarbons form and gather. A better understanding of the nature of these rocks is extremely important for evaluating the quality of unconventional, fine-grained carbonate reservoirs. Various lithofacies components were discriminated in this study with a combination of petrographic observations and carbon isotope analyses. These finegrained carbonate rocks comprise terrigenous, biogenic and diagenetic materials. Terrigenous input and biologically induced precipitation are the main sources of the materials in the lake. Five lithofacies were identified based on the observations of sedimentary features（core and thin section） and mineralogical data：（1） varve-like laminated calcilutite,（2） graded laminated calcilutite,（3） interlaminated calcisiltitecalcilutite,（4） massive calcilutite, and（5） massive calcisiltite-calcarenite. Their origins were recorded by various lithofacies components, which are controlled by the interactions of physical, chemical and biological processes. This study indicated that the lithology of the bedrocks was the key factor controlling carbonate accumulation. The tectonics and climate can influence the weathering and types of lithofacies. Primary productivity controlled the precipitation of the endogenic calcite. These factors jointly determined the abundant fine-grained carbonate rocks that have accumulated in the Shulu sag.
基金supported by the RFBR projects 13-05-00871,14-02-00631
文摘1 Introduction Meromictic Shira Lake is a good represfor detail climate modeling due to its locainformation and annually laminated bottomsediment column of 155 cm in length wahammer corer in the deepest(24 m)central in 2009.2 Sample Preparations and Measuring
基金supported by the RFBR projects 13-05-00871,14-02-00631
文摘1 Introduction Annually laminated(varve)sedimentary deposits are considered as one of the most important archives,since they offer precise temporal information(years)in combination with high time resolutions.Bottom sediments of the lakes contain detailed geochemical information on
文摘We developed a software performing laminae counting, thickness measurements, spectral and wavelet analysis of laminated sediments embedded signal. We validated the software on varved sediments. Varved laminae are automatically counted using an image analysis classification method based on K-Nearest Neighbors (KNN) algorithm. In a next step, the signal corresponding to varved black laminae thickness variation is retrieved. The obtained signal is a good proxy to study the paleoclimatic constraints controlling sedimentation. Finally, the use of spectral and wavelet analysis methods on the variation of black laminae thickness revealed the existence of frequencies and periods which can be linked to known paleoclimatic events.
文摘There are many different processes generating soft-sediment deformation. This paper is confined to deformations generated by paleoseismic events in Sweden. The Paleoseismic Catalogue of Sweden includes 66 events. The structural characteristics and driving forces of liquefaction are discussed in details. “Crypto-deformations” refer to a special type of fluidization not affecting the sedimentary bedding itself, but the internal orientation of the ChRM and AMS carrying particles. Extensive turbidites are formed at some events. They constitute useful “marker-varves”. Out of the 66 paleoseismic events, 31 are dated by varves as to a single year (in one case even to the season of a year). Tsunamites are recorded from 19 of the paleoseismic events;some with wave-heights up to 15 - 20 m.
基金financially supported by the National Natural Science Foundation of China(Grant No.42072150).
文摘Lamina structure, a typical feature of shale, has significant implications for hydrocarbon generation, shale oil and gas reservoir evaluation, and palaeoenvironmental studies. In this study, we conducted a high-resolution astronomical analysis of shale strata from the Kongdian Formation in the Cangdong Sag, Bohai Bay Basin, China, and performed macroscopic and microscopic textural characterization of core samples. The time series analysis of the G108-8 Well indicates that stratigraphic cycles of 113.2–25.3 m, 12.7–7.8 m, 4.7–2.7 m, and 2.3–1.3 m are controlled by long eccentricity, short eccentricity, obliquity, and precession, respectively. The sedimentary accumulation rate (SAR) is estimated to be approximately 20.3 cm/kyr. The core description reveals that Ek2 primarily consists of laminated shale with individual laminae less than 1 cm in thickness. Using a polarizing microscope, the average thickness of a single lamina is approximately 250 μm, with most laminae being less than 400 μm. We constructed a time-depth model for lacustrine laminated sediments and compared it with other ancient lacustrine strata and modern lakes. The sediment accumulation rate of ancient lacustrine strata ranges from 1.3 to 20.3 cm/kyr. The sedimentation rate of shale and the thickness distribution of individual laminae provide evidence for the annual nature of the lamina couplets. Finally, we propose a simplified model to illustrate the sedimentation process, emphasizing the record of laminated sediments in semi-deep to deep facies. Our results contribute to the understanding of lacustrine sedimentary processes, laminated sedimentary records, organic matter enrichment processes, palaeoenvironments, and their potential relationships.
基金Project supported by the Science and Technology Research of the 9th Five-Year Plan from China National Petroleum & Gas Company.
文摘Characteristics of organic matter content, hydrocarbon generation and expulsion of carbonate rocks are discussed by analysis of organic carbon and pyrolysis. There is a strong inhomogeneity in distribution of organic matter in carbonate rocks. The organic matter abundance is higher in stylolites, carbonate varves or marls, while it is the lowest in matrixes (purer carbonate rocks around stylolites). Because of stable thickness and broad area, marls and carbonate varves may become good source rocks. At the same depth, stylolites, carbonate varves and matrixes generate and expel hydrocarbons almost at the same time. Expulsion efficiency of carbonate varve is the highest; that of rnatrixes is the lowest and that of stylolites is between marl’s or carbonate varve’s and matrix’s.
基金supported by Pan-Third Pole Environment Study for a Green Silk Road of the Strategic Priority Research Program of Chinese Academy of Sciences(XDA20090000)the National Key Research and Development Program of China(2018YFA0606400)+1 种基金Part laboratory and fieldwork costs were supported by the National Natural Science Foundation of China(41772178,91747207,and 41620104007)Field expedition was supported by the Second Tibetan Plateau Scientific Expedition(2019QZKK0601)。
文摘During the 7-9th century,the Tibetan Empire constituted a superpower between the Tang Empire and Abbasid Caliphate:one that played significant roles in geopolitics in Asia during the Early Medieval Period.The factors which led to the rise and rapid decline of this powerful Empire,the only united historical regime on the Tibetan Plateau(TP),remain unclear.Sub-annual scale precipitation and decadalscale temperature records of the central TP are presented,indicating that the height of this Empire coincided with a two-century long interval of uncharacteristically warm and humid climate.The ameliorated climate enabled the expansion of arable land and increased agricultural production.The close relationship between the precipitation records and historical events implied that the Empire implemented flexible strategies to tackle the effects of climate changes.This has implications for agricultural production in alpine regions including the TP,in the context of current global warming.
