The Qarhan Salt Lake area is the Quaternary depocenter of the Qaidam Basin, and carries thick lacustrine sediments, as well as rich potassium and magnesium salt deposits. The abundant resources and thick sediments in ...The Qarhan Salt Lake area is the Quaternary depocenter of the Qaidam Basin, and carries thick lacustrine sediments, as well as rich potassium and magnesium salt deposits. The abundant resources and thick sediments in this lake provide an ideal place for the study of biogas formation and preservation, salt lake evolution, and the uplift of the Tibetan Plateau. In this study, we attempt to construct a paleomagnetic and ^(230)Th age model and to obtain information on tectonic activity and salt lake evolution through detailed studies on a 1300-m-long drill core(15DZK01) from the northwestern margin of the Qarhan Salt Lake area(Dongling Lake). Based on gypsum ^(230)Th dating, the age of the uppermost clastic deposit was calculated to be around 0.052 Ma. The polarity sequence consist of 13 pairs of normal and reversed zones,which can be correlated with subchrons C2r.1r-C1n of the geomagnetic polarity timescale(GPTS 2012)(from ~2.070 Ma to ~0.052 Ma). Sedimentary characteristics indicate that Dongling Lake witnessed freshwater environment between ~ 2.070 Ma and 1.546 Ma. During this period, the sedimentary record reflects primarily lakeshore, shallow-water and swamp environments, representing favourable conditions for the formation of hydrocarbon source rocks. Between 1.546 Ma and ~ 0.052 Ma, the Dongling Lake was in sulphate deposition stage, which contrasts with the central Qarhan Salt Lake area, where this stage did not occur in the meantime. During this stage, Dongling Lake was in a shallow saltwater lake environment, but several periods of reduced salinity occurred during this stage. During the late Pleistocene at ~0.052 Ma, the Dongling Lake experienced uplift due to tectonic activity, and saltwater migrated through the Sanhu Fault to the central Qarhan Salt Lake area, resulting in the absence of halite deposition stage. The residual saline water was concentrated into magnesium-rich brine due to the lack of freshwater, and few potassium salt deposits occur in the Dongling Lake area.展开更多
The study of magnetostratigraphy and cyclostratigraphy in the last two decades has provided a great deal of opportunities to improve the geologic time scale.The Cenozoic and Mesozoic geologic timescale have been well ...The study of magnetostratigraphy and cyclostratigraphy in the last two decades has provided a great deal of opportunities to improve the geologic time scale.The Cenozoic and Mesozoic geologic timescale have been well calibrated(Gradstein et al..2012;Ogg et al,2012;Cohen et al.,2018).However,for the Paleozoic era the uncertainty over boundary ages are still very large.展开更多
The palaeoposition of India after its breakup from Gondwana and its subsequent northward journey during the Mesozoic poses many tectonic riddles. A magnetostratigraphy pattern has been constructed for the Ammonoid ric...The palaeoposition of India after its breakup from Gondwana and its subsequent northward journey during the Mesozoic poses many tectonic riddles. A magnetostratigraphy pattern has been constructed for the Ammonoid rich Middle Jurassic Bathonian succession of Jumara Dome, Kachchh, western India. We present the first magnetostratigraphic results from the Ammonoid bearing exposed Bathonian sediments in Kachchh. The Jumara Dome comprised of mixed carbonate-siliciclastic succession is represented by the Jhurio and Patcham formations and siliciclastic-dominating Chari Formation in the Kachchh Mainland. The Jumara Dome sediments were deposited during sea-level fluctuating, and were interrupted by storms in the shallow marine environment. This study is based on collection of 60 oriented samples from 13 successive levels. Both thermal and AF demagnetization investigations were carried out to isolate the Characteristic Remanent Magnetization (ChRM) directions. Palaeolatitudes were computed using the ChRM directions. Magnetostratigraphic column is prepared and correlated with Geological Time Scale (GTS) of [1] [2], and this column readily matched with GTS at M41 to below and exhibits the dominance of normal polarity in Jumara.展开更多
The timing of onset of deposition of the Lulehe Formation is a significant factor in understanding the genesis of the Qaidam basin and the evolution of the Tibetan Plateau. Here, we describe a detailed magnetostratigr...The timing of onset of deposition of the Lulehe Formation is a significant factor in understanding the genesis of the Qaidam basin and the evolution of the Tibetan Plateau. Here, we describe a detailed magnetostratigraphic and magnetic fabric study of the middle and lower parts of the Lulehe Formation. A total of 234 samples were collected from 117 sites throughout a thickness of almost 460 m of fluvial and lacustrine deposits at the Xitieshan section in the northeastern Qaidam basin. Out of these sites, 94 sites yielded well-defined characteristic remanent magnetization components by stepwise thermal demagnetization and were used to establish the magnetostratigraphy of the studied section. Based on correlation with the geomagnetic polarity timescale, the studied section spans the period from 53.8 Ma to 50.7 Ma. Our results show a three-fold decrease in sedimentation rates as well as marked change in facies from braided river to delta and shore-shallow lake around 52.6 Ma, which suggests tectonic uplift of the northeastern Qaidam basin margin ridge was rapid at the onset of formation of the Qaidam basin and subsequently weakened after 52.6 Ma. The anisotropy of magnetic susceptibility results indicate that tectonic compression stress had reached the northeastern Tibetan Plateau by the early stages of Indo-Eurasian plate collision and that the direction of stress in the study area was NE-SW. Furthermore, a weakening of tectonic compression stress around 52.6 Ma is consistent with sedimentary records. The age of initial deposition of the Qaidam basin (around 53.8 Ma) was almost synchronous with that of the Qiangtang, Hoh Xil, Xining, and Lanzhou basins, which implies that stress was transferred rapidly through the Tibetan Plateau during or immediately after the onset of Indo-Eurasian collision.展开更多
Loess deposits with varying thickness are widely distributed on the intermontane valleys and piedmont zones on the northern side of the central Shandong mountainous regions. However, the basal ages and material resour...Loess deposits with varying thickness are widely distributed on the intermontane valleys and piedmont zones on the northern side of the central Shandong mountainous regions. However, the basal ages and material resources of the loess deposits are not clear. The paper studied the Qingzhou loess profile in Shandong with magnetostratigraphic and optical stimulated luminescence (OSL) methods and further investigated its main provenances with the mineralogical methods. The magnetostratigraphic results showed that the Brunhes/Matuyama (B/M) reversal boundary was not recognized, suggesting a basal age younger than 0.78 Ma. Extrapolations by sedimentation rates, based on the upper part depositional rate from the OSL age, the basal age of the Qingzhou loess is about 0.5 Ma. Until now, older loess deposits have not been reported on the northern side of the central Shandong mountainous regions. The results of the paper indicate that the loess deposits in this area might have strated from the Middle Pleistocene. The basal age of Qingzhou loess is approximately synchronous with the Xiashu loess in the middle-lower reaches of Yangtze River. Major components of clay minerals in the Qingzhou profile are dominated by illite. Other clay mineral compositions are mainly smectite, chlorite and kaolinite, which are similar with the Xifeng loess in the Loess Plateau. However, the contents of smectite and the ratios of illite and kaolinte in the Qingzhou loess samples are higher than those in the Xifeng loess samples of the Loess Plateau, indicating that the loess in the northern side of the central Shandong mountainous regions has different sources from that of the loess deposits in the Loess Plateau. The clay mineral analysis further reinforces the earlier conclu- sion that the marine strata exposed in the Laizhou Bay and the fluvial plain of the lower reaches of Yellow River during the glacier periods are the main material sources for the Qingzhou loess deposits, which is an indicator to the local aridification of the lower reaches of the Yellow River. Loess deposition in the central Shandong mountainous regions started at around 0.5 Ma. The age of Qingzhou loess is approximately synchronous with the ongoing high-latitude cold since the Middle Pleistocene, which indicates that strengthened East Asian winter monsoon was sufficiently energetic to bring substantial quantities of material from the marine strata exposed in the Laizhou Bay and the fluvial plain of the lower reaches of the Yellow River to the central Shandong mountainous regions. The results therefore suggest that both regional geological process and global changes were responsible for the formation of Qingzhou loess since Middle Pleistocene.展开更多
The Maoming Basin is one amongst a group of Cretaceous-Teniary basins in South China. 347 samples were collected from drill cores MR and MB and sechon MS (110°54’E, 21°45 ’N). Most of the lithological unit...The Maoming Basin is one amongst a group of Cretaceous-Teniary basins in South China. 347 samples were collected from drill cores MR and MB and sechon MS (110°54’E, 21°45 ’N). Most of the lithological units are of Tertiary age. The cores include the Laohuling, Shangcun,Huangniuling and Youganwo formations . The MR core (874m in length) has recorded the polarity history from Normal Zone 18 to Normal Zone 11 on the Geomagnetic Polarity Time Scale (GPTS).The strata were formed from about 42Ma to 32Ma, that is from Late Eocene to Early Oligocene.A mean sedimentation rate of this stratigraphic column is 8.1 cm/ka.展开更多
Cenozoic sediments in the foreland basin--Jiuquan Basin in west Hexi Corridor recorded tectonic uplift information of the Qilian Mountains. High resolution paleomagnetic dating of the Laojunmiao (LJM) section across t...Cenozoic sediments in the foreland basin--Jiuquan Basin in west Hexi Corridor recorded tectonic uplift information of the Qilian Mountains. High resolution paleomagnetic dating of the Laojunmiao (LJM) section across the central LJM anticline in the southern Jiuquan Basin reveals ages of the Getanggou Member, Niugetao Member in the Shulehe Formation, the Yumen Conglomerate, Jiuquan Conglomerate and Gobi Formation at >13-8.3 Ma, 8.3-4.9 Ma, 3.66-0.93 Ma, 0.84-0.14 Ma and 0.14-0 Ma, respectively. Sedimentary evolution study suggests that the Qilian Mountains should begin to rise gradually since ～8-6.6 Ma, accompanied by sedimentary environments changing from lacustrine mudstones-sandstones to alluvial conglomerates. Rapid uplift of the Qilian Mountains began at ～3.66 Ma, followed by a series of stepwise or intermittent intensive uplifts at about <1.8-1.23 Ma, 0.93-0.84 Ma and 0.14 Ma, which finally resulted in the present high Qilian Mountains.展开更多
Two Red Clay profiles near Xi’ an and Xifeng were investigated in an attempt to determine magne-tostratigraphic and palaeoclimatic records. The results show that aeolian dust accumulation and the related East Asia pa...Two Red Clay profiles near Xi’ an and Xifeng were investigated in an attempt to determine magne-tostratigraphic and palaeoclimatic records. The results show that aeolian dust accumulation and the related East Asia palaeomonsoon system had begun by 6.5 Ma, and it is deduced that the Tibetan Plateau had reached a significant elevation at that time. The late Tertiary palaeoclimatic history of the Red Clay as reflected by magnetic susceptibility is reconstructed during the period of 6.5-2.5 Ma. Stepwise increase in susceptibility of aeolian dust accumulation appears to have a close correlation to the uplift processes of the Tibetan Plateau. The remarkable increase of aeolian dust accumulation at 3.2 Ma appears to be due to the influence of global ice volume on the East Asia monsoon. Palaeomonsoon variation during the late Tertiary as recorded in the Red Clay sequences from the Chinese Loess Plateau can be regarded as the product of a number of interacting factors, such as uplift of the Tibetan Plateau,展开更多
The Late Tertiary red clay/bed sediments underlying the Quaternary loess-paleosol in the Chinese Loess Plateau possesses high-resolution paleoclimatic changes related to the uplift of the Tibetan Plateau. Magnetostrat...The Late Tertiary red clay/bed sediments underlying the Quaternary loess-paleosol in the Chinese Loess Plateau possesses high-resolution paleoclimatic changes related to the uplift of the Tibetan Plateau. Magnetostratigra-phy and susceptibility measurements are discussed in this paper. The paleomagnetic results show that the red clay/bed began to accumulate at about 8.1 Ma, which represents the oldest Late Tertiary deposit continuously in the central Loess Plateau. The magnetic susceptibility curves show stepwise increases since the initiation of red clay, superimposed on several peaks. Moreover, the magnetic susceptibility increased abruptly since 3.8 Ma, which probably indicates the inception of the modern East Asia monsoon system. Between 3.8 and 2.6 Ma, the stepwise increases of susceptibility may imply progressively intensified East Asia summer monsoon activity related with the stepwise uplift process of the Tibetan Plateau.展开更多
A hundred and eleven samples were collected from the Permian-Triassic boundarysection of Meishan (31.1°N, 119.7°E) which includes the Changxing Formation of thelate Permian and the Qinglong Formation of earl...A hundred and eleven samples were collected from the Permian-Triassic boundarysection of Meishan (31.1°N, 119.7°E) which includes the Changxing Formation of thelate Permian and the Qinglong Formation of early Triassic. The thickness of the sectionis about 60 m. Paleomagnetic results indicate that six normal and reversed polarity zoneswere recorded in the section which all belong to the Illawarra mixed interval. Theboundary of Permo-Triassic lies at 1.2 m (or 2.7 m) above the bottom of normal polarityzone V. The magnetic minerals in the rocks of the lower part of the Changxing Forma-tion mainly are goethite, haematite and titaniferous magnetite while in the upper part ofthe formation are chiefly titanomagnetite and magnetite, goethite is secondary. Magne-tite and haematite as the main magnetic minerals were included in marl and mudstone ofthe Qinglong Formation. Based on the results of the magnetically stable samples thepaleopole position of 50.7°N, 230.3°E was obtained, meanwhile, the展开更多
The Sulu orogenic belt is an uplift zone that was formed in the Late Triassic.Several Jurassic to Cretaceous sedimentary successions have been recognized within the Sulu orogenic belt in recent studies,including outcr...The Sulu orogenic belt is an uplift zone that was formed in the Late Triassic.Several Jurassic to Cretaceous sedimentary successions have been recognized within the Sulu orogenic belt in recent studies,including outcrops that are considered to be related to the newly discovered Riqingwei Basin.This basin has been the focus of extensive study due to its continuous Cretaceous rock sequence,geological location and petroleum resource potential.However,the lack of a consolidated chronology for the strata has precluded a better understanding of stratigraphy,tectonic evolution and resource potential of the Riqingwei Basin.Here,we present the results of a new magnetostratigraphic study of the continental scientific drilling borehole LK-1,which is located on Lingshan Island,offshore Shandong province,eastern China.The goals of this study are to(1)refine the Late Jurassic to Early Cretaceous chronostratigraphic framework of the Riqingwei Basin,and(2)investigate the location of the J/K boundary in the Borehole Core LK-1.The observed patterns of the paleomagnetic polarity zone in the LK-1 borehole correlate well with the geomagnetic polarity time scale(GPTS),and the continuous magnetostratigraphy profile defined in this core indicates an age ranging from 146.5 to 125.8 Ma for the samples interval.The sediment accumulation rates(SAR)of LK-1 show one period of high SAR(~10.5 cm kyr^(-1))at 135.3–130.6 Ma and two periods of low SAR(~4.8 and~2.2 cm kyr^(-1))at145.7–135.3 and 130.6–125.8 Ma,respectively.In addition,the magnetostratigraphic results suggest that the Jurassic-Cretaceous(J/K)boundary of the LK-1 is located within the magnetozone N21.2 n(~1254 m).This comprehensive geochronologic framework provides a good correlation of the marine Upper Jurassic to Lower Cretaceous strata in the Riqingwei Basin to other marine strata and continental sequences,in addition to providing a foundation for the study of the structural evolution of eastern China.展开更多
A calibration among magnetic polarity sequence, biostratigraphy zonation and isotopicage reveals that the boundary between the Carboniferous-Permian reversed Polarity Superzone and Permian-Triassic Mixed Polarity Supe...A calibration among magnetic polarity sequence, biostratigraphy zonation and isotopicage reveals that the boundary between the Carboniferous-Permian reversed Polarity Superzone and Permian-Triassic Mixed Polarity Superzone occurs at the top of the wordian Stage of the Guadalupian Series and is dated as 265 Ma. The Late Permian magnetic polarity sequence integrates four polarity zones, corresponding to the Upper Guadalupian Series, the wuchiapingian Stage, and the Lower and the Upper Changhsingian Stage of the Lopingian Series. This reference magnetostratigraphy polarity sequence may serve as a useful guide to the chronostratigraphic correlation of Late Permian strata across major biogeographic and facies barriers.展开更多
This paper is the result of research on the Cretaceous magnetostratigraphy in the Songliao Basin. The palaeomagnetic experiment on 2235 specimens from 24 drills and an outcrop profile in Quantou shows that most specim...This paper is the result of research on the Cretaceous magnetostratigraphy in the Songliao Basin. The palaeomagnetic experiment on 2235 specimens from 24 drills and an outcrop profile in Quantou shows that most specimens have stable remanent magnetization.The features of polarities associated with all the rock formations of the Cretaceous in the Songliao plain have been summarized. The reversed polarity zones have been found in the Yingcheng, Dcnglouku, Yaojia and Nenjiang Formations. These reserved-polarity zones and their geologic ages have been argued. Accordingly. the polarity columns for different drills and a comprehensive column have been compiled, and the classification and correlation of the Cretaceous stratigraphy in the Songliao Basin have been discussed.展开更多
Magnetostratigraphic studies of 112 cores specimens (249 samples) in a Precambrian-Cambrian section at Meishucun, Jinning County, Yunnan Province reveal the following: (ⅰ) Around the Sinian-Cambrian boundary in the M...Magnetostratigraphic studies of 112 cores specimens (249 samples) in a Precambrian-Cambrian section at Meishucun, Jinning County, Yunnan Province reveal the following: (ⅰ) Around the Sinian-Cambrian boundary in the Meishucun section existed a mixed polarity zone in which the Meishucun fauna went through an evolution of appearance—flourish—extinction. (ⅱ) The Meishucun section had a paleolatitude of no more than 20° during the Sinian-Cambrian, The phosphate deposits in this region and in the Zhongyicun Member were formed in the low-latitude environments.展开更多
Two parallel loess-soil sequences from Xuancheng and Fanchang in southern Anhui Province are dated using geomagnetic and luminescence methods. The Brunhes/Matuyama (B/M) reversal boundary is recognized within the lowe...Two parallel loess-soil sequences from Xuancheng and Fanchang in southern Anhui Province are dated using geomagnetic and luminescence methods. The Brunhes/Matuyama (B/M) reversal boundary is recognized within the lower part of the so-called Vermiculated Red Soil (VRS) in the Xuancheng section while the entire Fanchang sequence is of Brunhes age. This indicates that the most recent VRS in southern China, a stratigraphic marker and an indication of extremely warm-humid conditions, was formed during the middle Pleistocene, chronologically correlative with the S4 and S5 soil units in northern China. Microscopic and sedimentologic investigations reveal that eolian deposition started in this region at about 0.85 MaBP, roughly synchronous with the well-known Mid-Pleistocene climate change of global significance. The strengthening of both summer and winter monsoon circulations and the consequent river hydrological changes at that time would have provided favorable conditions for sustained eolian deposition in the middle-lower reaches of the Yangtze River since 0.85 MaBP.展开更多
The Kunlun Pass Basin, located in the middle of the eastern Kunlun Mountains, received relatively continuous late Cenozoic sediments from the surrounding mountains, archiving great information to understand the deform...The Kunlun Pass Basin, located in the middle of the eastern Kunlun Mountains, received relatively continuous late Cenozoic sediments from the surrounding mountains, archiving great information to understand the deformation and uplift histories of the northern Tibetan Plateau. The Kunlun-Yellow River Movement, identified from the tectonomorphologic and sedimentary evolution of the Kunlun Pass Basin by Cui Zhijiu et al. (1997, 1998), is roughly coincident with many important global and Plateau climatic and environmental events, becoming a crucial time interval to understand tectonic-climatic interactions. However, the ages used to constrict the events remain great uncertainty. Here, we present the results of detailed magnetostratigraphy of the late Cenozoic sediments in the Kunlun Pass Basin, which show the basin sediments were formed between about 3.6 Ma and 0.5 Ma and the Kunlun-Yellow River Movement occurred at 1.2 to ～0.78 Ma. The lithology, sedimentary facies and lithofacies associations divide the basin into five stages of tectonosedimentary evolution, indicating the northern Tibetan Plateau having experienced five episodes of tectonic uplifts at ～3.6, 2.69－2.58, 1.77, 1.2, 0.87 and ～0.78 Ma since the Pliocene.展开更多
The Zanda basin is one of the very important basins at the north slope of the Himalaya Range. Thus the study of the basin strata will provide critical information about the tectonic evolution of the Himalayan Orogenic...The Zanda basin is one of the very important basins at the north slope of the Himalaya Range. Thus the study of the basin strata will provide critical information about the tectonic evolution of the Himalayan Orogenic Belt. 268 oriented block samples were collected in the 750-m-thick sections of the Zanda ba- sin. The characteristic remanent magnetization (ChRM) was isolated that decays linearly to the origin between 500oC and 690oC for most studied samples. An age range of 9.5―2.6 Ma was estimated from the correlation between our observed polarity column and the Geomagnetic Polarity Time Scale (GPTS). The age of the Zanda basin does not support the models that the South Tibetan Detach system (STDS) is one of the basin controlling faults. Given the sedimentological features in the basin and the tectonic features at the north edge of the basin, the Zanda basin was a half graben that was possibly controlled by the Karakorum fault on the northeast.展开更多
基金co-supported by the Geological Survey Project of China(Grant No. 1212331413023)the National Natural Science Foundation of China(Grant No. U1407207)
文摘The Qarhan Salt Lake area is the Quaternary depocenter of the Qaidam Basin, and carries thick lacustrine sediments, as well as rich potassium and magnesium salt deposits. The abundant resources and thick sediments in this lake provide an ideal place for the study of biogas formation and preservation, salt lake evolution, and the uplift of the Tibetan Plateau. In this study, we attempt to construct a paleomagnetic and ^(230)Th age model and to obtain information on tectonic activity and salt lake evolution through detailed studies on a 1300-m-long drill core(15DZK01) from the northwestern margin of the Qarhan Salt Lake area(Dongling Lake). Based on gypsum ^(230)Th dating, the age of the uppermost clastic deposit was calculated to be around 0.052 Ma. The polarity sequence consist of 13 pairs of normal and reversed zones,which can be correlated with subchrons C2r.1r-C1n of the geomagnetic polarity timescale(GPTS 2012)(from ~2.070 Ma to ~0.052 Ma). Sedimentary characteristics indicate that Dongling Lake witnessed freshwater environment between ~ 2.070 Ma and 1.546 Ma. During this period, the sedimentary record reflects primarily lakeshore, shallow-water and swamp environments, representing favourable conditions for the formation of hydrocarbon source rocks. Between 1.546 Ma and ~ 0.052 Ma, the Dongling Lake was in sulphate deposition stage, which contrasts with the central Qarhan Salt Lake area, where this stage did not occur in the meantime. During this stage, Dongling Lake was in a shallow saltwater lake environment, but several periods of reduced salinity occurred during this stage. During the late Pleistocene at ~0.052 Ma, the Dongling Lake experienced uplift due to tectonic activity, and saltwater migrated through the Sanhu Fault to the central Qarhan Salt Lake area, resulting in the absence of halite deposition stage. The residual saline water was concentrated into magnesium-rich brine due to the lack of freshwater, and few potassium salt deposits occur in the Dongling Lake area.
基金supported by the Fundamental Research Funds for the Central Universities(Grant No.lzujbky-2017-k27)contributed to IGCP 652.
文摘The study of magnetostratigraphy and cyclostratigraphy in the last two decades has provided a great deal of opportunities to improve the geologic time scale.The Cenozoic and Mesozoic geologic timescale have been well calibrated(Gradstein et al..2012;Ogg et al,2012;Cohen et al.,2018).However,for the Paleozoic era the uncertainty over boundary ages are still very large.
文摘The palaeoposition of India after its breakup from Gondwana and its subsequent northward journey during the Mesozoic poses many tectonic riddles. A magnetostratigraphy pattern has been constructed for the Ammonoid rich Middle Jurassic Bathonian succession of Jumara Dome, Kachchh, western India. We present the first magnetostratigraphic results from the Ammonoid bearing exposed Bathonian sediments in Kachchh. The Jumara Dome comprised of mixed carbonate-siliciclastic succession is represented by the Jhurio and Patcham formations and siliciclastic-dominating Chari Formation in the Kachchh Mainland. The Jumara Dome sediments were deposited during sea-level fluctuating, and were interrupted by storms in the shallow marine environment. This study is based on collection of 60 oriented samples from 13 successive levels. Both thermal and AF demagnetization investigations were carried out to isolate the Characteristic Remanent Magnetization (ChRM) directions. Palaeolatitudes were computed using the ChRM directions. Magnetostratigraphic column is prepared and correlated with Geological Time Scale (GTS) of [1] [2], and this column readily matched with GTS at M41 to below and exhibits the dominance of normal polarity in Jumara.
基金supported by Foundation of Geological Survey of China(no.1212011121261)the National Natural Science Foundation of China (no.40902049)+1 种基金the Special Fund for Basic Scienctific Research of Central Colleges, China University of Geoscience (Wuhan) (no.CUGL09206)the State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences(no.GBL11207)
文摘The timing of onset of deposition of the Lulehe Formation is a significant factor in understanding the genesis of the Qaidam basin and the evolution of the Tibetan Plateau. Here, we describe a detailed magnetostratigraphic and magnetic fabric study of the middle and lower parts of the Lulehe Formation. A total of 234 samples were collected from 117 sites throughout a thickness of almost 460 m of fluvial and lacustrine deposits at the Xitieshan section in the northeastern Qaidam basin. Out of these sites, 94 sites yielded well-defined characteristic remanent magnetization components by stepwise thermal demagnetization and were used to establish the magnetostratigraphy of the studied section. Based on correlation with the geomagnetic polarity timescale, the studied section spans the period from 53.8 Ma to 50.7 Ma. Our results show a three-fold decrease in sedimentation rates as well as marked change in facies from braided river to delta and shore-shallow lake around 52.6 Ma, which suggests tectonic uplift of the northeastern Qaidam basin margin ridge was rapid at the onset of formation of the Qaidam basin and subsequently weakened after 52.6 Ma. The anisotropy of magnetic susceptibility results indicate that tectonic compression stress had reached the northeastern Tibetan Plateau by the early stages of Indo-Eurasian plate collision and that the direction of stress in the study area was NE-SW. Furthermore, a weakening of tectonic compression stress around 52.6 Ma is consistent with sedimentary records. The age of initial deposition of the Qaidam basin (around 53.8 Ma) was almost synchronous with that of the Qiangtang, Hoh Xil, Xining, and Lanzhou basins, which implies that stress was transferred rapidly through the Tibetan Plateau during or immediately after the onset of Indo-Eurasian collision.
基金funded by the National Natural Science Foundation of China (41072260 and 40402026)
文摘Loess deposits with varying thickness are widely distributed on the intermontane valleys and piedmont zones on the northern side of the central Shandong mountainous regions. However, the basal ages and material resources of the loess deposits are not clear. The paper studied the Qingzhou loess profile in Shandong with magnetostratigraphic and optical stimulated luminescence (OSL) methods and further investigated its main provenances with the mineralogical methods. The magnetostratigraphic results showed that the Brunhes/Matuyama (B/M) reversal boundary was not recognized, suggesting a basal age younger than 0.78 Ma. Extrapolations by sedimentation rates, based on the upper part depositional rate from the OSL age, the basal age of the Qingzhou loess is about 0.5 Ma. Until now, older loess deposits have not been reported on the northern side of the central Shandong mountainous regions. The results of the paper indicate that the loess deposits in this area might have strated from the Middle Pleistocene. The basal age of Qingzhou loess is approximately synchronous with the Xiashu loess in the middle-lower reaches of Yangtze River. Major components of clay minerals in the Qingzhou profile are dominated by illite. Other clay mineral compositions are mainly smectite, chlorite and kaolinite, which are similar with the Xifeng loess in the Loess Plateau. However, the contents of smectite and the ratios of illite and kaolinte in the Qingzhou loess samples are higher than those in the Xifeng loess samples of the Loess Plateau, indicating that the loess in the northern side of the central Shandong mountainous regions has different sources from that of the loess deposits in the Loess Plateau. The clay mineral analysis further reinforces the earlier conclu- sion that the marine strata exposed in the Laizhou Bay and the fluvial plain of the lower reaches of Yellow River during the glacier periods are the main material sources for the Qingzhou loess deposits, which is an indicator to the local aridification of the lower reaches of the Yellow River. Loess deposition in the central Shandong mountainous regions started at around 0.5 Ma. The age of Qingzhou loess is approximately synchronous with the ongoing high-latitude cold since the Middle Pleistocene, which indicates that strengthened East Asian winter monsoon was sufficiently energetic to bring substantial quantities of material from the marine strata exposed in the Laizhou Bay and the fluvial plain of the lower reaches of the Yellow River to the central Shandong mountainous regions. The results therefore suggest that both regional geological process and global changes were responsible for the formation of Qingzhou loess since Middle Pleistocene.
文摘The Maoming Basin is one amongst a group of Cretaceous-Teniary basins in South China. 347 samples were collected from drill cores MR and MB and sechon MS (110°54’E, 21°45 ’N). Most of the lithological units are of Tertiary age. The cores include the Laohuling, Shangcun,Huangniuling and Youganwo formations . The MR core (874m in length) has recorded the polarity history from Normal Zone 18 to Normal Zone 11 on the Geomagnetic Polarity Time Scale (GPTS).The strata were formed from about 42Ma to 32Ma, that is from Late Eocene to Early Oligocene.A mean sedimentation rate of this stratigraphic column is 8.1 cm/ka.
基金the NSFC(Grant No.40334038,40121303)the National Key Project for Basic Research on the Tibetan Plateau(Grant No.G1998040809)CAS"Hundred Talents Project"(Grant No.Ren-Jiao-Zi[2000]02821.
文摘Cenozoic sediments in the foreland basin--Jiuquan Basin in west Hexi Corridor recorded tectonic uplift information of the Qilian Mountains. High resolution paleomagnetic dating of the Laojunmiao (LJM) section across the central LJM anticline in the southern Jiuquan Basin reveals ages of the Getanggou Member, Niugetao Member in the Shulehe Formation, the Yumen Conglomerate, Jiuquan Conglomerate and Gobi Formation at >13-8.3 Ma, 8.3-4.9 Ma, 3.66-0.93 Ma, 0.84-0.14 Ma and 0.14-0 Ma, respectively. Sedimentary evolution study suggests that the Qilian Mountains should begin to rise gradually since ～8-6.6 Ma, accompanied by sedimentary environments changing from lacustrine mudstones-sandstones to alluvial conglomerates. Rapid uplift of the Qilian Mountains began at ～3.66 Ma, followed by a series of stepwise or intermittent intensive uplifts at about <1.8-1.23 Ma, 0.93-0.84 Ma and 0.14 Ma, which finally resulted in the present high Qilian Mountains.
基金Project supported by the National Natural Science Foundation of China and the Foundation of Xi'an Laboratory of Loess and Quatemary Geology,Chinese Academy of Sciences
文摘Two Red Clay profiles near Xi’ an and Xifeng were investigated in an attempt to determine magne-tostratigraphic and palaeoclimatic records. The results show that aeolian dust accumulation and the related East Asia palaeomonsoon system had begun by 6.5 Ma, and it is deduced that the Tibetan Plateau had reached a significant elevation at that time. The late Tertiary palaeoclimatic history of the Red Clay as reflected by magnetic susceptibility is reconstructed during the period of 6.5-2.5 Ma. Stepwise increase in susceptibility of aeolian dust accumulation appears to have a close correlation to the uplift processes of the Tibetan Plateau. The remarkable increase of aeolian dust accumulation at 3.2 Ma appears to be due to the influence of global ice volume on the East Asia monsoon. Palaeomonsoon variation during the late Tertiary as recorded in the Red Clay sequences from the Chinese Loess Plateau can be regarded as the product of a number of interacting factors, such as uplift of the Tibetan Plateau,
基金This work was co-supported by the CAS "Hundred Talents Project" (Grant No. Renjiaozi [2000J 005) and the National Key Project for Basic Research on Tibet Plateau (Grant No. G1998040809).
文摘The Late Tertiary red clay/bed sediments underlying the Quaternary loess-paleosol in the Chinese Loess Plateau possesses high-resolution paleoclimatic changes related to the uplift of the Tibetan Plateau. Magnetostratigra-phy and susceptibility measurements are discussed in this paper. The paleomagnetic results show that the red clay/bed began to accumulate at about 8.1 Ma, which represents the oldest Late Tertiary deposit continuously in the central Loess Plateau. The magnetic susceptibility curves show stepwise increases since the initiation of red clay, superimposed on several peaks. Moreover, the magnetic susceptibility increased abruptly since 3.8 Ma, which probably indicates the inception of the modern East Asia monsoon system. Between 3.8 and 2.6 Ma, the stepwise increases of susceptibility may imply progressively intensified East Asia summer monsoon activity related with the stepwise uplift process of the Tibetan Plateau.
文摘A hundred and eleven samples were collected from the Permian-Triassic boundarysection of Meishan (31.1°N, 119.7°E) which includes the Changxing Formation of thelate Permian and the Qinglong Formation of early Triassic. The thickness of the sectionis about 60 m. Paleomagnetic results indicate that six normal and reversed polarity zoneswere recorded in the section which all belong to the Illawarra mixed interval. Theboundary of Permo-Triassic lies at 1.2 m (or 2.7 m) above the bottom of normal polarityzone V. The magnetic minerals in the rocks of the lower part of the Changxing Forma-tion mainly are goethite, haematite and titaniferous magnetite while in the upper part ofthe formation are chiefly titanomagnetite and magnetite, goethite is secondary. Magne-tite and haematite as the main magnetic minerals were included in marl and mudstone ofthe Qinglong Formation. Based on the results of the magnetically stable samples thepaleopole position of 50.7°N, 230.3°E was obtained, meanwhile, the
基金supported by the National Natural Science Foundation of China(Grant Nos.42002030,42072169)National Science and Technology Major Project(Grant No.2016ZX05024-002-001)+1 种基金the Key R&D Plan of Shandong Province(Grant No.2017CXGC1608)the Natural Science Foundation of Shandong Province(Grant No.ZR201910280267)。
文摘The Sulu orogenic belt is an uplift zone that was formed in the Late Triassic.Several Jurassic to Cretaceous sedimentary successions have been recognized within the Sulu orogenic belt in recent studies,including outcrops that are considered to be related to the newly discovered Riqingwei Basin.This basin has been the focus of extensive study due to its continuous Cretaceous rock sequence,geological location and petroleum resource potential.However,the lack of a consolidated chronology for the strata has precluded a better understanding of stratigraphy,tectonic evolution and resource potential of the Riqingwei Basin.Here,we present the results of a new magnetostratigraphic study of the continental scientific drilling borehole LK-1,which is located on Lingshan Island,offshore Shandong province,eastern China.The goals of this study are to(1)refine the Late Jurassic to Early Cretaceous chronostratigraphic framework of the Riqingwei Basin,and(2)investigate the location of the J/K boundary in the Borehole Core LK-1.The observed patterns of the paleomagnetic polarity zone in the LK-1 borehole correlate well with the geomagnetic polarity time scale(GPTS),and the continuous magnetostratigraphy profile defined in this core indicates an age ranging from 146.5 to 125.8 Ma for the samples interval.The sediment accumulation rates(SAR)of LK-1 show one period of high SAR(~10.5 cm kyr^(-1))at 135.3–130.6 Ma and two periods of low SAR(~4.8 and~2.2 cm kyr^(-1))at145.7–135.3 and 130.6–125.8 Ma,respectively.In addition,the magnetostratigraphic results suggest that the Jurassic-Cretaceous(J/K)boundary of the LK-1 is located within the magnetozone N21.2 n(~1254 m).This comprehensive geochronologic framework provides a good correlation of the marine Upper Jurassic to Lower Cretaceous strata in the Riqingwei Basin to other marine strata and continental sequences,in addition to providing a foundation for the study of the structural evolution of eastern China.
文摘A calibration among magnetic polarity sequence, biostratigraphy zonation and isotopicage reveals that the boundary between the Carboniferous-Permian reversed Polarity Superzone and Permian-Triassic Mixed Polarity Superzone occurs at the top of the wordian Stage of the Guadalupian Series and is dated as 265 Ma. The Late Permian magnetic polarity sequence integrates four polarity zones, corresponding to the Upper Guadalupian Series, the wuchiapingian Stage, and the Lower and the Upper Changhsingian Stage of the Lopingian Series. This reference magnetostratigraphy polarity sequence may serve as a useful guide to the chronostratigraphic correlation of Late Permian strata across major biogeographic and facies barriers.
文摘This paper is the result of research on the Cretaceous magnetostratigraphy in the Songliao Basin. The palaeomagnetic experiment on 2235 specimens from 24 drills and an outcrop profile in Quantou shows that most specimens have stable remanent magnetization.The features of polarities associated with all the rock formations of the Cretaceous in the Songliao plain have been summarized. The reversed polarity zones have been found in the Yingcheng, Dcnglouku, Yaojia and Nenjiang Formations. These reserved-polarity zones and their geologic ages have been argued. Accordingly. the polarity columns for different drills and a comprehensive column have been compiled, and the classification and correlation of the Cretaceous stratigraphy in the Songliao Basin have been discussed.
文摘Magnetostratigraphic studies of 112 cores specimens (249 samples) in a Precambrian-Cambrian section at Meishucun, Jinning County, Yunnan Province reveal the following: (ⅰ) Around the Sinian-Cambrian boundary in the Meishucun section existed a mixed polarity zone in which the Meishucun fauna went through an evolution of appearance—flourish—extinction. (ⅱ) The Meishucun section had a paleolatitude of no more than 20° during the Sinian-Cambrian, The phosphate deposits in this region and in the Zhongyicun Member were formed in the low-latitude environments.
基金This work was supported by the National Natural Science Foundaution of China(Grant Nos.49894170-06 and 40231001).
文摘Two parallel loess-soil sequences from Xuancheng and Fanchang in southern Anhui Province are dated using geomagnetic and luminescence methods. The Brunhes/Matuyama (B/M) reversal boundary is recognized within the lower part of the so-called Vermiculated Red Soil (VRS) in the Xuancheng section while the entire Fanchang sequence is of Brunhes age. This indicates that the most recent VRS in southern China, a stratigraphic marker and an indication of extremely warm-humid conditions, was formed during the middle Pleistocene, chronologically correlative with the S4 and S5 soil units in northern China. Microscopic and sedimentologic investigations reveal that eolian deposition started in this region at about 0.85 MaBP, roughly synchronous with the well-known Mid-Pleistocene climate change of global significance. The strengthening of both summer and winter monsoon circulations and the consequent river hydrological changes at that time would have provided favorable conditions for sustained eolian deposition in the middle-lower reaches of the Yangtze River since 0.85 MaBP.
基金This work was supported by the National Natu-ral Science Foundation of China(Grand Nos.40421101,40121303,40334038).
文摘The Kunlun Pass Basin, located in the middle of the eastern Kunlun Mountains, received relatively continuous late Cenozoic sediments from the surrounding mountains, archiving great information to understand the deformation and uplift histories of the northern Tibetan Plateau. The Kunlun-Yellow River Movement, identified from the tectonomorphologic and sedimentary evolution of the Kunlun Pass Basin by Cui Zhijiu et al. (1997, 1998), is roughly coincident with many important global and Plateau climatic and environmental events, becoming a crucial time interval to understand tectonic-climatic interactions. However, the ages used to constrict the events remain great uncertainty. Here, we present the results of detailed magnetostratigraphy of the late Cenozoic sediments in the Kunlun Pass Basin, which show the basin sediments were formed between about 3.6 Ma and 0.5 Ma and the Kunlun-Yellow River Movement occurred at 1.2 to ～0.78 Ma. The lithology, sedimentary facies and lithofacies associations divide the basin into five stages of tectonosedimentary evolution, indicating the northern Tibetan Plateau having experienced five episodes of tectonic uplifts at ～3.6, 2.69－2.58, 1.77, 1.2, 0.87 and ～0.78 Ma since the Pliocene.
基金Supported by the National Natural Science Foundation of China (Grant Nos. 40672142 and 40334038)China National Key Project (Grant Nos. 2005CB422000 and 2002CB412601)
文摘The Zanda basin is one of the very important basins at the north slope of the Himalaya Range. Thus the study of the basin strata will provide critical information about the tectonic evolution of the Himalayan Orogenic Belt. 268 oriented block samples were collected in the 750-m-thick sections of the Zanda ba- sin. The characteristic remanent magnetization (ChRM) was isolated that decays linearly to the origin between 500oC and 690oC for most studied samples. An age range of 9.5―2.6 Ma was estimated from the correlation between our observed polarity column and the Geomagnetic Polarity Time Scale (GPTS). The age of the Zanda basin does not support the models that the South Tibetan Detach system (STDS) is one of the basin controlling faults. Given the sedimentological features in the basin and the tectonic features at the north edge of the basin, the Zanda basin was a half graben that was possibly controlled by the Karakorum fault on the northeast.
