Based on the geochemical elements Rb and Sr in sediments with three different grain size fractions from profile H3 on the northern lacustrine bottomland 13 m above the Huangqihai Lake surface in 1986,the paper investi...Based on the geochemical elements Rb and Sr in sediments with three different grain size fractions from profile H3 on the northern lacustrine bottomland 13 m above the Huangqihai Lake surface in 1986,the paper investigates the record of palaeolake stand state, sedimentary environmental evolution,and winter monsoon change.First,these samples are separated into three different grain size fractions,i.e.,total sediments,77-20μm and〈20μm. Second,the chemical elements-Rb and Sr-of the grain size separation were tested and analyzed systematically in this paper.Then the elements compositions of these samples are measured using VP-320 mode fluorescence spectrum instrument,respectively.The magnetic susceptibility of these samples is measured using Kappabridge KLY-3 mode instrument made in Czech AGICO Company.The results showed the elements and the ratios varied regularly with the grain size.But the ratio of Rb/Sr in the sediments〈20μm correlates positively with the magnetic susceptibility of these samples.Therefore,the ratio of Rb/Sr in the fraction〈20 μm from the lake sediments reflected the strengthening of the weathering in the deposition sites.It is a good indicator of the summer monsoon-induced weathering and pedogenesis fluctuations and can be used to reconstruct the conditions of the paleoclimate and paleoenvironment.展开更多
The detailed magnetic susceptibility anisotropy study on the sediments of two sections, which are located in the lake-center and the lakeshore of the Huangqihai Lake, Inner Mongolia, revealed their hydrodynamics and s...The detailed magnetic susceptibility anisotropy study on the sediments of two sections, which are located in the lake-center and the lakeshore of the Huangqihai Lake, Inner Mongolia, revealed their hydrodynamics and sedimentary environment changes in the recent 2000 years. The results show that the sediments of two sections both display normal depositional magnetic fabrics, of which the minimum susceptibility axes （K3） are oriented perpendicular to the bedding plane and the maximum magnetic susceptibility axes （K~） lie parallel with the bedding plane. In addition, the iakeshore presents higher magnetic anisotropy degree （P）, magnetic foliation （F） and current factor （F~） than the lake-center, showing that the lakeshore has higher flow velocity. For the west Huangqihai Lake （HQW） section in the lake-center, the magnetic matrix grain degree （Q） and the inclination of the minimum susceptibility axes sharply increased and decreased, respectively, at a depth of about 10 cm, 24 cm, 45 cm and 74 cm, which indicate abnormal depositional events with strong kinetic energy. Through comparative analysis, the HQW section can be divided into three stages from top to bottom. The upper stage was a stable depositional environment with strong hydrodynamic energy and low water level, which shows relatively higher Fs value and the Q value varies similarly with P and F. The middle stage was a stable depositional environment with high water level and low hydrodynamic energy, intermitted with high-energy abnormal events, which shows relatively lower Fs and the Q value was negatively correlated with P and F. The lower stage was an unstable depositional environment with low hydrodynamic energy and high water level, which shows relatively lower P, F, and F~ value.展开更多
A consensus on Holocene climate variability at the modern northern fringe of the East Asian summer monsoon(EASM) region remains elusive. Here, we present a pollen-based reconstruction of vegetation history and associa...A consensus on Holocene climate variability at the modern northern fringe of the East Asian summer monsoon(EASM) region remains elusive. Here, we present a pollen-based reconstruction of vegetation history and associated climate variations of a sediment core from Huangqihai Lake, central Inner Mongolia. During 10.7 to 8.8 cal kaBP, typical steppe with small patches of forest dominated the lake area, suggesting a moderately wet climate, followed by ameliorating climatic conditions until 8.0 cal kaBP as deduced by the expansion of forest. Typical steppe recovered the lake area between 8.0 and 7.2 cal kaBP, reflecting a deterioration of climatic conditions;in combination with other proxy records in the study region, we noticed that severe aridity was prevailed in the lake area between 8.0 and 7.6 cal kaBP. During 7.2 to 3.2 cal kaBP, abundant tree pollen indicated dominance of forest-steppe around the lake, marking regionally wet conditions. A notable absence of broadleaved trees after 5.2 cal kaBP reveals a slight drying trend, and climate deterioration from 4.5 to 4.1 cal kaBP might be linked to the 4.2 ka event. After 3.2 cal kaBP, a transition to steppe was associated with dry conditions in the region. Based on our pollen record and prior paleoclimatic reconstructions in the Huangqihai Lake region, there was a generally-accepted, stepwise shift to a wet climate during the early Holocene, an overall humid climate from 7.2 to 3.2 cal kaBP, and then severe drought for the rest of the Holocene. Moreover, regional comparisons among pollen records derived from lakes situated in the temperate steppe region suggested a roughly synchronous pattern of vegetation and climate changes during the Holocene and demonstrated an intensified EASM during the middle Holocene.展开更多
Ground-penetrating radar and trenching studies of a barrier spit on the north shore of Huangqihai Lake were made,that reveal important implications for the coastal washover barrier boundary hierarchy and interpretatio...Ground-penetrating radar and trenching studies of a barrier spit on the north shore of Huangqihai Lake were made,that reveal important implications for the coastal washover barrier boundary hierarchy and interpretations of this depositional record.A four-fold hierarchy bounding-surface model,representing different levels of impact and genesis,is defined.Each level of the hierarchy is enclosed by a distinct kind of surface characterized by different ground-penetrating radar reflection features,sedimentary characteristics(color,grain size,sorting,rounding and sedimentary structures) and origin.We suggest that this hierarchical model can be applied to any coastal washover barrier deposits.展开更多
基金National Natural Science Foundation of China, No.40401006
文摘Based on the geochemical elements Rb and Sr in sediments with three different grain size fractions from profile H3 on the northern lacustrine bottomland 13 m above the Huangqihai Lake surface in 1986,the paper investigates the record of palaeolake stand state, sedimentary environmental evolution,and winter monsoon change.First,these samples are separated into three different grain size fractions,i.e.,total sediments,77-20μm and〈20μm. Second,the chemical elements-Rb and Sr-of the grain size separation were tested and analyzed systematically in this paper.Then the elements compositions of these samples are measured using VP-320 mode fluorescence spectrum instrument,respectively.The magnetic susceptibility of these samples is measured using Kappabridge KLY-3 mode instrument made in Czech AGICO Company.The results showed the elements and the ratios varied regularly with the grain size.But the ratio of Rb/Sr in the sediments〈20μm correlates positively with the magnetic susceptibility of these samples.Therefore,the ratio of Rb/Sr in the fraction〈20 μm from the lake sediments reflected the strengthening of the weathering in the deposition sites.It is a good indicator of the summer monsoon-induced weathering and pedogenesis fluctuations and can be used to reconstruct the conditions of the paleoclimate and paleoenvironment.
基金granted by NSFC projects 40830316,the Basic Outlay of Scientific Research Work from the Ministry of Science and Technology(Grant No. J1001,J1210)China Geological Survey Project (Grant No.1212010911027,1212011087116)
文摘The detailed magnetic susceptibility anisotropy study on the sediments of two sections, which are located in the lake-center and the lakeshore of the Huangqihai Lake, Inner Mongolia, revealed their hydrodynamics and sedimentary environment changes in the recent 2000 years. The results show that the sediments of two sections both display normal depositional magnetic fabrics, of which the minimum susceptibility axes （K3） are oriented perpendicular to the bedding plane and the maximum magnetic susceptibility axes （K~） lie parallel with the bedding plane. In addition, the iakeshore presents higher magnetic anisotropy degree （P）, magnetic foliation （F） and current factor （F~） than the lake-center, showing that the lakeshore has higher flow velocity. For the west Huangqihai Lake （HQW） section in the lake-center, the magnetic matrix grain degree （Q） and the inclination of the minimum susceptibility axes sharply increased and decreased, respectively, at a depth of about 10 cm, 24 cm, 45 cm and 74 cm, which indicate abnormal depositional events with strong kinetic energy. Through comparative analysis, the HQW section can be divided into three stages from top to bottom. The upper stage was a stable depositional environment with strong hydrodynamic energy and low water level, which shows relatively higher Fs value and the Q value varies similarly with P and F. The middle stage was a stable depositional environment with high water level and low hydrodynamic energy, intermitted with high-energy abnormal events, which shows relatively lower Fs and the Q value was negatively correlated with P and F. The lower stage was an unstable depositional environment with low hydrodynamic energy and high water level, which shows relatively lower P, F, and F~ value.
基金funded by the Geological Survey Projects of China(Grant Nos.DD20190370 and DD20190009)supported by Natural Science Foundation of Shaanxi Province,China(Grant No.2019JQ-835)Research Foundation of Education Bureau of Shaanxi Province,China(Grant No.2019JK-0404)。
文摘A consensus on Holocene climate variability at the modern northern fringe of the East Asian summer monsoon(EASM) region remains elusive. Here, we present a pollen-based reconstruction of vegetation history and associated climate variations of a sediment core from Huangqihai Lake, central Inner Mongolia. During 10.7 to 8.8 cal kaBP, typical steppe with small patches of forest dominated the lake area, suggesting a moderately wet climate, followed by ameliorating climatic conditions until 8.0 cal kaBP as deduced by the expansion of forest. Typical steppe recovered the lake area between 8.0 and 7.2 cal kaBP, reflecting a deterioration of climatic conditions;in combination with other proxy records in the study region, we noticed that severe aridity was prevailed in the lake area between 8.0 and 7.6 cal kaBP. During 7.2 to 3.2 cal kaBP, abundant tree pollen indicated dominance of forest-steppe around the lake, marking regionally wet conditions. A notable absence of broadleaved trees after 5.2 cal kaBP reveals a slight drying trend, and climate deterioration from 4.5 to 4.1 cal kaBP might be linked to the 4.2 ka event. After 3.2 cal kaBP, a transition to steppe was associated with dry conditions in the region. Based on our pollen record and prior paleoclimatic reconstructions in the Huangqihai Lake region, there was a generally-accepted, stepwise shift to a wet climate during the early Holocene, an overall humid climate from 7.2 to 3.2 cal kaBP, and then severe drought for the rest of the Holocene. Moreover, regional comparisons among pollen records derived from lakes situated in the temperate steppe region suggested a roughly synchronous pattern of vegetation and climate changes during the Holocene and demonstrated an intensified EASM during the middle Holocene.
基金Supported by the Specialized Research Fund for the Doctoral Program of Higher Education of China(No.20120022130002)the State Scholarship Fund from the China Scholarship Council(No.201406400030)
文摘Ground-penetrating radar and trenching studies of a barrier spit on the north shore of Huangqihai Lake were made,that reveal important implications for the coastal washover barrier boundary hierarchy and interpretations of this depositional record.A four-fold hierarchy bounding-surface model,representing different levels of impact and genesis,is defined.Each level of the hierarchy is enclosed by a distinct kind of surface characterized by different ground-penetrating radar reflection features,sedimentary characteristics(color,grain size,sorting,rounding and sedimentary structures) and origin.We suggest that this hierarchical model can be applied to any coastal washover barrier deposits.
