Liu Jiaqi

Changes in hydrological conditions in the central Qing-Zang (Tibetan) Plateau inferred from lake bottom sediments

Abstract Grain particle and chemical analyses of core samples obtained from Siling-co, a lake on the central Tibetan Plateau, and a sedimentation model for the lake with 14 C dating show fluctuations in the hydrological environment of the area during the past 15,000 yr. The area of the lake was small and the water level low in the late part of the last glacial period. Thereafter, the lake became larger and the water level high because of meltwater and rainfall. This hydrological environment continued until 4000 yr B.P., at about which time the level of the lake fell sharply and the lake area shrank. After a short period of low level and aridity, the water level increased markedly but did not reach the previous high level. After the large water inflow for a short period, the climate became again arid at about 3500 yr B.P. The change in this interval is closely related to global change. Statistical analyses of the datasets of the grain particle components of bottom sediments preserved in an aquatic condition over the past 13,000 yr show that most datasets for grain size and chemical parameters had a common period of 2000–2200 yr during this interval.

Effect of Miocene basaltic volcanism in Shanwang (Shandong Province, China) on environmental changes

Miocene (16–10 Ma) basalts, together with significantly well-preserved fossils (including animal and plant fossils) in the contemporaneously tephra-rich Maar sediments, are located in Shanwang volcanic region, Shandong Province, China. Distribution area of the basaltic eruption products is about 240 km2. Detailed field observations indicate that most of basaltic rocks are fissure eruptive products and some are central eruptives constrained by linear faults. The well-preserved fossils in the lacustrine deposits have been considered to be a result of mass mortalities. Based on physically volcanologic modeling results, eruption column of the basaltic fissure activities in the Shanwang volcanic region is estimated to have entered the stratosphere. Petrographic observations indicate that the basalts have porphyritic textures with phenocrysts of olivine, pyroxene, plagioclase feldspar and alkali feldspar setting in groundmass of plagioclase feldspar, alkali feldspar, quartz, apatite and glass. Based on observations of tephra, tuff and tuffites collected in the Maar sediments of the Shanwang area, we determined major element oxide concentrations and volatile composition of melt inclusions in phenocrysts and matrix glasses by electron microprobe analysis. Volatile (including S, Cl, F and H2O) concentrations erupted into the stratosphere were estimated by comparing pre-and post-eruptive volatile concentrations. Our determination results show that contents of S, Cl, F and H2O emitted into the stratosphere were 0.18%–0.24%, 0.03%–0.05%, 0.03%–0.05% and 0.4%–0.6%, respectively, which was characterized by high-S contents erupted. Amounts of volatiles emitted in the Shanwang volcanic region are much higher than those in eruptions which had a substantial effect on climate and environment. According to the compositions and amounts of the volatiles erupted from the Miocene basaltic volcanism in Shanwang, we propose a hypothesis that volatile-rich basaltic volcanism could result in the mass mortalities by injecting volatiles (e.g., SO2, H2S, HCl, HF and H2O) into the stratosphere that would have triggered abrupt environmental changes (including formation of acid rain, temperature decline, ozone depletion, etc.) and altered lake chemistry, and subsequently volcanic ash fall buried and covered the dead animals and plants, forming well-preserved fossils in Shanwang Maar sediments.

Effect of gas emissions from Tianchi volcano (NE China) on environment and its potential volcanic hazards

The Tianchi volcano in the Changbai Mountains is located on the boundary between China and North Korea. There are many times of eruptions of the Tianchi volcano during the Holocene. One of its large eruptions occurred around 1000 years ago dated by 14C method and historical records. Composition of products of the largest Tianchi volcanic eruption studied is characterized by comenditic Plinian fallout and unwelded ignimbrite, which are mainly distributed in China and North Korea. Caldera is about 4.4 km long and 3.4 km wide, which had filled with water (e.g. Tianchi Lake). The Tianchi volcanic cone is about 2700 m high above sea level. The Tianchi Lake is located on the summit of the volcanic cone, that is also highest peak of the Changbai Mountains in northeastern China. This study analyzed Cl, F, S and H2O concentrations of melt inclusions in the phenocryst minerals (anorthoclase and quartz) and co-existing matrix glasses using the electron microprobe and estimated environmental effect of Tianchi volcanic gases. The authors proposed a new method to evaluate future eruption of active volcano and estimate potential volcanic hazards based on contents of volatile emissions. Using this method, we made a perspective of future volcanic hazard in this region.

Geochemical Characteristics of Volcanic Rocks from ODP Site 794, Yamato Basin: Implications for Deep Mantle Processes of the Japan Sea

Deep mantle processes and the dynamic mechanism of magmatism in the Japan Sea Basin are important processes that have not been studied in detail. In this paper, systematic evaluation of basalt samples from the ocean drilling program Site 794 in the Japan Sea was performed, which included petrography, whole-rock major- and trace-element analysis, Sr-Nd-Pb isotopic composition, and electron microprobe analysis of plagioclase and clinopyroxene. These basalts belong to the tholeiitic series with porphyritic texture and massive Ca-rich plagioclase, clinopyroxene, and minor olivine phenocrysts. The basalts are characterized as flat rare earth elements and high-field-strength elements with remarkably low ratios of (La/Yb)N (0.75–2.51), significant positive anomalies of Ba, Sr, and Rb and no Eu anomaly (δEu = 0.99–1.36). The samples showed relatively high 87Sr/86Sr (0.70425–0.70522), 207Pb/204Pb (15.511–15.610), and 208Pb/204Pb (38.064–38.557) values and a low 143Nd/144Nd ratio (0.51271–0.51295). The basalts from Site 794 can be divided into upper, middle, and lower volcanic rocks (UVR, MVR, and LVR) on the basis of their stratigraphic level. The MVR was geochemically derived from the depleted mantle, whereas the UVR and LVR originated from a nondepleted and relatively enriched mantle source with contributions from subducted Pacific plate fluid and sediments. Use of geothermobarometers indicates that the crystallization pressure for the UVR and LVR (6.25–11.19 kbar) was significantly higher than that of the MVR (3.48–5.84 kbar). The UVR and LVR may have been derived from the low-degree (5%–10%) partial melting of spinel lherzolite, while the MVR originated from a shallower mantle source with a high degree (10%–20%) of partial melting. In addition, the geochemical characteristics of the samples are consistent with a younger age (13–17 Ma) and the depleted composition of the MVR and an older age (17–23 Ma) and slightly enriched composition of the UVR and LVR. Therefore, temporal changes in the mantle source from old and enriched to young and depleted and subsequently to old and nondepleted may have been associated with progressive lithospheric extension and thinning, as well as at least two episodes of diverse asthenospheric upwelling and pull-apart tectonic motion in the Yamato Basin.

Vegetation history and climate change recorded by stomata evidence during the late glacial in the Great Khingan Mountain Region, Northeastern China

The research on the evolution of larch forest is significant to understand the vegetation and climate change in mid-high latitude region of the Northern Hemisphere. However, the pollen records to reconstruct the larch forest are problematic due to low pollen representation caused by severely poor pollen productivity and dispersal. New proxy of microfossils is needed to solve this problem. Using coniferous stomata as a proxy to reconstruct the evolution of conifers has some advantages, such as well preserved, locally deposited, continuously remained in lake sediments and can be accurately identified to the genus level. Therefore, a high-resolution stomata record covering 20.3–10.8 cal ka BP from Lake Moon was presented, in order to reconstruct larch forest history from the Last Glacial Maximum to early Holocene in the Great Khingan Mountain Region, Northeast China. Reference conifer stomata from fresh leaves of the local coniferous species and lake surface samples were prepared for the identification of the fossil stomata. Larix , Sabina and Picea stomata were identified from the sedimentary sequence of Lake Moon, and the results of stomata influx from this study and pollen influx from the previous study indicate that the vegetation evolution has gone through distinct stages. Before 15.0 cal ka BP, no Larix existed in the vicinity of study site. The first arrival of larch is inferred by the continuous presence of stomata at 15.0 cal ka BP, which manifests that the vegetation turned into forest steppe. The coverage of forest increases slightly from 15.0 to 12.8 cal ka BP with an interruption between 14.3 and 14.0 cal ka BP. During 12.8–11.8 cal ka BP, the vegetation were characterized by the expansion of conifers mainly Larix and the shrinkage of broadleaves and herbs. From 11.8 to 10.8 cal ka BP, the vegetation type remained as forest steppe with the shrinkage of conifers dominated by Larix , in conjunction with the expansion of broadleaves and herbs with high vegetation coverage. The establishment of larch forest inferred by the continuous presence of stomata marks the onset of the late glacial in the Great Khingan Mountain Region at 15.0 cal ka BP. The application of stomata analysis provides detailed scenes of coniferous evolution surrounding the Lake Moon. It is suggested that the analysis of fossil stomata is a valuable tool to demonstrate unambiguous evidence for the local presence of the conifers in study region, even better than pollen records when the component of larch is low in vegetation. The evolution of the forest communities in the late glacial period in the Great Khingan Mountain Region is comparable with the vegetation evolution of other regions at different latitudes in East Asian monsoon region, which indicates that the climate change at millennial/centennial scale in late glacial is roughly synchronous in East Asian monsoon region. The series of climatic periods in this study revealed by the stomata and pollen records is also similar to that of Europe, like Meiendorf interstadial, Oldest Dryas cold event, Bolling-Allerod warm phases, Younger Dryas cold event, warm and humid early Holocene. The temperature change is probably the main factor to impact the vegetation change. The study shows that the vegetation succession in the study area is responsive to the temperature change of the Northern Hemisphere controlled by the global ice volume, and reveals the synchronization of the late glacial climate change in the mid latitude region of East Asia and the North Atlantic region.

火山灰全岩与原位分析差异：以四海龙湾记录的1 600年前金龙顶子火山喷发为例

火山灰地层学主要依靠火山玻璃的成分进行源区的识别，然而，当火山玻璃成分不均一时就会对源区识别造成影响.四海龙湾玛珥湖位于东北新生代龙岗火山区内，其湖泊沉积物可以记录周边的火山喷发，电子探针等方法得到的火山玻璃成分可以揭示其喷发来源.同时，玛珥湖的纹层年龄可以限定其喷发年龄.在四海龙湾沉积物(钻孔2008) 的78~79 cm岩芯处出现一层火山灰层，其纹层年龄为AD 308 a，电子探针结果显示火山玻璃具有不均一的主量元素组成，为玄武质粗安岩到碱玄质响岩.FeO、TiO2及Al2O3等与MgO协变图解更清楚地显示了此次火山喷发的火山玻璃成分的不均一性.火山玻璃与火山灰全岩对比分析显示，全岩分析在火山灰地层学应用中容易造成对比偏差.

Development and application of tour geographic information system (TGIS) — Taking Mount Longhushan World Geopark as an example

Mt. Longhushan, a scenic spot located in Jiangxi Province, China, is famous for its beautiful and characteristic Danxia landform, long-history Taoism and mysterious cliff tomb. In recent years, the tourism resources, especially geological landscape have been developed greatly and tourists increases unprecedentedly. However, the tourism management in Mt. Longhushan still lags behind the development of the new technology, such as management combining with Geographic Information System (GIS). In this study, the application of GIS to the tour management and development is discussed and a tour geographic information system (TGIS) is developed based on MAPGIS. TGIS is a modern management method in tourism geographic information for comprehensive collection, dynamical analysis and application.