Gangdise Mountains Research Articles

Glacial cirque identification based on Convolutional Neural Networks

Cirques provide important information about the palaeoclimate conditions that produced past glaciers. However, mapping cirques is challenging, time-consuming, and subjective due to their fuzzy boundaries. A recent study tested the potential of using a deep learning algorithm, Convolutional Neural Networks (CNN), to predict boundary boxes containing cirques. Based on a similar CNN method, RetinaNet, we use a dataset of >8000 cirques worldwide and various combinations of digital elevation models and their derivatives to detect these features. We also incorporate the Convolutional Block Attention Module (CBAM) into RetinaNet for training and prediction. The precision of cirque detection with or without the addition of the CBAM is evaluated for various input data combinations, and training sample sizes, based on comparison with mapped cirques in two test areas on the Kamchatka Peninsula and the Gangdise Mountains. The results show that the addition of CBAM increases the average precision by 4–5 % (p < 0.01), and the trained model can detect the cirque boundary boxes with high precision (84.7 % and 87.0 %), recall (94.7 % and 86.6 %), and F1 score (0.89 and 0.87), for the two test areas, respectively. The inclusion of CBAM also significantly reduces the number of undetected cirques. The model performance is affected by the quantity and quality of the training samples: the performance generally increases with increasing training samples and a training dataset of 6000 cirques produces the best results. The trained model can effectively detect boundary boxes that contain cirques to help facilitate subsequent cirque outline extraction and morphological analysis.

Palaeoglacier and palaeoclimate reconstruction since the Neoglacial of the central Gangdise Mountains, southern Tibetan Plateau

Palaeoglacier modelling is a crucial approach for reconstructing palaeoclimate. Although the timing of glaciations during the Little Ice Age (LIA) and Neoglacial in the central Gangdise Mountains has been partially determined, there are still undated fresh-looking moraines. This study utilized coupled mass balance and ice flow models to simulate the palaeoclimate during the five LIA glacial events (LIA-1 to LIA-5) and two Neoglacial glacial events (Neo-1 and Neo-2). The results revealed that the glacial volumes in the Gangdise Mountains during the LIA and Neoglacial periods ranged from ∼1.10 to 1.57 km3. Comparing the reconstructed climate with other proxies, it was found that Neo-2 and Neo-1 exhibited temperatures 0.54 to 0.82 °C and 0.7 to 1.0 °C lower than the present, respectively, with precipitation levels at 110–140% of the present. The temperatures during the LIA periods were 0.36 to 1 °C lower than the present, with precipitation levels at 80–120% of the present. The interannual variability of climate at decadal or centennial scales may have played a significant role in the formation of the LIA moraines.

Spatio-Temporal Dynamic Characteristics of Carbon Use Efficiency in a Virgin Forest Area of Southeast Tibet

The sequestration of carbon in forests plays a crucial role in mitigating global climate change and achieving carbon neutrality goals. Carbon use efficiency (CUE) is an essential metric used to evaluate the carbon sequestration capacity and efficiency of Vegetation. Previous studies have emphasized the importance of assessing CUE at specific regions and times to better understand its spatiotemporal variations. The southeastern region of Tibet in the Qinghai-Tibet Plateau is recognized as one of the most biodiverse areas in China and globally, characterized by diverse vegetation types ranging from subtropical to temperate. In this study, we focused on Nyingchi, which is the largest virgin forest area in southeast Tibet, to explore the spatial-temporal dynamic characteristics of regional CUE based on MODIS remote sensing products. The following results were obtained: (1) On a monthly scale, regional CUE exhibits significant seasonal variations, with varying patterns among different vegetation types. Specifically, the fluctuation of CUE is the lowest in high-altitude forest areas and the greatest in grasslands and barrens. On an annual scale, forests exhibit higher fluctuations than areas with sparse vegetation and the overall volatility of CUE increased over the past 11 years. (2) There are regional differences in the trend of CUE changes, with a substantial downward trend in the Himalayan region and a significant upward trend in the residual branches of the Gangdise Mountains. More than 75% of the regions exhibit no persistent trend in CUE changes. (3) Vegetation type is the main determinant of the range and characteristics of vegetation CUE changes, while the geographical location and climatic conditions affect the variation pattern. CUE in the southern and northern regions of Nyingchi at 28.5°N exhibits different responses to temperature and precipitation changes, with temperature having a more significant impact on CUE.

Cirques of the Southeastern Tibetan Plateau and Their Links to Climatic and Non-Climatic Factors.

Cirque morphology is used to reflect the patterns of paleoclimate, paleoglaciation, and landscape evolution. Cirque study has been conducted in the Gangdise Mountains of the southern Tibetan Plateau (TP) and the central TP (dominated by a weak Indian summer monsoon (ISM) or a continental climate). This study focused on the cirques in the southeastern TP, which is dominated by a strong ISM, to analyse the controlling factors on cirque morphology. A total of 361 cirques were mapped in the Taniantaweng Range of the southeastern TP, and their metrics were calculated. The results showed that the cirque sizes increased with temperature and decreased with precipitation, which may be due to the development of valley-type glaciers and the effect of non-climatic factors. The cirques tended to face NE, implying that they prefer leeward slopes, and they were under the ‘morning–afternoon’ effect. With altitude, the tendency of the cirque aspect shifted from N to SE, and the cirque size decreased. The former may indicate the ability of the high altitude to support cirque development on climatically unfavourable slopes; the latter may be due to the development of valley-type glaciers or insufficient space for cirque development. The cirque size and shape did not show statistical differences between aspects. The cirques on soft bedrocks had larger heights than those on hard bedrocks, indicating that soft bedrocks promote subglacial erosion. A comparison with the results of the western, central, and eastern sectors of the Gangdise Mountains and the central TP reveals that the strength of the ISM did not necessarily increase the cirque density but limited the cirque size on a regional scale. The CFA did not show a reverse relationship with precipitation, but it showed a positive correlation with the cirque Zmean, which implies that the CFA was greatly affected by altitude, and its distribution does not always reflect paleoclimatic patterns.

Palaeoclimate Reconstruction of the Central Gangdise Mountains, Southern Tibetan Plateau, Based on Glacier Modelling

Palaeoglacier modelling is an important approach for reconstructing the palaeoclimate. The timing of glaciations in the central part of the Gangdise Mountains has been constrained previously, but the palaeoclimate remains unclear. In this paper, the palaeo-temperature and precipitation of the early marine isotope stage (MIS) 2, the Last Glacial Maximum (LGM), and the early Holocene were reconstructed using coupled mass balance and ice flow models. The results show that a series of temperature changes (ΔT) and precipitation factors (Fp) resulted in optimum palaeoglacial extents. The modelled palaeoglaciers during the early MIS 2, the LGM, and the early Holocene cover areas of ~18.1 km2, ~17.4 km2, and ~16.3 km2, respectively, with ice volumes of ~2.18 km3, ~1.99 km3, and ~1.95 km3, respectively. Previous studies on ice cores, pollen samples, and lake sediments were referenced to narrow the range of palaeo-temperatures and precipitations. The reconstructed temperatures during the early MIS 2, LGM, and early Holocene were constrained to 2.4–2.9 °C, 2.15–3.05 °C, and 0.95–1.5 °C lower than today, respectively. Their precipitation levels were 60–80%, 50–80%, and 100–150% of the present-day level, respectively.

Rock glaciers in the Gangdise Mountains, southern Tibetan Plateau: Morphology and controlling factors

Rock glaciers are linked to palaeoenvironment, water storage, sediment transport, and natural hazards. Previous rock glacier studies have been conducted in many places globally, but detailed studies have not been done in the Gangdise Mountains of the southern Tibetan Plateau (TP). In this study, 132 rock glaciers were mapped in the western, central, and eastern sectors of the Gangdise Mountains and their metrics calculated. The smallest rock glacier length in the east and the increasing trends of rock glacier density and specific area eastward reflect the effect of temperature and precipitation. The decreasing trend of mean altitude and minimum altitude of the rock glacier front towards east highlight the role of precipitation. Rock glaciers with altitudes of 5143–5651 m above sea level (asl) tend to face N, but their vector strength values decrease with altitude. Rising above 5651 m asl, rock glaciers tend to face SE. These results imply the ability of high altitude to promote rock glacier development on climatically unfavourable slopes. Bedrocks that mainly produce finer or platy debris are rarely sources of rock glacier materials. High altitude may diminish this effect. Aspect does not affect rock glacier size and shape, but rock glaciers on northern slopes have lower altitudes than those on southern slopes due to the effect of solar radiation. Welch’s test shows that rock glacier size is mainly controlled by non-lithological factors. By comparing with the previous results of the TP, it is found that increasing temperature and precipitation increase rock glacier occurrence but limit its size.

Cirque Floor Altitude of the Gangdise Mountains and its Controlling Factors

The cirque floor altitude (CFA) was used to indicate the patterns of paleoprecipitation, paleocloudiness, palaeoglaciation, and paleo-equilibrium line altitude (ELA). However, CFA is also affected by non-climatic factors, which limits its efficacy of being a paleoclimatic indicator. This study focuses on the Gangdise Mountains with an aim to investigate the controlling factors on CFA and test the CFA efficiency as an indicator of paleoclimate. A total of 1652 cirques were identified, and their CFAs were analysed in this study. The results show that the lowest CFA is in the eastern part of the Gangdise Mountains, followed by the western and central parts. This spatial distribution is in contrast with that of precipitation. This means that the development of the cirque is favoured by high precipitation. The high CFA values on southern and western slopes are due to effects of solar radiation and wind. The weak correlation between the cirque height and CFA and their different spatial distributions imply that cirque deepening is not the main factor affecting CFA. Various bedrocks of cirques manifest different CFA values, while the spatial patterns of the CFAs in the western, central and eastern parts can be partly explained by their bedrock types. The CFA values of the Gangdise Mountains are higher than those of the central Tibetan Plateau (TP). The CFA spatial distribution of the central TP is in contrast with that of precipitation, highlighting that precipitation is the primary control of the CFA. The relief and glacier type significantly control the CFAs. These findings lead to the conclusion that CFA is not always an actual indicator of paleoclimate on a large regional scale.

Cirques of the central Tibetan Plateau: Morphology and controlling factors

Cirque morphology represents the characteristics of palaeoglaciations and palaeoclimate. This study mapped and analysed 70 cirques in the central Tibetan Plateau (TP) with dominant continental climate. The results show that from northwest to southeast, cirque dimensions (i.e., length, width, and area) increase, while cirque floor altitudes decrease. A likely reason is the high precipitation rate caused by the Indian summer monsoon in the southeastern part. The diversity of cirque aspect values indicates weak or inconsistent prevailing winds during cirque development. Cirques enlarge with altitude, which might imply that cirques at high altitudes developed early and thus increased in size. Cirque aspect diversity increases with altitude from 5100 to 5600 m above sea level (asl), which indicates the capacity of high altitudes to support cirques at less favourable slopes. If altitude increases above 5600 m asl, the diversity of cirque aspect first increases and then decreases, which may be because of local topography. Mountain orientation and lithology had an effect on cirque aspect/size. Cirque numbers and sizes were compared between western, central, and eastern sectors of the Gangdise Mountains in the southern TP with those in the central TP. This comparison showed that a strengthening Indian summer monsoon can raise the value of ‘cirque density’ (i.e., cirque number per unit area), promote glacier development into valley-type, and limit cirque enlargement. • Cirques of a climatic transitional zone of the central Tibetan Plateau were studied. • Climatic and non-climatic effects were analysed. • A comparison with cirques in the Gangdise Mountains is presented.

Integrated Assessments of Meteorological Hazards across the Qinghai-Tibet Plateau of China

Recent decades have witnessed accelerated climate changes across the Qinghai-Tibet Plateau (QTP) and elevated socioeconomic exposure to meteorological hazards. The QTP is called the “the third pole”, exerting remarkable impact on environmental changes in its surrounding regions. While few reports are available for addressing multi-hazard risks over the QTP, we develop an integrated indicator system involving multiple meteorological hazards, i.e., droughts, rainstorms, snowstorms and hailstorms, investigating the spatiotemporal patterns of major hazards over the QTP. The hazard zones of droughts and rainstorms are identified in the southern Gangdise Mountains, the South Tibet Valley, the eastern Nyenchen-Tanglha Mountains, the Hengduan Mountains and West Sichuan Basin. Snowstorm hazard zones distribute in the Himalayas, the Bayan Har Mountains and the central Nyenchen-Tanglha Mountains, while hailstorm hazard zones cluster in central part of the QTP. Since the 21st century, intensified rainstorms are detectable in the densely populated cities of Xining and Lhasa and their adjacent areas, while amplified droughts are observed in grain production areas of the South Tibet Valley and the Hengduan Mountains. Snowstorm hazards show large interannual variations and an increase in pastoral areas, although the overall trend is declining slightly. The frequency of hailstorms gradually decreases in human settlements due to thermal and landscape effects. Mapping meteorological hazards regionalization could help to understand climate risks in the QTP, and provide scientific reference for human adaptation to climate changes in highly sensitive areas.

Rapid expansion of lakes in the endorheic basin on the Qinghai-Tibet Plateau since 2000 and its potential drivers

The QTP (Qinghai-Tibet Plateau) holds the greatest concentration of high-elevation inland lakes in the world, and most of these lakes are located in the QTP endorheic basin. Accelerated lake expansion in the endorheic basin since 2000 has been confirmed by many studies, but there is disagreement as to which components of the water balance explain most of the lake expansion. In this paper, based on Landsat images, meteorological data, glacier data and permafrost monitoring data, we analyzed the spatial–temporal changes in lake area and further explored the driving factors behind rapid lake expansion in different zones in the endorheic basin. The results suggested that the spatial pattern of trends in lake area in the endorheic basin from 2000 to 2017 showed a southwest-northeast transition from contracting to slightly expanding to rapidly expanding. More importantly, the dramatic lake expansion observed in most regions was statistically significant (0.01 ~ 26.29 km2/yr). Although retreating glaciers may have contributed to lake growth, this can not fully explain the recent lake expansion. We find that increasing precipitation was the primary driver behind lake expansion, and that permafrost degradation accelerated lake expansion. Lakes on the northern slope of the Gangdise Mountains, fed by the most rapidly retreating glaciers, were relatively stable or even contracted. In contrast, most of the non-glacier-fed lakes in the Hoh Xil region and the central endorheic basin nevertheless experienced significant expansion and slight expansion, respectively, which were mainly attributed to the greatest increase in AP (annual precipitation). Remarkable lake expansion was found in the continuous permafrost zone. The increasing ALT (active layer thickness) and soil temperature of permafrost resulted in an increase in meltwater from ground ice, the partial release of soil moisture and an amount of unfrozen water content, which has contributed to supply lakes and accelerated lake expansion.

Palaeoglacial and palaeoenvironmental conditions of the Gangdise Mountains, southern Tibetan Plateau, as revealed by an ice-free cirque morphology analysis

Cirque morphology can be used to indicate patterns of palaeoglaciations and palaeoclimate. Many cirque morphological analyses have been conducted worldwide, but only a few studies focus on the Tibetan Plateau (TP). In this study, we mapped 1652 ice-free cirques in the western, central, and eastern sectors of the Gangdise Mountains, southern TP. We calculated the cirque size, shape, and topography, and categorized them into fifteen lithological units to study their morphological parameters. Results show that cirque size decreases from west to east, implying that the western sector frequently developed cirque-type glaciers or was eroded by dynamic glaciers during the initial period of cirque development. Bedrock type can also explain the difference in cirque size in the three sectors, as the dominating bedrocks of the cirques in the western sector are relatively ‘soft’. The relatively small L/W ratios for the cirques in the western sector implies the important effect of widening on cirque planar enlargement in this sector. The decreasing trend of L/H and W/H ratios and the increasing trend of A3D/A2D ratios from west to east imply the importance of deepening for the cirques in the eastern sector. Moreover, the different bedrock types may be attributed to the different cirque shapes. The NE-facing bias for the cirques reveals the impact of solar radiation. This implies that the Gangdise Mountains were characterized by a relatively low cloudiness during the ablation season. The E bias for the cirques in the eastern sector reveals that the Indian Summer Monsoon was not strong.

Analysis of the Contribution of Water Vapor from the Arabian Sea to the Local Rainstorm Process in Southern Xinjiang

In order to investigate the water vapor sources of summer precipitation in southern Xinjiang, especially Hotan area. Based on NCEP FNL 1°*1° analysis data and Xinjiang meteorological bureau area numerical operation prediction, a local precipitation event in southern Xinjiang on June 26 was analyzed, and the results showed that the water vapor involved in this process originated from the northwestern Gangetic Plain and was transported along the Indus River plain and over the northwestern end of the mountains. Driven by the Iranian low-pressure trough, water vapor at 500 hPa was transported across the northwestern end of the Gangdise Mountains, past Georgoli Peak, and northwest over the Kunlun Mountains to arrive in southern Xinjiang. And a zonal profile was made along the northern foothills of the Kunlun Mountains (latitude 36°N), and the width was limited to the longitude range [70°E, 80°E] and the height range [500 hPa, 300 hPa] according to the water vapor channel scope of the process. In the first 24 hours after the end of the precipitation process, the total water vapor input and transmission amount was more than 3*107kg. That is, the water vapor transmitted over the preceding 24 hours far exceeded the precipitation during the precipitation event. So, under the combined influence of the Iranian vortex and equatorial vortex, moisture from the Arabian Sea at heights above 500 hPa can directly cross the Indus River plain traverse the Qinghai-Tibet Plateau and reach the southern region of Xinjiang. Therefore, the southern upper air passage is an important water vapor source in southern Xinjiang. Under appropriate conditions, it can cause short-term local heavy rainfall and lead to secondary meteorological disasters such as debris flow.

Quaternary glaciations in the Lopu Kangri area, central Gangdise Mountains, southern Tibetan Plateau

The Gangdise Mountains are located in a transition zone between the Indian Summer Monsoon-dominated Himalaya Mountains and the Westerlies-dominated Qiangtang Plateau. The timing and extent of the paleoglaciations in the central Gangdise Mountains remain unclear. We investigated the glacial history of the southeastern slopes of Lopu Kangri using 10Be exposure dating and summarized the dating results for the western and eastern sectors of the Gangdise Mountains. Glacial events were constrained to ≥243.88 ± 25.88 ka, ≥ 43.09 ± 4.18 ka, 24.19 ± 2.29 ka, 19.78 ± 1.9 ka, 10.62 ± 1 ka, 2.75 ± 0.37 ka, 1.8 ± 0.18 ka, 0.32 ± 0.04 ka and 0.22 ± 0.04 ka, representing paleoglaciations which occurred during marine isotope stage (MIS) 8/7 or earlier, MIS 3 or earlier, early MIS 2, the global Last Glacial Maximum (LGM), the early Holocene, the Neoglacial and the Little Ice Age (LIA). Evidence of MIS 5 or earlier glaciations, and the glaciations during MIS 3, early and late MIS 2, the global LGM and the LIA, can be found in the western or eastern sectors of the Gangdise Mountains. The spatial trend in ΔELA values in the Gangdise and surrounding mountain ranges would appear to have been controlled by particular precipitation distribution patterns. The glacial events identified in the Gangdise Mountains during MIS 2, the Neoglacial and the LIA appear consistent with previously-identified cold periods. Precipitation was most likely a contributory cause of the glaciations during the MIS 3, early Holocene, the Neoglacial and the LIA.

Glacier change in the Gangdise Mountains, southern Tibet, since the Little Ice Age

Delineating glacier change during the Little Ice Age (LIA) is of great importance when attempting to understand regional climatic changes and can also help to improve the understanding of any predictions of future glacial changes. However, such knowledge is still lacking for some critical regions of the Tibetan Plateau (TP). In this study, we mapped 4188 contemporary glaciers and reconstructed 1216 LIA areas of glacial coverage in the Gangdise Mountains to the north of the Himalaya using Google Earth satellite imagery. We estimated their paleoglacial areas and equilibrium line altitudes (ELAs) based on the toe-to-headwall altitude ratio (THAR) method. Results show that most glaciers are small (<1 km2), with slope/hanging glaciers the most common (2844 out of 4188 glaciers), while valley glaciers have the greatest coverage (1009.0 km2 out of a total area of 1723.7 km2). Contemporary glaciers have retreated significantly since the LIA, with reductions in length of between 5.5% and 94.7% (mean glacier length 696 m; mean reduction in length 41.7%) and reductions in glacier area of between 4.1% and 94.9% (mean glacier area 0.42 km2; mean reduction in area 44.8%). These reductions have occurred under different local climatic and topographic conditions. The contemporary ELA ranges from 5516 to 6337 m asl; the LIA ELA ranged from 5476 to 6329 m asl. Contemporary and LIA ELA values rise from southeast to northwest. As a general rule, the rise in the ELA value decreases from the eastern to the central Gangdise Mountains and then increases westward, with a mean ELA rise of 45 m. Multiple regression models suggest that 46.8% of the glacier area loss can be explained by glacier elevation, area, and slope. However, only 15.5% of the rise in ELA values can be explained by glacial geometric, topographic, or locational parameters. The spatial pattern of modern ELA values in this region appears inversely related to precipitation, which decreases from southeast to northwest, implying that precipitation is one of the key controls of ELAs. This is also consistent with results from elsewhere in High Asia. In contrast to the Gangdise Mountains' eastern and western sectors, glaciers in the central sector have undergone less change, i.e., in terms of reductions in length, area loss, and rises in ELA. Topography can of course also influence glacial change by creating shielding and/or rainshadow effects and by affecting local temperatures.

Combined ICESat and CryoSat-2 Altimetry for Accessing Water Level Dynamics of Tibetan Lakes over 2003–2014

Long-term observations of lake water level are essential to our understanding of the evolution of Tibetan lake system. CryoSat-2 radar altimetry data over the Tibetan Plateau (2010–2014, P2) is used to extend lake level measurements from ICESat laser altimetry (2003–2009, P1). This study evaluates the performance of CryoSat-2 data by comparing with gauge-based water levels that are calibrated by ICESat-observed water level time series, and quantifies the uncertainty of water-level change rate estimates from satellite altimetry measurements. We completely investigate the 131 lakes that were observed by both ICESat and CryoSat-2. The mean change rate of water level for all of examined lakes in P2 (0.19 ± 0.03 m·year–1) is slightly lower than that (0.21 ± 0.02 m·year–1) observed in P1. The extended lake level time series also indicates that, in the past few years, lakes in the Northern Changtang (especially in Hol Xil) showed accelerated growth; and that the extensive lake level rises north to the Gangdise Mountains, during 2003–2009, were found dampened during the CryoSat-2 observation period. The spatio-temporal heterogeneity of precipitation observed from weather stations can be used to partly explain the observed temporal pattern of lake level changes over different sub-zones of the plateau.

Risk analysis of snow disaster in the pastoral areas of the Qinghai-Tibet Plateau

Snow disaster is one of the top ten natural disasters worldwide, and the most severe natural disaster to affect the pastoral areas of the Qinghai-Tibet Plateau. Based on the hazard harmfulness data collected from historical records and data collected from entities affected by this hazard in 2010, a comprehensive analysis of the 18 indexes of snow disaster on the Qinghai-Tibet Plateau was conducted, encompassing the hazard harmfulness, the amount of physical exposure the hazard-bearing entities face, the sensitivity to the hazard, and the capacity to respond to the disaster. The analysis indicates that: (1) areas at high-risk of snow disaster on the Qinghai-Tibet Plateau are located in certain areas of the counties of Yecheng and Pishan in the Xinjiang region; (2) areas at medium-risk of snow disaster are found between the Gangdise Mountains and the Himalayas in the central-western part of the Qinghai-Tibet Plateau, and the southeastern part of the southern Qinghai Plateau; (3) the risk of snow disaster is generally low throughout the large area to the south of 30°N and the region on the border of the eastern Qinghai-Tibet Plateau. Overall, the risk of snow disaster in high-altitude areas of the central Qinghai-Tibet Plateau is higher than that at the edge of the plateau.

Palynological stratigraphy of the Late Cretaceous and Cenozoic collision-related conglomerates at Qiabulin, Xigaze, Xizang (Tibet) and its bearing on palaeoenvironmental development

The stratigraphy, age, depositional environment and correlation of the collision-related variegated sandstone and conglomerate beds exposed along the southern side of the Gangdise Mountains to the north of the Yarlung Zangbo suture in the Xigaze region, Xizang (Tibet) have been much debated. Generally referred to as the Dagzhuka Formation, these beds of great thickness have, until recently, not been reported to contain any convincing fossils. Two distinctly different palynological assemblages, indicating Late Cretaceous and Oligocene–Early Miocene ages respectively, have now been recovered from lithologically distinguishable units of the sedimentary succession at Qiabulin to the west of the town of Xigaze. This means that instead of one stratigraphic unit, as has been generally accepted hitherto, at least two are represented. As a result, the Dagzhuga Formation is considered here to refer only to the Cenozoic deposits and the Qiabulin Formation, previously regarded as a synonym, is resurrected to accommodate the Cretaceous beds. These two formations were juxtaposed by tectonic movements. Our finding indicates that the stratigraphic successions on the southern Laurasian continental margin of Xizang reflect changes from a deep forearc basin through shallow littoral environments to a mountainous landscape during the Late Cretaceous and early Cenozoic. This interpretation compares well with those documented from the Gamba and Tingri districts to the south of the Yarlung Zangbo suture.

Climatic changes in the Qinghai-Xizang (Tibetan) region of China during the Holocene

Climatic changes in the Qinghai-Xizang Plateau of China were studied by analyzing the composition of peat and layers of sand and gravel distributed along the southern slopes of Nianqing-Tanggula and Gangdise Mountains, cross sections of deposits near a number of interior lakes in Xizang, past glacial variations on the southern slope of Nianqing-Tanggula Mountain, and landform changes south of the Yaluzangbu River. Such geologic evidence suggests a division of five climatic periods since the beginning of the Holocene: (1) The Wumadung interval, 10,000–7500 yr B.P., slightly cold and dry; (2) Qilongduo interval, 7500-3000 yr B.P., warm and moist; (3) the mid-Neoglacial period, 3000-1500 yr B.P., cold, except between 2500 and 200 yr B.P. when it was warmer; (4) the Dawelong interval, 1500-300 yr B.P., mild; and (5) the Little Ice Age, 300-0 yr B.P., cold. These changes progressed in a similar but not identical pattern as those in the northeastern part of China and in the northern region of Europe.