Late Quaternary environmental studies on salt lakes in western Rajasthan,India: a summarised view

The paper reviews pollen analytical and palaeoenvironmental work carried out on saline lakes in western Rajasthan, northwest India. The saline lakes are salient geomorphological features within the arid and semi-arid landscapes to the west of the Aravalli mountain ranges. Preliminary palynological work was carried out on two profiles from a gypsum-rich lake depression around Thob (District of Barmer). The varied pollen data are indicative of a fluctuating vegetational assemblage, possibly in response to local hydrological conditions and not necessarily indicative of climatic change. Pollen of Ephedra sp. (a typical desert species) in the lower levels suggests episodes of relatively dry conditions during the early phase of lake sedimentation at the end of the Pleistocene. Other work at four lake sites, on the basis of pollen analysis has indicated shifts in climatic and vegetational belts during the early Holocene, especially during the period of Indus Valley Culture. Later in the Holocene, between 5000 and 3500 yr BP, rainfall variations have been related to the dynamics of the monsoon. Pioneering geoarchaeological studies carried out at the palaeolithic site of 16 R and the adjacent Didwana lake have illustrated palaeoclimatic fluctuations and accompanying changes in cultural stages from the lower palaeolithic to mesolithic. These studies have been extended geochemically and sedimentologically through a detailed study documenting a history of salinity from 20000 to 13000 yr BP and freshwater conditions from 9000 to 6000 yr BP. Later studies have illustrated a sequence of changes reflecting summer and winter precipitation. These have indicated steppe vegetation during the last Glacial Maximum along with hypersaline lake conditions at Didwana, inferring a weakened summer monsoon and relatively high winter precipitation. The taxa indicative of both summer and winter precipitation in the mid-Holocene declined during the late Holocene, at the same time as falling lake levels around 4000 yr BP, a time when other lakes, at Sambhar, Lunkaransar and Pachpadra, also became ephemeral. © 1997 John Wiley & Sons, Ltd.     

Coleopteran evidence for a mosaic of environments at high altitude in the eastern Pyrénées,France, during the climatic transition between the Allerød and Younger Dryas

Late‐glacial environmental and climatic implications are inferred from an insect fauna from organic sediments infilling a palaeochannel on the banks of the River Têt, eastern Pyrénées, France. A pine cone in association with the insect fauna has been radiocarbon dated to 10 920 ± 60 yr BP, namely close to the Allerød – Younger Dryas boundary. Two distinct insect associations appear to be recognisable here. One is an assemblage typical of the high altitude forest and a second is characteristic of an alpine grassland. The close coexistence of these two assemblages is attributed to the climatic cooling towards the start of the Younger Dryas Stadial, when the forest cover broke up into remnant patches interspersed by alpine grassland. It is suggested that in a region of such high relief a mosaic of habitats may have been caused by patchy differences in insolation aspect, especially during a period of climatic deterioration. Copyright © 1999 John Wiley & Sons, Ltd.     

吐哈盆地北缘中侏罗世植物化石稳定碳同位素的古环境意义

新疆吐哈盆地北缘三道岭煤田中侏罗统西山窑组的植物化石属于Coniopteris-Phoenicopsis植物群的典型组合。从该植物群中挑选出优势属种,分别为似银杏、拟刺葵、枝脉蕨以及斯堪尼狭轴穗,对其进行稳定碳同位素分析。前3种为叶片化石,它们的δ13C值分布在-21.66‰~-23.83‰,属于典型的C3植物。最后一种为繁殖器官化石,其δ13C值为-20.91‰,比叶片的值高。将δ13C值根据公式转换为大气CO₂的δ13C_a值,发现基于银杏类叶片获得的现代和中侏罗世的δ13C_a值与其他方法获得的值相似。这说明银杏类叶片是重建地质历史时期δ13C_a的一类可靠植物,为今后研究中生代-新生代δ13C_a变化提供了一个简便而可行的方法。C_i/C_a比值是一重要的植物生理生态特征值,因此进一步将银杏类化石叶片的δ13C值换算成C_i/C_a。化石似银杏的C_i/C_a值为0.6,而现生银杏的C_i/C_a为0.63,二者相似。虽然三道岭地区中侏罗世的CO₂浓度约为现在的4.5倍,但是化石和现生银杏类植物的C_i/C_a值仍然保持恒定,表明银杏植物的气孔参数对CO₂变化比较敏感,是重建古CO₂浓度的良好指示植物。这也为判断一种植物能否用来重建古CO₂浓度提供了一种简便而有效的检测方法。     

珠江三角洲中部晚更新世以来的有孔虫记录与古环境演化*

珠江三角洲中部钻孔PRD20和PRD17晚第四纪以来的沉积记录较为完整,尤其是晚更新世海侵记录良好。以其为研究对象,对两孔的有孔虫微体动物群记录和沉积特征进行了分析和对比,并结合前人研究成果,重建珠江三角洲晚更新世以来的古环境演变,并着重分析了晚更新世海侵事件。约44500 cal a BP以前,研究区为河流环境,发育河道砂砾沉积。约44500—21300 cal a BP,发生晚更新世海侵,形成溺谷型河口湾,两孔沉积物中有孔虫的垂直分布记录了水体条件发生的多次变化,可辨识出2次海侵海退次级旋回;其中PRD20孔中有孔虫以滨岸广盐型占绝对优势,PRD17孔中以滨岸广盐型为主、海相—半咸水型有孔虫占有一定比例,表明研究区位于溺谷湾中径流与潮流共同作用的区域,且PRD20孔受径流影响更大。约21300 cal a BP后,受末次冰盛期海退影响,研究区暴露于地表遭受风化剥蚀,风化产物在PRD20孔表现为1层褐红色砂砾,在PRD17孔表现为1层花斑黏土。约8000 cal a BP,海平面回升导致河水滞留形成沼泽环境,PRD20孔发育1层泥炭层。约8000—5500 cal a BP,PRD20孔发育受径流影响较大的河口湾湾头沉积,仅在全新世海侵最盛时含有少量有孔虫记录。约5500 cal a BP后,研究区发育三角洲平原沉积。受构造抬升影响,PRD17孔地势较高,于约4700 cal a BP才开始重新接受沉积,零星出现潮水搬运而来的有孔虫。     

内蒙古中东部达里湖湖岸堤记录的12.5 cal ka BP以来湖面波动过程*

内蒙古中东部位于东亚夏季风过渡区,对气候变化响应敏感。广泛发育的湖泊沉积物提供了全新世以来的环境变化的理想材料。湖岸沉积物直接记录的古水位,与高分辨率的湖心钻孔记录相结合,有助于全面认识古气候的变化历史和湖面波动的定量重建。运用AMS¹⁴C测年和GPS、DEM及1︰5万地形图等相结合的方法确定了达里湖北侧湖岸堤的年代和高程,并结合湖岸堤剖面的沉积序列指示的湖面变化过程,重建了12.5 cal ka BP以来达里湖的波动历史。12.5 cal ka BP,达里湖湖面海拔高度约为1253,m,至12.3 cal ka BP湖面经历短暂上升,至海拔1266,m左右;之后湖面下降,至全新世早期(11.2 cal ka BP),水位降至1254,m左右;随后湖面开始逐步上升,10.7 cal ka BP湖面水位稳定在1274,m左右;全新世中期湖面继续上升至某一高度(至少在1291,m)后,于全新世晚期4.8 calka BP 湖面高度降至1279,m,并于4.6 cal ka BP湖面继续下降至1275,m的高度。通过对比湖心钻孔记录的湖泊波动历史以及区域湖泊沉积记录,认为达里湖的水位波动受东亚季风活动的影响,具有区域的一致性。达里湖的水位变化较区域内的其他湖泊更为强烈,认为除了受区域气候变化的影响外,达里湖全新世晚期的湖面下降可能还与区域内强烈的构造活动和西拉木伦河溯源侵蚀导致区域水系的改变有关。     

The Qijurittuq site (IbGk-3), Eastern Hudson Bay: An IPY Interdisciplinary Study

Geografisk Tidsskrift—Danish Journal of Geography 110(2):227–243, 2010

An interdisciplinary study was conducted at Qijurittuq (IbGk-3), an archaeological site located on Drayton Island along the eastern shore of Hudson Bay, Nunavik. Local Inuit made important contributions to the research. High school students participated in the field school, and elders shared their traditional knowledge. The elders expressed an interest in the source of the wood used to construct Qijurittuq's semi-subterranean dwellings, and this inspired us to expand our research in that direction. This interdisciplinary study included a reconstruction of the geomorphological and environmental history of Drayton Island, wood provenance and dendrochronology studies, research on house architecture and settlement patterns, and a zooarchaeological analysis. This paper synthesizes the preliminary results of this interdisciplinary investigation within the context of climate change. We discuss the persistence of semi-subterranean dwellings in eastern Hudson Bay long after they had been abandoned elsewhere. At Qijurittuq, their abandonment corresponds with the end of Little Ice Age. However, at the same time, the development of more permanent contact with Euro-Canadians was having a strong impact upon Inuit culture.     

Influence of precipitation and deep saline groundwater on the hydrological systems of Mediterranean coastal plains: a general overview

Abstract

The increasing water demand is a concern affecting many regions in the Mediterranean Basin. To overcome this situation rim countries resorted during the last decades to a massive mobilization of their water resources, often resulting in excessive water exploitation. In such a context, understanding the effects of present recharge and aquifer salinization is crucial for correct water management. Understanding the present hydrogeological situation of coastal plains requires the knowledge of both their past morphologic conditions and their recent geological evolution. Within this framework, this paper presents a review of water related problems in the Mediterranean Basin. It suggests a conceptual model for groundwater resources in Mediterranean coastal plains, deriving from the present and past recharge processes. Special attention is paid to providing a better understanding of climate change impacts on water quantity and quality, and conservation of ecological diversity.

Citation Re, V. & Zuppi, G. M. (2011) Influence of precipitation and deep saline groundwater on the hydrological systems of Mediterranean coastal plains: a general overview. Hydrol. Sci. J. 56(6), 966–980.     

Late Eocene foraminifers and palaeoenvironment,Cascade Seamount,southwest Pacific Ocean: implications for seamount subsidence and Australia Antarctica Eocene correlation

A Late Eocene foraminiferal fauna of free specimens is recorded from Cascade Seamount, a feature of volcanic origin, whose age and fauna were previously studied only in thin section. The fauna is of Late Eocene (P15) age because of the presence of Globigerapsis index, Globigerapsis rubriformis, Subbotina linaperta, Subbotina angiporoides and Chiloguembelina cubensis. Many typical Eocene indicators, such as Hantkenina, Pseudohastigerina and key globorotaliids, are absent. The age is a little older than that estimated for previous samples from the seamount. The fauna is dominated (78%) by benthic species, especially species of Cibicides that have greater affinities with New Zealand faunas than with coeval southern Australian faunas. The sediment and its fauna accumulated near the lower limits of wave activity, off the coast of a volcano that probably stood at least 400 m above sea level. The location has subsided nearly 1000 m over the past 40 million years to its present water depth of 1000 m, suggesting that the entire East Tasman Plateau was approximately 1000 m above its current depth at the time. Conditions were cool temperate and the fauna lacks any warm water indices, consistent with a palaeolatitude of 55–60°S, but also with cool waters at a time of oscillating conditions in southern Australia and also in Antarctica. There is essentially no infauna and the waters were highly oxygenated in the turbulent zone.     

The geology of Ewarara Intrusion,Giles Complex,Central Australia

Ewarara is a small layered ultramafic intrusion which forms part of the Giles Complex. The flat‐lying body displays both sub‐horizontal and vertical layering, which appear to have different origins. Petrographically the intrusion consists of a lower olivine bronzitite unit and an upper pyroxenite unit. These display a small cryptic variation with the upper layer being the more iron‐rich. Many of the primary igneous textures have been destroyed by deformational effects but the intrusion retains many features of a body formed by gravity accumulation of crystals precipitating from a magma. Crystallisation of the magma is believed to have occurred near the base of the crust.     

四川盆地西北缘早-中三叠世界线附近沉积岩地球化学特征及古环境意义

通过分析四川盆地峨眉山地区嘉陵江组-雷口坡组沉积岩元素地球化学及碳、氧同位素特征,探讨了其古环境意义,为四川盆地西北缘早-中三叠世古环境研究提供基础信息。结果表明：样品∑(CaO+MgO+LOI)为13.98%～93.31%,反映了相对动荡的沉积环境。δ¹³C值的变化范围是-6.95‰～0.36‰,δ¹⁸O值变化范围为-9.06‰～-0.99‰,δ¹³C值总体表现趋势为降低-升高-降低-升高。海水盐度呈现先升高、后降低、复又升高的多段式变化;海水温度7.11～34.94℃,平均温度21.99℃,古海水温度经历了降低-升高-降低的变化趋势,在早-中三叠世界线附近温度急剧升高。研究区整体处于氧化的沉积环境,间有贫氧的沉积环境出现。以上各个地球化学指标间耦合关系较好,一致反映了研究区早-中三叠世为相对潮湿-相对干热-相对潮湿气候下的海相沉积环境。