西藏仲巴县隆格尔地区渐新统日贡拉组孢粉组合的发现及其意义

笔者在西藏仲巴县隆格尔地区进行1∶5万区域地质调查过程中,在渐新统日贡拉组地层中上部采集了孢粉化石,为裸子植物花粉(Abietineaepollenites sp.、Pinuspollenites sp.、Tsugaepollenites sp.、Piceapollis sp.)、被子植物花粉(Artemesiaepollenites sp.、Betulaceoipollenites sp.、Rutaceoipollenites sp.、Betulaepollenites sp.、Graminipidites sp.)、蕨类植物孢子(Deltoidospora sp.、Lycopodiumsporites sp.、Toroisporis sp.)等组合,时代属于古近纪渐新世,可能跨及中新世。孢粉组合的发现对隆格尔地区日贡拉组地层的划分、对比及沉积时期的古气候、古地理和古植被的分析提供了依据,丰富了地层的古生物数据。在这一时期,古植被以松科和蒿属为主,反映了一次与构造运动密切相关的古环境变化事件,同时指示了古气候的轨迹及特征,揭示了构造的演化发展和沉积盆地响应过程与古气候的耦合关系。     

Reorganization of the Asian Monsoon System at About 2. 6 Ma Ago and Its Implications for the Rising of the Tibetan Plateau

REORGANIZATION OF THE ASIAN MONSOON SYSTEM AT ABOUT 2.6 Ma AGO AND ITS IMPLICATIONS FOR THE RISING OF THE TIBETAN PLATEAUheChineseResearchFoundation(KZ 951 A1 2 0 4 )     

河南西峡晚白垩世恐龙蛋化石壳碳同位素组成特征及其意义

利用显微镜和碳同位素分析法对自河南西峡盆地晚白垩世的１６枚恐龙蛋化石进行了研究。在显微镜下观察到恐龙蛋化石壳由原生碳酸盐矿物和次生碳酸盐矿物两部分组成。利用图像分析法得到了两者所占的比例分别为６０．５％和３９．５％。恐龙蛋内充填的次生碳酸盐矿物的δ＾１３Ｃ值在－５．６３‰￣－５．６８‰之间,平均为－５．６５‰。恐龙蛋化石壳的δ＾１３Ｃ同位素值在－５．８８‰￣－７．７９‰之间。经计算,获得了恐龙蛋壳     

Stratigraphy and structural summary of the Cooma Metamorphic Complex

A technique for obtaining age estimates for regolith profiles in Australia, based on the oxygen‐isotope composition of the clay mineral assemblage in a profile, is applied to a variety of regolith profiles and kaolinitic sediments from across Australia. Excluding monsoonal regions in the north of the continent, it is possible to distinguish profiles formed in the Late Mesozoic‐Early Tertiary (δ¹⁸O values between +15 and +17.5%δō) from profiles formed in post‐mid‐Tertiary times (>+17.5%ō). In addition it is concluded that there remain widespread remnants of a deep‐weathered regolith which developed in pre‐Late Mesozoic (Early Cretaceous or Jurassic?) times when Australia was at high latitude. The low δ¹⁸O values associated with clays formed in pre‐Late Mesozoic times (+10 to +15%o) suggest that deep weathering took place in a cool to cold and presumably humid climate, contrary to the traditional belief that deep weathering requires tropical to subtropical temperatures. The formation of deep‐weathered profiles at high latitude in a comparatively cold climate may be linked in part to higher past atmospheric CO₂ levels.     

Interprétation paléoclimatique et paléohydrologique de l'origine des nodules carbonatés des terrasses du Niger aux environs de Niamey (Niger) au moyen des outils isotopiques et géochimiques

Résumé

Cette étude se situe au Niger en région sahélienne, près de la ville de Niamey, et a pour but la reconstitution des conditions de formation des différents types de nodules carbonatés que l'on trouve sur les anciennes terrasses du fleuve Niger. La chimie, la géochimie isotopique (radioactif et stable) et l'étude minéralogique des carbonates ont été utilisées pour dater les nodules et reconstituer les conditions de précipitation. Les résultats montrent bien l'authigénie et l'accrétion dans le premier mètre du sol des nodules de la vallée du Niger. L'âge de formation des nodules apparaît ancien, entre 1500 et 7000 ans BP. Cette plage de temps correspondrait à une période transitoire entre les conditions de sécheresse actuelles et l'importante phase humide régionale située entre 10 000 et 4500 ans BP. Cependant, la diversité des âges obtenus, ainsi que les différentes formes de nodules montrent que des facteurs très locaux (état de la nappe localement, végétation, texture du sol) ont dû aussi jouer un rôle dans le processus de précipitation des nodules.     

Modern and early Holocene mollusc fauna of the Ounianga lakes (northern Chad): implications for the palaeohydrology of the central Sahara

The fresh and saline lakes of Ounianga Kebir and Serir in northeastern Chad are among the very few permanent aquatic ecosystems currently existing in the hyper‐arid core of the Sahara desert. The confirmed modern fauna of aquatic molluscs at Ounianga comprises three widespread species (Melanoides tuberculata, Biomphalaria pfeifferi and Lymnaea natalensis), of which only the first appears to maintain a thriving population. We recovered seven more species of gastropods, among which one is new to science (Gabbiella ouniangaensis), and one bivalve species from early Holocene outcrops of diatomaceous limestone at Ounianga Serir. All species except one are known to be commonly spread between lake and river systems by birds, and in its entirety this species‐rich fossil mollusc fauna of Ounianga Serir resembles that of other Saharan lake sites known to have been hydrologically isolated during the early Holocene. The impoverished modern mollusc fauna, which lacks even the widespread and opportunistic species Bulinus truncatus, may have become established relatively recently through new colonisation events, following eradication of the early Holocene mollusc fauna during a later episode of high salinity or desiccation. Copyright © 2011 John Wiley & Sons, Ltd.     

Quantitative inter‐annual and decadal June–July–August temperature variability ca. 570 BC to AD 120 (Iron Age–Roman Period) reconstructed from the varved sediments of Lake Silvaplana,Switzerland

Annually resolved June–July–August (JJA) temperatures from ca. 570 BC to AD 120 (±100 a; approximately 690 varve years) were quantified from biogenic silica and chironomids (Type II regression; Standard Major Axis calibration‐in‐time) preserved in the varved sediments of Lake Silvaplana, Switzerland. Using 30 a (climatology) moving averages and detrended standard deviations (mean–variability change, MVC), moving linear trends, change points and wavelets, reconstructed temperatures were partitioned into a warmer (+0.3°C; ca. 570–351 BC), cooler (?0.2°C; ca. 350–16 BC) and moderate period (+0.1°C; ca. 15 BC to AD 120) relative to the reconstruction average (10.9°C; reference AD 1950–2000 = 9.8°C). Warm and variable JJA temperatures at the Late Iron Age–Roman Period transition (approximately 50 BC to AD 100 in this region) and a cold anomaly around 470 BC (Early–Late Iron Age) were inferred. Inter‐annual and decadal temperature variability was greater from ca. 570 BC to AD 120 than the last millennium, whereas multi‐decadal and lower‐frequency temperature variability were comparable, as evident in wavelet plots. Using MVC plots of reconstructed JJA temperatures from ca. 570 BC to AD 120, we verified current trends and European climate model outputs for the 21st century, which suggest increased inter‐annual summer temperature variability and extremes in a generally warmer climate (heteroscedasticity; hotspot of variability). We compared these results to MVC plots of instrumental and reconstructed temperatures (from the same sediment core and proxies but a different study) from AD 1177 to AD 2000. Our reconstructed JJA temperatures from ca. 570 BC to AD 120 showed that inter‐annual JJA temperature variability increased rapidly above a threshold of ～10°C mean JJA temperature. This increase accelerated with continued warming up to >11.5°C. We suggest that the Roman Period serves with respect to inter‐annual variability as an analogue for warmer 21st‐century JJA temperatures in the Alps. Copyright © 2011 John Wiley & Sons, Ltd.     

A Porites lutea climate record from Sodwana Bay,South Africa

We report on a 41-year (winter 1970 to winter 2010) Porites lutea coral core climate record from Two-Mile Reef, Sodwana Bay, in the South-Western Indian Ocean. X-ray analysis, ultraviolet fluorescent photography and stable isotope (δ¹⁸O and δ¹³C) analysis revealed skeletal high-density, late-winter and low-density, late-summer bands with very little terrestrial humic input. An overall decrease in coral growth rate was seen over this period, possibly linked to global temperature and acidification trends. The stable isotopes δ¹⁸O and δ¹³C were predominantly out of phase, with calculated temperatures showing a slight increase over the 41-year period but with an overall decrease from 1994 to 2010. The insignificant ocean warming recorded in the coral supports the existence of a local, self-regulating, cold-water upwelling system from the adjacent shelf break and canyons that is potentially moderating coastal water temperature rise in Sodwana Bay.     

Taking varves to bits: Scanning electron microscopy in the study of laminated sediments and varves

Conventional high resolution studies of varved sediments are able to identify clastic and biogenic laminae, but are often unable to resolve the nature of fine-scale lamination contained therein. This intra-annual signal provides us with the highest potential resolution from the sedimentary record and can be resolved using scanning electron microscopy (SEM). Six case studies from lacustrine and marine settings are presented to illustrate the combination of clastic and biogenic fabric types typically found in laminated sediments. Clastic laminae fabrics include those which originate through grain settling and those which are event deposits. The correct identification of event deposits is essential if varves are to be used chronologically. SEM-based biogenic laminae fabric studies have identified seasonal faunal successions where individual laminae may be less than 100 thick and most recently, deep chlorophyll maxima (DCM) summer diatom floras, providing an insight into seasonal scale processes. High resolution lamina fabric studies can provide a basis for generating records of seasonal and inter-annual variability, thus contributing to our understanding of lacustrine and marine processes and palaeoenvironmental interpretation.