The challenge of dating early pleistocene fossil teeth by the combined uranium series–electron spin resonance method: the Venta Micena palaeontological site (Orce,Spain)     

Mathieu Duval  Christophe Falguères  Jean‐Jacques Bahain  Rainer Grün  Qingfeng Shao  Maxime Aubert  John Hellstrom  Jean‐Michel Dolo  Jordi Agusti  Bienvenido Martínez‐Navarro  Paul Palmqvist  Isidro Toro‐Moyano 《第四纪科学杂志》2011,26(6):603-615

The palaeontological site of Venta Micena (Orce, Andalusia, Spain) lies in the eastern sector of the Guadix–Baza basin, one of the best documented areas in Europe for Plio‐Pleistocene biostratigraphy. The combination of biochronological and palaeomagnetic results, combined with the radiometric data obtained for Atapuerca Sima del Elefante, indicated that the Venta Micena stratum was formed between the Jaramillo and Olduvai palaeomagnetic events, most likely between 1.22 and 1.77 Ma. Five fossil teeth from two outcrops (sites A and B) were selected to assess the potential of combined uranium series–electron spin resonance (US‐ESR) dating of Early Pleistocene sites. Although the US‐ESR results of the first outcrop showed a large scatter between the three teeth, the mean age of 1.37 ± 0.24 Ma can be considered a reasonable age estimate for Venta Micena. The mean ESR age of 0.62 ± 0.03 Ma obtained for site B seems to be a severe underestimation when compared with the independent age control. This underestimation is attributed to a relative recent U‐mobilization event that led to some U‐leaching. The results show that any ESR age calculations of old samples are extremely sensitive to variations in the measured ²³⁰Th/²³⁴U ratios in dental tissues. Although the results demonstrate that ESR can in principle be applied to Early Pleistocene sites, they also reveal the complexity of dating such old teeth. It is necessary to continue research in several directions, such as study of the behaviour of ESR signals in old teeth and understanding recent U‐mobilization processes, to improve the reliability of the combined US‐ESR dating method applied to Early Pleistocene times, a period for which the number of available numerical dating techniques is very limited. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Glacial forest refugium in Howard Valley,South Island,New Zealand     

Maureen J. Marra  Glenn D. Thackray 《第四纪科学杂志》2010,25(3):309-319

Fossils of forest habitat beetles and leaves of Nothofagus menziesii provide evidence of a forest refugium at times between ca. 34 000 and ca. 18 500 cal. a BP at an upland site in Howard Valley, located adjacent to glaciated valleys in South Island, New Zealand. The stratigraphy of the glacial‐aged terrace sequence of organic‐rich silts and fluvial sand/gravels indicates that soil development occurred episodically for around 15 000 a. Fifty‐four beetle taxa represent seven habitat types: forest, forest or scrub, riparian and aquatic, litter, grass/tussock, marshland and moss habitats. Leaf and beetle fossils indicate that forest dominated by N. menziesii persisted at the site for most of the time period represented, and tree line taxa such as Taenarthrus sp. 1 (Carabidae) and Podocarpus sp. (Podocarpaceae) indicate that the site may represent the upper tree limit for full‐glacial time. The finding of forest at this elevated site adds to the growing fossil evidence for multiple forest refugia in New Zealand during the last glaciation and is consistent with the pollen records, which have consistently indicated the presence of forest species during the last glaciations. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

Observations and model estimates of diurnal water temperature dynamics in mosquito breeding sites in western Kenya     

K. P. Paaijmans  A. F. G. Jacobs  W. Takken  B. G. Heusinkveld  A. K. Githeko  M. Dicke  A. A. M. Holtslag 《水文研究》2008,22(24):4789-4801

Water temperature is an important determinant of the growth and development of malaria mosquito immatures. To gain a better understanding of the daily temperature dynamics of malaria mosquito breeding sites and of the relationships between meteorological variables and water temperature, three clear water pools (diameter × depth: 0·16 × 0·04, 0·32 × 0·16 and 0·96 × 0·32 m) were created in Kenya. Continuous water temperature measurements at various depths were combined with weather data collections from a meteorological station. The water pools were homothermic, but the top water layer differed by up to about 2 °C in temperature, depending on weather conditions. Although the daily mean temperature of all water pools was similar (27·4–28·1 °C), the average recorded difference between the daily minimum and maximum temperature was 14·4 °C in the smallest versus 7·1 °C in the largest water pool. Average water temperature corresponded well with various meteorological variables. The temperature of each water pool was continuously higher than the air temperature. A model was developed that predicts the diurnal water temperature dynamics accurately, based on the estimated energy budget components of these water pools. The air–water interface appeared the most important boundary for energy exchange processes and on average 82–89% of the total energy was gained and lost at this boundary. Besides energy loss to longwave radiation, loss due to evaporation was high; the average estimated daily evaporation ranged from 4·2 mm in the smallest to 3·7 mm in the largest water pool. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

Two paleoecological histories spanning the period of human settlement in southeastern Brazil     

Marco F. Raczka  Paulo E. De Oliveira  Mark Bush  Crystal H. McMichael 《第四纪科学杂志》2013,28(2):144-151

The absence of human occupation sites in southeastern Brazil during the mid Holocene has been referred to as the 'Archaic Gap' (8970–1940 cal. a BP) and is predicted to have resulted from increased aridity. A ca. 14 000 cal. a pollen history from two well‐dated lake sediment cores located within the archeological district of Lagoa Santa, in the State of Minas Gerais, southeastern Brazil, was used to test this hypothesis. Our analyses indicated that the present cerrado and tropical semi‐deciduous forest mosaic persisted throughout the mid Holocene, until ca. 5500 cal. a BP, and the Lagoa Santa region did not experience especially dry conditions during the Holocene period. The early Holocene pollen spectra contained an assemblage of cold‐adapted taxa such as Podocarpus, Myrsine and Araucaria, co‐occurring with taxa from cerrado, e.g. Caryocar. A replacement of cold taxa by the modern cerrado–semi‐deciduous forest vegetation took place progressively, but appears to have been completed by the mid Holocene. No evidence of sustained drought was found in sedimentation or forest composition, nor any prolonged dry event in the study region. Holocene dryness as an explanation for the abandonment of Lagoa Santa region is not supported by the palynological analyses conducted in this study. Rather it is suggested that unpredictable climate may have underlain that abandonment. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Vegetation in western Central Mexico during the last 50 000 years: modern analogs and climate in the Zacapu Basin     

A. Correa‐Metrio  S. Lozano‐García  S. Xelhuantzi‐López  S. Sosa‐Nájera  S. E. Metcalfe 《第四纪科学杂志》2012,27(5):509-518

The late glacial and the transition towards the Holocene marked a period of significant environmental change at a global scale. In western Central Mexico, few records span beyond the Holocene, and little is known about Pleistocene climatic and environmental variability. Here we report on the pollen record of a composite sequence made of three cores that cover the last 50 ka (thousands of calibrated radiocarbon years before present) in the Zacapu Basin, western Central Mexico (～1970 m asl). The conjunction of modern pollen rain from the area with the composite fossil pollen sequence from cores Cantabria, Cantabria 1 and CEMCA Point‐1 provided a detailed history of the vegetation of the area. Recognition of modern environmental patterns through individual modern pollen taxa proved difficult, but multivariate analysis separated different vegetation types. No‐modern‐analog communities relative to the modern vegetation cover of the area were evident, especially during periods of drought. Apparently, summer precipitation was significant before 40 ka and after the deglaciation. However, this moisture source declined from ～40 to 10 ka because tradewinds from the Gulf of Mexico were blocked by the eastern mountains of Central Mexico as a result of lower temperatures. By contrast, westerly and northerly winds were enhanced by maximum ice cover from ～19 to 17 ka, providing abundant winter precipitation and therefore preventing extreme drought in the area. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

140OΜα前的后生动物实体化石?     

胡健民  孟庆任  李文厚 《地球科学与环境学报》1991,(2)

本文首次报道了在我国豫西晚前寒武系白草坪组中发现的一种可能的蠕虫状后生动物实体化石:Ruyangia Cylindrica Hu et Meng,1989。化石产于砂岩表面浪成波痕之波谷中,圆筒状,已压扁,中空,可见长度4.5～9.5cm,直径4mm左右,虫体外壁具体环,环背间距1.5～2mm,虫体一端较大,具平行纵向边缘的纵纹,可能为头部;另一端渐尖,可能为尾部。与该实体化石伴生的有大量遗迹化石。已知白草坪组的时代超过1400Ma,因此,该实体化石的发现对研究地球上后生动物起源与早期演化等具重要意义。  相似文献   

Holocene environmental reconstruction from deltaic deposits in northeast Greenland     

Hanne H. Christiansen  Ole Bennike  Jens Bcher  Bo Elberling  Ole Humlum  Bjarne H. Jakobsen 《第四纪科学杂志》2002,17(2):145-160

Terraces of different age in the Zackenberg delta, located at 74°N in northeast Greenland, have provided the opportunity for an interdisciplinary approach to the investigation of Holocene glacial, periglacial, pedological, biological and archaeological conditions that existed during and after delta deposition. The raised Zackenberg delta accumulated mainly during the Holocene Climatic Optimum, starting slightly prior to 9500 cal. yr BP (30 m a.s.l.) and continued until at least 6300 cal. yr BP (0.5 m a.s.l.). Evidence of sea‐level change is based on conventional ¹⁴C dates of shells from the marine delta bottomsets, ¹⁴C AMS dating of macroscopic plant material from the foresets and of fluvial deposits. Arthropod and plant remains from 7960 cal. yr BP in the delta foresets include the oldest evidence of the arctic hare in Greenland and evidence of a rich herb flora slightly different from the modern flora. Empetrum nigrum and Salix herbacea remains indicate a summer temperature at least as high as today during delta deposition. Post‐depositional nivation activity, dated by luminescence, lichenometry and Schmidt Hammer measurements indicate mainly late Holocene activity, at least since 2900 yr BP, including Little Ice Age (LIA) avalanche activity. Pedological analyses of fossil podsols in the Zackenberg delta, including ¹⁴C AMS dating of selected organic rich B‐horizons, show continued podsol development during the Holocene Climatic Optimum and into the subsequent colder period of the late Holocene, until 3000–2400 yr BP. A Neo‐Eskimo house ruin found on the lower part of the delta, presently being eroded by the sea, is dated to AD 1800. It presumably was abandoned prior to AD 1869, and suggests that some of the last Eskimos that lived in northeast Greenland might have occupied the Zackenberg delta. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

青田芝溪头鹤溪群浅变质岩系中发现动物化石     

朱德寿  胡耀华  石关根 《浙江国土资源》1994,(2)

作者于1993年4月在浙江青田芝溪头鹤溪群剖面上采集了白云质大理岩标本样品，送南京地质古生物研究所进行标本浸泡处理。首次获得鱼骨、管状化石及土菱子介等海相化石，经鉴定认为其时代可能属石岩—二叠纪。本文根据以往的同位素资料、沉积环境分析和区域对比，认为这套变质岩系的原岩为二叠纪含煤沉积岩，可与福建的童子岩组中上部层位对比。  相似文献   

海相遗迹化石对显生宙生物大辐射事件的响应^*          下载免费PDF全文

许晴旸  范若颖  龚一鸣 《古地理学报》2023,25(2):431-450

通过系统梳理前寒武纪和显生宙海相遗迹化石记录及笔者自己的研究,发现在寒武纪生命大爆发、奥陶纪生物大辐射、中生代海洋革命共3次里程碑式的生物大辐射过程中,海相遗迹化石的属级多样性变化和歧异度增减均与生物多样性呈正相关,生物扰动强度和深度明显增加,造迹生物的觅食策略和行为习性多样化明显增多。寒武纪生命大爆发时期,最有代表性的生物行为变化是出现了具有垂向分量的潜穴; 奥陶纪生物大辐射期间,海相遗迹化石的分布逐渐从滨、浅海扩展至半深海和深海,表现为造迹生物群落栖息地的扩张; 中生代海洋革命时期,海相和陆相遗迹化石同步增加,生物对生态空间利用的深度、广度和集约性同步增强,遗迹化石面貌表现为深海雕画迹的多样性和歧异度大幅增加、形态类型多样、多种觅食策略共存。地史时期的海相遗迹化石面貌受环境外因和生物内因控制,表现出形态由简到繁、分布范围由小到大的变化趋势,对生态空间的利用表现为由沉积物表层至浅层再到深层、由二维到三维、由局域(浅水)到广域(浅水和深水以及陆地)的发展,印证了生物获取生态机会的过程。  相似文献   

内蒙古赤峰市敖汉旗宾夕法尼亚亚纪酒局子组植物化石     

李斌  杨涛  杨佳林  杨雅军  陈井胜  李伟  刘淼 《地质与资源》2022,31(4):465-472

内蒙古赤峰市敖汉旗水泉南山附近采集到酒局子组植物化石,通过系统鉴定,共计12属18种,包括楔叶类、木贼类、瓢叶类、真蕨和种子蕨类及科达类等,其中以Pecopteris (Asterotheca) hemitelioides和Cordaites principalis为代表,均为晚古生代华夏植物群常见分子或代表分子,表明赤峰地区在宾夕法尼亚亚纪时应属华夏植物地理大区.酒局子组的时代应当归于宾夕法尼亚亚纪.植物群中发现高大的科达类,并有大量反映热带、亚热带气候的真蕨和种子蕨类,显示该区当时应处于亚热带-暖温带雨量充沛的湿热环境.  相似文献