The relationship between Euramerican and Cathaysian tropical floras in the Late Palaeozoic: Palaeobiogeographical and palaeogeographical implications     

《Earth》2008,86(3-4):85-116

Wetland plant communities persisted though much of the Pennsylvanian in Euramerica and are the dominant coal forming vegetation in this region. Distribution of these floras show a dramatic decline at the end of the Carboniferous with many of the plant genera and species becoming extinct by the onset of the Permian. This has been correlated with climate change and in particular aridification associated with northwards plate motion and Euramerica moving into the doldrums, but is also associated with the Variscan orogeny and forefront destroying large areas of formerly lowland basinal settings. Other factors may include Pennsylvanian glaciations as evidenced by cyclothem and rhythmical deposition in lowlying wetland settings, and change in eustatic base level. Evidence from Euramerica demonstrates extinction of this kind of wetland biota by the earliest Permian and the development of drier floras including conifer dominated assemblages. However, new data from other parts of the world, most notably North China, confirm this model and highlight the presence of similar coal swamps ranging from the Late Pennsylvanian through the Permian. In this paper we summarise and synthesize recent taxonomic and systematic investigations undertaken on the plant fossils from the Pennsylvanian Benxi Formation – the oldest recognised wetland plant community in China – and the Early Permian Taiyuan Formation – the best preserved wetland plant community from China. Results indicate a remarkable similarity of the Pennsylvanian–Early Permian floras of North China with the older assemblages in the Pennsylvanian of Euramerica, and the presence of typical ‘Euramerican’ coal swamp plant families, genera and in some cases species in China. Conclusions include the presence of the Ameriosinian phytogeographical realm uniting Euramerica and northern Cathaysia at this time, coal swamps in the Permian of North China evolving from a ‘Euramerican’ origin, and the dramatic floral turnover at the end of the Carboniferous representing a regional event rather than a global extinction episode. Patterns of plant distribution through this interval have profound implications on established palaeogeographical models and support continental connection between Euramerica and Cathaysia before the end of the Carboniferous, contradicting ideas of Cathaysian island biogeography and biotic distinction. Continental connection appears to be related to glacial eustatic low-stand and previously shallow marine environments becoming vegetated. Also important is the fact that in both Euramerica and North China the pattern of floristic demise within wetland plant communities are similar to each other, implying the same causal mechanisms, with plants occupying waterlogged positions being the most severely devastated. However, ecosystem demise occurred at the end of the Carboniferous in Euramerica and in the middle Permian in North China, but in both cases the primary cause was climate change.  相似文献   

Cr-spinel/olivine and Cr-spinel/liquid nickel partition coefficients from natural samples     

Chusi Li  Edward M. Ripley  Edmond A. Mathez 《Geochimica et cosmochimica acta》2008,72(6):1678-1684

The Nernst partition coefficient of nickel (D^Ni) between Cr-spinel and silicate melt in natural systems has been investigated using mid-ocean ridge basalts (MORB) and other volcanic rocks. The Cr-spinel/olivine D^Ni values in volcanic rocks are between 1.2 and 0.3, indicating that the Cr-spinel/liquid D^Ni values vary from slightly higher to significantly lower than the olivine/liquid D^Ni values in natural systems. The Cr-spinel/liquid D^Ni values from the MORB samples vary between 6 and 11, slightly higher than those from the S-bearing experiments of Satari et al. [Satari P., Brenan J. M., Horn I. and McDonough W. F. (2002) Experimental constraints on the sulfide- and chromite-silicate melt partitioning behavior of rhenium and platinum-group elements. Economic Geology97, 385-398]. The results of the MORB samples and the experiments of Satari et al. (2002) indicate a negative correlation between the Cr-spinel/liquid D^Ni and the X_Cr values in Cr-spinels (Cr cation number on the basis of 3 total cations in the spinel structure). Variations of Cr-spinel/liquid D^Ni values with Cr-spinel compositions can be estimated from an empirical equation based on the results of the MORB samples and the experiments by Satari et al. (2002). The choice of Cr-spinel/liquid D^Ni = 10 for numerical modeling by Righter et al. [Righter K., Leeman W. P. and Hervig R. L. (2006) Partitioning of Ni, Co, and V between spinel-structured oxides and silicate melts: importance of spinel composition. Chemical Geology227, 1-25] is reasonable for basaltic systems. For picritic and komatiitic systems a lower value of ∼5 is more appropriate.  相似文献   

Oviraptorosaurian Eggs (Dinosauria) with Embryonic Skeletons Discovered for the First Time in China     

Yen-nien CHENG  JI Qiang  Xiao-chun WU  Hsi-yin SHAN 《《地质学报》英文版》2008,82(6):1089-1094

Two elongatoolithid dinosaur eggs from the Upper Cretaceous of Ganzhou, Jiangxi Province and the embryonic skeletons they bear are described. They represent the first oviraptorosaurian eggs with embryonic skeletons in China and provide the first example that an oospecies can be correlated to certain dinosaur taxon/taxa. The two eggs are the same as the pair of the eggs inside a female oviraptorosaurian pelvis from the same horizon of the same area in both macro- and micro-structures of the egg shells, and can he referred to the oospecies, Macroolithus yaotunensis Zhao, 1975. The morphology of the preserved part of the embryonic skeletons indicates that they may have been laid by an oviraptorid, Heyuannia huangi from Guangdong Province or a closely related oviraptorosaurian, which may have been lived in the Ganzhou area too in the Late Cretaceous. The embryonic skeletons of the two eggs are not in the same developing stage. In one of the eggs, the postzygapophysis of the preserved vertebrae are well ossified, indicating that it was just hatched.  相似文献   

烟台市城市土地可持续利用评价     

郑璐璐  ;张鲁府 《山东地质》2008,(12):27-29

以烟台市为例,从生态环境协调性、经济可行性、社会可接受性等方面,构建了2004年城市土地可持续利用评价的指标体系,采用特尔斐等方法计算了其可持续利用度。结果表明,烟台城市土地利用目前仍处于可持续利用起步阶段。  相似文献   

河南西峡地区晚白垩世介形虫的发现及其地层意义     

庞其清  张志军  卢立伍  韩迎建  方晓思 《地质通报》2008,27(6):769-784

2005年在河南西峡含恐龙蛋层中首次发现介形虫化石,产自红山水库-丹水剖面上白垩统赵营组下段64层,是以Eucypris-Mongolocypris-Cypridea-Talicypridea为特征的介形虫化石组合,由12属20余种组成.其中Talicypridea是中国、蒙古和东亚晚白垩世最典型的化石,在非洲刚果及南美阿根廷的晚白垩世地层中也有分布,因此赵营组的时代无疑应归属为晚白垩世.赵营组介形虫化石的新发现,为地层的划分对比、沉积环境的演变和盆地的演化研究提供了重要的依据.  相似文献   

记内蒙古阿拉善右旗晚白垩世的绘龙属(甲龙科)化石     

谭锴  陈晓云  卢立伍  姬书安 《地质学报》2022,96(11):3733-3740

本文记述了内蒙古西部阿拉善右旗阿拉腾敖包镇巴音塔拉一带上白垩统乌兰苏海组一件甲龙类不完整头后骨架，其愈合荐骨至少由4枚背荐椎、4枚荐椎组成，最后1对背荐肋中部和远端强烈加宽且显著向后弯曲，游离尾椎10枚，后部尾椎神经棘、前关节突与脉棘明显拉长且包裹后部尾椎椎体，应被归入甲龙亚科Ankylosaurinae的绘龙属Pinacosaurus，但种名暂未确定。阿拉善右旗巴音塔拉也成为绘龙属在内蒙古自治区继乌拉特后旗巴音满都呼、阿拉善左旗“栅栏呼都克”之后的第3个分布地点，扩展了该属化石的地理分布范围，并为阿拉善右旗巴音塔拉与乌拉特后旗巴音满都呼晚白垩世恐龙动物群的对比提供了新的古生物学依据。  相似文献   

The Sevsk woolly mammoth (Mammuthus primigenius) site in Russia: Taphonomic,biological and behavioral interpretations     

《Quaternary International》2006

Excavations at Sevsk, Bryansk Region, Russia, by the Paleontological Institute of the Russian Academy of Sciences in 1988–1991 recovered 3800 bones of woolly mammoth (Mammuthus primigenius Blum.) representing a minimum of 33 individuals. The locality is one of the largest naturally occurring deposits of mammoth remains in Europe and is inferred to be a catastrophic death assemblage. The material includes five skeletons of juvenile mammoths, from 1 month to 6 or 7 years of age, as well as partial skeletons and isolated bones of adult individuals. A femur and humerus of an approximately 10–12-month-old fetus are also among the finds. Morphological features suggest that the Sevsk mammoths belonged to one family group; the age structure and sexual composition of the assemblage do not differ significantly from that of a family group of Modern African elephants. In contrast to other localities in Siberia and central Russia, relatively more (about 45% of individuals) prepubertal animals are preserved at Sevsk. Radiocarbon dates indicate that the mammoths died about 14,000 years ago. Data from diatoms, pollen and rodents, as well as archeological evidence, corroborate this age, and provide the basis for a paleoenvironmental reconstruction at the end of the Valdaian Glaciation in western Russia.  相似文献   

Biogenic Silica Record in Lake Biwa of Central Japan over the Past 145,000 Years   总被引：2，自引：0，他引：2  

Jule Xiao  Yoshio Inouchi  Hisao Kumai  Shusaku Yoshikawa  Yoichi Kondo  Tungsheng Liu  Zhisheng An 《Quaternary Research》1997,47(3):277-283

The record of the biogenic silica flux (BSF, g cm⁻²(10³yr)⁻¹) in Lake Biwa reflects changes in diatom productivity in the lake and provides information regarding changes in paleoclimatic conditions. The BSF record of Lake Biwa demonstrates five periods over the past ca. 145,000 yr when the BSF values were significantly greater than 7.5 g cm⁻²(10³yr)⁻¹, and five intervals when they were lower. The data imply that paleoclimatic conditions were warmer and wetter from ca. 123,000 to 115,000, 103,000 to 95,000, 88,000 to 72,000, 57,000 to 32,000 yr B.P., and around ca. 6000 yr B.P. when the BSF values were greater, and relatively dry and cold from ca. 141,000 to 123,000 yr B.P. and during intervals between two of the five warm and wet episodes when the BSF values were lower. Time series of the BSF record can be correlated with the record of biogenic silica content in Lake Baikal and the marine oxygen isotope stages 1 through 6. Furthermore, the BSF values varied with much higher amplitude during the last interglaciation than during the last glaciation, probably implying that the diatom productivity in Lake Biwa was likewise more variable and had a larger range under interglacial conditions than under glacial conditions.  相似文献   

The age of supergene manganese deposits in Katanga and its implications for the Neogene evolution of the African Great Lakes Region     

《Ore Geology Reviews》2015

Supergene manganese deposits commonly contain K-rich Mn oxides with tunnel structure, such as cryptomelane, which are suitable for radiometric dating using the ³⁹Ar–⁴⁰Ar method. In Africa, Mn deposits have been dated by this method for localities in western and southern parts of the continent, whereas only some preliminary data are available for Central Africa. Here we present new ³⁹Ar–⁴⁰Ar ages for Mn oxide samples of the Kisenge deposit, in southwestern Katanga, Democratic Republic of the Congo. The samples represent supergene Mn oxide deposits that formed at the expense of primary Paleoproterozoic rhodochrosite-dominated carbonate ores. Main phases of Mn oxide formation are dated at c. 10.5 Ma, 3.6 Ma and 2.6 Ma for a core that crosses a mineralized interval. The latter shows a decrease in age with increasing depth, recording downward penetration of a weathering front. Surface samples of the Kisenge deposits also record a ≥ c.19.2 Ma phase, as well as c. 15.7 Ma, 14.2 Ma and 13.6 Ma phases. The obtained ages correspond to distinct periods of paleosurface development and stability during the Mio-Pliocene in Katanga. Because Katanga is a key area bordered to the North by the Congo Basin and to the East by the East African Rift System, these ages also provide constraints for the geodynamic evolution of the entire region. For the Mio-Pliocene, the Kisenge deposits record ages that are not systematically found elsewhere in Africa, although the 10.5–11 Ma event corresponds to a roughly simultaneous event in the Kalahari Manganese Field, South Africa. The rest of the Katanga paleosurface record differs somewhat from records for other parts of Africa, for which older, Eocene ages have been obtained. This difference is most probably related to the specific regional geodynamic context: uplift of the East African Plateau, with associated erosion, and the opening of the East African Rift System at c. 25 Ma are events whose effects, in the study area, interfere with those of processes responsible for the development of continent-wide paleosurfaces.  相似文献   

The first record of “spelaeoid” bears in Arctic Siberia     

Andrei V. Sher  Jacobo Weinstock  Gennady F. Baryshnikov  Sergey P. Davydov  Gennady G. Boeskorov  Vladimir S. Zazhigin  Pavel A. Nikolskiy 《Quaternary Science Reviews》2011,30(17-18):2238-2249

For a long time, “spelaeoid” (cave-bear-like) bears, Ursus (Spelearctos) spp., were believed to be almost purely European animals. Their geographic range has recently been extended to the east, in southern Siberia, Transbaikalia, Kirghizia, Mongolia and Korea. Two unexpected new findings, presented here in detail, significantly change existing views on the distribution of cave bears; both were found in North-Eastern Siberia, far beyond the Arctic Circle, more than 1500 km to the north-east of the previously accepted range.One of the fossils is a mandible, found near the town of Cherskiy at 68.73°N, 161.38°E. The analysis of local geology and accompanying mammal fossils suggests that it comes from the Olyorian Fauna (Early to early Middle Pleistocene). Morphologically, the Cherskiy mandible is closest to Ursus savini, a small middle Pleistocene cave bear from the British Cromer Forest-bed Formation, but differs in having a slightly more advanced dentition, and thus it is described as a new subspecies Ursus savini nordostensis. Another newly recognized fossil of the “spelaeoid” bear is an astragalus found at the Oskhordokh site at 67.54°N, 135.67°E, on a large gravel bar on the right bank of the Adycha River. This specimen is attributed to Ursus cf. deningeri.The paper also presents an interesting example of the interaction between classical and “molecular” palaeontology.The new finds significantly change existing ideas on the ecology and evolution of cave bears, some of the most remarkable members of the extinct Pleistocene megafauna.  相似文献