A high resolution,multiproxy Late‐glacial record of climate change and intrasystem responses in northwest England

A lacustrine carbonate sequence from Hawes Water, Lancashire, UK, has been studied using stable isotopic, lithological, pollen and mineral magnetic analysis. The data reveal four abrupt climatic oscillations in the Late‐glacial Interstadial leading up to the onset of the Loch Lomond Stadial. The data also point to climatic warming relatively early within the stadial, ca. 12 500 GRIP yr, prior to the onset of the Holocene. The oxygen isotope record is taken as a signature of climate forcing against which the response of the lake‐system can be monitored. By adopting this approach it is revealed that the response of the biological system to the rapid climatic oscillations is non‐linear and primarily a function of the antecedent conditions. A significant end‐Devensian isotopic excursion (A) is matched by only minor changes in the cold‐adapted floras and faunas. During the warmer interstadial, the response of the biological ecosystem (events B–D) is clearly influenced by thresholds: major changes in the catchment vegetation associated with relatively minor oscillations in the isotopic signature. The stratigraphical patterns reveal significant lag effects between the onset of climate deterioration and resulting changes in vegetation. Copyright © 2002 John Wiley & Sons, Ltd.     

Late Quaternary vegetation changes around Lake Rutundu,Mount Kenya,East Africa: evidence from grass cuticles,pollen and stable carbon isotopes

Woody, subalpine shrubs and grasses currently surround Lake Rutundu, Mount Kenya. Multiple proxies, including carbon isotopes, pollen and grass cuticles, from a 755‐cm‐long core were used to reconstruct the vegetation over the past 38 300 calendar years. Stable carbon‐isotope ratios of total organic carbon and terrestrial biomarkers from the lake sediments imply that the proportion of terrestrial plants using the C₄ photosynthetic pathway was greater during the Late Pleistocene than in the Holocene. Pollen data show that grasses were a major constituent of the vegetation throughout the Late Pleistocene and Holocene. The proportion of grass pollen relative to the pollen from other plants was greatest at the last glacial maximum (LGM). Grass cuticles confirm evidence that C₄ grass taxa were present at the LGM and that the majority followed the cold‐tolerant NADP‐MEC₄ subpathway. Copyright © 2003 John Wiley & Sons, Ltd.     

The Upper Pleistocene to Holocene sediments on the Mediterranean island of Lampedusa (Italy)

The island of Lampedusa lies on the northern edge of the African continental shelf, but during some Quaternary marine lowstands it was joined to the African continent. The study and dating of the aeolian, alluvial, detrital sediments, calcareous crusts and speleothems have established that the climatic–environmental variations recorded on the island can be related chronologically to those known for northern Libya, Tunisia and the Italian peninsula. During the Last Glacial Maximum, phases of Saharan dust accumulation on Lampedusa occurred, and were coeval with dust accumulation in crater lakes and on high mountains in central‐southern Italy, and with phases of glacial advance in the Apennines and in the Alps. During the late Holocene, accumulation of Saharan dust on Lampedusa occurred but there was little accumulation of dust on the northern side of the Mediterranean Sea. With the new data from Lampedusa, it is possible to envisage two different scenarios of atmospheric circulation relating to the Last Glacial Maximum and to the late Holocene. During the Last Glacial Maximum, southerly atmospheric circulation brought rainfall to the southern slopes of the Alps and to the Apennines. During the late Holocene, a prevalent westerly atmospheric circulation became established in the northern Mediterranean. Copyright © 2004 John Wiley & Sons, Ltd.     

Stratigraphic evidence for multiple drainings of glacial Lake Missoula along the Clark Fork River, Montana, USA

Glacial Lake Missoula, a source of Channeled Scabland flood waters, inundated valleys of northwest Montana to altitudes of ∼ 1265 m and to depths of  >600 m, as evidenced by shorelines and silty lacustrine deposits. This study describes previously unrecognized catastrophic lake-drainage deposits that lie stratigraphically beneath the glacial-lake silts. The unconsolidated gravelly flood alluvium contains imbricated boulder-sized clasts, cross-stratified gravel with slip-face heights of 2-> 35 m, and 70- to 100-m-high gravel bars which all indicate a high-energy, high-volume alluvial environment. Gravel bars and high scablands were formed by catastrophic draining of one or possibly more early, high lake stands (1200-1265 m). Most glacial-lake silt, such as the Ninemile section, was deposited stratigraphically above the earlier deposits, represents a lower lake stand(s) (1050-1150 m), and was not deposited in lake(s) responsible for the highest discharge events. The glaciolacustrine silt-covered benches are incised by relict networks of valleys formed during the drainage of the last glacial lake. Significant erosion associated with the last lake draining was confined to the inner Clark Fork River canyon.     

Secular variations of the upper crust composition: Implication of geochemical data on the Upper Precambrian shales from the Southern Urals western flank and Uchur-Maya region

In the mid-1980s, it was concluded based on geochemical study that Th, Sc, La concentrations and ratios Th/Sc, La/Sc and Eu/Eu* did not wary significantly in the post-Archean time. It was impossible to judge about compositional variations of upper crust during the Riphean and Vendian, because data of that time characterized a limited number of samples from the post-Archean basins of Australia, New Zealand, and Antarctic. Considered in this work are variations of Eu/Eu*, LREE/HREE, Th/Sc, and La/Sc ratios in Upper Precambrian fine-grained siliciclastic rock of the Southern Urals western flank (Bashkirian meganticlinorium) and Uchur-Maya region (Uchur-Maya plate and Yudoma-Maya belt). As is established, only the Eu anomaly in the studied siliciclastic rocks is practically identical to this parameter of the average post-Archean shale. Three other parameters plot on the Riphean-Vendian variation curves with positive and negative excursions of diverse magnitude, which do not coincide always in time. It is assumed that these excursions likely mark stages of local geodynamic activity, destruction of pre-Riphean cratons, and progressing recycling of sedimentary material during the Riphean.     

Geodynamic significance of granitoid magmatism in the southeast Anatolian orogen: geochemical and geochronogical evidence from Göksun–Afşin (Kahramanmaraş, Turkey) region

In southeast Anatolia, there are number of tectonomagmatic units in the Kahramanmaraş–Malatya–Elazığ region that are important in understanding the geological evolution of the southeast Anatolian orogenic belt during the Late Cretaceous. These are (a) metamorphic massifs, (b) ophiolites, (c) ophiolite-related metamorphics and (d) granitoids. The granitoids (i.e. Göksun–Afşin in Kahramanmaraş, Doğanşehir in Malatya and Baskil in Elazığ) intrude all the former units in a NE–SW trending direction. The granitoid in Göksun–Afşin (Kahramanmaraş) region is mainly composed of granodioritic and granitic in composition. The granodiorite contains a number of amphibole-bearing mafic microgranular enclaves of different sizes, whereas the granite is intruded by numerous aplitic dikes. The granitoid rocks have typical calcalkaline geochemical features. The REE- and Ocean ridge granite-normalized multi-element patterns and tectonomagmatic discrimination diagrams, as well as biotite geochemistry suggest that the granitoids were formed in a volcanic arc setting. The K–Ar geochronology of the granitoid rocks yielded ages ranging from 85.76±3.17 to 77.49±1.91 Ma. The field, geochemical and geochronological data suggest the following Late Cretaceous tectonomagmatic scenario for southeast Anatolia. The ophiolites were formed in a suprasubduction zone tectonic setting whereas the ophiolite-related metamorphic rocks formed either during the initiation of intraoceanic subduction or late-thrusting (∼90 Ma). These units were then overthrust by the Malatya–Keban platform during the progressive elimination of the southern Neotethys. Thrusting of the Malatya–Keban platform over the ophiolites and related metamorphic rocks was followed by the intrusion of the granitoids (88–85 Ma) along the Tauride active continental margin in the southern Neotethys.     

塔里木及邻区晚古生代早期古气候与构造

影响塔里木及邻区晚古生代早期气候的地球内部因素为古昆仑和南天山两个古洋盆封闭及有关的两条缝合构造带演化，从而形成上述时空段内热带海洋气候、热（亚热）带季风气候、热带沙漠气候以及热带滨岸干湿气候区域的更替，古气候特征的判断主要依据古地磁数据、古生态气候学、沉积环境诸方面。     

Sedimentary environment and development controls of the hydrocarbon source beds:Middle and Upper Proterozoic in northern North China

Problem on development control of marine source bed hold in Chinese petroleum industry progression. The Hongshuizhuang Formation,Tieling Formation and Xiamaling Formation in the Middle and Upper Proterozoic are important hydrocarbon source beds in northern North China, and investigation of their sedimentary environments and the controls has great significance for petroleum exploration in North China. Based on sedimentology (sequence stratigraphy), palaeoecology, sedimentary geochemistry, and sedimentary palaeogeography, their development pattern is discussed. All these studies indicate that the development controls of the hydrocarbon source beds include a favorite palaeogeographic location, exceeding propagation of biomes in low and middle latitudes, anoxic environments, enrichment of phosphorus element and the adsorption of clay minerals during the preservation of organic matter in the marine carbonates.     

23,000 yr of vegetation history of the Upper Lerma, a tropical high-altitude basin in Central Mexico

Pollen analysis on a 9.54-m sediment core from lake Chignahuapan in the upper Lerma basin, the highest intermontane basin in Central Mexico (2570 m asl), documents vegetation and limnological changes over the past ∼23,000 ¹⁴C yr. The core was drilled near the archaeological site of Santa Cruz Atizapán, a site with a long history of human occupation, abandoned at the end of the Epiclassic period (ca. 900 AD). Six radiocarbon AMS dates and two well-dated volcanic events, the Upper Toluca Pumice with an age of 11,600 ¹⁴C yr B.P. and the Tres Cruces Tephra of 8500 ¹⁴C yr B.P., provide the chronological framework for the lacustrine sequence. From ca. 23,000 ¹⁴C yr B.P. to ca. 11,600 ¹⁴C yr B.P. the plant communities were woodlands and grasslands based on the pollen data. The glacial advances MII-1 and MII-2 correlate with abundant non-arboreal pollen, mainly grasses, from ca. 21,000 to 16,000 ¹⁴C yr B.P., and at ca. 12,600 ¹⁴C yr B.P. During the late Pleistocene, lake Chignahuapan was a shallow freshwater lake with a phase of lower level between 19,000 and 16,000 ¹⁴C yr B.P. After 10,000 ¹⁴C yr B.P., tree cover in the area increased, and a more variable lake level is documented. Late Holocene (ca. 3100 ¹⁴C yr B.P.) deforestation was concurrent with human population expansion at the beginning of the Formative period (1500 B.C.). Agriculture and manipulation of the lacustrine environment by human lakeshore populations appear at 1200 ¹⁴C yr B.P. (550 A.D.) with the appearance of Zea mays pollen and abundant charcoal particles.