Submillennial environmental fluctuations during marine Oxygen Isotope Stage 2: a comparative analysis of diatom and pollen evidence from Lago Grande di Monticchio,South Italy

High temporal resolution pollen and diatom analyses carried out on sediments from Lago Grande di Monticchio span the interval 23 700–21 200 calendar yr. BP, a brief interstadial during marine Oxygen Isotope Stage 2. Both records exhibit marked changes that are interpreted as responses to climatic changes. The diatoms and terrestrial vegetation appear to respond at the same time; any relative lag in the response of the vegetation was less than the ca. 60 yr resolution of the two records. The interval coincides, at least in part, with the Campo Imperatore Stade, when the Gran Sasso ice sheet reached its maximum extent and water level was high in the Fucino Lake. Correlation of the marked environmental oscillation with one of the Dansgaard–Oeschger Events recorded by stable oxygen isotope records from the Greenland ice–cap is proposed. This follows an interval interpreted as having a cold dry climate and correlated with a Heinrich Event in the North Atlantic. Together the two records enable a multifactorial interpretation of the palaeoclimate changes that characterise the oscillation, providing additional insight to that obtained from studies of ice and ocean‐sediment cores, especially with respect to the seasonality of temperature and precipitation. Copyright © 1999 John Wiley & Sons, Ltd.     

南沙群岛永暑礁晚全新世软体动物记录与古环境变化

对南沙群岛永暑礁南永3井软体动物的丰度、营养结构、化学元素和堆积速率的定量分析表明,晚全新世永暑礁漏湖经历了数次相对开放与封闭、与外海交流时强时弱以及盐度多次显著变化的过程。与氧同位素和北半球晚全新世快速气候事件的进一步对比表明,晚全新世快速变化的气候事件也波及到南海,由此造成的溺湖水动力环境、古盐度和沉积速率的变化深刻地影响着软体动物的发育。基于软体动物的替代指标和氧同位素变化的综合分析,初步划分了晚全新世永暑礁漏湖7个变化阶段。     

Signature of the last shelf-centered glaciation at a key section in the Pechora basin,Arctic Russia

The Vastiansky Kon' is the largest exposure of Quaternary deposits in the Pechora lowland, northern Russia. Morphologically the site belongs to the so-called Markhida Moraine; a complex, east–west trending zone of ice-marginal landforms deposited by the Kara Sea Ice Sheet during the last glaciation. The site exhibits a succession of sediments more than 100 m thick that, according to previous studies, covers the interval from the end of the Elsterian to the beginning of the Holocene. Unfortunately both the strong glaciotectonic deformation of the sedimentary succession and few absolute dates have made the chronological interpretation of the section difficult. The present paper reviews previous studies of the site published in Russian, and presents the results of a reinvestigation focusing on the post-Eemian stratigraphy. A marine Eemian clay more than 8 m thick is overlain erosionally by 20 m of fluvial deposits of Late Eemain or Early Weichselian age. The fluvial succession is overlain by a till and a marine clay, which, according to one interpretation, may represent an Early or Middle Weichselian advance of the Kara Ice Sheet followed by a transgression. The clay shows a transition into 15 m of estuarine and fluvial sediments overlain by more than 12 m of tundra–floodplain deposits. The whole succession has been upthrusted glaciotectonically by the last ice advance, which deposited a more than 12 m thick till on top of the section. Based on a number of subtill radiocarbon age-estimates from the site, in the range 25–32 ka BP, the youngest ice advance is considered to be of late Weichselian age, although a Middle Weichselian age cannot be excluded. © 1998 John Wiley & Sons, Ltd.     

Late Pleistocene sediments and environmental change at Plaza Creek,Falkland Islands,South Atlantic

Late Pleistocene organic-rich sediments exposed in coastal bluffs near the head of Plaza Creek, East Falkland, have yielded conventional and AMS ¹⁴C dates of between 36 and 28 ka BP, and possess a pollen spectrum dominated by grasses, indicating a vegetation assemblage similar to that of the present day. Although some sample dates are anomalous and contamination by non-contemporaneous carbon cannot be ruled out entirely, the age estimates are consistent with evidence and dates from Antarctica, South America and the amphi-North Atlantic for climate shifts to interstadial conditions at around that time. The organic-rich units are developed in and enclosed by deposits attributed to processes of periglacial mass wasting. Grain-size characteristics suggest that these sediments may have been emplaced by solifluction, shallow translational landsliding and surface wash in at least five mass-wasting episodes. Some of the mass-wasting sediments might correlate with solifluction deposits above and below a podsolic soil dated to 26 ka BP at San Carlos, East Falkland, and with periods of cirque and valley glaciation identified in the uplands of the Falkland Islands. The similarity between late Pleistocene interstadial, Holocene and present-day pollen assemblages, and the lack of vegetation change within these periods, is characteristic of most cool temperate Southern Ocean islands, and may reflect the lack of sensitivity of the vegetation to climate change and/or a lack of climate variability for the time intervals covered. © 1998 John Wiley & Sons, Ltd.     

青海省治多西北上三叠统巴塘群划分对比与环境分析

青海南部晚三叠世巴塘群沿金沙江缝合带南侧呈带状分布,地质构造复杂,研究程度较低,地层序列的划分存在争议。在1∶250000区域地质调查基础上,通过实测剖面的详细研究和区域对比,将治多西北巴塘群自下而上划分为下组、中组和上组。对研究区巴塘群的岩石组合、生物群面貌、地质时代进行了分析,并利用本次工作中新发现的具重力流沉积泥晶灰岩、具枕状构造玄武岩、具鲍马序列浊流沉积,结合火山岩岩石化学所反映的构造属性,初步探讨了研究区沉积环境和构造背景的演化,为青海南部巴塘群地层的研究提供了基础资料。     

金沙江三堆子-乌东德河段阶地研究

中更新世晚期,古金沙江曾在金坪子河段发生堵江,使得金坪子河段成为金沙江发育的局部侵蚀基准点,并影响着三堆子-乌东德河段的河流下切速率。金坪子、凹嘎、龙街和鱼鲊的平均下切速率分别为196~217、145~172、257~305、82~97 cm/ka。凹嘎河段和鱼鲊河段在河谷地貌形态和阶地堆积物形成年代上都有很大差异,其原因为金沙江河谷中存在着多级构造裂点或岩性裂点,两河段性质存在差异,所以该河段不宜做传统的阶地位相分析。金沙江三堆子-乌东德河段的阶地沉积物的重矿物种类较多,以磁铁矿、赤褐铁矿、绿帘石、石榴石为主,并含有稳定矿物锆石、金红石和白钛石,以及十字石、兰晶石等典型的变质矿物。     

成藏期后的断层活动对油气聚集与保存的控制作用

针对油气勘探中同一断层不同部位油气富集差异性,利用地震解释资料和钻探资料,研究辽河西部凹陷齐家—鸳鸯沟地区沙二段油气聚集与保存所需最低的断层后期活动强度.结果表明:沙二段内主要发育4条走向相同的断层,在主要油气成藏期—东营组沉积末期之后馆陶组—第四系的活动过程中,其中f1断层活动强度最大,对油气聚集的破坏作用最强;其次是f3断层,再次是f4断层,f2断层活动最弱,断层后期活动强度与油气分布之间具有密切关系,断层后期活动强度越小的断层或部位,油气越富集,油气钻探成功率越高;反之,则越低.沙二段油气聚集与保存所需最低的断层后期活动强度约为2m/Ma.