Recognition of the 1811–1812 New Madrid earthquakes in Reelfoot Lake, Tennessee sediments using pollen data

Reelfoot Lake is located within the New Madrid Seismic Zone, a region characterized by ongoing seismic activity and the locus of a series of large earthquakes (m _b >7) during 1811–1812. Coseismic uplift and subsidence from the 1811–1812 events formed the lake basin from a partially inundated alluvial bottomland forest. Lithologic, chronologic, and palynologic data from a vibracore are used here to characterize the 1811–1812 earthquake record in lacustrine sediments. The stratigraphic record consists of a poorly consolidated upper silt, an intervening 10-cm sand layer, overlying a compact lower silt. Calibrated radiocarbon age estimates on wood samples from both silt units indicate deposition during historical time (1490–1890 AD).Better age estimates were obtained by correlating pollen assemblage data from the upper and lower silt with the historical record of land-use change in the Reelfoot Lake region. Two factors resulted in changing plant distributions (and hence pollen assemblages) in Reelfoot Lake sediments: 1) altered drainage patterns of Reelfoot Creek and Bayou de Chien resulting from 1811–1812 uplift and subsidence, and 2) deforestation and subsequent cultivation beginning approximately 1850 AD. The upper silt is characterized by a oak/cedar arboreal pollen (AP) assemblage, showing a mixture of upland and alluvial bottomland AP influx from the region to the open lake basin. Non-arboreal pollen (NAP) in the upper silt shows increasing abundance of Composites, particularly ragweed pollen indicating cultivation. This unit was deposited after the 1811–1812 earthquakes. The intervening sand layer was apparently emplaced by earthquake activity, or represents colluvium derived from most recent (1811–1812) coseismic uplift of Reelfoot scarp, which forms the western margin of the lake. The lower silt is characterized by a baldcypress/cedar AP assemblage with minor percentages of other flood-tolerant AP genera, interpreted as a baldcypress-dominated bottomland forest. Pollen influx in this environment is dominated by gravity-component deposition from local sources. The NAP in the lower silt shows that ragweed is rare or absent, suggesting pre-settlement conditions and deposition prior to 1811–1812.This is the 15th in a series of papers published in this special AMQUA issue. These papers were presented at the 1994 meeting of the American Quaternary Association held 19–22 June, 1994, at the University of Minnesota, Minneapolis, Minnesota, USA. Dr Linda C. K. Shane served as guest editor for these papers.     

Terrain analysis of the Racetrack Basin and the sliding rocks of Death Valley

The Racetrack Playa's unusual surface features known as sliding rocks have been the subject of an ongoing debate and several mapping projects for half a century, although the causative mechanism remains unresolved. Clasts ranging in volume from large pebbles to medium boulders have, unwitnessed, maneuvered around the nearly flat dry lake over considerable distances. The controversy has persisted partly because eyewitness accounts of the phenomenon continue to be lacking, and the earlier mapping missions were limited in method and geographic range. In July 1996, we generated the first complete map of all observed sliding rock trails by submeter differential Global Positioning System (DGPS) mapping technology. The resulting map shows 162 sliding rocks and associated trails to an accuracy of approximately 30 cm. Although anemometer data are not available in the Racetrack wilderness, wind is clearly a catalyst for sliding rock activity; an inferred wind rose was constructed from DGPS trail segment data. When the entire trail network is examined in plan, some patterns emerge, although other (perhaps expected relations) remain elusive: terrain analysis of the surrounding topography demonstrates that the length and morphology of trails are more closely related to where rocks rested at the onset of motion than to any physical attribute of the rocks themselves. Follow-up surveys in May 1998, May 1999, August 1999, and November 1999 revealed little modification of the July, 1996 sliding rock configuration. Only four rocks were repositioned during the El Niño winter of 1997–1998, suggesting that activity may not be restricted to winter storms.     

长江中下游成矿带成矿规律和成矿模式

长江中下游成矿带作为中国东部重要的成矿带之一,成矿地质条件、成矿规律和成矿模式的相关研究已经十分深入,形成了一系列公认的理论研究成果,本文重点论述了成矿带成矿地质条件和成矿规律方面研究的新进展,并在此基础上构筑了成矿带的成矿模式。本文主要开展了以下总结工作:(1)将成矿带的构造要素突破以往按构造单元分解的做法,确立跨构造单元的"复合构造系统",结合成矿带成岩成矿作用特点,重新确定了长江中下游成矿带的范围,并对成矿亚带进行了重新划分;(2)收集汇总了长江中下游成矿带近年来国内外学者最新的成岩成矿年龄数据,总结了矿床时空分布规律;(3)从地质,地球物理和地球化学等方面,总结归纳了沿基底结合带复活的网状断裂系统,阐明了成矿带的控矿构造格架,分析了长江中下游成矿带的成因规律;(4)补充和完善了断隆区和断凹区的成矿模式,并初步构筑了长江中下游成矿带综合成矿模式。提出长江中下游成矿带内主体成岩成矿作用总体上分为走滑挤压阶段(146~135Ma)、走滑引张阶段(135~126Ma)和拉张伸展阶段(126~123Ma)等三个阶段,古太平洋板块作用导致的壳幔过程,引发含元古代弧岩浆岩源区活化和中生代的构造活化("双活化")是长江中下游成矿带形成的主要机制。     

Asynchroneity of maximum glacier advances in the central Spanish Pyrenees

The deglaciation history of the Escarra and Lana Mayor glaciers (Upper Gállego valley, central Spanish Pyrenees) had been reconstructed on the basis of detailed geomorphological studies of glacier deposits, sedimentological and palynological analyses of glacial lake sediments and an accelerator mass spectrometry (AMS) ¹⁴C chronology based on minimum ages from glacial lake deposits. The maximum extent of the Pyrenean glaciers during the last glaciation was before 30 000 yr BP and pre‐dated the maximum advances of the Scandinavian Ice Sheet and some Alpine glaciers. A later advance occurred during the coldest period (around 20 000 yr BP), synchronous with the maximum global ice extent, but in the Pyrenees it was less extensive than the previous one. Later, there were minor advances followed by a stage of debris‐covered glaciers and a phase of moraine formation near cirque backwalls. The deglaciation chronology of the Upper Gállego valley provides more examples of the general asynchroneity between mountain and continental glaciers. The asynchroneity of maximum advances may be explained by different regional responses to climatic forcing and by the southern latitude of the Pyrenees. Copyright © 2002 John Wiley & Sons, Ltd.     

Greta Coal Measures in the Muswellbrook Anticline area,New South Wales

The Greta Coal Measures are the lower of two main coal‐bearing intervals in the Permian northern Sydney Basin. High quality outcrop and continuous core data are available from the Muswellbrook Anticline area in the Hunter Valley, enabling a sequence‐stratigraphic interpretation of the Greta Coal Measures to be presented for the first time. Age and core relationships indicate an unconformity at the base and the top of the Greta Coal Measures. A correlation between dated tuffs in the upper Greta Coal Measures in the Muswellbrook area and the Maitland Group in the Cessnock area establishes a clear diachronous upper boundary for the Greta Coal Measures resulting from a northwest‐ward marine transgression. The Greta Coal Measures are interpreted to occupy a single sequence in which the lower fluvial and lacustrine Skeletar Formation makes up a transgressive systems tract, the Ayrdale Sandstone Member is an estuarine unit around the maximum flooding surface, and the upper fluvial to deltaic Rowan Formation occupies a highstand systems tract. The overlying Jasdec Park Sandstone Member of the Maitland Group infills incised valleys above a sequence boundary and then occurs as a transgressive shoreline system before passing into the glacial marine Branxton Formation. The Greta Coal Measures represent high accommodation where subsidence and sediment supply were approximately balanced over more than 100 m of accumulation, and the development of 14 recognisable coal seams occurred in a single sequence.     

Freshwater flow to the San Francisco Bay‐Delta estuary over nine decades (Part 1): Trend evaluation

The San Francisco Bay‐Delta estuary and its upstream watershed have been highly modified since exploration and settlement by Europeans in the mid‐18th century. Although these hydrologic alterations supported the growth of California's economy to the eighth largest in the world, they have been accompanied by significant declines in native aquatic species and subsequent efforts to reverse these declines through flow management. To inform ongoing deliberations on management of freshwater flows to the estuary, we examined a recent nine‐decade hydrologic record to evaluate seasonal and annual trends in reported Delta outflow. Statistically significant trends were observed in seasonal outflows, with decreasing trends observed in 4 months (February, April, May, and November) and increasing trends observed in 2 months (July and August). Trend significance in early‐to‐mid autumn (September and October) is ambiguous due to uncertainty associated with in‐Delta agricultural water use. In spite of increasing water use over the period examined, we found no statistically significant annual trend in Delta outflow, a result likely due to large inter‐annual variability. Linkages between outflow trends and changes in upstream flows and coincident developments such as reservoir construction and operation, out‐of‐basin imports and exports, and expansion of irrigated agriculture are discussed. To eliminate inter‐annual variability as a factor, change attribution is explored using modelled flows and fixed climatology in a companion paper.     

庐枞盆地与A型花岗岩有关的磁铁矿-阳起石-磷灰石矿床——以马口铁矿床为例

庐枞中生代火山岩盆地位于长江中下游断陷带内,地处扬子板块的北缘.庐枞盆地内的火山岩和侵入岩分布广泛,包括龙门院、砖桥、双庙和浮山四组火山岩以及34个侵入岩体.最近在庐枞盆地南部正长岩中发现一种新类型铁矿床——马口铁矿床.本次工作通过详细野外地质和室内研究,系统开展了马口铁矿床矿床地质特征、成矿年代学和成矿流体特征研究.马口铁矿床的矿体沿石英正长斑岩体中构造破碎带产出,产状严格受构造破碎带控制,矿床围岩蚀变晕范围较为局限.矿床的成矿作用可分为碱性长石阶段、磁铁矿阶段、石英-硫化物阶段和碳酸盐阶段,其中磁铁矿阶段是主要成矿阶段,形成与宁芜玢岩型铁矿床相类似磁铁矿-磷灰石-阳起石三矿物组合.矿床中与磁铁矿共生的磷灰石流体包裹体均一温度范围为252.2 ～ 322.6℃,反映其成矿温度略低于典型的玢岩铁矿床.通过赋矿岩体锆石LA-ICP-MS U-Pb定年和金云母Ar-Ar方法,确定马口铁矿床的成矿时代为127.3 ±0.8Ma,赋矿岩体的形成时代为129.4±1.4Ma,结合矿床地质特征,可以得出矿区内石英正长斑岩只是提供了赋矿空间,矿床的形成与其无直接成因联系,而可能与黄梅尖A型花岗岩体有关.马口铁矿床是庐枞盆地成矿作用最后阶段的产物,也可能是长江中下游成矿带中最晚一次成矿事件的代表,具有显著的特色.     

ESR chronology of the Somme River Terrace system and first human settlements in Northern France

The Somme Valley, Northern France, is famous for its archaeological sequence, where numerous rich Palaeolithic sites, such as Saint-Acheul, the type site of the Acheulian, have been discovered. The archaeological levels are often directly associated with fossil alluvial sediments of the River Somme or with slope deposits, including loess and palaeosols. In the middle reaches of the valley, near Amiens, the system of fossil-stepped fluvial terraces is particularly well developed and preserved, and occurs on 10 alluvial formations. These terraces, from +5 to +55 m above the present-day valley bedrock, allow the study of the environmental changes and the human settlement of this area through the Pleistocene.

Since 1988, ESR dating was systematically applied on bleached quartz extracted from the fossil fluvial deposits, in order to better describe the geological evolution of the stepped system. More recently, U-series/ESR dating has also been performed on teeth collected from the different terrace deposits. Here we present a synthetic review of the main ESR results, and propose an ESR chronology for the geological evolution of the Somme fluvial system and for the Middle Pleistocene human settlement of northern France.     

美国田纳西河流域地区综合开发与城镇化

田纳西河流域地区原为美国典型的贫困地区,经过60年开发建设,1990年时已接近美国平均发展水平。通过实地调查考察,本文分析了该区综合开发与城镇化过程,及其区域城镇体系特征,指出其城镇化经验对于我国黄河上中游等内陆欠发达地区具有重要的借鉴意义。     

石棉干海子沟一带成矿地质背景及找矿方向

通过分析石棉县干海子沟一带大地构造位置、区域地层、构造、岩浆岩等综合成矿地质背景,提出该区域近一步的找矿方向,并结合已发现的典型找矿实例进行论证,得出该区具有较好的地质找矿潜力的结论。