New radiometric and geomorphologic evidences of a last glacial maximum older than 18 ka in SW European mountains: the example of Redes Natural Park (Cantabrian Mountains,NW Spain)

Abstract

The first numerical age determinations from radiocarbon dating establish the chronology of glacial events in Redes Natural Park (Cantabrian Mountain, NW Spain). A core drilled in an ice-dammed deposit provided a minimum age of 28 990 ± 230 years BP for the maximum glacial expansion (phase I). Another core from a cirque bottom-fill provided organic sediment with 20 640 ± 300 years BP, a minimum age for the first glacial retreat (phase II). Radiometric dating of proglacial deposits interpreted as synchronous with the last glacial maximum phase in neighbouring Cornelia basin (Picos de Europa), yield ages of 40 480 ± 820 years BP. The chronological data presented in this work are consistent with the model of glacier evolution established in the Pyrénées, with a glacial maximum phase for the last glacial period older than 18 ka. © 2002 Éditions scientifiques et médicales Elsevier SAS. AU rights reserved.     

Seismic stratigraphy and geomorphology of a tide or wave dominated shelf-edge delta (NW Australia): Process-based classification from 3D seismic attributes and implications for the prediction of deep-water sands

Shelf-edge deltas (SEDs) forming during periods of relative sea level fall and lowstand are generally efficient in transferring sediments to the slope and basins, and their identification in subsurface data is often considered a good indication of coeval development of slope and basin-floor turbidite reservoirs. This study investigates the seismic stratigraphic evolution of a forced-regressive and normal regressive shelf-edge delta (Bonaparte SED) that accumulated on the edge of the NW Australian margin during the late Quaternary. High resolution 2D and 3D reflection seismic data allow reconstruction of the main episodes of delta progradation and understanding of the extrinsic and intrinsic controls on their deposition. The lack of a significant turbidite system forming off the shelf-edge delta throughout the Quaternary is a striking feature of the Bonaparte SED. Instead, slope sedimentation is dominated by the accumulation of plume-derived mud belts and their reworking through mass-transport processes. Seismic geomorphology permits interpretation of the process regime of the youngest shelf-edge depocentre by applying a new process-based shallow-marine classification scheme to the 3D seismic attribute data. Results suggest either a tide or wave dominated delta with fluvial processes being of tertiary significance. A tide or wave-dominated, fluvial-affected shelf-edge delta classification is consistent with the paleogeographical reconstruction of the margin during the last glacial maximum (ca. 25 ka BP). The comparison of this mixed-process shelf-edge delta and starved slope system with a fluvial-dominated counterpart with significant sandy slope deposits emphasizes the potential of assessing the process regime of shelf-edge deltas as a rapid, first approach for predicting the presence or absence of coeval slope and basin-floor reservoirs.     

Seismic geomorphological analysis of deepwater gravity-driven deposits on a slope system of the southern Colombian Caribbean margin

Gravity-driven processes are important agents for transporting sediments downslope into deep-marine environments. The Pliocene to Holocene offshore succession of the Colombian Caribbean margin and its stratigraphic distribution, have been affected by faulting and mud diapirism, and have been characterized using 3D seismic data. Nine stratigraphic intervals were characterized within the study, and are interpreted to consist of a range of seismic geomorphologies, including slumps and debrites. Nine gravity-driven deposits were defined within the study area, interpreted to have been transported to the north and northwest. Slumps display high-amplitude, high continuity, elongated, stratified, lobate and confined morphologies, while debrites have a reflection-free pattern or show discontinuous, low-amplitude and chaotic reflections. Mixed slumps-turbidites-debrites deposits are composed by a succession of laterally and vertically interfingered slumps, debrites and turbidites. These deposits are morphologically lobate and broadly scattered. In addition, erosional features such as basal small scours, megascours, linear scours and rafted blocks were used as kinematic indicators within the gravity-driven deposits. There are several candidates triggering mechanism, including over-steepening of slope (related to high sediment supply or slope tectonism). In the study area, confined slumps and debrites with a main transport direction from south to north have been observed, while transport direction of the mixed slumps-turbidites-debrites was toward northwest. Additionally, the fact that slumps and debrites are found in depocenters between periclines suggests a confined environment of deposition. Finally, mixed slumps-turbidites-debrites are unconfined without evident structural control. We suggest that local intraslope sub-basin margin become over-steepened as a result of mud diapirism in the subsurface. In this situation, the paleobathymetry was sufficient to trap the resultant gravity-driven deposits within the sub-basins, suggesting a local origin. Seismic evidence of BSR (Bottom Simulating Reflector) suggests the presence of gas hydrate in the study area, and is taken as an additional potential mechanism to provide instability of slope and generate gravity-driven deposits.     

南通近岸海域水质特征的因子及聚类分析研究

基于2012年5月、8月和10月3个航次水质环境调查资料,利用因子分析探讨南通近岸海域海水水质主要影响因素的空间分布特征;通过站位聚类分析进行了区域类别划分,并对各区的主要影响因素及其季节变化进行了分析。因子分析结果显示,南通近岸海域主要存在4种水质影响因素,总体表现为受近岸污染源的控制影响,其中F1(NO-2-N、石油类)高值区位于冷家沙西北侧,是北上长江径流与外海水在冷家沙浅滩处相遇作用的结果;F2(DO、NO-3-N)体现了外海水进入的影响,其值由近岸向离岸逐渐增大;F3(COD、PO3-4-P)显示了河流输入的影响,F4(NH+4-N)体现了人为源的作用,两者高值区均分布于栟茶运河河口和长江口北侧。站位聚类分析显示,南通近岸海域可划分为5个类型区,其中A区(小洋口港近岸区域)受陆源河口排污影响,且所处水道尾部水文动力条件弱,污染严重;B区(烂沙洋海域)受西侧相邻的河口排污区和近岸污染影响,在主要潮汐通道的强动力作用下,污染程度较轻;C区(冷家沙区域)为B、D两区之间的潮滩区,受到B、D两区域污染的综合影响;D区(冷家沙南侧近岸海域)主要受近岸污染影响,为小庙洪和网仓洪的强动力控制区;长江入海携带污染物及水流扰动对E区(东南部离岸海域)有一定干扰。不同空间类型分区体现了区域动力地貌在海洋污染物分布中的强烈影响。     

Mapping sediment-dispersal characteristics using seismic geomorphology: Late Paleogene to Neogene,Qinan Sag,Huanghua Depression,China

The main objective of this article has been to demonstrate the utility of stratal slice images for exploring the sequence stratigraphy and sedimentology of complex depositional systems. The seismic-geomorphology study and sedimentary interpretation were performed to map sediment-dispersal characteristics from late Paleogene to Neogene in Qinan Sag, located in Huanghua Depression of China. The Qinan Sag is underlain by a non-marine Mesozoic and Cenozoic-age stratigraphic section. Main data types in this study area are lithology, wire-line logs and 3D seismic. The main study strata, Member one of Shahejie Formation to Minghuazhen Formation, divided into two second-order sequences and four third-order sequences. The older of the two second-order sequences, SE, corresponds to the formations from Kongdian to Dongying. The younger of the two second-order sequences, SN, correspond to Guantao and Minghuazhen formations. Guided by third-order sequence-stratigraphic correlations from seismic and wireline-log data, we prepared stratal slices from a three-dimensional seismic volume to reveal high-resolution (10-m) sediment dispersal characteristics in a relative geologic-time domain. Using techniques of 3-D seismic geomorphology, we defined four types of depositional systems: braided deltas, deltas, braided rivers and meandering rivers. Stratal slices indicated that the depositional evolution of these interest sequences was from braided-delta front to delta front, braided river and finally meandering river system. Many factors related to the structural evolution history controlled the sediment-dispersal characteristics, such as the basin type, dynamic mechanism, faulting activity, subsidence rate and paleo-high.     

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基于多时相Landsat TM/ETM的阿尼玛卿山冰川变化监测

采用遥感及地理信息系统技术,利用多时相Landsat TM/ETM影像和数字高程模型(SRTMDEM),结合中国冰川目录,获得阿尼玛卿山地区不同年份的冰川范围,进行冰川变化监测。综合分析该冰川的变化情况,计算冰川进退变化速率,并对其中4个变化较大的冰川进行详细的分析统计。结果表明:从1991年至2009年,阿尼玛卿山地区既有退缩冰川也有前进冰川,其中冰川退缩面积为15.30km2,前进面积为4.46km2。总体面积持续退缩,其中退缩最大的冰川长度缩短了900m,其它冰川也存在不同程度的变化。     

Geomorphic characterization of seafloor using Digital Elevation Model derivatives – a case study around Bombay High,Western Indian offshore

The present study demonstrates the use of gridded bathymetry in the form of a Digital Elevation Model (DEM) in a geographic information system (GIS) in geomorphic characterization of the seafloor in the Western Indian offshore around Bombay High region and presents the salient findings. The variography of bathymetry and its derivatives and their spatial correlation provides a technique to measure the presence of seafloor features and provides an insight into the processes involved. The current study utilizes tools available within a GIS for processing of a DEM and its derivatives involving spatial techniques like spatial correlation and variography studies for geomorphic characterization. A broad regional analysis for the study area comprising the near shore coast to the deep waters is discussed, followed up by a detailed study limiting to the coastal region around Bombay High.     

Pedoiogisk kortlægning og jordbundsbonitering i et geestrandområde ved Tønder

Jakobsen, Bjarne Holm: Pedoiogisk kortlægning og jordbundsbonitering i et geestrandområde ved Tønder. Geografisk Tidsskrift 81: 17–32. København, Juni 1, 1981.

The result is presented of a detailed pedological survey of the geest at the margin of the Tønder Marsh-Area. Maps showing the parents sediments, the pedology and the drainage class have been constructed. Furthermore a soil capability map is shown using the land valuation principles of the Federal Republic of Germany.     

Observations of sea ice influence on the littoral sediment exchange,North Zealand,Denmark

Nielsen, Niels: Observations of sea ice influence on the littoral sediment exchange, North Zealand, Denmark. Geografisk Tidsskrift 88:61–67. Copenhagen. 1988.

In 1985 and 1986 monthly surveys of sediment volumes were carried out on a sandy beach and its nearshore platform at the north coast of Zealand. Both winters in the research period had temperatures below average, and consequently abundant sea ice formations. ‘Ice winters’ in open Danish waters occur statistically about 1/3 of the winters. The appearance of sea ice resulted in marked loss of sediment from the whole littoral zone, but by far the largest net erosion could be detected on the nearshore plane. An important factor is assumed to be the interaction of waves with the icefoot and ice pile-ups. For the beach itself, ice-glazing of the beach surface and interstitial frost in the foreshore sediments caused wave erosion within and just off the swash zone due to variations of the percolation parameter. This dynamic was observed during both the freeze-up and thaw-up periods. On the backshore, wind-derived forms characterized the winter beach, but here the net sediment budget was less affected.