Depositional environments in an extensive tide-influenced delta plain, Middle Devonian Gauja Formation, Devonian Baltic Basin     

ANNA PONTÉN  PIRET PLINK-BJÖRKLUND† 《Sedimentology》2007,54(5):969-1006

The Middle Devonian Gauja Formation in the Devonian Baltic Basin preserves tide‐influenced delta plain and delta front deposits associated with a large southward prograding delta complex. The outcrops extend over 250 km from southern Estonia to southern Lithuania. The succession can be divided into 10 facies associations recording distributary channel belts that became progressively more tide influenced when traced southwards towards the palaeo‐shoreline, separated by muddy intra‐channel areas where deposition was characterized by crevasse splays, delta plain lakes, abandoned channel deposits and tidal gullies. Tidal currents influenced deposition over the entire delta plain, extending up to 250 km from the contemporary shoreline. Tidal facies on the upper delta plain differ from those on the lower delta plain and delta front. In the former case, deposition from river currents was only occasionally interrupted by tidal currents, e.g. during spring tides, resulting in mica and mudstone drapes, and distinctive graded cross‐stratification. The lower delta plain was dominated by tidal facies and tidal currents regularly influenced deposition. There was a change from progradation to aggradation from the lower to the upper part of the Gauja Formation coupled with a vertical decrease in tidal influence and a decrease in coarse‐grained sediment input. The Gauja Formation contrasts with established models for tide‐influenced deltas as the active delta plain was not restricted by topography. The shape of the delta plain, the predominant southward (basinward)‐directed palaeocurrents, and the thick sandstone succession, show that although tidal currents strongly influenced deposition at bed scale, rivers still controlled the overall morphology of the delta and the larger‐scale bedforms. In addition, there are no signs of wave influence, indicating very low wave energy in the basin. The widespread tidal influence in the Devonian Baltic Basin is explained by changes in the wider basin geometry and by local bathymetrical differences in the basin during progradation and aggradation of the delta plain, with changes in tidal efficiency accompanying the change in basin geometry produced by shoreline progradation.  相似文献   

福建近44年雾日趋势变化特征及可能影响因素   总被引：13，自引：1，他引：13       下载免费PDF全文

吴滨  施能  李玲 《应用气象学报》2007,18(4):497-505

应用1961—2004年福建省50个气象站逐月大雾及浓雾日数资料, 分析了全省大雾日数及浓雾日数的年、季分布特点、长期变化趋势、年代际变化特征以及可能的影响因素。结果表明:全省年、季雾日数分布均表现为中部及三明西部的多雾区, 沿海及南部地区的少雾区, 而多雾区中浓雾所占的比率达30%以上; 全省年、季大雾日数大部分地区表现为明显的减少趋势, 仅在龙岩西部呈增加趋势, 而浓雾的减少趋势不如大雾; 年、季雾日数具有明显的年代际变化特征, 年、季雾日数在20世纪80年代中期左右转为明显偏少期, 之前则为明显的偏多期。文中还重点分析了6个代表站大雾与浓雾的趋势与月际分布特征。进一步研究指出, 年雾日数与年平均气温有较好的负相关关系, 而与年平均相对湿度有很好的正相关关系, 同时与森林覆盖率的变化有一定关系。  相似文献   

影响和田冬季设施农业的气候变化特征分析   总被引：7，自引：0，他引：7  

马宏武  玉素甫·阿布都拉  MA Hong-wu  YUSUP·Abudula 《沙漠与绿洲气象(新疆气象)》2007,1(4):46-48

利用和田地区1961—2006年4个代表站的气候资料,对设施农业主要生产阶段冬季(12月—次年2月)的平均最低气温、浮尘日数、降雪日数、日照时数等气候因子的变化特点进行分析,结果表明:平均最低气温上升,日照时数增加,浮尘日数下降,上述变化对设施农业生产是有利的;但是降雪日数增加,对设施农业生产不利。针对和田地区气候特征,在加大设施农业发展力度,建立南疆特色瓜果蔬菜基地的同时,需要加强雪灾、冷害防御措施。  相似文献   

朔州市"8·12"暴雨分析     

张小平  张晓  梁桂花  赵刚  李睿 《山西气象》2007,(1):6-8

利用MICAPS系统资料对2005年8月12日发生在山西朔州市北部的暴雨天气过程的大尺度环流背景和物理量场进行分析。结果表明:这次暴雨天气过程发生在纬向环流向经向环流调整的过程中,西太平洋副热带高压有一次明显的西伸北抬,是一次典型的副高西北侧西南气流型暴雨。降水水汽主要来自南海,中低层的水汽输送十分充沛,并在朔州市北部形成辐合。低空急流的建立,为此次强降水提供了丰富的水汽和位势不稳定能量;过程期间,物理量场表现出强水汽输送辐合及上升运动;冷空气与暖湿气流及特殊地形的综合作用激发出中尺度降水云团,造成此次强降水。  相似文献   

晋中市近50年气候变化对水资源的影响     

马荣田  郭彩萍  乔丽霞  田珏  陈红萍 《山西气象》2006,(4):20-22

本文根据晋中市1956年～2004年的气温、降水的变化特征以及由此引起的水资源量的变化进行了统计分析,得出:晋中市年平均气温整体呈上升趋势,平均以0.3℃/10a上升,气温偏高主要是冬季,夏季变化幅度不大;降水量的变化总体上呈减少趋势,降水量以35.9mm/10a的速度在递减,20世纪90年代是降水量减少幅度最大的一个时期;全市的水资源总量、地下水、河川径流量呈减少趋势,与降水的变化具有明显的一致性。  相似文献   

Area Influence Kriging     

Abdullah Arik 《Mathematical Geology》2002,34(7):783-796

This paper presents a modified ordinary kriging technique referred to as the Area Influence Kriging (AIK). The method is a simple and practical tool to use for more accurate prediction of global recoverable ore resources in any type of deposit. AIK performs well even in deposits with skewed grade distributions when the ordinary kriging (OK) results are unreasonably smooth. It is robust and globally unbiased like OK. The AIK method is not intended to replace OK, which is a better estimator of the average grade of the blocks. Rather it aims to complement OK with its excellent performance in predicting recoverable resources that have been the major pitfalls of OK in many resource estimation cases. The paper details the methodology of AIK with a couple of examples. It also reports the results from its application to a gold deposit.  相似文献   

NUMERICAL STUDY OF THE INFLUENCE OF WAVES AND TIDE-SURGE INTERACTION ON TIDE-SURGES IN THE BOHAI SEA     

尹宝树侯一筠  程明华苏京志林明祥  李明悝M.I.El-Sabh 《中国海洋湖沼学报》2001,19(2):97-102

Abstract The author‘s combined numerical model consisting of a third generation shallow water wave model and a 3-D tide-surge model with wave-dependent surface wind stress were used to study the influence of waves on fide-surge motion. For the typical weather case, in this study, the magnitude and mechanism of the influence of waves on tide-surges in the Bohai Sea were revealed for the first time. The results showed that although consideration of the wave-dependent surface wind stresses raise slightly the traditional surface wind stress, due to the accumulated effects, the computed results are improved on the whole. Storm level maximum modulation can reach 0.4 m. The results computed by the combined model agreed well with the measured data.  相似文献   

加入WTO对成都法律专业人才的影响与对策     

曹向兰  郭谊  熊文枫 《成都信息工程学院学报》2005,20(4):496-498

加入WTO,使我国法律服务市场范围扩大,各级法院、检察院受理的案件数量上升,这急需一大批高素质的法律专业人才.目前成都法律专业人员的数量质量,均不能满足这种需要.为此,可通过加强现有高校法学专业建设,对在职人员进行培训、进修,严把司法考试关,大力发展JM教育,选派优秀人才到国外考察、学习等措施来加快成都高素质法律专业人才的培养.  相似文献   

江苏沿海互花米草盐沼动态变化及影响因素研究   总被引：8，自引：2，他引：8  

刘永学  李满春  张忍顺 《湿地科学》2004,2(2):116-121

收集1988～2001年12个时相的江苏盐城幅卫星影像，提取双洋河口至梁垛河闸之间的互花米草盐沼，统计不同时期的分布信息。分析表明：互花米草盐沼在江苏扩张非常迅速，到2001年7月互花米草盐沼分布面积达129．28km^2,从射阳河口至梁垛河闸之间的潮间中上带泥滩大部分已被互花米草盐沼所覆盖；由于生态位的影响，互花米草盐沼沿平行于海岸线方向扩张速度快于垂直于海岸线方向的扩张速度；依据野外调查和卫星影像分析，互花米草盐沼扩张可分为立地、快速扩张及成熟3个阶段。此外，还对互花米草盐沼的影响因素进行了探讨。  相似文献   

曲靖“2·6”寒潮诊断分析     

白波  尤临  郭菊馨 《云南地理环境研究》2004,(Z1)

2004年2月6日发生在云南省曲靖市的大-暴雪是近年来较强的一次降雪天气过程。现用Micaps实时资料,对2004年2月6日曲靖地区发生大-暴雪时的主要影响系统、垂直速度、散度、水汽通量散度等物理量特征进行分析,发现500hPa图上中高纬为稳定的两槽一脊,这种形势有利于源源不断的冷空气南下;700hPa图上有明显强劲的低空急流,有水汽输送带。大量水汽和不稳定能量,配合高空槽、切变线和低空急流是造成此次降雪的主要因素,其次冷暖空气的交汇是此次降雪过程的必要条件。这些结论的发现为认识和预报曲靖此类天气可提供参考依据。  相似文献