Two bioerosion ichnofacies produced by early and late burial associated with sea-level change     

Richard G. Bromley  Ulla Asgaard 《International Journal of Earth Sciences》1993,82(2):276-280

In bioerosion, as in trace fossils as a whole, deeply emplaced structures have greater survival value than shallow structures. That is to say, tiering (the relative depth to which rasping, etching and boring organisms penetrate their substrate) is of paramount importance for the preservation potential of individual trace fossils. An Entobia ichnofacies is established for trace fossil assemblages dominated by deep tier borings and arising from long-term bioerosion, such as occurs on sediment-free submarine cliffs or hardgrounds. A Gnathichnus ichnofacies comprises assemblages containing all tiers, including superficial sculptures produced by radulation that have very little preservation potential. Such assemblages occur in short-term bioerosion situations as on shell surfaces and hardgrounds buried early by sedimentation. Correspondence to: R. G. Bromley  相似文献   

Sequence stratigraphy in the upper cretaceous of the Basco-Cantabrian Basin (northern Spain)     

K. -U. Grafe  J. Wiedmann 《International Journal of Earth Sciences》1993,82(2):327-361

The sedimentary cycles of the Cenomanian to Maastrichtian were investigated in the Basco-Cantabrian Basin (BCB) in northern Spain (Provinces of Alava, Vizcaya and Burgos). The depositional area was a distally steepened carbonate ramp which extended from Catalonia northwestwards to the Basque country. The investigated sediments range from calciturbidites and pelagic marls to marl-limestone alternations deposited on a distal carbonate ramp. Shallow marine limestones, marls and intertidal clastics and carbonates were deposited on the proximal part of the carbonate ramp. The establishment of a regional sequence analysis is based on the investigation of seismic profiles, well logs and outcrop sections. Examples of outcrop sections are interpreted in terms of sequence stratigraphy (unconformities of third- and second-order cycles, depositional geometries, systems tracts). The sequence stratigraphic interpretation of outcrop sections is based on facies analysis, interpretation of observed depositional geometries and correlation of unconformities and marine flooding surfaces through the basin. A biostratigraphic framework is established based on ammonites, inoceramids, planktonic and benthic foraminifera. As a result, a regional sequence stratigraphic cycle chart is presented and compared with published global cycle charts. The correlation of the regional cycle chart with published cycle charts is good. In the Cenomanian and Turonian, several sequence boundaries in the BCB are shifted by up to one biozone compared with the global chart. Some type 1 boundaries of the standard chart are only type 2 in the BCB. Important type 1 boundaries in the BCB are: top Geslinianum Zone with a 100 m lowstand wedge at the basis of the sequence (sequence boundary 92.2) ; base Petrocoriense Zone with a 250 m shallowing-upwards lowstand wedge at the basis (sequence boundary 89.2); and within the Syrtale Zone (sequence boundary 85.0).The Campanian-Maastrichtian sequence record is strongly disturbed by local compressive tectonics. Several sequences are recognizable and can be correlated with the global cycle chart. Correlation is hampered by the low biostratigraphic resolution in the western basin part. Subsidence analysis of several sections of the Upper Cretaceous of the BCB and its interpretation in the regional tectonic context leads to a discussion of the causes of the observed cyclicity. A regional eustatic curve is presented for the Upper Cretaceous of the BCB. Stage and substage names were used according Code-Committee (1977). Correspondence to: K.-U. Gräfe  相似文献   

气溶胶气候效应的一维模式分析   总被引：4，自引：1，他引：4  

赵凤生  石广玉 《大气科学》1994,18(Z1):902-909

本文首先采用一线辐射对流模式，分析了乡村型、城市型气溶胶和平流层气溶胶含量增加对全球地表气温的直接影响以及硫酸盐粒子含量增加对全球地表气温的间接影响。然后利用考虑了海洋热惯性作用的ＥＢＭ／ＢＤ模式，模拟了近百年来由于大气中硫酸盐粒子含量变化、火山爆发和大气温室气体浓度增加共同引起的全球地表平均气温变化。结果表明：气溶胶的气候效应在地气系统辐射收支和全球气温变化研究中起着非常重要的作用。  相似文献   

Channel and floodplain response to recent abrupt climate change: The tyne basin,Northern England     

Barbara T. Rumsby  Mark G. Macklin 《地球表面变化过程与地形》1994,19(6):499-515

This paper examines the timing, nature and magnitude of river response in upland, piedmont and lowland reaches of the Tyne basin, northern England, to high-frequency (20–30 year) changes in climate and flood regime since 1700 AD. Over this period fluvial activity has been characterized by alternating phases of river-bed incision and stability coinciding with non-random, decadal-scale fluctuations in flood frequency and hydroclimate that appear to be linked to changes in large-scale upper atmospheric circulation patterns. Episodes of widespread channel bed incision (1760–1799, 1875–1894, 1955–1969) result from a higher frequency of large floods (> 20 year return period) and cool, wet climate under meridional circulation regimes. Phases of more moderate floods (5–20 year return period), corresponding to zonal circulation types (1820–1874, 1920–1954), are characterized by enhanced lateral reworking and sediment transfer in upper reaches of the catchment, and channel narrowing and infilling downstream. Rates of fluvial activity are reduced in intermediate periods (1800–1819, 1895–1919) with no dominant circulation regime associated with lower flood frequency and magnitude. The results of this study provide a valuable guide for forecasting probable drainage basin and channel response to future climate change.  相似文献   

近三十年来非洲的旱灾与环境变化   总被引：3，自引：0，他引：3  

丁登山 《地理研究》1994,13(4):43-49

本文简要介绍了近三十年来非洲旱灾的基本情况,分析了其形成的原因,并指出,总的说来,干旱是形成非洲旱灾的一个自然因素,但它不等于旱灾.从环境的角度来看,非洲旱灾更重要的原因是人类不适当的土地利用和管理.文章最后提出了非洲防止旱灾的若干战略原则和建议.  相似文献   

High-frequency climatic oscillations during the last deglaciation as revealed by oxygen-isotope records of benthic organisms (Ammersee,southern Germany)   总被引：5，自引：0，他引：5  

U. von Grafenstein  H. Erlenkeuser  A. Kleinmann  J. Müller  P. Trimborn 《Journal of Paleolimnology》1994,11(3):349-357

High-resolution oxygen-isotope records of benthic ostracods and molluscs from Ammersee, southern Germany, show high-frequency climatic changes during the last deglaciation and parallel in great detail published faunal and floral variations reconstructed from Norwegian Sea sediments and isotope variations in Greenland ice cores. The marine and the terrestrial records give evidence of a synchronous late glacial climatic development in Greenland, NW- and Mid-Europe. However,¹⁴C-ages of the supraregional climatic events and of two tephra layers in the marine sediments of the northeastern Atlantic Ocean are significantly older than the¹⁴C-ages of the corresponding horizons on land. These differences strongly suggest that major short-term events have affected the exchangeable carbon on earth during the dramatic environmental changes related to the deglaciation and in particular have affected the CO₂-distribution within the ocean and between ocean and atmosphere. Dating methods independent of climatic variations and of the global carbon budget should be given priority to refine the timescales of the marine and atmospheric processes during the last deglaciation.This is the fourth paper in a series of papers published in this issue on high-resolution paleolimnology. These papers were presented at the Sixth International Palaeolimnology Symposium held 19–21 April, 1993 at the Australian National University, Canberra, Australia. Dr. A. F. Lotter and Dr. M. Sturm served as guest editors for these papers.  相似文献   

Influence of climate on the radioactivity of lake and sea sediments: first results     

I. Liritzis  R. B. Galloway  M. Kovacheva  V. B. Kalcheva 《Geophysical Journal International》1994,116(3):683-687

  相似文献   

博斯腾湖流域气候及湖陆风   总被引：8，自引：0，他引：8  

王容  杜勇 《干旱区地理》1994,17(3):90-94

通过流域多个气象站的资料，分析了流域气候条件，并通过对湖区测点的气象观测资料与陆区测点－ 焉耆站的同步资料对比分析，讨论了博斯腾湖区域小气候其湖陆风特征。  相似文献   

华山树木年轮年表的建立   总被引：83，自引：2，他引：83  

邵雪梅  吴祥定 《地理学报》1994,49(2):174-181

本文以秦岭东部的华山为例，论述了建立常规标准化、差值、自回归标准化这三种树木年轮年表的途径，指出了在半湿润地区利用这种途径建立树木年轮气候学年表的必要性，并进一步分析了三种年表对气候要素的响应及其差异。在取样环境较复杂的地点，建立多种年表有利于深入探讨气候要素与树木生长之间的关系，有推广的价值。  相似文献   

Sedimentary Features of Shallow Ancient River Channels on the Northern Shelf of the South China Sea1     

Kou Yangqi  Du Deli 《《地质学报》英文版》1995,8(1):85-98

Abstract Quaternary buried ancient river channels are widespread in the shallow-level sediments of the northern shelf of the South China Sea. The sedimentary sequence mainly of fluvial deposits comprise an important component part of the low-stand system tract and transgressive system tract in the study region. The plannar variation and spatial association of the sedimentary features such as incised valley fillings, deltaic foreset wedges and block slides of shelf-marginal fans reflect the palaeogeographic environment during the fall of the regional sea level in the northern part of the South China Sea. Based on the high-resolution seismic reflection data and gelogical data from boreholes, the present paper makes an integrated interpretation of the Quaternary ancient river channels in the shallow sediments of the study area, studies the sedimentary features of the ancient channels such as their spatial distribution, seismic facies reflection indicators, sedimentary facies and sand-body types, and discusses their formational setting and evolutionary model, with the main purpose to render a service to the hydrocarbon resources exploration and development and marine engineering in the northern shelf of the South China Sea.  相似文献