Upper Holocene sea-level changes: Paleogeographic evolution and its impact on coastal archaeological sites and monuments     

N. D. Mourtzas  P. G. Marinos 《Environmental Geology》1994,23(1):1-13

The paper presents the evolution of the geographic environment imposed by sea-level changes in selected sites of the Aegean Sea region during the Upper Holocene. The changes are due, mainly, to paroxysmic phases of the actual neotectonic evolution and to differential—in time and space—block movements, and emerged or submerged coasts. The reconstitution of these coasts is presented and, in some cases, natural harbor morphology is revealed. The use and evolution of these sites is discussed. Other sites concern coastal or inland ancient settlements or constructions affected by submersion by the sea, by the rise of the groundwater table, or by uplift movements. A general discussion on engineering measures to be applied for protection of the antiquities affected by these geographic changes closes the presentation.  相似文献   

Toxic metals in Venice lagoon sediments: model,observation, and possible removal   总被引：1，自引：0，他引：1  

A. Basu  E. Molinaroli 《Environmental Geology》1994,24(3):203-216

We have modeled the distribution of nine toxic metals in the surface sediments from 163 stations in the Venice lagoon using published data. Three entrances from the Adriatic Sea control the circulation in the lagoon and divide it into three basins. We assume, for purposes of modeling, that Porto Marghera at the head of the Industrial Zone area is the single source of toxic metals in the Venice lagoon. In a standing body of lagoon water, concentration of pollutants at distancex from the source (C ₀) may be given byC=C ₀e^–kx wherek is the rate constant of dispersal. We calculatedk empirically using concentrations at the source, and those farthest from it, that is the end points of the lagoon. Averagek values (ppm/km) in the lagoon are: Zn 0.165, Cd 0.116, Hg 0.110, Cu 0.105, Co 0.072, Pb 0.058, Ni 0.008, Cr (0.011) and Fe (0.018 percent/km), and they have complex distributions. Given thek values, concentration at source (C ₀), and the distancex of any point in the lagoon from the source, we have calculated the model concentrations of the nine metals at each sampling station. Tides, currents, floor morphology, additional sources, and continued dumping perturb model distributions causing anomalies (observed minus model concentrations). Positive anomalies are found near the source, where continued dumping perturbs initial boundary conditions, and in areas of sluggish circulation. Negative anomalies are found in areas with strong currents that may flush sediments out of the lagoon. We have thus identified areas in the lagoon where higher rate of sediment removal and exchange may lessen pollution.  相似文献   

Results of the studies of monsoon circulation with radon as a tracer     

C. Rangarajan  S. K. Subramanian  C. D. Eapen 《Pure and Applied Geophysics》1984,122(1):124-132

Radon-222 activity levels have been measured at deck level in regions of the Arabian Sea, Indian Ocean, and Bay of Bengal during the summer monsoon periods of 1973, 1977, and 1979, as part of the Monex programme. The aim of the measurements was to find the source regions of the monsoon air and the variations in its composition under different synoptic conditions. The radon data confirm that the monsoon air is predominantly of southern-hemisphere origin, with a small continental component. The continental component, as indicated by radon values, increases at higher latitudes and seems to vary with different circulation patterns in the synoptic scale. The use of radon as a tracer in monsoon studies is thus demonstrated.  相似文献   

东海陆架盆地岩石密度与磁性   总被引：9，自引：0，他引：9  

高德章 《上海国土资源》1995,(2):38-45

本文在东海陆架盆地２０口钻井１６０块岩心标本物测定和１７口钻井密度测井的基础上，通过整理、分析、统计，给出了东海陆架盆地的岩石密度和磁性特征。  相似文献   

油气成藏组合在东海陆架盆地油气评价中的应用     

任征平  顾惠荣 《上海国土资源》1995,(4):41-48

运用Ｄａｖｉｄ Ａ．Ｗｈｉｔｅ，１９８８介绍的方法，编制东海陆架盆地西湖凹陷和瓯江凹陷油气成藏组合图。通过图件编制的启示，对两个凹陷成藏主要特征和控制油气规律提出了一些新认识，并确定有利勘探区和勘探对象。  相似文献   

Potentialities,uncertainties and complexities in the response of coral reefs to future sea-level rise     

T. Spencer 《地球表面变化过程与地形》1995,20(1):49-64

Coral islands formed of largely unconsolidated sands only a few metres above sea level are thought to be particularly vulnerable to sea-level rise consequent upon global warming. However, scenarios which predict catastrophic flooding and loss of island area need reassessment, particularly in the light of the continued downwards revision of projected rates of future sea-level rise. Revised questions concern the interactions between reef growth and sea-level change, biophysical constraints on coral growth, and the importance to reef systems of potential changes in the magnitude, frequency and location of tropical cyclones and hurricanes. It is clear that most reefs have the growth potential to meet even the highest of future sea-level rise scenarios, but too little is known about physiological and physical constraints to reef growth to adequately evaluate the importance of these two factors in constraining this potential at the present time. Future sea-level rise in the tropical oceans, and coral reef responses, will take place against a backdrop of inter-regional differences in Holocene sea levels, resulting from the varying interaction of eustatic and hydro-isostatic processes. These differences have generated varying constraints on the development of modern reefs and varying inherited topographies upon which future sea-level changes will be superimposed. These controls are particularly important in assessing differences in vulnerability to future sea-level rise for reef islands in the Pacific Ocean and the Caribbean Sea.  相似文献   

Rapid entrenchment of stream profiles in the salt caves of Mount Sedom,Israel     

Amos Frumkin  Derek C. Ford 《地球表面变化过程与地形》1995,20(2):139-152

Rock salt is approximately 1000 times more soluble than limestone and thus displays high rates of geomorphic evolution. Cave stream channel profiles and downcutting rates were studied in the Mount Sedom salt diapir, Dead Sea rift valley, Israel. Although the area is very arid (mean annual rainfall ≈ 50 mm), the diapir contains extensive karst systems of Holocene age. In the standard cave profile a vertical shaft at the upstream end diverts water from a surface channel in anhydrite or clastic cap rocks into the subsurface route in the salt. Mass balance calculations in a sample cave passage yielded downcutting rates of 0–2 mm s^?1 during peak flood conditions, or about eight orders of magnitude higher than reported rates in any limestone cave streams. However, in the arid climate of Mount Sedom floods have a low recurrence interval with the consequence that long-term mean downcutting rates are lower: an average rate of 8·8 mm a^?1 was measured for the period 1986–1991 in the same sample passage. Quite independently, long-term mean rates of 6·2mm a^?1 are deduced from ¹⁴C ages of driftwood found in upper levels of 12 cave passages. These are at least three orders of magnitude higher than rates established for limestone caves. Salt cave passages develop in two main stages: (1) an early stage characterized by high downcutting rates into the rock salt bed, and steep passage gradients; (2) a mature stage characterized by lower downcutting rates, with establishment of a subhorizontal stream bed armoured with alluvial detritus. In this mature stage downcutting rates are controlled by the uplift rate of the Mount Sedom diapir and changes of the level of the Dead Sea. Passages may also aggrade. These fast-developing salt stream channels may serve as full-scale models for slower developing systems such as limestone canyons.  相似文献   

中国东北及邻区大陆边缘构造   总被引：82，自引：1，他引：82       下载免费PDF全文

唐克东  王莹 《地质学报》1995,69(1):16-30

中国东北及邻区大陆边缘包括两个构造带。内带由裂解的古陆碎块组成，其北部与古亚洲洋的演化有关，南部与古太平洋演化有关。外带由中生代地体组成。它们是晚古生代到早中生代的洋壳碎块与晚中生代的深海沟堆积组成的混杂体带。古亚洲洋封闭后到现代太平洋板块活动前，即由泥盆纪到侏罗纪曾存在过另一个大洋－古太平洋，其洋底扩张活动形成了上述的构造带。晚侏罗世后本区发育左旋平移断裂系，晚白垩世一早第三纪形成了大陆缘火山－  相似文献   

从贝丘遗址看绳纹人与环境的相互关系   总被引：1，自引：0，他引：1  

袁靖 《地球科学进展》1995,10(4):383-386

介绍了自本世纪７０年代末以来，日本学者在绳纹时代的考古研究中开辟的一个新领域，即通过分析贝丘遗址和周围的自然环境去认识绳纹的环境变化及绳纹人与环境的关系。同时提出了笔者关于绳纹时代人与环境关系的一个模式。  相似文献   

Source models for the 1993 Hokkaido Nansei-Oki earthquake tsunami   总被引：1，自引：0，他引：1  

Tomoyuki Takahashi  Takeyuki Takahashi  Nobuo Shuto  Fumihiko Imamura  Modesto Ortiz 《Pure and Applied Geophysics》1995,144(3-4):747-767

A source model for the 1993 Hokkaido Nansei-Oki tsunami must satisfy certain conditions. Such conditions are presented in this paper, and two methods are used to determine the best source model for this event. A trial-and-error method selects DCRC-17a as the best among 24 different models. This model has three fault planes dipping westward. To reproduce well the tide gauge records at two locations, an inversion analysis is used to modify the dislocation of DCRC-17a.  相似文献