首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 15 毫秒
1.
Investigation of a 19th-century shipwreck site on Cockburn Reef, northeastern Australia, suggests the wrecked ship was a British-/European-built vessel of 350–450 tons. The accompanying large quantity of ballast-rock suggests the vessel was sailing “in-ballast.” Of the nine 19th-century ships reported lost on or near Cockburn Reef, these findings narrow contenders to the brig Druid (343 tons), wrecked there on a voyage from Hobart, Tasmania to Singapore or the barque Lady Sale (388 tons), wrecked there on a voyage from Sydney to Ceylon. The petrographic characteristics of a block of ballast-rock from the site prove it to be Hawkesbury (Sydney) Sandstone from New South Wales. This geoarchaeological evidence confirms the identity of the wreck to be that of the Lady Sale which departed Sydney in-ballast. Historical evidence suggests that ballast-rock originating from Hobart probably comprised basalt, thus discounting the Druid. © 1998 John Wiley & Sons, Inc.  相似文献   

2.
The Nullarbor Plain is the largest karst area in Australia (220,000 km2) and one of the largest in the world. Its climate is arid (Köppen BWk and BWh), and the surface relief is less than 10m. The landscape is divided into extensive closed karstic depressions separated by low rocky ridges, and the dominant vegetation is chenopod shrubland. The extent and severity of soil degradation has been assessed using remote sensing. GPS rectified images from 1972–1973, 1979, 1983, 1988, and 1991 have been compared for two sites on the Nullarbor. Over the 19 years the total extent of bare soil has reduced significantly, but some areas around water points have degraded and there is some disturbance due to fossorial wombats. Sheet-flow processes occur during intense rainfall events, which happen two or three times per decade. Runoff only occurs after the 10– or 50– year return frequency events, and at these times turbid water ponds in depressions and enters caves. Surface soil sorptivity and hydraulic conductivity differ markedly between ridges and depressions; the ridges are clearly zones of groundwater recharge, while ponding is evident in most depressions. Sorptivity is influenced by the extent and nature of ground cover and cryptogam crusts on the soil. The landscape has been divided into classes on the basis of vegetation type and percentage of foliage cover. In each class the activities of fallout radionuclides will be determined by high resolution spectroscopy. Preliminary results suggest that in undisturbed sites little sediment movement has occurred over the time scale of cesium-137 (the last 35 years) but that the landscape has been well sorted over a much longer time scale. Future work will investigate disturbed sites to estimate relative soil loss during the pastoral period.  相似文献   

3.
4.
In this article, the authors summarize 20 years of scholarship and two field projects on geoarchaeology in Nara, Japan, carried out by researchers from 12 different institutions in 4 countries. The research goal was to test an aerial photographic reconstruction of surface landforms in the Nara Basin with subsurface data. Project A was conducted at Asawa; it tested, through geological coring, whether a suspected swampy backmarsh in the eastern basin existed and whether it would yield data on the transition to wet rice agriculture in the mid‐1st millennium B.C. Project B was conducted at Miwa; it tested, through geological coring and subsequent excavation, the nature of upland agricultural terrace formation in the southeastern basin and whether the suspected existence of a 4th‐century palace site could be confirmed. Two layers of carbonaceous clay at Asawa were dated to the Early (˜5000–3500 B.C.) and Final (˜1000‐300 B.C.) phases of the Jomon period. Pollen data revealed the establishment of an evergreen oak forest from 5,000 years ago and anthropogenic changes in forest cover from 2,000 years ago. Phytoliths from rice, millets, reeds, and bamboo were recovered in layers postdating the Final Jomon carbonaceous clay. A fault scarp with anthropogenic modification of the terraces was identified at Miwa. It was discovered that an incised stream valley had been infilled in the Medieval period at the same time surface layers were razed; the front of the terrace was extended in the premodern period. Remains were recovered from the Middle Yayoi (˜100 B.C.–A.D. 100) and the Medieval (˜A.D. 1185–1603) periods. However, as the terracing involved razing the early historic levels, no data were recovered on the alleged 4th‐century palace site. The significance of these findings lies in the identification of (a) a swampy backmarsh at Asawa, where initial agricultural efforts in growing wet rice in the basin may have occurred, confirming the aerial photographic reconstruction; and (b) hillside terracing activities at Miwa, from the Medieval period onwards, which have radically changed the configuration of the natural topography. © 2005 Wiley Periodicals, Inc.  相似文献   

5.
袁同星  刘东生 《地球学报》2000,21(2):177-181
邯郸市东部平原区属华北平原冀南坳陷 ,新生界厚度约 1500m。热储层为上第三系馆陶组和明化镇组下部砂砾岩含水层。地热类型为受上地幔传导热流加热的盆地边缘水热型层状温热水。根据地热地质条件及邻区地热信息和地温梯度 ,邯郸市东部平原区有望找到50~58℃以上的温热水。  相似文献   

6.
The organic matter-rich Toolebuc Formation of eastern Australia was deposited in a Lower Cretaceous epicontinental sea. Parameters from biological marker studies indicate that the organic matter is immature to marginally mature for hydrocarbon generation. The occurrence of abundant coccoliths and the distribution of alkane biomarkers suggest that the organic matter (Type II) is largely of planktonic origin and only in the southeastern part of the depositional area can a terrestrial influence be discerned. Variations in kerogen composition can be attributed to the extent of the oxidation of the source materials and the degree of incorporation of sulphur. The atomic H/C ratios (c. 1.1) are remarkably constant for most of the Toolebuc Formation. Atomic O/C ratios vary from 0.1 and 0.4 and can be related both to depth and paleogeographic position. Kerogen sulphur contents range up to 7%, and the highest values occur in the most carbonate-rich sediments. Total sulphur (inorganic + organic) to carbon ratios in the sediments vary from 1 to <0.2 and are a function of paleogeographic position and lithology. Most of the sulphur in the sediments is in the form of pyrite, but the proportion of sulphur in organic form increases as the total sulphur content decreases. The evidence for oxidation of the organic matter and incorporation of sulphur into it during deposition suggests that bituminite, which is the dominant organic maceral in the Toolebuc Formation, was formed from an organic gel derived by decay of predominantly algal material. These data support a modified gyttja model (Kauffman, 1981) for the deposition of organic matter in the Toolebuc Formation.  相似文献   

7.
Over the past thirty years, geoarchaeology has moved from the fringe to mainstream status within Mesoamerican archaeological investigations. This review focuses on works published since the year 2000. Five themes are identified as central to recent studies: (1) the correlation of environmental change and cultural history; (2) anthropogenic environmental impacts; (3) ancient land cover, land use, and diet; (4) archaeological prospection; and (5) provenance studies. These themes are often interwoven in the application of complex systems approaches that allow scientists to more accurately model the intricacies of ancient human–environment interactions.  相似文献   

8.
 Arid karst landscapes that have been degraded by human activities provide a challenge for rehabilitation and an opportunity to test ideas about the stability and resilience of limestone ecosystems. The Nullarbor Plain is the largest arid karst area in Australia (220 000 km2) and is divided into extensive closed karstic depressions separated by low rocky ridges, while the dominant vegetation is chenopod shrubland. Since European settlement there has been considerable change in the vegetation, with significant reduction in shrub and grass cover over large areas of the plain. These changes are related to a state and transition model of vegetation dynamics which incorporates climatic variability, fire history and grazing pressure from sheep, kangaroos and rabbits. A partial sediment budget using 137Cs inventories reveals local and regional patterns of soil redistribution within this arid karst landscape. Rehabilitation of eroded soil in pastoral lands has been accomplished at several sites but is labour intensive and vulnerable to climatic fluctuations. Given the low stock numbers, limited number of people involved, and poor economic returns, it would be sensible to make pastoral activities on the Nullarbor secondary to conservation priorities. This would necessitate a change in land ethic to stewardship, with emphasis on rehabilitation and control of feral animals. Management of increased numbers of visitors to the caves and karst also requires that resource inventories and management plans for each area be drawn up and used. Received: 1 June 1995 · Accepted: 4 December 1995  相似文献   

9.
中国东部主要入海河流As元素分布、来源及影响因素分析   总被引:2,自引:2,他引:2  
为查明中国河流中As等重金属元素的分布规律,于2007—2008年分丰水期和枯水期对中国东部30余条入海河流水体、悬浮物统一进行采样分析。结果表明:东部河流中As元素溶解态含量均值为3.1μg/L,同世界河流相比,明显偏高;且频率分布直方图具有多个峰值,反映出明显的人为污染。利用富集系数的研究表明,悬浮物同样受到较明显的人为污染。As在河水中的迁移形式以溶解态为主,pH值和温度对As的迁移形式有明显影响。流域内岩石类型对河流中As含量影响显著,火山岩、火山碎屑岩类广泛分布的流域河水中As含量明显偏高,花岗岩及中、深变质岩广泛分布的流域河流中As含量则偏小。利用生活、工业污水作为As元素人为来源端元,对海河、黄河、长江、珠江等河流人为源进行了估算,分别为46.7%、18.7%、13.5%、8.3%。  相似文献   

10.
Four major periods of palaeochannel activity have been identified on the Murrumbidgee sector of the Riverine Plain of southeastern Australia. On the basis of stratigraphic information the channels reveal a picture of changing flow conditions during the last full glacial cycle. The ages of the periods were determined from nearly 40 thermoluminescence dates on surficial fluvial and aeolian sediments. These are named the Coleambally phase, which occurred from 105 to 80 ka (the mid- to latter part of Oxygen Isotope Stage 5), the Kerarbury phase from 55 to 35 ka (Stage 3), the Gum Creek phase from 35 to 25 ka (late Stage 3 to early Stage 2) and the Yanco phase from 20 to 13 ka (late Stage 2). The present flow regime was established by about 12 ka (Stage 1). The first two phases correlate with episodes of enhanced fluvial activity in northern and central Australia and with reduced dust activity globally. The phases in Stage 2 appear to be associated with seasonal snow melt and increased peak flows in periods flanking the Last Glacial Maximum. Source-bordering aeolian dunes associated with the Coleambally, Kerarbury and Yanco phases were found, however, the TL dates show that some have undergone aeolian reworking. Thermoluminescence dating and fluvial stratigraphy have revealed a detailed picture of Late Quaternary climate and flow regime changes that has the potential to extend to identified deposits stratigraphically older than those described here.  相似文献   

11.
The complex debate on prehistoric settlement decisions is no longer tackled from a purely archaeological perspective but from a more landscape‐oriented manner combined with archaeological evidence. Therefore, reconstruction of several components of the former landscape is needed. Here, we focus on the reconstruction of the groundwater table based on modeling. The depth of the phreatic aquifer influences, for example, soil formation processes and vegetation type. Furthermore, it directly influences settlement by the wetness of a site. Palaeogroundwater modeling of the phreatic aquifer was carried out to produce a series of full‐coverage maps of the mean water table depth between 12.7 ka and the middle of the 20th century (1953) in Flanders, Belgium. The research focuses on the reconstruction of the input data and boundary conditions of the model and the model calibration. The model was calibrated for the 1924–1953 time period using drainage class maps. Archaeological site data and podzol occurrence data act as proxies for local drainage conditions over periods in the past. They also served as a control on the simulated phreatic palaeogroundwater levels. Model quality testing on an independent validation data set showed that the model predicts phreatic water table levels at the time of soil mapping well (mean error of 1.8 cm; root mean square error of 65.6 cm). Simulated hydrological conditions were in agreement with the occurrence of archaeological sites of Mesolithic to Roman age at 96% of the validation locations, and also with the occurrence of well‐drained podzols at 97% of the validation locations.  相似文献   

12.
河流沉积砂体定量表征是油田高效勘探开发的重要基础。文章综合利用定量岩心分析、测井相分析、定量地震沉积学和三维地震剖面识别方法,对霸县凹陷文安斜坡东营组古河道砂体厚度,河道(带)宽度,(满岸)河道水深等河流参数进行了定量化计算。研究表明,文安斜坡东营组发育北部苏桥、中部文安和南部长丰镇三个物源输入口,河流呈NEE-SWW向分散于文安斜坡带,其中河道带宽度(w)为1.04~2.61 km,平均宽度(wcb)为1.71 km;主河道宽度(W)为15.2~179.6 m,平均宽度(Wc)为84.4 m;主河道沉积水深(D)为1.34~5.21 m,平均水深(Dc)为3.29 m;主河道满岸水深(Dmax)为2.35~9.15 m,平均满岸水深(Dmaxa)为5.77 m;主河道沉积厚度(H)为2.15~8.32 m,平均厚度(Hc)为5.25 m,河道长度(L)为18.5~28.2 km,平均河道带长度(Lcb)为25.1 km,流向(A)为40°~65°。确定文安斜坡东营组发育辫状河沉积,斜坡东侧中外带为主要的砂岩卸载区,河流以垂向挖掘性河流为主,侧向迁移为辅,河道砂岩平面呈“条—带”状。文安斜坡西侧内带以侧向迁移河流为主,下蚀作用为辅,河道砂岩呈“席—带”状。东营组河道砂岩具有“下生上储”的有利成藏条件,具有良好的岩性、构造—岩性圈闭(油气藏)勘探前景。  相似文献   

13.
Small Archaean, pre-metamorphic layered sill-like intrusions showing Stillwatertype differentiation are widespread in the Eastern Goldfields region of Western Australia. The sills have undergone low-grade metamorphism, but the retention of some original minerals and excellent preservation of primary textures have enabled most of their original features to be reconstructed. Despite their small size in comparison with well known layered intrusions, simple differentiation sequences are developed ranging upwards from dunite and harzburgite through orthopyroxenite, norite, norite-gabbro and gabbro to granophyre and anorthosite. The parent magma for the sills appears to have been rich in MgO (15–18%) and is probably represented by the spatially associated high-Mg basalts found in the region. The complexes are interpreted as being contemporaneous with volcanism and may be high-level emplacements.  相似文献   

14.
A complex late Quaternary alluvial history was documented along Henson Creek, a low order tributary on the Fort Hood Military Reservation in central Texas. Three Quaternary alluvial landforms were recognized: terrace 2 (T2), terrace 1 (T1), and the modern floodplain (T0). The late Pleistocene T2 terrace may contain an array of sites spanning the entire known cultural record, while T1 may have sites spanning the last 5000 years only. Five fluvial units, three colluvial facies, two alluvial fan facies, and two buried paleosols were also recognized. Fluvial deposition was occurring approximately 15,000 yr B.P., 10,000-8000 yr B.P., 7000–4800 yr B.P., 1650-600 yr B.P., and during the last 400 years. Colluvial deposition was ongoing mainly in the early and middle Holocene, while alluvial fan aggradation was proceeding primarily in the middle Holocene. Because of erosional unconformities, there is minimal potential for recovering buried sites dating to intervals between depositional eposides for most of the drainage basin. Preservation potentials for buried sites are greatest in fine-grained fluvial deposits dating to the late Pleistocene, early Holocene, and parts of the late Holocene, and in fine-grained colluvial deposits dating to the early and middle Holocene. This investigation demonstrates that within the study area, and perhaps throughout much of central Texas, a greater continuum of sediments and preservation potentials exists in late Quaternary alluvial deposits of rivers than in low-order tributaries.  相似文献   

15.
为系统客观的评价地下水饮用水源地的安全状态,基于“驱动力-压力-状态-影响-响应”(DPSIR)框架初步建立备选评价指标,运用专家咨询法对备选指标进行筛选及合理性检验,采用层次分析法确定指标权重,构建地下水饮用水源地安全度综合评价体系。以滹沱河浅层孔隙水水源地为例,确定了包含5个准则层,18个指标的地下水饮用水源地安全评价指标体系。滹沱河浅层孔隙水水源地实例研究表明,准则层中压力系统和状态系统所占权重较大,分别为0.257和0.339;水源地安全度为0.67,尽管处于较安全级别,但非常接近警戒值(0.4~0.6)。通过实例分析可知,筛选的指标具有一定的实用性,可以为评价浅层孔隙水水源地的安全状态及面临的风险提供参考。  相似文献   

16.
The late Palaeozoic granitoids of the Moonbi district are derived both from igneous (I‐type) and sedimentary (S‐type) sources. Field and petrographic observations and chemical data on the I‐type granitoids show that they are derived from four separate and distinct source‐rock compositions and that, consequently, these granitoids may be grouped into four suites. Mafic xenoliths and microxenoliths are relatively more abundant in more mafic I‐type granitoids. Such xenoliths are interpreted as restite, or material residual from partial melting of the source rocks. Variation within the granitoids is ascribed to varying degrees of separation of restite from the melt produced during each fusion event. The source material of the I‐type granitoids is considered to have been material underplated beneath the crust during an earlier subduction event. Two suites of S‐type granitoids can be recognized. These are derivatives of pelitic materials that have undergone only a small amount of chemical weathering.  相似文献   

17.
Petrographic, petrological and geochemical studies have demonstrated the presence of three distinctive basic volcanic suites in the Eastern Goldfields Province, Yilgarn Block, Western Australia. These are termed the high magnesian series basalts (HMSB), the low magnesian series basalts (LMSB) and the siliceous high magnesian series basalts (SHMSB).The HMSB and SHMSB constitute differentiation series which contain both high MgO (9.5–14 wt.%) and low MgO (<9.5 wt.%) members. These suites are commonly characterized by igneous textures indicative of very rapid crystallization suggesting high eruption temperatures. This feature clearly distinguishes those low MgO members of HMSB which contain amphibole pseudomorphs after spherulitic-textured pyroxene from compositionally similar LMSB. The LMSB are generally characterized by an intergranular texture consisting of plagioclase laths and interstitial amphibole pseudomorphs after pyroxene grains. Variolitic-textured basalts are common and appear to be restricted to the SHMSB suite of basic volcanics.The HMSB and LMSB were derived from source mantle regions which were variably depleted in the incompatible elements. Archaean komatiites were derived from similarly depleted source regions and it is argued that the main petrogenetic difference between these three volcanic suites was the degree of partial melting from which they were derived. The depleted nature of the source regions may have been induced by earlier small degree (< 5%) partial melting events with subsequent extraction of a proportion of that melt. Variations in both the degree of such melting, and the proportions of melt removal, could induce considerable heterogeneity of incompatible elements in the Archaean upper mantle.Source mantle regions of the SHMSB were variably enriched in the incompatible elements and water and parental magmas of the SHMSB were derived from moderately hydrous conditions of partial melting.The relative proportions of each basalt suite varies considerably between the layered successions examined. For example, the basic volcanics overlying the komatiites at Kambalda are SHMSB, while the footwall volcanics consist predominantly of HMSB with subordinate LMSB. However, the Norseman succession, where no ultramafic volcanics are known to occur, is comprised mainly of LMSB with a smaller proportion of HMSB.  相似文献   

18.
Passive seismic approaches, using a single-station, enable rapid, cost-effective and non-invasive estimates of the thickness of sedimentary rocks overlying crystalline basement. This approach was applied to estimate the Cenozoic and Cretaceous succession beneath the Nullarbor Plain in southeastern Western Australia. Passive seismic data acquired at the majority of the 94 sites show a single, strong resonance frequency peak between 0.4 and 0.6 Hz suggesting an impedance contrast of a single subsurface layer. Modelling these resonance frequencies against known stratigraphy at 12 drill holes shows that this impedance contrast corresponds to the contact of the base of the Cenozoic–Cretaceous sedimentary succession of the Eucla and Bight basins with the crystalline basement. Data from the remaining sites produced sediment thickness estimates ranging from only tens of metres near the western edge of the Nullarbor Plain to over 860 m near its southern margin. Near this margin, rapid thickening of the sedimentary cover is coincident with an interpreted paleosea-cliff or indicative of localised faulting. Beneath the Western Australian portion of the Nullarbor Plain the sedimentary cover is on average 320 m thick with the succession thinning gradually towards the margins of the basin. A passive seismic approach is thus seen as a useful screening tool for the mineral exploration industry in areas that are under cover allowing for better targeting and cost-reduction in greenfields exploration.  相似文献   

19.
邢台市东部平原地热开发远景初探   总被引:1,自引:0,他引:1  
方连育  康清普 《地球学报》2000,21(2):155-159
在简述邢台市东部平原地质构造、地层、地热地质模型、地质变异常区分布特征基础上,对邢台市东部平原地热开发远景进行了分析探讨,并提出了在邢台市东部平原进行地热资源开发的合理化建议。指出地热异常区内的远景开发区应优先开发;准地热异常区的地热资源开发应引起足够重视;在不具备完整地热地质模型的地热异常区内也有地热资源存在的可能。  相似文献   

20.
The hornfelsed Skiddaw Slates in the River Caldew, Cumberland, exhibit one of the best displayed sets of folds in the country. Patterns resulting from an analysis of these folds and the structures on the valley sides, indicate that the rocks have suffered several phases of deformation. Evidence is produced to suggest that folding was initiated during the pre-Bala movements, and re-folding occurred during the main end-Silurian orogeny. During the end-Silurian movements, folding due to collapse under gravity also occurred.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号