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1.
对渤海湾西部潮间带和浅海区106个表层底质样品的活体与死有孔虫进行分析,筛选出8个优势种。利用死体有孔虫研究了优势种随水深(高程)变化的垂直分布特征,讨论了不同属种、不同有孔虫垂直组合带与地质环境、海面的定量关系。结果表明,有孔虫属种和组合的指示范围决定其作为地质环境及海面变化指标的灵敏性和精度。确立了研究区有孔虫海相性评价指数及与水深(高程)的相关性。根据对研究结果的实例应用的分析,恢复了研究区一个局部地点的相对海面变化曲线,为全新世地质环境和海面变化研究提供了一个新的尝试案例。  相似文献   

2.
莺歌海—琼东南盆地自晚第三纪海侵以来 ,可划分出 3个二级层序和 1 3个三级层序 ,利用生物化石 (主要为浮游有孔虫 )基准面确定层序的界面年龄值 ,自上而下分别为 1 .9Ma、2 .2Ma、 2 .8Ma、 3 .4 Ma、 5.1 Ma、 6.0 Ma、 1 0 .2 Ma、 1 2 .6Ma、 1 5.2 Ma、 1 9.6Ma、 2 1 .0 Ma、2 3 .7Ma、 2 5.5Ma、 3 0 Ma。通过各层序沉积期的环境演变 ,探讨了海平面变化的周期性 ,并与同时代的全球海平面旋回作了对比。本区最高海平面时期为早上新世 ,即相当于浮游有孔虫N1 9带至 N2 1 带下部 ,其次为中中新世早期 ,相当于浮游有孔虫 N9至 N1 2 带。  相似文献   

3.
The distribution of calcareous nannofossils and foraminifers occurring in the Callovian-Oxfordian deposits in the southwest of Moscow is studied. Nannoplankton-bearing beds and foraminiferal zones are distinguished. The Retecapsa incompta Beds correspond in range to the Ophthalmidium sagittum-Epistomina volgensis and Ophthalmidium strumosum-Lenticulina brestica foraminiferal zones as well as the lower part of Epistomina uhligi-Lenticulina russiensis Zone. The Watznaueria manivitae, Crepidolithus perforata, and Watznaueria fossacincta (lowermost part) beds span interval of the Epistomina uhligi-Lenticulina russiensis Zone. The Watznaueria fossacincta Beds are concurrent to the Lenticulina ponderosa-Flabellamina lidiae Zone of the foraminiferal scale.  相似文献   

4.
Brines can have a profound influence on the relative abundance of calcareous and agglutinated foraminiferal faunas. Here we investigated the distribution of benthic foraminiferal species in four cores from a brine‐enriched environment in Storfjorden, Svalbard. Stratigraphically, the cores comprise the last 15 000 years. The purpose of the study was to reconstruct changes in the palaeoecology and palaeoceanography of Storfjorden in relation to past climate changes, and to identify potential indicator species for brine‐affected environments. The benthic foraminifera in Storfjorden all have widespread occurrences in the Arctic realm. Calcareous species dominated Storfjorden during the deglaciation and early Holocene until c. 8200 a BP. However, agglutinated species increased in abundance whenever conditions became colder with more sea ice and stronger brine formation, such as during the Older Dryas, the Intra‐Allerød Cold Period and the Younger Dryas. Following a moderately cold period with numerous agglutinated foraminifera from c. 8200–4000 a BP, conditions became more changeable from c. 4000 a BP with repeated shifts between warmer periods dominated by calcareous species and colder periods dominated by agglutinated species. The warmer periods show a stronger influence of Atlantic Water, with reduced brine formation and less corrosive conditions at the sea bottom. Conversely, the colder periods show a stronger influence of Arctic water, with higher brine production and more corrosive bottom water. The distribution patterns of the calcareous species are basically the same whether calculated relative to the total fauna (including agglutinated specimens) or relative to calcareous specimens alone. Moreover, the patterns are similar to the patterns found elsewhere along western Svalbard in areas without the influence of brines. No particular species appear to be specifically linked to brine formation. However, the most persistent agglutinated species R. scorpiurus and A. glomerata are also the species most tolerant of the acidic bottom water that normally is associated with brine formation.  相似文献   

5.
The foraminiferal fauna from two holes near the coastal section of marls and limestones at Torquay is dominated by inner to mid‐shelf benthic forms, especially the cibicidids, discorbids and miliolids. Planktonic species are rare and rarely age‐diagnostic. A cluster analysis of the species occurrences and relative abundances identified four assemblages, A to D up‐section. These assemblages also closely correspond to lithological changes characterising lithostratigraphic units: Angahook Formation (assemblage A), lower and upper Jan Juc Formation (B, C) and Puebla Clay (D). Biofacies trends based on the relative abundances of inner and outer neritic taxa led to the recognition of third‐order sequences and boundaries equivalent to TB1.1 to TB1.4, confirming a previous identification on sedimentological grounds. They demonstrate that foraminiferal assemblages were directly influenced by third‐order sea‐level fluctuations and can be used to predict third‐order sequences. The long‐uncertain regional Oligocene‐Miocene boundary is placed at the Jan Juc Formation—Puebla Clay contact, across which there was a major faunal change. Several benthic forms disappeared, at least temporarily: Cibicidoides perforatus, Amphistegina lessonii and Pararotalia mackayi. The typical Miocene planktonic taxa Globoquadrina dehiscens and Globoturborotalita brazieri made their first appearance. These events were associated with an increase in inner neritic benthos signalling a low sea‐level, consistent with the contemporaneous global pattern.  相似文献   

6.
周洋  陈芳  苏新  刘坚  庄畅 《沉积学报》2014,32(3):527-536
本文对南海北部陆坡SH7B孔底栖有孔虫群落结构组成及壳体氧碳同位素值变化特征进行研究,旨在了解该区晚中新世以来的中层水体演化历史。利用因子和聚类分析对该钻孔128个样品中的35个底栖有孔虫优势属种的相对百分含量数据进行统计分析,识别出4个组合:Globocassidulina subglobosa-Stilostomella spp.（Gs-St）,Chilostomella mediterranensis-Globobulimina spp. (Cm-Gl),Hoglundina elegans-Pyrgo spp. (He-Py),Melonis affinis-Pyrgo spp. (Ma-Py)。晚中新世晚期至上新世早期（5.8~2.8 Ma）相对高海平面温暖期,SH7B孔底栖有孔虫为相对稳定的Gs-St组合,反映了低到中等营养物质供给的低氧水体环境。其中5.8~3.79 Ma底栖有孔虫壳体碳同位素偏负和强烈的碳酸盐溶解现象在全球其他海区均有发现,指示当时南海北部陆坡底层水体低氧环境可能受到因全球大洋环流格局变化影响的太平洋偏腐蚀性的缺氧中层水体影响。3.79~2.8 Ma底栖有孔虫丰度和喜氧类表生种含量逐渐增加,指示水体流通性趋于增强,水体氧含量稍有增加。晚上新世2.4 Ma以来,底栖有孔虫组合与氧碳同位素值波动变化频繁,反映了中等到高表层输出生产力的富氧到缺氧中层水体环境,南海北部陆坡底栖有孔虫的分布主要受陆源有机质输入量的多寡和南海中深层水体的循环状况共同控制。  相似文献   

7.
The marine Quaternary of Vendsyssel has been studied in a series of new boreholes in the area, and the climatic development is discussed on the basis of foraminiferal assemblages and stable isotopes. The foraminiferal zones are correlated with previously published records from northern Denmark, and the spatial local and regional distribution is discussed in details based on the new evidence. The new data show that the marine sedimentation in Vendsyssel was not continuous from the Late Saalian to the Middle Weichselian, as previously thought. For example, there is indication of a hiatus at our key site, Åsted Vest in the central part of Vendsyssel, at the transition between regional foraminiferal zones N4 and N3, i.e. at the Late Saalian (MIS 6) – Eemian (MIS 5e) transition. The hitherto most complete Early Weichselian succession (zone N2) in Vendsyssel is presented from Åsted Vest. Deposits from the Early Weichselian sea‐level lowstands (MIS 5d and 5b) may, however, be missing in parts of the area. Two major breaks in the marine deposition during the Middle Weichselian represent glacial advances into northern Denmark. The first event occurred just after deposition of the regional foraminiferal zone N2 (late MIS 4), and the second event in the middle part of zone N1 (early MIS 3). Zone N1 is succeeded by a series of non‐marine units deposited during the sea‐level lowstand of the Weichselian maximum glaciation (late MIS 3 and MIS 2), including deeply incised tunnel valleys, which have been refilled with non‐marine sediments during the Late Weichselian. Vendsyssel was inundated by the sea again during the Late Weichselian, at c. 18 kyr BP. Subsequently, the marine conditions were gradually changed by forced regression caused by local isostatic uplift, and around the Weichselian–Holocene transition most of Vendsyssel was above sea level. A continuous deposition across the Late Weichselian–Holocene boundary only occurred at relatively deep sites such as Skagen. The environmental and climatic indications for Vendsyssel are in accordance with the global sea‐level curve, and the Quaternary record is correlated with the oxygen isotope record from the NorthGRIP ice core, as well as the marine isotope stages.  相似文献   

8.
Planktonic foraminiferal assemblages from the Late Cretaceous-Early Tertiary sedimentary sequence in Quseir (Hammadat section), Safaga (Wasif section) and Esh El-Mellaha (Esh El-Mellaha section) areas along the Red Sea Coast, provide a database for biostratigraphical subdivisions and marking of faunal changes. Ten planktonic foraminiferal zones were found. There are, from base to top, the Late Cretaceous Globotruncana ægyptiaca and Gansserina gansseri Zones and the Early Tertiary Parasubbotina pseudobulloides, Praemurica trinidadensis, P. uncinata, Morozovella angulata, Igorina pusilla, Globanomalina pseudomenardii, Morozovella velascoensis and M. edgari zones.Two intervals of non-deposition of sediments (hiatuses) in the study areas are recorded, indicating tectonic events. The first hiatus occurred all over the study areas near the Cretaceous/Tertiary boundary. The second hiatus is restricted to the Late Palæocene of the Safaga area.Two global planktonic foraminiferal faunal turnover events are identified, reflecting major palæoceanographic changes. The faunal turnover event I occurred near the M. angulata/I. pusilla boundary near the Palæocene/Eocene boundary. These turnovers are characterised by the appearance and disappearance of species and changes in relative abundance, diversity and richness of species. Oscillation in the mean sea level in the study areas during the Late Cretaceous-Early Tertiary may be related to a true eustatic change in addition to the evidence for local tectonic control.  相似文献   

9.
Knudsen, K. L., Jiang, H., Kristensen, P., Gibbard, P. L. & Haila, H. 2011: Early Last Interglacial palaeoenvironments in the western Baltic Sea: benthic foraminiferal stable isotopes and diatom‐based sea‐surface salinity. Boreas, 10.1111/j.1502‐3885.2011.00206.x. ISSN 0300‐9483. Stable isotopes from benthic foraminifera, combined with diatom assemblage analysis and diatom‐based sea‐surface salinity reconstructions, are used for the interpretation of changes in bottom‐ and surface‐water conditions through the early Eemian at Ristinge Klint in the western Baltic Sea. Correlation of the sediments with the Eemian Stage is based on a previously published pollen analysis that indicates that they represent pollen zones E2–E5 and span ～3400 years. An initial brackish‐water phase, initiated c. 300 years after the beginning of the interglacial, is characterized by a rapid increase in sea‐surface and sea‐bottom salinity, followed by a major increase at c. 650 years, which is related to the opening of the Danish Straits to the western Baltic. The diatoms allow estimation of the maximum sea‐surface salinity in the time interval of c. 650–1250 years. After that, slightly reduced salinity is estimated for the interval of c. 1250–2600 years (with minimum values at c. 1600–2200 years). This may be related to a period of high precipitation/humidity and thus increased freshwater run‐off from land. Together with a continuous increase in the water depth, this may have contributed to the gradual development of a stratified water column after c. 1600 years. The stratification was, however, particularly pronounced between c. 2600 and 3400 years, a period with particularly high sea‐surface temperature, as well as bottom‐water salinity, and thus a maximum influence of Atlantic water masses. The freshwater run‐off from land may have been reduced as a result of particularly high summer temperatures during the climatic optimum.  相似文献   

10.
南黄海西部日照海域晚更新世海侵沉积地层广泛出露。基于本区18个站位柱状岩芯的剖面观察、有孔虫和介形虫鉴定、粒度分析、腹足类纹沼螺（Parafossarulus striatulus (Benson)）和钙质结核的AMS 14C年龄识别了沉积相，并探讨了MIS 3阶段的沉积历史和古环境特征，同时大致估算出末次海侵过程中水下平原的剥蚀厚度。结果表明，在日照外海、废黄河水下三角洲以北，表层覆盖着全新世早期海侵过程中所形成的砂质改造层，灰色，席状，无层理，厚度薄，通常在10~40 cm左右。海侵沙席之下为海陆过渡相沉积，可细分为滨岸潟湖相、沙坝相和滨海相等。底栖有孔虫组合几乎都以Ammonia beccarii (Linné) vars.为优势种，其他常见种为Elphidium magellanicum Heron?Allen et Earland、Cribrononion subincertum (Asano)、Textularia foliacea Heron?Allen & Earland、 Elphidium advenum (Cushman)、Protelphidium tuberculatum (d'Orbigny)、Cavarotalia annectens (Parker et Jones)和Pararotalia nipponica (Asano)等，指示滨岸浅水沉积环境。地层沉积年代为MIS 3阶段的中期或中早期，当时的海平面波动区间主要位于现今海平面以下20 m至31 m之间。这套地层为海进沉积，是海平面波动过程中所形成的沉积旋回，沉积过程中曾经历过反复的暴露和氧化，从下向上，其垂向层序可分为两个序列:1）滨岸潟湖—沙坝沉积或仅见沙坝沉积，为砂质沉积，分布在海侵沉积区的北部和西部；2）滨岸潟湖—滨海相沉积，为粉砂质沉积，分布在海侵沉积区的东南部。前者沿着古海岸线分布，后者距离古海岸线较远。表层钙质结核的大量富集，可能意味着末次海侵的强度已经剥露至土壤剖面下部的钙积层。据此估计，在末次海侵过程中，本区水下平原的平均剥蚀厚度约为50~70 cm。  相似文献   

11.
On the basis of researches over several years on biostratigraphy of Changhsingian at Meishan Section D in Changxing County, the abundant materials were accumulated. This paper studies the escostratigraphy and establishes 7 community zones (CZ), in ascending order, Sinoplatysomus-Gernitzina-Clarkina subcarinata, Tapashanites-Nodosaria-Clarkina subcarinata,Crurithyris-Geinitzina-Clarkina subcarinata,Glomospira-Clarkina changxingensis, Colaniella-Clarkina changxingensis,Rotodiscoceras-Palaeofusulina-Hindeodus typicalis,Clarkina meishanensis-Hypophiceras.The habitat type (HT) is diffent from upper shallow sea to the lower part of the lower shallow sea.  相似文献   

12.
孙泽轩 《铀矿地质》2000,16(2):79-84
本文介绍了盈江盆地的构造格架及构造分区、晚第三纪盆地沉积特征 ,对盆地盖层发育的氧化带进行分类 ,论述了氧化带的发育特征及其与铀矿化的关系。认为阻水断裂上方的潜水顺层氧化带及遭受后期潜水顺层氧化的古潜水氧化带铀矿化是区内砂岩型铀矿的主要类型  相似文献   

13.
Abstract: Abundant benthic foraminifera have been identified in thin sections of the siliceous black ore in the Ezuri Kuroko deposit, Hokuroku, Japan. By treating samples with conventional hydrofluoric acid digestion techniques, sponge spicules and radiolaria have also been recognized in the residue. Under microscopic observations, 94 individual foraminiferal specimens have been detected. However, as it is difficult to identify species or genera by means of microscope observations alone, only a small number of genera have been identified based on morphology. The foraminiferal assemblage is composed predominantly of agglutinated species (83%) with subordinate calcareous species (17%), and is assigned to the Cyclammina Assemblage based on the preponderance of Cyclammina (57%). The foraminifera are generally well preserved within micro‐crystalline to cryptocrystalline quartz, and exhibit no obvious features related to compaction or secondary deformation. Textural observations suggest that the siliceous component of this rock was not derived from an allochthonous block but instead constitutes autochthonous proto‐Kuroko sediment. The Cyclammina Assemblage in the ore is different from recently described foraminiferal assemblages in the vicinity of present deep‐sea hydrothermal vents, but is identical to those found in black shales of the Onnagawa to Funakawa stages in the Green Tuff region. The proto‐Kuroko sediment is assumed to have been deposited in an oxygen‐deficient environment within a closed, deep‐seated basin. The existence of siliceous microfossils suggests that the silica in the siliceous ore did not originate from silica sinter deposits produced by submarine hydrothermal activities, but from a biogenic siliceous ooze, probably composed of diatoms. Sulfide mineralization in the interstices of some of the microfossils is inferred to relate primarily to bacterial sulfate reduction associated with the decomposition of organic matter. The later sulfide mineralization associated with larger crystals (which contain fluid inclusions with homogenization temperatures of approximately 250C) cuts across the siliceous masses and foraminiferal septa, and may have been formed after consolidation of the siliceous ooze, accompanying the formation of acidic intrusive rocks during the late Onnagawa stage.  相似文献   

14.
Microfossil‐based transfer function models are increasingly used to provide decimeter‐scale sea‐level change reconstructions. In this paper I demonstrate that in the tropical location of northern Australia problems arise in selecting the appropriate elevation range for the modern training set used to calibrate fossil calcareous foraminiferal assemblages. Most calcareous foraminiferal species found in cores occur in both modern intertidal and shallow subtidal environments. A lack of independent measures to indicate whether fossil assemblages come from intertidal environments forces use of a training set that includes intertidal and subtidal environments. This results in decreased precision compared to using a training set solely from intertidal environments. The widely used method of assessing model fit to fossil assemblages (modern analogue technique) often fails to discriminate between acceptable and unacceptable reconstructions. It is important to investigate a number of different measures including modern analogue technique, canonical correspondence analysis and changing bootstrapped sample specific transfer function errors to fully understand the level of similarity between modern and fossil foraminiferal samples, to judge the reliability of transfer function‐predicted sea‐level reconstructions. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

15.
Seagrass beds provide important habitat for fishes and invertebrates in many regions around the world. Accordingly, changes in seagrass coverage may affect fish communities and/or populations, given that many species utilize these habitats during vulnerable early life history stages. In lower Chesapeake Bay, seagrass distribution has contracted appreciably over recent decades due to decreased water clarity and increased water temperature; however, effects of changing vegetated habitat on fish community structure have not been well documented. We compared fish community composition data collected at similar seagrass sites from 1976–1977 and 2009–2011 to investigate potential changes in species richness, community composition, and relative abundance within these habitats. While seagrass coverage at the specific study sites did not vary considerably between time periods, contemporary species richness was lower and multivariate analysis showed that assemblages differed between the two datasets. The majority of sampled species were common to both datasets but several species were exclusive to only one dataset. For some species, relative abundances were similar between the two datasets, while for others, there were notable differences without directional uniformity. Spot (Leiostomus xanthurus) and northern pipefish (Syngnathus fuscus) were considerably less abundant in the contemporary dataset, while dusky pipefish (Syngnathus floridae) was more abundant. Observed changes in community structure may be more attributable to higher overall bay water temperature in recent years and other anthropogenic influences than to changes in seagrass coverage at our study sites.  相似文献   

16.
There are known to be enormous Cenozoic coal-type oil and gas resources located in the basins of the South China Sea,among which the Paleogene coal-measure source rock are one of the main source rock.In order to more effectively analyze the distribution laws of coal-measure source rock in marginal sea basins and guide coal-type oil and gas explorations,the Oligocene coal-measure source rock in the Qiongdongnan Basin were selected as examples in order to systematically analyze the types,development characteristics,control factors,and distribution prediction methods of coalmeasure source rock in marginal sea basins.The Qiongdongnan Basin is located in the northern region of the South China Sea.Previous explorations of the area have determined that the Oligocene coal-measure source rock in the Qiongdongnan Basin have typical"binary structures",which include coal seams and terrigenous marine mudstone.Among those,the terrigenous marine mudstone has been found to greatly expand the scope of the coal-measure source rock.In addition,the coal seams which have been exposed by drilling have been observed to have the characteristics of thin single layer thickness,many layers,and poor stability.Meanwhile,the terrigenous marine mudstone has the characteristics of large thickness and wide distribution.The development of coal-measure source rock is known to be controlled by many factors,such as paleoclimate and paleobotany condition,paleo-structure and topography,paleo-geography,rise and fall of base level,and so on.In accordance with the comprehensive analyses of various control factors of coal-measure source rock,and the changes in water body energy in sedimentary environments,a genetic model of the"energy belt"for the development and distribution of coal-measure source rock was proposed.Also,the development and distribution characteristics of coalmeasure source rock in different types of energy belts were clarified.Then,based on the development and distribution characteristics of coal-measure source rock and their controlling factors,prediction methods of the distribution ranges of coal-measure source rock were proposed from both qualitative and(semi-)quantitative aspects.That is to say,a method for(semi-)quantitative predictions of the distribution ranges of coal-bearing intervals based on model wave impedance inversion and neural network wave impedance inversion,along with a method for(semi-)quantitative predictions of the distribution ranges of terrigenous marine mudstone based on topographical slopes,were introduced in this study.  相似文献   

17.
Based on four shallow drillings in the outer part of the Bjørnøya trough, palaeoenvironments of foraminifera in glacigenic sediments are discussed. Different methods were used; detailed foraminiferal analysis, oxygen and carbon stable isotope analysis and transfer functions. Six different foraminiferal assemblage zones were found. One zone, AA, appears to be pre-Pleistocene in age and contains an abundance of reworked early Tertiary foraminifera. Four of the assemblage zones have a dominant arctic foraminiferal content; however, a marked boreal input is evident, particularly in zone B where B. marginata dominates. We suggest that B. marginata has been resedimented from pre-Eemian 'warm' deposits. Its occurrence in these older warm intervals possibly reflects a lower input of the Norwegian Current into the area and possibly an increase in the relative nutrient content of the water masses. The six zones have also differing numbers of foram./gram sediment. An assemblage zone where a boreal component of foraminifera ( E. nipponica, P. bulloides ) dominates was found, zone C. We define this particular assemblage zone to be of Eemian age (isotope substage 5e). The foraminiferal assemblage composition and the oxygen and carbon isotopes from zone C indicate that oceanographic conditions in the Barents Sea during the Eemian were slightly different from those of the present and that, possibly, Atlantic waters were more prevalent.  相似文献   

18.
Benthic foraminifera, preserved in the Late Cretaceous organic carbon-rich sediments of Gamba, southern Tibet, provide high-resolution proxies for sea-level changes and dissolved oxygen fluctuations of southeastern Tethys. The fossils were statistically analyzed and divided into three faunas of "Cenomanian fauna", "Turonian fauna", and "Coniacian fauna". A middle neritic-upper bathal environment (50-250m) was estimated considering the ratios of planktonic and epifaunal benthic foraminifera (P/(P+E)), the morphological analysis according to the studies of recent foraminifera and the abundant distributions of depth-related species such as Alabamina creta, Laevidentalina sp., Praebulimina spp., Pleurostomella cf. naranjoensis, Pyrulina sp., Quinqueloculina spp., Haplophragmoides spp., etc. The result shows an almost parallel trend with the global transgressive and regressive cycles, but the former fluctuates more frequently at upper Cenomanian, which probably indicates tectonic instability of the continental margin. According to the benthic foraminiferal richness (BFN), Shannon-Weiner diversity (H(s)), as well as benthic foraminiferal oxygen index (BFOI), five periods of oxygen depleted conditions (dysoxic-anoxic) have been recognized. They correspond to the OAE2, the lower Turonian, the upper Turonian, the Turonian-Caniacian boundary event and the probably OAE3. In addition, the oxygen fluctuations in Gamba might be controlled directly by sea-level changes, while the paleoproductivity and oxygen conditions interacted with each other under oxygen deficiency environments.  相似文献   

19.
Holocene changes in the benthic and planktic foraminiferal fauna (>63 µm) from a marine sediment core (ARC‐3 Canadian Arctic Archipelago, 74° 16.050′ N, 91° 06.380′ W, water depth 347 m) show that significant environmental and palaeoceanographic variations occurred during the last 10 ka. Foraminiferal assemblages are restricted to the ca. 4.5–10 ka interval as younger samples are mostly barren of foraminifera due to intense carbonate dissolution after ca. 4.5 ka. Foraminiferal assemblages in the ca. 4.5–10 ka interval are dominated by the benthic species Islandiella helenae and Cassidulina reniforme (57% of total), with Elphidium clavatum, Cibicides lobatulus and Buccella frigida also being common in this interval. The dominance of these species indicates a seasonal sea ice regime which is consistent with the occurrence of the sea ice diatom‐derived organic geochemical biomarker IP25 throughout the core. The abundances of C. reniforme and E. clavatum decline upcore; consistent with more frequent mixing of the Barrow Strait water column during the early Holocene. It is likely that the influence of CO2‐rich Arctic surface water masses have caused an increase in bottom water corrosivity after ca. 8.5 ka, and dissolution has been further enhanced by sea ice‐related processes after ca. 6 ka, concomitant with increased IP25 fluxes. Dissolution is strongest when IP25 fluxes are highest, suggesting a link between the sea ice and benthic systems. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

20.
We present early to Mid‐Holocene paleo‐geographic reconstructions for the Ramore Head area (Northern Ireland). This coastal area is characterized by Mesolithic occupation (c. 10–6 ka) and preserved early–Mid‐Holocene peats both on‐ and offshore. This paper improves on previous reconstructions by employing a backstripping methodology, which removes accumulated recent deposits from identified buried paleo‐landsurfaces instead of using modern topography as an analogue to the past landscape. Paleo‐landsurfaces are identified offshore from seismic profiles supplemented by cores, and onshore through legacy borehole records. The paleo‐landsurface can be traced offshore to depths of −2 to −19 m and is buried by <5 m of modern sediment. It extends onshore under the coastal town of Portrush and is buried <2.5–10 m below modern ground level. The identified paleo‐landsurface is combined with sea‐level curves from recent Glacio‐Isostatic‐Adjustment models to reconstruct marine transgression during the early–Mid‐Holocene. Comparison is also made with reconstructions based on modern topography. Together, the identified paleo‐landsurfaces and revised reconstructions can assist future site prospection on‐ and offshore and delimit high‐potential areas for heritage management. Revised reconstructions also allow placement of extant archaeology into a more accurate context of landscape change and help develop insights into local‐scale site location patterns.  相似文献   

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