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1.
A high-resolution micropalaeontological study, combined with geochemical and sedimentological analyses was performed on the Tiefengraben, Schlossgraben and Eiberg sections (Austrian Alps) in order to characterize sea-surface carbonate production during the end-Triassic crisis. At the end-Rhaetian, the dominant calcareous nannofossil Prinsiosphaera triassica shows a decrease in abundance and size and this is correlated with a increase in δ18O and a gradual decline in δ13Ccarb values. Simultaneously, benthic foraminiferal assemblages show a decrease in diversity and abundance of calcareous taxa and a dominance of infaunal agglutinated taxa. The smaller size of calcareous nannofossils disturbed the vertical export balance of the biological carbon pump towards the sea-bottom, resulting in changes in feeding strategies within the benthic foraminiferal assemblages from deposit feeders to detritus feeders and bacterial scavengers. These micropalaeontological data combined with geochemical proxies suggest that changes in seawater chemistry and/or cooling episodes might have occurred in the latest Triassic, leading to a marked decrease of carbonate production. This in turn culminated in the quasi-absence of calcareous nannofossils and benthic foraminifers in the latest Triassic. The aftermath (latest Triassic earliest Jurassic) was characterised by abundance peaks of “disaster” epifaunal agglutinated foraminifera Trochammina on the sea-floor. Central Atlantic Magmatic Province (CAMP) paroxysmal activity, superimposed on a major worldwide regressive phase, is assumed to be responsible for a deterioration in marine palaeoenvironments. CAMP sulfuric emissions might have been the trigger for cooling episodes and seawater acidification leading to disturbance of the surface carbonate production at the very end-Triassic.  相似文献   

2.
Integrating analysis of the benthic palaeoecological record with multivariate ordination techniques represents a powerful synergy able to provide an improved characterization of coastal depositional facies in a sequence stratigraphical perspective. Through quantitative analysis of benthic foraminifer, ostracod and mollusc associations from the postglacial succession of Core M3 (Arno coastal plain, Tuscany, Italy), and application of detrended correspondence analysis (DCA) to the mollusc sub‐data set, we offer a refined picture of stratigraphical variations in faunal content from a paralic depositional setting, and reconstruct the palaeoenvironmental gradients that account for such variations. Despite distinct ecological behaviours, and taphonomic and sedimentological constraints, a strong ecological control on meio‐ and macrofaunal biofacies and taxa turnover is documented across the study succession. Amongst all possible mechanisms that may play a role in ‘shaping’ fossil distribution, the ecological signal driven by salinity represents the most prominent factor controlling the composition of fossil associations in the cored succession. Molluscs can even provide outstanding quantitative estimates of palaeosalinity along the sampled core. When plotted stratigraphically, the three fossil sub‐data sets show consistent patterns of vertical evolution that enable prompt identification of the key surfaces for sequence stratigraphical interpretation in otherwise lithologically indistinguishable deposits. The concomitant maximum richness of species with strong marine affinity, paralleled by the highest DCA salinity estimates, allows recognition of the maximum flooding zone, dated to ～7.7 cal. ka BP, within a homogeneous succession of outer lagoon clays. These clays are sandwiched between early transgressive, swamp to inner lagoon deposits and overlying prograding coastal?alluvial plain facies.  相似文献   

3.
INTRODUCTIONThe L ower Yangtze sedimentary basin in South Chinawas a typical carbonate ram p slightly inclining northwestwardduring the Early Triassic. The rhythmic L ower TriassicGriesbachian is m ainly composed of thin- bedded mudrock andmarl (or lim estone) alternations,which can be observed overthe region.Due to the wide distribution and well- comparativestructures of these cyclic sedim ents,it was proposed that thesedim ents originated from som e periodic regional environmen-tal e…  相似文献   

4.
Geochemical, mineralogical and biological indicators preserved in sediments are widely used to reconstruct past climate change, but proxies differ in the degree to which their utility as climate indicators has been validated via laboratory experiments, modern spatial calibrations, or down‐core comparisons with instrumental climate data. Multi‐proxy studies provide another means of evaluating interpretations of proxies. This paper presents a multi‐proxy assessment comparing 19 sub‐centennially resolved late Holocene proxy records, covering the period 300–1900 AD, from seven Icelandic marine and lacustrine core sites. We employ simple statistical comparisons between proxy reconstructions to evaluate their correlations over time and, ultimately, their utility as proxies for regional climate. Proxies examined include oxygen isotopic composition of benthic and planktonic foraminifera, abundance of the sea‐ice biomarker IP25, allochthonous quartz in marine sediments (a proxy for drift ice around Iceland), marine carbonate abundance, total organic carbon concentration, chironomid assemblages, lacustrine biogenic silica and carbon/nitrogen ratios in lake sediments. Most of the examined proxy records, including temperature and sea‐ice proxies, correlate strongly with each other over multi‐centennial timescales, and thus do appear to record changes in regional climate. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

5.
Data from agglutinated benthic foraminiferal assemblages and geochemical proxies make it possible to characterise different order sea-level dynamics —from a geological scale third-order transgressive-regressive cycle to a minor-scale, ecological range, maximum flooding-initial regressive phase—in part of the Valanginian from Spitsbergen. The transgressive-regressive cycle starts with abundance (foram/100 g) of opportunist epifaunal forms related to deep waters and low productivity conditions on oxygenated sea-bed. The increase of these foraminifera, together with increased condensation and an impoverishment of trophic resources, is associated with the maximum flooding phase. The beginning of the subsequent regression shows a progressive diminution in foraminiferal abundance as a result of the greater sedimentation rate, the mounting proportions of deep infaunal forms, and the diminution of genera of deep-water environments. This initial regressive phase is associated with more arid climatic conditions (abrupt increase of eolian detrital proxies), and high palaeoproductivity (increase of Ba/Al, Sr/Al and P/Ti ratios and TOC), determining a diminution in the oxygenation (high values in Co/Al, Ni/Al and Mo/Al ratios and hydrogen index). After the initial productivity bloom, the foraminiferal abundance decreases, whereas diversity increases, favoured by the stability of environmental conditions (no fluctuations in palaeoproductivity, detrital and redox proxies), in turn related to deceleration of sea-level fall. The peaks of maximum foraminiferal abundance (optimum) of each morphogroup during the transition from maximum flooding to the beginning of regression allow us to identify an ecological replacement inter- and intra-microhabitats. In the different phases of ecological replacement, the dominant morphogroups are distributed in distinct microhabitats (epifaunal, shallow infaunal and deep infaunal) as a result of competition.  相似文献   

6.
冷泉区底栖有孔虫研究进展   总被引：1，自引：0，他引：1  
海底冷泉区是海洋能源和生物资源同时富集的一类特殊区域。底栖有孔虫群落及其地球化学组成是海底冷泉区发育的重要指示标志之一。海底冷泉区的底栖有孔虫及其碳同位素研究,对于探讨冷泉演化、评估古冷泉甲烷排放对全球气候变化的影响有重要的研究意义。综述了全球一些主要冷泉区的底栖有孔虫研究方法及其进展,对比了各冷泉区底栖有孔虫群落结构的主要特征及地域差异,评述了冷泉区底栖有孔虫的碳同位素记录特征、影响因素及其对冷泉活动的潜在指示意义,最后提出了南海北部冷泉活动区底栖有孔虫方面的研究展望。  相似文献   

7.
In this paper, we present an integrated study of the macrofauna (Cephalopoda), microfauna (Ostracoda and Foraminifera), microflora (Pithonella, Dinoflagellata, Acritarcha and Prasinophyta) and geochemical signals (carbon δ13C and oxygen δ18O stable isotopes) of the upper Cenomanian and lower Turonian succession in Puentedey, Iberian Trough, Spain. This palaeontological and geochemical study has enabled us to identify numerous species of cephalopods (29), ostracods (19), benthic foraminifers (31), planktonic foraminifers (15), dinoflagellates (63), and acritarchs and prasinophytes (11), and to recognise two positive excursions of the δ13C signal related to the OAE2 (in the Metoicoceras geslinianum and the Spathites (Jeanrogericeras) subconciliatus zones, respectively). Variations of these macrofaunal, microfaunal, microfloral and geochemical signals have been interpreted to identify important events of the palaeoenvironmental evolution of the inner platform of the Iberian Trough during the studied interval of the Late Cretaceous. Benthic ecosystems were severely affected by the establishment of the Oceanic Anoxic Event 2 (OAE2) at the end of the late Cenomanian. This event is evidenced by the depletion of calcareous microfauna (benthic calcareous free intervals, BCFI) and the survival of opportunistic microfauna (platycopic ostracods and textulariid foraminifers). The response was different for microflora (dinoflagellates and acritarchs), which were less affected by the anoxic event.  相似文献   

8.
Sea level fluctuation is common in the stratigraphical record and is partly explained by periodic polar glaciation. Such fluctuation in the absence of polar glaciation, during the warm periods of Earth's history, is poorly understood and currently under discussion. Here, I reconsider the palaeo-environmental information extracted from the variation in the carbon-isotope record and explain the phenomenon by coupling the levels of marine and fresh-water reservoirs through long-term wet and arid climate modes. The arido-eustasy model produces a standard anti-covariation pattern of marine organic and carbonate carbon-isotope records, which may appear throughout the geochemical record of the last 200 Myr. Under the model, orbitally forced periods of extremely wet climate result in environmental crisis, sea level falls, and carbon cycle perturbations, during which negative excursions in the marine organic carbon-isotope record of sediments containing matter from terrestrial vegetation should be understood as a proxy reporting periods of high precipitation rather than changes in the global carbon reservoir. I propose that the early Toarcian oceanic anoxic event is an example of arido-eustasy.  相似文献   

9.
The Toarcian Oceanic Anoxic Event (T-OAE, ～183 Ma) was characterized by enhanced carbon burial, a prominent negative carbon-isotope excursion (CIE) in marine carbonate and organic matter, and numerous geochemical anomalies. A precursor excursion has also been documented at the Pliensbachian/Toarcian boundary, but its possible causes are less constrained. The T-OAE is intensively studied in the Cleveland Basin, Yorkshire, UK, whose sedimentary deposits have been litho-, bio- and chemostratigraphically characterised. Here, we present new elemental data produced by hand-held X-ray fluorescence analysis to test the expression of redox-sensitive trace metals and detrital elements across the upper Pliensbachian to mid-Toarcian of the Cleveland Basin. Detrital elemental concentrations (Al, Si, Ti, Zr) are used as proxies for siliciclastic grain content and thus, sea-level change, which match previous sequence stratigraphic interpretations from the Cleveland Basin. The timescale of the event is debated, though our new elemental proxies of relative sea level change show evidence for a cyclicity of 350 cm that may be indicative of ～405 kyr eccentricity cycles in Yorkshire. Trends in total organic carbon and redox-sensitive elements (S, Fe, Mo, As) confirm scenarios of widespread ocean deoxygenation across the T-OAE. The correlation of comparable trends in Mo across the T-OAE in Yorkshire and the Paris Basin suggests a similar oceanic drawdown of this element accompanying widespread anoxia in the two basins. Data from Yorkshire point to a transgressive trend at the time of the Mo drawdown, which contradicts the “basin restriction” model for the euxinic conditions that characterise the CIE interval.  相似文献   

10.
Two estuaries with very different inflow characteristics were compared to test the hypothesis that benthic standing crops are enhanced by freshwater inflow. Assuming predation pressure is similar in both estuaries, this would imply that freshwater inflow enhances secondary production. The Guadalupe Estuary had 79 times more freshwater inflow than the Nueces Estuary, and a third of the salinity. The Guadalupe had higher macrofaunal densities and biomass than the Nueces, and both parameters increased with decreasing salinity within the Guadalupe Estuary. Macrofauna density increased with increasing salinity in the Nueces Estuary, due to invasion by marine species. However, meiofauna population size responds differently than macrofauna. Meiofaunal densities were higher in the low-inflow Nueces Estuary, and increased with increasing salinity in both estuaries. Macrofauna diversity increased with salinity, both within and between estuaries. The macrofauna response supports the hypothesis that increased freshwater inflow stimulates secondary production. A review of past benthic studies in these estuaries and the historical climatic patterns indicate that wet years with high inflow result in increased macrofaunal productivity. Since, macrofaunal diversity decreased with lower salinity both within and between the estuaries, the enhanced productivity is due to increases by freshwater and estuarine species that can tolerate low salinities. Increased macrofaunal densities are associated with decreasing meiofaunal densities. The latter result could be due to either increased macrofaunal competition with or predation on meiofauna, or a lack of low-salinity tolerance by meiofauna.  相似文献   

11.
The effect of seeping of methane on marine sediment records has been studied in four gravity cores from Vestnesa Ridge, Svalbard margin. The area shows acoustic signs in the form of flares indicating active methane gas seepage. For a better understanding of the timing and variability of the flux of methane in the past and the effects on potential proxies, a detailed study of the diagenetic processes that may affect the composition and structure of both sediments and foraminiferal shells is needed. Here we discuss deep‐sea records from methane‐influenced environments in three cores from an active and very heterogeneous seep‐area (pockmark) and one core from outside the pockmark for background. The results include the distribution and stable isotopes of authigenic carbonates and of benthic and planktonic foraminifera, magnetic susceptibility, AMS‐14C dates, sedimentary data and biostratigraphy. Extremely low δ13C values recorded in both benthic and planktonic foraminifera during the Bølling‐Allerød interstadials indicate possible increased methane flux beginning at late Heinrich event H1. The recorded low values are mainly a result of diagenetic overprint by methane‐derived authigenic carbonates. The δ18O signals of authigenic carbonates are close to those of foraminiferal calcite and thus the δ18O records remain a valid stratigraphical tool in methane seep sites, except in the case of severely encrusted samples. In addition, the records from the active pockmark show nearly constant values of low magnetic susceptibility in contrast to higher and more variable magnetic susceptibility values from the control station and other published records from normal sediments west of Svalbard. This phenomenon is probably caused by dissolution of magnetic minerals in the reducing environmental conditions of methane seep sediments, associated with anaerobic oxidation of methane and formation of paramagnetic minerals (pyrite). This process enables magnetic susceptibility to be used as a common diagnostic tool for identifying methane‐related palaeo‐reductive environments.  相似文献   

12.
This two-part study examined the benthic macrofaunal community in Delaware salt marsh impoundments having partial tidal restriction. The first part compared abundance, diversity, and taxonomic composition in three habitat types in impoundments—creeks, vegetated creek banks, and ponds—to those found in natural marshes. Impoundment effects were present but were habitat-specific. Abundances were higher in natural marsh creeks than in impoundment creeks, and diversities were higher in impoundment ponds than in natural marsh ponds. Vegetated bank communities in impoundments were about 50% insects and arachnids and 50% oligochaetes, while natural bank communities were primarily oligochaetes and the polychaeteManayunkia aestuarina. This is likely due to the decrease in flooding of the vegetated high marsh caused by partial impoundment. Pond and creek community composition also showed impoundment effects: in comparison with natural marshes, impoundments had higher proportions of the burrowing anemoneNematostella vectensis, nemerteans, andTubificoides sp. oligochaetes and lower proportions of the oligochaeteClitellio arenarius. The second part of the study compared benthic macrofauna in an impoundment before, during, and after the water level was lowered so that some bottom sediments were exposed and some covered with just a few centimeters of water for several weeks. During this event, macrofaunal abundances were reduced and the community shifted from being dominated by annelids, anemones, and nemerteans toward one dominated by annelids and insects. About 6 wk after reflooding, persistent effects of this disturbance were still suggested by greatly increased abundances and 96% dominance by one species of oligochaete,Paranais litoralis. Impoundment management plans calling for periods of sediment exposure or very low water may want to consider the potential for strong and persistent effects on the macrofaunal community.  相似文献   

13.
Freitas  M.C.  Andrade  C.  Moreno  J.C.  Munhá  J.M.  Cachão  M. 《Geologie en Mijnbouw》1998,77(3-4):283-293
The inner Tagus estuary is essentially a sedimentation basin that receives cohesive sediment from terrestrial, marine, biological and anthropogenic sources. Three short cores from one site in a marsh area of this estuary (Seixal Bay) were analysed for sedimentary, geochemical and micropalaeontological contents (benthic foraminifera and nannoplankton). The length of the cores represents about half a millennium of sedimentation. Textural analysis suggests a highly uniform mud sedimentation for most of the cores but geochemical, mineralogical and micropaleontological results indicate climatic and environmental changes and anthropogenic disturbance. Three Foraminifera zones were identified. The lower part of the lower zone indicates sedimentation in an open channel or a lower domain of an exposed high-energy sandflat. Sediments of the upper part of the lower zone and of the middle zone were deposited in a lower-energy environment, probably associated with a sheltered, vertically aggrading mudflat located within the Seixal Bay. Biological and mineralogical indicators suggest that periods of total or partial closure of this bay occurred. Clay minerals indicate that drier and colder conditions prevailed in the lower half of this zone evolving gradually to a wetter and warmer environment towards the top. The upper zone indicates persistence of low-energy sedimentation and evolution towards the present salt-marsh conditions. Anthropogenic pollution is clear in geochemical proxies at the top of the sedimentary column and was used for dating purposes.  相似文献   

14.
Climatic reconstruction of glacial to interglacial episodes from oxygen isotopes in sediment cores from the Nordic seas is complicated by strong local meltwater contributions to the oxygen isotope changes. Combination of benthic and planktic foraminiferal isotope data with foraminiferal abundances and ice-rafted debris (IRD) allows separation of local and global effects and subdivision of the marine oxygen isotope events 6.2–5.4, which include the last interglaciation, into: (1) a meltwater phase after glacial stage 6, recorded by large amounts of IRD and low foraminiferal abundance, indicating surface water warming; (2) an IRD-free period with high deposition rates of subpolar foraminifera and other CaCO3pelagic components, recognized here as the “full” interglaciation; and (3) a phase with the recurrence of IRD and the demise of subpolar species. Comparison of ice-core records and marine data implies that the global climate during the last full interglaciation and that during the postdeglacial Holocene were similar. The records show no significantly different variations in the proxy data. In contrast, the oxygen isotopes of planktic foraminifera and ice cores indicate significant differences during each of the deglacial transitions (Terminations I and II) that preceded these two interglaciations. These suggest that during Termination II the climatic evolution in the Nordic seas was less affected by abrupt changes in ocean–atmosphere circulation than during the last glacial to interglacial transition.  相似文献   

15.
The abundance and structural diversity of bacteriohopanepolyols (BHPs) was examined in three marine pelagic environments that are characterized by strong vertical redox gradients and water column suboxia or anoxia. The abundance and, in most instances, structural diversity of BHPs was highest at depths where conditions were suboxic or anoxic. However, the majority of the BHP structures that were identified are environmentally cosmopolitan and their biological sources are presently not well constrained. An isomer of bacteriohopanetetrol (denoted BHT II) was observed at all three study sites in association with anoxic and suboxic conditions within the water column. Based on the absence of BHT II from terrigenous and oxic marine environments studied to date, and its strong association with suboxic and anoxic marine pelagic environments, we propose that BHT II is a promising candidate biomarker for water column suboxia and anoxia in the marine geologic record. The molecular fingerprint of BHPs in suspended and sinking particles and core-top sediments indicates that hopanoids produced within the water column are exported to marine sediments and that their biological source is most likely associated with settling particles and not the free-water phase. Based on our observations, BHPs likely represent an important input to the sedimentary hopanoid inventory, particularly in upwelling environments characterized by pelagic oxygen minimum zones (OMZ) and anoxic marine basins.  相似文献   

16.
The Kungurian ocean-climate system has received little attention, but a new compilation of geochemical and paleoclimatic proxies suggest more complex climate dynamics during the Late Paleozoic icehouse–greenhouse transition than previously considered. Here, integrated carbon isotope stratigraphical, sedimentological, and geochemical data across two Early–Middle Permian successions in the Youjiang Basin, South China, is presented. These proxies indicate widespread anoxia below or near the water-sediment interface in South China during the Kungurian. High primary productivity, high sedimentation rate, and a relative sea-level rise are here proposed as being responsible for this process in the late Kungurian, but cannot account for the remaining anoxia at cycle boundaries. We put forward a hypothesis that divergent climate trends between the tropics and Gondwana might have played an important role in ocean stagnation and prevailing O2-deficient conditions in and probably outside South China during the Kungurian. The termination of anoxia in this region during the latest Kungurian is attributed to an intensification of oceanic circulation, a rise in atmospheric pO2 concentrations, a sea-level drop, depressed primary productivity, and low sedimentation rates. This study calls for further high-resolution sedimentological and geochemical investigations on the paleotropics outside South China, in order to elucidate the icehouse-greenhouse transition at the global scale.  相似文献   

17.
The stratigraphic distribution of sedimentary organic matter in Anisian carbonate series of southern Poland is studied with respect to relative sea-level fluctuations. Palynofacies patterns clearly reflect transgressive–regressive trends that are interpreted in terms of third-order cyclicity. Major flooding phases are detected by maximum abundance of marine plankton in the upper Bithynian and Pelsonian. Transgressive and highstand deposits are recognized by changes in the terrestrial input of organic particles and the relative percentages and diversity of the plankton group. The palynological data support the sequence stratigraphic interpretation based on sedimentological features and geochemical signatures. The corresponding eustatic signals of sedimentary and organic facies are discussed. The study highlights the potential of palynofacies analysis for sequence stratigraphical interpretation.  相似文献   

18.
古海洋生产力指标研究进展   总被引：20，自引：1，他引：19  
寻求反映古海洋生产力变化的指标是古海洋学研究的重要内容。生物沉积物、营养元素、微量元素和同位素、古生物资料等与古海洋生产力具有一定的关系,常用于古海洋生产力的重建工作:(1)生物沉积物主要包括有机碳、生物碳酸盐和生物硅质沉积等,其埋藏速率在很大程度上受到古海洋生产力的控制,常常用作古海洋生产力的替代性指标;(2)在地质时间尺度上,古海洋生产力主要受到大洋中营养元素可利用程度的控制,因此营养元素的相关记录可以提供古海洋生产力状况的重要信息;(3)海洋中某些微量元素的地球化学行为或者与有机质的改造有关,或者受到氧化还原条件变化的控制,或者受到某种浮游生物的生长的影响,从而能够直接或者间接地指示古海洋生产力的变化;(4)海相碳酸盐和有机质的碳同位素记录,海相有机物的氮同位素比值也用以再造古生产率等古海洋学参数;(5)可以利用对微体化石丰度值及其组合反映古生产力的变化。  相似文献   

19.
This study was designed to investigate seasonal changes on food available for benthic consumers in relation to tidal levels and sediment depth in an estuarine beach. The relationships between the biochemical characteristics of sedimentary organic matter and benthic macrofauna were analyzed quarterly over 2 years (from January 1997 to January 1999), in an estuarine soft intertidal zone from the NW coast of Spain (42°64′04″N, 8°88′36″W). Sediment samples were collected to provide a two-dimensional view of macroinfauna distribution in the intertidal zone and its relationship with the quantity and quality of the organic matter. The nutritional value of organic matter (i.e., lipid, protein, and carbohydrate) and the content of chlorophyll a of the sediment were measured. Macrofaunal assemblages and food availability in the sediment were studied at three tidal levels on the shore: two intertidal and one supratidal. Macroinfauna and biochemical compounds showed a clear vertical stratification with the highest macrofaunal abundance at the superficial layer of the sediment, where redox potential discontinuity was also observed. Crustaceans were found mainly inhabiting the supratidal level of the estuarine beach, while polychaetes and mollusks occupied the intertidal level. Food availability, measured as biopolymeric carbon, and also chlorophyll a from the sediment were better related to macroinfauna abundance, biomass, and abundance of main taxonomic groups. Macrofauna assemblages showed particular distribution in both vertical and horizontal ranges suggesting specific preferences to several abiotic factors. No clear seasonal pattern was found in macrofauna and sedimentary organic characteristics suggesting that macrofaunal assemblages are controlled by complex and unpredictable factors, including small-scale changes in substrate and hydrological characteristics.  相似文献   

20.
Sedimentological, micropalaeontological (benthic foraminifers and dinoflagellate cysts), stable isotope data and AMS 14C datings on cores and surface samples, in addition to acoustic data, have been obtained from Voldafjorden, western Norway. Based on these data the late glacial and Holocene sedimentological processes and variability in circulation and fjord environments are outlined. Glacial marine sedimentation prevailed in the Voldafjorden between 11.0 kyr and 9.2 kyr BP (radiocarbon years). In the later part of the Allerød period, and for the rest of the Holocene, there was deposition of fine‐grained normal marine sediments in the fjord basin. Turbidite layers, recorded in core material and on acoustic profiles, dated to ca. 2.1, 6.9–7.6, ca. 9.6 and ca. 11.0 kyr BP, interrupted the marine sedimentation. The event dated to between 6.9 and 7.6 kyr BP probably corresponds to a tsunami resulting from large‐scale sliding on the continental margin off Norway (the Storegga Tsunami). During the later part of the Allerød period, Voldafjorden had a strongly stratified water column with cold bottom water and warm surface water, reaching interglacial temperatures during the summer seasons. During the Younger Dryas cold event there was a return to arctic sea‐surface summer temperatures, possibly with year‐round sea‐ice cover, the entire benthic fauna being composed of arctic species. The first strong Holocene warming, observed simultaneously in bottom and sea‐surface temperature proxies, occurred at ca. 10.1 kyr BP. Bottom water proxies indicate two cold periods, possibly with 2°C lowering of temperatures, at ca. 10.0 (PBO 1) and at 9.8 kyr BP (PBO 2). These events may both result from catastrophic outbursts of Baltic glacial lake water. The remainder of the Holocene experienced variability in basin water temperature, indicated by oxygen isotope measurements with an amplitude of ca. 2°C, with cooler periods at ca. 8.4–9.0, 5.6, 5.2, 4.6, 4.2, 3.5, 2.2, 1.2 and 0.4–0.8 kyr BP. Changes in the fjord hydrology through the past 11.3 kyr show a close correspondence, both in amplitude and timing of events, recorded in cores from the Norwegian Sea region and the North Atlantic. These data suggest a close relationship between fjord environments and variability in large‐scale oceanic circulation. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

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