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1.
The northern Wanganui Basin, New Zealand, is one of the key global sites for understanding marine cyclic sedimentation during the Quaternary. This paper presents the first evidence of marine cyclic sedimentation from its central-southern parts. Sedimentological, micropalaeontological and palynological analyses on a 280-m-deep borehole encountered units dating back to MIS 10. The sequence includes four marine cycles spanning MIS 9–5, which are overlain by terrestrial fluvial aggradation surfaces dating from MIS 4–2. Each marine unit represents a progressively shallowing depositional environment from the mid-shelf to coastal plain. This is overlain by a terrestrial sequence of lowstand fluvial terraces. Localized fault movements appear to have influenced the sedimentary character of the sequence during MIS 7a and 5e producing basement highs which provided protection to the shoreline. The cyclothems described in this paper now extend the already extensive, previously described record from MIS 17–10 to produce a combined eustatic record of Quaternary sea level change within the basin to MIS 5. They also provide an excellent example of the sedimentary response of a coastal basin to a progressive loss of sedimentation accommodation space.  相似文献   

2.
Holocene sedimentation patterns and environmental development in Aarhus Bay, Denmark, were reconstructed based on proxy analyses of two sediment cores (M1 and M5). Together, the two cores offer an opportunity to examine the history of the area during the past c. 10 000 years. The investigation consisted of acoustic mapping and multi-proxy analyses of the sediment cores including macrofossils, sediment physical properties, sediment accumulation rates, grain size, and X-ray fluorescence elemental counts. Radiocarbon dating of the two sediment successions revealed that they cover the periods c. 10 000–3700 cal. a BP (M1) and c. 4400 cal. a BP to the present (M5). The data from the M1 site indicate the presence of a near-shore lake environment between c. 10 000 and 9000 cal. a BP. The first intrusion of marine water into the area is dated to c. 9000 cal. a BP. In the following c. 1300 years, brackish-water conditions prevailed in the area characterized by a mixture of taxa from marine, limnic and terrestrial habitats, reflecting a shallow estuarine environment. Around 7700 cal. a BP full marine conditions were established, accompanied by a marked increase in sedimentation rates. The changes to full marine conditions and higher sedimentation rates are probably due to a significant sea-level rise leading to flooding of former land areas and intensified erosion. A subsequent distinct decrease in sedimentation rates around 6350 cal. a BP is presumably linked to a previously documented sea-level drop about this time. Continuous sedimentation ceased around 3700 cal. a BP in the central part of the bay, most probably due to a major sea-level lowering involving widespread erosion. In the eastern and deeper part of the bay, sedimentation continued until today. Fully marine conditions prevailed there for at least the last 4400 years.  相似文献   

3.
In this study, we use a combined biomarker and macrofossil approach to reconstruct the Holocene climate history recorded in Trifna Sø, Skallingen area, eastern North Greenland. Chronological information is derived from comparison of lithological, biogeochemical and macrofossil characteristics with a well‐dated record from nearby Lille Sneha Sø. Following local deglaciation around c. 8 cal. ka BP, the local peak warmth occurred between c. 7.4 and 6.2 cal. ka BP as indicated by maximum macrofossil abundances of warmth‐demanding plants (Salix arctica and Dryas integrifolia) and invertebrates (Daphnia pulex and Chironomidae). Warm conditions were dominated by terrestrial organic matter (OM) sedimentation as implied by the alkane‐based Paq ratio, but increased aquatic productivity is indicated when temperature was highest around 6.5 cal. ka BP. The n‐C29/n‐C31 alkane ratio shows that vegetation in the catchment was dominated by shrubs after deglaciation, but shifted towards relatively more grassy/herbaceous vegetation during peak warmth. After 5.4 cal. ka BP, the disappearance of warmth‐demanding plant and invertebrate macrofossils indicates cooling in the Skallingen area. This cooling was characterized by a significant shift towards dominance of aquatic OM sedimentation in Trifna Sø as implied by high Paq ratios. Cooling was also associated with a shift in vegetation type from dwarf‐shrub heaths towards relatively more herbaceous vegetation in the catchment, stronger erosion and more oligotrophic conditions in the lake. Our data show that mean air temperatures inferred using branched glycerol dialkyl glycerol tetraethers (brGDGTs) do not seem to accurately reflect the local climatic history. Irrespective of calibration, methylation of branched tetraethers (MBT) palaeothermometry cannot be reconciled with the macrofossil evidence and seems to be biased by either changing brGDGT sources (in situ vs. soil‐derived) or changing species assemblages and/or an unknown physiological response to changing environmental conditions at high latitude.  相似文献   

4.
The Araucaria Plateau is a geomorphological unit that occupies approximately three-quarters of the terrain in the southern region of Brazil. The plateau displays different altitudinal levels (600 to <1400 m a.s.l.) that are locally recognized as remnants of planed surfaces (S8–S1). These surfaces are maintained by basic (S3–S8) and acidic (S1 and S2) volcanic flows from the Neocretaceous period of the Paraná Basin. The largest extent of this plateau is located in a humid subtropical climate zone. Colluvial, colluvial–alluvial, alluvial sediments and paleosols (Ab diagnostic horizons) occur predominantly in S2. The paleosols are located in low-hierarchical-order fossil valleys (first- to fourth-order in Strahler's stream classification) and valley heads, which are referred to as paleovalleys in this paper. We employed these paleosols as stratigraphic level markers of the pedogenesis of the regional Upper Quaternary and propose their importance as records of the paleoenvironmental conditions of the Araucaria Plateau in areas above 1200 m a.s.l. These paleosols were dated by 14C and show ages between 23.8 ± 0.05 kyr BP (28.06–29.08 kyr cal. BP) and 41.16 ± 0.48 kyr BP (44.13–45.58 kyr cal. BP). The calibrated ages are related to Marine Isotope Stage 3 (MIS 3), in which the last period of global warming occurred (approximately 60–25 kyr cal. BP). We integrated the morphological, pedogeochemical, clay fraction mineralogy, micromorphological and δC-13 analyses of five paleosols from S2 to verify the paleoenvironmental conditions of the Araucaria Plateau and its correspondence with the paleoclimatic phenomena that were identified on a global scale during MIS 3 in the Southern Hemisphere. We obtained the following conclusions: a) the properties of paleosols reflect pedological processes that are adjusted to the paleoenvironmental conditions at the end of MIS 3 and the transition to MIS 2 (Last Glacial Maximum); b) aplasmogenic partial acidolysis was the predominant pedogeochemical process during MIS 3; c) during this period, the water regime was sufficiently humid to develop hydromorphic horizons in the valley bottoms of the entire drainage network to the valley heads; d) regional change toward a drier hydric regime occurred in MIS 2, when erosion of the paleosols predominated; and e) in MIS 1 (current Holocene interglacial), burial of the paleosols and relief inversion occurred, which resulted in fossilization of the valleys.  相似文献   

5.
The aim of this paper is to show the stratigraphic record of the Late Pleistocene corresponding to the distal region of the Paraná River basin. It displays sedimentological, paleontological and geochronological evidences that characterise the last interglacial–glacial cycle. In particular, strong environmental records are shown for the Last Interglacial Stage (LIS). Salto Ander Egg Formation (SAEF) is defined as a new lithostratigraphic unit representative of the Late Pleistocene in southwestern Mesopotamia. This unit is formed of complex fluvial deposits, which contains a heterogeneous collection of sub-environments, of ages ranging from 120 to 60 ky BP. The clast-supported gravel facies containing sparse boulders indicate high flow during a humid climate. The large and middle-scale architectures of fluvial sedimentary bodies evidence the relationship between the sediment accommodation and the sea level oscillations. Three sub-sequences identified in the succession suggest a transgressive trend during the MIS5e, a highstand stage in MIS5c, and a minor transgressive cycle during MIS3. A Brazilian faunal association collected at the bottom of the sequence and sedimentological interpretations display wet and warm climatic conditions, typical of tropical or subtropical environments. Such environmental conditions are characteristic of the maximum of the last interglacial stage (MIS5e) and show a signal stronger than the signal of the current interglacial stage. All these data show a direct correlation between the increases of paleodischarges and the elevation of the sea level. The whole sequence is completed with transitional swampy deposits, accumulated probably during the MIS3/MIS2 transition, and the typical loess of the Tezanos Pinto Formation, mantled during the Last Maximum Glacial.  相似文献   

6.
《Quaternary Science Reviews》2007,26(9-10):1223-1235
High-precision U-series dating allows a direct correlation to be made between terrestrial records of the penultimate interglacial (Marine Oxygen Isotope Stage 7 (MIS 7)) in Britain and sub-stage climate forcing in the marine oxygen isotope sequence. U-series ages of surficial tufa deposits are of sufficient precision to correlate discrete episodes of temperate conditions with individual warm sub-stages within MIS 7. Furthermore, detailed biostratigraphy allows periods of faunal turnover to be correlated with cold climates and lowered sea level. Ecological and environmental conditions in Britain during MIS 7 are therefore driven by the short-lived, sub-stage climate forcing that is observable in the marine isotope record. It is clear that interglacial climates are highly dynamic, producing multiple climatic optima and a diverse range of environments within single warm episodes. Consequently sub-stage records of climate forcing are crucial frameworks for reconstructing terrestrial records of environmental change.  相似文献   

7.
渤海湾西岸晚第四纪海相地层划分及地质意义   总被引：5，自引：0，他引：5  
BT113孔和BT114孔是位于渤海湾西岸地区的2个80 m全取心钻孔。通过对钻孔岩心的岩性、沉积构造及生物组合等特征分析,结合AMS14C和OSL（光释光）测年结果,揭示中更新世晚期以来本地区主要发育3个海相地层：自下而上为中更新统上部的第三海相地层（简称“海三”）、上更新统的第二海相地层（简称“海二”）和全新统的第一海相地层（简称“海一”）,指示中更新世晚期以来研究区发生的3次主要海面波动。与全球海面变化曲线对比,海三,海二和海一分别发育于MIS（深海氧同位素阶段）7、MIS5和MIS1的高海面时期,说明渤海湾西岸中更新晚期以来地层记录的海面变化趋势与全球变化一致。与前人的传统认识不同,认为受全球海面及渤海海峡地貌共同影响,MIS3时期研究区并未发生大范围海侵。通过多个钻孔的对比分析,3个海相地层在渤海湾西岸地区的分布较广,具有良好的可对比性,不同钻孔之间同一海相地层的高程和厚度的较大差异指示本地区在晚更新世期间发生较强的差异性沉降活动。  相似文献   

8.
Planktonic foraminifera and pollen data from core GNS84-C106 (Gulf of Salerno, Tyrrhenian Sea) were analysed through the Modern Analogue Technique, Constrained Cluster Analysis and relative variation biplots. A long period of mild climate, centred around 25 ka BP, is evident in both marine and continental reconstructions. The cooling phase from 17 to 14.7 ka BP, correlated to the H1 Heinrich event, is indicated by a sea surface temperature (SST) decrease, which roughly coincides with the cold-arid phase identified by annual and January temperatures. A rapid increase in atmospheric temperatures and precipitation, culminating at 13.8 ka BP, marks the BA cronozone. The corresponding increase in summer and winter SSTs, of 11 and 6.5 °C, respectively, occurred over 600 years. The beginning of the YD, centred around 12.5 ka BP, is marked by a decrease in summer and winter SSTs of, respectively, 4.5 and 3.5 °C in one century. The atmospheric evidence of the YD is primarily reflected in low January temperatures, reaching −6 °C, the lowest values ever experienced in the analysed time interval. The Late Glacial–Holocene transition is clearly recorded in both the continental and marine realms. From 11.5 to 9 ka BP, atmospheric temperatures record a period of substantial stability followed by a drop at 8.9 ka BP, which chronologically fall within the first RCC event (9–8 ka BP) of Mayewski et al. [2004. Holocene climate variability. Quaternary Research 62, 243–255], in correspondence with a phase of relatively high seasonality, indicated by foraminifera.  相似文献   

9.
The impact of the Laurentide Ice Sheet (LIS) deglaciation on Northern Hemisphere early Holocene climate can be evaluated only once a detailed chronology of ice history and sea‐level change is established. Foxe Peninsula is ideally situated on the northern boundary of Hudson Strait, and preserves a chronostratigraphy that provides important glaciological insights regarding changes in ice‐sheet position and relative sea level before and after the 8.2 ka cooling event. We utilized a combination of radiocarbon ages, adjusted with a new locally derived ΔR, and terrestrial in‐situ cosmogenic nuclide (TCN) exposure ages to develop a chronology for early‐Holocene events in the northern Hudson Strait. A marine limit at 192 m a.s.l., dated at 8.1–7.9 cal. ka BP, provides the timing of deglaciation following the 8.2 ka event, confirming that ice persisted at least north of Hudson Bay until then. A moraine complex and esker morphosequence, the Foxe Moraine, relates to glaciomarine outwash deltas and beaches at 160 m a.s.l., and is tightly dated at 7.6 cal. ka BP with a combination of shell dates and exposure ages on boulders. The final rapid collapse of Foxe Peninsula ice occurred by 7.1–6.9 cal. ka BP (radiocarbon dates and TCN depth profile age on an outwash delta), which supports the hypothesis that LIS melting contributed to the contemporaneous global sea‐level rise known as the Catastrophic Rise Event 3 (CRE‐3).  相似文献   

10.
A possible asynchronicity of the spatial and temporal moisture availability on the Tibetan Plateau has been a controversial subject of discussion in recent years. Here we present the first attempt to systematically investigate possible spatial and temporal variations in moisture availability by examining two lakes, Tangra Yumco and Nam Co, on an east–west transect on the southern Tibetan Plateau using identical proxies for palaeoenvironmental reconstruction. In this study, an independent record from Tangra Yumco was analysed applying a multi‐proxy approach to reconstruct variations in moisture availability since the Lateglacial. Results were subsequently compared with previously published records from Nam Co and additional records from Tso Moriri (northwestern Himalaya) and Naleng Co (southeastern Tibetan Plateau). Our results show that Tangra Yumco was at least partially ice covered prior to 17.1 cal. ka BP. A temperature rise after 17.1 cal. ka BP probably resulted in thawing of the permafrost. At 16.0 cal. ka BP moisture availability increased, representing an initial monsoonal intensification. Warmer conditions between 13.0 and 12.4 cal. ka BP and cooler conditions between 12.4 cal. ka BP and the onset of the Holocene reflect the Bølling‐Allerød and Younger Dryas. At the onset of the Holocene moisture availability rapidly increased, with moisture highest prior to 8.5 cal. ka BP when temperatures were also highest. After 8.5 cal. ka BP the moisture availability gradually decreased and showed only minor amplitude variations. These findings are consistent with the records from large lakes like Nam Co, Tso Moriri, and Naleng Co, revealing a synchronous pattern of moisture availability on the southern Tibetan Plateau.  相似文献   

11.
The Okanagan Centre section is the stratotype for marine oxygen isotope stage (MIS) 4 sediments (Okanagan Centre Drift) in the southern interior of British Columbia, Canada. Previous work suggested that these sediments record two glacial and two interglacial cycles. This study reports on detailed sedimentological and geochronological investigations of lithostratigraphic units comprising the Okanagan Centre sequence, revealing successive deposition of subaqueous and subaerial outwash, a subglacial till and glaciolacustrine sediments during MIS 4. A limiting optical age of 113 ± 8 ka defines the base of this sequence. Sedimentological, paleopedological, optical dating and tephrochronological data from sediments near the middle of the sequence reveal soil development (MIS 3) in eolian sediments deposited on a river terrace overlying a deglaciated surface. Within these sediments, identification of Mt. St. Helens set C tephra suggest sedimentation between 50 and 35k 14C a BP. Optical dating corroborates the tephrochronology and suggests that this surface formed after ～52 ± 7 ka. The record of MIS 2 glaciation is restricted to deglaciation, and overlies MIS 3 sediments above an unconformity possibly related to regional subglacial meltwater erosion. Eolian sediments containing Mt Mazama set O tephra (～7.62k cal a BP) cap the sequence.  相似文献   

12.
渤海湾西岸BT113孔35ka以来的沉积环境演化与海陆作用   总被引：1，自引：0，他引：1  
根据渤海湾西岸有孔虫和介形虫与年代学(AMS14C和OSL测年)研究,将该段岩心自下而上划分为6个沉积单元(U1—U6),它们依次形成于晚更新世的河流及全新世的潮滩、浅海、前三角洲、三角洲前缘和三角洲平原沉积环境,结束于约35 ka的U1单元的陆相环境,证实晚更新世低海面时渤海湾西岸未受海水影响。U1和U2单元之间,存在历时约27 ka的沉积间断(35～8.5 ka cal BP),研究区因此缺失早全新世沉积。U2单元的潮滩环境指示全新世海侵于8.5 ka cal BP到达渤海湾西岸,当时相对海平面为-16.7 m。U3单元为浅海环境,约6 ka cal BP时相对海平面上升到-6.8～-1.8 m。8.5～6 ka cal BP期间的海面上升速率是0.4～0.6 cm/a,可能与MWP1C事件有关。U4—U5单元,转为三角洲环境,沉积速率增大,反映自3.7 ka cal BP河流输入影响加强,约1.3 ka cal BP时成陆,形成U6单元。晚更新世35 ka以来的陆海环境演化,总体上是对气候变化控制下的海面变化的响应。  相似文献   

13.
AMS 14C ages of post-glacial core sediments from the subaqueous Yangtze delta, along with sedimentary structures and distributions of grain size, pollen spores, and dinoflagellate cysts, show an estuarine depositional system from 13 to 8.4 cal ka BP and a deltaic system from 5.9 cal ka BP to the present. The estuarine system consists of intertidal to subtidal flat, estuarine, and estuarine-front facies, characterized by sand–mud couplets and a high sedimentation rate. The deltaic system includes nearshore shelf and prodelta mud featured by lower sedimentation rate, markedly fewer coastal wetland herbaceous pollens, and more dinoflagellate cysts. We explain the extremely high sedimentation rate during 9.2–8.4 cal ka BP at the study site as a result of rapid sea-level rise, high sediment load due to the unstable monsoonal climate, and subaqueous decrease of elevation from inner to outer estuary. A depositional hiatus occurred during 8.2–5.9 cal ka BP, the transition from estuarine to deltaic system, caused possibly by a shortage of sediment supply resulting from delta initiation in paleo-incised Yangtze valley and strong tidal or storm-related reworking in offshore areas. The subsequent development of deltaic system at the study site indicates accelerated progradation of Yangtze delta post-5.9 cal ka BP.  相似文献   

14.
As a future warm-climate analog, much attention has been directed to studies of the Last Interglacial period or marine isotope substage (MIS) 5.5, which occurred ～120,000 years ago. Nevertheless, there are still uncertainties with respect to its duration, warmth and magnitude of sea-level rise. Here we present new data from tectonically stable peninsular Florida and the Florida Keys that provide estimates of the timing and magnitude of sea-level rise during the Last Interglacial period. The Last Interglacial high sea stand in south Florida is recorded by the Key Largo Limestone, a fossil reef complex, and the Miami Limestone, an oolitic marine sediment. Thirty-five new, high-precision, uranium-series ages of fossil corals from the Key Largo Limestone indicate that sea level was significantly above present for at least 9000 years during the Last Interglacial period, and possibly longer. Ooids from the Miami Limestone show open-system histories with respect to U-series dating, but show a clear linear trend toward an age of ～120 ka, correlating this unit with the Last Interglacial corals of the Key Largo Limestone. Older fossil reefs at three localities in the Florida Keys have ages of ～200 ka and probably correlate to MIS 7. These reefs imply sea level near or slightly above present during the penultimate interglacial period. Elevation measurements of both the Key Largo Limestone and the Miami Limestone indicate that local (relative) sea level was at least 6.6 m, and possibly as much as 8.3 m higher than present during the Last Interglacial period.  相似文献   

15.
In this study we present a recent compilation of 286 modern surface pollen spectra from the southern part of the Russian Far East (42–54°N, 131–141°E) and use it to test the biome reconstruction method. Seventy terrestrial pollen taxa were assigned to plant functional types and then classified to eight regional biomes. When applied to 286 surface pollen spectra, the method assigns about 70% (201 sites) of the samples to the cool mixed forest biome, 17% – to the taiga, 2% – to the cool conifer forest, 3% – to the temperate deciduous forest, and 7% – to the steppe. The steppe reconstruction is characteristic of the pollen spectra from the agricultural areas around Lake Khanka. A visual comparison shows good agreement between pollen-derived biomes and actual vegetation distribution in the region. However, pollen and botanical data, compared with the potential vegetation distribution simulated from the modern climate dataset using the BIOME1 model, demonstrate that spatial distribution of cool mixed forest is underrepresented in the model simulation. The model sets the mean temperature of the coldest month of −15 °C as the factor limiting distribution of the temperate deciduous broadleaf taxa, while vegetation and pollen data from the region demonstrate that this limit should be lowered to −26 °C. Application of the method to the Gur 3–99 pollen record (50°00′N, 137°03′E) demonstrates that tundra vegetation predominated around the site prior to 14 ka BP (1 ka = 1000 cal. years). However, the local presence of boreal trees and mixed forest-tundra vegetation is suggested by relatively high taiga scores. Soon after 14 ka BP the scores of taiga become slightly higher than tundra scores. During 11.4–10.5 ka BP a cool conifer forest is reconstructed. Establishment of the full interglacial conditions is marked by the onset of cool mixed forest by 10.5 ka BP. Between 10.3 and 2.5 ka BP the scores of temperate deciduous forest are close to those of cool mixed forest and become distinctly lower during the late Holocene.  相似文献   

16.
Modern global warming is likely to cause future melting of Earth's polar ice sheets that may result in dramatic sea-level rise. A possible collapse of the West Antarctic Ice Sheet (WAIS) alone, which is considered highly vulnerable as it is mainly based below sea level, may raise global sea level by up to 5–6 m. Despite the importance of the WAIS for changes in global sea level, its response to the glacial–interglacial cycles of the Quaternary is poorly constrained. Moreover, the geological evidence for the disintegration of the WAIS at some time within the last ca. 750 kyr, possibly during Marine Isotope Stage (MIS) 11 (424–374 ka), is ambiguous. Here we present physical properties, palaeomagnetic, geochemical and clay mineralogical data from a glaciomarine sedimentary sequence that was recovered from the West Antarctic continental margin in the Amundsen Sea and spans more than the last 1 Myr. Within the sedimentary sequence, proxies for biological productivity (such as biogenic opal and the barium/aluminum ratio) and the supply of lithogenic detritus from the West Antarctic hinterland (such as ice-rafted debris and clay minerals) exhibit cyclic fluctuations in accordance with the glacial–interglacial cycles of the Quaternary. A prominent depositional anomaly spans MIS 15–MIS 13 (621–478 ka). The proxies for biological productivity and lithogenic sediment supply indicate that this interval has the characteristics of a single, prolonged interglacial period. Even though no proxy suggests environmental conditions much different from today, we conclude that, if the WAIS collapsed during the last 800 kyr, then MIS 15–MIS 13 was the most likely time period. Apparently, the duration rather than the strength of interglacial conditions was the crucial factor for the WAIS drawdown. A comparison with various marine and terrestrial climate archives from around the world corroborates that unusual environmental conditions prevailed throughout MIS 15–MIS 13. Some of these anomalies are observed in the pelagic Southern Ocean and the South Atlantic and might originate in major ice-sheet drawdown in Antarctica, but further research is required to test this hypothesis.  相似文献   

17.
《Quaternary Science Reviews》2007,26(3-4):536-559
The Ironshore Formation on Grand Cayman is formed of six unconformity-bounded packages (units A–F). Units A, B, C, and D, known from the subsurface in the northeastern part of Grand Cayman, formed during Marine Isotope Stages (MIS) 11(?), 9, 7, and 5e, respectively. Unconformities at the tops of units A, B, and C are highlighted by terra rossa and/or calcrete layers. Strata in core obtained from wells drilled in George Town Harbour and exposed on the west part of Grand Cayman belong to unit D, and the newly defined units E and F. Corals from unit E yielded Th/U ages of ∼104 ka whereas conch shells from unit F gave ages of ∼84 ka. Unit E equates to MIS 5c whereas unit F developed during MIS 5a.Th/U dating of corals and conchs from the Ironshore Formation on the western part of Grand Cayman shows that unit D formed during the MIS 5e highstand whereas units E and F developed in association with highstands at 95–110 ka (MIS 5c) and 73–87 ka (MIS 5a). Unit E, ∼5 m thick in the offshore cores, is poorly represented in onshore exposures. Unit F, which unconformably overlies unit D at most localities, is formed largely of fossil-poor, cross-bedded ooid grainstones. The unconformity at the top of unit D, a marine erosional surface with up to 2.5 m relief, is not characterized by terra rossa or calcrete in the offshore cores or onshore exposures. Unit D formed with a highstand of +6 m asl, whereas units E and F developed when sea level was +2 to +5 asl and +3 to +6 m asl, respectively. Thus, the highstands associated with MIS 5e, 5c, and 5a were at similar elevations.  相似文献   

18.
以渤海湾西岸现代岸线附近的NP3、CH110和BT113三个钻孔全新世岩心为研究对象,采用沉积岩石学、AMS 14C(accelerator mass spectrometry 14C,加速器质谱14C)测年、微体生物聚类分析等方法精细判别沉积相,重建渤海湾西岸全新世沉积演化历史,并利用微体生物组合分带对水深变化的指示,定量讨论全新世相对海面变化。结果表明:渤海湾西岸全新世受海陆交互作用影响,经历了沼泽-潮滩-浅海-前三角洲-三角洲前缘-三角洲平原环境的演化过程。全新世初始阶段,研究区中部和北部发育沼泽环境,南部未见沉积,与上更新统河流相沉积呈不整合接触。全新世早期,研究区潮滩环境发育。潮滩层厚度约1 m,历时数百至1千余年。至7000 cal BP前后水深增大,研究区进入浅海环境。约6000 cal BP,沿岸南北两端先后进入三角洲过渡环境,中部三角洲环境约开始于1500 cal BP。渤海湾西岸地区全新世的环境演化同时记录了该地区的相对海面变化:约10000 cal BP前后,渤海湾相对海平面已接近21.3~20.4 m。约8000 cal BP,相对海平面介于18.6~17.0 m。约6000 cal BP时相对海平面低于6.8 m,5000~1000 cal BP,相对海平面高于-2.5 m,1000~800 cal BP,相对海平面介于-1.3~-0.4 m。8000~5000 cal BP时,相对海面上升约15.0 m,上升速率达5 m/1 ka。  相似文献   

19.
Sedimentological and benthic foraminifera analyses carried out on a core (length 4.15 m, collected at 22°56′31″S and 41°58′48″W, at a water depth of 43 m) sampled from the inner shelf of Cabo Frio, southeastern Brazilian continental margin, allowed identification of different hydrodynamic and productivity regimes related to sea-level fluctuations and/or climatic changes, during the last 9.4 ka cal BP. Prior to 7.0 ka cal BP, a less intense hydrodynamic and lower productivity regime occurred at lower sea levels and under drier climatic conditions. Between 7.0 and 5.0 ka cal BP, relatively stronger local oceanic circulation and relatively high productivity were observed, in a scenario of rising sea levels and more humid conditions. From 5.0 to 3.0 ka cal BP, bottom currents weakened and input of nutrients increased, with productivity levels similar to the previous phase at lower sea level and in a drier climate. From 3.0 ka cal BP up to the present, stronger hydrodynamic conditions and a higher productivity regime are linked to the establishment of the upwelling process in Cabo Frio. From 2.5 ka cal BP to the present, upwelling enhancement has been recognized, resulting from the combined action of NE winds and the intensification of the meandering pattern of the Brazil Current (BC).  相似文献   

20.
AMS~(14)C测年揭示的渤海湾沿海低地第Ⅱ海相层年龄(Ⅱ)   总被引：1，自引：0，他引：1  
商志文  王福  李建芬  姜兴钰  陈永胜  王宏 《地质通报》2016,35(10):1607-1613
在初步获得渤海湾海河南部沿海低地第Ⅱ海相层年龄大于43.5ka BP的基础上,在沧州北部和海河北部的沿海低地又利用6个新的机械钻孔岩心,建立了2条垂直于现代岸线的长剖面。根据沉积物岩性和有孔虫查明了第Ⅱ海侵层在剖面中的空间分布,并获得一组新的AMS~(14)C年龄数据。结果显示,在第Ⅱ海相层中新获得的9个AMS~(14)C年龄同样均大于43.5ka BP。至此,渤海湾3条垂直现代岸线剖面10个钻孔的第Ⅱ海相层的21个AMS~(14)C年龄均大于43.5ka BP,进一步证实了普遍发育于渤海湾沿海低地的第Ⅱ海相层形成于MIS 3阶段早期或MIS 5阶段,而不是前人认为的23~39ka BP。  相似文献   

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