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1.
Three sediment cores from the Laptev Sea continental margin were investigated for their clay mineralogy by X-ray diffraction to study the fluvial sediment supply since the late Weichselian. In the study area, the clay-mineral composition of surface sediments is characterized by distinct regional variations. The source area for smectite in the eastern Eurasian Basin is the Putoran Plateau drained by the Khatanga and Yenisei rivers. Currents caused by river discharge and the inflow of Atlantic water masses along the Eurasian continental margin are responsible for sediment distribution. In the sediment cores, smectite and illite contents show an opposite trend which mainly results from variable smectite supply. During MIS 2 the amount of smectite on the Laptev Sea continental margin never exceeds 10 rel.%. Probably, reduced river discharge and the lowered sea level during MIS 2 caused a decreased sediment supply to the Laptev Sea. Additionally, the Putoran Plateau was covered by an ice sheet during the Late Weichselian preventing the erosion of smectite-rich soils. In contrast, maximum smectite contents (up to 30 rel.%) in Holocene sediments result from increased sediment input by the Khatanga River and from the Kara Sea through the Vilkitsky Strait and via St. Anna Trough into the western Laptev Sea. 相似文献
2.
Carolina Bernal Frédéric Christophoul José Darrozes Jean-Claude Soula Patrice Baby José Burgos 《International Journal of Earth Sciences》2011,100(7):1759-1782
The geomorphological study by means of remote sensing imagery of the Rio Pastaza Megafan (Ecuador and northern Peru) reveals
the traces of numerous avulsions. One hundred and eight avulsion sites have been defined. The location of these sites, the
available radiocarbon ages as well as historical maps of the seventeenth century, enable us to propose an evolution history
of the migration and avulsions of the Rio Pastaza since the Last Glacial Maximum. The first avulsions of the Río Pastaza occurred
after the LGM in a zone close to and roughly parallel to the sudandean front, where the developed avulsion gave a distributive
pattern to the ancient stream of the Río Pastaza in an area located between the modern Río Morona and Pastaza, where they
caused the Rio Pastaza to develop a fan-like distributary pattern. This is interpreted as a response to thrust-related forelimb
tilt, progressively shifting eastward the Rio Pastaza and the apex of the megafan. This sequence of events ended with the
Great Diversion of the Rio Pastaza towards the modern Rios Corrientes and Tigre. Avulsions occurred in the Tigre-Corrientes
Area between 9200 and 8,500 years Cal BP. Afterwards, the Río Pastaza was diverted to its present-day north–south course.
This last significant avulsion occurred before AD 1691. In the area located between the modern Río Morona and Pastaza, avulsion
frequency—probably overestimated—ranges between 100 and 200 years. In the Ríos Tigre and Corrientes area, avulsion frequency—probably
underestimated—ranges from 300 to 400 years. Regional tectonics is likely to have triggered most of the avulsions in the Morona
Pastaza area but its influence is restricted to this area. The factors controlling the avulsions in the Tigre-Corrientes area
are less clear because the frequently described “hydrologic”-driven avulsion as observed in areas characterized by contrasted
hydrologic cycles are inconsistent with the characteristics of the hydrologic cycles of the Rio Pastaza. 相似文献
3.
The reflectance of sediments (gray level) were measured on 11 sediment cores from the Norwegian–Greenland–Iceland Sea (Nordic
seas). The analyzed time interval covers the past five glacial–interglacial cycles. Although the results demonstrate that
the gray-level method has a potential for stratigraphic purposes, it is indicated that gray-level changes in the Nordic seas
are not necessarily driven by variations in the content of biogenic calcite. A detailed comparison of gray-level values with
contents of total CaCO3 (carbonate) and total organic carbon (TOC) reveals no overall causal link between these proxies. However, specific glacial
core sections with layers containing organic-rich sediment clasts as a consequence of iceberg-rafting seem to correlate well
with law gray-level values. Of those cores which show relatively high and comparable carbonate values in the last three main
interglacial intervals (stages 11, 5.5, and 1), stage 11 is always marked by the highest gray-level values. A close inspection
of the surface structure of the foraminiferal tests as well as the conduction of reflectance measurements on these tests leads
to the conclusion that enhanced carbonate corrosion occurred during stage 11. The test corrosion not only affected the reflectance
of the tests by making them appear whiter, it also seems responsible for the comparatively high gray-level values of the total
sediment in stage 11. In contrast, the relatively low gray-level values found in stages 5.5, and 1 are not associated with
enhanced test corrosion. This observation implies that variable degrees of carbonate corrosion can have a profound effect
on total sediment reflectance.
Received: 6 September 1998 / Accepted: 4 April 1999 相似文献
4.
Paired measurements of Mg/Ca and δ18O of Globigerenoides sacculifer from an Eastern Arabian Sea (EAS) sediment core indicate that sea-surface temperature (SST) varied within 2°C and sea-surface salinity within 2 psu during the last 100 ka. SST was coldest (∼ 27°C) during Marine Isotope Stage (MIS) 4 and 2. Sea-surface salinity was highest (∼ 37.5 psu) during most of the last glacial period (∼ 60–18 ka), concurrent with increased δ18OG.sacculifer and C/N ratios of organic matter and indicative of sustained intense winter monsoons. SST time series are influenced by both Greenland and Antarctic climates. However, the sea-surface salinity time series and the deglacial warming in the SST record (beginning at ∼ 18 ka) compare well with the LR04 benthic δ18O-stack and Antarctic temperatures. This suggests a teleconnection between the climate in the Southern Hemisphere and the EAS. Therefore, the last 100-ka variability in EAS climatology appears to have evolved in response to a combination of global climatic forcings and regional monsoons. The most intense summer monsoons within the Holocene occurred at ∼ 8 ka and are marked by SST cooling of ∼ 1°C, sea-surface salinity decrease of 0.5 psu, and δ18OG.sacculifer decrease of 0.2‰. 相似文献
5.
6.
Kolka V. V. Korsakova O. P. Lavrova N. B. Shelekhova T. S. Zaretskaya N. E. 《Doklady Earth Sciences》2019,485(1):312-316
Doklady Earth Sciences - This paper reports on the lithological, micropaleontological, and chronometric data (radiocarbon dating) for one of the areas of the White Sea coast. The sedimentary... 相似文献
7.
8.
The stable carbon isotope (δ13C) and elemental C/N ratios in Total Organic Carbon (TOC) extracted from radiometrically dated cores from two Midwestern USA
lakes were determined to investigate the factors that control these values in temperate lakes. The range of δ13C values (-26 to -32%) and C/N ratios (mean value ∼10.8) are typical of values reported for other temperate lake organic matter
in this region. In the core from Lake Winnebago, Wisconsin, a negative correlation was seen between the TOC and δ13C, which can be interpreted in terms of a re-mixing and consumption of sedimented organic carbon along with rapid equilibration
throughout the water column. No correlation was seen between the TOC and δ13C in the record from Ladd Lake, Ohio, implying that in this latter lake productivity alone was not a singular process controlling
the isotope ratio. Here, it is suggested that equilibrium conditions are maintained such that the DIC of the water is never
depleted of aqueous CO2 during high organic production and the resulting δ13C of the organic carbon lacks correlation with the TOC. Further, in this lake a fine resolution analysis was carried out which
indicated a possible anthropogenic influence on the isotope ratio around times when human settlement (∼300 yrs ago) and enhanced
agricultural practices (∼80 yrs ago) were significant. The study shows that carbon isotope studies are useful in paleolimnologic
investigations. 相似文献
9.
Geotectonics - Structural-cartographic geological and geophysical materials were analyzed in order to construct a series of models of structural–geodynamic systems of the basement of the... 相似文献
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11.
Jian-Wei Li Xin-Fu Zhao Mei-Fu Zhou Chang-Qian Ma Zorano Sérgio de Souza Paulo Vasconcelos 《Contributions to Mineralogy and Petrology》2009,157(3):383-409
Late Mesozoic dioritic and quartz dioritic plutons are widespread in the Daye region, eastern Yangtze craton, eastern China.
Detailed geochronological, geochemical, and Sr–Nd isotopic studies have been undertaken for most of these plutons, in an attempt
to provide a comprehensive understanding in the age, genesis and geodynamical control of the extensive magmatism. SHRIMP and
LA-ICP-MS zircon U–Pb dating indicate that the plutons were emplaced in the range of latest Jurassic (ca. 152 Ma) to early
Cretaceous (ca. 132 Ma), which was followed by dyke emplacement between 127 and 121 Ma and volcanism during the 130–113 Ma
interval. Both diorites and quartz diorites are sodic, metaluminous, high-K calc-alkaline, and characterized by strongly fractionated,
sub-parallel REE patterns without obvious Eu anomalies. The rocks are enriched in highly incompatible elements and large ion
lithophile elements, but depleted in high field strength elements. Samples of diorite and quartz diorite have similar Sr–Nd
isotopic compositions that are consistent with the early Cretaceous basalts and mafic intrusions throughout the eastern Yangtze
craton. The geochemical and isotopic data, together with results of geochemical modeling, indicate an enriched mantle source
for the plutonic rocks. The quartz diorites have geochemical signatures resembling adakites, such as high Al2O3 (15–19 wt.%), Sr (630–2,080 ppm), Na2O (>3.5 wt.%), negative Nb–Ta anomalies, low Y (7–19 ppm), Yb (0.5–1.8 ppm), Sc (5–15 ppm), and resultant high Sr/Y (45–200)
and La/Yb (31–63) ratios. Genesis of the adakitic quartz diorites is best explained in terms of low-pressure intracrustal
fractional crystallization of cumulates consisting of hornblende, plagioclase, K-feldspar, magnetite, and apatite from mantle-derived
dioritic magmas. Mantle-derived magmatism broadly coeval with that of the Daye region also is widespread in other regions
of the eastern Yangtze craton, reflecting large-scale melting of the lithospheric mantle during the Late Mesozoic. The large-scale
magmatism was most likely driven by lithospheric extension associated with thinning of lithospheric mantle beneath the eastern
China continent. 相似文献
12.
The Barents Sea shelf is an attractive target as a prospective large petroleum province. Further development of geological and geophysical exploration in the area requires high-resolution biostratigraphic constraints and update stratigraphic charts. The zonal succession of Lower and Middle Jurassic assemblages of foraminifers and ostracodes of the Barents Sea fits well the division for northern Siberia based on correlated independent Jurassic and Cretaceous zonal scales on all main microfossil groups, of which some scales were suggested as the Boreal Zonal Standard. The stratigraphic range of the Barents Sea microfossil assemblages has been updated through correlation with their counterparts from northern Siberia constrained by ammonite and bivalve data. Joint analysis of foraminiferal and ostracode biostratigraphy and lithostratigraphy of the sections allowed a revision to the stratigraphic position and extent of lithological and seismic units. The discovered similarity in the Lower and Middle Jurassic lithostratigraphy in the sections of the Barents Sea shelf and northern Siberia, along with their almost identical microfossil taxonomy, prompts similarity in the Early and Middle Jurassic deposition and geological histories of the two areas. 相似文献
13.
Relationships between the communities and environment surrounding these communities can be disclosed by the application of different archeological, geological and environmental historical methods. This includes the deployment of numerous tools in scientific investigation including the application of chronological, sedimentological, geochemical and paleoecological analytical methods on sequences accumulated in historical catchment basins of peat-bog. The Nádas-tó at Nagybárkány is a small peatbog in the northern part of Hungary, on the Sub-Carpathian region. The formation of the lake can be traced back to the Late Glacial period. The sediments deposited in the lakebed provide a record of climatic and hydrologic changes. A higher water level could be demonstrated from the Late Glacial to the Mid-Holocene, when the reed-beds covered a small area only. This was followed by a hiatus spanning ca. 4400 years, caused by the deepening and cleaning of the lakebed during the Late Iron / Imperial Age, between 2100 - 1900 cal BP years. After this change the water level decreased and the water quality was more eutrophic. A reed-bed evolved around the lake. Paludification started with a bulrush floating mat phase at the close of the Middle Age, ca. 1500 cal AD years. The endowments and settlement pattern persisted from the Neolithic onwards until the terminal Modern Age, when measures aimed to ordain the area substantially altered the natural landscape. Although some anthropogenic disturbances can be reconstructed in the development of the peatland, some climatic effects and authogenic processes might be separated by paleoecological analyses. 相似文献
14.
A. N. Drozdova A. A. Vetrov E. A. Romankevich N. A. Prokuda S. V. Sukhoverkhov S. Yu. Bratskaya V. I. Sergienko I. P. Semiletov A. S. Ulyantsev 《Doklady Earth Sciences》2016,468(1):496-499
The distribution and genesis of polycyclic aromatic hydrocarbons (PAHs) were studied in a 40-m core from a lagoon of the Laptev Sea that appeared during the Holocene resulting from the flooding of seawater into a freshwater lake in the area of the Buor-Khaya Gulf. The bulk of the core is constituted of permafrost rocks, thawed partially in their upper layers and covered with recent sediments (mainly by the products of intense thermoabrasion). The ratio of petrogenic and pyrogenic PAHs was evaluated. 相似文献
15.
Lithology and Mineral Resources - Signs of extensive migration of gas-bearing fluids from the sedimentary cover into the water column were identified in the northern Barents Sea during Cruises 25... 相似文献
16.
Alfred N. N. Muzuka 《Journal of Earth System Science》2000,109(4):481-489
The stable isotope compositions of sedimentary organic carbon and content of organic carbon for sediment cores recovered at
two sites (sites 724C and 725C) during Ocean Drilling Program (ODP) Leg. 117 on the Oman continental margin are used to document
variability of the monsoon winds for the past 350 ka. Although both sites have a mean δ13C value of -20.1‰, three zones depleted in13C are observable at site 724C during isotope stages 3, 8 and 10, while only one zone is recognizable at site 725C. Increased
coastal upwelling during isotope stage 3 owing to intense SW monsoon winds resulted in higher concentration of CO2 in the water column causing the formation of organic matter that was depleted in13C. The other two zones deposited during oxygen isotope stages 8 and 10, which are also characterized by low values of organic
carbon, nitrogen and C/N ratios, could be attributed to the dilution by terrestrial material derived from paleosol by transported
by northwester lies. Because of utilization of13C enriched dissolved CO2 during the last glacial maximum Holocene sedimentary organic materials are depleted in13C relative to the the fomer. The content of residues organic carbon (ROC) is higher at site 724C (with an average of 2.3 ±
1.2%) relative to site 725C, which averages to 0.9 ± 0.4% probably because of differences in the degree of preservation. Organic
material deposited at site 725C has undergone more degradation relative to site 724C as reflected by a systematic downcore
decrease in13C resulting from a loss of13C enriched organic compounds. Owing to lack of good chronology at site 725C, a zone that is characterized by low δ13C values it could not be correlated with the other three zones observed at Site 724C. 相似文献
17.
《Quaternary Science Reviews》2004,23(3-4):245-260
In Arctic and sub Arctic seas, shell growth and/or secondary calcite overgrowth of Neogloboquadrina pachyderma (left coiled)—Npl—occur along the pycnocline, and their δ13C and δ18O-values are size and weight dependent. However, whereas the Npl 18O data from the NW Atlantic indicate near-equilibrium conditions with ambient waters and a positive relationship between shell weight and 18O-content, assemblages from box-cored sediments of the Chukchi Sea (western Arctic) are depleted by ∼2‰ with respect to equilibrium values with modern conditions, and depict a negative relationship between shell weight and its δ18O-value (−0.15±0.03‰/μg on VPDB scale). A similar feature is also depicted by the dextral form of N. pachyderma (Npd). We associate the reverse shell-size or weight vs. δ18O relationship to the reverse temperature gradient observed along the thermocline between the surface cold and dilute water layer, and the underlying near 3°C-warmer saline North Atlantic water mass. The analysis of two late to post-glacial sedimentary sequences from the Chukchi Sea indicates that such a water mass stratification with a reverse thermocline persisted throughout the Holocene, thus reflecting an early onset of the modern-like linkage between the Arctic Ocean and the North Atlantic. Moreover, lower δ18O-values in both Npl and Npd together with larger δ18O-gradients between the different shell sizes at ca 9–7 ka BP suggest ∼3°C higher temperatures in the upper North Atlantic water mass, in comparison with the present (approximately +1°C, at the study site), thus likely a higher inflow rate of this water mass during the early Holocene. 相似文献
18.
To help describe the paleoenvironmental interpretation of one the most extensive marine Devonian successions in Brazil, palynofacies analyses were conducted on 46 samples from the Itaim (Pragian–Givetian), Pimenteira (Givetian–Frasnian) and Cabeças (Famennian) formations of the Parnaíba Basin in north–central Brazil. For the palynofacies analyses, kerogen categories were counted and subjected to cluster analyses. Five palynofacies associations were identified for three studied sections: PseudoAOM palynofacies, which consists of amorphous organic matter (AOM), pseudoamorphous and coenobial algae Quadrisporites; Transl/Nbiostr. palynofacies, which consists of translucent non-biostructured phytoclasts (well-preserved and degraded), cuticles (well-preserved and degraded), Spongiophyton and Botryococcus; Marine microplankton palynofacies, which consists of acritarchs, prasinophytes and translucent biostructured phytoclasts; Opaque palynofacies, which consists of opaque phytoclasts (equidimensional and lath shaped); and Sporomorphs palynofacies, which consists of zoomorphs (e.g., Chitinozoa) and sporomorphs (e.g., spores). The stratigraphic distribution of the five palynofacies associations reflects a continuous terrestrial influx throughout marine succession. At the Pragian–Emsian age, the woody material of Transl/Nbioestr. palynofacies prevails, suggesting a marine depositional paleoenvironment (presence of marine palynomorphs), but under deltaic influence due to the input of terrigenous material. An increasing trend of marine elements of Marine microplankton palynofacies is recorded for the Givetian, which suggests a progressive marine influence. However, during the Frasnian, the highest abundance of marine elements was recorded (Marine microplankton palynofacies). Moreover, a bloom of Maranhites spp. and prasinophytes (e.g., Tasmanites and Cymatiosphaera) was also recorded. The abrupt increase of marine palynomorphs in the Frasnian – here termed the “Maranhites Event” – has been recorded by other authors. Finally, in the Famennian, woody material was most abundant in Transl/Nbiostr. palynofacies and Sporomorphs palynofacies, which reflects a depositional trend that is strongly controlled by fluvial input into a shallow marine environment. 相似文献
19.
《International Geology Review》2012,54(10):1184-1202
Based on metamorphic studies of the Yadong high-pressure (HP) granulite and multiple thermochronological investigations of granitoids from both upper and lower parts, the Yadong section in the eastern Himalaya constrains the Cenozoic tectonic evolution of the Greater Himalayan Sequence (GHS). The Yadong HP granulite, located at the top of the GHS, underwent a peak-stage HP granulite facies metamorphism and two stages of retrograde metamorphism. Granulite and hornblende facies retrograde metamorphism took place at 48.5 and 31.8 Ma, respectively, marking the time of exhumation of the subducted Indian slab to lower and middle crustal levels. Subsequently, an average young zircon U–Pb age obtained from the Yadong HP granulite indicated that this unit was captured by its surroundings in a partially molten condition at 16.9 Ma. In addition, three granitoids from both the lower and the upper parts of the GHS yielded biotite 40Ar/39Ar ages of 11.0, 11.3, and 11.5 million years. These consistent ages suggest that the GHS along the Yadong section was laterally extruded and synchronously cooled to ~300°C at ~11.3 Ma. Furthermore, the granitic gneisses yield apatite fission track ages of ~7 million years, documenting the cooling of the GHS to ~110°C. A two-stage model describes the Cenozoic tectonic evolution of the GHS: (1) the Indian slab had subducted under Tibet before ~55 Ma, and was exhumed to the lower crust (50-40 km) at 48.5 Ma, and to the middle crust (22-15 km) at 31.8 Ma; and (2) the partial melting occurred at middle crustal levels during the period 31.8 to 16.9 Ma, causing channel flow. In the late stage, the GHS was laterally extruded by ductile mid-crustal flow during the period 16.9 to ~7 Ma, characterized by a fast cooling rate of ~2 mm per year. 相似文献
20.
Late cretaceous tectonic change of the eastern margin of the Tibetan Plateau — results from multisystem thermochronology 总被引:2,自引:0,他引:2
Bin Deng Shugen Liu Zhiwu Li Junxing Cao Wei Sun 《Journal of the Geological Society of India》2012,80(2):241-254
Partially due to lack of structural and sedimentary records to constrain the Jurassic-to-Cretaceous evolution, there was a
missing process here in the eastern margin of Tibetan Plateau as it changed from the Paleo-Tethyan to Neo-Tethyan regime.
Based on the analysis of 125 thermochronology ages (U/Pb, 40Ar/39A, 87Rb/86Sr, FT, U-Th/He) of igneous rocks from the eastern margin of Tibet, we propose a multisystem thermochronology approach to
restore the cooling and emplacement of granites and decipher the missing process. Our integrated study suggests that a key
Late Cretaceous (about 100Ma) tectonic change from the Paleo-Tethyan to Neo-Tethyan regime took place there. In the Late Triassic
period, the initial emplacement of granite in the Songpan-Ganzi Fold Belt (SGFB) was characterized by a decrease in emplacement
age and depth from west to east, and from north to south. Subsequently, all were followed by a very long period of slow cooling,
which was followed by a rapid emplacement of about 100Ma. The intensive granite emplacement took place all over except northeastern
SGFB, with a decrease in emplacement depth from west to east, which was linked with the far-field effect of Lhasa-Qiangtang
collision. After this episode, the cooling history of granite in SGFB had a rapid emplacement on the subsurface under the
control of the Neo-Tethyan regime. This process has control of the post Late Cretaceous regional magmatic activity and tectonics,
as well as the sedimentary response in Sichuan and Xichang basin. 相似文献