GEOLOGY Stratigraphy of Bottom Sediments in the Mendeleev Ridge Area (Arctic Ocean (original) (raw)
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Global and Planetary Change, 2009
Arctic Ocean Mendeleev Ridge sediment stratigraphy Late Quaternary glaciations last interglacial Sediment core HLY0503-8JPC raised by the HOTRAX'05 expedition from the Mendeleev Ridge was analyzed for multiple lithological, paleontological, and stable-isotopic proxies to reconstruct paleoceanographic conditions in the western Arctic Ocean during the Late Quaternary. The core, extensively sampled in the upper 5 m, reveals pronounced changes in sedimentary environments during the ca. 250 kyr interval encompassing Marine Isotopic Stages (MIS) 1 to 7. An estimated average resolution of 500 yr/sample, at least for the last glacial cycle including the last interglacial, provides more detail than seen in other sedimentary records from the western Arctic Ocean. The age control is provided by 14 C and amino acid racemization measurements on planktonic foraminifers and correlations with the stratigraphy developed for the central Lomonosov Ridge and with glacial events at the Eurasian Arctic margin. Cyclic variations in lithology combined with foraminiferal abundance and stable-isotopic composition indicate profound changes in hydrographic and depositional environments between interglacial-type and glacial-type periods apparently reflecting a combination of 100-kyr and precessional time scales. This periodicity is complicated by abrupt iceberg-and/or meltwater-discharge events with variable (Laurentide vs. Eurasian) provenance. The proxy record from the interval identified as the last interglacial (MIS 5e), which may aid in understanding the future state of the Arctic Ocean, indicates low ice conditions and possibly enhanced stratification of the water column.
Quaternary Science Reviews, 2012
Inclination patterns of natural remanent magnetization (NRM) in Quaternary sediment cores from the Arctic Ocean have been widely used for stratigraphic correlation and the construction of age models, however, shallow and negative NRM inclinations in sediments deposited during the Brunhes Chron in the Arctic Ocean appear to have a partly diagenetic origin. Rock magnetic and mineralogical studies demonstrate the presence of titanomagnetite and titanomaghemite. Thermal demagnetization of the NRM indicates that shallow and negative inclination components are largely "unblocked" below w300 C, consistent with a titanomaghemite remanence carrier. Following earlier studies on the Men-deleeveAlpha Ridge, shallow and negative NRM inclination intervals in cores from the Lomonosov Ridge and Yermak Plateau are attributed to partial self-reversed chemical remanent magnetization (CRM) carried by titanomaghemite formed during seafloor oxidation of host (detrital) titanomagnetite grains. Distortion of paleomagnetic records due to seafloor maghemitization appears to be especially important in the perennially ice covered western (MendeleeveAlpha Ridge) and central Arctic Ocean (Lomonosov Ridge) and, to a lesser extent, near the ice edge (Yermak Plateau). On the Yermak Plateau, magnetic grain size parameters mimic the global benthic oxygen isotope record back to at least marine isotope stage 6, implying that magnetic grain size is sensitive to glacialeinterglacial changes in bottom-current velocity and/or detrital provenance.
Quaternary Science Reviews, 2014
Mineral assemblage, trace element content and Nd and Pb isotope signatures were analysed on the fine fraction (<20 mm) of sedimentary records from the Northern Mendeleev Ridge in the Central Arctic Ocean. Our aim was to identify the detrital particle provenance and to interpret the changes over the past w250 ka in the relative contribution of the different source-areas in relation to paleoenvironmental conditions. The clay mineral assemblage and the Nd and Pb isotope signatures depict systematic changes over the Late Quaternary. The bulk mineralogy exhibits increases in the relative contribution of carbonate minerals vs. silicates in interglacial/deglacial intervals. In glacial intervals, the mineral assemblage of the <20 mm fraction is characterised by an enrichment in kaolinite, counterbalanced by a decrease in illite. The Nd and Pb isotope signatures of <20 mm fraction are interpreted using a three end-member mixing model, involving crustal supplies from North America and Canada, from the Siberian margin and some from volcanic material. A compilation of geochemical signatures of geological terraines surrounding the Arctic Ocean allowed each end-member to be assigned a representative signature, averaging the signal of the eroded terraines. The Suspended Particulate Matter (SPM) of the MacKenzie River represents an average signature of the sedimentary supplies delivered from the North American platform and Canadian margin. The SPM of the Lena River reflects the mean sedimentary signature of the Siberian platform. The Okhotsh-Chukotka province from the Eastern border of Siberia is identified as the most probable volcanic source. Late Quaternary evolution of the estimated relative contribution of the three end-members confirms that the sediment provenances in the Central Arctic Ocean remain close to the current conditions during past interglacials/deglacials MIS1e3, MIS5/TII and MIS7/TIII. In contrast, glacial conditions (MIS4 and MIS6) record minimum supplies from the American margin, associated with increased volcanic contribution, to the Mendeleev Ridge core location suggesting a different sea-ice circulation associated with a low sea-level and reduced shelf area.
Paleoceanography, 2001
Three long sediment cores from the Makarov Basin have been subjected to detailed paleomagnetic and rock magnetic analyses. Investigated sediments are dominated by normal polarity including short reversal excursions, indicating that most of the sediments are of Brunhes age. In general, the recovered sediments show only low to moderate variability in concentration and grain size of the remanence-carrying minerals. Estimations of relative paleointensity variations yielded a well-documented succession of pronounced lows and highs that could be correlated to published reference curves. However, together with five accelerator mass spectrometry •4C ages and an incomplete løBe record, still two different interpretations of the paleomagnetic data are possible, with long-term sedimentation rates of either 1.3 or 4 cm kyr-•. However, both models implicate highly variable sedimentation rates of up to 10 cm kyr-•, and abrupt changes in rock magnetic parameters might even indicate several hiatuses. 1. reversal excursions within the Brunhes Chron, such as the Laschamp [Bonhommet and Babkine, 1967; Gillot et al., 1979] or the Blake [Smith and Foster, 1969] excursions, can, in principle, provide a more or less detailed age model. Just these short reversal excursions were frequently found in Arctic marine sediments:
Global and Planetary Change, 2001
High resolution seismoacoustic chirp sonar data and piston cores were collected from the Lomonosov Ridge in the central Ž . Arctic Ocean 858-908N; 1308-1558E . The chirp sonar data indicate substantial erosion on the ridge crest above 1000 mbsl while data from deeper sites show apparently undisturbed sedimentation. Piston cores from both the eroded ridge crest and the slopes have been analyzed for a variety of properties, permitting inter-core correlation and description of paleoenvironmental change over time. Based on the evidence of extensive sediment erosion at depths above 1000 mbsl, we infer that the top of the Lomonosov Ridge has been eroded by grounded ice during a prominent glacial event that took place during MIS 6 according to a newly published age model. This event is coeval with a dramatic shift from low amplitude glacial-interglacial variability to high amplitude variability recorded in the sedimentary record. The new age model used in our study is based on nannofossil biostratigraphy and correlation between sedimentary cycles and a low-latitude oxygen isotope record and confirmed by paleomagnetic polarity studies where negative paleomagnetic inclinations are assigned to excursions. Due to the controversy between this age model and age models that assign the negative paleomagnetic inclinations to polarity w Ž .
Paleomagnetic study of the sediment from Amerasian Basin of the Arctic Ocean
2006
The cores for paleomagnetic study were sampled during voyage of the Research Vessel "Academician Fedorov" in 2000. The region of investigation was eliminated by coordinates 81§° 54.90'-82O 05.22' N and 167O 52.32'-179O 56.17' E; sea depth in the 7 sites of the core sampling was between 1.5 and 3.3 km, total length of cores was 19.2 m. Magnetic susceptibility ¦Ê and natural remanent magnetization Jn were measured using a special set of equipment. Specimen selection along the cores was executed with minimal possible interval 2-2.5 cm. All in all 824 specimens were collected and measured. The measured magnetic susceptibility ¦Ê was varied in limits (2-6) 10-4 SI with average value 3.4 10-4 SI. Natural remanent magnetization Jn in cores was varied in limits (1.7-3.2) nT with average value Jn=2.5 nT. The position of ¦Ê and Jn extrema is coinciding in all cores, what creates the possibility for definition and correlation of sediment layers. Boundary Bruhnes-Matuyama (0.73 my BP) and subchron Jaramillo (1.07-0.99 my §£§²) were clearly fixed in all seven cores; subchron Olduvai (1.95-1.77 my §£§²) was marked in two cores, subchron Reunjon (2.13 my §£§²) ¨C in one core, boundary of subchron Matuyama-Gauss (2.6 my §£§²) was marked in three cores. The Bruhnes- Matuyama boundary was marked in all cores by especially big values of ¦Ê. Estimation sedimentation rate during Bruhnes epoch is, according to our measurement data, 1-1.4 mm/ky in five cores from Mendeleev Ridge, and 2.6-3.0 mm/ky ¨C in two cores from Podvodnikov Basin. This result coincides coinciding with published data relating to site of Mendeleev Ridge locating to north from 83° N. Evidences about low sedimentation rate in Amerasian Basin of the Arctic Ocean are the favorable precondition for search of ferromanganese nodules in this area. Work is carried out using support of RFFI (grant 06-05-64200)
New data on the age of dolerites and basalts of Mendeleev Rise (Arctic Ocean)
Doklady Earth Sciences, 2014
We present results of 40 Ar/ 39 Ar isotopic investigations concerning the dating of dolerites and basalts that were sampled during the Arctica 2012 polar expedition. Basalts were sampled by means of deep underwater drilling with wells up to 2 m in outcrops on the seafloor (basalts), and dolerite samples were obtained from the bottom of an escarp of Mendeleev Rise using a manipulator on the research submarine. The analysis results of the obtained mono mineral fractions (amphibole, plagioclase, pyroxene) from the studied rocks yielded an Early Paleozoic age of the dolerites and basalts from Mendeleev Rise. The oldest ages obtained for amphibole reach 471.5 ± 18.1 and 466.9 ± 3.3 Ma, which corresponds to the Early-Middle Ordovician. The isotopic composition of argon was measured on two mass spectrometers: the Micromass Noble Gas 5400 (UK) and the Thermo Scientific Argus (Germany). The determined Early Paleozoic age of igneous rocks of Mendeleev Rise and seismic data obtained during the last Russian expedition Arctica 2012 [2] let us suppose that this continental block of the Earth's crust has a Precambrian basement similar to the basement identified for the New Siberian islands including the De Long archipelago.
Revised magnetostratigraphies confirm low sedimentation rates in Arctic Ocean cores
Quaternary Research, 1988
The general lack of an age-diagnostic biostratigraphy in the Neogene sediments of the abyssal Arctic Ocean has emphasized the importance of magnetostratigraphy in providing chronostratigraphic control in these sediments. Sedimentation rates interpreted from early magnetostratigraphic studies of cores taken from the T3 ice island in the western Mendeleev Plain were estimated to be on the order of 1 mm/IO3 yr; however, recent amino acid epimerization studies of a core from the same area have suggested sedimentation rates of almost 15 mm/IO3 yr. This controversy has led us to reexamine the paleomagnetism of several of these cores. Our alternating field demagnetization studies indicate that many of these cores have an intense, high coercivity overprint, acquired after the core was opened, that is adequately removed only after treatment at 20 to 70 mT. We have remeasured samples from two cores after demagnetizations up to 80 mT and can confirm the position of the BnmheslMatuyama boundary originally identified in the cores. In addition, the Jaramillo and Olduvai subchrons are identified. Average sedimentation rates in these two cores are 2-3 mm/IO3 yr, similar to the original estimates based on reversal stratigraphy, as well as those determined from recent radiocarbon studies, but incompatible with the amino acid-based dates. 0 1988 University of Washington.