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21.
Rodrigo Scalise Horodyski Michael Holz Yngve Grahn Elvio Pinto Bosetti 《International Journal of Earth Sciences》2014,103(1):367-380
The Eifelian–Givetian (Middle Devonian) transition constituted an important paleoenvironmental event for the Malvinokaffric Realm in the Apucarana Sub-basin (Paraná Basin). This study highlights integration between taphonomy and sequence stratigraphy, and four depositional sequences are identified during the transition. In Sequence 1, the presence of a typical normal-sized Malvinokaffric fauna is recorded. In the transgressive systems tract (TST) of Sequence 2, no benthic fossils are present, and this is interpreted as a stratigraphic marker of an event of significant paleoenvironmental change (KA?ÁK Event). In Sequence 3, the TST has abundant bioclasts, which become rarer toward the top of the section, i.e., within the transgressive systems tract. The original habitat of this autochthonous to parautochthonous fauna was a low-energy environment between the fair weather wave base and the storm wave base of the Devonian epicontinental sea. In the highstand systems tract of this sequence, the presence of normal-sized Pennaia paulianna and lingulids demonstrates the return of more ambient conditions. Sequence 4 is of Carboniferous age. Its limit is a second-order sequence boundary recording a lowstand systems tract formed by a fluvial depositional system. The low diversity and the disappearance of taxa are not the result of a taphonomic bias, but reflect the post-KA?ÁK Event. 相似文献
22.
Vibeke Bruvoll Yngve Kristoffersen Bernard J. Coakley John R. Hopper 《Marine Geophysical Researches》2010,31(3):149-171
The first high resolution multichannel seismic data from the Mendeleev and Alpha Ridges in the Arctic Ocean have been used
to investigate the depositional history, and compare acoustic stratigraphies of the three main sub-marine ridges (Mendeleev,
Alpha and Lomonosov) in the polar ocean. Acoustic basement on the Mendeleev Ridge is covered by a ~0.6–0.8 s thick sediment
drape over highs and up to 1.8 s within grabens. A pronounced angular discordance at 0.18–0.23 s below the seafloor along
the middle to upper slopes divides the succession into an upper, undisturbed, uniformly thick, hemipelagic drape (Unit M1)
and a partially truncated lower unit (Unit M2) characterized by strong reflection bands. Unit M2 is thicker in intra-ridge
grabens and includes three sub-units with abundant debris flows in the uppermost subunit (M2a). The discordance between Units
M1 and M2 most likely relates to instability along the middle to upper slopes and mass wasting, triggered by tectonic activity.
The scars were further smoothed by bottom current erosion. We observe comparable acoustic stratigraphy and discordant relationships
on the investigated northwestern part of Alpha Ridge. Similarly, on the central Lomonosov Ridge, Paleocene and younger sediments
sampled by scientific drilling include an uppermost ~0.2 s thick drape overlying, highly reflective deposits with an angular
unconformity confined to the upper slope on both sides of the ridge. Sediment instability on the three main ridges was most
likely generated by a brief phase of tectonic activity (~14.5–22 Ma), coinciding with enhanced bottom circulation. These events
are coeval with the initial opening of the Fram Strait. The age of the oldest sediments above acoustic basement on the Mendeleev-
and west-central Alpha Ridges is estimated to be 70–75 Ma. 相似文献
23.
Yngve Öhman 《Solar physics》1973,28(2):399-402
Some comments are presented on the important observations of faint prominences made recently by Dr Jean-Louis Leroy at the Pic du Midi Observatory. The writer draws attention to the very probable connection with faintly luminous H obscuring prominences which appear sometimes as dark lanes and markings in ordinary prominences. 相似文献
24.
25.
Yngve Öhman 《Solar physics》1979,62(2):407-412
Attention is drawn to a very simple instrumental arrangement for eclipse observations of the spectra of the chromosphere and prominences using a plane grating as polar heliostat and a short focus camera. A discussion is made of an infrared chromospheric spectrum showing traces of Thomson-scattered Ca ii absorption lines in the continuous spectrum. If the effect is real, it indicates a temperature of the order of 5000 K. A simple vector formula is presented describing various types of Doppler effects appearing in radiation scattered by moving particles. 相似文献
26.
Yngve Öhman 《Solar physics》1968,3(2):354-356
Observations are reported of an H filament clearly visible in the image of the chromosphere at the limb as well as in the H spectrum of the same part of the chromosphere. Observations of this kind may give valuable information about the absorption mechanism at work in filaments. 相似文献
27.
Water samples were collected monthly for 3 years at 66°N, 2°E in the Norwegian Sea, 250 nautical miles off the Norwegian coast. Concentrations of mono- and polysaccharides were measured with the 2,4,6-tripyridyl-s-triazine (TPTZ) spectroscopic method. Total dissolved carbohydrates varied from 3.4 to 28.2 μM C of all samples and the ratio of carbohydrate to dissolved organic C (DOC) varied from an average of 14% at 0–25 m depth to 11% at 800–2000 m depth. This indicates that dissolved carbohydrates were a significant constituent of DOC in the Norwegian Sea. Polysaccharides varied from 0.4 to 21.5 μM C and monosaccharides from 0.7 to 11.7 μM C at all depths. The level of monosaccharides was relatively constant at 2.8–3.2 μM C below the euphotic zone, whereas polysaccharides showed more varying concentrations. Dissolved carbohydrates accumulated during the productive season, reaching maximum concentrations during summer although interannual differences were observed. A significant positive correlation between Chl a and soluble carbohydrate was found in one growing season with nutrient analyses. Average values for total carbohydrates were highest in the surface – 0 to 25 m – with 13.3 μM C and decreased to 8.4 μM C at 800–2000 m depth. The ratio of monosaccharides to polysaccharides exhibited a marked seasonal variation, increased from January to a maximum in June of 1.1, and declined to 0.5 in July. 相似文献
28.
Late glacial and Holocene marine records from the Independence Fjord and Wandel Sea regions, North Greenland 总被引：1，自引：0，他引：1
The first marine sediment cores from the unexplored Independence Fjord system and the Wandel Sea, North Greenland, have been investigated to reveal the glacial marine history of the region. Two key sites in the Independence Fjord system, and an earlier analysed site from the Wandel Sea continental slope, off the mouth of Independence Fjord, are presented. The Independence Fjord sites reveal an early Holocene record (10.0–8.9 Kya) of fine-grained reddish muds with calcareous microfossils, dominated by the benthic foraminifera Cassidulina neoteretis . We suggest that a semi-permanent fast ice cover characterized the region in the early Holocene, and that the deeper troughs in the mouth region of the Independence Fjord system were intruded by subsurface Atlantic water. A stiff diamicton, at least 1.3 m thick, with coal and sandstone clasts of mainly local origin, and a 0.5-m-thick Holocene cover, are found in one of the sites. The diamicton is assumed to represent a subglacial till predating the early Holocene sediments (>10 Kya). Shallow seismic records off the mouth of Independence Fjord reveal kilometre-sized troughs with signs of glacial erosion, till deposition and a Holocene glaciomarine deposition. These features could indicate that glacial ice debouching from the Independence Fjord system at some time during the last glacial period extended to the mid-outer Wandel Sea shelf. Data from a high-resolution sediment core previously retrieved from the adjacent Wandel Sea slope indicate that the maximum ice sheet advance in this area culminated about 25–20 Kya. 相似文献
29.
An identification of anomalies 31–34 is presented for the North Atlantic. North of the Azores-Gibraltar Ridge this implies a revision of the identification of the magnetic anomalies older than anomaly 26. DSDP site 10 in the western North Atlantic appears to be located on the old end of anomaly 33. The relative spacings of anomalies 29–34 in the North and South Atlantic, North and South Pacific and Indian Oceans are compared and the estimated relative widths of the magnetic polarity intervals in the Late Cretaceous are revised. 相似文献
30.
Seismic multi-channel data collected during Norwegian Antarctic Research Expeditions in 1976–1977 and 1978–1979 outline aspects of the Cenozoic depositional environment in the Weddell Sea Embayment. Acoustic basement, probably representing the East Antarctic craton, is exposed in a 50–100 km wide swath along the ice barrier between 78°S–75.5°S on the eastern side of the Crary Trough. The shelf prograded westward and northward from the craton into a subsiding basin colinear with the Transantarctic Mountain Range. Measured sediment thicknesses exceed 5 km. During middle and late Tertiary times a submarine fan complex—the Crary Fan—developed on the southeastern margin of the Weddell Sea Embayment. The glacially eroded Crary Trough is located at the contact between the craton and a sedimentary basin to the west. The entire sedimentary section is undisturbed by faulting or folding, which indicates that any movements related to Cenozoic uplift of the Trans-Antarctic Mountains and/or relative motion of East Antarctica had little effect in the area north of the Filchner Ice Shelf east of 41°W. 相似文献