Kara Shelf Research Articles

The eastern extent of the Barents–Kara ice sheet during the Last Glacial Maximum based on seismic-reflection data from the eastern Kara Sea

We present sub-bottom profiling (sparker and Parasound) results from the eastern Kara Sea, on the Eurasian Arctic margin, which enable the identification of the Last Glacial Maximum (LGM) ice extent. The analysed profiles show that glacigenic diamicton is ubiquitous at the seafloor, east of about 95°E and 78°N. The eastern margin of this diamicton is expressed in a conspicuous morainic ridge at the entrance to the Vilkitsky Strait, and to the south the diamicton projection aligns with the LGM limit mapped at the north-western Taymyr. The bottom of the Voronin Trough further north is also covered with diamicton and has numerous erosional bedforms, indicating a streamlined flow of grounded ice along the trough. Accurate dating of the diamicton is not attainable, but the correlation of pre-diamict sediments to well-dated sections in the Laptev Sea, and available 14 C ages from sediments on top of the diamicton, indicate its LGM age. These results support the palaeogeographic reconstruction that assumes the extension of the LGM Barents‐Kara ice sheet as far east as Taymyr. This configuration implies that LGM ice blocked the drainage of the Ob and Yenisey rivers on the Kara shelf. This inference is consistent with the presence of large (>100 km wide) lenses of basin infill adjacent to the southern margin of the diamicton. However, the limited distribution of the eastern Kara ice lobe, not extending on Severnaya Zemlya, suggests that the ice was fairly thin and short-lived: insufficient for the accumulation of the gigantic proglacial lakes that occurred during earlier glaciations.

New geochronological data on Palaeozoic igneous activity and deformation in the Severnaya Zemlya Archipelago, Russia, and implications for the development of the Eurasian Arctic margin

The Severnaya Zemlya Archipelago, located close to the continental edge of the Kara Shelf in the Russian high Arctic, represents, together with northern Tajmyr, the exposed Neoproterozoic and Palaeozoic part of the North Kara Terrane. This terrane has been interpreted as an independent microcontinent or part of a larger entity, such as Arctida or Baltica, prior to collision with Siberia in Late Carboniferous time. A major stratigraphic break, the Kan'on (canyon) River Unconformity, separates folded Late Cambrian from Early Ordovician successions in one area, October Revolution Island. New geochronological U–Th–Pb ion-microprobe data on volcanic and intrusive rocks from this island constrain the age of an important magmatic episode in the earliest Ordovician. A tuff, in association with Tremadocian fossils, overlying the Kan'on River Unconformity, has been dated to 489.5 ± 2.7 Ma. The youngest rocks beneath the unconformity are of the Peltura minor Zone, and the latter has been dated previously, in western Avalonia, to 490.1+1.7−0.9 Ma. Thus, little time is available for the tectonic episode recorded by the unconformity, and the similarities in radiometric dates may indicate problems with the correlation of faunal markers for the Cambrian–Ordovician boundary across palaeo-continents. The other extrusive and intrusive rocks which have been related to Early Ordovician rifting in the Severnaya Zemlya area yield ages from 489 Ma to 475 Ma. An undeformed granite, cutting folded Neoproterozoic successions on neighbouring Bol'shevik Island has been dated to 342 ± 3.6 Ma and 343.5 ± 4.1 Ma (Early Carboniferous), in accord with evidence elsewhere of Carboniferous strata unconformably overlying the folded older successions. This evidence conflicts with the common interpretation that the structure of the Severnaya Zemlya Archipelago originated during the collision of the North Kara Terrane with Siberia in Late Carboniferous time. An alternative interpretation is that Severnaya Zemlya was located in the Baltica foreland of the Caledonide Orogen and that the eastward-migrating deformation of the foreland basin reached the area of the archipelago in latest Devonian to Early Carboniferous time. This affinity of the North Kara Terrane to Baltica is further supported by 540–560 Ma xenocrysts in Ordovician intrusions on October Revolution Island, an age which is characteristic of the Timanide margin of Baltica.

Low-frequency emissions and related phenomena in the ionosphere above the lithosphere deep faults inferred from satellite data

The comparative analysis of the variations of the low-frequency emission (0.1–20 kHz) intensity, low-energy electron fluxes and the plasma temperature at satellite altitudes (on 10 orbits of the “Intercosmos 19” satellite) above the lithosphere deep faults of the Norwegian Sea, the Baltic Shield, the Barents–Kara shelf and the West-Sibirian Lowland has been carried out. All these regions represent consistent changes in the Earth crustal structure and its geodynamic characteristics in the zone of transition from the Euroasian continent to the Arctic Ocean. The tectonic structures of these regions have different physical parameters and seismic activity. It has been detected that a special character of the low-frequency electromagnetic emission characterises each type of the lithosphere structure.

Dissolved oxygen extrema in the Arctic Ocean halocline from the North Pole to the Lincoln Sea

Dissolved oxygen (O 2) profiling by new generation sensors was conducted in the Arctic Ocean via aircraft during May 2003 as part of the North Pole Environmental Observatory (NPEO) and Freshwater Switchyard (SWYD) projects. At stations extending from the North Pole to the shelf off Ellesmere Island, such profiles display what appear to be various O 2 maxima (with concentrations 70% of saturation or less) over depths of 70–110 m in the halocline, corresponding to salinity and temperature ranges of 33.3–33.9 and −1.7 to −1.5 °C. The features appear to be widely distributed: Similar features based on bottle data were recently reported for a subset of the 1997–1998 SHEBA stations in the southern Canada Basin and in recent Beaufort Sea sensor profiles. Oxygen sensor data from August 2002 Chukchi Borderlands (CBL) and 1994 Arctic Ocean Section (AOS) projects suggest that such features arise from interleaving of shelf-derived, O 2-depleted waters. This generates apparent oxygen maxima in Arctic Basin profiles that would otherwise trend more smoothly from near-saturation at the surface to lower concentrations at depth. For example, in the Eurasian Basin, relatively low O 2 concentrations are observed at salinities of about 34.2 and 34.7. The less saline variant is identified as part of the lower halocline, a layer originally identified by a Eurasian Basin minimum in “NO,” which, in the Canadian Basin, is reinforced by additional inputs. The more saline and thus denser variant appears to arise from transformations of Atlantic source waters over the Barents and/or Kara shelves. Additional low-oxygen waters are generated in the vicinity of the Chukchi Borderlands, from Pacific shelf water outflows that interleave with Eurasian waters that flow over the Lomonosov Ridge into the Makarov Basin and then into the Canada Basin. One such input is associated with the well-known silicate maximum that historically has been associated with a salinity of ≈33.1. Above that ( 32 < S < 33 ), there is a layer moderately elevated in temperature (summer Bering Sea water) that we show is also O 2-depleted. We propose that these low O 2 waters influence the NPEO and SWYD profiles to varying extents in a manner reflective of the large-scale circulation. The patterns of halocline circulation we infer from the intrusive features defy a simple boundary-following cyclonic flow. These results demonstrate the value of the improved resolution made feasible with continuous O 2 profiling. In the drive to better understand variability and change in the Arctic Ocean, deployment of appropriately calibrated CTD-O 2 packages offers the promise of important new insights into circulation and ecosystem function.

Remote identification of radioactive contamination by satellite measurements

The simultaneous measurements of the magnetic and electric component of ELF/VLF emission field, low-energy electrons and ambient satellite plasma temperature by “Intercosmos 19” satellite data are analyzed. It is established, that in the Barents–Kara Sea region the areas of the observation of simultaneous fluctuations of these parameters have coincided with zones of high contents of cesium ( 137Cs) at bottom sediments. The observation results in conjunction with ionospheric anomalies observed by the Japan ISS-b satellite instruments, that was active above Barents–Kara shelf region also, were analyzed (analysed). We prepare the maps of the hydrogen, helium and oxygen ions distribution above South Barents hollow by using the data of Japan satellite. It is established, that the area of registration of light ions by Japan satellite ISS-b has coincided with the area of the observation of simultaneous small-scale fluctuations of plasma parameters by Intercosmos 19 satellite data. On the basis of the all the method of detection of radiological contamination in the near-ground atmosphere layer, in the bottom sediment and in the water layer is offered. The method includes simultaneous measurement of parameters of near-earth plasma: magnetic and electrical component of ELF/VLF emission field, of low-energy electrons, of ambient satellite plasma temperature and intensity of light ions. Received results of our investigation can be utilised for forecasting in an ecology, seismology, in geology of oil and hydrogeology.

The geomorphology of the South Kara shelf

Abstract The paper presents the Cenozoic history of the topography of the South Kara shelf. It represents a peripheral part of the West Siberian plate submerged beneath the Kara Sea. The principal morphostructures are remnants of the South Kara arch, the Baidaratsk foredeep, and the East Novaya Zemlya trench. Structural‐denudational levels are identified as having been formed during regressive episodes in the Late Oligocene, Late Miocene, the Late Pliocene/Pleistocene, the late Middle Pleistocene, and at the Pleistocene/Holocene boundary. Submarine erosional‐depositional levels were formed during transgressive epochs during the Early/Middle Miocene, Pliocene, Early/Middle Pleistocene, Late Pleistocene, and Holocene.

Peculiarities of the morphology of glacial dislocations on the Kara sea coast

Abstract The author describes tight, asymmetrical minor folds in well‐bedded sands, loams and clays exposed by thermal abrasion of ice‐rich sediments on the west coast of Yamal and the north coast of Yugor Peninsula. The folds are commonly underlain by massive bodies of ground ice. The author postulates that the folds are the product of a southward flow of ice within an ice‐sheet sitting on the Kara Shelf, over unconsolidated sediments which were already frozen.

The hypothesis of a late Würm arctic ice sheet

Abstract On the basis of geomorphological and geological data as well as radiocarbon dates, the author rebuts the hypothesis of the existence during the Late Pleistocene and Early Holocene of an extensive ice sheet on the Barents and Kara shelves and the adjacent northern lowlands.

Geologic History of North-Central Siberia: ABSTRACT

The post-Archean history of north-central Siberia is essentially the reconstruction of the history of the North Asian craton in relation to the evolution of the surrounding mobile belts. The formation of the craton dates to the early Proterozoic (1,900 m.y. ago). It was bordered by the Olenek fold system on the east and in the west by geosynclinal belts, which completed their development through a succession of Baikalian, Caledonian, and Hercynian movements. The most ancient Archean rocks (charnokite) are exposed on the Anabar shield; the youngest rocks of the craton are represented by the Taimyr Kara gneisses. During the Proterozoic a sedimentary platform cover was deposited across the craton; this platform is broken into plates by troughs with eugeosynclinal formations (presumably-Grenville). The sedimentary cover rocks are unmetamorphosed-terrigenous and marine-carbonate deposits of Riphean age. Within the craton the Cambrian to Devonian is characterized by a platform regime. Troughs within the platform are filled with black shale and terrigenous-carbonate marine formations, including gypsiferous sequences. Mottled terrigenous and gypsiferous strata of a lagoonal facies and marine limestone and sandstone were deposited in the pericraton trough in Severnaya Zemlya. The Carboniferous to Triassic was marked by intensive movements of the Pacific orogenic cycle which also affected many areas outside of the geosynclinal belts. Pacific-cycle movements rejuvenated the craton structures and those of the Caledonian and Hercynian systems bordering it. The linear zones of arcogenesis and the associated parageosynclinal trough formed the Taimyr-Severnaya Zemlya fold system on the periphery of the craton. The Tunguska synclinorium and the Anabar anticlinorium formed in the center of the craton. In the eastern part of the region the area of activization joined the Verkhoyansk-Chukotsk geosyncline. The Tunguska synclinorium, the Taimyr trough, and the Verkhoyansk geosyncline formed a single system of troughs filled with continental coal-bearing, paralic coal-bearing, and marine terrigenous sediments, respectively. Plateau basalts also are present in the epicraton troughs; granitic magmatism is displayed in arcogenesis zones. The Jurassic to Paleogene was characterized by the return of a platform regime in former areas of activization. The basal layer of sedimentary cover becomes younger from west (Liassic) to east (Cenomanian) as the folding decreased. Terrigenous Mesozoic-Cenozoic marine and paralic formations filled isometric and linear troughs and swells. Two sedimentary basins representing the Kara and Laptev sea shelves formed on the platform basement during the Neogene-Quaternary stage. The structural framework of these basins differs; their formation is connected with the development of the Arctic Ocean basin. End_of_Article - Last_Page 2511------------