Polar Research (E-Journal)
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Ice-free conditions in Novaya Zemlya 35 000–30 000 cal years B.P., as indicated by radiocarbon ages and amino acid racemization evidence from marine molluscs
No full textNovaya Zemlya was covered by the eastern part of the Barents–Kara ice sheet during the glacial maximum of marine isotope stage 2 (MIS 2). We obtained 14C ages on 37 samples of mollusc shells from various sites on the islands. Most samples yielded ages in the range of 48–26 14C Ky. Such old samples are sensitive to contamination by young 14C, and therefore their reliability was assessed using replicate analyses and amino acid geochronology. The extent of aspartic acid racemization (Asp D/L) indicates that many of the 14C ages are correct, whereas some are minimum ages only. The results indicate that a substantial part of Novaya Zemlya was ice-free about 35–27 14C Kya, and probably even earlier. Corresponding shorelines up to >140 m a.s.l. indicate a large Barents–Kara ice sheet during early MIS 3. These results are consistent with findings from Svalbard and northern Russia: in both places a large MIS 4/3 Barents–Kara ice sheet is postulated to have retreated about 50 Kya, followed by an ice-free interstadial that lasted until up to ca. 25 Kya. The duration of the MIS 2 glaciation in Novaya Zemlya was calculated by applying the D/L values to a kinetic equation for Asp racemization. This indicates that the islands were ice covered for less than 3000 years if the basal temperature was 0oC, and for less than 10 000 years if it was -5oC
Iron ooid beds of the Carolinefjellet Formation, Spitsbergen, Norway
No full textIron ooid beds are unusual deposits that have been linked to greenhouse conditions and the transgressive flooding of shallow shelves, and which were globally prevalent during certain periods. Within the marine, Aptian–Albian, Carolinefjellet Formation of Spitsbergen, chamosite ooids have been found within distinctive sandstone beds at six localities, and at a consistent stratigraphic position within the basal Dalkjegla Member. Distinctive characteristics include the iron ooids themselves, a coarser grain size, intercalation with silty siderites, grading, cross-beds indicating offshore or longshore transport, and a lack of burrowing. The enclosing sands display planar and hummocky crossstratification and abundant oscillation ripple marks, and are interpreted as lagoon-attached bar complexes. The stratigraphic position and traits of the iron ooid sands are consistent with seaward storm transport and preservation within interbar swales. Ooids vary in shape considerably, and display evidence for multiple growth events. Nuclei of quartz, opaques, carbonate clasts and laminated crusts are typically encircled by finer grained tangential chamosite and opaque laminae, sometimes with outer overgrowths of calcite and/or radial chamosite. The Dalkjegla Member is the marine portion of a large-scale transgressive tract, attached to underlying fluvio-estuarine Helvetiafjellet Formation strata. A lagoonal environment associated with the basal shales of the Dalkjegla Member represents a logical setting, where riverine iron concentration and iron silicate growth could occur. The Spitsbergen iron ooid beds extend the known occurrence of Cretaceous examples, representing a less common High-Latitude example, and one not directly associated with a transgressive flooding surface
Ice-rafted detritus events in the Arctic during the last glacial interval, and the timing of the Innuitian and Laurentide ice sheet calving events
No full textIce-rafted detritus (IRD) layers in the Arctic Ocean not only indicate the source of this detrital sediment, but give insights into the ice drift and ice sheet history. Detrital sand-sized Fe oxide mineral grains that are matched to precise sources using the microprobe chemical fingerprint of each grain, along with elevated coarse IRD abundance and radiocarbon ages, are used to define IRD peaks from the Innuitian and Arctic portions of the Laurentide ice sheets. Because grains from these two areas can be entrained by sea ice from the shelves just offshore of the calving areas, peaks in these grains must be correlated to coarse IRD to identify iceberg calving events, and to distinguish them from sea-ice rafting. The sequence of IRD peaks deposited by icebergs from these two ice sheets indicate that both ice sheets calved bergs at accelerated numbers, six or seven times, from 11 to 36 Kya. The relatively short times between most of these IRD events suggest that the ice sheets did not completely collapse with each IRD event, except the last event. Although there is some indication that one ice sheet may have begun calving bergs before the other, the resolution of the Arctic cores does not allow definitive determination of this. This emphasizes the need for higher resolution cores from the central Arctic, as well as from near the terminus of large Pleistocene ice sheets. Sea-ice rafting occurs throughout the last glacial stage, even during some glacial IRD events, as indicated by Fe grains from non-glacial sources
Tasmanites algae—contributors to the Middle Triassic hydrocarbon source rocks of Svalbard and the Barents Shelf
No full textWhen moving from west to east across Svalbard, organic geochemical, palynological and sedimentological data from the Middle Triassic dark shales of the Sassendalen Group show an improved quality of hydrocarbon source rock (kerogen type II/III), and an increased abundance of structured algal material, including Tasmanites. Triassic specimens of Tasmanites in palynological residues from Svalbard are generally of small size (500 mm in diameter) are recorded in silty shales and siltstones palynologically dated as being of Ladinian–Carnian age. Similar occurrences are also present in deposits of the Norwegian Barents Sea. Our organic geochemical analyses suggest that Tasmanites is a major source for the hydrocarbons encountered in these rocks. Tasmanites algae are also enriched in Ladinian–Norian deposits in Taimyr, Siberia. The development of a marine embayment, the direction of the ocean currents, the supply of clastic material and freshwater, and the palaeolatitude all show similarities to the conditions in the present Mediterranean, and adjacent Atlantic Ocean. Ecological conditions in the water column (light intensity, nutrient supply and temperature) are expected to have been similar, and favoured the growth and accumulation of Tasmanites. The accumulation of monotypic, large Tasmanites cells in silty shales is explained as a result of contemporaneous recirculation and sorting
Intercalibration of Boreal and Tethyan time scales: the magnetobiostratigraphy of the Middle Triassic and the latest Early Triassic from Spitsbergen, Arctic Norway
No full textAn integrated biomagnetostratigraphic study of the latest Early Triassic to the upper parts of the Middle Triassic, at Milne Edwardsfjellet in central Spitsbergen, Svalbard, allows a detailed correlation of Boreal and Tethyan biostratigraphies. The biostratigraphy consists of ammonoid and palynomorph zonations, supported by conodonts, through some 234 m of succession in two adjacent sections. The magnetostratigraphy consists of 10 substantive normal— reverse polarity chrons, defined by sampling at 150 stratigraphic levels. The magnetization is carried by magnetite and an unidentified magnetic sulphide, and is difficult to fully separate from a strong present-day-like magnetization. The biomagnetostratigraphy from the late Olenekian (Vendomdalen Member) is supplemented by data from nearby Vikinghøgda. The early and middle Anisian has a high sedimentation rate, comprising over half the ca. 140-m thickness of the Botneheia Formation, whereas the late Anisian and lower Ladinian is condensed into about 20 m. The two latest Boreal Ladinian ammonoid zones are absent as a result of erosional truncation below the Tschermakfjellet Formation. Correlation with Tethyan biomagnetostratigraphies shows the traditional base of the Boreal Anisian (base of the Grambergia taimyrensis Zone) precedes the base of the Anisian (using definitions based on the De? sli Caira section in Romania). The Boreal upper Anisian Gymnotoceras rotelliforme and Frechites nevadanus ammonoid zones correlate with most of the Tethyan Pelsonian and Illyrian substages. The base Ladinian defined in the Tethyan global boundary stratotype and point (GSSP) is closely equivalent to the traditional base of the Boreal Ladinian at the Intornites oleshkoi Zone. The latest Olenekian—early Anisian magnetic polarity time scale is refined using the Spitsbergen data
The most extensive Holocene advance in the Stauning Alper, East Greenland, occurred in the Little Ice Age
No full textWe present glacial geologic and chronologic data concerning the Holocene ice extent in the Stauning Alper of East Greenland. The retreat of ice from the late-glacial position back into the mountains was accomplished by at least 11 000 cal years B.P. The only recorded advance after this time occurred during the past few centuries (the Little Ice Age). Therefore, we postulate that the Little Ice Age event represents the maximum Holocene ice extent in this part of East Greenland
The Upper Triassic of northern Middle Siberia: stratigraphy and palynology
No full textThe Lower Carnian succession in northern Middle Siberia includes continental and marine deposits. Bivalves, nautiloids and ammonites in the marine units provide biostratigraphic control for a palynological study of three important sections. Palynomorph associations from the base of the succession include forms that have previously been reported only from Norian and Rhaetian deposits in the Tethyan and Boreal realms. This suggests that, in comparison with other areas, the palynoflora of Siberia was more uniform throughout the Late Triassic, and that the Carnian and Norian stages have a miospore assemblage that is recognizable in a wide belt through Arctic Canada and northern Eurasia
Review of A complete guide to Arctic wildlife, by Richard Sale
No full textA complete guide to Arctic wildlife is a lavishly illustrated, highly informative and comprehensive volume that will be an important addition to the library of anyone with a deep and abiding interest in Arctic natural history
Evolution of the Triassic shelf in the northern Barents Sea region
No full textThe interpretation of an unpublished data set of shallow stratigraphic cores and deep, seismic profiles from the northern Barents Shelf has provided new information about the Middle and Late Triassic development of the Barents Shelf and Svalbard. At that time, sediment sources along the eastern and south-eastern margins of the Barents Sea controlled the infilling of a previously deeper shelf area, gradually converting it into a paralic platform. Compared with the eastern source, sediment volumes from other areas were small. In our data, there are no indications of a provenance area north of Svalbard. Progradation from the ESE resulted in diachronous lithostratigraphic boundaries. The organic-rich shales of the Botneheia and Steinkobbe formations were deposited in the remaining deeper shelf areas in the western and north-western Barents Sea shelf, from the Olenekian to the latest Ladinian, by which time the progradation from the ESE had reached eastern Svalbard. In mid-Carnian times, the area of paralic deposits extended from the eastern Barents Sea into the Svalbard Archipelago
Mountain-derived versus shelf-based glaciations on the western Taymyr Peninsula, Siberia
No full textThe early Russian researchers working in central Siberia seem to have preferred scenarios in which glaciations, in accordance with the classical glaciological concept, originated in the mountains. However, during the last 30 years or so the interest in the glacial history of the region has concentrated on ice sheets spreading from the Kara Sea shelf. There, they could have originated from ice caps formed on areas that, for eustatic reasons, became dry land during global glacial maximum periods, or from grounded ice shelves. Such ice sheets have been shown to repeatedly inundate much of the Taymyr Peninsula from the north-west. However, work on westernmost Taymyr has now also documented glaciations coming from inland. On at least two occasions, with the latest one dated to the Saale glaciation (marine isotope stage 6 [MIS 6]), warm-based, bedrock-sculpturing glaciers originating in the Byrranga Mountains, and in the hills west of the range, expanded westwards, and at least once did such glaciers, after moving 50–60 km or more over the present land areas, cross today’s Kara Sea coastline. The last major glaciation affecting southwestern Taymyr did, however, come from the Kara Sea shelf. According to optically stimulated luminescence dates, this was during the Early or Middle Weichselian (MIS 5 or 4), and was most probably not later than 70 Kya. South-western Taymyr was not extensively glaciated during the last global glacial maximum ca. 20 Kya, although local cold-based ice caps may have existed