Late pleistocene and holocene loess deposits of the Southeastern Buenos Aires province,Argentina

The Late Pleistocene and Holocene loess deposits of the SE Buenos Aires province are composed of four allostratigraphic units that represent four episodes of loess deposition. The first and the second episodes occurred in Late Pleistocene times. The second episode was followed by a soil forming interval (Early Holocene to Mid-Holocene times). The third episode took place at about 5000 yr BP, after the Holocene sea-level maximum when marine regression began. The fourth episode constitutes a historical event of only local significance.Loess shows a fairly constant granulometric and mineralogical composition. The modal fraction consists of very fine sand and coarse silt (3 to 5 phi). They are classified as sandy silts or silty sands. Three grain-size subpopulations are differentiated: coarse, medium and fine. The medium-size subpopulation, which is the most important, consists of most of the very fine sand and coarse silt. It is thought to be transported by modified saltation and short-term suspension during local dust-storms.The mineralogical composition of loess consists of a volcaniclastic assemblage derived mainly from reworked pyroclastic deposits, primary tephras and volcaniclastic sediments. The source area of these materials was located in the lower Colorado river valley about 400 km SW of the studied area. There was also a direct supply by volcanic ash falls.     

Postglacial relative sea-level history: sediment and diatom records of emerged coastal lakes, north-central Kola Peninsula, Russia

Sediment cores recovered from four emerged lakes (54, 41, 22, and 7 m a.s.l.) provide new data on the deglaciation and relative sea-level history of the Murman coast, Kola Peninsula. The transition from marine to lacustrine sediment is identified in the cores by analysis of sediment physical properties and diatom assemblages. Fourteen AMS-radiocarbon ages on organic macrofossils isolated from core sediment provide chronology for the records. Basal ages from two of the cores indicate deglaciation of the area prior to 11000 BP. Radiocarbon ages associated with the marine-lacustrine sediment transition in the cores further constrain the emergence history of the area. The prominent late-glacial shoreline on the Murman coast (48 m a.s.l.) is dated to c . 10500–10300 BP, the emergence ages of lake basins 54 and 41 m a.s.l. Glaciofluvial terraces graded to this shore level indicate remnant glaciers on the north-central Kola Peninsula during the Younger Dryas.     

Age of mammoth remains from the submoraine sediments of the Kola Peninsula and Karelia

Doklady Earth Sciences -     

Isotope composition of neodymium in neo-Archean banded iron formations of Karelia and Kola Peninsula

Studies of three deposits of neo-Archean banded iron formations from the West Karelian domain (the Kostomuksha deposit) and from the Central Kola block (the Olenegorsk and Kirovogorsk deposits) showed a pronounced difference in the isotope compositions of Nd from quartz and magnetite–hematite interlayers. The less radiogenic Nd of iron-containing layers compared to that of the quartz component may be considered as an indication of the formation mechanism of the treated banded iron formations. Thus, silicon-containing layers are related to submarine volcanism and iron was supplied to the sedimentation zone from other sources.     

Late pleistocene/early holocene environments and climates,fauna, and human occupation in the argentine altiplano

The Barro Negro site (23°S lat., 65°37′W long.) in the Altiplano (Puna) of northwestern Argentina contains a well stratified sequence of remains of Hippidion, the American extinct horse, camelids, and archaeological materials, which is the focus of this study. In addition to establishing a reliable chronology, paleoenvironmental information was obtained based on analyses of pollen and stable isotopes (oxygen and carbon) from bone and marl. The data indicate that Hippidion was present at the site between 12,000 and 10,000 yr B. P., at a time when Altoandean grasslands had expanded to lower elevations. By 10,000 yr B.P., when modern semi-arid sub-puna scrub had replaced the Altoandean grasslands, only camelids (Lama or Vicugna) were present, simultaneous with the first evidence of local human occupation. This suggests that a climatic shift from cool and moist (winter rain regime) to warm and dry (summer rain regime) conditions took place simultaneously with the disappearance of the American horse and the appearance of camelids and man.     

Late pleistocene sedimentation history of the Shirshov Ridge, Bering Sea

The analysis of the lithology, grain-size distribution, clay minerals, and geochemistry of Upper Pleistocene sediments from the submarine Shirshov Ridge (Bering Sea) showed that the main source area was the Yukon-Tanana terrane of Central Alaska. The sedimentary materials were transported by the Yukon River through Beringia up to the shelf break, where they were entrained by a strong northwestward-flowing sea current. The lithological data revealed several pulses of ice-rafted debris deposition, roughly synchronous with Heinrich events, and periods of weaker bottom-current intensity. Based on the geochemical results, we distinguished intervals of an increase in paleoproductivity and extension of the oxygen minimum zone. The results suggest that there were three stages of deposition driven by glacioeustatic sea-level fluctuations and glacial cycles in Alaska.     

Holocene pollen stratigraphy and bog development in the western part of the Kola Peninsula, Russia

Pollen and macrofossil investigations and radiocarbon datings were carried out at a bog in the Khibiny mountains and the northernmost bog in European Russia on the Rybachiy Peninsula (69°98'N) on the western part of the Kola Peninsula. Peat accumulation on the Kola Peninsula started at c . 8500–7500 BP. Pinus sylvestris reached its present northern limit on the peninsula by 7000 BP, while 6000–5000/4500 BP was a time of maximal progress of birch forest tundra up to the Barents Sea shoreline. Alnus ineana grew up to the Rybachiy Peninsula c . 40 km north of its present-day northern limit. By c , 5500/5300 BP Picen ohovata had immigrated to the Khibiny mountains. After 5000/4500 BP the forested area had retreated in the northern part of the Kola Peninsula and the tundra belt bordering the Barents Sea shore was formed. By 3500 BP spruce had reached its modern northern limit.     

Chronology of Late Weichselian glaciation in the western part of the East European Plain

A database consisting of radiocarbon (¹⁴C), optically stimulated luminescence (OSL), thermoluminescence (TL) and beryllium (¹⁰Be) dates was used for timing the advance of the Late Weichselian Scandinavian Ice Sheet (SIS), determining the age of the Last Glacial Maximum (LGM) and the rate of deglaciation. The study area encompasses the southeastern sector of the last SIS between the Baltic Sea and the LGM position in the western part of the East European Plain, covering the Karelian Ice‐Stream Complex (ISC) area in the east and the Baltic ISC area in the west. The linear advance and recession rates of the last SIS were estimated to be between 110 and 330 m a^?1 and between 50 and 170 m a^?1, respectively. The onset of the last SIS in the Karelian ISC area reached the western shores of Latvia not before 26 OSL ka, and in the Baltic ISC area, on the southern shores of the Gulf of Finland, not before 21 OSL ka. The last SIS reached close to the LGM position earliest in NW Belarus, not earlier than 22.6 cal. ¹⁴C ka BP, and latest in the NE of Belarus, not earlier than 19.1 cal. ¹⁴C ka BP. The Baltic ISC area between the LGM position and the western shores of Latvia was deglaciated in about 8 ka, and in the Karelian ISC area, between the LGM position and the southern shores of the Gulf of Finland, in about 2.6 ka. The whole area between the LGM position and the Baltic Sea was deglaciated between 14.2 ¹⁰Be ka and 13.3 cal. ¹⁴C ka BP.     

Age paradoxes of Devonian magmatism of the northeastern part of the Kola Peninsula

A structural-geochemical study has been conducted on the dikes of presumably Devonian mafic rocks confined to a small graben filled in with Riphean sedimentary rocks hosted by Early Precambrian granite-gneiss of the Murmansk block. It has been demonstrated that the dolerite dikes of this region can be considered as manifestations of trap magmatism whose products fill in the foundation of the East Barents riftogenic downfold. In turn, manifestations of alkaline and kimberlite rocks of the White Sea region are confined to the peripheral portion of the trap magnetism area. Zircons from dolerite transecting Late Riphean sediments examined in two laboratories have a concordant age of 2.74–2.72 Ba, while zircons from a similar dike located in granite-gneiss of the basement are characterized by an age range of 2700–155 Ma, and the concordant age based on 4 points is 790 Ma. All these factors indicate that the age determinations of the mafic rocks are ambiguous, particularly in the zone of transition from the center of the trap province to its periphery, where alkaline magmatism is observed.     

Behavior of Pt and Pd compounds during metamorphism in the easternmost part of the Pana Intrusion,Kola Peninsula

The role of metamorphic processes (including postmagmatic ones) in the origin of mineral assemblages is estimated for the layered unit (LU) and barren rocks (BR) in the Pana Intrusion. Numerical simulations indicate that metamorphic processes simultaneously modified the mineralogical composition of the rocks, Pt and Pd compounds, and the fluids. The process resulted in systematic changes in the mineralogical and fluid composition and is realistically reproduced by physicochemical numerical simulations. Our results make it possible to estimate the effect of P-T parameters on the composition of metallic Pt and Pd and their sulfides, selenides, and tellurides and the composition of the fluid phase during the transformations and localization of the PGE ore mineralization.     

A preliminary study on the climatic and environmental changes at the turn from pleistocene to holocene in East Asia

This paper examines the regional climatic and environmental changes from the late Pleistocene to middle Holocene in Central-East Asia. A review is made of the published literature that are specific to pelaeoclimate and physical environment in some geographical regions.It is shown that (1) during the late Pleistocene the annual mean temperature was 5°–6° C lower than present in Qinghai-Xizang (Tibet) plateau, 6° to 9° C lower than today in NE China, 6° C lower than today in E China, and 4° C lower than present in Taiwan island; (2) during the middle Holocene, the annual mean temperature was 4° C warmer than present in Qinghai-Xizang (Tibet) plateau, 3° to 4° C warmer than today in NE China, 2° to 3° C warmer than today in Shanghai area, and only 2° to 2.5° C warmer in Taiwan island.     

Late pleistocene and early holocene climate of Ny-Alesund,Svalbard (Norway): A study based on biological proxies

Subsurface sediments of a 120 cm deep trench from Ny-Alesund, Svalbard, were analysed for pollenspores and other organic matter contents. This study is supported by two AMS ¹⁴C dates (27, 200 yrs BP and 8,762 yrs BP) at the bottom and topmost litho-unit of the trench, respectively. The pollen record provides an evidence of a warm interval at about 27,200 yr BP (Late Weichselian and MIS 3) and cooling episode around 8,762 yr BP. This is also supported by the amount and type of organic matter as well as sediment type and depositional history of the trench sediments.     

Variation of chemical composition of alkaline granitic rocks in the central part of the Kola Peninsula

Chemical composition and origin of alkaline granitic rocks in the Keivy area on the Kola Peninsula were investigated. Linear correlation analysis and principal-component analysis were used to determine the interrelation of major petrogenetic elements in alkaline granite and surrounding alkaline metasomatites. Estimates of linear correlation coefficients turned out to be different, and principal-component analysis of the chemical data revealed that there were three main components influencing variation of chemical composition. These factors can be interpreted in terms of petrological processes, which are different for alkaline granite and for the surrounding metasomatites, indicating a different origin of the rocks.     

Late Weichselian and holocene sea-level history for a cross-section of western Norway

The postglacial sea-level history along a cross-section of western Norway has been studied in detail. Ten local sea-level curves were used to construct an equidistant shoreline diagram, covering the last 13000 years. This includes 76 radiocarbon dates, of which the majority represent lacustrine sediments at the marine/lacustrine boundary in cores from emerged lakes. The distance between the westernmost and easternmost sites is 170 km and the difference in total emergence along this profile is more than 200 m. The shorelines all dip westward with a decreasing gradient through time. The Late Weichselian lines are all slightly curved whereas the Holocene lines are apparently straight. After the formation of the uppermost shoreline by around 12 800 BP there was a rapid emergence that decelerated with time to a near standstill during the Younger Dryas. From about 10 300 there was again a rapid emergence followed by the Tapes transgression along the coast and a standstill in the most easterly areas. At the western end of this profile, the Tapes transgression started around 9000 and culminated approximately 6000 BP, when a gradual regression occurred. To the east the early Holocene regression minimum occurs at a younger date and the transgression maximum is up to 1500 years older.     

Pyroxenes of the Khibiny alkaline pluton, Kola Peninsula

Seven pyroxene varieties were identified in nepheline syenites and foidolites of the Khibiny pluton: enstatite, ferrosilite, diopside, hedenbergite, augite, aegirine-augite, and aegirine. Enstatite and augite are typical of alkaline and ultramafic rocks of dike series. Ferrosilite was found in country quartzitic hornfels. Diopside is a rock-forming mineral in alkaline and ultramafic rocks, alkali gabbroids, hornfels in xenoliths of volcanic and sedimentary rocks and foyaite, melteigite-urtite that assimilate them, and certain hydrothermal pegmatite veins. Hedenbergite was noted in hornfels from xenoliths of volcanic and sedimentary rocks and in a hydrothermal pegmatite vein at Mount Eveslogchorr. Aegirine-augite is the predominant pyroxene in all types of nepheline syenites, phonolites and tinguaites, foidolites, alkaline and ultramafic rocks of dike series, fenitized wall rocks surrounding the pluton, and xenoliths of Devonian volcanic and sedimentary rocks. Aegirine is an abundant primary or, more often, secondary mineral in nepheline syenites, foidolites, and hydrothermal pegmatite veins. It occurs as separate crystals, outer zones of diopside and aegirine-augite crystals, and homoaxial pseudomorphs after Na-Ca amphiboles. Microprobe analyses of 265 pyroxenes samples allowed us to distinguish ten principal trends of isomorphic replacement and corresponding typomorphic features of pyroxenes. Compositional variations in clinopyroxenes along the sampled 35-km profile from the margin of the Khibiny pluton to its center confirm the symmetric zoning of the foyaite pluton relative to semicircular faults of the Minor Arc and the Main (Central) Ring marked by Devonian volcanic and sedimentary rocks, foidolites, and related metasomatic rocks (rischorrite, albitite, and aegirinite). Changes in the composition of pyroxenes are explained mainly by the redistribution of elements between coexisting minerals of foyaites in the process of their intense differentiation under the effect of foidolite melts that have intruded into the circular fault zones.     

Reconstruction of Late Pleistocene events in the periglacial area in the southern part of the East European Plain

An integrated study of the loess–soil sequence in the coastal exposure near the settlement of Beglitsa (Rostov oblast) allowed us, for the first time, to reconstruct the landscape-climatic changes that occurred in the eastern Azov region over the course of the Late Pleistocene. In the south of the periglacial zone, considerable differences between intensity of the loess accumulation in the Early and Late Valdai Cryochrons were revealed. In the Early Valdai Epoch, which corresponds roughly to the end of Marine Isotope Stage (MIS) 5 and MIS 4, loess accumulation occurred after completion of development of the Mezin pedocomplex and before the beginning of the Bryansk stage of soil development, i.e., over more than 20 000 years. In the much shorter Late Valdai Cryochron MIS 2 (10 000–12 000 years), loess accumulation reached 5 m. The data evaluation shows that the loess accumulation rates in the Early Valdai Epoch (~0.07 mm/year) and the Late Valdai Epoch (~0.5 mm/year) differ from each other by an order of magnitude.     

PGM in chromite ore of the Sopcheozero deposit, Kola Peninsula

The Sopcheozero chromite deposit is hosted in dunite of the Monchegorsk layered intrusion as a sheetlike body of disseminated ore with a chromite grade varying from 20 to 60%. The total PGM content in the ore attains 0.5–0.8 g/t. The composition of host rocks varies from plagioclase peridotite to dunite, but PGM were found only in chromite-bearing dunite. PGM inclusions were detected in the interstices of chromite and olivine grains and within grains themselves. The data obtained confirm the known tendency toward variation in PGM composition with increasing sulfur and light PGE contents in the residual magmatic melt. The first particles of refractory Ir, Os, and Ru intermetallides appeared at the final stage of olivine crystallization, whereas laurite (Ru,Os,Ir)S₂ and pentlandite (Fe,Ni)₉S₈ were formed at the final stage of chromite crystallization, when the sulfur concentration in the residual melt became sufficient.     

Kalsilite of the Khibiny and Lovozero alkaline plutons,Kola Peninsula

Kalsilite—a typical mineral of ore-bearing zones of the Khibiny and Lovozero plutons—was formed after low-Si and high-K nepheline in one of three ways: (1) by relatively high-temperature replacement of Na with K; (2) due to orthoclase-kalsilite poikiloblastesis in foidolites and overlapping foyaites; or (3) by replacement of nepheline with zeolite.