Boreal Transgression Research Articles

FIRST DATA ON PALEOGEOGRAPHICAL SETTINGS AND CHRONOLOGY OF THE LAST INTERGLACIAL ON ZIMNII COAST OF THE WHITE SEA

Field lithostratigraphic studies, microfaunistic and palynological analyses, as well as optically stimulated luminescence (OSL) dating revealed for the first time that the lower part of Quaternary sediment sequences exposed along Zimnii Coast of the White Sea accumulated in marine and nearshore environments during the Boreal transgression at the beginning of the Last Interglacial and thus form the Upper Pleistocene Mikulinian Horizon. This is confirmed by lithology of sediment beds; species composition of foraminifers, ostracods and aquatic palynomorphs; and OSL dates in the range of 118–104 ka. The composition of benthic microfossils indicates that during the early Boreal transgression the entire Zimnii Coast was occupied by an coastal arctic ice-covered basin with water depths of 50 m, high sedimentation rates, and water stratification induced by melt/river water inflow. At the stage of regression, sedimentation in shallow marine environments was dominant along Zimnii Coast.

New data on the palynostratigraphy of the Mikulinian (Eemian) deposits in the lower reaches of the Pyoza River (northeastern White Sea region)

The palynological method was used to study a 455 cm thick marine sediment sequence, which overlies the Moscovian moraine in the Bychye-2 section on the Pyoza River (Arkhangel’sk region). The pollen records obtained allowed us to make a palynozonal subdivision of the section and to trace the plant cover transformations that occurred in the northeastern White Sea region during the Boreal transgression. When comparing the established local palynozones with the regional subdivisions of the reference sections Bychye-1, located 5 km upstream on the Pyoza River from the Bychye-2 site, and Peski on the Karelian Isthmus, we also employed the methods of correlation and event palynostratigraphy. It has been found that the marine sediments in the Bychye-2 section accumulated from the end of the Moscovian glaciation (~ 131 ka BP) until ~ 119,5 ka BP. The seven local palynozones established in the Bychye-2 section indicate a consistent change in climatic conditions and vegetational feedbacks. The main trend is the rapid displacement of Arctic-type shrub-herbaceous communities by pine-birch forests at the very beginning of the Mikulinian (Eemian) interglacial and the subsequent rise in the proportion of dark coniferous elements in the forests due to the growing humidity of the climate in the course of the transgression. A significant warming of the climate led to the emergence of thermophilic deciduous plants (oak, elm, hazel, and possibly even hornbeam) in the forests of the region. The predominance of pine-birch forests and the disappearance of all thermo- and hygrophilic elements of the vegetation followed the deterioration of climatic conditions during the final stage of the Mikulinian interglacial.

The penultimate interglaciation of northern Russia

This paper presents new field and laboratory data combined with previously published materials on interglacial sediments underlying two upper tills of northern European Russia and West Siberia. The emphasis is on the structure and chronometric data of marine strata with shells of boreal molluscs of Cyrtodaria genus indicative of the Atlantic marine invasion into these sedimentary basins during the late Middle Pleistocene. Another line of evidence for this time span is inferred from inter-till terrestrial sequences in the European Northeast with forest pollen spectra suggesting a climate much warmer than today. The decisive correlation signal is provided by optically stimulated luminescence and electron-spin resonance dates, indicating MIS 7 time, and by the geological position of two interglacial formations between the first, second and third from the surface glacial complexes. The collected evidence disagrees with the model of the unique boreal transgression and confirms that saline Atlantic water at least twice invaded northern Russia during the last 250 kyears. The sedimentary formations of the penultimate interglaciation can serve as a new intra-regional stratigraphic marker for the northern Pleistocene.

Upper Pleistocene and Holocene stratigraphy in the Kola Peninsula and Northern Karelia (N–W Russia): Marine and glacial units

Data on litho- and biostratigraphy of major sedimentary sequences and their geochronological records were compiled and summarized to describe the Late Pleistocene–Holocene marine and glacial events in the Kola-Northern Karelia region. In the coastal Kola Peninsula and its inner part, three marine units and two glacial events were identified in the Upper Pleistocene sequences. The first marine unit (Ponoi Beds in the regional stratigraphy) can be definitely referred to the significant Late Pleistocene transgression known as the Boreal in northern Eurasia. Data on the Kola Peninsula show that the warm-water Boreal transgression was longer than the Eemian one in western Europe, comprising at least MIS 5e-d (from 130–120 to 105–100 ka BP) in the White Sea depression and MIS 5e-c (earlier at least 90 ka BP) in the Barents Sea. Forested environments dominated on the Kola Peninsula at that time. The second Interglacial marine unit (Strelna Beds) attributed to the subsequent Belomorian transgression was deposited in relatively cold settings at the final phase of the Mikulinian Interglacial (MIS 5), about 100 to 70–80 ka BP. Adjacent areas were covered with open forest and tundra. The third marine unit referred to the Interstadial Leningrad Group was formed 60–40 ka BP in rather a cold marine reservoir, when the environmental conditions were more severe than now. The Late Pleistocene glacial events are correlated to the Podporozhie and Ostashkov Groups (MIS 4 and 2). The Podporozhian glacial unit seems to be associated with the Barents-Kara Ice Sheet and its melting caused the glacioeustatic transgression in the White Sea during the Leningradian Substage (MIS 3).During the Late Glacial and Holocene, a periglacial freshwater lake, brackish-water basin and marine reservoir successively appeared in the White Sea depression successively. Two marine events are suggested here based on the key sedimentary sequences from the coastal isolated lake, i.e. the Late Glacial transgression and the early-middle Holocene (Tapes) transgression.

Фораминиферы и биостратиграфия апта северного палеобиогеографического района Западной Сибири

Several (7) boreholes have been drilled between the territories of the Pur and Taz rivers which are assigned to the Northern Palaebi-ogeographical district on the base of finding Foraminifera. The marine Aptian deposits have been discovered in this district for the first time. The southern boundary of the Aptian foraminiferal finds in the sections of the wells lies between the Pur and Taz rivers. Based on these finds, one may think that the Aptian boreal transgression has spread in the West Siberian basin from the Arctic one. The Aptian assemblages have also been found in the territory of the Yjamal Peninsula. For the most part, transgression may have occurred in the Middle Aptian age because there exist many Foraminifera Assemblages which conditionally are assigned to this age. The author of the paper has studied the Aptian Foraminifera Assemblages from the section wells of the South-Russkaya area, the line sections of wells from the Taseiskaya area (well P-159), the West-Tambeiskaya area (wells 42, 45, 124), the North-Tambeiskaya area (wells 201, 205). In theese sections agglutinated quartz - siliceous Foraminifera related to the Aptian age were discovered. Foraminiferal Assemblages proved to be of a small systematic diversity and a quantity of specimen species along with their rather poor preservation. This made it difficult to determine comparatively well-preserved specimens. Content rocks are mainly grey aleuro-lites with the interlayers of dark-grey argillites and light-grey millstone grit of the Viculian Horizon. The systematic composition of most assemblages of the identified sections allows us to establish the deposits of the conditionally Middle Aptian age in the middle part of the Viculian Horizon. The deposits concerned are documented in the section of borehole 55 (the South-Russkaya area) in the depth intervals 1841,50-1834,30 m. In the assemblage of this section the species Trochamminoides aff. ivanetzi Podobina, Labrospira aff. rotunda Podobina, Haplophragmoides topagorukensis Tappan, Pseudoverneuilina (?) aptica Podobina sp. n., Siphogaudryina rayi (Tappan) are present. Rounded forms of the Labrospira, Haplophragmoides, Trochammina genera are prevalent in established Aptian assemblages. Almost all the foraminiferal assemblages in this and the other established sections are supposedly of the Middle Aptian age. Based on the Foraminifera finds, the Aptian transgression is supposed to have reached its maximum in the Middle Aptian time. In addition, conditionally early and late Aptian foraminiferal assemblages are established in solitary sections. In the well sections of the Yjamal Peninsula in the Viculian Horizon the Aptian microfauna - agglutinated quartz-siliceous foraminifera and ostracod nucleis are also discovered. The foraminifera in all the sections are not abundant, they are approximately of a similar systematic composition and of rather a poor preservation. The paper concerned presents factual data on the first discovered Aptian foraminiferal assemblages related to the rocks of the Viculian Horizon. All Aptian Assemblages (mainly the Middle Aptian ones) are illustrated in 8 accompanying photos (drawing) which to some extent allow us to form an opinion about their systematic composition and quantative content. In addition an illustration of Pseudoverneuilina (?) aptica Podobina sp. n. species are shown in the fig. 9. Also there are brief description of this species.

Foraminifera and Late Cenomanian-Turonian biostratigraphy of the northern palaeobiogeographic district of Western Siberia

Abstract The study of 114 core samples from seven borehole sections of the Van-Eganskaya area in the central part of Western Siberia yielded sufficient data to investigate the Late Cenomanian-Turonian foraminifers, palaeoenvironments, and the Late Cenomanian-Turonian biostratigraphy of this poorly studied area. Two Late Cenomanian foraminifer zones were established, viz. a (lower) Saccammina micra - Ammomarginulina sibirica Zone and an (upper) Trochammina wetteri tumida - Verneuilinoides kansasensis Zone. They reflect changes in the species composition of the foraminifer assemblages and lithology of the host rocks of the Uvatskian Horizon. In the lower part of the upper zone, beds with Gaudryinopsis nanushukensis elongatus are present. The changes in the species composition and lithology of the upper Cenomanian resulted from water-depth variations during the Boreal transgression. Two distinct assemblages and two homonymous zones, viz. the (lower) Gaudryinopsis angustus and the (upper) Pseudoclavulina hastata zones occur in the Turonian clayey cap-rocks of the superimposed Kuznetsovskian Horizon. Comparison of the Late Cenomanian-Turonian assemblages from the West-Siberian and Canadian provinces of the same Arctic palaeobiogeographical realm shows that the West-Siberian species are the same as, and closely related to, Canadian taxa, along with geographical subspecies. This comparison allows a detailed correlation, which results in a precise dating of the foraminifer zones.

Pleistocene marine deposits in the coastal areas of Kola Peninsula (Russia)

On the basis of field data, datings from both electron spin resonance – and optically stimulated luminescence, and micro- and macrofauna, in addition to presence of diatoms, three Late Pleistocene marine units have been identified in the coastal areas of the Kola Peninsula. The stratigraphically lowest sequence is correlated to the Ponoi Beds and the Boreal transgression, attributed to the marine isotope stages (MIS) 5e to 5d in the White Sea depression and to MIS 5e to 5c in the Barents Sea. Thermophilic fauna and diatoms indicate normal water salinity and a water temperature above zero. The second marine unit, referred as the Strel'na Beds, can be correlated with the Early Weischselian transgression, termed the Belomorian transgression. With low water salinity and a water temperature similar or colder than the present times, Belomorian transgressions are reliably detected in the White Sea and are not clearly found in the Barents Sea. The results obtained from the sediments of the Ponoi and Strel'na Beds indicate a continuously existing marine reservoir from 130 to 80–70 ka ago (entire MIS 5) in the White Sea depression. The early Middle Weichselian Barents–Kara ice-sheet invasion and its recession might have caused the glacioeustatic Middle Weichselian (MIS 3) transgression, and the third Late Pleistocene marine sequence has been deposited in the regressing shallow cold sea with less saline waters. The results help in the understanding of the history of Late Quaternary ice sheets in North Eurasia and provide evidence for the debatable Early and Middle Weichselian marine events.

ESR/OSL ages of long‐debated subtill fossil‐bearing marine deposits from the southern Kola Peninsula: stratigraphic implications

The occurrence of sandy clay deposited in a warm marine environment just below the till of the last glaciation has created controversy about its age and stratigraphic position in the sedimentary basin of the Kola Peninsula. Data on marine microfauna, diatoms, malacofauna and pollen composition indicate that during the period when the sandy clay was deposited the climate was similar or even warmer than at present. According to 14C dates, sedimentation of the sandy clay occurred around 40 ka BP. Based on these data, some researchers have attributed these marine deposits to the third Late Pleistocene Belomorian (sensu Lavrova 1960) interglacial transgression. At the same time there are geological indications suggesting re‐deposition of these subtill sediments. To solve this problem we have reinvestigated the subtill interglacial marine deposits from the Varzuga section (˜66.4° N and 36.6° E). Four different marine shell species and enclosing sandy clay sediments taken from the subtill marine unit of the section were dated by the electron spin resonance (ESR) and optically‐stimulated luminescence (OSL) methods at about 103 and 104 ka, respectively. The results indicate that the subtill marine deposits belong to the first Late Pleistocene Boreal transgression that, according to our previous studies of the marginal areas of the Eurasian North, has occurred in the time interval from approximately 145 to 70 ka BP.

Cretaceous palaeogeography of the North-Eastern Peri-Tethys

The Cretaceous stratigraphy and main palaeogeographic features of the North-Eastern Peri-Tethys are briefly summarised on the base of new data. The study is mainly focused on the time-slices that were chosen for the recently published Peri-Tethys Atlas: Early Hauterivian, Early Aptian, Late Cenomanian, Early Campanian and Late Maastrichtian. Two main epochs in the development of this area are recognised. The Early Cretaceous is characterised by the prevalence of the terrigenous sedimentation and the existence of a large longitudinal strait through the Russian Platform, which controlled the Boreal/Tethyan connection. The southward Boreal water movement prevailed during the Neocomian. The strongest Boreal transgression took place in the Late Hauterivian, when cool water reached the Crimea basin. The Aptian–Albian time was characterised by a northward Tethyan water movement, interrupted by the Early Albian Boreal transgression. Tectonic rebuilding of the region took place in the Albian–Cenomanian. It resulted in the disappearance of the sea-strait through the Russian Platform and in the opening of another sea-strait in the Turgai area in the Turonian. This strait connected the Peri-Tethyan seas, the Western Siberia Boreal basin and joined with the Western Interior Seaway in the other side of the Hemisphere. The Northern Hemisphere Megastrait appeared. During this time mainly carbonate sedimentation prevailed, but the existence of a new longitudinal strait determined a two-way water and faunal exchange. Tethyan water moved up to the south and the south-east parts of the Western Siberian basin, while the cold Boreal water influence can be recognised along the northern margin of the Russian Platform basin.

The age of Upper Pleistocene marine deposits of the Boreal transgression on the basis of electron‐spin‐resonance (ESR) dating of subfossil mollusc shells

The potential use of a new ESR method for the dating of subfossil shells is discussed on an example from the northern part of the East‐European Plain. A variant of the ESR technique, elaborated at the Institute of Geology of the Academy of Sciences of the Estonian SSR, is described and the Eemian age of the Boreal transgression proved.

ESR dating of quaternary shells: Recent advances

This paper deals with the key problems of the ESR dating of subfossil mollusc shells — the estimation of the stored palaeodose of natural radiation. It is shown that the use of the analytical line (or peak in the integrated spectrum) at g = 2.0012 ± 0.0001 with the half-width 0.6 mT seems most advisable for the estimation of the relative concentration of radiation defects equivalent to the stored palaeodose in the calcareous shell skeleton. Optimal ESR spectrometer settings have been determined. Results of ESR dating of subfossil mollusc shells from Eemian deposits of Boreal transgression are discussed.

Effect of Climatic Changes on Chemical Content of Deep-Water Muds Exemplified by Deposits of Arctic and Atlantic Oceans: ABSTRACT

1. Within deep-water deposits formed in different Quaternary physiographic environments, characteristic changes in mud chemical content are observed. 2. Investigations of the Arctic Ocean deposits (Makarov basin) showed compositional variation in absorbed complexes. For cold epochs (during Sartan, Zyryan, and Samar glaciations, as well as during the Boreal transgressions), the K content of absorbed complexes ranges from 14 to 15.5%. For warm epochs (postglacial time, Kargin transgression, Boreal transgression) the K content is between 16 and 17.5%. 3. While studying the Atlantic Ocean deposits (50°28^primeN and 26°23^primeW), it was observed that the higher absorbed K content was related to higher carbonate content of the deposits. Relative K content of 18-20% corresponds to warm periods, whereas that of 9.5-17.5% is connected with cold periods; carbonate content (CaCO + MgO weight %) is 23-40% for warm periods, and 9-16.5% for cold periods. 4. Investigations in the Caribbean showed that the higher relative carbonate content correlates with an increase in seawater temperatures. 5. Compositional variations in absorbed complexes and relative carbonate contents also may be correlative with physiographic conditions. If true, it may be possible to correlate the values of various chemical components End_Page 2505------------------------------ of deep-water muds with the physiographic conditions. End_of_Article - Last_Page 2506------------

Cretaceous Paleogeography of Arctic Canada: ABSTRACT

In Early Cretaceous time Berriasian-Valanginian boreal seas covered North Yukon and Sverdrup basins and were connected at the site of the present Beaufort Sea. Dawson City strait connected the North Yukon sea with the North Pacific sea of the Saint Elias trough across the present Klondike plateau. The remainder of Arctic Canada was dry land. In latest Valanginian time, uplift excluded the Hauterivian-Barremian seas from Sverdrup basin but North Yukon basin and Dawson City strait remained flooded after partial, early Hauterivian regression. An Aptian boreal transgression flooded the Sverdrup basin and restored direct connection with the North Yukon sea which subsequently spread eastward into Darnley Bay and lower Peel River areas. Aptian orogeny closed the Dawson City strait and separated permanently the Canadian Boreal and North Pacific seas. The early and middle Albian boreal seas covered Sverdrup and North Yukon basins and most of Mackenzie Lowlands and Mountains but late Albian and Cenomanian seas were restricted to a residual seaway east of Mackenzie River that connected the Mowry sea with that of Sverdrup basin. An early Turonian transgression flooded the present regions of northern Yukon, Mackenzie Mountains, and, possibly, the Sverdrup basin; its total extent is still obscure. In the late Turonian the sea left the Mackenzie Mountains region but the North Yukon and Sverdrup basins remained flooded and were connected with a residual seaway east of Mackenzie River. A new seaway, connecting Sverdrup basin with the West Greenland sea across Ellesmere Island and Baffin Bay, opened in the late Turonian. The most extensive flooding of Arctic Canada was caused by the Coniacian to mid-Santonian transgression which covered the areas of the Mackenzie Mountains, North Yukon basin, and Sverdrup basin, and extended east as far as Coppermine River. Strong late Santonian uplifts on the west side of the Mackenzie Lowlands were followed by a series of increasingly intense uplifts that caused progressive eastward retreat of the Campanian-Maestrichtian seas. A residual seaway connecting the Bearpaw sea with that of West Greenland across the Canadian Arctic Archipelago and Baffin Bay continued to exist east of Mackenzie River until late Maestrichtian time. All of Arctic Canada became dry land in late Maestrichtian or early Paleocene time. End_of_Article - Last_Page 2488------------