Lithostratigraphic Investigations Research Articles

Nappe stack of Piemonte–Ligurian units south of Aosta Valley: New evidence from Urtier Valley (Western Alps)

New results of structural and lithostratigraphic investigations performed in the Urtier Valley, located south of Aosta Valley at the northern flank of the Gran Paradiso Massif, shed new light on the nappe stack architecture of the Western Alps. Two distinct Piemonte–Ligurian units were recognized in the area: (a) the blueschist facies Broillot unit, with a well‐preserved lithostratigraphic succession that includes ophiolites and their metasedimentary cover and (2) the eclogitic Bardonney unit with clasts and/or slices of ophiolites embedded in a carbonate/quarzitic and/or metabasic matrix. Three major deformation stages have been recognized (D1, D2, and D3). D1 phase occurred during the peak metamorphic conditions (i.e., eclogite or blueschist facies). D2 and D3 phases are related to multistage exhumation processes, from early stacking to late refolding of former nappe contacts. Despite the intensity of deformation and metamorphism, the original lithostratigraphic succession of the Broillot unit allowed us to use a lithostratigraphic approach to reconstruct the structures in the study area. For the first time, differences in the nappe stack exposed south and north of the Aosta Valley are reported. In fact, contrary to what is observed in the north, the eclogitic units exposed in the Urtier Valley lay above and not below the blueschist units. A new model for the tectonic evolution, which ranges from stages of subduction to large‐scale nappe refolding, is proposed. It is able to explain the difference in the architecture of the north and south of the Aosta Valley.

Characterization of Alluvial Gold Bearing Sediments of Betare Oya District-East Cameroon, Implication for Gold Exploration and Recovery

Field studies (location Au pits, sampling of different layers of sedimentary sequences filling the pits, panning of sediments), litho-stratigraphic investigations, grain size analysis and outlining of depositional conditions revealed a characteristic fining upward sequence in all the sections of 08 Au-pits within the Betare Oya basin. A typical profile is 2.5 to 4.5 m thick and is composed of a 30 to 50 cm organic topsoil layer, underlain by a 1.5 m thick reddish brownish gold free saprolite, which is underlain by 1.5 m sandy section. From litho-stratigraphic investigations and grain size analysis results a quartz dominated gravelly 1.4 m thick layer consisting in boulders (275 mm), cobbles (2-−0.0148x2 + 1.2187x + 2.0344, R2 = 0.6929 (sandy layer); 2) y = 0.0617x2 + 1.0849x + 0.8097, R2 = 0.8694 (gravelly layer); and y > R2 is satisfied in both cases. This implies that Au recovery from these layers could be effective through gravity separation using sieves mounted on classifiers of 7 cm (sandy layer) and 10 cm (gravelly layer) diameter.

Lithostratigraphy and Microbiostratigraphy of Gadvan and Darian Formations in South Semirom, East of Zagros Basin, South-Central Iran

This research focuses on the lithostratigraphy and microbiostratigraphy implications of the Gadvan and Darian Formations in a part of Zagros sedimentary basin. The Gadvan and Darian Formations in the study area with a thick-ness of 520 meters consist of gray to green marls and shales, dark-grey limestones and Orbitolina limestone with Late Barremian-Aptian age. According to the lithostratigraphic investigations, the Gadvan and Darian Formations in the study area are subdivided into eleven units. The upper boundary of the Darian Formation with the Kazhdomi Formation and the lower boundary of Gadvan Formation with the Fahliyan Formation are in the form of disconformity. Micropaleontological study of the Gadvan and Dariyan Formations has led to the recognition 20 families, 45 genera, 35 species of benthic foraminifera, 2 genera of pelagic foraminifera and 8 genera and species of the calcareous algae. In this research, three biozones have been recognized by distribution of the larger benthic foraminifera in the Gadvan and Dariyan Formations of the South Semirom, including: 1) Palorbitolina lenticularis-Choffatella decipiens Concurrent Range Zone (middle Late Barremian to early Early Aptian); 2) Praeorbitolina cormyi-Orbitolina (Mesorbitolina) lotzei Assemblage Zone (late Early Aptian); 3): Orbitolina (Mesorbitolina) texanae-Orbitolina (Mesorbitolina) parva Assemblage Zone (Middle to Late Aptian). Based on the identified foraminifera, the age of the Gadvan and Darian Formations in the study area is assigned to Late Barremian to Aptian.

Barremian-Aptian Biostratigraphy in Yazd Block, Central Iran

The Lower Cretaceous benthic Limestone in Yazd Block (Central Iran zone) is known as the Taft and Shahkuh Formations. In this study, the age of the Taft and Shahkuh Formation, is examined based on biostratigraphic and paleontological investigations of Taft Formation in sections of Herisht (NE Ardakan) and Abanbar (NE Ardakan) and Shahkuh Formation in Chahpalang section (North Ardakan). According to the lithostratigraphic investigations, the taft and Shahkuh Formation in these sections include of thin bedded to medium bedded and massive limestone. Micropaleontology study of the Taft and Shahkuh Formation has led to the recognition of numerous genus and species which belong to Orbitolinidae Families such as: Dictyoconus pachymarginalis, Montseciellaarabica, Mesorbitolina parva, Paleodictyoconus sp., Paleodictyoconusactinostoma, Palorbitolina sp., Palorbitolina lenticularis, Praeorbitolinacormyi, Praeorbitolina cf. wienandsi, Praeorbitolina claveli, Praeorbotolinasp., cf. Paleodictyoconus sp., Palorbitolina ultima. and Calcareous Algae such as: Acroporella sp., Acroporella cf. Radoicicae, Actinoporella sp., Arabicodiumsp., Arabicodium cf. elongates, Augioporella cf. fouryae, Bacinellairregularis, Bueina sp., Boueina cf. hochstetteri, Boueina minima, Bueina cf.pygmaea, Cayeuxia sp., Cayeuxia anae, Garwoodia sp., Garwoodia cf. maxima,Girvanella sp., Griphoporella aff. Cretacea, Halimeda sp., Kopedagaria sp.,Kopedagaria sphaerica, Lithocodium aggregatum, Marinella sp., Montiellaelitzae, Marinella lugeoni, Marinella cf. yogoslavica, Neomeris sp., Neomeriscf. cretacea, Neomeris cf. pfenderae, Parachaetetes asvapatii, Permocalculussp., Permocalculus dragastani, Permocalculus minutes, Pseudoactinoporella sp.,Pseudoactinoporella iranica, Pseudoactinoporella cf. iranica, Pycnoporidiumlobatum, Rivularia sp., Salpingoporella sp., Salpingoporella cf. patruliusi,Salpingoporella cf. johnsoni, Salpingoporella pygmaea, Salpingoporellamehlbergii, Salpingoporella aff. Turgida, Salpingoporella cf. dinarica,Suppiluliumaella cf. praebalkanica, Udotea flabellum. Based on the identified Microfossil, such as Orbitolinid fossil, the age of the Taft Formation in the Kuh-e Herisht is assigned to Upper Barremian-Middle Aptian, and in the Abanbar area is determined as Upper Barremian-Lower Aptian, at least the age of the Shahkuh Formation in the Chahpalang area is determined as Upper Barremian-Lower Aptian.

Aptian biostratigraphy in South Zagros Basin, southwest Iran

The Khami group within the petroliferous Zagros Basin of Iran includes the Surmeh, Hith, Fahliyan, Gadvan and Dariyan formations. The Dariyan Formation, previously known as Orbitolina limestone is very significant as a reservoir rock in the Zagros Basin. In this study, the age of the Dariyan Formation is examined based on biostratigraphic and paleontological investigations. 236 m of Dariyan Formation sediments in the sections at Kuh-e Rahmat (north) and Nour-Abad (west) of Iran were selected to study its biostratigraphy. According to the lithostratigraphic investigations, the Dariyan Formation in these sections is subdivided into three: lower, middle and upper, which include thin-bedded to medium-bedded and massive limestone. Micropaleontologic study of the Dariyan Formation has led to the recognition of two biozones in the Nour-Abad area and one biozone in the Kuh-e Rahmat stratigraphic column. Diagnostic foraminifera in these sections are as follows: Globigerinelloides algerianus Cushman and Ten Dam, Globigerinelloides ferreolensis Moullade, Globigerinelloides maridalensis (Bolli), Globigerinelloides paragottisi Verga and Permoli Silva, Hedbergella aptiana Bartenstein, Hedbergella excelsa Longoria, Hedbergella luterbacheri Longoria, Hedbergella occulta Longoria, Hedbergella ruka (Banner et al.), Hedbergella similis Longoria, Hedbergella trocoidea (Gandolfi), Muricohedbergella delrioensis (Carsey), Pseudoplanomalina cheniourensis Sigal, Conicorbitolina conica d'Archiac, Iraqia sp., Mesorbitolina parva Douglass, Mesorbitolina pervia Douglass, Mesorbitolina ovalis Gorog and Arnaud-Vanneau, Mesorbitolina subconcava Leymerie, Mesorbitolina texana (Roemer), Mesorbitolina ovalis-pervia Cherchi and Schroeder, Debarina hahounerensis Fourcade et al., Marssonella trochus (d'Orbigny), Nezzazata sp., Orbitolina sp., Textularia sp.Based on the identified foraminifera, the age of the Dariyan Formation in the Kuh-e Rahmat area is assigned to Aptian, and in the Nour-Abad area is determined as upper Aptian.

Orbital imprint on Holocene palaeohydrological variations in west‐central Europe as reflected by lake‐level changes at Cerin (Jura Mountains, eastern France)

AbstractThis paper presents a lake‐level record for the Holocene at Lake Cerin (Jura Mountains, eastern France). It is based on a range of sedimentological techniques validated in previous studies, with a combination of systematic lithostratigraphic investigations of the infillings accumulated in the lacustrine basin, and sediment analyses of two selected cores. The chronology is based on 10 radiocarbon dates and pollen stratigraphy. On a millennial scale, the Cerin lake‐level record shows three distinct successive phases characterised by higher lake‐level conditions until ca. 9000 cal. a BP, followed by a maximal lowering at ca. 9000–8500 cal. a BP, and a progressive rise until the present. This rise was punctuated by centennial‐scale fluctuations, with major events around 4000, 2800 and after 1500 cal. a BP. Considered on a multimillennial scale, the general pattern of palaeohydrological changes reconstructed at Cerin reflects the impact of orbitally driven summer insolation. This is in agreement with other regional and extra‐regional palaeoclimatic records, although every record shows peculiarities in timing and shape depending on the proxy used for reconstruction. In this general context, centennial to multicentennial oscillations appear to have been second‐order events in comparison with the major influence of the orbital factor. Copyright © 2011 John Wiley & Sons, Ltd.

Ice sheet advance, dynamics, and decay configurations: evidence from west central Scotland

A 3700-km 2 area adjacent to the Firth of Clyde, Scotland, is examined to constrain the development and dynamics of the western central sector of the last British and Irish Ice Sheet. Results from geomorphological mapping, lithostratigraphic investigations, three-dimensional geological modelling and field observations are combined to produce an empirically constrained, five-stage conceptual model of ice sheet evolution. (A) Previously published dates on interstadial organic deposits and mammalian fossils suggest that the Main Late Devensian (MLD) (MIS 2) glaciation of central Scotland began after 35 ka cal BP. During build-up, ice advanced from the western Scottish Highlands into the Clyde and Ayrshire basins. Glaciomarine muds and shelly deposits scavenged from the Firth of Clyde were redeposited widely as shelly tills and glacial rafts. Ice advance against reverse slopes generated, and subsequently overtopped, ice-marginal sediment accumulations. We hypothesise that some of these formed pre-cursor ridges which were moulded into suites of ribbed moraine during the glacial cycle. (B) Sustained stadial conditions at the Last Glacial Maximum (LGM) (c 30–25 ka cal BP) resulted in development of a major dispersal centre over the Firth of Clyde and Southern Uplands. This dispersal centre locally preserved previously formed subglacial bedforms, and fed a wide corridor of fast-flowing ice east towards the Firth of Forth. (C) Initial deglaciation promoted a substantial re-configuration of the ice surface, with enhanced westward drawdown into the outer Firth of Clyde and eastward migration of an ice divide towards the Clyde-Forth watershed. (D) Renewed ice sheet thickening over the Firth of Clyde may have accompanied growth of the Irish Ice Sheet during the Killard Point Stadial (c 17.1–15.2 ka cal BP); it was associated with limited bed modification. Subsequent ice sheet retreat was characterised by substantial meltwater production, ponding and erosion. (E) Late stages of MLD ice sheet retreat were punctuated by one or more significant ice margin oscillations. Discovery of De Geer moraines at the site of a former proglacial lake in western Ayrshire allows glacier flow at the ice margin to be approximated as ≤290 m a −1 during one such oscillation. Such velocities were probably enabled by basal sliding and shallow sediment deformation. At this stage those parts of the MLD ice sheet margin that were grounded in the Firth of Clyde were extremely vulnerable to collapse. Final disintegration of glacier ice in the Clyde basin probably occurred early in the Lateglacial Interstadial (Greenland Interstadial-1), coinciding with marine incursion to c 40 m above present day sea level.

The last interglacial pedocomplexes in the litho- and morpho-stratigraphical framework of the central-northern Apennines (Central Italy)

Recently in Italy, a great deal of effort has been devoted to the mapping of Quaternary continental deposits. Several Unconformity Bounded Stratigraphic Units (UBSU) have been defined. The unconformities indicate important phases of changing dynamics linked to Quaternary climatic changes, and have been related to valley downcutting simultaneous with paleosol formation during interglacials. However, glacial periods are characterised by deposition of thick continental sequences. We suggest that the UBSU's belonging to the late Middle Pleistocene (MIS 6) and Late Pleistocene can also be defined under a pedostratigraphic point of view. Locally at the top of the UBSU attributed to MIS 6, buried or relict paleosols are preserved. The paleosols developed in calcareous fluvial and moraine gravels with minor flints. The pedocomplexes are made of three paleosols separated by erosion surfaces and/or stonelines. The older paleosol (MIS 5e) is severely truncated and is characterised by a Ck horizon overlain by strongly leached reddish Bt horizons with flinty rock fragments (with a diagnostic wavy lower boundary). In some sites, subsequent secondary precipitation of carbonates transformed this horizon into a Btk. This paleosol is buried by a younger paleosol (MIS 5c) with less leached reddish Btk horizons, quartz of aeolian origin, and very small and scarce calcareous clasts. The main pedofeatures are associated with colluvial processes, biological activity, and carbonate precipitation. This paleosol is also truncated and buried under a similar paleosol (MIS 5a). Therefore, the lower paleosol of the pedocomplex can be attributed to the Eemian, and constitutes a valid marker for the definition and mapping of the underlying and overlying sedimentary units. In other parts of the Apennines, no sedimentary units have been found that correspond to the unconformities separating different pedostratigraphical units. In order to map the different UBSU's, due to the poor lateral continuity of the preserved paleosols, morpho- and litho-stratigraphical investigations and correlation are always recommended.

Early and Middle Valdaian glaciations, ice-dammed lakes and periglacial interstadials in northwest Russia: new evidence from the Pyoza River area

The Pyoza River area in the Arkhangelsk district exposes sedimentary sequences suitable for study of the interaction between consecutive Valdaian ice sheets in Northern Russia. Lithostratigraphic investigations combined with luminescence dating have revealed new evidence on the Late Pleistocene history of the area. Overlying glacigenic deposits of the Moscowian (Saalian) glaciation marine deposits previously confined to three separate transgression phases have all been connected to the Mikulinian (Eemian) interglacial. Early Valdaian (E. Weichselian) proglacial, lacustrine and fluvial deposits indicate glaciation to the east or north and consequently glacier damming and meltwater run-off in the Pyoza area around 90–110 ka BP. Interstadial conditions with forest-steppe tundra vegetation and lacustrine and fluvial deposition prevailed at the end of the Early Valdaian around 75–95 ka BP. A terrestrial-based glaciation from easterly uplands reached the Pyoza area at the Early to Middle Valdaian transition around 65–75 ka BP and deposited glaciofluvial strata and subglacial till (Yolkino Till). During deglaciation, laterally extensive glaciolacustrine sediments were deposited in ice-dammed lakes in the early Middle Valdaian around 55–75 ka BP. The Barents–Kara Sea ice sheet deposited the Viryuga Till on the lower Pyoza from northerly directions. The ice sheet formed the Pyoza marginal moraines, which can be correlated with the Markhida moraines further east, and proglacial lacustrine deposition persisted in the area during the first part of the Middle Valdaian. Glacio-isostatic uplift caused erosion followed by pedogenesis and the formation of a deflation horizon in the Middle Valdaian. Widely dispersed periglacial river plains were formed during the Late Valdaian around 10–20 ka BP. Thus, the evidence of a terrestrial-based ice sheet from easterly uplands in the Pyoza area suggests that local piedmont glaciers situated in highlands such as the Timan Ridge or the Urals could have developed into larger, regionally confined ice sheets. Two phases of ice damming and development of proglacial lakes occurred during the Early and Middle Valdaian. The region did not experience glaciation during the Late Valdaian.

Biostratigraphy of the Upper Cretaceous-Lower Eocene succession in the Bani Walid area, northwest Libya

Litho- and planktonic foraminiferal biostratigraphical studies were carried out on the Upper Cretaceous-Lower Eocene succession in three measured sections in the Bani Walid area, northwest Libya. The lithostratigraphical investigations led to the recognition of three formations and six members, from base to top: (i) Zmam Formation, which includes: (a) the Lower Tar Marl Member (Late Cretaceous, Maastrichtian); (b) the Upper Tar Member (Early Palæocene, Danian); and (c) the Had Limestone Member (Middle Palæocene, Selandian); (ii) Shurafah Formation, which comprise: (a) the Bu Ras Marl Member; and (b) the Galta Chalk Member (Late Palæocene, Thanetian); and (iii) Beshima Formation (Kheir Member) of Early Eocene (Ypresian) age. Based on the abundance and stratigraphical distribution of the planktonic foraminiferal species, 12 planktonic foraminiferal zones were recognised, from base to top: Globotruncana aegyptiaca, Gansserina gansseri, Abathomphalus mayaroensis and Plummerita hantkeninoides zones of Late Cretaceous (Maastrichtian) age; Parasubbotina pseudobulloides and Praemurica trinidadensis zones of Early Palæocene (Danian) age; Praemurica uncinata and Morozovella angulat, as well as Igorina pusilla pusilla zones of Middle Palæocene (Selandian) age; Globanomalina pseudomenardii and Morozovella velascoensis zones of Late Palæocene (Thanetian) age and Morozovella formosa formosa zone of Early Eocene (Ypresian) age. The litho- and biostratigraphical results show the presence of two hiatuses in the studied sequence. The first is placed at the Late Cretaceous-Early Palæocene boundary (K/P boundary) and is located within the Zmam Formation, more precisely at the contact between the Lower and Upper Tar Marl Members and is accompanied by a palæontological gap, indicated by the absence of the earliest Palæocene Guembelitria cretacea (P 0) and Parvularugoglobigerina eugubina zones (P 1a). The second one is located between the Late Palæocene Galta Chalk Member of the Shurafah Formation ( Morozovella velascoensis zone) and the Early Eocene Kheir Member of Beshima Formation ( Morozovella formosa formosa zone) and is detected by the absence of the Morozovella edgari and Morozovella subbotinae zones, indicating the instability of the study area during Late Cretaceous-Early Eocene times.

Lithostratigraphy of Permian marine sequences, Khao Pun Area, central Thailand: Paleoenvironments and tectonic history

AbstractGeologic mapping and subsurface lithostratigraphic investigations were carried out in the Khao Pun area (4 km2), central Thailand. More than 250 hand specimens, 70 rock slabs, and 70 thin sections were studied in conjunction with geochemical data in order to elucidate paleoenvironments and tectonic setting of the Permian marine sedimentary sequences. This sedimentary succession (2485 m thick) was re‐accessed and re‐grouped into three lithostratigraphic units, namely, in ascending order, the Phu Phe, Khao Sung and Khao Pun Formations. The Lower to lower Upper Permian sedimentary facies indicated the transgressive/regressive succession of shelf sea/platform environment to pelagic or abyssal environment below the carbonate compensation depth. The sedimentological and paleontological aspects, together with petrochemical and lithological points of view, reveal that the oldest unit might indicate an Early Permian sheltered shallow or lagoonal environment. Then the depositional basin became deeper, as suggested by the prolonged occurrence of bedded chert‐limestone intercalation with the local exposure of shallower carbonate build‐up. Following this, the depositional environment changed to pelagic deposition, as indicated by laminated radiolarian (e.g. Follicucullus sp.) cherts. This cryptic evidence might indicate the abyssal environment during middle Middle to early Late Permian; whereas, previous studies advocated shelf‐facies environments. Following this, the depositional condition might be a major regression on the microcontinent close to Indochina, from the minor transgressive/regressive cycles that developed within a skeletal barrier, and through the lagoon with limited circulational and anaerobic conditions, on to the tidal flat to the sheltered lagoon without effective land‐derived sediments.

Flandrian vegetational history of sout‐heastern England. Stratigraphy of the Brede valley and pollen data from Brede Bridge

summaryThe results of palaeoecological analyses and lithostratigraphic investigations are used to reconstruct the Flandrian evolution of a valley in the East Sussex Weald, the Brede. Particular emphasis is placed upon mid‐Flandrian vegetational history. Palynological data collected from one site, Brede Bridge, include detailed resolution of declines in Ulmus and Tilia pollen. Predominantly inorganic sediments were deposited in the valley during the early Flandrian. Marine conditions penetrated the lower valley under the general influence of sea level rise. After c, 6000 BP, peat formation became widespread and Alnus‐dominated communities occupied the valley floor. Despite forest clearance on the adjacent slopes, relatively little sediment was deposited in the period c. 3700 to c. 1800 BP. The lower valley again came under a marine influence after c. 1800 BP. The dryland forests of the valley were, during the mid‐Flandrian, dominated by Tilia. A general upward decline in Tilia pollen through the sequence is attributed to the valley floor widening and the Brede Bridge site becoming more distant from dryland areas. The first signs of human activity accompany the Ulmus decline, though major forest clearance is not evident until the Tilia decline c. 3700 BP. Comparison of the latter event with sires across south‐eastern and southern England offers support for a phase of human expansion in the late Neolithic/early Bronze Age involving the preferential exploitation of areas of lime forest.

Late Weichselian glacial maximum on Andøya, North Norway

Morphological, seismic and lithostratigraphic investigations of a moraine deposit at Bleik (the Bleik moraine), northern Andøya, show short‐distance transported till overlying long‐distance transported predominantly glaciofluvial ice‐marginal deposits. Consolidated glaciomarine sediments from a core at present sea‐level, c. 400 m distally to the moraine complex, contain 31 species of foraminifera, among which Cassidulina reniforme, Islandiella helenae and Trifarina fluens dominate, and fragments of the molluscs Mya truncata and Astarte sp. and the echinoid Strongylocentrotus sp. Amino acid analyses of the foraminifera Cibicides lobatulus and the mollusc Mya truncata indicate ages between 22,000 and 16,000 BP. Radiocarbon dating of fragments of Mya truncata from the upper part of the core gave an age of 17,940 ± 245 BP, while a dating of unidentified shell fragments from the lower part gave an infinite age (>40,000 BP). The sediment was probably disturbed by icebergs beyond the end moraine zone, and the radiocarbon and amino acid dating of Mya truncata therefore represent a maximum age for this process. This new evidence indicates two phases with a higher relative sea‐level than at present at Bleik, c. 18,000 and >40,000 BP. The Bleik moraine probably represents the early Late Weichselian glacial maximum (c. 22,000 BP), while the underlying deglaciation deposit and associated beach‐ridge (Bruvollen) is of pre‐Late Weichselian age. Moraine ridges 3–4 km to the south of Bleik probably indicate advances of local glaciers between 22,000 and 18,000 BP.

Late quaternary fluvial sedimentation in the voidomatis basin, Epirus, Northwest Greece

Detailed morpho- and lithostratigraphic investigations, allied with radiometric dating, in the Voidomatis basin, Epirus, northwest Greece, have identified four Quaternary terraced alluvial fills that range from middle Pleistocene to historic in age. Major-periods of alluviation during the late Quaternary were associated with valley glaciation (ca. 26,000–20,000 yr B.P.) and subsequent deglaciation (ca. 20,000–15,000 yr B.P.) in the Pindus Mountains during Late Würmian times, and more recently linked to overgrazing sometime before the 11th century AD. The late Quaternary alluvial stratigraphy of the Voidomatis River is more complex than the “Older Fill” and “Younger Fill” model outlined previously, and it is suggested that these terms should no longer form the basis for defining alluvial stratigraphic units in the Mediterranean Basin.

The amphi-atlantic distribution of the younger dryas paleoclimatic oscillation

Interest in significant climatic fluctuations affecting large geographic areas but having a time range that is too brief to adduce the Milankovitch radiation cycles has focused on the Alleröd/Younger Dryas event, which is a well-established phenomenon of western Europe manifested by glacial and vegetational reconstructions. It is also shown by the foraminiferal evidence for shifts in the polar front in the North Atlantic. Recent pollen and lithostratigraphic investigations in the Maritime Provinces of eastern Canada and in the till plains of west-central Ohio on opposite sides of the late-glacial spruce forest indicate that the event also left a record in eastern North America. Experiments with an atmospheric general circulation model, with the temperature of North Atlantic surface waters depressed to full-glacial levels, lowered summer temperatures in ‘upwind’ periglacial eastern North America by 2°C — just as far inland as they did downwind in western Europe, where the paleoecological record of cooling is clear. A leading hypothesis for the cause for the Younger Dryas cooling appeals to the influx of tabular icebergs released from arctic ice shelves around the wasting Scandinavian and Siberian ice sheets during the Alleröd warming. The resulting cooling of the North Atlantic waters during the Younger Dryas could be facilitated or precipitated by the abrupt influx of glacial meltwater derived from almost the entire southern margin of the Laurentide ice sheet and emerging from the Gulf of St Lawrence, as brought about by a major shift in drainage direction from the Mississippi River to the St Lawrence River about 10.8 ka BP. A supplemental influx of fresh water may have come from the contemporaneous drainage of the Baltic Ice Lake. The diversion of Laurentide meltwater to the Atlantic was caused by retreat of an ice lobe in northwestern Ontario north of Minnesota, allowing the huge Glacial Lake Agassiz in Saskatchewan and Manitoba to drain into the Great Lakes and more than double the inflow of meltwaters in the North Atlantic, thereby diverting the Gulf Stream and permitting the influx of icebergs from the north to cool the ocean surface. Minor readvance of the ice lobe about 10 ka BP temporarily diverted the Lake Agassiz drainage to the south. With the final retreat of the ice, the drainage again went to the east, but by this time the ice sheets were much diminished and the regional climate had warmed enough so that the effects of the meltwater flux on the Gulf Stream were muted, and the ice sheets bordering the North Atlantic had retreated onto the land and no longer delivered enough icebergs to cool the surface waters. The Younger Dryas interval thus was terminated, and the warming manifested in the Alleröd was renewed.

Holocene transgression maximum about 6000 years BP at Ramså, Vesterålen, North Norway

Lithostratigraphic investigations, pollen and diatom analysis, and 14C datings of three sections at Ramsa on Andoy in Vesteralen indicate an age of c. 6000 BP for the Holocene (Tapes) transgression maximum. Two dates from Lofoten (Leknes and Eggum) give a similar age.

Late Weichselian Glacial Geology of the Lower Borgarfjördur Region, Western Iceland: a Preliminary Report

Morphological and lithostratigraphical investigations have,revealed two successive glacial advances of Late Weichselian age in the lower Borgarfjordur region, Western Iceland. Studies of the Melabakkar-Asbakkar coastal cliffs have disclosed a complex of glaciomarine sediments ' and tills, accompanied by glaciofluvial deposits from ice marginal sources. A brief description is given for each of the major lithostratigraphical units, and a depositional model for the sequence is outlined. The first glacial advance occurred some time shortly after 12 OOO radiocarbon years before present (BP), and the second one around 11 OOO BP. By 10 OOO BP the glaciers had retreated from the lowlands and the sea transgressed to 60 m above present sea level, where extensive marine terraces were formed.

Socioprofessional structure of the population of the USSR and its employment pattern

The Pyoza River area in the Arkhangelsk district exposes sedimentary sequences suitable for study of the interaction between consecutive Valdaian ice sheets in Northern Russia. Lithostratigraphic investigations combined with luminescence dating have revealed new evidence on the Late Pleistocene history of the area. Overlying glacigenic deposits of the Moscowian (Saalian) glaciation marine deposits previously confined to three separate transgression phases have all been connected to the Mikulinian (Eemian) interglacial. Early Valdaian (E. Weichselian) proglacial, lacustrine and fluvial deposits indicate glaciation to the east or north and consequently glacier damming and meltwater run-off in the Pyoza area around 90–110 ka BP. Interstadial conditions with forest-steppe tundra vegetation and lacustrine and fluvial deposition prevailed at the end of the Early Valdaian around 75–95 ka BP. A terrestrial-based glaciation from easterly uplands reached the Pyoza area at the Early to Middle Valdaian transition around 65–75 ka BP and deposited glaciofluvial strata and subglacial till (Yolkino Till). During deglaciation, laterally extensive glaciolacustrine sediments were deposited in ice-dammed lakes in the early Middle Valdaian around 55–75 ka BP. The Barents–Kara Sea ice sheet deposited the Viryuga Till on the lower Pyoza from northerly directions. The ice sheet formed the Pyoza marginal moraines, which can be correlated with the Markhida moraines further east, and proglacial lacustrine deposition persisted in the area during the first part of the Middle Valdaian. Glacio-isostatic uplift caused erosion followed by pedogenesis and the formation of a deflation horizon in the Middle Valdaian. Widely dispersed periglacial river plains were formed during the Late Valdaian around 10–20 ka BP. Thus, the evidence of a terrestrial-based ice sheet from easterly uplands in the Pyoza area suggests that local piedmont glaciers situated in highlands such as the Timan Ridge or the Urals could have developed into larger, regionally confined ice sheets. Two phases of ice damming and development of proglacial lakes occurred during the Early and Middle Valdaian. The region did not experience glaciation during the Late Valdaian.