An optical age chronology of Late Pleistocene fluvial deposits in the northern lower Mississippi valley

The lower Mississippi valley (LMV) contains many large braided channel belts that are preserved west of the Holocene floodplain. Previous efforts to establish geochronologic control on channel-belt construction have been hindered by the lack of organic material for radiocarbon dating. Luminescence techniques provide a burial date for the sediment itself and may prove useful in this context. Samples from three channel belts in the northern LMV were analyzed using the single aliquot-regenerative technique on 90–125 μm quartz. Optical ages (19.7–17.8, 16.1–15.0 and 12.5–12.1 ka) are consistent with geomorphic relationships and indicate that channel belts were formed in the late Pleistocene under glacial conditions. These optical ages provide the first detailed chronology of LMV channel-belt formation and are the first step towards developing a chronology for the entire LMV.     

Neotectonics and intraplate continental topography of the northern Alpine Foreland

Research on neotectonics and related seismicity has hitherto been mostly focused on active plate boundaries that are characterized by generally high levels of earthquake activity. Current seismic hazard estimates for intraplate domains are mainly based on probabilistic analyses of historical and instrumental earthquake catalogues. The accuracy of such hazard estimates is limited by the fact that available catalogues are restricted to a few hundred years, which, on geological time scales, is insignificant and not suitable for the assessment of tectonic processes controlling the observed earthquake activity. More reliable hazard prediction requires access to high quality data sets covering a geologically significant time span in order to obtain a better understanding of processes controlling on-going intraplate deformation.The Alpine Orogen and the intraplate sedimentary basins and rifts in its northern foreland are associated with a much higher level of neotectonic activity than hitherto assumed. Seismicity and stress indicator data, combined with geodetic and geomorphologic observations, demonstrate that deformation of the Northern Alpine foreland is still on-going and will continue in the future. This has major implications for the assessment of natural hazards and the environmental degradation potential of this densely populated area. We examine relationships between deeper lithospheric processes, neotectonics and surface processes in the northern Alpine Foreland, and their implications for tectonically induced topography.For the Environmental Tectonics Project (ENTEC), the Upper and Lower Rhine Graben (URG and LRG) and the Vienna Basin (VB) were selected as natural laboratories. The Vienna Basin developed during the middle Miocene as a sinistral pull-apart structure on top of the East Alpine nappe stack, whereas the Upper and Lower Rhine grabens are typical intracontinental rifts. The Upper Rhine Graben opened during its Late Eocene and Oligocene initial rifting phase by nearly orthogonal crustal extension, whereas its Neogene evolution was controlled by oblique extension. Seismic tomography suggests that during extension the mantle-lithosphere was partially decoupled from the upper crust at the level of the lower crust. However, whole lithospheric folding controlled the mid-Miocene to Pliocene uplift of the Vosges–Black Forest Arch, whereas thermal thinning of the mantle–lithosphere above a mantle plume contributed substantially to the past and present uplift of the Rhenish Massif. By contrast, oblique crustal extension, controlling the late Oligocene initial subsidence stage of the Lower Rhine Graben, gave way to orthogonal extension at the transition to the Neogene.The ENTEC Project integrated geological, geophysical, geomorphologic, geodetic and seismological data and developed dynamic models to quantify the societal impact of neotectonics in areas hosting major urban and industrial activity concentrations. The response of Europe's intraplate lithosphere to Late Neogene compressional stresses depends largely on its thermo-mechanical structure, which, in turn, controls vertical motions, topography evolution and related surface processes.     

Late Pliocene and Pleistocene small mammal chronology in the Italian peninsula

The abundant documentation of small mammals in the Italian peninsula, collected over recent years, furnishes a detailed biochronological sequence mainly from the Late Pliocene onwards. An updated stratigraphic framework is here presented, based on the European small mammal biozonation. The Early Villanyian is characterized by Mimomys hassiacus, M. stehlini, and, later, poorly documented M. polonicus. The Late Villanyian localities are well characterized with M. pliocaenicus, M. pitymyoides and M. tigliensis. The older part of the Early Biharian is documented by assemblages containing Microtus (Allophaiomys) ex gr. pliocaenicus, M. pusillus, M. cf. ostramosensis and M. tornensis, while the later part of the Early Biharian, is characterized by advanced Microtus (Allophaiomys) species occurring together with M. pusillus or M. blanci. In the Late Biharian M. savini, Microtus hintoni-gregaloides, Microtus (Iberomys) ex gr. huescarensis-brecciensis and Terricola arvalidens occur. The Early Toringian with A. mosbachensis, Allocricetus bursae, Pliomys episcopalis and small-sized Microtus brecciensis, and the Late Toringian with A. terrestris in diversified associations are quoted. The most important faunal events are calibrated by independent chronological controls, thanks to the record of small mammals from lacustrine deposits. Several figures illustrate the most significant rodent species occurring in the succession of selected Italian localities.     

Late Pleistocene equilibrium-line reconstructions in the northern Peruvian Andes

Equilibrium-line-altitude (ELA) reconstructions using the toe-to-headwall-altitude ratio method for paleoglaciers in the Cordilleras Blanca and Oriental, northern Peruvian Andes (7–10°S; 77°20'–77°35'W), indicate that ELAs during the last glacial maximum (LGM; marine isotope stage 2) were c . 4300 m in the Cordillera Blanca, c . 3900–3600 m on the west side of the Cordillera Oriental, and c . 3200 m on the east (Amazon Basin) side of the Cordillera Oriental. Comparison with estimated modern ELAs and glaciation thresholds indicate that ELA depression ranged from c . 700 m in the Cordillera Blanca to c . 1200 m on the east side of the Cordillera Oriental. This augments data from many mountain ranges in middle- and low-latitude regions that indicate that ELAs during the LGM were depressed by c . 1000 m. Published palynological evidence for drier conditions during the LGM in the tropical Andes suggests that ELA depression of this amount involved a temperature reduction (> 5–6°C) that greatly exceeded the tropical sea-surface temperature depression estimates of CLIMAP (< 2°C). The west to east increase in ELA depression during the LGM indicates that the steep modern precipitation gradients may have been even steeper during the LGM.     

Late Pleistocene carbonate aeolianites on Mallorca, Western Mediterranean: a luminescence chronology

Coastal outcrops of Upper Pleistocene deposits in north-eastern Mallorca (Balearic Islands, Spain) have been examined and a chronological framework established using Optically Stimulated Luminescence (OSL) dating. The outcrops record a complex interaction between aeolian, colluvial and alluvial fan deposition that result in a variable stratigraphical architecture. Dating and facies analysis make it possible to identify four aeolian activity episodes during MIS 5c/b, 4 and 3, and also add to the understanding of the environmental history of north-eastern Mallorca over the last 100 ka. The new data suggest enhanced aeolian transport and dune formation during cold climatic intervals when sea level was low, sediment supply (exposed marine carbonate sediment) was high, winter windiness was high, and vegetation on coastal plains at a minimum.     

晚更新世以来内蒙古哈素海钻孔地层记录及其年龄

“河套古大湖”对于研究区域环境及气候演化具有重要的意义,然而,其形成与消亡的时代仍存在争议。依托于哈素海西南岸边获取的HSH钻孔,采用AMS14C、OSL测年方法确定了沉积物年代,结合岩心的岩性、沉积结构等特征,分析了哈素海的演化历史,并探讨了河套古大湖存亡的时期。结果表明,哈素海地区晚更新世以来的沉积环境主要经历了以下转变过程：150~70 ka为较稳定的湖泊,70~55 ka湖泊水位下降,为滨湖相沉积,55~27 ka为湖沼沉积,27~0 ka为滨湖相沉积。根据哈素海的沉积演化历史,结合河套盆地相关研究成果,认为河套古大湖早在150~110 ka就已形成,其后水位下降,直至55 ka之后,萎缩消亡,河套盆地局部地区形成湖沼沉积,但已不再是统一的大湖。研究结果对于深入探讨河套盆地演化历史乃至黄河的变迁具有重要意义。     

Late Pleistocene glaciers in Darhad Basin, northern Mongolia

Late Pleistocene glaciers around Darhad Basin advanced to near their maximum positions at least three times, twice during the Zyrianka glaciation (at ∼ 17-19 ka and ∼ 35-53 ka), and at least once earlier. The Zyrianka glaciers were smaller than their predecessors, but the equilibrium-line altitude (ELA) difference was < 75 m. End moraines of the Zyrianka glaciers were ∼ 1600 m asl; ELAs were 2100-2400 m asl. ¹⁴C and luminescence dating of lake sediments confirm the existence of paleolake highstands in Darhad Basin before ∼ 35 ka. Geologic evidence and ¹⁰Be cosmic-ray exposure dating of drift suggests that at ∼ 17-19 ka the basin was filled at least briefly by a glacier-dammed lake ∼ 140 m deep. However, lake sediments from that time have not yet been recognized in the region. A shallower paleolake briefly occupied the basin at ∼ 11 ka, but between ∼ 11 and 17 ka and after ∼ 10 ka the basin was probably largely dry. The timing of maximum glacier advances in Darhad appears to be approximately synchronous across northern Mongolia, but different from Siberia and western Central Asia, supporting the inference that paleoclimate in Central Asia differed among regions.     

Late Pleistocene stratigraphy at Boliden, northern Sweden

Till-covered sand and silt sediments with organic material from Boliden, northern Sweden, have been resampled and reinvestigated. Texture and petrographic analyses demonstrated one till bed overlying, and one underlying the sandy sediments. Low frequencies of diatoms were noted, representing freshwater, halophilous and brackish water taxa. The diatoms may be allochthonous or autochthonous, or redeposited from older deposits. Pollen analysis revealed a new picture of the composition of the vegetation, as compared with earlier investigations. The flora consisted of an arctic-subarctic treeless shrub and herb vegetation dominated by Salix, Betula nana , Gramineae and Cyperaceae. Artemisia and several arctic-alpine herbs were important elements. The identification of Salix wood as well as fruits and fruit scales of Betula nana and Betula cf. humilis is in agreement with the pollen-analytical results, as is the occurrence of Nordicboreal species of Coleoptera. Two radiocarbon datings resulted in an age of c. 45,000 B. P. and >40,000 B.P. The Boliden till-covered sediments were most probably deposited during an Early or Middle Weichselian interstadial, but the initial or final stage of an interglacial (Eemian) is also possible.     

Late Pleistocene chronology and environment of the “ice-free corridor” of northwestern Alberta

Pollen and macrofossil analyses of two radiocarbon-dated lake sediment cores in the upper Peace River district were used to investigate the controversial late-glacial geochronology of the “ice-free corridor.” The basal mineral-rich sediments contain reworked, radiogenically “dead” palynomorphs, as well as intrusive “modern” carbon. Analyses of the basal sediments from Boone Lake show that two ¹⁴C ages greater than 12,000 yr B.P. are spuriously old due to contamination by organic matter of Cretaceous age. The data support occlusion or near occlusion of Laurentide and Cordilleran ice in the Peace River area during the late Wisconsinan period. The sediment record began around 12.000 yr B.P. in the ice-dammed and enlarged Boone Lake. An initially open, sedge-dominated cover was invaded by sage, willow, grass, and poplar by 11,700 yr B.P., suggesting that a habitable landscape has existed in the area for at least 12 millennia. The data, however, do not support the ice-free corridor arguments of B. O. K. Reeves (1973, Arctic and Alpine Research5,1–16; 1983, In “Quaternary Coastlines and Marine Archaeology: Towards the Prehistory of Land Bridges and Continental Shelves” (P. M. Masters and N. C. Fleming, Eds.), pp. 389–411. Academic Press. New York), who suggests that ice occlusion did not occur in the Peace River Valley during the last 55,000 yr.     

Late Pleistocene glacial chronology of the Taylor Valley,Antarctica, and the global climate

Carbonate-rich lacustrine and deltaic deposits, containing thin beds of finely laminated carbonates and thick beds of silt, crop out at several sites in the Taylor Valley and have been encountered in cores obtained by the Dry Valley Drilling Project (DVDP). Fragments of the more indurated carbonate beds have widespread occurrence as part of the desert “lag gravel” which covers much of the valley floor. Analysis of the carbonates suggests that they were deposited as algal limestones from waters derived from the East Antarctic Ice Sheet via the Taylor Glacier at times which correspond to the previous three global interglacial periods, as evidenced by the ice volumes deduced from oxygen-isotopic analysis of oceanic cores. The lacustrine carbonates have been found up to 30 km beyond the present terminus of the Taylor Glacier, and up to 100 m above the level of Lake Bonney, into which the Taylor Glacier at present discharges. It is concluded that the Taylor Glacier has advanced during each of the previous three interglaciations, and it is suggested that this has been caused by a thickening of the East Antarctic Ice Sheet during the interglaciations.     

Pleistocene glaciation chronology of Spitsbergen

Troitsky, Leonid, Punning, Jaan-Mati, HÜtt, Galina & Rajamäe, Raivo 1979 12 01: Pleistocene glaciation chronology of Spitsbergen. Boreas , Vol. 8, pp. 401–407. Oslo. ISSN 0300–9483.
Geomorphological and geochronological studies of Pleistocene deposits were carried out in sections along Billefjorden and Bellsund as well as on Bröggerhalvöya and Prins Karls Forland. For purposes of correlation and development of a time scale, radiocarbon (¹⁴C) and thermoluminescent (TL) dating methods were used. The dates obtained indicate the presence of older Pleistocene deposits on Spitsbergen and also provide information on the distribution of Middle Pleistocene glacial deposits. A correlation scheme of Pleistocene deposits of Spitsbergen with stratigraphic units of the Alps and northwestern Europe is presented.     

A Late Pleistocene coarse-grained spit-platform sequence in northern Jylland, Denmark

Several well-preserved Late Pleistocene spit systems occur uplifted in northern Jylland, Denmark. Their present-day morphological expression allows detailed study of spit growth patterns while the internal sedimentological organisation can be examined in a series of pits distributed along the length of the spits. Two characteristic vertical sequences are recognized in the systems. The first (Sequence I) consists of a giant-scale cross-bedded foreset unit, overlain by topset and beach units, while the second (Sequence II) consists of the foreset unit overlain by bar-trough and beach units. The two sequence types pass laterally into each other with a short overlap zone. They can be interpreted in terms of Meistrell's (1966, 1972) model for spit-platform growth based on scaled wave tank experiments. The giant-scale cross-bedded unit corresponds to prograding of a coarse-grained subaqueous spit-platform while the topset, bar-trough and beach units reflect the growth of the subaerial spit. The alternation between sequence I and II reflects the inversely related growth of the spit and platform structures: when the rate of subaqueous platform progradation declines, the subaerial spit grows uniformly, and when the platform progrades uniformly spit growth declines. The model is probably only valid for relatively coarse-grained systems because only these deposits would have a relatively steep front. The water depth in which the spit system progrades and thus bottom topography, determines the thickness of the giant-scale cross-bedded foreset unit because the water depth over the top of the platform is relatively constant. If the water is less than a few metres deep the spit-platform is not developed as seen where the Late Pleistocene spit systems prograded over elevations of the sea bottom. Conversely, the correct recognition of spit-platform sequences allows precise determination of sea-level and water depth at the time of formation. Finally, the model adds one further mode of formation of giant-scale cross-bedding to those already known from fluvial transverse, lateral and point bars, subtidal sand waves and Gilbert deltas.     

Re‐interpretation of the Meikirch pollen record,Swiss Alpine Foreland,and implications for Middle Pleistocene chronostratigraphy

The Meikirch drilling site in the Swiss Midlands north of Bern is re‐interpreted using a combination of sedimentological logging, pollen analyses and luminescence dating. The sedimentary sequence comprises about 70 m of lacustrine deposits, overlain by about 39 m of coarse glacial outwash interpreted to represent at least two independent ice advances. Pollen analyses of the apparently complete limnic sequence reveal a basal late glacial period followed by three warm phases that are interrupted by two stadial periods (Meikirch complex). The warm periods were previously correlated with the Holsteinian and Eemian Interglacials. According to luminescence dating, and with consideration of evidence for Middle Pleistocene climate patterns at other central European sites, a correlation of the Meikirch complex with marine isotope stage (MIS) 7 is now proposed. If this correlation is correct, it implies the presence of three intervals with interglacial character during MIS 7. However, the late Middle Pleistocene vegetational features of the Meikirch complex show significant differences when compared with the pollen record from the Velay region, central France. Possible explanations for this discrepancy are distinct Middle Pleistocene patterns of atmospheric circulation over central Europe and a different distribution of vegetation refugia compared to the Eemian Interglacial and the Holocene. Copyright © 2005 John Wiley & Sons, Ltd.     

藏北高原环纳木错首次发现晚更新世湖滩岩

200-2001年夏,在开展藏北高原"纳木错第四纪环境演变调查研究"与"1:25万当雄幅"区域地质填图工作中,笔者首次在环纳木错湖岸阶地上发现了一种与湖泊演化有关的湖相沉积岩石--湖滩岩.目前,国际上只有海滩岩一说,湖滩岩尚罕见正式报道.     

大兴安岭北段雅鲁河断裂晚更新世活动记录

大兴安岭北段雅鲁河断裂为典型的活动断层,对区域晚更新世地质和地貌演化及现代地震具有控制意义。在扎兰屯市成吉思汗镇北雅鲁河东侧发现雅鲁河断裂活动记录,以野外资料为基础,通过相关松散堆积物的光释光测年,厘定断层活动特征和活动时限,并结合相关经验公式,估测该记录反映的古地震特征。研究结果显示,雅鲁河断裂晚更新世在扎兰屯南部地区存在断层活动,断层走向近SN向、倾向265°、倾角约55°,性质为逆断层;断层活动错断了中生代流纹岩和晚更新世早-中期洪冲积物,并被晚更新世晚期残积和冲积物覆盖,断层活动发生在距今53.4±6.7~39.1±3.6ka之间;活动记录所反映的古地震矩震级(M0)和面波震级(Ms)为6.7级,地震发生时地表破裂长度(SRL)约为30.2~37.8km。     

Late Pleistocene remains of giant deer (Megaloceros giganteus Blumenbach) in Scandinavia: chronology and environment

This article presents new data on the Late Pleistocene giant deer, Megaloceros giganteus (Blumenbach), describing its distribution in time and space, geographical and sexual variation and general biology. Twenty‐three south Scandinavian fossils found in situ in lacustrine sediments or redeposited in glaciofluvial material form the basis of this investigation. Fourteen C dates show that the giant deer inhabited southern Scandinavia in the ice‐free late Middle Weichselian from c. 40000 to 28000 BP (the Sandnes Interstadial) and again in the Late Weichselian from c. 12000 to 10700 BP (Older Dryas, Allerød and early Younger Dryas Chronozones), corresponding to a calibrated range from c. 14300 to 12400 cal. yr BP. Osteometric analyses show that the Scandinavian giant deer belonged to the upper size range of the lateglacial Irish population and that a marked sexual dimorphism existed, the males being 10–11% larger than the females. Investigations furthermore point at an antler cycle similar to that among extant northern cervids, and subsequently at a rutting season in autumn. The skeletal remains also prove the occurrence of twin delivery and the possibility of reaching an ontogenetic age of at least 23 years. During both occurrences the Scandinavian giant deer population was part of the northernmost distribution of the species in Europe and the palaeogeographical settings and palaeoenvironmental conditions of the two periods show striking similarities. Clearly, the giant deer were able to colonize and survive in a landscape dominated by grasses and sedges with scattered shrubs and dwarf shrubs. They came as close as 200–250 km to the ice front and their distribution included coastal areas along a cold sea with drifting icebergs. They were present in the area at least from March until November. However, the pure arctic conditions created during the early phase of the Younger Dryas event led to a new local extinction around 10700 ¹⁴C yr BP. This was the beginning of a total Eurasian extinction which, at least in Europe, was completed before the Pleistocene/Holocene transition.     

西藏羌北高原多格错仁盐湖中更新世晚期以来的环境演化记录

通过对西藏藏北高原多格错仁盐湖湖岸3101cm高度剖面进行地形地貌、地层沉积特征、矿物学特征及粒度、频率磁化率等气候环境变化指标的分析研究发现,整个剖面反映出大致6个较大的气候变化过程：233. 3kaBP～223. 5kaBP气候波动较大,总体趋势气候趋于干冷,期间出现过两次较温暖气候,之后气候逐渐变冷;在223. 5kaBP～213. 6kaBP总体变化为气温大幅度上升,但在期间有一次较大的相对冷干过程;213. 6kaBP～170kaBP之间总体变化气候趋于变冷,中间有2次明显的气候变暖湿过程及两次冷干过程;170kaBP～117. 1kaBP气候转为明显湿热;117. 1kaBP～75. 6kaBP气候变化趋势明显降低;75. 6kaBP～56. 7kaBP气候又明显上升达到湿热状态。以上气候波动规律与极地冰芯记录及深海氧同位素记录的古气候波动规律有很好的一致性,同时本盐湖区与柴达木盆地察尔汗盐湖区的CH0310钻孔及青海湖南岸二郎剑阶地的 QH 86钻孔所揭示的中更新世晚期以来的气候变化的分析对比,发现西藏羌北的多格错仁盐湖区与青海的察尔汗盐湖区及青海湖湖区在更新世中晚期以来的气候环境变迁存在极好的可比性,说明青藏高原的气候演化在中晚更新世以来基本具有一致性,在时间上的微小超前与滞后具有区域上的细微变化,说明气候变迁在不同的区域又具有各自的独特性。     

Loess chronology of the Middle and Upper Pleistocene in Tadjikistan

The loess/paleosol sequences of Central Asia are continuous terrestrial records of the Quaternary period and enable detailed comparison with paleoclimatic archives such as marine and ice core records in order to reconstruct regional and global paleoclimatic and paleoecological development during the past 130?000 years. Thermoluminescence (TL) and infrared stimulated luminescence (IRSL) dating methods are applied to the extensively studied loess/paleosol sequence of the section at Darai Kalon/Chashmanigar, Tadjikistan, in order to determine a more accurate chronological framework and climatostratigraphic reconstruction for the last interglacial/glacial cycle. Luminescence dating suggests that the loess above the first pedocomplex from the top, PC1, accumulated during the last glacial period. A high accumulation rate of up to 1.20?m per 1000 years was determined for the last glacial loess, especially for the uppermost 5–8?m. PC1 formed during the last interglacial period (oxygen-isotope stage 5). The loess between PC1 and PC2 is designated to be of penultimate glacial deposition age. Infrared stimulated luminescence and TL age estimates are in agreement to 80?000 years before present (BP), indicating a long-distance transport of the aeolian dust prior to deposition. The upper numerical age-limit range is between 300?000 and 450?000 years. However, reliable dating of the loess older than 130?000 years is not possible due to age scatter between samples and an inadequate increase of paleodose with depth. This high-resolution dating study underlines the importance of the section at Darai Kalon and indicates that it is one of the most continuous loess/paleosol records of the Northern Hemisphere. The chronological results are particularly important for the reconstruction of the human evolution in Central Asia, suggesting much older age estimates than previously obtained for most of the archeological key sites associated with PC5 and PC4 in Tadjikistan.     

Aeolian activity in northern Amazonia: optical dating of Late Pleistocene and Holocene palaeodunes

Palaeodunes were examined on the eastern margin of the Rio Branco–Rupununi savanna, northeast Amazonia. Optical dating suggests that the onset of aeolian activity was between 17 000 and 15 000 yr ago, just after the Last Glacial Maximum. Both the palaeodune axes and modern dominant wind directions have northeast to east‐northeast directions, implying no significant shift in atmospheric circulation patterns over northeast Amazonia during the Late Pleistocene to Holocene. Major regional climate change events, such as the Younger Dryas, do not appear to have had any effect on the rates of aeolian deposition at the study site. Aeolian activity appears to have continued to the present day, showing a remarkably constant deposition rate of around 0.13 m kyr^?1 initially, increasing smoothly to the present. Until more palaeodunes in northern Amazonia are dated, it is impossible to determine if this record of gradual aeolian deposition is a reliable regional palaeoclimate indicator, rather than being the result of local bioclimatic and geomorphological effects. Copyright © 2004 John Wiley & Sons, Ltd.