Luminescence chronology of the Upper Pleistocene loess record at Kurtak in M iddle Siberia

The loess/palaeosol sequence of Kurtak, situated at the western bank of the upper Yenisei in Middle Siberia, represents one of the best developed Middle and Upper Pleistocene sediment records in Yenisei Siberia. More than 40 m thick loess and loess-like sediments intercalated by at least four pedocomplexes are exposed at a steep erosional slope at the bank of the Krasnoyarsk Water Reservoir. Infrared optically stimulated luminescence (IRSL) and thermoluminescence (TL) dating techniques have been applied on 38 fine grain samples from the upper 23 m of the profile, representing the penultimate and last interglacial–glacial cycle. The IRSL and TL age estimates are in good agreement with the geological estimates up to the last interglacial soil horizon (oxygen isotope substage (OIS) 5e). The luminescence ages show that the lowermost truncated palaeosol of kastanosjem-type is likely to have formed during the penultimate interglacial upon subaerial deposits. Three weak reddish brown palaeosols intercalated by reworked loess-like sediments correlate with early Upper Pleistocene interstadials (OIS5dion of -a), and a succession of humic horizons alternated by cryoturbation processes (Kurtak pedocomplex) is linked with OIS 3. Thick loess deposits between the pedocomplexes show now significant age increase with depth, indicating high accumulation rates at around 23 ka (OIS 2) and 60 ka (OIS 4).     

Luminescence dating of loessic sediments from the Loess plateau, China

Loess/palaeosol sequences from the Loess plateau in China were investigated by combined infrared optically stimulated luminescence (IRSL) and thermoluminescence (TL) dating techniques in order to study the luminescence properties of the loessic sediments and to provide a direct chronological link for correlation and position of the last interglacial soil in Central Asia and the Loess plateau in China. Sensitivity changes were found for all samples through artificial bleaching of the samples. The greatest sensitivity changes, of up to 50%, were found for very old loess samples designated to be older than the Matu-yama/Brunhes magnetic boundary and hence older than 788,000±1,800 years. The upper dating limit, as investigated by the very old loess samples, ranges from 250,000 to 300,000 years, if the TL additive dose method is applied. The chronological position of the last interglacial soil S1 at the section near Lanzhou indicates luminescence age estimates ranging from 82,000 to 75,000 years for the marine-isotope stage 5 to 4 transition. However, the loess from below S1 yielded luminescence age estimates between 153,200±14,200 and 110,100±20,100 years for TL and IRSL additive dose methods, respectively. Thus, a direct correlation between the S1 and the first intercalated pedocomplex PC1 in Central Asia is most likely. Received: 31 March 1998 / Accepted: 25 October 1998     

Late Pleistocene loess‐palaeosol sequences in the Vojvodina region,north Serbia

Late Pleistocene loess‐palaeosol sequences are widespread in the Vojvodina region, with thicknesses reaching a maximum of about 20 m. Our investigations include more than 40 of these loess sections. Geochronology of the last glacial loess‐palaeosol sequences, based on luminescence dating and amino acid racemisation, provides correlations between Upper Pleistocene loess‐palaeosol sediments in Vojvodina and comparable deposits at other European localities. Sedimentary logs of magnetic susceptibility, grain‐size measurements and carbonate content, combined with malacological evidence, indicate two main relatively cold and arid phases during the last glacial period, related to intensive accumulation of loess units L1L1 and L1L2, as well as many brief episodes of dry and windy climatic conditions, suggesting a possible relationship with cold events recorded in the North Atlantic region. Generally, late Pleistocene climate in the region was dry and relatively warm, compared with glacial period sites in central Europe, and was characterised by sharp differences between glacial and interglacial modes. New data and interpretations presented in this study emphasise the significance of loess‐palaeosol sequences in Vojvodina for the reconstruction of the temporal and spatial evolution of late Pleistocene palaeoclimate in this part of Europe. Copyright © 2007 John Wiley & Sons, Ltd.     

Geochronology of Middle and Upper Pleistocene Loess Sections in Hungary

The application of both thermoluminescence and infrared stimulated luminescence dating to the extensively studied “classical” Hungarian loess/paleosol sequences from Basaharc, Mende, and Paks provides a reliable chronological framework and climatostratigraphic reconstruction for the last interglacial/glacial cycle. Based on this combined luminescence dating study a new chronology is proposed for the “Young Loess” in Hungary. Luminescence dating suggests that the loess below the MF2 horizon formed during the penultimate glaciation. The MF1 horizon probably formed during an interstade within oxygen isotope stage 3. For the youngest loess, overlying MF1, a very high accumulation rate was determined. Large time gaps occur above MF2 and MF1, indicating that most of the record of the last glaciation is missing in the standard sections at Basaharc, Mende, and Paks. Either large discontinuities or a very low accumulation rate occurred in all three type sections during the soil-forming periods. High-resolution studies of climatic proxies using this combined luminescence dating approach provide a reliable chronological framework for loess and loess derivatives of the last glacial cycle in Hungary, although a precise and complete chronostratigraphic reconstruction cannot be achieved from the incomplete records found at these sites.     

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.     

A 180 ka record of environmental change at Erdut (Croatia): a new chronology for the loess–palaeosol sequence and its implications for environmental interpretation

While there are numerous thick loess–palaeosol sequences preserved across the Carpathian Basin, well dated sites that provide terrestrial palaeoenvironmental records extending beyond last glacial–interglacial cycle are scarce. Robust chronologies are essential for correlations of loess with other long-term Quaternary records and to further understanding of the palaeoenvironment and climate of this important region beyond the last 125 ka. Here a new geochronology based on 13 post-infrared infrared stimulated luminescence ages focused on the lower part of the loess–palaeosol sequence at Erdut is presented. The results show that the lower part of the Erdut profile spans the penultimate glacial cycle (MIS 7 to MIS 5). The considerable sediments overlaying the investigated part of the profile suggest that this section spans two glacial cycles, rather than the previously suggested one. The most likely source of the discrepancy is the use of uncorrected infrared stimulated luminescence signal, which can cause age underestimation if not accounted for. This study demonstrates the need to revisit sites such as Erdut, re-date them using updated measurement protocols, and update existing palaeoenvironmental interpretations.     

Chronology of the Last Climatic Cycle (Upper Pleistocene) of the Surduk loess sequence, Vojvodina, Serbia

The Surduk loess section in Serbia provides a 20 m thick pedosedimentary record of the last interglacial–glacial climatic cycle (Upper Pleistocene). Based on optical dating, a chronostratigraphy could be established for the last climatic cycle, yielding the first numerical ages of a loess record from the middle Danube basin. Infrared-stimulated luminescence (IR-OSL) dating has been applied to the polymineral silt fraction using a multiple aliquot additive-dose protocol to determine the equivalent dose ( D _E ). Within error limits, all age estimates are in stratigraphic order. Owing to the application of shine-plateau tests, the samples showed no evidence of insufficient bleaching. The Surduk loess section comprises three major periods of soil formation. Based on the IR-OSL chronostratigraphy, the lowermost pedocomplex is attributed to the Last Interglacial and to the Early Glacial (Marine Isotope Stage – MIS 5e to 5a). The middle part of the section exhibits a succession of weakly developed brown soils and a humic horizon, named 'Surduk soil', formed during MIS 3. On top of the section, recent soil formation is related to the Holocene. Thick loess deposits are preserved between these palaeosols and are attributed to the Lower and Upper Pleniglacials (MIS 4 and 2), respectively. Estimated mean sedimentation rates are 0.1–0.2 mm/yr for the last glacial cycle, with a strong increase to 0.6 mm/yr with onset of the Pleniglacial.     

New insights into Southern Caucasian glacial–interglacial climate conditions inferred from Quaternary gastropod fauna

In the present study, we performed gastropod analyses on loess–palaeosol sequences from northeast Armenia (Southern Caucasia) covering at least three glacial–interglacial cycles. The elaborated ecostratigraphy shows significant patterns of species composition related to the succession of pedocomplexes and loess, respectively. Pedocomplexes included species that can be associated with high-grass to forest-steppe biomes, indicating increased humidity for these sections compared to the loess layers. In contrast, loess layers that relate to glacial periods are associated with gastropod species of semidesert environments with shrub- and shortgrass-steppes, indicating semiarid to arid conditions. Furthermore, the loess deposits do not show any evidence for cold-adapted gastropod species. Therefore, we suggest that average July temperatures in the study area were above 10 °C, even during periods of loess deposition. Consequently, we propose that the limiting factor for tree growth during glacial periods was aridity, rather than temperature. In addition, we observe environmental differences between the various glacial times, with our results indicating a trend towards steadily increasing aridity in Southern Caucasia across the Middle to Late Pleistocene.     

The last 750 ka in loess–palaeosol sequences from northern France: environmental background and dating of the western European Palaeolithic

This study presents an overview of Middle Pleistocene loess–palaeosol sequences (LPS) in northern France and discusses the palaeoclimatic significance of the pedosedimentary record in the context of western European LPS and of global climatic cycles for the last 750 ka. In this area, the oldest loess deposits (early Middle Pleistocene) are preserved in sedimentary traps (leeward scarps of fluvial terraces and dissolution sinkholes). They result from local deflation processes reworking Pleistocene sandy fluvial deposits or relicts of Tertiary sands. A large extension of typical calcareous loess over the landscape, the Loess Revolution, is then observed during MIS 6, with heavy mineral assemblages testifying to long-distance transport from the polar desert area of the dried eastern Channel. A correlation scheme is proposed between the global records of northern France in continental environments and both global palaeoclimatic records and other main western European LPS. After 30 years of research, northern France LPS stand as a fundamental archive of the impact of interglacial–glacial climatic cycles as well as millennial events. Finally, these works provide a robust chronoclimatic framework for the study of the western European Late Acheulean and Middle Palaeolithic and for the relative dating of the various fluvial terraces that they fossilise.     

Dust deposition and climate in the Carpathian Basin over an independently dated last glacial–interglacial cycle

Loess in the Carpathian Basin is some of the thickest and most complete in Europe. Located in the Vojvodina region of the southern Carpathian Basin the Crvenka loess-palaeosol section appears to preserve a detailed climate proxy archive of the last glacial–interglacial cycle. Central to the interpretation of the site is a detailed and independent age model. Here, the results of detailed optically stimulated luminescence (OSL) dating and elevated temperature post-IR infrared stimulated luminescence (post-IR IRSL) dating are presented. Quartz OSL ages appear accurate to about 50–60 ka, where 2D₀ values are reached, while elevated temperature post-IR IRSL yields more accurate ages below this. In line with recent results, the latter signal appears to show negligible fading rates. Two age models are developed that combine (a) OSL and post-IR IRSL ages and (b) OSL ages and ‘expected’ ages from tying unit boundaries to the marine record. If the luminescence model is regarded as accurate, differences between this and the OSL/marine age model raise questions over the accuracy of the latter, as well as the processes controlling the zeroing of luminescence dates. The luminescence based age model is then used to derive the first fully independent reconstruction of climate proxies and accumulation rates from Carpathian loess. Such reconstructions can be used to compare to other independent records without assumptions inherent in correlation-based approaches. The findings demonstrate how variable accumulation rate is at the site, and compared to other independently dated Carpathian loess records. Average values vary north–south but are of similar order throughout the basin. Accumulation rate was highest during the later part of the last glacial, but variation on millennial timescales does not always match shifts in grain-size, suggesting diverse and complex influences. Environmental reconstructions using grain-size and magnetic susceptibility show that no one atmospheric system or air mass can explain the changes in the Carpathian Basin and that millennial-scale variability can only intermittently be tied to North Atlantic Heinrich events. Expanded ice sheets during the peak last glacial, combined with other atmospheric teleconnections, may have served to develop a strong anticyclone in the region. It was likely windier during earlier parts of the last glacial, but Atlantic and Mediterranean moisture was probably less abundant than during more humid interglacials.     

A luminescence‐based chronology for the Harletz loess sequence,Bulgaria

The Harletz loess‐palaeosol sequence is located in northwestern Bulgaria and represents an important link between well‐studied loess sequences in eastern Romania and further sites to the west of the Carpathians (e.g. Serbia and Hungary). The aim of this study was to establish a chronostratigraphy of the deposits, using various methods of luminescence dating, together with basic stratigraphical field observations as well as magnetic properties. Luminescence dating was carried out using the quartz fine grain fraction and a SAR protocol, and the feldspar coarse grain fraction, applying the MET‐pIRIR protocol. Due to underestimation of the quartz fine grain fraction in the lower parts of the sequence, the resulting chronology is mainly based on the feldspar ages, which are derived from the stimulation temperature at 150 °C. A comparison with nearby sequences from Serbia, Hungary and Romania, and interpretations obtained through the stratigraphical and sedimentological signature of the sequence, supports the established chronology. Our data suggest that the prominent palaeosol (soil complex) in the upper quarter of the sequence was formed during MIS 5. It would follow that large parts of the Last Glacial loess overlying this palaeosol were probably eroded, and that the thick loess accumulation underlying this soil complex can be allocated to the penultimate glacial (MIS 6). A prominent MIS 6 tephra, which has been reported from other sequences in the area, is also present at Harletz.     

The loess sequence of Dolní Věstonice,Czech Republic: A new OSL‐based chronology of the Last Climatic Cycle

The Dolní Věstonice loess section in the Czech Republic is well known for its high‐resolution loess–palaeosol sequence of the last interglacial–glacial climatic cycle (Upper Pleistocene). The loess section is situated in a climatic transition zone between oceanic and continental climates and is therefore of great value in reconstructing past regional climate conditions and their interaction with climate systems, in particular that of the North Atlantic. Based on a combination of optically stimulated luminescence (OSL) ages, stratigraphic field observations and magnetic susceptibility measurements, a chrono‐climatic interpretation of the Dolní Věstonice loess section is presented. To establish a reliable Upper Pleistocene chronology, a quartz OSL approach was applied for equivalent dose (D_e) determination. Monomineralic quartz extracts of three distinct grain sizes, fine (4–11 μm), middle (38–63 μm) and coarse (90–200 μm), were used and compared. Within error limits, the calculated OSL ages are the same for the different grain sizes, and the OSL ages are in stratigraphic order. The established OSL chronology is in agreement with a Weichselian litho‐ and pedostratigraphy. The Dolní Věstonice loess section is characterized by four pedosedimentary subsequences. At the base of the profile, subsequence I is characterized by a distinct Early Glacial soil complex, OSL‐dated to c. 110 to 70 ka, representing one of the most complete records of environmental change in the European loess belt. Subsequence II is allocated to the Lower Pleniglacial and is characterized by laminated sandy loess. Middle Pleniglacial subsequence III is represented by a brown soil complex, and is followed by the uppermost subsequence IV, characterized by a thick body of laminated sandy loess, indicating strong wind activity and a high sedimentation rate of more than ～1 mm a^?1 during the Upper Pleniglacial. According to the OSL chronology, as well as to the sedimentological and palaeopedological investigations, it is likely that the sequence at Dolní Věstonice has recorded most of the climatic events expressed in the NGRIP δ¹⁸O reference record between 110 and 70 ka.     

近13万年来黄土高原干湿气候的时空变迁

第四纪时期，黄土高原粉尘物质的搬运、沉积及其后的成土过程受控于干湿气候的变化。对黄土高原这一特定地区而言，风成沉积序列在地域上的差异主要与东亚地区的季风环流在时间和空间上的变化有关。本文的研究揭示出，近１３万年里，最为显著的成壤期有６期，与这６个成壤期对应的时段也应当是夏季风环流加强、气候温湿的时期；在空间上，全新世适宜期及末次间冰期中与深海氧同位素阶段５ａ，５ｃ，５ｅ对应的时期，夏季风足可以深入到毛乌素沙漠腹地，并具有占优势的环境效应。在阶段３的早、晚期及５ｂ时期夏季风虽然也能深入沙漠－黄土边界带，但其环境效应在黄土高原北部及毛乌素沙漠南缘已不再显著。在阶段２、阶段４及阶段３的中期夏季风已不能深入沙漠－黄土边界带。     

Inland aeolian deposits of south‐west France: facies,stratigraphy and chronology

Archaeological investigations undertaken along a proposed highway together with the compilation of available geological and pedological data made it possible to give a first overview of the distribution of Pleistocene aeolian deposits in south‐west France. A chronological framework for deposition has been obtained using both radiocarbon (n = 24) and luminescence (n = 26) dating. It shows that aeolian transport was very active during the Late Pleniglacial, between 15 and ～23 ka, leading to sand emplacement over a 13 000‐m² area at the centre of the basin. The Pleniglacial coversands are typified by extensive fields of small transverse to barchanoid ridges giving way to sandsheets to the east. Subsequent aeolian phases, at ca. 12 ka (Younger Dryas) and 0.8–0.2 ka (Little Ice Age), correspond to the formation of more localized and higher, mainly parabolic dunes. At the southern and eastern margins of the coversand area, aeolian dust accumulated to form loess deposits, the thickness of which reaches ～3 m on the plateaus. Luminescence dates together with interglacial‐ranking palaeoluvisols between the loess units clearly indicate that these accumulations built up during the last two glacial–interglacial cycles. The chronology of sand and loess deposition thus appears to be consistent with that already documented for northern Europe. This suggests that it was driven by global climate changes in the northern hemisphere. The relatively thin aeolian deposits (and particularly loess) in south‐west France is thought to reflect both a supply‐limited system and a moister climate than in more northern and continental regions. Copyright © 2011 John Wiley & Sons, Ltd.     

Advances and Issues in Luminescence Dating of Loess Deposits in Arid Central Asia

High-resolution loess deposits are widely distributed in Arid Central Asia (ACA) and provide important records associated with dust transportation, paleoenvironmental and paleoclimatic evolution. The chronology is the foundation of the research into loess deposits as an environmental archive. In recent decades, the gradually developed optical dating method has been increasingly matured and become an important approach to establishing the loess-paleosol sequences. Here, we summarized and discussed previous work on loess chronology mainly based on optical dating approach in ACA. The following understandings have been listed: ① In comparison with optical dating method, the suitable material for ¹⁴C dating is uncommon in ACA. However, the dating range of luminescence dating is more extensive, and the dating materials are accessible. Thus, the optical dating is widely applicable in the establishment of loess framework in this area. ② Until now, the quartz Single Aliquot Regeneration (SAR) method can be applied to the establishment of loess-paleosol sequence since last glacial period. But several issues remain unaddressed. For example, the Optically Stimulated Luminescence (OSL) signal sensitivity of quartz grains are low in some areas. Furthermore, the results of OSL dating of different grain sizes within a single sample are inconsistent in some areas. The solution of these problems still requires more methodological research. ③ The post-IR IRSL (pIRIR) and multiple elevated temperature stimulation (MET-pIRIR) protoCols of feldspar have basically overcome the anomalous fading issue in the traditional IRSL dating process. In ACA, the framework since MIS 7 can be established with K-feldspar luminescence dating method. Compared with quartz luminescence characteristics, the K-feldspar luminescence signals are more sensitive and exhibit a high saturation level. In specific applications, it is necessary to establish the age frame according to the luminescence sensitivity, the age of samples or other factors.     

Luminescence evidence for two Middle Pleistocene interglacial events at Tourville, northwestern France

The infrared stimulated luminescence (IRSL) dating method is applied to alkali feldspar coarse grains from the two distinct Middle Pleistocene interglacial estuarine deposits of Tourville, located along the Seine Valley. The upper deposit (unit D), previously dated at 200 ka by ESR on in situ shells and correlated with a stage 7 high sea-level stand (186–245 ka), yields a measured IRSL age of 176 ± 21 ka. The lower deposit (unit B) assigned to a distinctly older high sea-level event (stage 9: 303–339 ka) yields a measured IRSL age of 273 ± 28 ka. The nearby stage 7 raised beach of Sangatte, in Northwestern France, previously dated by TL on quartz (229 ± 18 ka) yields a measured IRSL age of 186 ± 19 ka. These IRSL age estimates systematically underestimate the expected geological ages. This could be due to the long-term fading or instability of the luminescence signal in alkali feldspars. The correction for long-term fading has been tested on these samples. At Tourville, it yields corrected IRSL ages of 196 ± 23ka and 314 ± 32ka, for the upper and lower units respectively and, at Sangatte, a corrected IRSL age of 206 ± 20 ka. These corrected IRSL age estimates are in better agreement with the expected geological ages. This study demonstrates the potential of the feldspar luminescence dating method to provide chronological information on Middle Pleistocene interglacial estuarine sediments within the North Sea-English Channel Basin.     

The Požarevac loess–paleosol sequence: a record of increased aridity in the south-eastern margin of the Carpathian Basin during the last 350 ka

The loess sequence preserved in the Požarevac brickyard in north-eastern Serbia comprises eight loess units separated by seven paleosols. Geochronological investigation using amino acid racemization and luminescence dating support stratigraphic correlations of loess units L3, S2LL1 and L1 at the Požarevac section with loess of glacial cycles E [Marine Isotope Stage (MIS) 10], D (MIS 9–8), C (MIS 7–6) and B (MIS 5–2) across central Europe. Correlation with the marine oxygen-isotope stratigraphy and associated paleoclimatic inferences are further supported by magnetic susceptibility, particle size and carbonate content measured in Požarevac sediments. Malacological investigations at the Požarevac section reveal the continuous presence of the Chondrula tridens and Helicopsis striata faunal assemblages throughout the last 350 ka. The loess malacological fauna, which is characterized by the complete absence of cold-resistant and cold-preferring species, suggests a stable, dry and relatively warm glacial and interglacial climate, compared with other central European loess localities. Together these data suggest that the south-eastern part of the Carpathian (Pannonian, Middle Danube) Basin was a refugium for warm-preferring and xerophilous land-snails during the generally unfavorable glacial climates of the late Middle and Late Pleistocene.     

Loess sedimentation in Tibet: provenance,processes, and link with Quaternary glaciations

Well-preserved loess deposits are found on the foothills of mountains along the middle reaches of the Yarlung Zangbo River in southern Tibet. Optically stimulated luminescence (OSL) dating is used to determine loess ages by applying the single-aliquot regeneration technique. Geochemical, mineralogical, and granulometric measurements were carried out to allow a comparison between loess from Tibet and the Chinese Loess Plateau. Our results demonstrate that (i) the loess deposits have a basal age of 13–11 ka, suggesting they accumulated after the last deglaciation, (ii) loess in southern Tibet has a “glacial” origin, resulting from eolian sorting of glaciofluvial outwash deposits from braided river channels or alluvial fans by local near-surface winds, and (iii) the present loess in the interior of Tibet has accumulated since the last deglaciation when increased monsoonal circulation provided an increased vegetation cover that was sufficient for trapping eolian silt. The lack of full-glacial loess is either due to minimal vegetation cover or possibly due to the erosion of loess as glaciofluvial outwash during the beginning of each interglacial. Such processes would have been repeated during each glacial–interglacial cycle of the Quaternary.     

Palaeoclimatic inferences from upper Palaeozoic siltstone of the Earp Formation and equivalents, Arizona-New Mexico (USA)

The Late Palaeozoic configuration of Pangaea contributed to a palaeoclimatic extreme that was characterized by both icehouse and monsoonal conditions. This study uses sedimentological, geochemical, and provenance data from silty facies of the Earp and equivalent Supai Formations (Arizona, New Mexico) to shed light on atmospheric circulation and glacial–interglacial climate change in westernmost equatorial Pangaea. Five silt‐rich facies comprise both loessite and marine and fluvially reworked loessite. An initial aeolian origin for the silt is indicated by the remarkably invariant grain size and the laterally continuous, sheet‐like geometry of beds. The silt‐rich facies occur in repetitive facies associations (1–20 m scale) that form mixed continental‐marine (loess, marine‐reworked loess), shallow‐marine, and continental (loess, palaeosol) ‘sequences’. Facies repetitions of both mixed continental‐marine and shallow‐marine sequences reflect a linked glacioeustatic–glacioclimatic control, whereas the continental (loess–palaeosol) couplets reflect a primary glacial–interglacial climatic cyclicity linked to glacioeustasy. Stratigraphic interpretations suggest that aeolian silt flux maximized during glacial to incipient interglacial stages (lowstand to early transgression), and decreased significantly or ceased during interglacials (highstand to early falling stage). Detrital‐zircon geochronological data indicate a transition from dominantly north‐easterly winds during the Middle Pennsylvanian to north‐westerly and south‐easterly winds by the Early Permian, which trend is inferred to reflect the onset of monsoonal circulation in western Pangaea. Relative grain‐size data support the detrital‐zircon data, and exhibit a significant decrease from the Sedona arch/Central Arizona shelf (north) to the Pedregosa basin (south) sections. Whole‐rock geochemical data suggest a relatively unweathered source for the silt in the north, and detrital‐zircon data indicate significant silt was derived from the local basement. These large piles of silt(stone) preserve valuable information for reconstructing both long‐term evolution in atmospheric circulation and short‐term fluctuations in glacial–interglacial climate. Many such indicators for long have been applied to ‘recent’ (Plio‐Pleistocene) loess, but are equally applicable to ‘deep‐time’ strata.     

五十万年来毛乌素沙漠的变迁

对沙漠-黄土边界带的古风成砂-黄土-古土壤序列的研究表明，毛乌素沙漠至少在0.5MaB.P.就已出现，但也并非从其出现之初就持续至今。沙漠-黄土边界带的风成沉积所记录的沙丘活化和固定的多次转变是第四纪时期毛乌素沙漠对气候振荡响应的结果。五十万年来，沙漠-黄土边界带的石峁剖面记录了13层古风成砂，代表了13次沙漠大规模的南侵。沙漠的南侵不仅可以发生在冰期鼎盛之时，同样也可以发生在间冰期中的寒冷气候幕出现之时。此外，鉴于沙漠-黄土边界带具有气候敏感性的特点，石峁剖面的地层记录还表明了第四纪时期不仅有冷期与暖期的多次旋回，而且冷期和暖期发生时还有次一级的气候波动。