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。     

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.     

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.     

Climate‐controlled aggradation and cyclicity of continental loessic siliciclastic sediments in Asselian–Sakmarian cyclothems,Permian, Hugoton embayment,USA

Siliciclastic intervals in Lower Permian carbonate–siliciclastic cyclothems in western Kansas record climate control on facies progression, deposition and preservation. The 26 000 km² study area comprises seven marine‐continental (carbonate–siliciclastic) cyclothems caused by glacioeustasy. Core data and a three‐dimensional geological model provide a detailed view of the sub‐surface on a gently sloping ramp. Siliciclastic intervals in the cyclothems are fine‐grained red beds with extensive pedogenic features, indicating a continental origin. Bed geometry (sheet‐like deposits that thin to the east), lateral grading, grain size (very fine‐grained sand to silt) and grain angularity (sub‐angular to angular) suggest that the sediment is loess sourced from the west, probably the Ancestral Rocky Mountains. There is a repeated record of glacial‐cycle‐scale, climate‐controlled cyclicity within siliciclastic intervals that has not been recognized previously. Aeolian silt grain size coarsens upward towards the middle, then fines upward in each siliciclastic interval. When sea‐level was high (interglacial) and carbonate production flourished, aeolian sedimentation nearly ceased, suggesting increased vegetation and rainfall at the source. As sea‐level fell, fine‐grained siliciclastic sediments were deposited under relatively dry, but seasonally wet conditions on an exposed ramp. Laterally graded coarser grained siliciclastic sediments with diagnostic fabrics indicate drier conditions with seasonal rainfall during a continued relative fall in sea‐level. The coarsest siliciclastic sediments were deposited during the lowest sea‐level and driest conditions, but still with sufficient seasonal moisture to allow vegetative cover and bioturbation. Subsequent upward fining is correlated with sedimentological indications of wetter conditions during relative sea‐level rise. Unlike common sequence stratigraphic models that relate siliciclastic sediment accumulation to base‐level rise, continental deposits were preserved because plants and pedogenesis stabilized aeolian sediment. The aggradational landscape formed by this process had several metres of positive relief that reduced accommodation for overlying marine carbonate strata. Thus, this mechanism for continental siliciclastic aggradation has a significant effect on sequence stratigraphic architecture.     

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).     

江西修水地区震旦系南沱组冰成岩研究

通过对江西修水地区震旦系南沱组地层、沉积相的研究，识别出5种沉积相类型：碎屑流沉积相、滑塌沉积相、冰筏海洋沉积相、陆架砂泥互层相和陆架泥岩相，重力流沉积分布在该组下部。确定其主要为一套叠加在陆架、陆坡背景沉积之上的冰成岩系。按演化自下而上可分为：先驱冰期、间冰期、主冰期及余冰期几个阶段，与邻区能很好的对应。     

晚新生代黄土高原风尘序列的粒度和沉积速率与中国北方大气环流演变

文章以风尘沉积的粗粒和细粒组分与季风和西风环流的联系为基础,利用黄土高原中部的洛川剖面、西峰剖面和灵台剖面的粒度和沉积速率记录,讨论了晚新生代中国北方季风环流和西风环流的演变历史,总结了这一时期大气环流演变的基本规律和大气环流演变的动力机制.研究表明,自8～7Ma风尘沉积发育至5Ma左右,西风环流和季风环流都有减弱的趋势;自5Ma以来,西风环流和季风环流的强度都在逐步加强;与此同步,季风环流对风尘沉积的贡献增加,而西风环流对风尘的贡献逐渐减小,这一逐渐发展的大气环流趋势与北半球高纬冰盖的逐步发展有关;大气环流的这种趋势变化在8～7Ma,3.4Ma和1.2～0.9Ma这几个时期存在着突变,可能反映了青藏高原的阶段性隆升对中国北方季风环流演化的决定性作用以及对西风环流结构和强度的重要影响.中国北方大气环流在轨道尺度变化的基本特征是,低空季风环流在冰期加强,在间冰期减弱.西风环流和季风环流在冰期和间冰期的强度和格局可能主要与全球冰量的基本状况和青藏高原原面的性质有关.黄土高原的风尘记录在万年尺度和千年尺度的气候事件上都表现出相当明显的区域差异,可能主要与局部地形的大气环流效应有关.     

Geochemical evidence of aeolian deposits in European soils

Hafnium (Hf) and zirconium (Zr) concentrations measured in over 4100 agricultural soil samples from Europe were assessed with the focus on their relationship to the distribution of aeolian deposits, such as loess and coversands. Comparison of extractable (aqua regia; ICP‐MS) and total (XRFS) concentrations shows that only 1.0 to 1.7% of the total Hf and Zr is chemically extractable because of the resistant nature of their host minerals. Resistate minerals, such as zircon, are commonly found in the predominantly silty fraction of loess deposits. In this study a statistical analysis of total Hf and Zr soil data from areas with and without loess was carried out to derive threshold values of 10 mg kg^?1 (Hf) and 318 mg kg^?1 (Zr). These values were subsequently applied across the project area in an attempt to indicate the presence of aeolian deposits. The spatial distribution of above‐threshold concentrations suggests a more extensive and coherent loess belt across central and eastern Europe, providing additional evidence of loess across Brittany, Aquitaine and near the Vosges mountains in France as well as in the basins of central and northern Spain. Above‐threshold concentrations were also detected in loess regardless of its thickness, emphasising the importance of the abundance of zircon in the upper part of the soil profile rather than the actual thickness of the deposit. Soil data however, failed to indicate various loess facies within most of the Pannonian Basin, suggesting that this approach only works where deposits contain a sufficient amount of zircon. This may also explain why the extensive coversands across northern Germany and Poland were largely undetected. This study demonstrates that continental‐scale soil geochemical data can help identify and map the distribution of zircon‐rich loess and coversand, and subsequently enhance and improve current knowledge of the extent of these deposits.     

Regional lithofacies and pedofacies variations along a north to south climatic gradient during the Last Glacial period in the central Loess Plateau,China

Five lateral sand–loess–palaeosol continua occur within the last glacial sediments of the central Loess Plateau of China along a 500 km north to south climatic gradient. The continua shift southward or northward in concert with desert expansion or contraction, respectively. Lateral lithofacies (desert sand to loess) variations are evident at the north end of the gradient and follow Walther's Law of the correlation of facies. Lateral pedofacies (loess to palaeosol) variations are present near the south end of the gradient, where the climate was warmer and wetter. The lateral stratigraphic changes from sand to loess or loess to soil are driven by variations in the rate of sedimentation along a climatic gradient.Vertical stratigraphic profiles at the north end of the gradient reveal alternating sand and loess beds. In contrast, alternating loess and palaeosols occur within the same stratigraphic interval in the southern Loess Plateau, where dust accretion rates were lower. However, in high resolution studies of climate change vertical profiles of alternating loess and palaeosols (especially weak palaeosols) may not reflect regional or global climate change. Alternating loess and weak palaeosols may reflect local variations in the balance between the rates of dust accretion and pedogenesis. Local fluctuations in either of these rates could result in the presence of time equivalent loess and palaeosols at high resolutions. Thus, some of the high resolution loess-palaeosol alternations may reflect local climatic variation rather than global or hemispherical climate change.     

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 late Pleistocene Pampa loess from the Córdoba area in Argentina

In Argentina, loess/palaeosol sequences were studied from the two sections at Monte Ralo and Corralito, located near to the city of Córdoba in the east of the Pampean ranges. Infrared optically stimulated luminescence (IRSL) and thermoluminescence (TL) dating techniques were applied to set up a more reliable chronological framework for the Upper Pleistocene loess record. IRSL ages increase with depth and are stratigraphically consistent. The oldest loess exposed correlates at least to the penultimate glaciation. The luminescence dating study gives evidence for humid climate conditions with soil formation during the last interglacial period and the middle pleniglacial correlating to Marine Isotope Stage (MIS) 5 and 3, respectively. Three extended periods of soil formation are recorded in the loess/palaeosol sequences at the Corralito section. These buried soils most likely correlate with the last interglacial and early last glacial period. During the Middle Pleniglacial, two palaeosols are intercalated in the loess successions. In the Córdoba area, the periods of increased loess accumulation and deposition of loessic sediments correlate with more arid and glacial periods during the Early Pleniglacial, the Middle Pleniglacial and the Late Glacial. Copyright © 2009 John Wiley & Sons, Ltd.     

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.     

Depositional regimes in the Norwegian-Greenland Sea: the last two glacial to interglacial transitions

Various models of surface and deep-water circulation in the Norwegian-Greenland Sea (NGS) have been proposed for the last two glacial to interglacial transitions. Although much progress has been made in understanding the sedimentary response to climatic and oceanographic changes, conflicting interpretations have been developed. To clarify some of these discrepancies and to test or modify the existing circulation concepts, a multiparameter approach is applied, combining sedimentological, micropaleontological, organic-geochemical and isotopic methods. On the basis of indicative properties a combined litho- and organofacies concept is developed and calibrated with modern depositional settings beneath different surface water masses. Sedimentary regimes are then derived for glacial and deglacial settings.Atlantic water intrusions in the NGS reveal complex and highly dynamic patterns for the last two glacial and interglacial periods, with repetitive inflows during Isotope Stage 6 and a high variability in Isotope Stage 5. Specific facies patterns show maximum extensions of Atlantic Water intrusions during the climatic highstands 5.5.1, 5.3 and 5.1 and narrowest intrusions in the cool phases 5.4 and most pronounced in 5.2. In contrast, different glacio-marine depositional regimes depict variable sea ice coverage and supply of ice-rafted debris. Most conspicuous are short-term depositional events marked by diamictons, which are related to the high instabilities of continental ice sheets. Some of the diamictons seem to occur contemporaneously with Heinrich layers H1 and H2. The probable temporal and obvious phenomenological concidence of Heinrich layers and NGS diamictons suggests a common trigger mechanism which caused an almost simultaneous disintegration of huge continental ice masses along the shelves of North America and the eastern margin of the NGS.A previous estuarine circulation model claims regional upwelling along the eastern margin of the NGS for specific periods of the last deglaciation. The organic character of sediments covering the same time intervals show a clear predominance of reworked fossil organic matter and thus does not support the estuarine model.     

Elsterian‐Holsteinian deposits at Kås Hoved,northern Denmark: sediments,foraminifera, ostracods,and stable isotopes

The coastal cliff section at Kås Hoved in northern Denmark represents one of the largest exposures of marine interglacial deposits in Europe. High‐resolution analyses of sediments, foraminifera, ostracods, and stable isotopes (oxygen and carbon) in glacial‐interglacial marine sediments from this section, as well as from two adjacent boreholes, are the basis for an interpretation of marine environmental and climatic change through the Late Elsterian‐Holsteinian glacial‐interglacial cycle. The overlying glacial deposits show two ice advances during the Saalian and Weichselian glaciations. The assemblages in the initial glacier‐proximal part of the marine Late Elsterian succession reveal fluctuations in the inflow of sediment‐loaded meltwater to the area. This is followed by faunal indication of glacier‐distal, open marine conditions, coinciding with a gradual climatic change from arctic to subarctic environments. Continuous marine sedimentation during the glacial‐interglacial transition is presumably a result of a large‐scale isostatic subsidence caused by the preceding extended Elsterian glaciation. The similarity of the climatic signature of the interglacial Holsteinian and Holocene assemblages in this region indicates that the Atlantic Ocean circulation was similar during these two interglacials, whereas Eemian interglacial assemblages indicate a comparatively high water temperature associated with an enhanced North Atlantic Current. The foraminiferal zones are correlated with other Elsterian‐Holsteinian sites in Denmark, as well as those in the type area for the Holsteinian interglacial in northern Germany and the southern North Sea. Correlation of the NW European Holsteinian succession with the marine isotope stages MIS 7, 9 or 11 is still unresolved.     

最后4个冰期旋回中国黄土记录的东亚冬季风变化

开展高分辨率的黄土记录研究, 是揭示过去气候变迁和变率的主要途径.选择黄土高原中部的灵台和赵家川剖面, 对L5以上的黄土-古土壤序列进行了石英颗粒的提取和粒度分析.结果表明, 石英粗颗粒(> 43μm) 体积分数变化揭示了最后4个冰期旋回东亚冬季风存有的快速变化特征, 并同深海氧同位素记录具有良好的对应关系; 然而, 在每一个冰期时段, 石英粗颗粒体积分数的变化幅度和频率存有较大差异, 可能意味着对应的冰期下垫面状况和气候系统内部的非线性响应机制并不相同.值得注意的是由石英粗颗粒体积分数反映的东亚冬季风变化, 在某些时段不仅同磁化率记录的夏季风变化不协调, 而且同深海氧同位素记录存有明显差异.深入研究这种由不同代用指标反映的古气候变化间的差异, 对理解黄土记录的全球性意义显得尤为重要.      

An overview of the role of weathering in the production of quartz silt

Quartz silt is a widespread detrital sediment with large aeolian (loess) and alluvial silt deposits forming important components of many contemporary landscapes. Despite research findings which indicate that a range of opportunities exist for the comminution of quartz into silt particles within a wide variety of geomorphic environments (e.g. glacial grinding, fluvial comminution, aeolian abrasion, frost weathering, salt weathering, insolation weathering and deep weathering), the ‘glacial-aeolian’ hypothesis has traditionally been favoured as the most likely explanation for loess formation and loess is seen as primarily a Quaternary phenomenon. As a consequence there has been a tendency to underestimate sediment inputs into loess systems by geomorphological processes operating within pre-Quaternary environments. In particular, earth scientists may have considerably underestimated the role of weathering in global silt generation, as there are now many references to the existence of a patchy but widespread distribution of pre-Quaternary weathering profiles across the glacial and periglacial landscapes of the Northern Hemisphere (e.g. North America, British Isles, north and central Europe), landscapes within which many of the classical loess deposits are located. These observations suggest that weathering profiles may have covered large tracts of the Northern Hemisphere land surface prior to the Quaternary glaciations. This, in turn, may have important implications for quartz silt generation as: (1) experimental studies indicate that many weathering processes are capable of generating significant quantities of silt-sized debris, and (2) particle characteristics displayed by saprolitic material that has developed on quartz rich crystalline source rocks often include significant quantities of either silt-sized material, or quartz grains that are weakened by weathering derived microfractures. Thus, weathering profiles may represent ‘mines’ of actual and potential quartz silt, available for release into sedimentary systems when these profiles are subsequently reworked by geomorphological processes such as glacial, fluvial and aeolian erosion.     

Quaternary vegetation changes derived from a loess‐like permafrost palaeosol sequence in northeast Siberia using alkane biomarker and pollen analyses

Zech, M., Andreev, A., Zech, R., Müller, S., Hambach, U., Frechen, M. & Zech, W.: Quaternary vegetation changes derived from a loess‐like permafrost palaeosol sequence in northeast Siberia using alkane biomarker and pollen analyses. Boreas, Vol. 39, pp. 540–550. 10.1111/j.1502‐3885.2009.00132.x. ISSN 0300‐9483 Alkane biomarker and pollen data were obtained from a 15‐m‐high and probably c. 240‐kyr‐old loess‐like permafrost palaeosol sequence (‘Tumara Palaeosol Sequence’, TPS) in northeast Siberia. The alkane results were corrected for degradation effects by applying an end‐member model and were evaluated by comparing them with the palynological results. The two data sets are generally in good agreement and suggest that the lower part of the TPS developed mainly under larch forests, whereas the upper part of the sequence reflects the expansion of mammoth steppes during the Weichselian glaciation and finally reforestation during the Lateglacial and the early Holocene. For the lower part of the TPS, the palaeoclimatic interpretation according to modern analogue methods would indicate warm, interglacial conditions, but this is at odds with the climate chronostratigraphy based on a multi‐proxy palaeopedological approach and numeric dating. Provided that the correlation of the discussed stratigraphic unit with the Late Saalian glaciation and the Marine Oxygen Isotope Stage 6 is correct, our results suggest that temperature was not a limiting factor for tree growth at that time. Furthermore, it seems very likely that it was not mainly temperature changes but rather increasing aridity and continentality during the course of the last glacial that favoured the expansion of the mammoth steppe.     

Neoproterozoic glacial and gravitational sedimentation on a continental rifted margin: The Jequitaı́–Macaúbas sequence (Minas Gerais,Brazil)

This paper is a contribution to the knowledge of the sedimentation of Neoproterozoic sequences, known as the Jequitaı́ Formation and Macaúbas Group. These sequences are present along the transitional zone between the São Francisco Craton and the Brasiliano (≌600 Ma) Araçuaı́ fold belt in Minas Gerais, Brazil. A sedimentological study of these Neoproterozoic sequences enables us to distinguish between true continental and marine glacial facies and glacial material reworked by various subaqueous gravitational processes. The cratonic Jequitaı́ Formation consists of massive and stratified diamictites up to 100 m thick. This diamictite association is tentatively interpreted as glaciomarine in origin. It continues eastward, in the Araçuaı́ fold belt, as the metasedimentary Macaúbas Group, which is composed of metadiamictites, quartzites and schists from 5–12(?)km thick. The Macaúbas Group consists of resedimented glacial material deposited by subaqueous debris flows and turbidity currents. A depositional model is proposed for the Jequitaı́–Macaúbas glacial/gravitational sequence. From west to east, a glaciomarine sequence, possibly deposited from an ice-sheet and slightly reworked by gravitational processes, was reworked along the São Francisco cratonic border and generated a slope apron system made up of diamictites associated with turbidites and rhythmites.     

Were Ediacaran siliciclastics of South Australia coastal or deep marine?

The Late Neoproterozoic Ediacara Member of the Rawnsley Quartzite in South Australia has been considered aeolian, fluvial, intertidal and deep marine by various authors. Palaeosols would not be expected for the deep marine interpretation, but some palaeosols should be evident for the aeolian–fluvial–intertidal interpretations, and this is the first study to examine the Ediacara Member at a petrographic and geochemical scale appropriate to recognize potential palaeosols. Recognition of palaeosols and floodplain facies in Neoproterozoic rocks is a challenge because such rocks are too ancient for diagnostic non‐marine fossils such as root traces. The varied thickness of Ediacara Member red siltstones and white sandstones is distinct from laterally persistent overlying and underlying grey shales and limestones with acritarchs, stromatolites and other marine fossils. The sandstones are trough cross‐bedded and fill palaeovalleys. The red siltstones have poorly sorted, highly angular, silt‐size grains characteristic of loess. Particular sandy and silty beds were sampled for detailed petrographic and geochemical studies, because they include desiccation cracks, sand crystals, ice cracks, carbonate nodules and soft‐sediment deformation like those of palaeosols. Chemical and grain‐size variations within these beds reveal surficial clay formation and oxidation from feldspar as in soils. Petrographic studies also revealed surficial disruption of these palaeosols by filamentous structures comparable with microbial ropes of biological soil crusts. This array of palaeosol features may be of use for recognizing palaeosols in other Neoproterozoic siliciclastic sequences.