Stratigraphy of a Late Pleistocene ice-cored moraine at Kap Herschell, Northeast Greenland

At Kap Herschell, in the outer fjord zone of central northeast Greenland, exposed sections in a Late Pleistocene ice-cored moraine revealed four major stratigraphic units deposited during the complex Kap Herschell Stade . All contain fragmented and redeposited marine shells that most likely belong to an Eemian or Early Weichselian marine episode. The oldest unit consists of buried ground ice with folded and sheared debris bands. Isotopic analyses show that the slope of the regression line for δ²H vs. δ¹⁸O of the ice is about 8.5. which suggests correlation with the Global Meteoric Water Line (GMWL). Data strongly suggest that the ground ice at Kap Herschell is a remnant of a Late Pleistocene glacier. It was probably generated at low altitudes (< 1000 m) in the inner fjord region or in the nunatak zone. The ground ice is unconformably overlain by all younger stratigraphic units, the oldest of which is a diamicton probably deposited as ablation till from the ice. A complex unit composed of mainly glaciolacustrine deposits and subordinate beds of fluvial and deltaic origin overlies the till and ground ice. Luminescence dating of the lacustrine sediments indicates maximum ages younger than 43 ka BP, suggesting deposition during isotope stages 3 or 2. The glaciolacustrine deposits suffered strongly from glaciotectonic deformation, caused by renewed glacier advance through the fjord. It reached the inner shelf and led to deposition of a discordant till at Kap Herschell, most probably during the Late Weichselian.     

The geochemistry of hydrothermal alteration at the Salgadinho copper deposit,Portugal

The recently discovered Salgadinho copper deposit, 7 km NNE of S. Luis, Portugal is located in the southernmost linear belt of outcropping low metamorphic grade deformed Palaeozoic rocks (Famennian) in the SW part of the Iberian Pyrite Belt. The stratabound replacement pyrite-chalcopyrite mineralisation is present in variably altered felsic pyroclastic rocks which are overlain by pyritic graphitic shales and tuffs which have undergone alteration in the lowermost 5m. The altered pyroclastic rocks are characterised by pale green celadonitic fluoro-muscovite and, in the most intense zone of alteration, quartz, ankerite, and ore minerals are present (pyrite, chalcopyrite, sphalerite, tetrahedrite, galena, bournonite). No exhalative Cu-Zn or Zn-Pb ore has been discovered associated with the submarine volcanic stratabound Cu-rich alteration zone. Alteration of feldspars and groundmass has involved a net loss from the system and gains in Fe²⁺, F, H₂O, Mg, Fe³⁺, Ca, Mn, P, Ti, S, Cu, Zn, Pb, As, Sb, Ag and Au at the expense of Si, K, Al and Na. The great enrichment of F in the altered rocks, the association of zonal alteration facies with coarse grained pyroclastic masses and the intimate association of pale green celadonitic fluoro-muscovite with mineralisation at Salgadinho and most other deposits of the Iberian Pyrite Belt represents a powerful exploration guide for submarine exhalative ores.Text of paper presented at the 26th I.G.C., Paris, July 1980     

Evidence for Pleistocene wet aeolian dune and interdune accumulation,S. Pedro da Maceda,north‐west Portugal

Outcrops and cored/counter‐flushed boreholes in the coastal area between Espinho and Aveiro (north‐west Portugal) were investigated to reconstruct the changing patterns of sedimentation during the Late Pleistocene–Holocene. To obtain a common comparison basis, the grain‐size data from outcrop and borehole samples were analysed. The outcrops and the cored parts of the boreholes were dated by radiocarbon and optically stimulated luminescence. The results show that, on top of pebble‐rich beds of fluvial origin, a wet aeolian dune and interdune environment was active during the later part of the Pleistocene, turning to dry aeolian at the transition to the Holocene. The data indicate also that aeolian accumulation was controlled by vegetation changes (climate) and groundwater table fluctuations. During the Holocene, a podzol formed on the Pleistocene dunes and extensive vegetation precluded major aeolian accumulations. Remobilization of sand started again because of human deforestation and – last but not least – the Little Ice Age.     

Stratigraphy and lithology of Late Pleistocene sediments at Møvatn, Hardangervidda, South Norway

Stratigraphic, textural, mineralogical, geochemical and palynological investigations indicate the existence of: lacustrine clay from late Eemian (Hovden thermomer); dark indicateclayey basal till of the Early Weichselian age (Hovden kryomer); lacustrine sediments from an Early or Middle Weichselian interstadial (Førnes thermomer); and basal till from Middle/ Late Weichselian (Førnes kryomer). The environment during the thermomers is discussed.     

Site formation processes at Donggutuo: a major Early Pleistocene site in the Nihewan Basin,North China

Understanding site formation processes is crucial for interpreting archaeological context patterns and hominin behaviour as these affect the preserved condition of a site and the integrity of archaeological remains. The fluvio‐lacustrine sequences in the Nihewan Basin of North China are rich sources of early Pleistocene archaeological sites, which offer an important opportunity to investigate human evolution and adapted behaviours in East Asia. Although many Palaeolithic sites have been reported from the Nihewan Basin, North China, few of them focus on site formation processes before interpreting the hominin behaviour patterns. Here, we present a site formation study of four archaeological layers (Layers 6D, 6C, 6B and 6A) in Trench 1 from the Donggutuo (namely DGT‐T1) site in the Nihewan Basin with an age of 1.1 Ma. Through the study of sedimentary contexts, spatial distributions of artefacts and fossils, intra‐assemblage category ratios, debitage size distributions, lithic abrasion, artifact orientation and planar dip, our results show that all the layers had been disturbed by low‐energy sheet wash across the lake shore setting, but to differing extents. The post‐depositional disturbance caused by water decreased from the lower to the upper layers, from Layer 6D to Layer 6A. This indicates that the archaeological remains in DGT‐T1 have not been subject to significant natural modifications and are thus suitable for studying early hominin behaviour in North China. Copyright © 2019 John Wiley & Sons, Ltd.     

Geoarchaeology of Pleistocene open-air sites in the Vila Nova da Barquinha-Santa Cita area (Lower Tejo River basin, central Portugal)

This paper aims to provide insight into human occupation and landscape change during the Pleistocene in a central area of the Lower Tejo basin (Portugal). Detailed geomorphological mapping, coupled with lithostratigraphy, sedimentology and luminescence dating, supports the identification of a complete terrace staircase sequence. It consists of six gravely terraces located below the culminant (Pliocene) basin unit. A chronological framework for the sedimentary sequences and associated human industries is proposed and correlated with marine oxygen isotope stages (MIS): T1 terrace, not dated; T2, not dated; T3, >300 ka; T4, ∼300-160 ka (MIS8, MIS7 and MIS6); T5, ∼136-75 ka (MIS5); T6, ∼62-30 ka (MIS3); colluvium and aeolian sands, ∼30-14 ka (MIS2); valley fill deposits, ∼14 ka to present (MIS1). The oldest artefacts were found at the base of the T4 terrace, with the local stratigraphic level dated to ≥175 ± 6 ka (Middle Pleistocene). The lithic assemblages collected from distinct stratigraphic levels (T4, T5 top, T6 terraces and colluvium) are characterized by the predominance of opportunistic technological choices, a feature that can be attributed partly to the preferential exploitation of the available raw material, dominated by local-sourced quartzites and quartz pebbles. The adaptation to local raw material (texture and volume), together with subsistence patterns and behaviours, could explain the rarity of Acheulian types (handaxes and cleavers) and picks in the T4 terraces of the Tejo tributaries; this is in contrast to the same terrace of the Tejo valley, in which these types are found. Interpretation of the environmental conditions (controlled by climate and glacio-eustatic sea-level changes) affecting the hunter-gatherer human groups is also presented.     

Importance of hydrogeological conditions during formation of the karstic bauxite deposits,Central Guizhou Province,Southwest China: A case study at Lindai deposit

Karstic bauxite deposits are widespread in Central Guizhou Province, SW China, and high-grade ores are frequently sandwiched with overlying coal and underlying iron-rich layers and form a special “coal–bauxite–iron” structure. The Lindai deposit, which is one of the most representative karstic bauxite deposits in Central Guizhou Province, was selected as a case study. Based on textural features and iron abundances, bauxite ores in the Lindai deposit are divided into three types of ores, i.e., clastic, compact, and high-iron. The bauxite ores primarily comprise diaspore, boehmite, kaolinite, illite, and hematite with minor quartz, smectite, pyrite, zircon, rutile, anatase, and feldspar. The Al₂O₃ (53–76.8 wt.%) is the main chemical contents of the bauxite ore samples in the Lindai district, followed by SiO₂, Fe₂O₃, TiO₂, CaO, MgO, S, and P etc. Our geological data on the Lindai deposit indicated that the ore-bearing rock series and its underlying stratum have similar rare earth elements distribution pattern and similar Y/Ho, Zr/Hf, and Eu/Eu¹ values; additionally, all ore-bearing rock samples are rich in MgO (range from 0.16 wt.% to 0.68 wt.%), and the plots of the dolomites and laterites lie almost on or close to the weathering line fit by the Al-bearing rocks in Zr vs. Hf and Nb vs. Ta diagrams; suggesting that the underlying Middle Cambrian Shilengshui Formation dolomite is the parent rock of bauxite resources in the Lindai district.Simulated weathering experiments on the modern laterite from the Shilengshui Formation dolomite in the Lindai bauxite deposit show that hydrogeological conditions are important for karstic bauxite formation: Si is most likely to migrate, its migration rate is several magnitudes higher than those of Al and Fe under natural conditions; the reducing inorganic acid condition is the most conducive to Al enrichment and Si removal; Fe does not migrate easily in groundwater, Al enrichment and Fe removal can occur only in acidic and reducing conditions with the presence of organic matter.The geological and experimental studies show that “coal–bauxite–iron” structure in Lindai deposit is formed under certain hydrogeological conditions, i.e., since lateritic bauxite or Al-rich laterite deposited upon the semi-closed karst depressions, Si can be continuously removed out under neutral/acidic groundwater conditions; the coal/carbonaceous rock overlying the bauxitic materials were easily oxidized to produce acidic (H₂S, H₂SO₄, etc.) and reductant groundwater with organic materials that percolated downward, resulting in enrichment of Al in underlying bauxite; it also reduced Fe³⁺ to its easily migrating form Fe²⁺, moving downward to near the basal carbonate culminated in precipitating of ferruginous (FeS₂, FeCO₃, etc.) strata of the “coal–bauxite–iron” structure. Thus, the bauxitic materials experienced Al enrichment and Si and Fe removal under above certain hydrogeological conditions forming the high-quality bauxite.     

Genesis of REE minerals in the karstic bauxite in western Guangxi,China, and its constraints on the deposit formation conditions

Karstic bauxites in western Guangxi, China, comprise two subtypes: Permian bauxite and Quaternary bauxite. The Quaternary bauxite originated from the breaking up, rolling, and accumulating of Permian bauxite in karstic depressions in Quaternary. Various types of rare earth element (REE) minerals were discovered during the formation of the Permian and Quaternary bauxites from the Xinxu, Longhe, and Tianyang bauxite deposits in this study. Five types of REE minerals, including bastnäsite, parisite, cerianite, rhabdophane, and churchite, were identified. Bastnäsite and parisite are the most abundant, and they are widely developed in the Permian ore and also present in the Quaternary ore. Obvious variations in bastnäsite and parisite REE compositions were observed, which is ascribed to distinctions in the source materials in the primary weathering profile from different areas. The mode of occurrence of bastnäsite and parisite suggests they were mainly precipitated under alkaline and reducing conditions during the Permian bauxite-forming stage and underwent intensive corrosion in the Quaternary. Churchite was formed during the Permian weathering stage under acidic condition. Both cerianite and rhabdophane occur in fractures within the Permian bauxite ore, indicating that both formed during the Quaternary weathering stage. It is considered that the rhabdophane enriched in Ce have formed locally, in the process of that the Ce^3 +, released from bastnäsite rapidly, entered the rhabdophane lattice before being oxidized to Ce^4 +. Cerianite was mainly found in association with Mn–Al hydroxides, suggesting that the released Ce^3 + was oxidized into Ce^4 + and precipitated cerianite in fractures within the Permian bauxite ore. Mass balance equations reveal a depletion in nearly all REEs during the transformation from the Permian to the Quaternary bauxite ore, mainly caused by the dissolution of bastnäsite and parisite. The genesis of the REE minerals, together with the occurrence of other minerals, indicates that intensively acidic and oxidizing conditions developed before the formation of the Permian bauxite ore. Towards the end of the Permian, the conditions became reducing and alkaline, favorable for the large-scale bauxitization. The Quaternary bauxite-forming stage was characterized by variable pH and Eh conditions, with acidic (pH = 4–6) and oxidizing (Eh > 2) conditions at the surface of the exposed Permian bauxite ore.     

Climatostratigraphy of Upper Pleistocene Vertebrates and the conditions of loess formation in Hungary

Having revised some reference vertebrate faunas from Hungary and from Central Europe their biostratigraphic positions could be determined more accurately. By extending the vole thermometer method to the continental parts of Central Europe fairly well identifiable average July temperature curves could be obtained for the Upper Pleistocene. The main events shown by the climatic curve for Hungary can be well correlated with the soil and loess complexes of the Paks loess profile, and also with the global climatostratigraphic scale.     

A micromorphological and mineralogical study of site formation processes at the late Pleistocene site of Obi‐Rakhmat,Uzbekistan

Site formation processes at the Late Pleistocene rockshelter deposit of Obi‐Rakhmat were reconstructed through soil micromorphology and Fourier transform infrared spectroscopy (FTIR). The entire sequence has undergone limited diagenesis and is well preserved. The base of the stratified sequence represents a karstic setting with intermittent, low‐energy deposition of autochthonous gravitational debris and anthropogenic material in a wet, muddy environment. These sediments were post‐depositionally affected by episodic waterlogging. The bulk of the sequence overlying the karstic layers comprises a continuous series of primary freshwater spring deposits containing reworked anthropogenic material that was buried penecontemporaneously with calcium carbonate deposition. The top of the sequence is weakly cryoturbated, indicating a periodically cold, wet environment. No alluvial elements that could suggest sediment inputs from the nearby river terraces were documented. A single exogenous layer was identified, representing an episode of colluviation from directly above the rockshelter preceding a major roofspall event. The basal part of the sequence contains slightly reworked anthropogenic remnants of intense activities, including combustion. The anthropogenic elements present in the spring deposits show higher degrees of reworking, suggesting within‐layer translocation. The development of spring activity at the site did not cause humans to abandon the rockshelter; they continued to carry out their activities throughout a changing local environment. © 2009 Wiley Periodicals, Inc.     

Genesis of the Guangou karstic bauxite deposit in western Henan,China

The Guangou bauxite deposit in western Henan, China, is located in the North China Block and to the north of the North Qinling orogenic belt. The orebody is hosted within the lower member of the Carboniferous Benxi Formation, which overlies unconformably upon the Ordovician Majiagou Formation. In the lower member of the Benxi Formation, the bauxite orebody (with a diaspore–illite–anatase mineral assemblage) is sandwiched between underlying ferric clay (illite–hematite–goethite) and overlying top clay (kaolinite–quartz–goethite). According to field observations and geochemical evidence including trace- and rare-earth-element (REE) compositions, especially Zr/Hf ratios, the ferric clays were weathered from the underlying argillaceous limestones in the Majiagou Formation. During this weathering process, trace elements S, Zn, Ni, Cr, V, Sc, F, Ba, and Be are depleted; Li, Rb, and B are enriched; and Zr, Hf, Bi, Ta, Ga, Nb, and Th are relatively immobile. REEs exhibit evident differentiation with enrichment of La, Ce, Pr, and Nd and depletion of Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. The bauxite formed in weak reducing, slightly basic water conditions according to the geneses of coexisting diaspore and anatase, and it was altered during the epigenetic and second exposure periods, forming kaolinite and goethite, respectively. Interelemental relationship analyses of the ores suggest that the elemental behaviors of trace elements and REEs in the bauxitization process are mainly controlled by the mineral compositions in bauxite ore and chemical properties of the elements. For instance, zircon, rutile, and anatase contain Zr, Hf, Nb, Ta, W, and U. Based on geochemical evidence, together with age data and chemical compositions of the detrital minerals, both distant igneous rocks in the plate margin and Paleozoic carbonates and Precambrian rocks inside North China Block provide the miscellaneous material for the bauxite ore and the top clay.     

华北平原晚更新世以来岩石地层、生物地层及气候地层

前人对华北平原晚更新世以来的地层虽有较多的研究,但由于历史的原因,其所采的样品均过稀(一般为1个样品/2 m),所以,其地层界线的划分不够精细,争论也很大。对华北平原的HG1孔和HN1孔进行了加密采样(HG1孔1个样品/0.20 m,HN1孔1个样品/0.07 m),对HN1孔还加大了其微量14C年龄的测定数量(共测试17个样品),并对HG1孔的有孔虫进行了详细鉴定,对HN1孔的有孔虫进行了高分辨率鉴别。在此基础上,对华北平原晚更新世以来的岩石地层、生物地层及气候地层进行了进一步的研究,厘定了华北平原全新世与晚更新世地层的年龄界线。与此同时,结合前人的研究成果,建立了华北平原第四纪地层的标准模式地层层系。     

Genesis of garnet-bearing rocks at the Berezitovoe deposit,Upper Amur Region,Russia

The geological position, composition of mineral assemblages, and typomorphism of major minerals from garnet-bearing rocks at the Berezitovoe gold-base-metal deposit in the Upper Amur Region have been studied in detail. These are ore-bearing metasomatic rocks and metamorphosed porphyritic dikes. The garnet-bearing metasomatic rocks reveal zoning, which is caused by various degrees of metasomatic transformation of the Paleozoic porphyritic granodiorite that hosts the ore zone. The metasomatic replacement of granodiorite was accompanied by loss of Na, Ca, Ba, Sr and gain of K, Mn, and Rb. Garnet-bearing metamorphosed intermediate dikes occur within the metasomatic zone. The PT conditions of metamorphism and metasomatism are similar and estimated at 3.9 kbar and 500°C from various mineral equilibria. The results of physicochemical simulation of garnet-bearing mineral assemblages carried out by minimizing the Gibbs free energy and the geological data show that garnet-bearing mineral assemblages arose at the Berezitovoe deposit as a result of local high-temperature thermal metamorphism of previously formed low-temperature metasomatic rocks close in composition to classic beresite. In this connection, we propose considering garnet-bearing metasomatic rocks as high-temperature metamorphosed beresites.     

Fluid chemistry and processes at the Porgera gold deposit, Papua New Guinea

The Porgera gold deposit in Papua New Guinea is a world-class example of an alkalic-type epithermal gold system (stage II), which overprints a precursor stage of magmatic-hydrothermal gold mineralization (stage I). Gas and ion chromatographic analyses of fluid inclusions contained in vein minerals from both mineralization stages have been carried out in order to constrain the compositions of the fluids involved in, and the processes attending, ore deposition. These data indicate the presence of three end-member liquids, the most dilute of which was present throughout the mineralization history and is interpreted to represent evolved groundwater of meteoric origin. Its composition is estimated to have been approximately 500 mM Na⁺, 10 mM K⁺, 5 mM Li⁺, 250 mM Cl⁻, 0.15 mM Br⁻, and 0.01 mM I⁻, plus significant concentrations of dissolved gases. More saline liquids were also present during the two main stages of ore formation, and although their compositions differ, both are interpreted to have been derived at least in part from magmatic fluids, and to have been the media by which gold was introduced into the system. Stage I minerals contain fluid inclusions which decrease in salinity towards this dilute end-member composition through the vein paragenesis, reflecting progressive dilution at depth of the magmatic fluid source by groundwaters. Ore deposition is thought to have been caused largely by simple cooling and/or wallrock reactions, although limited in situ fluid mixing may also have occurred. The most saline fluids, present in early quartz and pyrite, contain at least 810 mM Na⁺, 530 mM Ca²⁺, 130 mM K⁺, 12 mM Li⁺, 87 mM SO₄ ²⁻, 960 mM Cl⁻, 1.1 mM Br⁻, and 0.05 mM I⁻, plus significant but variable concentrations of dissolved gases. Fluid inclusions from stage II hydraulic breccia veins reveal the presence of two distinct liquids with contrasting salinities, which were present at different times during vein formation. A higher salinity liquid appears to have predominated during mineralization, whereas lower salinity groundwaters filled the structures during intervening periods. The ore-forming fluid may have been forcibly injected into the veins from depth during fracturing and depressurization events, displacing the resident groundwaters in the process. The original composition of this fluid is estimated to have been at least 1770 mM Na⁺, 59 mM K⁺, 180 mM Li⁺, 210 mM SO₄ ²⁻, 680 mM Cl⁻, 1.4 mM Br⁻, and 0.09 mM I⁻, plus 1.5 mol% CO₂, 0.19 mol% CH₄, and 0.04 mol% N₂. Gas chromatographic analyses of fluid inclusions from stage II samples show a decrease in total gas content between early unmineralized veins and post-mineralization vuggy quartz (suitable samples could not be obtained from the ore stage itself). Post-mineralization samples plot along an experimental gas-saturation curve in the CO₂-CH₄-H₂O-NaCl system, obtained at conditions similar to those attending stage II ore deposition at Porgera (200–300 bar, ˜165 °C). These results are interpreted to indicate a period of depressurization-induced phase separation during hydraulic fracturing, which resulted in rich ore deposition. Volatile gases such as CH₄ and N₂, in addition to CO₂ in solution, are shown to have a significant negative effect on total gas solubility. This effect may be of critical importance in lowering the temperature and increasing the depth (pressure) at which phase separation can occur in epithermal systems. Received: 28 November 1995 / Accepted: 17 July 1996     

内蒙古河套盆地晚更新世地层划分、环境演变及黄河的贯通

内蒙古河套盆地为受断裂控制形成的新生代断陷盆地,盆地中积水成湖,称河套古湖。晚更新世时期,河套古湖为继承性闭塞型断陷湖。上更新统主要为湖泊沉积体系,地层划分建组为上部东河村组、中部万水泉组、下部达拉特组。达拉特组在湖盆连续沉降条件及半深湖深湖中硫酸盐型、碳酸盐型湖水交替环境下沉积形成。万水泉组在湖盆沉降速率与沉积速率大体平衡条件及浅湖半深湖中半咸水湖环境下沉积形成。东河村组在湖盆沉降速率小于沉积速率条件下以及半咸水湖、局部时期为碳酸盐湖环境下的滨浅湖中沉积形成。晚更新世末期,河套古湖处于大湖水期,晋陕内蒙古交界处河流袭夺、河套盆地北侧山前断裂强烈活动和超强地震导致河套古湖湖水快速外泄,银川盆地、河套盆地、晋陕峡谷贯通而形成今日黄河河道。     

Stratigraphy of Upper Cretaceous and Cenozoic deposits of the Bakchar iron ore deposit (southwestern Siberia): New data

The results of complex palynological and microfaunistic studies of Upper Cretaceous and Cenozoic deposits of the Bakchar iron ore deposit are presented. Geochronologically, the age of the deposits varies from Campanian to Quaternary. It was established that the Slavgorod, Gan’kino, and Jurki (?) formations contain four biostratons in the rank of beds with dinocysts and three biostratons in the rank of beds with spores and pollen. The Cenozoic continental deposits contain four biostratons in the rank of beds, containing spores and pollen. As a result of the study, a large stratigraphic gap in the Cretaceous–Paleogene boundary deposits, covering a significant part of the Maastrichtian, Paleocene, Ypresian, and Lutetian stages of the Eocene, was established. The remnants of a new morphotype of heteromorphic ammonites of genus Baculites were first described in deposits of the Slavgorod Formation (preliminarily, upper Campanian). The distribution features of the different palynomorph groups in the Upper Cretaceous–Cenozoic deposits in the area of study due to transgressive-regressive cycles and climate fluctuations were revealed.     

OSL ages and possible bioturbation signals at the Upper Paleolithic site of Lagoa do Bordoal,Algarve, Portugal

Three sediment samples were collected from a soil profile at the Lagoa do Bordoal site, Algarve, Portugal. Quartz extracted from soil horizons within the profile, was optically dated using the single-aliquot regenerative-dose (SAR) protocol outlined by Murray and Wintle (Radiation Measurements 5 (2000) 523). The optically stimulated luminescence (OSL) emitted by quartz within the 90–150 μm size range was measured using three aliquot sizes. The equivalent doses (D_E) that were obtained show an asymmetric distribution. As the numbers of grains in each aliquot are reduced, the distribution of doses is clearly shifted to lower D_E values including zero doses on single grain aliquots. This shift is accompanied by an increase in the asymmetry of the distribution. These patterns indicate that as the aliquot size decreases, the distributions are increasingly characterized by aliquots with lower D_E's. With respect to the present day modern surface, this shift is most evident in the sample collected from a depth of 37 cm, within an ancient B-horizon. It is least evident in the sample located only 10 cm below it, within a sand unit. An asymmetric distribution of D_E's can be a result of a large number of grains that were well bleached at burial being mixed with a small number of grains that were partially bleached at that time (Radiation Measurements 30 (1999) 207). However, the shift in D_E's that is seen in the Lagoa East samples is most likely due to the postburial downward movement of fully and partially bleached grains from the surface, with possible contributions from the downward movement of grains that received low doses while buried in overlying horizons. The simplest explanation for our results is that grains carrying zero or small D_E's have been moved downward during bioturbation events. These results suggest that downward bioturbation in ancient soil profiles can be identified based on the OSL characteristics of quartz grains. We are also able to provide a minimum age of 24.4±3.2 ka for the Upper Palaeolithic lithic assemblage at the site.