Fossil Rotifers and the Early Colonization of an Antarctic Lake

Early Holocene sediments from a continental Antarctic lake (Ace Lake, Vestfold Hills, East Antarctica) contained abundant fossil rotifers of the genus Notholca. The fossil is similar to specimens of Notholca sp. present in modern-day Ace Lake and other fresh and brackish lakes of the Vestfold Hills. Cyanobacteria and protists (chrysophyte cysts, dinoflagellate cysts, and rhizopod tests) were also recovered from the core samples. These sediments were deposited early in the freshwater phase of Ace Lake, soon after deglaciation of the area. The occurrence of this trophically diverse assemblage of organisms at an early stage in the evolution of the lake suggests either that they were part of an endemic Antarctic flora and fauna which pre-dated the last glacial maximum and survived in glacial refugia or that efficient intercontinental dispersal had occurred.     

柴达木盆地察尔汗贝壳堤剖面年代学研究*

利用常规¹⁴ C、加速器(AMS)和²³⁰ Th等测年方法,对位于青藏高原东北部柴达木盆地察尔汗古湖贝壳堤剖面化石贝壳、湖泊沉积(包括现代沉积)样品有机质(包括碱性残留和胡敏酸组分)、碳酸盐(CaCO₃)和剖面顶部石盐(NaCl)晶体在不同实验室进行了系统的实验研究,探讨了不同样品测年结果的可靠性和精确性,并通过与已有研究结果的对比,对柴达木盆地贝壳堤剖面记录的察尔汗古湖高湖面演化历史进行了探讨,得出察尔汗古湖高湖面形成于约39.7~17.5 ¹⁴ C kaB.P. ; 研究证明柴达木盆地沉积物中有机质含量很低,且主要来源于菌藻类等低等藻类和微生物,受老碳和溶解物质影响强烈,因此必须经过多种方法综合测年才能比较可靠地确定所测样品的形成年代; 测年结果的不确定性不仅来源于样品自身元素(同位素)的特性和沉积过程中再沉积作用的影响,也可能源自于放射性¹⁴ C产生过程的不稳定性; 对比发现贝壳化石老于同层位有机质¹⁴ C年龄15~18ka,这可能与柴达木盆地所处的特殊地理位置和巨大的古湖泊面积及水体有关; 同时,不平衡铀系测年在确定开放体系矿物晶体年代应用中的可靠性尚须进一步深入分析,其机理也还需要探讨和实验研究。     

Radiocarbon chronology of Holocene hydrologic changes in northeastern Mali

A detailed chronology of hydrological changes that occurred in northeastern Mali during the Holocene is based on approximately 30 ¹⁴C dates of molluscs which were collected from the lacustrine and paludal deposits of the Ine Sakane sand sea. The presence of cemented paleodunes indicates that the end of the Pleistocene was and arid period. This was followed by an early Holocene lacustrine episode (ca. 9500–6500 yr B.P.) during which numerous lakes occupied depressions formed in the Cretaceous limestones and between the sand ridges. These lakes reflect a significant rise in the water table. Between ca. 6500 and 5500 yr B.P. the lakes dried up, although the water table remained close to the ground surface in several areas. Calcareous concretions formed at the water table fringe during this time, thereby “fossilizing” some of the middle Holocene dunes. A second lacustrine episode is dated between ca. 5500 and 4500 yr B.P.; it corresponds to the establishment of numerous Neolithic settlements in the area. Arid conditions have developed since about 4500 yr B.P. to attain the conditions of the present day. The isotopic composition (¹⁸O and ¹³C) of the fauna reflects highly variable hydrological conditions. Groundwaters were recharged by precipitation which was occasionally very depleted in heavy oxygen (δ¹⁸O ? ?13%.). Evaporation induced an enrichment in ¹⁸O; high concentrations characterize some lakes. The ¹³C content of fossil shells reflect: (1) species ecological requirements, (2) isotopic composition of the total inorganic dissolved carbon (TIDC) in groundwaters, and (3) the lake metabolism.     

The last glacial cycles in East Greenland, an overview

Marine, fluvial and glacigene sediments exposed in coastal cliffs and stream-cut sections in East Greenland between latitudes 69° and 78° N display a record of Quaternary climatic and environmental change going back to pre-Saalian times (> 240 ka), but with main emphasis on the last interglacial/glacial cycle. The stratigraphical scheme is based on studies on the Jameson Land peninsula, and contains five glacial stages and stades with the Greenland ice sheet or its outlets reaching the outer coasts. Individual sites are correlated and dated by a combination of biostratigraphy, luminescence dating, amino acid analyses, as well as ¹⁴C- and uranium series dating. The pre-Weichselian Lollandselv and Scoresby Sund glaciations were the most extensive. During the Weichselian the Inland Ice margin in this part of East Greenland was apparently very stable. The Aucellaelv, Jyllandselv and Flakkerhuk stades mark the advance and subsequent retreat of outlet glaciers from the Inland Ice which advanced through the wide Scoresby Sund basin and reached the inner shelf. In-between the glacier advances, three interglacial or interstadial periods have been recognized. During the Langelandselv interglacia-tion (≅ Eemian) the advection of warm Atlantic water was higher than during the Holocene, and the terrestrial flora and insect faunas show that summer temperatures were 3–4°C higher than during the Holocene optimum. There is no unambiguous evidence for cooling in the sediments from this interval. Later, in isotope stage 5, there were apparently two ice-free periods. During the Hugin Sø interstade, stable Polar water dominated Scoresby Sund, and the terrestrial flora suggests summer temperatures 2° -3° lower than the present. The marine and fluvial sediments from the second ice-free period, the Mønselv interstade, are devoid of organic remains.     

Age and significance of fossil white spruce (Picea glauca), Tunica Hills, Louisiana-Mississippi

Radiocarbon dates indicate a Farmdalian through Woodfordian age for fossil white spruce (Picea glauca) in the Tunica Hills, a greater time span than previously documented. These dates, furthermore, require revision of the ages of fluvial terrace deposits in the region. Spruce-bearing Terrace 1 sediments, previously regarded as late Woodfordian to Holocene age, are of Farmdalian to late Holocene age. Terrace 2 sediments, previously assigned a Sangamonian or Farmdalian age, are of probable Altonian age. Plant fossils in Terrace 1 sediments represent two climatically and temporally distinct assemblages: a cool-temperate, Farmdalian-Woodfordian assemblage dominated by white spruce but including deciduous hardwoods suggestive of an oak-hickory association; and a warm-temperate Holocene assemblage composed of southern hardwoods and nonarboreal species representative of the modern flora of the Tunica Hills. Locally, fossils of white spruce have been reworked into younger Terrace 1 sediments containing the warm-temperate plant assemblage. The transition from the cool-temperate flora to the modern warm-temperate flora in the Tunica Hills probably occurred around 12,000 yr B.P.     

关中地区2万年以来黄土序列中蜗牛化石及其有机质的14C AMS测年初探

前人在黄土—古土壤地层的¹⁴C年代学研究中,探讨了不同测年物质的可靠性,但不同物质组分获得的年代差异较大,这是由于选用的样品不符合定年条件,所以选择可靠的样品组分和有效的前处理方法显得尤为重要。对关中地区2万年以来黄土序列中有机质、花粉浓缩物和蜗牛化石进行了AMS¹⁴C年代学研究。运用现生蜗牛壳体的AMS¹⁴C测定来校正化石蜗牛的年龄,结合剖面中孢粉浓缩物、土壤有机质的AMS¹⁴C年代学对比研究,发现蜗牛化石壳体的文石可以提供较可靠的年代数据,为¹⁴C测年的可靠性研究提供了一种可能的途径。     

河海交互作用与苏北平原成因*

苏北平原向海侧分布着大冈、上冈两列古贝壳堤以及依此而建的范公堤;西侧有低山丘陵环绕,江淮水系河流汇入平原内侧的湖泊群,发育了伸出型三角洲;兴化、里下河地区是平原的最低洼处。这一系列地貌组合与分布特点,启迪着探究平原的成因。146m深的宝应望直港钻孔,穿透了2.58Ma以来的第四纪地层。沉积相、微体古生物、古地磁测定与沉积层常量元素分析等综合研究,阐明了4次主要的海洋作用沉积环境,尤其是晚更新世3.9~2.6万年前的浅海环境沉积更为显著。河湖相泛滥平原沉积与潮滩浅海沉积交互成层,证实了苏北平原是第四纪时期由河-海交互作用,从古海湾发育堆积成宽大平原。进一步工作需探索相关时期的江-海分布变化及黄河和黄渤海通道与苏北平原发育的关系。     

Modern and Holocene carbonate sedimentology of two saline volcanic maar lakes, southern Australia

The Basin Lakes are two adjacent maar lakes located in the centre of the Western Volcanic Plains District of Victoria, Australia. Both lakes are saline and alkaline; West Basin Lake is meromictic whereas East Basin is a warm monomictic lake. The carbonate mineral suite of the modern offshore bottom sediments of these Basins consists mainly of dolomite and calcite, with smaller amounts of hydromagnesite and magnesite in West Basin and monohydrocalcite in East Basin. The dolomite, hydromagnesite, magnesite, and monohydrocalcite are endogenic in origin, being derived by primary inorganic precipitation within the water columns of the lakes or at the sediment-water interface. The calcite is biologically precipitated as ostracod valves. In addition to the carbonates in the modern offshore (deep-water) sediments, the lakes also contain a girdle of nearshore carbonate hardgrounds. Both beachrock and microbialites (algal boundstones) are present. These modern lithified carbonate units exhibit a wide range of depositional and diagenetic fabrics, morphologies and compositions. In West Basin, the hardgrounds are composed mainly of dolomite, hydromagnesite, and magnesite, whereas dolomite and monohydrocalcite dominate the East Basin sediments. Aragonite, high-Mg calcite, kutnahorite, siderite, and protohydromagnesite also occur in these lithified carbonate units. Stratigraphic variations in the carbonate mineralogy of the Holocene sediment record in the lakes were used to help decipher the palaeochemistry and palaeohydrology of the Basins. These changes, in conjunction with fluctuations in organic remains and fossil content, indicate a pattern of lake level histories similar to that deciphered from other maar lakes in western Victoria.     

The late Quaternary limnological history of Lake Kinneret (Sea of Galilee), Israel

The freshwater Lake Kinneret (Sea of Galilee) and the hypersaline Dead Sea are remnant lakes, evolved from ancient water bodies that filled the tectonic depressions along the Dead Sea Transform (DST) during the Neogene-Quartenary periods. We reconstructed the limnological history (level and composition) of Lake Kinneret during the past ∼40,000 years and compared it with the history of the contemporaneous Lake Lisan from the aspect of the regional and global climate history. The lake level reconstruction was achieved through a chronological and sedimentological investigation of exposed sedimentary sections in the Kinnarot basin trenches and cores drilled at the Ohalo II archeological site. Shoreline chronology was established by radiocarbon dating of organic remains and of Melanopsis shells.The major changes in Lake Kinneret level were synchronous with those of the southern Lake Lisan. Both lakes dropped significantly ∼42,000, ∼30,000, 23,800, and 13,000 yr ago and rose ∼39,000, 26,000, 5000, and 1600 yr ago. Between 26,000 and 24,000 yr ago, the lakes merged into a unified water body and lake level achieved its maximum stand of ∼170 m below mean sea level (m bsl). Nevertheless, the fresh and saline water properties of Lake Kinneret and Lake Lisan, respectively, have been preserved throughout the 40,000 years studied. Calcium carbonate was always deposited as calcite in Lake Kinneret and as aragonite in Lake Lisan-Dead Sea, indicating that the Dead Sea brine (which supports aragonite production) never reached or affected Lake Kinneret, even during the period of lake high stand and convergence. The synchronous level fluctuation of lakes Kinneret, Lisan, and the Holocene Dead Sea is consistent with the dominance of the Atlantic-Mediterranean rain system on the catchment of the basin and the regional hydrology. The major drops in Lake Kinneret-Lisan levels coincide with the timing of cold spells in the North Atlantic that caused a shut down of rains in the East Mediterranean and the lakes drainage area.     

Quaternary paleoecology of the Lower Mississippi Valley

In 1938, Clair A. Brown published his classic paleobotanical discoveries from the Tunica Hills of southeastern Louisiana, indicating ice-age plant migrations of more than 1100 km. Brown collected fossils of both boreal trees such as white spruce (Picea glauca) and southern coastal plain plants from deposits mapped as the Port Hickey (Prairie) river terrace by Harold N. Fisk. Subsequent revisions of terrace mapping, radiocarbon dating, and paleoecological analysis reconciled Brown's conceptual and stratigraphic “mixing” of these two ecologically incompatible fossil plant groups. An older Terrace 2 (of Sangamonian to Altonian age) contains the warm-temperate assemblage. A younger Terrace 1 (of Farmdalian, Woodfordian, and Holocene age) includes full-glacial and late-glacial remains of both boreal and cool-temperate plants; and a warm-temperate suite of plants dates from the Holocene interglacial. New plant fossil localities with radiocarbon chronologies are now available from within the Lower Mississippi Valley of Missouri and Arkansas as well as from the adjacent Ozark Plateaus, the Interior Low Plateaus of Kentucky and Tennessee, and the bordering Blufflands of Tennessee, Mississippi, and Louisiana. These studies demonstrate that glacial and interglacial patterns of vegetation have been influenced by regional changes in climate, glacial runoff, and regime of the Mississippi River.     

Late Holocene tephrochronology of the northern Antarctic Peninsula

Andesitic and basaltic andesitic tephra layers are abundant in Holocene deposits from the Antarctic Peninsula. Visually discernible tephra horizons occur in three lakes on Livingston Island. Tephra in two other lakes and in a moss bank on Elephant Island, with very low ash concentrations, were detected magnetically. Deception Island is the most likely volcanic source for the tephra. With direct ¹⁴C dating, age/depth curves, and cross-correlations at least 14 tephra horizons dating to between ca. 4700 and 250 yr B.P. were identified and now form the basis for a preliminary regional tephrochronology that will be a valuable dating tool for investigating the Holocene climatic history of Antarctica.     

Modern and early Holocene mollusc fauna of the Ounianga lakes (northern Chad): implications for the palaeohydrology of the central Sahara

The fresh and saline lakes of Ounianga Kebir and Serir in northeastern Chad are among the very few permanent aquatic ecosystems currently existing in the hyper‐arid core of the Sahara desert. The confirmed modern fauna of aquatic molluscs at Ounianga comprises three widespread species (Melanoides tuberculata, Biomphalaria pfeifferi and Lymnaea natalensis), of which only the first appears to maintain a thriving population. We recovered seven more species of gastropods, among which one is new to science (Gabbiella ouniangaensis), and one bivalve species from early Holocene outcrops of diatomaceous limestone at Ounianga Serir. All species except one are known to be commonly spread between lake and river systems by birds, and in its entirety this species‐rich fossil mollusc fauna of Ounianga Serir resembles that of other Saharan lake sites known to have been hydrologically isolated during the early Holocene. The impoverished modern mollusc fauna, which lacks even the widespread and opportunistic species Bulinus truncatus, may have become established relatively recently through new colonisation events, following eradication of the early Holocene mollusc fauna during a later episode of high salinity or desiccation. Copyright © 2011 John Wiley & Sons, Ltd.     

渤海湾西北岸大吴庄牡蛎礁测年与古环境变化

对位于渤海湾牡蛎礁平原东部的大吴庄牡蛎礁一个完整剖面的系统^14C年代测定与校正表明,该礁体的持续时间约为1600年(7200～5600calBP)。以壳体生长纹层氧、碳同位素获得的礁体平均建造速率1cm／yr来计算礁体的持续时间,结果仅为^14C计年历时的三分之一。^14C测年与壳体同位素计年结果的对比表明,礁体的每一水平层平均占据了一定的时间(约200年),这一时间段是不适宜礁体正常建造的“缓变型地质环境恶化期”。礁体正常建礁层及水平夹层的时空分布与地区性气候变化曲线对比结果表明,水平夹层与正常建礁层的转换与地区性气温波动相对应。水平夹层代表的“缓变型地质环境恶化期”,对应着地区性气温偏冷时期。     

Sample-size implications of the trace-element variability of ostracod shells

The magnesium and strontium contents of fossil ostracod-shell calcite have been used extensively in the reconstruction of water composition and temperature in lakes and, to a lesser degree, in marginal-marine waters and in the deep ocean. Current instrumentation may allow single shells of these calcite microfossils to be analysed and most studies have taken advantage of this capability. However, there is now good evidence for large intra-sample variability in the trace-element content of ostracod shells, both in living populations and in fossil assemblages, and this has implications for any attempt to distinguish the low-frequency (∼decadal or longer) trends in water temperature and composition that are often the goals of palaeoenvironmental studies, from higher-frequency (seasonal or interannual) ‘noise’. In this study, the Mg and Sr contents of living and fossil populations of six species of marine, marginal-marine and shallow-marine ostracods from 11 sites are used to investigate sources of variability and to estimate critical sample sizes for stratigraphic studies. Results confirm that variability amongst individual samples is generally wide and cannot be attributed to instrumental error or sample handling alone. In some instances, variability can be explained by fluctuations in water composition and/or temperature, although this has to be evaluated in each case. Some evidence points to non-environmental control on variability in shell composition, perhaps connected to genetically-controlled differences in physiology that affected calcification, early diagenetic alteration, or the role of environmental factors other than temperature or water composition. However, further work is needed to verify this. In some stratigraphic studies, large numbers (>20) of individual shells would need to be analysed in order to detect low-frequency environmental changes with any degree of confidence, although fewer shells may often suffice. The critical sample size depends on the variability at each study site, which should ideally be evaluated using pilot studies.     

A regional-scale climate reconstruction of the last 4000 years from lakes in the Nebraska Sand Hills,USA

High-resolution paleohydrological reconstructions were carried out in five shallow lakes in the Nebraska Sand Hills across an east–west transect in order to 1) determine whether long-term droughts of the past 4000 years were spatially and temporally coherent across the region, 2) distinguish local variation in climate or hydrology from regional patterns of change, and 3) compare the paleolimnological results with the existing dune-inferred drought records. Diatom-inferred lake-level was reconstructed for all sites and compared with other regional records. Alterations between high and low lake-levels were frequent during the past 4000 years, which suggests that shifts between dry and wet periods were prevalent across the Sand Hills. Extended multi-decadal to centennial-scale droughts were more common prior to 2000 years BP, while the last two millennia were hydrologically more variable and climate conditions alternated on shorter timescales. Despite some discrepancies among the five records, the paleohydrological reconstructions refine the Holocene drought history of the Nebraska Sand Hills, particularly between ～2200 and 4000 cal a BP. Many of the observed drought events are contemporaneous with severe droughts documented at sites in the northern Great Plains and Rocky Mountains, lending support for the severity and regional significance of these events in western North America.     

Climate and environment on the Karelian Isthmus, northwestern Russia, 13000-9000 cal. yrs BP

Sediment sequences retrieved from Lake Medvedevskoye (60°13'N; 29°54'E) and Lake Pastorskoye (60°13'N; 30°02'E), Karelian Isthmus, northwestern Russia, were analysed for lithology, pollen and diatom stratigraphy, total organic carbon content and mineral magnetic parameters. Age control for both sequences was provided by AMS ¹⁴C measurements and the Vedde Ash tephra. The reconstructed climatic and environmental development shows the deglaciation of the sites and the establishment of sparse shrub and herb/grass vegetation before 12650 cal. yrs BP ('Allerød'; GI-1a). Steppe tundra and cold, dry conditions prevailed until about 11000 cal. yrs BP, i.e. throughout the 'Younger Dryas' (GS-1) and the earliest Holocene. The establishment of open Picea-Pinus-Betula forest around the lakes at about 11 000 cal. yrs BP coincides with the first distinct change towards gradually warmer and more humid climatic conditions. Boreal forest with Picea, Pinus, Betula, Alnus incana and Corylus was present at the lower altitude site between c. 10700 and 10200 cal. yrs BP, while open Betula-Pinus forest continued to dominate the vegetation around the higher altitude site. After a short, possibly colder, phase around 10200-10000 cal. yrs BP, which is expressed by a marked reduction in vegetation cover and decreased lake productivity, climatic conditions became significantly warmer and possibly more humid. Boreal forest with Pinus, Betula, Picea, Alnus incana, Corylus and Ulmus became widespread in the region after 10000 cal. yrs BP. The delayed environmental response of the lakes and their catchment to hemispheric warming at the Pleistocene/Holocene boundary may be explained by a sustained blocking of westerly air masses due to the presence of the Scandinavian ice sheet and associated strengthened easterlies and anticy-clonic circulation and/or extensive permafrost.     

Sedimentation Rates in Lakes of the Caucasus and Their Changes in the Late Holocene

Doklady Earth Sciences - The sedimentation rates in lakes of the Caucasus in the Late Holocene are estimated on the basis of radioisotopic dating. The lakes are located in different altitude zones....     

Holocene environmental reconstruction from deltaic deposits in northeast Greenland

Terraces of different age in the Zackenberg delta, located at 74°N in northeast Greenland, have provided the opportunity for an interdisciplinary approach to the investigation of Holocene glacial, periglacial, pedological, biological and archaeological conditions that existed during and after delta deposition. The raised Zackenberg delta accumulated mainly during the Holocene Climatic Optimum, starting slightly prior to 9500 cal. yr BP (30 m a.s.l.) and continued until at least 6300 cal. yr BP (0.5 m a.s.l.). Evidence of sea‐level change is based on conventional ¹⁴C dates of shells from the marine delta bottomsets, ¹⁴C AMS dating of macroscopic plant material from the foresets and of fluvial deposits. Arthropod and plant remains from 7960 cal. yr BP in the delta foresets include the oldest evidence of the arctic hare in Greenland and evidence of a rich herb flora slightly different from the modern flora. Empetrum nigrum and Salix herbacea remains indicate a summer temperature at least as high as today during delta deposition. Post‐depositional nivation activity, dated by luminescence, lichenometry and Schmidt Hammer measurements indicate mainly late Holocene activity, at least since 2900 yr BP, including Little Ice Age (LIA) avalanche activity. Pedological analyses of fossil podsols in the Zackenberg delta, including ¹⁴C AMS dating of selected organic rich B‐horizons, show continued podsol development during the Holocene Climatic Optimum and into the subsequent colder period of the late Holocene, until 3000–2400 yr BP. A Neo‐Eskimo house ruin found on the lower part of the delta, presently being eroded by the sea, is dated to AD 1800. It presumably was abandoned prior to AD 1869, and suggests that some of the last Eskimos that lived in northeast Greenland might have occupied the Zackenberg delta. Copyright © 2002 John Wiley & Sons, Ltd.     

Chronology of the shell bar section and a discussion on the ages of the Late Pleistocene lacustrine deposits in the paleolake Qarhan, Qaidam basin

Shell bar, composed of abundant fossil shells of Corbicula fluminea müller and Corbicula largillierti philippi and located at the southeastern end (36°30′N, 96°12′E) of the paleolake Quarhan, is one of the most prominent features in the Qaidam basin. It is the highest site where such species of fossil shells have been found in the Late Pleistocene age. A 2.6-m-thick fresh profile was manually excavated to determine the formation ages and the scope of the high paleolake levels. Accelerator mass spectrometry (AMS), conventional radiocarbon dating, and sector inductively coupled plasma-mass spectroscopy ²³⁰Th methods were used to investigate the reliability and accuracy of dating results in different laboratories. Ages of various components (e.g. acid residual and acid soluble fraction of the organic matter) from the same sample were determined. Age differences of a variety of materials (e.g. organic matter, fossil shells, and salt crystals), and age differences at the same sampling position were evaluated. Dating shows that the AMS ages given by alkali residue and acid soluble fractions vary greatly, e.g., from 124.5 cm upwards. The dates given by the acid soluble fraction were normal. Down the column, the dates show a reverse pattern and those of alkali residues, especially the lower part of the section, show an unstable pattern. These imply that organic matter had been influenced by two separate processes. One possible explanation is that the alkali residual fraction most likely had been contaminated by dead carbon-bearing reworked material because the study section is located near the edge of the paleolake and could have been easily influenced by old eroded deposits. Another is that the acid soluble fraction could have been contaminated by upward-flowing groundwater containing soluble organic matter. The amount of this soluble organic material should be very small because the strongest age reversal is in the lower part, where the TOC content remains low, meaning that the change of soluble organic fraction alters neither TOC content nor the δ ¹³C dramatically. It is concluded that a uniform mega-paleolake developed in the Qaidam basin in the northeastern Tibetan plateau between 39.7 and 17.5 ¹⁴C kaB.P. During the period when the high paleolake level of Qarhan was formed, the huge paleolake covered a vast area with dramatic lake level fluctuations. It is found that the ages determined may be influenced by either radioactive ¹⁴C variations of repeated deposition or content variations in the atmosphere. The ages given by fossil shells are 15–18 ka older than those given by organic matter. The large differences between the ages of fossil shells and organic matter might have resulted from the large water areas and huge water volume and the special location of the high-elevation Qaidam basin. This study also shows the reliability and accuracy of the ²³⁰Th dating method on the salt crystals but further study is needed to determine whether this method could be applied to the study area. __________ Translated from Quaternary Sciences, 2007, 27(4): 511–521 [译自: 第四纪研究]     

Holocene molluscs from archaeological sites of the Pampean region of Argentina: Approaches to past human uses

The aim of this study is to provide a regional review and update our knowledge of molluscan records from Late Quaternary (12.2–0.4 ka B.P.) archaeological sites of the Pampean region. Comparisons with molluscs from the modern littoral, Holocene beach ridges, and estuarine sediments are made, allowing a synthesis of the main taxa recovered and reinterpretations of the probable past human uses. Overall, the biological and archaeological data gathered reinforce the conclusion that most taxa living far from the intertidal zone were not linked to subsistence of Pampean hunter‐gatherers. However, sporadic consumption cannot be discarded, considering the sea‐level changes during the Holocene. Other uses including ornamentation, containers, tools, or symbolic meaning can be assigned to marine molluscs which were probably collected as dead shells from the fossil deposits or from the contemporary beach. Selection of the shells by humans related mainly to shell size, shape, and color, and not to their nutritional value. © 2009 Wiley Periodicals, Inc.