Geochronological Methods Research Articles

Dating recent sediments from the subaqueous Yangtze Delta and adjacent continental shelf, China

In this study we analyzed sediment lithology, fallout of 210Pb and 137Cs, and spheroidal carbonaceous particles (SCPs) for two short cores, YZE and CX38, obtained by gravity corer from the Yangtze River mouth offshore and adjacent continental shelf, to compare geochronological methods on the recent sediments of this area. Lithology and grain size changes in YZE suggested the re-discharging of the North Channel of the Yangtze River mouth by flood events during 1949–1954 and associated accretion in the offshore area. This event was validated by a remarkable zone of declination in both 137Cs and 210Pb activities and the absolute ages derived from the 137Cs and SCPs. In contrast, 210Pb results show obvious disturbance of grain size by sediment mixing and cannot be interpreted above 100cm. In CX38, absolute ages for the early- and mid-1950s were derived by the 137Cs and the SCP profile respectively, which occurred in a reasonable sequence. The excess 210Pb distribution shows exponentially decreasing activities with depth, and the mean sedimentation rate agrees roughly with the one inferred from the SCP profile. We suggest that the limitation of the 210Pb method needs consideration while the SCP profile has the potential to provide a useful and independent dating method for recent Yangtze offshore and adjacent shelf sediments.

Provenance of Palaeo‐Rhine sediments from zircon thermochronology, geochemistry, U/Pb dating and heavy mineral assemblages

AbstractSediments deposited in the Late Cenozoic basins of the Central European Rift System, including the Upper Rhine Graben (URG) and the Lower Rhine Embayment (LRE), document the drastic extension of the Rhine's catchment towards the Central Alps in the Late Pliocene by distinct heavy mineral assemblages. This outstanding change in principal sediment sources should be accompanied by a change towards distinctly younger (i.e. Tertiary) detrital mineral cooling ages. Therefore, it provides a particularly well‐suited framework to explore the thermochronological provenance record in relation to heavy mineral assemblages. In this multi‐proxy approach we (i) exploit and elaborate detrital zircon (U–Th)/He thermochronology (ZHe) for sediment provenance surveys, (ii) document shortcomings if only a single geochronological method is employed, and (iii) obtain tighter constraints on the sources of Paleo‐Rhine sediments. Our results are based on Pliocene and Pleistocene sediment samples from the northern URG (drill core Ludwigshafen P36) and the LRE (lignite mine Hambach). In a Late Pliocene URG sample, Variscan and Permo‐Triassic cooling ages dominate the age spectra of the ZHe and Zircon fission track (ZFT) thermochronometers. The youngest ages are Late Cretaceous and these zircons show rare earth element signatures that suggest derivation from hydrothermally affected basement rocks of the URG margins. In contrast, a Lower Pleistocene URG sample contains significant Tertiary age components that unequivocally indicate Alpine sources. This cardinal difference coincides well with a significant change in the heavy mineral assemblage. The extension of the catchment of the Rhine towards the Central Alps is considered to occur no earlier than the latest Pliocene (i.e. after ~3.0 Ma). Despite strongly contrasting heavy mineral compositions, the Pliocene and Pleistocene samples from the LRE show largely similar ZHe and ZFT age distributions dominated by Permo‐Triassic and Variscan ages. Admixture of zircon‐dominated, but overall heavy mineral‐poor sediment derived from local drainages of the Rhenish Massif likely explains this apparent contradiction in sediment provenance proxies. Tertiary cooling ages occur in both Pliocene and Pleistocene LRE samples. Zircon Th/U ratios and U/Pb ages reveal that the young age component in Late Pliocene sediments from the LRE is not derived from the Alps but from Oligocene trachytic members of the Central European volcanic centres of the Vogelsberg, Westerwald, and/or Siebengebirge. The integration of ZHe and ZFT techniques with zircon geochemistry and U/Pb geochronology adds the respective advantages of each method and allows for a very detailed picture of detrital zircon provenance.

A determinação da idade das rochas

Em pouco mais de 200 anos, a idade da Terra admitida pela ciência passou de alguns milhares para cerca de 4,56 bilhões de anos. Muitas analogias são empregadas para facilitar a compreensão dos conceitos de “tempo profundo” ou “abismo do tempo” mas, não obstante, essas idéias permanecem de difícil assimilação, pois as escalas e relações envolvidas são incomuns e freqüentemente complexas. A profunda inflexão no pensamento, e até mesmo na perspectiva humana, sobre a idade da Terra, decorre do amadurecimento da Geologia como ciência. Métodos específicos são necessários para determinação de idades de rochas e sua aplicação mais direta: o estudo do tempo geológico. Os métodos estratigráficos, paleontológicos e geocronológicos são empregadosmuitas vezes de forma integrada, para garantir resultados confiáveis; constituem parte essencial do conceito moderno de Geociências ou de Ciências da Terra. É conveniente fazer um estudo dos princípios teóricos e das principais - e acaloradas - polêmicas envolvidas, para se compreender de que modo o conhecimento acumulado a partir desses princípios e métodos “tornou” o planeta tão antigo; são idéias que afetaram profundamente a visão atual sobre a duração e permanência da espécie humana na Terra.

Mid- and late Holocene fluvial dynamics in the tropical Guapi-Macacu catchment, Southeast Brazil: The role of climate change and human impact

Deeply incised middle to late Holocene fluvial sediments of several streams in the tropical Guapi-Macacu River catchment in the state of Rio de Janeiro were investigated with stratigraphical, sedimentological and geochronological methods. These investigations revealed multiple changes of the fluvial dynamics during the Holocene, triggered by a millennial climate change and the post-colonial increase of land use. Reduced fluvial dynamics and geomorphic stability prevailed in this region during the relatively dry mid-Holocene from 6.6 until 4.7 cal ka BP. This phase of stability was followed by a period of geomorphic activity as indicated by increased fluvial dynamics from this date. This overall environmental change corresponds well with the onset of quasi-modern humid climate conditions in southeastern Brazil during the mid- to late Holocene transition. A new period of activity has taken place since 0.29 cal ka BP, in relation with the start of European colonization and increased land use pressure. Large areas of Atlantic Forests were converted into agricultural and pasture land, causing strong soil erosion and destabilized slopes. The results of these investigations improve the existing Holocene landscape evolution model and highlight that under the given specific climatic and environmental conditions, even a closed forest cover does not necessarily result in geomorphic stability. • The study focuses on fluvial deposits as natural geoarchives in SE-Brazil. • Reduced fluvial dynamics/geomorphic stability prevailed from 6.6 to 4.7 cal ka BP. • Increased fluvial dynamics prevailed during the late Holocene (after 4.7 cal ka BP). • Fluvial dynamics were triggered by climate and anthropogenic influences. • Specific environmental conditions should be regarded in landscape evolution models.

Cova del Rinoceront (Castelldefels, Barcelona): a terrestrial record for the Last Interglacial period (MIS 5) in the Mediterranean coast of the Iberian Peninsula

The Cova del Rinoceront, a site in NE Iberia, contains a thick sedimentary fill preserving a faunal archive from the penultimate glacial and the the last interglacial periods. Layers I to III have been dated to between 74 and 147 ka, coinciding with MIS 5a to 5e, a period poorly represented in the Mediterranean terrestrial record. The results from Cova del Rinoceront are of broader interest for the reconstruction of ecological dynamics during warm stages and the understanding of the evolution and geographical variation of several taxa. The palaeoecological evidence suggests a landscape dominated by mixed wooded vegetation with mild climatic conditions, slightly more humid than today. Several vertebrate taxa, including Haploidoceros mediterraneus, Stephanorhinus hundsheimensis and Glis glis, are documented for the first time in the early Upper Pleistocene of Europe, showing that these species persisted across the region for longer than previously thought. In addition, the recovery of a small lithic assemblage indicates human presence in the surroundings of the site. The 11 m-thick stratigraphic section also provides an ideal setting in which to compare several geochronological methods. U–Th dating of the flowstones that cap the deposit, of speleothems formed along the cave walls, and of speleothems buried by the deposit at different elevations provides minimum and maximum ages of 74 and 175 ka, respectively, for the accumulation. The ages obtained by luminescence, electron spin resonance (ESR), amino acid racemisation (AAR), palaeomagnetism and U-series dating of bone are in good agreement with each other and are stratigraphically consistent. This well-dated faunal succession presents a unique opportunity to assess changes in the Pleistocene fauna of the Mediterranean coast over an interval of more than 100 ka.

Paleomagnetism of the Jurassic Transantarctic Mountains revisited — Evidence for large dispersion of apparent polar wander within less than 3 Myr

The Transantarctic mountains predominantly consist of Jurassic continental flood basalts (Kirkpatrick) and sills (Ferrar) emplaced during the earliest phase of the break-up of Pangea. Published ages, based on a variety of geochronological methods all agree rather well and cluster around 180Ma suggesting emplacement during a rather short time interval of not more than 3Myr. Paleomagnetic studies, mostly carried out between the 60s and 90s of the last century, however, yield two well defined but significantly different groups of paleomagnetic pole positions plotting either in intermediate latitudes (A) or at latitudes exceeding 60°S (B). Pole positions belonging to group A are generally interpreted to be of primary origin whereas the significance of group B poles remains unclear. Here we report new data from the Kirkpatrick basalts of Northern Victoria Land, Antarctica, where 157 oriented paleomagnetic samples were taken, covering about 800m of stratigraphy and 23 volcanic flows in Gair Mesa (73.4666°S; 162.8666°E). After removal of a steep magnetic overprint with rather low coercivities straight linear segments of exclusively normal polarity trending toward the origin of projection are identified in 151 samples from 22 sites. Maximum unblocking temperatures do not exceed 580°C and maximum coercivities not 60mT. The resulting mean virtual geomagnetic pole (VGP) for the Gair Mesa plots at 66.4°S; 227.7°E (α95 of 6.2°, k=25.7) comparable to group B poles. Reflecting light microscopy reveals that the magnetic inventory of all samples analyzed is dominated by magnetite showing shrinking cracks and broad ilmenite lamellae, the latter being diagnostic for high temperature oxidation. Analysis of the distribution of the 22 pole positions obtained here shows that secular variation has successfully been averaged (Sb=15.9°) suggesting that the rocks studied here have recorded the time averaged geomagnetic field during early mid Jurassic times. Based on these new results we postulate that both clusters A and B of pole positions reflect primary magnetizations and that the Kirkpatrick basalts of Gair Mesa have been emplaced in a rather short normal polarity time interval of 3Myr. If our reasoning is correct, the apparent polar wander path for the latest early Jurassic might be more complex than previously thought. Whether this complexity is evidence for massif True Polar Wander remains speculative.

Late Holocene glacial advance and ice shelf growth in Barilari Bay, Graham Land, west Antarctic Peninsula

Three marine sediment cores were collected along the length of the fjord axis of Barilari Bay, Graham Land, west Antarctic Peninsula (65°55′S, 64°43′W). Multi-proxy analytical results constrained by high-resolution geochronological methods ( 210 Pb, radiocarbon, 137 Cs) in concert with historical observations capture a record of Holocene paleoenvironmental variability. Our results suggest early and middle Holocene (>7022–2815 cal. [calibrated] yr B.P.) retreated glacial positions and seasonally open marine conditions with increased primary productivity. Climatic cooling increased sea ice coverage and decreased primary productivity during the Neoglacial (2815 to cal. 730 cal. yr B.P.). This climatic cooling culminated with glacial advance to maximum Holocene positions and expansion of a fjord-wide ice shelf during the Little Ice Age (LIA) (ca. 730–82 cal. yr B.P.). Seasonally open marine conditions were achieved and remnant ice shelves decayed within the context of recent rapid regional warming (82 cal. yr B.P. to present). Our findings agree with previously observed late Holocene cooling and glacial advance across the Antarctic Peninsula, suggesting that the LIA was a regionally significant event with few disparities in timing and magnitude. Comparison of the LIA Antarctic Peninsula record to the rest of the Southern Hemisphere demonstrates close synchronicity in the southeast Pacific and southern most Atlantic region but less coherence for the southwest Pacific and Indian Oceans. Comparisons with the Northern Hemisphere demonstrate that the LIA Antarctic Peninsula record was contemporaneous with pre-LIA cooling and sea ice expansion in the North Atlantic–Arctic, suggesting a global reach for these events.

The stratigraphy of the Serbian Pleistocene Corbicula beds

Fossils of non-marine molluscs are among the most prominent in continental Pleistocene deposits of Europe. With stabilization of taxonomies in the 19th century, numerous publications appeared with faunal lists of warm/temperate stage taxa, but few attempts were made to interpret the data. The goal of recent work, along with the re-evaluation of sites and their molluscan assemblages described in the literature, is to enable non-marine molluscan faunas to be used as guide fossils for the analysed fluvial sequences in the classification of climato-lithostratigraphic principles. The biostratigraphic scheme developed in this work is comparable with parallel investigations of other fossil records and climato-lithostratigraphy combined with geochronologic methods. In earlier literature, the Pleistocene Corbicula record was mentioned in Makiš beds (“Makiški slojevi”), in the Corbicula fluminalis beds (“slojevi sa C. fluminalis”) of Szentes deposits (“Senteški slojevi”), as well as being associated with the Viviparus boeckhi Horizon as defined by Halaváts in the late 19th century.In Serbian records, the most important locations of the Pleistocene Corbicula beds are in the south-eastern part of the Pannonian Plain, which corresponds to the lowland river valleys of the (paleo) Danube, (paleo)Sava and (paleo)Tisza, and the western margin of the Dacian realm. Pleistocene Corbicula beds were formed as warm stage fluvial (and palustrine) deposits, and they are climate-lithostratigraphic units. Pleistocene Corbicula beds are younger than Upper Paludina beds (defined as the lower part of the Lower Pleistocene) in the Pannonian realm or the Romanian stage in the Dacian realm. According to the molluscan assemblage, palaeogeographical features and other paleontological contents (vertebrate fauna, ostracods), they are older than the Upper Pleistocene. According to the reference data and the composition of the molluscan assemblage, the V. boeckhi Horizon has been identified as a biostratigraphic unit. Fortunately, the V. boeckhi Horizon can be adopted to the Serbian climato-lithostratigraphy model of the fluvial warm stages and represents the lowermost part/subunit of the Pleistocene Corbicula beds of Lower Pleistocene age.

U-Th-He dating of native gold: First results, problems, and outlooks

In this paper, we consider the application of the U-Th-He method of isotope geochronology for native gold dating. It was shown that inclusions of uranium- and thorium-bearing minerals, including rare earth element phosphates, are one of the main form of uranium and thorium occurrence and, consequently, the main source of radiogenic helium in native gold. Since these inclusions are submicrometer-sized, the radiogenic helium formed in them is not accumulated but implanted in the structure of native gold, which suggests its good preservation over billions of years. This suggestion was experimentally supported by the investigation of the kinetics of radiogenic helium release from native gold. The first results of the U-Th-He dating of native gold from the Pedrolampi (central Karelia) and Witwatersrand (South Africa) deposits are in adequate agreement with available independent geochronological data. This allows us to consider native gold as a U-Th-He mineral geochronometer for the direct dating of ore-forming processes.

Fluvial sediments of the Algeti River in southeastern Georgia — An archive of Late Quaternary landscape activity and stability in the Transcaucasian region

In order to obtain information about landscape activity and stability during the Late Quaternary in the Transcaucasian region, fluvial sediments of the lower Algeti River in SE-Georgia were studied by means of geomorphologic, sedimentologic and geochronologic methods. These investigations show that sediments aggraded by the Late Pleistocene braided Algeti River were strongly incised around the Pleistocene/Holocene transition, and subsequently a small-scale pattern of diachronous fluvial terraces deposited by the now meandering river developed in the new valley during the Holocene. Prior to ca. 3cal.kaBP, active phases of river channel aggradation and overbank sedimentation about 6cal.kaBP and 3.4–3.2cal.kaBP can be linked with climate-driven vegetation changes, i.e. stronger fluvial dynamics with sedimentation occurred during more arid and colder periods whereas the Caucasian Holocene climate optimum between 6 and 3.4cal.kaBP was characterized by stable geomorphologic conditions. After 3cal.kaBP, strongly increased human impact documented by former pollen studies is reflected by the fluvial dynamics as well, i.e. an activity phase of strong overbank sedimentation 2.7–2.1cal.kaBP occurred during a period when forests in the Lesser Caucasus were burnt down. Two subsequent activity phases with fluvial sedimentation can be linked with historic events that probably both influenced vegetation distribution of the region, i.e. a period of flourishing of Georgia during the Middle Age and a time of large-scale destruction of the country due to a Persian invasion at the end of the 18th century AD, respectively.Thus, whereas no influence of tectonic events or fluctuations of the Caspian Sea level on the fluvial dynamics could be detected, SE-Georgia shows its fragile character with respect to climate- and human driven vegetation-changes similar to other semi-arid landscapes of the Mediterranean region.

Monazite ID-TIMS U-Pb geochronology in the LAGIR laboratory, Rio de Janeiro State University: protocols and first applications to the assembly of Gondwana supercontinent in SE-Brazil

The chemical and spectrometric procedures of the U-Pb geochronology method on monazites, recently installed in the LAGIR laboratory, are described in detail. In addition, preliminary results on monazite samples from the Brasília and Ribeira belts are reported and discussed in the context of the regional geology. Several experiments for calibration of ion exchange chromatographic columns with the AG-1x8 resin, were performed with HCl, using dissolved natural monazite samples. The Pb blanks of reagents are ∼0.5 pg/g in acids and ∼1 pg/g in H2O. The total Pb blanks in chemical procedures were below 22 pg. Preliminary results are presented from three case studies related to Brasiliano orogenic belts of SE-Brazil, which correlate very well with previous age determinations from literature: two sub-concordant grains from an Araxá Group quartzite (southern Brasília belt) define a concordia age of 602.6 ±1.4 Ma; a -0.8% discordant grain from a quartzite of the São Fidelis Group (Costeiro Domain, central Ribeira belt) yielded a concordia age of 535.3 ± 2.4 Ma; two 0.4 % and 1.3 % discordant monazite grains from the post-collisional Itaoca Granite (Costeiro Domain, central Ribeira belt) define a concordia age of 476.4 ± 1.8 Ma.

Micro- and nanobands in late Archean and Palaeoproterozoic banded-iron formations as possible mineral records of annual and diurnal depositions

The microbands in Precambrian banded-iron formations (BIFs) have been conjectured to record annual or even diurnal depositions. However, these bands have rarely been observed in high resolution at their true (micro) scale. Here, I suggest that nanobands of fine-grained hematite represent possible diurnal depositions and that microbands of chert/jasper represent possible annual depositions in three sets of BIFs: 2460-Myr BIFs from the Kuruman Iron Formation, Transvaal Supergroup of South Africa; 2480-Myr BIFs from the Dales Gorge Member of the Brockman Iron Formation, Western Australia; and 2728-Myr BIFs from the Hunter Mine Group, Abitibi Greenstone Belt, Canada. Observations made using scanning electron microscopy indicate that hematite and chert were syngenetic, and that there was a hiatus between their precipitation and the genesis of the remainder of the minerals containing structural Fe(II). Spindle-like grains of hematite, monocrystals of magnetite, and ferro-dolomite formed microbands of ∼30–70 μm in thickness, which appear cyclically in the matrix of the chert. Neither the band-bound magnetite and dolomite nor the linear formations of the hematite spindles represent annual depositions due to their diagenetic features. The thinnest microbands (∼3–∼12 μm) were observed in the chert and jasper, and indicate depositional rates of 6.6–22.2 m/Myr in the BIFs. These rates are consistent with the integrated deposition rates calculated by geochronologic methods for the BIFs, if annual deposition is assumed. The ∼26-nm nanobands observed only in hematite grains reflect an annual deposition of ∼18.6 μm, or ∼18.6 m/Myr, which is also consistent with the depositional rate calculated by geochronologic methods. It is tentatively suggested that these ∼26-nm nanobands were formed from the diurnal precipitation of Fe(III) resulting from the circadian metabolism of Fe(II)-oxidizing or oxygen-evolving photosynthetic microorganisms, which slowed down the rise of atmospheric oxygen. The diurnal precipitation of Fe(III) as hematite and the annual deposition of silica as chert/jasper in the BIFs provide internal clocks that may facilitate the examination of short-term processes, such as ecological, oceanographic and climatic cycles, that are recorded by the mineral or chemical compositions of BIFs.

New age constraints for Neogene sediments of the Sahabi area, Libya (Sirt Basin) using strontium isotope (87Sr/86Sr) geochronology and calcareous nannofossils

For almost half a century researchers have attempted to determine the absolute ages of Neogene sedimentary units in the Sahabi area of Libya. The age of these sediments is of particular interest to paleontologists who have worked on important vertebrate remains in the area since the late 1970s. To date, several geochronological methods have been attempted; however, no precise ages have been obtained for the various units. In this paper we report data for calcareous nannofossils and strontium isotope (87Sr/86Sr) analysis of macrofossils, which can be used to infer age of deposition of part of the Neogene section (Formation M). Because most Sahabi fossils are extensively altered by various diagenetic processes, including gypsification and dolomitization, we carefully screened tens of samples to select unaltered material for analysis. Among the many fossils collected from Formation M and analyzed by XRD, only two, Balanus sp. and a Cubitostrea digitalina show no evidence of diagenetic alteration of their shells, and thus retain their original low-Mg calcite (LMC) mineralogy. The strontium isotopic values from these fossils were plotted against the marine strontium isotopic curve, in order to infer the absolute age. The Balanus sp. has a 87Sr/86Sr value of 0.708917, whereas C. digitalina has a 87Sr/86Sr value of 0.708908. Based on the current estimated error (0.000008), the value of 0.708917 indicates an ages between 9.33Ma and 8.59Ma, centered on 8.99Ma, whereas the value of 0.708908 indicates ages between 9.61 and 9.03Ma, centered on 9.36Ma. The calcareous nannofossils found in this formation belong to biozone NN10b-NN11a and provide an age of 8.23Ma. These ages fall in the Late Miocene period (Tortonian Epoch). Therefore, Formation M should be considered Late Miocene (Tortonian) rather than Middle Miocene (Serravallian) as proposed by many previous workers. Age dating of Formation M will help in revising the stratigraphic nomenclature as well as in re-evaluating the stratigraphic position of this formation according to the Libyan Stratigraphic Code through the Earth Science Society of Libya (ESSL).

Continuity or discontinuity in the European Early Pleistocene human settlement: the Atapuerca evidence

The nature, timing, pattern, favourable circumstances and impediments of the human occupation of the European continent during the Early Pleistocene are hot topics in Quaternary studies. In particular, the problem of the (dis) continuity of the settlement of Europe in this period is an important matter of discussion, which has been approached in the last decade from different points of view. The Gran Dolina (TD) and Sima del Elefante (TE) cave sites in the Sierra de Atapuerca, (Spain) include large and quasi-continuous stratigraphic sequences that stretch back from at least 1.2 million years ago (Ma) to the Matuyama/Brunhes boundary. The archaeological and paleontological record from these sites can help to test different hypotheses about the character of the human settlement in this region and period. Furthermore, the TD6 level has yielded a large collection of human fossil remains attributed to Homo antecessor. According to different geochronological methods, as well as to paleomagnetic and biostratigraphical analyses, these hominins belong to an age range of 0.96–0.80 Ma. Unfortunately, the finding in 2007 of some human fossil remains in the TE9 level, dated to about 1.22 Ma, was not enough to conclude whether H. antecessor had deep roots in the European Early Pleistocene. A set of derived features of H. antecessor shared with both the Neanderthal lineage and modern humans suggests that this species is related, and not far, from the most recent common ancestor (MRCA) of Homo neanderthalensis and Homo sapiens. If we assume that there was a lineal biological relationship between the TE9 and TD6 hominins, we should reconsider many of the conclusions achieved in previous paleontological and genetic studies. In addition, we would be obliged to build a highly complicated paleogeographical scenario for the origin of the MRCA. Although continuity in the settlement of Europe during the entire late Early Pleistocene is not discarded (e.g. in refuge areas), it seems that this Western extreme of Eurasia, and the Iberian Peninsula in particular, was occupied by at least two different hominin populations.

Timing and spatial distribution of loess and loess-like sediments in the mountain areas of the northeastern Tibetan Plateau

Most studies on landscape evolution on the Tibetan Plateau during the late Quaternary have mainly focused on using lacustrine records. However, mantles of sandy silt and paleosols also provide valuable archives for reconstructing Holocene paleoenvironmental change. Yet little is known about the distribution and timing of these late Quaternary aeolian sediments. To enhance understanding and knowledge of aeolian sediments in Tibet and to help reconstruct the nature of Late Glacial through mid-Holocene landscape development, a loess–paleosol sequence, the Suohuduo section, located at the eastern margin of the Tibetan Plateau at about 4000m above sea level is examined using sedimentological, geochemical and geochronological methods. A chronostratigraphy is established using nine optically stimulated luminescence and one radiocarbon ages. Sedimentation increased during the Late Glacial and the early Holocene with an upwards fining of sediments in the lower part of the section. Two mid Holocene paleosols that date to about 8.5ka to 7ka and ~5.5ka to 4ka reflect more humid climate conditions during the mid-Holocene than earlier times. The upper part of the section is mainly silt, which reflects a more open landscape with higher aridity since 4 to 3ka this time. These data support evidence for similar climate/paleoenvironmental change in adjacent regions on the Tibetan Plateau.

Zircon U–Pb geochronology of the Zanhuang metamorphic complex: reappraisal of the Palaeoproterozoic amalgamation of the Trans-North China Orogen

AbstractAmphibolites and metapelites exposed in the Zanhuang metamorphic complex situated in the south-middle section of the Trans-North China Orogen (TNCO) underwent upper-amphibolite-facies metamorphism and record clockwise P–T paths including retrograde isothermal decompression. High-resolution zircon U–Pb geochronological analyses indicate that the metamorphic peak occurred during ~ 1840–1860 Ma, which is in accordance with the ubiquitous metamorphic ages of ~ 1850 Ma retrieved by miscellaneous geochronologic methods throughout the metamorphic terranes of the northern TNCO, confirming that the south-middle section of the TNCO was involved in the amalgamation of the Eastern and Western Blocks of the North China Craton during the Palaeoproterozoic.

The stratigraphical importance of the Viviparus boeckhi Horizon of Serbia

Fossils of non-marine molluscs are among the most prominent in Pleistocene deposits. With stabilization of taxonomies in the 19th century, numerous publications appeared with faunal lists of Quaternary warm stage molluscs, but few attempts were made to use those data for interpretation. The purpose of this work, along with reevaluation of sites and their molluscan assemblages described in the literature, is to make it possible for non-marine molluscan faunas to be used as biostratigraphic indicators. Biostratigraphic data obtained in this work are comparable with parallel investigation of other fossil records and lithostratigraphy, combined with geochronologic methods. The four most important localities with Viviparus boeckhi in Serbia are Subotica, Sombor, Zrenjanin, and the vicinity of Belgrade. According to the available data, the molluscan assemblage of the V. boeckhi Horizon is identified as fluvial warm stage assemblage which corresponds to the oldest part of the Pleistocene Corbicula Beds.It is generally considered that the age of the V. boeckhi Horizon(s) corresponds to the younger parts of the Early Pleistocene. However, according to the regional data, the V. boeckhi Horizon of Serbia is younger than the Paludina Beds (of Pliocene–Early Lower Pleistocene age). According to the vertebrate fauna, it is older than the upper Biharian stage (younger part of the Middle Pleistocene).

New geochronometer for the direct isotopic dating of native platinum minerals (190Pt-4He method)

A new method of isotope geochronology was proposed for dating native platinum minerals on the basis of the α-decay of the natural isotope 190Pt. The analysis of the thermal desorption of helium in the crystal lattice of native metals, including platinum, allowed us to predict a very high thermal stability (retentivity) of radiogenic 4He in native platinum minerals up to their melting temperatures. In order to validate the proposed 190Pt-4He method, direct isotopic dating was performed for isoferroplatinum from the Galmoenan dunite-clinopyroxenite and Kondyor alkaline ultramafic massifs. The results of dating obtained by this method for primary ore platinum from the Galmoenan Massif (70 ± 5 Ma) are consistent with geological observations and mean Sm-Nd and Rb-Sr isotopic age estimates. The 190Pt-4He age obtained for placer isoferroplatinum from the Kondyor Massif (112 ± 7 Ma) also agrees with geological observations and is close to the K-Ar and Rb-Sr ages of koswites (phlogopite-magnetite pyroxenites, gabbros, nepheline syenites, and metasomatic rocks after dunites). Our experimental data demonstrated that the 190Pt-4He method is a promising tool for dating native platinum minerals.

Age and substance sources of the Ilmeno-Vishnevogorsky Alkaline Complex (South Urals): Rb-Sr, Sm-Nd, U-Pb, and Lu-Hf isotope data

) ofmiaskites, fenites, and carbonatites with REE–Zr–Nb mineralization located in the Uralian foldbelt.Although the IVC is well studied, a number of important genesis and geochronological problems are currently debatable. Thus, because of the wide dispersionof datings obtained by the different isotope–geochronological methods on various rocks and minerals, ofcritical concern are the problems of geochronology ofalkaline rocks and carbonatites of the IVC. The keyquestion of the IVC genesis is the role of mantle andcrustal sources for rock and ore formation. Theseproblems may be solved on the basis of the complexand systematic study of the Rb–Sr, Sm–Nd, U–Pb,and Lu–Hf isotope systems of rocks and minerals,which currently have become an important and indispensable instrument for reconstruction of the sourceof magmatic rocks and solution of the problems oftheir origin.We applied the isochron methods based on theSm–Nd and Rb–Sr isotope systems of bulk samplesand rockforming minerals of miaskites and carbonatites (TIMS method, Institute of Geology andGeochemistry, Yekaterinburg; Institute of Precambrian Geology and Geochronology, Saint Petersburg;Institute of Geology, Apatity), as well as the local U–Pb isotope dating of zircons from carbonatites andmiaskites from Vishnevogorsky and Buldym massifs(ion microprobe SHRIMPII, Russian GeologicalResearch Institute, Saint Petersburg; laser ablationLaICPMS, GEMOC, Sydney) for dating of themain rock types of the IVC. The U–Pb isotope systems of pyrochlores from the IVC (TIMS, AllRussianGeological Research Institute, SaintPetersburg) wereused for dating as well. The initial isotope characteristics of rocks and minerals of the IVC were obtained inorder to establish the sources of substances for magmatic rocks and ores and the role of mantle in theirformation.The Ilmeno–Vishnevogorsky Complex is locatedat the boundary between the South and Middle Uralsin the Sysertsko–Ilmenogorsky block of Precambrianrocks occurring in the Uralian paleooceanic complexes. The core of this block is composed of granuliticgneisses and migmatites of the Selyankinskaya Series,as well as plagiogneisses and amphibolites of the Vishnevogorskaya Series (

Growth of fissure ridge travertines from geothermal springs of Denizli Basin, western Turkey

Fissure ridge travertines grown from geothermal springs of Denizli Basin, southwestern Turkey, are investigated through stratigraphic, structural, geochemical, and geochronological methods, with the aim of understanding the growth of these elongate mound-shaped structures. Two main types of travertine deposits are recognized: (1) bedded travertines, which grew as flowstone on sloping surfaces and form the bulk of fissure ridges, and (2) banded travertines, which grew as veins within the bedded travertine chiefly along its central feeding conduit. Stratigraphic and structural observations shed light on the bedded-banded travertine relationships, where the banded features grew through successive accretion phases, crosscutting the bedded travertine or forming sill-like structures. The bedded and banded travertines alternated their growth, as demonstrated by complicated crosscutting relationships and by the upward suture, in places, of banded travertine by bedded travertine that was, in turn, crosscut by younger banded travertine. The bedded travertine is often tilted away from the central axis of the fissure ridge, thus leaving more room for the central banded travertine to form. U-series ages confirm the bedded-banded travertine temporal relationships and show that the growth of the studied fissure ridges lasted up to several tens of thousands of years during Quaternary time. The banded travertine was deposited mainly during cold events, possibly in coincidence with seismic events that might have triggered the outflow of deep geothermal fluids. C and O stable isotope and rare earth element data indicate a shallow feeding circuit for the studied structures with a fluid component deriving from a deeper geothermal circuit. A crack-and-seal mechanism of fissure ridge growth is proposed, modulated by the interplay of local and regional influencing factors and mechanisms such as geothermal fluid discharge, paleoclimate, tectonics, and the progressive tilting of bedded travertine limbs over a soft substratum creating the necessary space for the central veins to grow.