Amino acid racemization in mono-specific foraminifera from Quaternary deep-sea sediments

The deep-sea environment is among the most stable on Earth, making it well suited for amino acid geochronology. Foraminifera with calcareous tests are distributed across the World Ocean and are often recovered in sufficient abundance from sediment cores to derive robust mean amino acid D/L values of multiple replicates from each stratigraphic level. The extent of racemization (D/L) can be compared with independent age control, which in most cases is based on correlation with global marine oxygen-isotope stages and radiocarbon ages from the same stratigraphic levels. In this study, we report the results of amino acid racemization analysis of multiple foraminifera species from well-dated sediment cores taken from the Pacific, Atlantic, and Arctic oceans. The composite of results analyzed to date (179 samples, each composed of an average of 8.6 subsamples = 1531 analyses) show that D/L values generally increase systematically down core, and are similar for samples of comparable ages from different deep-sea sites. Previously published equations that relate D/L values of aspartic and glutamic acids to post-depositional temperature and sample age for Pulleniatina obliquiloculata generally conform to the D/L trends for species analyzed in this study. Laboratory heating experiments were used to quantify the difference in the rate of racemization between P. obliquiloculata and other taxa. For example, aspartic acid in P. obliquiloculata racemizes an average of 12–16% faster than in the common high-latitude species, Neogloboquadrina pachyderma (s). Apparently, the unexpectedly high D/L values previously reported for N. pachyderma (s) older than 35 ka from the Arctic Ocean cannot be attributed to taxonomic effects.     

14C age anomalies in modern land snails shell carbonate from Southern Italy

Radiocarbon dating based on geomorphological, archaeological and biological data is widely used in geomorphological studies to reconstruct sequences of climatic variations and coastal evolution during the Holocene. The coastal area of Southern Italy is characterized by aeolian dune belts shaped during the Holocene that crop out along the present shoreline. Archaeological data and previous radiocarbon results suggest three aeolian morphogenetic phases. The first phase corresponds to the end of the rapid post-glacial transgression (7.0–6.0 ka BP); the second to the aeolian sand deposition during the “Greek–Roman” period (2.5–1.9 ka BP); and the most recent phase occurred in the period from the Middle Ages to the present time. The reconstruction of the sequence of the morphogenetic phases was mainly based on radiocarbon analyses carried out on both terrestrial gastropods and marine bivalves. The reliability of the radiocarbon analyses on terrestrial gastropod shells has been questioned by several Authors and a closer understanding of the carbon uptake mechanism in this kind of organisms is needed.A systematic study was carried out by performing Accelerator Mass Spectrometry (AMS) ¹⁴C dating on the shells of terrestrial gastropods sampled alive in different geomorphological settings along the Adriatic and Ionian coasts of Southern Italy. The results show significant anomalies in the radiocarbon content and in the carbon stable isotopic ratio. This can be due to the ingestion of ¹⁴C-depleted calcium carbonate in the diet of these organisms. We also calculated the carbon fraction from air X_a (between 16% and 48%), plants X_v (between 36% and 73%) and limestone X_c (between 3% and 23%) giving insight to the origin of the age anomalies.     

Amino acid racemization in four species of ostracodes: Taxonomic,environmental, and microstructural controls

Here we quantified the aspartic acid and glutamic acid racemization rates of the four main ostracode species (Herpetocypris reptans, Candona neglecta, Ilyocypris gibba and Cyprideis torosa) present in several Iberian Peninsula localities covering a wide chronological range (ca. 1 Ma to present). At low D/L values (at Asp D/L < 0.40; and Glu D/L = 0.09–0.18), H. reptans racemized at higher rates than C. neglecta, C. torosa and I. gibba. In contrast, for Asp D/L > 0.4 and Glu D/L > 0.18, H. reptans, C. neglecta and C. torosa showed similar racemization rates. I. gibba exhibited the lowest D/L values in old samples (Middle and Lower Pleistocene). We attribute these differences in amino acid racemization rates mainly to variations in valve protein composition. We found that the microstructure of the valves of each species (size, morphology, and arrangement of crystals) differed, but did not appear to change over time (at least for the last ca. 1 Ma). Such differences may also be linked to the type of proteins involved in the respective calcification processes of these organisms. On the basis of our results, and given that other studies have demonstrated that the majority of inter-crystalline proteins are leached early after death (a few centuries or millennia), we propose that the degradation rates of the most resistant inter- and intra-crystalline proteins in each species differ depending on the protein composition of the valves. Although further research is required, we suggest that amino acid racemization in each ostracode species might be related to valve microstructure.     

Large 14C age offsets between the fine fraction and coexisting planktonic foraminifera in shallow Caribbean sediments

Absolute chronologies in paleoceanographic records are often constructed using the ¹⁴C dating of coarse fraction foraminifera (>150 μm). However, due to processes such as changes in sediment sources or abundances, sedimentation rates, bioturbation, reworking, the adsorption of modern carbon, etc., several studies conducted in different environmental settings have shown time-lags between records obtained from various granulometric fractions. In this study, we examined temporal phasing between the coarse foraminifera and fine fractions by studying changes in the abundances of δ¹⁸O, the ¹⁴C ages of the planktonic foraminifera Globigerinoides ruber (G. ruber, 250–350 μm), and the sediment fine fraction (<63 μm) over the last 45 ka in a core obtained from the northern Caribbean Sea. All of the records were found to be in phase during part of the Holocene (at least for the last ≈6 ka). As determined from δ¹⁸O records and ¹⁴C ages, the fine fraction was younger than G. ruber during the Last Deglaciation (of 1.89 ka). The coupling between bioturbation and changes in the fine fraction, and G. ruber abundances, as tested using a numerical model of the bioturbation record within a mixed-layer depth of 8 cm, was sufficient to explain the results. ¹⁴C age discrepancies increased from 5.64 to 8.5 ka during Marine Isotopic Stages (MIS) 2 and 3, respectively. These chronological discrepancies could not be explained by only one process and seemed to result from the interplay between mechanisms: size-differentiated bioturbation (for 1.5 to 2.5 ka), the adsorption of modern atmospheric CO₂ (for 3.04 to 5.92 ka), and variations in sedimentological processes that influenced the fine carbonate fraction. However, even if variations in the mineralogical composition of the fine carbonate fraction were identified using scanning-electron microscopy observations, X-ray diffraction measurements, and geochemical analyses (the mol % MgCO₃ of magnesian calcite and the Sr/Ca ratio of the bulk fine fraction), they can not account for the observed age differences. The results presented for core MD03-2628 extend beyond this case study because they illustrate the need for a detailed characterization of the various size fractions prior to paleoclimate signal interpretations, especially for chronological studies.     

A chronological framework for the Clyde Foreland Formation,Eastern Canadian Arctic,derived from amino acid racemization and cosmogenic radionuclides

The most extensive terrestrial outcrops of glacial and glaciomarine deposits in the Eastern Canadian Arctic are exposed in sea cliffs along the Clyde Foreland and Qivitu Peninsula of Baffin Island. Collectively known as the Clyde Foreland Formation (CFF), these stacked deposits record at least seven glacial advances. Despite having been the focus of numerous investigations spanning nearly 50 years, no numerical chronological framework for the age of the deposits has been established. Previous studies relied on biostratigraphy and amino acid racemization (AAR) geochronology and postulated that the oldest units were Late Pliocene to Mid-Pleistocene in age. In this paper, we use a cosmogenic radionuclide isochron approach to determine a minimum age for the burial of a paleosol preserved within the CFF. Abundant palynomorphs in the paleosol are dominated by cool-climate taxa. Combining the paleosol burial age with a compilation of published and new CFF AAR data for marine bivalves Hiatella arctica and Mya truncata, we statistically define seven CFF aminozones and develop a piecewise isoleucine AAR calibration model for Baffin Island. From this, we estimate the minimum age of each aminozone, although the propagation of errors through all calculations produces large uncertainties for each age estimate. The youngest three CFF units, known as the Kogalu, Kuvinilk, and Cape Christian members, were most likely deposited during glaciations in the Mid- to Late-Pleistocene. The paleosol formed prior to 1.15 ± 0.20 Ma, and the underlying aminozones represent sedimentation during Early Pleistocene or latest Pliocene glaciations and record early advances of Laurentide ice across Baffin Island.     

Trace metals in harbour and slipway sediments from the island of Malta, central Mediterranean

Sediment samples collected from large harbours and public slipways on the island of Malta have been analysed for geochemically important metals (Al, Ca, Fe, Mn) and contaminant metals (As, Cd, Co, Cr, Cu, Ni, Pb, Sn, Zn) following fractionation (<63 μm) and digestion in aqua regia. Absolute and Al-normalised concentrations of contaminant metals exhibited relatively little dispersion both among different samples from the same location and between samples from different locations, notable exceptions including lower concentrations of Cr and Sn on the slipways than in the harbours. Sources of contaminant metals are attributed to diffuse and specific waste inputs from urban surroundings and boating and shipping activities. Overall, concentrations are similar to those reported for other large harbours in urban settings where equivalent sample fractionation-digestion has been performed. Relative to various sediment quality guidelines, Pb is predicted to exert the greatest threat to the marine environment of Malta.     

Age model, physical properties and paleoceanographic implications of the middle Pleistocene core sediments in the Choshi area, central Japan

Abstract   A continuous, well-preserved core was obtained from the Choshi area, on the Pacific side of Japan, to investigate paleoceanographic and paleoclimatic changes around the northwestern Pacific region during the middle Pleistocene. Siliciclastic sequences in the core are divided into five formations – the Obama, Yokone, Kurahashi and Toyosato Formations in the Inubo Group and the Katori Formation, in ascending order. Examination of calcareous nannofossils and magnetic polarities detected four datums in the core sediments of the Inubo Group: the top of Reticulofenestra asanoi , the base of Helicosphaera inversa , the top of Pseudoemiliania lacunosa and the Brunhes–Matuyama boundary. Fourteen marine isotope stages (MIS24–MIS11) were identified in the δ¹⁸O and δ¹³C records based on detected datums and the graphic correlation with the standard stack oxygen isotope curve. Magnetic susceptibility and gamma-ray attenuation porosity evaluator density were also measured and low values characterize the glacial intervals. Biogenic sedimentation by primary production may be larger during the glacial periods because of invasions of nutrient-rich northern surface-waters related to the southward shift of the Kuroshio front in the Choshi area.     

A retrospective analysis of trace metals, C, N and diatom remnants in sediments from the Mississippi River delta shelf

The development of oil and gas recovery offshore of the Mississippi River delta began in shallow water in the 1950s, expanded into deeper waters, and peaked in the 1990s. This area of the outer continental shelf (OCS) is the historical and present location of >90% of all US OCS oil and gas production and reserves. The juxtaposition of its 4000 producing platforms, recovering $10 billion yr(-1) of oil, gas and produced water in the same area where about 28% of the US fisheries catch (by weight) is made and near 40% of the US coastal wetlands, makes this an area worth monitoring for regional pollutant loading. This loading may come from several sources, including sources related to OCS development, but also from the Mississippi River watershed. In this context, any contaminant loading on this shelf may be neither detectable nor significant against a background of climatic or biological variability. We examined the sedimentary record for indicators of industrial byproducts from OCS oil and gas development and of industrial products entering via the Mississippi River, primarily using vanadium (V) and barium (Ba) concentrations normalized for aluminum (Al). Barium is primarily used in drilling muds in the form of barite, whereas V is an important strengthening component of metal alloys, including steel. The fluctuations in the accumulation of Ba, but not V, were coincidental with the presumed use of barite. The fluctuations in V concentration in the sediments were coincidental with the national consumption of V. Copper (Cu), cadmium (Cd) and zinc (Zn) concentrations in sediments fluctuate coincidentally with V, not Ba, thus indicating that the dominant source of these trace metals in offshore sediments were derived from riverine sources, and were not primarily from in situ industrial processes releasing them on the shelf. This is not to suggest that local site-specific contamination is not a significant management or health concern. The low oxygen (hypoxia; < or = 2 mg l(-1)) zone that consistently covers much of this continental shelf's bottom layer in summer is attributed to nitrate loading from the Mississippi River. Increased nitrogen loading from river to shelf stimulates diatom production whose loading to the bottom layer and subsequent metabolism results in oxygen being depleted faster than it is replaced. In the last two decades there has been an increased accumulation of organic matter in sediments near the mouth of the Mississippi River. This coupling between river water, surface water and bottom water has recently expanded westward of the Atchafalaya River delta towards the Texas coast. The accumulation of biogenic silica (BSi) and carbon in dated sediments is coincidental with variations in riverine nitrate flux, but not with either V or Ba accumulation rates. These analyses indicate that both OCS development and riverine sources exert strong influences on the sediment constituents offshore, and that these influences may be independent of one another.     

Chronology of Early to Mid-Pleistocene sediments in the northern North Sea: New evidence from amino acid and strontium isotope analyses

Sediments deposited during glacial-interglacial cycles through the Early to Mid-Pleistocene in the North Sea are chronologically poorly constrained. To contribute to the chronology of these units, amino acid racemization (AAR) and strontium (Sr) isotope analyses have been performed on samples from four shallow borings and one oil well along a transect in the northern North Sea. D/L Asp (aspartic acid) values obtained through reverse-phase liquid chromatography in the benthic foraminiferal species Elphidium excavatum is focused on because of consistent results and a good stratigraphic distribution of this benthic species. For the Early Pleistocene, an age model for the well 16/1–8, from the central part of the northern North Sea based on Sr ages allows for dating of the prograding wedges filling the pre-Quaternary central basin. A regional calibration curve for the racemization of Asp in Elphidium excavatum is developed using published ages of radiocarbon-dated samples and samples associated with the previously identified Bruhnes/Matuyama (B/M) paleomagnetic boundary and a Sr age from this study. Based on all the available geochronological evidence, samples were assigned to marine oxygen isotope stages (MIS) with uncertainties on the order of 10–70 ka.Sr ages suggest a hiatus of <2 million years (Ma) possibly due to non-deposition or low sedimentation between the Utsira Formation (Pliocene) and the Early Pleistocene. An increase in sedimentation rates around 1.5 ± 0.07 Ma (∼MIS 51) may partly be due to sediment supply from rivers from the south-east and partly due to the extension of ice sheet around 1.36 ± 0.07 Ma from the Norwegian coast to the central North Sea. A possible basin-wide glaciation occurred around 1.1 Ma (∼ MIS 32) (upper regional unconformity/top of unit Q4 in this study), resulting in erosion and regional unconformity. Two interglacials in the Norwegian Channel have been dated: the Radøy Interglacial to 1.07 ± 0.01 Ma (possibly MIS 31, the ‘super interglacial’), and the Norwegian Trench Interglacial to 0.50 ± 0.02 Ma (possibly MIS 13). A massive till unit identified at the same stratigraphic level in all shallow borings may partly represent an extensive MIS 12 glaciation. This study shows that the combined use of amino acid racemization data and Sr isotope chronology can refine the chronological ambiguities of Quaternary North Sea sediments related partly to the impact of glacial processes.     

Calculation of the reservoir age from organic and carbonate fractions of sediments in the Gulf of Cariaco (Caribbean Sea)

A set of 24 AMS ¹⁴C measurements were performed on different sediment fractions from short gravity cores taken from the Gulf of Cariaco (northeastern Venezuela) in order to construct a detailed sedimentary archive for recent centuries. A local reservoir effect was expected because of i) strong upwelling from the neighboring Cariaco Trough and anoxia and ii) the specific geomorphological setting related to active faults with seeps and diapirism. Measurements were thus performed on different components: sediment bulk organic fraction (SBOF), pteropods shells (surface water), bivalve shells (bottom), and plant fragments. Based on comparisons of the different results, we discuss different age corrections and calibrations, which lead us to consider a negligible local reservoir correction (ΔR) for the bivalve and pteropod shells, which show no reservoir age for carbonate and an absence of water stratification. However, a local 633 ± 64 yr ΔR appears in the organic fraction of the sediment, and its origin is primary related to the upwelling mechanism.     

Throughfall patterns in sugarcane and riparian forest: understanding the effect of sugarcane age and land use conversion

Sugarcane is an annual crop with a dynamic canopy that changes over time mainly because of genetic adaptation. There is uncertainty about the temporal trends of throughfall (TF) in this important commercial crop. In the present paper, we used troughs to measure TF in a third and fourth ratoon and subsequently in a fourth and fifth ratoon. Additional measurements were carried out in an adjacent riparian forest. There were no significant differences between cycles of sugarcane, growth phases and riparian forest. The TF results for ratoon crop and riparian forest in 2011/2012 were 76% and 79.5% of gross rainfall, respectively, while in 2012/2013, they were 79% and 78%, respectively. However, TF was remarkably lower in the riparian forest relative to ratoon from the second half of the culm formation and elongation phase (280 days after harvest) until harvest. Copyright © 2016 John Wiley & Sons, Ltd.     

Reworking effects in the Holocene Zhuye Lake sediments:A case study by pollen concentrates AMS 14C dating

Transported by wind and water,the relatively old sediments can deposit in the terminal lake of an inland drainage basin.The reworking effect can affect the lake sediments 14 C dating and explanations for proxies.The Zhuye Lake is the terminal lake of the Shiyang River Basin.Previous studies indicated that sediments in different locations of the lake basin showed different climatic change patterns.And then,some radiocarbon dates were inverted for some Late Pleistocene sections.Whether this phenomenon is related with the reworking effect? The pollen concentrates 14 C dating can avoid the reservoir effect,which is an ideal method for studying the reworking effect.In this study,we used the pollen concentrates as dating materials and dated five Holocene sections in the Zhuye Lake Basin.Based on the 14 C dates comparison between the pollen concentrates,organic matter,and shells,the pollen concentrates dates are relatively older than other dating materials.Based on the result,the reworking effect worked in the Zhuye Lake Basin during the Holocene;however,in different locations of the lake basin the reworking effects were in different levels.Furthermore,the Holocene lacustrine deposits were formed mostly during the early and middle Holocene.This study provided clues for reworking effect studies of other lakes in arid China.     

Using tephrostratigraphy and cryptotephrostratigraphy to re-evaluate and improve the Middle Pleistocene age model for marine sequences in northeast Japan (Chikyu C9001C)

We refine the tephrostratigraphy and cryptotephrostratigraphy of the Middle Pleistocene deep-sea sediments in the C9001C cores and reconstruct the age model of the cores to provide a standard stratigraphy for the NW Pacific Ocean area. In the lower half of the cores (corresponding to marine isotopic stages [MISs] 9–18), we newly identify nine concentrations (spikes) of glass shards (numbered G17–G25 from top to bottom) below sixteen previously reported spikes (numbered G1–G16) in the upper half of the cores (MISs 1–9). We correlated two spikes (both cryptotephras) with known widespread tephras: G18 with Naruohama-IV (MIS 10d; 357 ka) and G19 with Kasamori 5 (MIS 12b–c; 434–458 ka). Although the two cryptotephra spikes cannot be distinguished by the major- and trace-element compositions of glass shards, these correlations are based upon their stratigraphic occurrence within separate glacial periods (MISs 10 and 12) as indicated by the δ¹⁸O stratigraphy of the C9001C sequence. Based on the stratigraphic positions of the Naruohama-IV and Kasamori 5 tephras, we assign the sediment units corresponding to MISs 10, 11, and 12, and revise the previous assignment of core segments corresponding to MISs 7, 8, and 9. The resulting tephra-based age model is consistent with the last occurrence of Proboscia curvirostris, but it is inconsistent with the first occurrence of Emiliania huxleyi. According to the new age model, the sedimentation rate during MISs 18–2 has ranged from 0.21 m/ky (during MIS 17) to 0.74 m/ky (during MISs 8 and 9), however, the sedimentation rate was never as high as the rate of 1.1 m/ky indicated by an earlier age model.     

A power function model for the basic geometry of solution dolines: considerations from the classical karst of south‐central Slovenia

Solution doline geometry is generally too complex to be expressed in terms of a few parameters. A methodology previously designed by the author, based on acquisition of specific field data and subsequent processing by various Fourier techniques, enabled doline geometry to be considered in its entirety. This paper sets out to investigate which simple rotational body (rotated power function) best fits the geometry of 38 dolines studied within the Classical Karst of Slovenia. It transpires that doline radius to depth ratio changes as a function of volume, whereas the mode of change remains stable regardless of the actual dimensions of individual dolines, and is basically the same at different locations. Doline volumes are very close of those of regular cones of the same dimensions, growing relatively deeper as the volume increases. Two poly‐segment models implied by the power function model and based on earlier work are discussed. It transpires that the studied dolines may be relict forms superimposed upon pre‐existing hidden shafts formed by epikarstic water. Copyright © 2006 John Wiley & Sons, Ltd.     

A survey of antifoulants in sediments from Ports and Marinas along the French Mediterranean coast

Due to deleterious effects on non-target organisms, the use of organotin compounds on boat hulls of small vessels (<25 m) has been widely prohibited. The International Maritime Organisation (IMO) resolved that the complete prohibition on organotin compounds acting as biocides in antifouling systems should commence in 2008. As a result of restrictions on the use of organotin based paints, other antifouling formulations containing organic biocides have been utilised. This survey was conducted to assess the contamination of replacement biocides in the marine environment following the ban of TBT-based paints. Surface sediments samples were collected in the major ports and marinas along the France Mediterranean coastline (Cote d’Azur) and analysed for organotin compounds, Irgarol 1051, Sea-nine 211^TM, Chlorothalonil, Dichlofluanid and Folpet. Every port and marina exhibited high levels of organotin compounds, with concentrations in sediments ranging from 37 ng Sn g⁻¹dry wt in Menton Garavan to over 4000 ng Sn g⁻¹dry wt close to the ship chandler within the port of Villefranche-sur-Mer. TBT degradation indexes suggested that fresh inputs are still made. Among the other antifoulants monitored, only Irgarol 1051 exhibited measurable concentrations in almost every port, with concentrations ranging from 40 ng g⁻¹dry wt (Cannes) to almost 700 ng g⁻¹dry wt (Villefranche-sur-Mer, ship chandler).     

毛乌素沙地东南缘全新世湖相地层石英和钾长石释光测年对比

采集来自毛乌素沙地东南缘巴图湾、大沟湾和三岔河等3处典型湖相地层出露点的3个样品,分别提取石英和钾长石矿物组分,采用小片技术(样品直径2 mm)进行释光年代测试,并将两种矿物年代结果进行对比研究.应用单片再生剂量(SAR)流程测试了石英样品的等效剂量(预热温度选为260℃).剂量恢复实验和光释光特性显示,SAR流程测试条件选择合适,样品沉积前光释光信号晒退完全,说明石英年代结果可靠.另外,应用两步红外激发(激发温度分别为50℃和150℃)的单片再生剂量流程(post-infrared infrared-stimulated luminescence,简写为p IRIR流程)测试钾长石样品的等效剂量,剂量恢复实验和释光特性等各项检验均符合要求,剩余剂量在-0.2~0.026 Gy之间,可忽略不计.钾长石的p IRIR150信号异常衰减速率为0.55~1.71(%/decade),因造成的误差较小,故无需对年代结果进行校正.3处湖相地层的石英年代分别为11.3±0.9、6.5±0.6、2.7±0.2 ka BP,钾长石p IRIR150年代分别为10.0±0.7、6.9±0.5、2.4±0.2 ka BP,两者在误差范围内一致,说明毛乌素沙地东南缘的全新世湖相沉积物适合用钾长石p IRIR150流程进行释光测年.本研究为毛乌素沙地部分样品因石英信号较弱而无法测年问题提供了解决办法,也为该区域全新世,尤其是历史时期(近2000年)以来的环境变化研究提供了年代学支撑.     

Impact of land use changes on catchment soil erosion and sediment yield in the northeastern China: A panel data model application

Land use is an important factor influencing soil erosion and sediment yield (SESY). Regressing soil erosion intensity (SEI) and sediment yield (SY) to land use characteristics can provide necessary information for controlling soil loss. However, current simple regression methods emphasize cross sectional parameters, with less emphasis on temporal variability of relevant land use parameters so that the derived effects of land use change on SESY can be biased. Here, a panel data method was applied to quantify the impact of land use change on SESY in 1954, 1975, and 2015, based on the WaTEM/SEDEM model and seven landscape metrics for 25 reservoir catchments in northeastern China. The results indicate that SEI and area-specific SY (SSY) continuously decreased from 1954 to 2015, which were significantly correlated with landscape metrics such as area-edge metrics of mean patch area (AREA_MN), shape index of the mean related circumscribing circle (CIRCLE_MN), aggregation index of effective mesh size (MESH), patch cohesion index (COHESION), and diversity metrics such as Shannon's diversity index (SHDI), patch richness density (PRD), and modified Simpson's evenness index (MSIEI). The results suggested that catchment SESY can be reduced through decreasing mean patch area, patch mesh size, and physical connectivity of patches, enriching landscape types, and elongating land use patches. These findings are helpful to effectively implement soil conservation measures in northeastern China and similar regions worldwide. The current study also implies that the panel data approach will have beneficial potential applications in earth-science research fields.     

Organic facies and geochemical aspects in Neogene neritic sediments of the Takafu syncline area of central Japan: Paleoenvironmental and sedimentological reconstructions

Abstract Organic petrological observations of kerogen macerals and organic geochemical analyses of carbon isotopes of kerogen macerals and biomarkers were conducted on Neogene neritic sediments of the Takafu syncline area of central Japan. The Senmi, Sakainomiya and Lower Shigarami Formations in that area were deposited at the neritic provinces on the southern edge of the paleo‐Japan Sea during the Late Miocene to Early Pliocene. Sedimentary organic matter in these formations was almost terrigenous in origin. Changes in kerogen maceral compositions reflect sedimentological and tectonic histories evaluated in previous studies from sedimentary facies and paleontology. It was found that carbon isotope ratios (δ¹³C) of kerogen macerals increased from ?28‰ to ?25‰ from the Sakainomiya to the lower part of the Lower Shigarami Formations. The cause of that increase was presumably the expansion of C₄ plants into southwest Japan. The timing was concordant with that of the expansion of C₄ plant grasslands in East Asia. The oxicity (oxic to anoxic) conditions of sea bottoms evaluated from pristane/phytane ratios varied. Particularly, in the lower part of the Senmi Formation, layers in which no steroid biomarkers could be detected were found, and had presumably formed under oxic conditions when strong biodegradation had occurred. Concentrations of regular (C₂₇–C₂₉) steranes and dinosteranes were higher in the Sakainomiya and Lower Shigarami Formations. This indicates that dinoflagellates‐dominant primary productions were higher at those stages. In addition, concentrations of diatomaceous biomarkers such as C₂₆ norsterane increased from the Lower Shigarami Formation, thus adding diatoms to the major producers. Furthermore, similar associations between the increases of δ¹³C values of kerogen macerals and concentrations of diatomaceous biomarkers were observed in the Takafu syncline area. Thus, the expansion of C₄ plants was possibly associated with the high production of diatom in the shallow‐marine areas of the paleo‐Japan Sea during the Neogene Period.     

青海湖全新世硬水效应随时间变化性及其对沉积物~(14)C年龄的校正

通过研究青海湖全新世硬水效应变化与大气~(14)C浓度(X_(atm))之间的关系,确定了湖水溶解无机碳(DIC)与大气~(14)C浓度之比值(X_(DIC)/X_(atm))约为0.790.利用已知X_(atm)随时间变化曲线重建了青海湖全新世的硬水效应,并对沉积物年龄作了相应校正.结果表明,青海湖全新世沉积物(有机质)~(14)C年龄偏老主要缘于湖泊硬水效应,从全新世早期的1000a左右升高到核爆近前的2300a左右,核爆效应之后2005AD又降至1500a左右,其变化至少在很大程度上受控于X_(atm)的波动(对应于以上3个时期,根据X_(atm)所恢复的硬水效应分别为1100a、2150a、1313a).在此基础上,利用硬水效应校正表对青海湖全新世沉积物~(14)C年龄进行了分阶段校正,基于此校正年龄的红度曲线较好地响应了9000-8000cal aBP、6000-5000cal aBP、4200-3800cal aBP、3500-2500cal aBP、1200-1000cal aBP和600-150cal aBP等全球性冷事件.