Environmental significance of mid- to late Holocene sapropels in Old Man Lake,Coorong coastal plain,South Australia: An isotopic,biomarker and palaeoecological perspective

The Holocene successions of numerous shallow lakes located along the Coorong coastal plain in South Australia attest to the impact of rising sea level and changing climate on their depositional environment. Old Man Lake is one of the smallest perennial alkaline lakes in the region. Its succession comprises a basal lagoonal sand rich in humic organic matter (OM) overlain by a 3.7 m thick upward shoaling lacustrine mudstone. The latter features three discrete sapropel units deposited between 3270 and 4910 cal yr BP, a time of increasing aridity throughout southeastern Australia. A core taken from the lake’s eastern margin yielded sedimentological, mineralogical, geochronological and micropaleontological data. Coring at five other sites across the lake provided sections of the humic and sapropelic facies (n = 20) for total organic carbon and Rock–Eval analysis; isotopic characterization of their micritic carbonate (δ¹³C_carb, δ¹⁸O_carb) and co-existing OM (δ¹³C_org); and GC–MS and GC–irMS analysis of their free aliphatic hydrocarbons. For each ‘sapropel event’ high productivity of diatoms and green algae was the principal driver of the accumulation and preservation of OM in such high concentrations. The precursor algal blooms were likely triggered by the influx of fresh water following winter rainfall. The combination of kerogen hydrogen index and δ¹³C_carb–δ¹³C_org, previously employed to track secular changes in algal productivity and organic preservation, proved useful in identifying synchronous geographic differences in these processes across the lake. Highly branched isoprenoids (HBI: C_25:1 ≫ C_20:0) are prominent components of the aliphatic hydrocarbons in the sapropels, confirming the significant contribution of diatoms to their OM. The C isotopic signatures of the principal C_25:1 HBI isomer and the co-occurring C₂₃–C₃₁ odd carbon numbered n-alkanes further document the non-uniformity of biomass preservation within and between the three sapropel units. The evidence from this study suggests that seasonal algal blooms and meromixis, although not necessarily an anoxic hypoliminion, were required for sapropel formation in the Holocene lakes of the Coorong region. Higher resolution sampling, dating and comparative analysis (microfossil, biomarker and isotopic) of these sapropels is required to clarify their potential significance as palaeoclimate proxies.     

Analysis of foraminiferal paleocoenoses from the upper Ypresian sapropelic layers of the northeastern Peri-Tethys

A series of layers rich in organic matter (sapropelites) is known in the upper Ypresian deposits of the northeastern Peri-Tethys. Study of formainifers and quantitative analysis of their different ecological groups showed that proportion of infauna is considerably grater in sapropelic layers than in host deposits. In distinction from infauna, tests of species not burrowing into sediments (epifauna) are partially dissolved. The analyzed paleocoenoses of benthic foraminifers imply that sapropelites have been formed most likely in dysoxic environments, under conditions of the bottom waters contamination by carbon dioxide in response to a high C_org influx, weakened water circulation and low oxygen concentration. The comparison of foraminiferal assemblages with paleocoenoses studied previously in the Paleocene/Eocene boundary sapropelic interbed suggests that deposits rich in C_org originated under the same hydrogeochemical environments.     

Carbon and sulfur isotopic fluctuations associated with the end-Guadalupian mass extinction in South China

Concentrations of total organic matter (TOC), carbon isotopic compositions of carbonate and organic matter (δ¹³C_carb, δ¹³C_org), and sulfur isotopic compositions of carbonate associated sulfate (δ³⁴S_sulfate) across the Guadalupian–Lopingian (G–L) boundary were analyzed from identical samples of Tieqiao section, Laibin, Guangxi province, South China. The δ¹³C_carb values show a positive excursion from − 0.45‰ to the peak of 3.80‰ in the Laibin limestone member of the Maokou Formation, followed by a drastic drop to − 2.60‰ in the lowest Heshan formation, then returned to about 1.58‰. Similar to the trends of the δ¹³C_carb values, Δ¹³C_carb–org values also show a positive excursion followed by a sharp negative shift. The onset of a major negative carbon isotope excursion postdates the end Guadalupian extinction that indicates subsequent severe disturbance of the ocean–atmosphere carbon cycle. The first biostratigraphic δ³⁴S_sulfate values during the G–L transition exhibit a remarkable fluctuation: a dramatic negative shift followed by a rapid positive shift, ranging from 36.88‰ to − 37.41‰. These sulfate isotopic records suggest that the ocean during the G–L transition was strongly stratified, forming an unstable chemocline separating oxic shallow water from anoxic/euxinic deep water. Chemocline excursions, together with subsequent rapid transgression and oceanic anoxia, were likely responsible for the massive diversity decline of the G–L biotic crisis.     

Molecular and isotopic partitioning of low-molecular-weight hydrocarbons during migration and gas hydrate precipitation in deposits of a high-flux seepage site

Detailed knowledge of the extent of post-genetic modifications affecting shallow submarine hydrocarbons fueled from the deep subsurface is fundamental for evaluating source and reservoir properties. We investigated gases from a submarine high-flux seepage site in the anoxic Eastern Black Sea in order to elucidate molecular and isotopic alterations of low-molecular-weight hydrocarbons (LMWHC) associated with upward migration through the sediment and precipitation of shallow gas hydrates. For this, near-surface sediment pressure cores and free gas venting from the seafloor were collected using autoclave technology at the Batumi seep area at 845 m water depth within the gas hydrate stability zone.Vent gas, gas from pressure core degassing, and from hydrate dissociation were strongly dominated by methane (> 99.85 mol.% of ∑[C₁–C₄, CO₂]). Molecular ratios of LMWHC (C₁/[C₂ + C₃] > 1000) and stable isotopic compositions of methane (δ¹³C = ? 53.5‰ V-PDB; D/H around ? 175‰ SMOW) indicated predominant microbial methane formation. C₁/C₂₊ ratios and stable isotopic compositions of LMWHC distinguished three gas types prevailing in the seepage area. Vent gas discharged into bottom waters was depleted in methane by > 0.03 mol.% (∑[C₁–C₄, CO₂]) relative to the other gas types and the virtual lack of ¹⁴C–CH₄ indicated a negligible input of methane from degradation of fresh organic matter. Of all gas types analyzed, vent gas was least affected by molecular fractionation, thus, its origin from the deep subsurface rather than from decomposing hydrates in near-surface sediments is likely.As a result of the anaerobic oxidation of methane, LMWHC in pressure cores in top sediments included smaller methane fractions [0.03 mol.% ∑(C₁–C₄, CO₂)] than gas released from pressure cores of more deeply buried sediments, where the fraction of methane was maximal due to its preferential incorporation in hydrate lattices. No indications for stable carbon isotopic fractionations of methane during hydrate crystallization from vent gas were found. Enrichments of ¹⁴C–CH₄ (1.4 pMC) in short cores relative to lower abundances (max. 0.6 pMC) in gas from long cores and gas hydrates substantiates recent methanogenesis utilizing modern organic matter deposited in top sediments of this high-flux hydrocarbon seep area.     

Amino acid and amino sugar transformation during sedimentation in lacustrine systems

We compared the degradation behaviour of amino sugars (ASs) and amino acids (AAs) during sedimentation in two lakes. Concentrations of individual ASs and AAs were measured in plankton, sediment trap and sediment samples from Lake Zug (LZ; eutrophic, stratified, permanently anoxic below 170 m) and Lake Brienz (LB; oligotrophic, oxic throughout the water column). In the plankton samples AAs comprised 37–50% of the organic carbon (C_org) and 41–65% of the N. With increasing water depth the fraction of C_org and N as AAs almost halved in both lakes. At the sediment surface the contribution of AAs to the C_org pool was slightly greater, but in the sediments the proportion further decreased downwards to values of 1% of the C_org pool in LB and 8% in LZ, and 3% and 17% of the N pool, respectively. ASs contributed to a smaller extent to the planktonic organic matter (OM). Within the water column, the contribution decreased in both lakes. In contrast, in the sediments the contribution of ASs to the C_org and N pools increased slightly with depth, indicating AS accumulation. We applied degradation indices based on ASs, AAs and chlorins, which all revealed transformation with OM sedimentation. However, some indices were more sensitive to early degradation (e.g. reactivity index) and others to an intermediate level of degradation (e.g. chlorin index and non-protein AAs). Despite the different trophic status and redox conditions, the general pattern of degradation was similar in both lakes, but was more pronounced in the sediments of the eutrophic LZ.     

Organic geochemistry and depositional environment of the Aptian bituminous limestone in the Kale Gümüşhane area (NE-Turkey): An example of lacustrine deposits on the platform carbonate sequence

The Jurassic–Lower Cretaceous aged carbonate sequence is widely exposed in the southern zone of Eastern Pontides. Aptian black bituminous limestone is found in the upper part of this sequence in the Kale area (Gümüşhane). This limestone contains faunal remains (e.g., gastropod, ostracod, characean stems and miliolid type benthic foraminifera) that indicate a freshwater, lacustrine depositional environment.The total organic carbon (TOC) values of the bituminous limestone samples range from 0.11–1.30% with an average TOC value of 0.54%. The hydrogen index (HI) varies from 119–448 mg HC/g TOC (average HI 298 mg HC/g TOC) indicating that the limestone contains gas prone as well as oil prone organic matter. Pyrolysis data prove that the organic matter content in the bituminous limestone consists of Type II kerogen. The average T_max value for bituminous limestone samples is 438 °C (434–448 °C). Bitumen/TOC ratios for bituminous limestone are 0.05 and 0.04. The T_max values and the ratios indicate that the bituminous limestone samples contain early mature to mature organic matter.Analysis of solvent extracts from the two richest bituminous limestones show a predominance of high carbon number (C₂₆–C₃₀) n-alkanes. The Pr/Ph ratio and CPI value are 1.34 and 0.96, respectively. C₂₉ is the dominant sterane, with C₂₉ > C₂₇ > C₂₈. The bituminous limestone samples have low C₂₂/C₂₁ ratios, high C₂₄/C₂₃ tricyclic terpane ratios and very low C₃₁R/C₃₀ hopane ratios (<0.25). These data are consistent with the bituminous limestones being deposited in a lacustrine environment.     

Geochemistry and origin of the Neoproterozoic Dahongliutan banded iron formation (BIF) in the Western Kunlun orogenic belt,Xinjiang (NW China)

The Neoproterozoic (593–532 Ma) Dahongliutan banded iron formation (BIF), located in the Tianshuihai terrane (Western Kunlun orogenic belt), is hosted in the Tianshuihai Group, a dominantly submarine siliciclastic and carbonate sedimentary succession that generally has been metamorphosed to greenschist facies. Iron oxide (hematite), carbonate (siderite, ankerite, dolomite and calcite) and silicate (muscovite) facies are all present within the iron-rich layers. There are three distinctive sedimentary facies BIFs, the oxide, silicate–carbonate–oxide and carbonate (being subdivided into ankerite and siderite facies BIFs) in the Dahongliutan BIF. They demonstrate lateral and vertical zonation from south to north and from bottom to top: the carbonate facies BIF through a majority of the oxide facies BIF into the silicate–carbonate–oxide facies BIF and a small proportion of the oxide facies BIF.The positive correlations between Al₂O₃ and TiO₂, Sc, V, Cr, Rb, Cs, Th and ∑REE (total rare earth element) for various facies of BIFs indicate these chemical sediments incorporate terrigenous detrital components. Low contents of Al₂O₃ (<3 wt%), TiO₂ (<0.15 wt%), ∑REE (5.06–39.6 ppm) and incompatible HFSEs (high field strength elements, e.g., Zr, Hf, Th and Sc) (<10 ppm), and high Fe/Ti ratios (254–4115) for a majority of the oxide and carbonate facies BIFs suggest a small clastic input (<20% clastic materials) admixtured with their original chemical precipitates. The higher abundances of Al₂O₃ (>3 wt%), TiO₂, Zr, Th, Cs, Sc, Cr and ∑REE (31.2–62.9 ppm), and low Fe/Ti ratios (95.2–236) of the silicate–carbonate–oxide facies BIF are consistent with incorporation of higher amounts of clastic components (20%–40% clastic materials). The HREE (heavy rare earth element) enrichment pattern in PAAS-normalized REE diagrams exhibited by a majority of the oxide and carbonate facies BIFs shows a modern seawater REE signature overprinted by high-T (temperature) hydrothermal fluids marked by strong positive Eu anomalies (Eu/Eu¹_PAAS = 2.37–5.23). The low Eu/Sm ratios, small positive Eu anomaly (Eu/Eu¹_PAAS = 1.10–1.58) and slightly MREE (middle rare earth element) enrichment relative to HREE in the silicate–carbonate–oxide facies BIF and some oxide and carbonate facies BIFs indicate higher contributions from low-T hydrothermal sources. The absence of negative Ce anomalies and the high Fe³⁺/(Fe³⁺/Fe²⁺) ratios (0.98–1.00) for the oxide and silicate–carbonate–oxide BIFs do not support ocean anoxia. The δ¹³C_V-PDB (−4.0‰ to −6.6‰) and δ¹⁸O_V-PDB (−14.0‰ to −11.5‰) values for siderite and ankerite in the carbonate facies BIF are, on average, ∼6‰ and ∼5‰ lower than those (δ¹³C_V-PDB = −0.8‰ to + 3.1‰ and δ¹⁸O_V-PDB = −8.2‰ to −6.3‰) of Ca–Mg carbonates from the silicate–carbonate–oxide facies BIF. This feature, coupled with the negative correlations between FeO, Eu/Eu¹_PAAS and δ¹³C_V-PDB, imply that a water column stratified with regard to the isotopic omposition of total dissolved CO₂, with the deeper water, from which the carbonate facies BIF formed, depleted in δ¹³C that may have been derive from hydrothermal activity.Integration of petrographic, geochemical, and isotopic data indicates that the silicate–carbonate–oxide facies BIF and part of the oxide facies BIF precipitated in a near-shore, oxic and shallow water environment, whereas a majority of the oxide and carbonate facies BIFs deposited in anoxic but Fe²⁺-rich deeper waters, closer to submarine hydrothermal vents. High-T hydrothermal solutions, with infusions of some low-T hydrothermal fluids, brought Fe and Si onto a shallow marine, variably mixed with detrital components from seawaters and fresh waters carrying continental landmass and finally led to the alternating deposition of the Dahongliutan BIF during regression–transgression cycles.The Dahongliutan BIF is more akin to Superior-type rather than Algoma-type and Rapitan-type BIF, and constitutes an additional line of evidence for the widespread return of BIFs in the Cryogenian and Ediacaran reflecting the recurrence of anoxic ferruginous deep sea and anoxia/reoxygenation cycles in the Neoproterozoic. In combination with previous studies on other Fe deposits in the Tianshuihai terrane, we propose that a Fe²⁺-rich anoxic basin or deep sea probably existed from the Neoproterozoic to the Early Cambrian in this area.     

Physils and organic matter-base palaeoenvironmental records of the K/Pg boundary transition from the late Cretaceous-early Palaeogene succession of the Um-Sohryngkew River section of Meghalaya,India

A continuous, shallow marine succession of the Um-Sohryngkew River section is distinct as it contains late Maastrichtian-early Danian planktonic foraminiferal zones and the K/Pg boundary, although K/Pg transition events remain inconclusive. Physils divide entire succession in to lower, middle and upper sub-divisions and represent anomalous values of redox-sensitive elements (δCe, La/Yb and Gd/Yb) in biozone CF3. Organic matter when analyzed show TOC and C spikes in biozone CF3. Illite thermometry also revealed sudden increase in the palaeo-temperature (>140 °C) for yellowish brown 1–2 mm thick organic rich clay layer in biozone CF3. Interestingly, conspicuous increase in the short chain n-alkanes and fatty acids is observed in the biozone CF3, although, long chain n-alkanes (C₂₇–C₃₃) derived from terrestrial plants show low abundance throughout the succession.High amount of combustion derived fluoranthene, pyrene, chrysene, benzo(a) anthracene PAH compounds found in the biozone CF3 are analogous to those reported from the K/T boundary sections of Stevns Klint, Gubbio, Woodside Creek and Arroyo el Mimbral. The pyrolitic signatures of these organic macro-molecules reflect global fire, caused distress to biota (during the deposition of biozone CF3 layer) which is coincidental with the well documented Ce anomaly layer, but, preceded by planktonic foraminiferal change in biozone P0 and PGE anomaly bearing layer in the biozone CF2. These organic macro-molecules reflect global fire, induced by the heat supplied by the late Cretaceous Abor and/or Deccan extrusions perhaps linked with the K/T transition events as later initiated prior to the K/Pg boundary, however, the main episode of Deccan volcanic activity occurred ∼300 ky earlier or at the K/Pg boundary itself. The deposition of 1–2 mm thick, yellowish brown, smooth (with conchoidal fracture) pyrite nodules and micro-spherules bearing organic rich clay layer marked with the decrease in the carbonate content (2.43%) that lies at the contact between the silty mudstone and grey calcareous shale located in the biozone CF3 of this succession coincides with the first appearance of Pseudoguembelina hariaensis representing age of 66.83–65.45 Ma is also related to the India’s collision with the Eurasia and Burma andextrusion of Abor volcanic.These events also endorse succeeding events such as anomalous concentration of platinum group of elements and concentration of spherules during biozone CF2, which are other end Cretaceous events before the advent of the K/Pg boundary.     

Improved understanding of the petroleum systems of the Niger Delta Basin,Nigeria

Biomarker and n-alkane compound specific stable carbon isotope analyses (CSIA) were carried out on 58 crude oil samples from shallow water and deepwater fields of the Niger Delta in order to predict the depositional environment and organic matter characteristics of their potential source rocks. Using a source organofacies prediction approach from oil geochemistry, the presence in the western deepwater oils relatively abundant C₂₇ steranes, C₃₀ 24-n-propyl cholestane, low oleanane index, relatively low pr/ph ratios, gammacerane, and positive to nearly flat C₁₂–C₃₀ n-alkane compound specific stable carbon isotope profiles, suggests that the source facies that expelled these oils contain significant marine derived organic matter deposited under sub-oxic and stratified water column conditions. This contrasts with the terrigenous organic matter dominated source rocks accepted for shallow water Niger Delta oils. Oils in the shallow water accumulations can be separated into terrigenous and mixed marine-terrigenous families. The terrigenous family indicates expulsion from source rock(s) containing overwhelmingly higher plant source organic matter (average oleanane index = 0.48, high C₂₉ steranes) as well as having negative sloping n-alkane isotope profiles. Oxic source depositional conditions (pr/ph > 2.5) and non-stratified conditions (absence to low gammacerane content) are inferred for the terrigenous family. The mixed marine-terrigenous family has biomarker properties that are a combination of the deepwater and terrigenous shallow water oils. Bitumen extracts of the sub-delta Late Cretaceous Araromi Formation shale in the Dahomey Basin are comparable both molecularly and isotopically to the studied western deepwater oil set, but with an over all poor geochemical correlation. This poor geochemical match between Araromi shale and the western deepwater oils does not downgrade the potential of sub-delta Cretaceous source rock contribution to the regional oil charge in the deepwater Niger Delta.     

Characterization of organic matter and depositional environment of Tertiary mudstones from the Sylhet Basin,Bangladesh

The Sylhet Basin of Bangladesh is a sub-basin of the Bengal Basin. It contains a very thick (up to 22 km) Tertiary stratigraphic succession consisting mainly of sandstones and mudstones. The Sylhet succession is divided into the Jaintia (Paleocene–late Eocene), Barail (late Eocene–early Miocene), Surma (middle–late Miocene), Tipam (late Miocene–Pliocene) and Dupitila Groups (Pliocene–Pleistocene), in ascending order. The origin of the organic matter (OM) and paleoenvironment of deposition have been evaluated on the basis of C, N, S elemental analysis, Rock-Eval pyrolysis and gas chromatography–mass spectrometry (GC–MS) analysis of 60 mudstone samples collected from drill core and surface outcrops. Total organic carbon (TOC) content ranges from 0.11% to 1.56%. Sulfur content is low in most samples. TOC content in the Sylhet succession varies systematically with sedimentation rate, with low TOC caused by clastic dilution produced by high sedimentation rates arising from rapid uplift and erosion of the Himalaya.The OM in the succession is characterized by systematic variations in pristane/phytane (Pr/Ph), oleanane/C₃₀ hopane, n-C₂₉/n-C₁₉ alkane, Tm/Ts [17α(H)-22,29,30-trisnorhopane/18α(H)-22,29,30-trisnorhopane] and sterane C₂₉/(C₂₇ + C₂₈ + C₂₉) ratios during the middle Eocene to Pleistocene. Based on biomarker proxies, the depositional environment of the Sylhet succession can be divided into three phases. In the first (middle Eocene to early Miocene), deposition occurred completely in seawater-dominated oxic conditions, with abundant input of terrestrial higher plants, including angiosperms. The second phase (middle to late Miocene) consisted of mainly freshwater anoxic conditions along with a small seawater influence according to eustasic sea level change, with diluted OM derived from phytoplankton and a lesser influence from terrestrial higher plants. Oxygen-poor freshwater conditions prevailed in the third phase (post-late Miocene). Planktonic OM was relatively abundant in this stage, while a high angiosperm influx prevailed at times. T_max values of ca. 450 °C, vitrinite reflectance (R_o) of ca. 0.66% and methylphenanthrene index (MPI 3) of ca. 1 indicate the OM to be mature. The lower part (middle Eocene to early Miocene) of the succession with moderate TOC content and predominantly terrestrial OM could have generated some condensates and oils in and around the study area.     

Distribution of organic matter in rocks of the Bazhenov horizon (West Siberia)

We studied the distribution of organic carbon in rocks of the Bazhenov horizon, a unique object of predominantly biogenic sedimentation in the West Siberian sedimentary basin. The contents of organic carbon in the rocks were determined using the data from 4094 core analyses and core-log relationships derived from 48,500 radioactive- and electrical-log measurements. For the Bazhenov and Tutleima Formations, both approaches gave the same results. The average content of organic carbon in the rocks is 7.7%. These data were used to compile a detailed map of the distribution of organic carbon contents in sedimentary rocks of the basin. It was shown that the average organic carbon content in the rocks increases from 2-4% on the periphery of the basin to 10-12% in its central, deepest part. The distribution of C_org values in the basin is highly asymmetric. The highest C_org values are observed in the southwestern part of the basin interior, where beds with > 10% C_org range in thickness from 5 to 12-15 m. In sections, the highest C_org values are observed in their middle and upper parts, composed predominantly of silicites and mixtites enriched in biogenic silica.     

Changes of environments and human activity at the Sannai-Maruyama ruins in Japan during the mid-Holocene Hypsithermal climatic interval

Sannai-Maruyama is one of the most famous and best-researched mid-Holocene (mid-Jomon) archaeological sites in Japan, because of a large community of people for a long period. Archaeological studies have shown that the Jomon people inhabi1ted the Sannai-Maruyama site from 5.9 to 4.2 ± 0.1 cal kyr BP However, a continuous record of the terrestrial and marine environments around the site has not been available. Core KT05-7 PC-02, was recovered from Mutsu Bay, only 20 km from the site, for the reconstruction of high-resolution time series of environmental records, including sea surface temperature (SST). C₃₇ alkenone SSTs showed clear fluctuations, with four periods of high (8.4–7.9, 7.0–5.9, 5.1–4.1, and 2.3–1.4 cal kyr BP) and four of low (?8.4, 7.9–7.0, 5.9–5.1, and 4.1–2.3 cal kyr BP) SST. Thus, each SST cycle lasted 1.0–2.0 kyr, and the amplitude of fluctuation was about 1.5–2.0 °C. Total organic carbon (TOC) and C₃₇ alkenone contents, and the TOC/total nitrogen ratio indicate that marine biogenic production was low before 7.0 cal kyr BP, but was clearly increased between 5.9 and 4.0 cal kyr BP, because of stronger vertical mixing. During the period when the community at the site prospered (between 5.9 and 4.2 ± 0.1 cal kyr BP), the terrestrial climate was relatively warm. The high relative abundance of pollen of both Castanea and Quercus subgen. Cyclobalanopsis supports the interpretation that the local climate was optimal for human habitation. Between 5.9 and 5.1 cal kyr BP, in spite of warm terrestrial climates, the C₃₇ alkenone SST was low; this apparent discrepancy may be attributed to the water column structure in the Tsugaru Strait, which differed from the modern condition. The evidence suggests that at about 5.9 cal kyr B.P, high productivity of marine resources such as fish and shellfish and a warm terrestrial climate led to the establishment of a human community at the Sannai-Maruyama site. Then, at about 4.1 ± 0.1 cal kyr BP, abrupt marine and terrestrial cooling, indicated by a decrease of about 2 °C in the C₃₇ alkenone SST and an increase in the pollen of taxa of cooler climates, led to a reduced terrestrial food supply, causing the people to abandon the site. The timing of the abandonment is consistent with the timing (around 4.0–4.3 cal kyr BP) of the decline of civilizations in north Mesopotamia and along the Yangtze River. These findings suggest that a temperature rise of ～2 °C in this century as a result of global warming could have a great impact on the human community and especially on agriculture, despite the advances of contemporary society.     

Sicilian bottled natural waters: Major and trace inorganic components

Sixteen bottled waters of various Sicilian brands, 11 natural mineral waters and five normal drinking waters, were analyzed for major and trace inorganic components by ion chromatography (IC) and inductively coupled plasma-mass spectrometry (ICP-MS), respectively. The bottled waters represent a variety of water types with significantly different compositions in terms of salinity, major components and trace elements. Chemically, they range from Ca–HCO₃ and Ca–SO₄ to Na–HCO₃ types. Total dissolved solids ranges from 54 to 433 mg/L, total hardness from 25 to 238 mg/L CaCO₃, and measured Na content from 5.7 to 57 mg/L. According to total dissolved ions, all the bottled waters were classified as oligomineral (50 < TDS < 500 mg/L). All the bottled waters analyzed here had elemental concentrations which did not exceed the guideline and directive values, although a high concentration of Al was noted for one bottled water (O7, central Sicily) and high Rb and V in a bottled water (O1) from the Etna volcanic area. With regard to trace elements, the chemical quality of bottled waters was assessed by a metal index (MI). Chemical characteristics were compared with 10 tap water samples from private houses or public places, representative of the public water supply in Palermo, the largest and most densely populated city in Sicily. The municipal waters analyzed, belonging to HCO₃-alkaline earth and Cl–SO₄-alkaline earth waters, showed concentrations of chemical inorganic components well within drinking water limits. The data also indicated that the water supplied by the municipal authority is of fair quality, although fairly hard and high in Na concentration. Several considerations indicate that there is no sufficient reason to prefer bottled waters to tap waters.     

Statistical categorization geochemical modeling of groundwater in Ain Azel plain (Algeria)

Water analysis data of 54 groundwater samples from 18 uniformly distributed wells were collected during three campaigns (June, September and December 2004). Q-mode hierarchical cluster analysis (HCA) was employed for partitioning the water samples into hydrochemical facies. Interpretation of analytical data showed that the abundance of major ions was identified as follows: Ca ? Mg > Na > K and HCO₃ ? Cl > SO₄. Three major water facies are suggested by the HCA analysis. The samples from the area were classified as recharge area waters (Ca–Mg–HCO₃ water), transition area waters (Mg–Ca–HCO₃–Cl water), and discharge area waters (Mg–Ca–Cl–HCO₃ water). Inverse geochemical modeling suggests that relatively few phases are required to derive the water chemistry in the area. In a broad sense, the reactions responsible for the hydrochemical evolution in the area fall into two categories: (1) evaporite weathering reactions and (2) precipitation of carbonate minerals.     

Rerewhakaaitu Tephra,a land–sea marker for the Last Termination in New Zealand,with implications for global climate change

The Rerewhakaaiutu Tephra erupted from Okataina Volcanic Centre, North Island, New Zealand, at 14,700±95 ¹⁴C yr BP (ca 17,600 cal yr BP) at a time of rapid re-organisation of Earth's climate system at the end of the Last Glacial (Termination I). It provides a distinctive isochron in a range of different environments in North Island and in adjacent South Pacific Ocean sediments. Terrestrial evidence, based on fluvial aggradation and downcutting relationships, loess accumulation rates, palaeovegetation patterns, and buried soil development and mineralogy, shows that marked amelioration of climate occurred shortly before the Rerewhakaaitu Tephra was deposited. Similarly, marine evidence from around this time shows major changes in accumulation rates of sediment and aeolian quartz and in the abundance of various marine organisms, while foraminiferal oxygen and carbon isotope records indicate that the arrival of the glacial meltwater signal occurred close to or just after the deposition of the Rerewhakaaitu Tephra. These changes are discussed in relation to controls on climate by oceanic and atmospheric mechanisms. The re-organisation of climate commencing at ca 15,000–14,500 ¹⁴C yr BP (ca 18,000–17,400 cal yr BP) is detected elsewhere in the Southern Hemisphere and evidently was linked to orbitally forced warming which is thought to have initiated ice retreat in both hemispheres.     

Glacial–interglacial productivity and environmental changes in Lake Biwa,Japan: A sediment core study of organic carbon,chlorins and biomarkers

Temporal changes in paleoproductivity of Lake Biwa (Japan) over the past 32 kyr have been studied by analyzing bulk organic carbon and photosynthetic pigments (chlorins) in the BIW95-5 core. Primary productivity was estimated on the assumption of C/N_org values of 8 for autochthonous organic matter (OM) and 25 for allochthonous OM and using an equation developed for the marine environment. The estimate indicates that primary productivity ranges from 50 to 90 g C m^?2 yr^?1 in the Holocene, while it is ～60 g C m^?2 yr^?1 on average in the last glacial. Pheophytin a and pheophorbide a are the major chlorins. A downcore profile of chlorin concentration normalized to autochthonous organic carbon (OC) shows a decreasing trend. Chlorin productivity was corrected by removal of the effect of post-burial chlorin degradation. The temporal profile of chlorin productivity thereby obtained resembles that from autochthonous OC.The difference in primary productivity between the Holocene and the glacial for the lake is markedly smaller than that for Lake Baikal situated in the boreal zone. This difference between the two lakes is probably caused by the difference in their climatic conditions, such as temperature and precipitation. Precipitation at Lake Biwa is relatively large during the glacial and the Holocene because of the continuous influence of the East Asian monsoon. Lake Baikal precipitation is generally small as a result of control by the continental (Siberia) climate regime. In addition, a significant difference in productivity between the glacial and the Holocene for Lake Baikal may be essentially controlled by the hydrodynamic systems in the lake.Lake Biwa terrigenous OM input events occurred at least five times over the period 11–32 kyr BP, suggesting enhanced monsoon activity. Molecular examination of the layer with a large input of terrigenous OM during the Younger Dryas indicates that concentrations of terrigenous biomarkers such as n-C₂₇–C₃₁ alkanes, lignin phenols, cutin acids, ω-hydroxy acids and C₂₉ sterols are high, suggesting that soil OM with peat-like material entered the lake as a result of flooding. An enhanced sedimentation rate in the last 3000 years might have been partially caused by agricultural activity around the lake.     

Organic geochemical characteristics and oil generating potential of the Upper Jurassic Safer shale sediments in the Marib-Shabowah Basin,western Yemen

The organic rich Safer shales exposed in the north-central part of onshore Marib-Shabowah Basin are evaluated and their depositional environments are interpreted. Total organic carbon contents (TOC) of the shales range from 1.02–16.8 wt%, and yield hydrogen index (HI) values ranging from 130 to 820 mg HC/g TOC, consistent with mainly Type II with minor contributions from Type I and mixed Types II–III kerogens. The Safer shale samples have vitrinite reflectance values in the range of 0.5–1.0 R_o%, indicating early mature to peak mature stage for oil generation. T_max values range from 429–438 °C, which are in reasonably good agreement with vitrinite reflectance data. Kerogen microscopy shows that the Safer shales are characterized by high amounts of organic matter, consisting predominantly of yellow fluorescing amorphous organic matter and alginite of marine origin. This is supported by their high content of hydrogen rich Type II and I oil-prone kerogen.The biomarker distributions of the Upper Jurassic Safer extracts are characterized by dominant low to medium molecular weight compounds (n-C₁₄ to n-C₂₀), low Pr/Ph ratio (<1.0), high phytane/n-C₁₈ ratios (0.82–2.68), and predominant regular sterane C₂₇. All biomarker parameters clearly indicate that the organic matter was derived from marine algal inputs and deposited under anoxic (reducing) conditions. Hypersaline conditions also prevailed during deposition of these sediments, as indicated by the presence of gammacerane.     

Geochemical characterisation of Fika Formation in the Chad (Bornu) Basin,northeastern Nigeria: Implications for depositional environment and tectonic setting

Late Cretaceous shales of the Fika Formation in the Chad (Bornu) Basin, northeastern Nigeria, were analysed to define paleoenvironment and source of the organic matter, and their relation to tectonic setting. The organic carbon and sulphur contents of Fika shale samples are in the range of 0.51–2.13 and 0.31–1.65 wt.%, respectively, pointing that these shales were deposited in suboxic-anoxic marine conditions. The biomarker and chemical compositions provide evidence for a major contribution of aquatic algae and microorganisms with minor terrigenous organic matter input. Moderate salinity stratification and relatively anoxic-suboxic bottom water conditions are also likely in the Fika shales. Therefore, stratified water column with moderate salinity and relatively anoxic-suboxic bottom water conditions have contributed to organic matter (OM) preservation in the Fika shale layer. Fika shale samples are rich in SiO₂ (54.80 wt.%), followed by Al₂O₃ (23.75 wt.%) and Fe₂O₃ (10.19 wt.%). Compared with average shale, the analysed shale samples are obviously enriched in Al₂O₃ (23.75 wt.%), TiO₂ (1.34 wt.%), and P₂O₅ (0.30 wt.%), indicating that these sediments are rich in clay minerals and represent a good possibility for enhanced organic matter production and enrichment.Plots of Fika shale on bivariate discriminant function diagram suggest an active continental margin setting for the provenance. The inferred tectonic setting for the late Cretaceous shales of the Fika Formation of the Chad (Bornu) Basin is in agreement with the tectonic evolutionary history of the west and central Africa during the Cretaceous period.     

Pregnanes as molecular indicators for depositional environments of sediments and petroleum source rocks

Steroids with unconventional side chains have increasingly been applied as diagnostic markers for geological source and age assessments. However, one of the most distinctive characteristics, the abnormal abundance of pregnane and homopregnane in ancient sediments and petroleum, remains unresolved. Higher pregnane and homopregnane, as well as C₂₃–C₂₆ 20-n-alkylpregnanes, relative to the regular steranes were observed in samples collected from different petroleum basins in China. These included Precambrian marine carbonate-derived petroleum (NW Sichuan Basin), Lower Paleozoic marine marl derived crude oils (Tarim Basin), and Eocene hypersaline lacustrine carbonate source rocks and associated petroleum (Bohai Bay Basin). However, all of the samples have many common biomarker characteristics, such as pristane/phytane ratios < 1, low amounts of diasteranes and high C₂₉/C₃₀ hopane (∼0.6–1), C₃₅/C₃₄ hopane (mostly ⩾ 1) and dibenzothiophene/phenanthrene (DBT/PHEN, mostly 0.5–1) ratios revealing a contribution from anoxic carbonate/marl source rocks deposited in restricted, clastic-starved settings. We suggest that 5α,l4β,l7β-pregnane and homopregnane, as well as their higher C₂₃–C₂₆ homologues, are geological products derived from steroids bound to the kerogen by a sulfurized side chain. Carbon or carbonate minerals are considered to be natural catalysts for this cracking reaction via preferential cleavage of the bond between C-20 and C-22. Similar distributions occur in the short chain analogues of 4-methylsterane, triaromatic steroid and methyltriaromatic steroid hydrocarbons, providing circumstantial evidence for this proposal. The ratio of pregnane and homopregnane to the total regular steranes and the ratio of C₂₇ diasteranes to cholestanes can be sensitive indicators of sedimentary environments and facies. In general, high diasteranes and low pregnanes (with homologues) indicate an oxic water column or significant input of terrigenous organic matter in clay rich source rocks and some organic lean carbonate rocks. Low diasteranes with high pregnanes implies restricted, sulfur rich conditions, typical of anoxic carbonate source rocks. Furthermore, the two ratios may be useful to assess the variation of mineralogy and openness of source rock depositional settings.     

Arsenic,iron and organic matter in sediments and groundwater in the Pannonian Basin,Hungary

In the central part of the Pannonian Basin, factors controlling the distribution of As in sediments and groundwater of the upper 500 m were studied. In core samples, the amounts of As, Fe and Mn extractable with hydroxylamine hydrochloride (NH₂OH · HCl) in 25% acetic acid, the proportion of the <0.063 mm size fraction, and the sediment organic C (C_org) contents were measured. In the groundwaters concentrations of As, humic substances, and selected major chemical components were determined. In most core samples extractable Fe, as FeOOH, and C_org are correlated, but some samples have excess Fe, or organic matter. In cases where either excess Fe or excess organic matter is found, the amount of As is also elevated. The spatial distribution of As in the groundwater and the lack of a consistent correlation of As with a single component indicate that there is no single factor controlling the concentration of dissolved As over the entire study area. The only consistent feature is enrichment of As relative to Fe in the groundwater, compared to the sediments. This suggests that the dissolution of Fe minerals, which primarily adsorb As, is not congruent. In reducing conditions Fe(III) oxyhydroxides together with adsorbed As dissolve, and siderite with little or no As precipitates. When sub-regions are separated and studied individually, it can be shown that hydrogeological features of the sediments, the proportions of Fe minerals and sedimentary organic matter, and the concentration of dissolved humic materials, all influence the accumulation and mobilization of As. The significance of the different mobilizing processes, however, and the mean concentration of As, is different in the recharge, through-flow and discharge areas.