Normal alkanes from C12 to C36, pristane and phytane were identified in the Cretaceous/Tertiary (K/T) boundary sediments at Kawaruppu, Hokkaido, Japan. These compounds were found at the levels of sub- to a few nmol g-1. Total concentrations of the n-alkanes within the boundary claystone were generally one third to one half of those in the sediments above and below the claystone. The smaller concentrations within the claystone were mainly due to smaller concentrations of longer chain n-alkanes (C25 to C31) than in the sediments above and below it. The longer chain n-alkanes were likely from terrestrial plants and reflected their small population at the end of Cretaceous. The concentration of longer chain n-alkanes decreased rapidly at the base of the boundary claystone, indicating the sudden cease of terrestrial n-alkane input, continued low to the horizon at the upper two thirds of the claystone and then, started increasing toward the top of the claystone. The n-alkane concentration change indicates the period of the small input of terrestrial n-alkanes to be ca. 7, 000 years at most and the recovery period to be ca. 2, 000 years. The depth distribution pattern of pristane plus phytane concentrations in the K/T sediments roughly resembles that of the n-alkanes.
The integrated effects of photosynthesis-respiration and precipitation-dissolution of CaCO3 on the partial pressure of carbon dioxide in seawater (PCO2) by the carbonate-producing biological activities (e.g., coral reefs, coccolithophorids) have been extensively debated. Here we document PCO2 values inside and outside the lagoon of Majuro Atoll. The PCO2 was enhanced by 27 μatm on average within the atoll relative to ocean values. Alkalinity-total CO2 relationship in the lagoonal water indicates that calcification plays a major role in the net carbon cycle in this reef system while rapid turnover of organic matter results in no significant net air-sea flux. The data show that atoll- and barrier-type of coral reefs potentially work as a source of CO2.
Twenty six polycyclic aromatic hydrocarbons (PAHs) from naphthalene to coronene were found in the K/T boundary sediments at Kawaruppu, Hokkaido, Japan and their concentrations were estimated except for naphthalene. Another 28 PAHs were found qualitatively. The total concentration of those 25 PAHs (except naphthalene) in each sediment was in the range of 2.3 to 11.4 nmol g-1 and showed no specific feature for the boundary claystone or for sediments above and below it. Individual PAHs were present at the level of sub-nmol g-1 or less. Higher concentrations in the sediments within the claystone than those above and below it were observed for parent (i.e., non-alkylated) tetracyclic PAHs and to a certain extent larger peri-condensed parent PAHs. It is not likely that the higher concentrations within the claystone were due to the 65 million year diagenesis because of roughly constant ratios of β- to α-alkylated PAHs in the sediments above, within and below the boundary claystone. The observation may indicate a possible combustion origin of those PAHs within the boundary claystone, although evidence at Kawaruppu is not so strong as at Stevns Klint, Gubbio and Woodside Creek.
Temporal geochemical and isotopical variations in the Ulreungdo alkali volcanic rocks provide important constraints on the origin and evolution of the volcanic rocks in relation to backarc basin tectonism. We determined the K-Ar ages, major and trace element contents, and Nd and Sr isotopic ratios of the alkali volcanic rocks. The activities of Ulreungdo volcanoes can be divided, on the basis of radiometric ages and field occurrences, into five stages, though their activities range from 1.4 Ma to 0.01 Ma with short volcanic hiatus (ca. 0.05∼0.3 Ma). The Nd-Sr isotopic data for Ulreungdo volcanic rocks enable us to conclude that: (1) the source materials of Ulreungdo volcanics are isotopically heterogeneous in composition, which is explained by the mixing of mantle derived magma and continental crustal source rocks. There is no systematic isotopic variations with eruption stages. Particulary, some volcanic rocks of stage 2 and 3 have extremely wide initial 87Sr/86Sr isotopic variations ranging from 0.7038 to 0.7092, which are influenced by seawater alterations; (2) the Ulreungdo volcanic rocks show EMI characteristics, while volcanic rocks from the Jejudo, Yeong-il and Jeon-gok areas have slightly depleted mantle source characteristics; (3) the trachyandesite of the latest eruption stage was originated from the mantle source materials which differ from other stages. A schematic isotopic evolution model for alkali basaltic magma is presented in the Ulreungdo volcanic island of the backarc basin of Japanese island arc system.
The “El Taco Xe” trapped in graphite fractions of the El Taco IAB iron meteorite proposed by Mathew and Begemann (1995) was reexamined on the basis of the data normalized to 132Xe. On the Xe three-isotope diagrams, their data did not form a clear linear trend between atmospheric Xe and “El Taco Xe” due to the existence of Xe-HL in the samples. The Xe-HL released at high-temperature demands a slight modification of “El Taco Xe” by subtracting Xe-HL. The modified El Taco Xe proposed in this study can be explained by a mass-fractionation from solar Xe or U-Xe. High temperature data could be explained by the addition of a Q-HL mixture with a constant Q/HL ratio of ∼5 to the modified El Taco Xe.
Cubic sub-samples of 1 mm3 (about 0.5 mg) were obtained from a Porites coral slice collected from Xisha Island, South China Sea and analysed for Sr and Ca concentrations by ID-TIMS after precise weighing. Ca contents in the coral are quite uniform (mean = 38.16 wt%, 2σ = 0.11 wt%). The variation corresponds to ±0.4°C, about the level of uncertainty of the Sr/Ca-SST calibration. Sr concentrations and Sr/Ca ratios covary linearly, and the line can be defined by the equation Sr/Ca × 103 = 0.111Sr - 0.5061 (correlation coefficient r = 0.9955), where Sr is in μmol/gm. Consequently, our results demonstrate that the previously established coral Sr/Ca thermometer, Sr/Ca × 103 = A + B × T, can be simplified as a Sr thermometer, 0.111Sr - 0.5061 = A + B × T, where Sr is in μmol/gm. Therefore, measurement of Ca in corals could be unnecessary. If different levels of impurity exist in different corals, a few Ca measurements in each coral may be needed, but definitely there is no need to measure every sub-sample.