Petroleum-like products have been found in hydrothermally altered recent sediments of the submarine Wakamiko Caldera (depth = 200 m) in the northern Kagoshima Bay, southern Kyushu, Japan. High concentrations of polynuclear aromatic hydrocarbons (PAHs) of pyrolytic origin and biomarkers signatures representing diverse degrees of maturation have indicated that the associated bitumen is a typical hydrothermal petroleum. This is the first report on a significant content of hydrothermal petroleum related with a submarine volcanism of island-arc. The petroleum was generated by pyrolysis of organic matter in recent sediments deposited in the caldera. The hydrothermal petroleum and massive sulfide deposits are concluded to be currently forming within the caldera by hydrothermal activities below the seafloor where presently forming Kuroko-type sulfide deposits were also reported. Considering simultaneous formation of the hydrothermal petroleum and the Kuroko-type deposits in the Wakamiko Caldera, we propose a hypothesis that, during the middle Miocene, the same phenomena happened extensively in northeast Japan in association with the large-scale marine volcanisms, resulting in the formation of both petroleum and sulfide ore deposits (Kuroko) in the same geological horizons.

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K-Ar ages have been measured for calc-alkaline lavas from the Aegean volcanic arc in order to determine formation ages of the volcanic area of the islands. The samples from islands lying on the north side of the volcanic arc (e.g., Aegina, Kos) show older ages (2∼3.6 Ma) than those from the islands lying on the south side of the volcanic arc (e.g., Methana, Nisyros, Santorini) showing younger ages up to 1.2 Ma. These ages seem to be in agreement with the model that the volcanic front has migrated to the south. The migration velocity has been estimated to be about 1 cm/yr. in this study, which is comparable to, but slightly less than previously reported values.

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The Korean peninsula is composed of Precambrian to Holocene rocks. Structurally it is divisible into three massifs, separated by two fold belts. The Nangrim massif of North Korea is a high grade metamorphic terrain overlain by Palaeozoic sedimentary rocks. In South Korea the Gyeonggi massif is predominantly a metasedimentary gneiss terrain and in the Ryeongnam massif the orthogneisses are dominant. These Precambrian rocks are overlain by Paleozoic and Mesozoic sedimentary rocks and are intruded by Mesozoic plutons. In the Gyeonggi massif the oldest rocks dated here are the Gongju migmatite 2417 ± 39 Ma, and the Inje crystalline schist 2413 ± 21 Ma. The Seongnam migmatite has a younger age of 1868 ± 9 Ma. The Hwacheon banded gneiss has an age of 2164 ± 18 Ma, the Hongcheon porphyroblastic gneiss has an age of 1952 ± 13 Ma, and the Kanghwa granite gneiss has an age of 1673 ± 10 Ma. The Mesozoic Otanri gabbro was emplaced at 166.2 ± 1.2 Ma, and the Sachangri porphyritic granite at 164.7 ± 2.4 Ma. Comparison of U-Pb ages of Precambrian and Mesozoic rocks in the Gyeonggi massif with those in the Ryeongnam massif ages reveals a different age pattern, which suggests a different evolutionary history of these two cratonic blocks. The Precambrian rocks of Gyeonggi massif are more similar in age to those of southeast China than to those of the Ryeongnam massif. The Mesozoic plutonism in both the Gyeonggi and the Ryeongnam massifs is comparable to that of southeast China.

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Chemical characteristics of “diagenetic” and “hydrogenous” type deep-sea nodules from the central and northeastern Pacific were studied regarding their Ce anomalies and Y fractionation from heavy REE. Pacific nodules of both types show low Y/Ho ratios less than average shales or chondrites, contrasting to the other marine samples (seawaters, limestones, and phosphorites) having higher Y/Ho ratios than average shales or chondrites. The “hydrogenous” type nodules show large positive Ce anomalies up to log(Ce/Ce^∗) = +0.6, whereas the “diagenetic” type nodules display only small positive Ce anomalies or even small negative ones. Two nodule subsamples, which are characterized by 10 Å manganate but are chemically the intermediate between the two types, show Ce anomalies of log(Ce/Ce^∗) = +0.3 in the middle of the two end members. Interestingly, the Ce anomalies of the nodules vary coherently with their logarithmic Co/(Ni+Cu) ratios. This positive correlation is valid even after combing many literature data of Pacific nodules with our data. In the plot of Ce anomaly vs. log[Co/(Ni+Cu)], the three distinct types of Pacific nodules are systematically distinguished: “suboxic-diagenetis” ≤ “diagenetic” ≤ “hydrogenous”. The systematics strongly suggest that: (i) the Ce anomaly and log[Co/(Ni+Cu)] are similar geochemical indexes showing how effectively oxidative uptake of Ce and Co occurred in each nodule relative to non-oxidative uptake of nutrient-type metals in the respective metal groups, and (ii) there exists an initial source supplying metals common to all the types of Pacific nodules. We inferred from various reasons that the common initial source is biogenic particulates delivered from overlying surface water. Oxidative uptake of Ce and Co by fast sinking large biogenic particulates is less effective, but such particulates can more effectively convey nutrient-type metals involved with them to the sea floor because of their shorter residence time inoxic water. However, the relationship between metal transports of scavenged- and nutrient-type elements is reversed in the case of slowly sinking biogenic particulates. High surface productivity inevitably provides high flux of fast sinking large organic particulates, whereas low productivity gives rise to organic particulate flux dominated by slowly sinking small ones. These mechanisms explain the observed systematics of Ce anomaly vs. log[Co/(Ni+Cu)] plots for Pacific nodules.

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We propose a temperature-skeletal δ¹⁸O (relative to PDB) relationship of Porites australiensis coral from Ishigaki Island, the northwestern Pacific, with high frequency microsampling along the growth axis: δ¹⁸O = -0.611 - 0.165T (°C). Annual variation of sea surface temperature around Ishigaki Island is about 10°C while seasonal salinity change is less than 0.5. Therefore, the effects of seasonal variation on δ¹⁸O value of reef water can be neglected at the first approximation. As this coral colony was growing only 300 m apart from temperature monitoring station, sea surface temperature data from the station can represent those at the coral site. The equation is relatively close to those reported earlier for Porites corals from other regions of the Pacific, but differs from that of Mitsuguchi et al. (1996, Science, 274, 961-963) for Porites lutea from the eastern coast of the same island. The cause of this difference is unclear, but it might partly be attributed to lower frequency of their microsampling along the growth axis: 24 samples per annual growth increment were collected in this study while 15-17 samples were analyzed in their study. Lower sample frequency would result in the attenuation of seasonal oxygen isotope signals. Further research including examinations on oxygen isotope compositions in reef waters and the inter-species difference among the genera Porites are also needed to confirm this relationship.

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