Carbonate Minerals in the Warrawoona Group, Pilbara Craton: Implications for Continental Crust, Life, and Global Carbon Cycle in the Early Archean

Abstract: The occurrences of the Early Archean carbonate minerals are compiled and their precipitation processes are investigated for the Warrawoona Group, Pilbara Craton. Sedimentary carbonate rocks such as limestone and dolostone are very rare, and only a small amount of sedimentary carbonate minerals are sometimes contained in the hydrothermal bedded chert, implying that a sink of CO₂ was minor in the Early Archean sediments. Moreover, it is very likely that the activity of cyanobacteria forming stromatolites was considerably low in the Early Archean. Microfossils and carbonaceous matter in the hydrothermal cherts are probably derived from a non-photosynthetic microorganisms related to the seafloor hydrothermal activity. Their preservation in sediments may play a very minor role in carbon sink of the Earth's surface.
On the other hand, carbonatized volcanic rocks subjected to seafloor hydrothermal alteration occur ubiquitously in the Early Archean greenstone belts such as the Warrawoona Group, suggesting that the hydrothermally altered oceanic crust had large amounts of CO₂ as carbonate minerals. Global carbon cycle in the Early Archean is considered to have been controlled by the intense seafloor hydrothermal alteration. Large amounts of CO₂ were sunk into the oceanic crust by the alteration. The carbonatized oceanic crust was partly accreted to the continents and/or island–arcs, and partly subducted into the mantle without decomposition. Significant amounts of carbonate minerals in the carbonatized oceanic crust were very likely to store in the accretionary prisms and mantle, consequently giving rise to a decrease of atmospheric and oceanic CO₂.     

Unique Geochemistry of Sedimentary Iron Deposit Formed by Biologically Induced Mineralization

Abstract: Major, trace, and rare earth element contents were determined for sedimentary iron ores from the Gunma iron deposit. The deposit was precipitated from a spring water on the hillside of the active Kusatsu-Shirane Volcano. The ores are mainly composed of goethite and jarosite with various proportions of silicified andesitic detritus. Microbial fossils are often preserved well in goethite-rich ores. Goethite was likely precipitated by both inorganic and biogenic (biologically induced mineralization; BIM) processes, whereas jarosite was precipitated inorganically from the spring water. Si, Ti, Al, Mn, Mg, Ca, Na, Co, Rb, Y, Zr, Nb, Hf, Ta, U, and middle-heavy REEs (Sm-Lu) in the ores are dominantly derived from a detrital component (silicified andesitic rocks). On the other hand, Zn and V are likely to have been inorganically coprecipitated with goethite. Preferential uptake of P, Sc, Cu, Mo, Ba, Th, and light REEs occurs in the BIM ores. Unique enrichment of these elements is a promising indicator of biomineralization for ancient sedimentary iron deposits.     

Synchrotron X-ray analysis of norbergite, Mg2.98Fe0.01Ti0.02Si0.99O4(OH0.31F1.69) structure at high pressure up to 8.2?GPa

The natural norbergite, Mg_2.98Fe_0.01Ti_0.02Si_0.99O₄(OH_0.31F_1.69) is examined by synchrotron X-ray diffraction analysis at pressures up to 8.2 GPa. The measured linear compressibilities of the crystallographic axes are β _a  = 2.18(4) × 10⁻³, β _b  = 2.93(7) × 10⁻³, and β _c  = 2.77(7) × 10⁻³ (GPa⁻¹), respectively and the calculated isothermal bulk modulus of the norbergite is K _T = 113(2) GPa based on the Birch–Murnaghan equation of state assuming a pressure derivative of K′ = 4. The crystal structures of norbergite are refined at room temperature and pressures of 4.7, 6.3, and 8.2 GPa, yielding R values for the structure refinements of 4.6, 5.3, and 5.3%, respectively. The bulk moduli of the polyhedral sites are 293(15) GPa for the tetrahedron, 106(5) GPa for the M2 octahedron, 113(2) GPa for the M3 octahedron, and 113(3) GPa for the total void space. The bulk modulus exhibits a good linear correlation with the filling factor for polyhedral sites in structures of the humite minerals and forsterite, reflecting the Si⁴⁺ + 4O²⁻ ⇔ □ + 4(OH, F)⁻ substitution in the humite minerals. Moreover, two simply linear trends were observed in the relationship between bulk modulus and packing index for natural minerals and dense hydrous magnesium silicate minerals. This relationship would reflect that the differences in compression mechanism were involved with hydrogen bonding in these minerals. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

A channelised long run-out debris slide triggered by the Noto Hanto Earthquake in 2007, Japan

A strong earthquake (M _J 6.9, M _W 6.6–6.7) at about 11 km depth hit the western shore of the Noto Peninsula on Honshu, Japan, at about 00:42 coordinated universal time (9:42 a.m. local time) on 25 March 2007 (the Noto Hanto Earthquake in 2007). The earthquake triggered only 61 landslides, with most traveling short distances. It caused one long run-out landslide in the Nakanoya district of Monzen town, Wajima city, Ishikawa Prefecture, when a portion of a deep-seated landslide transformed into a moderate debris slide down a channel. The rock slide occurred on a south-facing convex-shaped slope on a small spur where earthquake ground shaking likely was strongly amplified by topography. A portion of the rock slide reached a small channel floored by materials containing abundant groundwater. Constant-volume box-shear tests on normally consolidated saturated specimens revealed that the apparent angle of internal friction of the channel-floor material was 33–36° at 10-mm shear displacement and did not show much decrease in effective normal stress during shearing. In situ rock-sliding testing on the exposed channel materials showed a low kinetic-friction angle of about 21°. We suggest that an unsaturated portion of the rock slide slid down the channel, with sliding between the rock-slide mass and the channel floor. Because the slope angle of the travel path nearly equaled the kinetic-friction angle, the unsaturated rock slide mass may have traveled at a moderately slow speed, or it might have decelerated and accelerated. Slow speed is supported by accounts from local residents that suggest movement of debris continued for 3 days after the main shock.     

A coronal condensation observed at the total solar eclipse of June 11, 1983 and a related transient prominence

A coronal condensation was observed simultaneously with Fexiv 5303, Fex 6374, Fe xi 7892, and H filtergraphs. The size and shape of the condensation in 5303 are different from those in other filtergrams. H filtergrams taken around the eclipse time show that a small transient prominence exists in close proximity to the condensation core and behaves like a post-flare loop system, though the appearance is quite different and no flare-report exists. A small-scale energetic phenomenon seems to have occurred at the top of magnetic loops.Contributions from the Kwasan and Hida Observatories, University of Kyoto, No. 285.     

Three-year investigations into sperm whale-fall ecosystems in Japan

We report the first study of sperm whale‐fall ecosystems, based on mass sinking of whale carcasses at shelf depths in the northwest Pacific. We conducted three observations over a 2‐year period on replicate sperm‐whale carcasses implanted at depths of 219–254 m off the southern part of Japan from July 2003 to August 2005. The study was made possible by a mass stranding of sperm whales in January 2002, and the subsequent sinking of 12 carcasses in the waters off Cape Nomamisaki. Dense aggregations of unique chemosynthesis‐based fauna had formed around the whale carcasses after 18 months (July 2003). The mytilid mussel Adipicola pacifica was the most abundant macrofaunal species and covered most of the exposed bone surfaces. The general composition of the fauna was similar to that of deep‐water reducing habitats, but none of the species appearing in this study has been found at hydrothermal vents, cold seeps or deep‐water whale falls. A new species of lancelet, which was the first record of the subphylum Cephalochordata from reducing environments, a new species of Osedax; a rarely encountered benthic ctenophore, and a rare gastropod species were discovered at this sperm whale‐fall site. Benthic communities were similar across all the carcasses studied, although the body sizes of the whales were very different. The succession of epifaunal communities was relatively rapid and the sulphophilic stage was considerably shorter than that of other known whale falls.     

Measurements of the Turbulent Energy Dissipation Rate around the Shelf Break in the East China Sea

Using the micro-structure profiler, TurboMAP, large values for the turbulent energy dissipation rate ε were found just above the bottom of the shelf and around the thermocline near the continental shelf break in the East China Sea. The values found above the bottom are produced by the bottom stress due to tidal currents, resulting in a distinct bottom mixed layer where the vertical eddy diffusivity Kz is also large. Distinct maxima in the values of ε detected around the thermocline are located at the depth of the fine-scale shear maxima detected with the moored ADCP. The vertical profiles of ε were compared with those of the current velocity, and it was found that the maxima in ε appear to correspond to those of the shear with fine scale. The magnitude of the observed ε coincided approximately with the ε calculated from the fine-scale shear and the buoyancy frequency according to the parameterization proposed by Gregg (1989), if the large-scale mean shear caused by the Kuroshio is subtracted. However, it is not clear whether the parameterization for the internal wave fields in the open ocean is applicable to the estimation of ε in the shelf break. Whereas the most predominant value of ε was found just above the bottom and around the thermocline, the maxima of ε could be found in the internal area. They could have been caused by the propagation of the vertically high wave number internal tides along the characteristic ray.     

Kuroko and Hydrocarbon Deposits from Northern Honshu,Japan: A Possible Common Hydrothermal/Magmatic Origin?

Abstract. Northern Honshu is the most important area for mineral and oil resources in Japan. Many kuroko deposits and oil and gas fields are distributed in two belts along the northeast Japan arc, the kuroko metal‐belt on the Pacific side and the oil‐belt on the Sea of Japan side. The kuroko deposits are located mainly in the Green Tuff strata which formed as a result of submarine vol‐canism during the late Miocene and Pliocene. Most of the source rocks of the oil and gas deposits formed at the same time as the kuroko deposits and some of them are located in reservoirs of hydrothermally‐altered volcanic rocks in the Green Tuff region. There is general agreement that the kuroko deposits formed as a result of submarine hydrothermal and magmatic activity whereas almost all petroleum geologists and geochemists consider that hydrocarbon deposits were generated independently of such activity. Since the discovery of hydrothermally‐generated petroleum in the Guaymas Basin, Gulf of California, however, it is clear that petroleum can be formed almost instantaneously in terrestrial and submarine hydrothermal areas. The paleo‐northeastern Sea of Japan is therefore considered to be a potential area for hydrothermal petroleum generation because thick organic‐rich sediments overlie an active submarine volcanic area. Several lines of geological and geochemical evidence suggest the possibility of hydrothermally‐enhanced maturation of organic matter and the contribution of magmatic activity to the formation of these deposits. Although most of the oil and gas in northern Honshu has been generated conventionally as a consequence of the high geothermal gradients there, it appears that some of the oil and gas fields may have formed as a result of extensive hydrothermal and magmatic activity during the late Miocene to Pliocene. Because of the much steeper angle of the faults in the vicinity of the Hokuroku basin than in the Akita basin, the magmatic contribution to the kuroko mineralization would have been far greater than to the oil and gas deposits of the Niigata and Akita basins. We therefore propose a strong relationship between metal and oil and gas generation in northern Honshu based on the structure and tectonics of the northern Honshu arc‐backarc system.