Chemical properties of surface waters in the limestone regions of western Japan: Evaluation of chemical conditions for the deposition of tufas

In order to understand the chemical conditions for the depositionof tufas, chemical properties of were investigated for the 201 surface waters collected from the limestone regions including newly discovered localities of tufas. The collected waters were categorized, according to the association with tufas, mainly into; category N (waters without tufa deposition), category T (waters depositing tufas), and category S (spring waters of tufa-depositing streams). These three categories clearly differ in Ca contents, equilibrium CO 2 partial pressure (PCO2), and saturation index for calcite (SIC); all of which are the most important chemical properties for the deposition of tufas. The waters of the category N are characterized by small Ca contents (mainly 15～35 ppm) and low PCO2(350～1,000 µatm) which indicate that they are basically flowing on a limestone substrate without an efficient CO2 uptake from soils. Their SIC never exceeds +0.5. The waters depositing tufas (category T) normally exhibitCa contents more than 45 ppm and PCO2 ranging 500～2,000 µatm. The waters of category S show comparable or slightly larger Ca contents than category T, however their PCO2 is considerably higher (than 2,000 µatm). Their raised values of Ca contents and PCO2 are ascribed to efficient CO2 uptake in a soil layer and subsequent dissolution of CaCO3. Furthermore, their SIC around 0.0 indicates that the waters dissolve CaCO3 until they reach the saturation in underground water systems. The large difference in PCO2 between categories T and S results from degassing of CO2 during flowing on the streams. The degassing increases pH and SIC of the waters. The SIC of category T mostly exceeds +0.5, that is probably the most important chemical condition for an efficient deposition of tufas. This study indicates that tufas are not very rare, but also that their distribution tends to be concentrated in a certain area, such as northwestern Okayama Prefecture. Local geological and hydrological conditions can be also important controls for deposition of tufas

Overview of Pleistocene Bryozoans in Japan

We compiled a list of bryozoan taxa reported between 1935 and 1995 from Pleistocene deposits in Japan. Our list adds many Pleistocene records to the 1980 checklist of Sakagami et al.: although only a handful of additional Pleistocene records of bryozoans have been published since 1980, many deposits previously considered to be of Pliocene age have now been more accurately dated as Pleistocene. These include the Setana, Hamada, Hirose, Daishaka, Shibikawa, Sawane, Haizume, and Omma Formations. Our list contains 358 taxa, including 97 new to science described from Pleistocene Japan. Previous studies have been concentrated in four regions of Japan: 1) Boso Peninsula, central Honshu, Pacific side; 2) SW Hokkaido and N Honshu in the vicinity of Tsugaru Strait; 3) Noto Peninsula and Niigata, central Honshu, Sea of Japan; and 4) Kikai-jima Island in the Nansei Archipelago south of Kyushu. We present the number of total taxa and new taxa reported per region and formation, and compare the similarities among regions. We report newly discovered Pleistocene deposits from two regions: the Setana Fm. near Kuromatsunai, Hokkaido, and the Oe and "Kita Arima" Fms. on the Shimabara Peninsula, Kyushu. Pleistocene bryozoans are relatively well known in Japan, and with increased taxonomic resolution can provide a 'model system' for investigating the effects of climate change on assemblages of sessile benthic marine animals.International Symposium, "The Origin and Evolution of Natural Diversity". 1–5 October 2007. Sapporo, Japan

Carbonate mineralogy and stable isotope composition of cool-water bryozoans from sediments of ODP Leg 182 sites

The carbon and oxygen isotopic compositions of selected bryozoan skeletons from upper Pleistocene bryozoan mounds in the Great Australian Bight (Ocean Drilling Program Leg 182; Holes 1129C, 1131A, and 1132B) were determined. Cyclostome bryozoans, Idmidronea spp. and Nevianipora sp., have low to intermediate magnesian calcite skeletons (1.5-10.0 and 0.9-6.4 molar percentage [mol%] MgCO3, respectively), but a considerable number include marine cements. The cheilostome Adeonellopsis spp. are biminerallic, principally aragonite, with some high magnesian calcite (HMC) (6.6-12.1 mol% MgCO3). The HMC fraction of Adeonellopsis has lower d13C and similar d18O values compared with the aragonite fraction. Reexamination of modern bryozoan isotopic composition shows that skeletons of Adeonellopsis spp. and Nevianipora sp. form close to oxygen isotopic equilibrium with their ambient water. Therefore, changes in glacial-interglacial oceanographic conditions are preserved in the oxygen isotopic profiles. The bryozoan oxygen isotopic profiles are correlated well with marine isotope Stages 1-8 in Holes 1129C and 1132B and to Stages 1-4(?) in Hole 1131A. The horizons of the bryozoan mounds that yield skeletons with heavier oxygen isotopic values can be correlated with isotope Stages 2, 4(?), 6, and 8 in Hole 1129C; Stages 2 and 4(?) in Hole 1131A; and Stages 2, 4, 6, and 8 in Hole 1132B. These results provide supporting evidence for a model for bryozoan mound formation, in which the mounds were formed during intensified upwelling and increased trophic resources during glacial periods