Early Miocene sedimentary sequences in the Chubu region of central Japan contain numerous tuff beds, and comparisons and correlations of these beds between sedimentary basins are expected to lead to a better understanding of the stratigraphic architecture of the sequences. In this study, we discuss the correlation of pumiceous tuff beds between the Himaka and lower Yamami Formations of the Morozaki Group in Aichi Prefecture and the Hazama Member of the Akeyo Formation of the Mizunami Group in Gifu Prefecture. We obtained zircon U-Pb ages of 17.87±0.75 Ma and 17.36±0.40 Ma for pumiceous tuff beds from the Himaka and lower Yamami Formations, respectively, and these ages are consistent with the published U-Pb age for the Hazama Member. Paleomagnetic analyses reveal reverse polarity magnetizations in the Himaka and lower Yamami Formations and the Hazama Member. These results suggest that these three units correspond to Chron C5Dr of the paleomagnetic chronology. Chemical analyses of volcanic glasses from pumiceous tuffs in the lower Yamami Formation and the Hazama Member display a single trend in chemical variation diagrams. Plagioclase compositions of pumiceous tuffs in the three units are also consistent. These chemical characteristics indicate that the volcanic glasses and plagioclase of the three units were generated from the same magma plumbing system. The volcaniclastic products of the Morozaki Group examined in this study are considered to have been supplied from the Hazama Member.

Futamatayama volcano is a Quaternary stratovolcano located 6 km north of the Nasu volcano group in southern Fukushima Prefecture, NE Japan. We investigated the eruption history and magmatic processes of the volcano using geological, petrological, and geochronological [thermoluminescence (TL) dating] analyses. The eruptive activity of the volcano can be divided into two stages. The lava flow stage (Stage 1: 3.56 km³ DRE) included at least seven lava flows, and the lava dome stage (Stage 2: 0.09 km³ DRE) involved the formation of two lava domes and a small pyroclastic flow. We obtained TL ages of 163±7 ka, 93±3 ka, and 79±3 ka from the lava flows (Stage 1) and 56±4 ka from a lava dome (Stage 2), which indicate that the volcano formed over a period of >100 ky. The eruption products of Futamatayama volcano commonly consists of felsic rocks (SiO₂ = 56.2-68.4 wt.%) that contain mafic enclaves (SiO₂ = 50.6-59.3 wt.%), indicating magma mixing. On an FeO*/MgO-SiO₂ (whole-rock) diagram, data from Stage 1 and Stage 2 form subparallel linear trends (Stage 1: FeO*/MgO = 1.9; Stage 2: FeO*/MgO = 2.2; at SiO₂ = 64.1 wt.%). These trends suggest that the magmatic system changed between Stage 1 and Stage 2, with different end-member magmas in each stage. Compositional variations between the mafic end-member magmas can be explained by olivine and pyroxene fractionation from a common basaltic magma. Variations in Rb/Ba ratios between the mafic and felsic end-members suggest that the latter could not have been derived from the former by simple fractional crystallization. The felsic end-member magmas of Stage 1 and Stage 2 were produced by different degrees of partial melting of crustal materials in response to heating by mafic end-member magmas.

Two chronologically distinct plant macrofossil assemblages, the Late Miocene Tokachihoroka and the Early Pleistocene Taushubetsu floras, are recognized in the Lake Nukabira area of eastern central Hokkaido on the northernmost island of the Japanese Archipelago. The Tokachihoroka flora from the lacustrine Tokachihoroka Formation comprises 47 taxa in 18 families and 27 genera. The Taushubetsu flora from the lacustrine Taushubetsu Formation comprises 42 taxa in 20 families and 26 genera. The dominant arboreal taxa of these two floras is Betula maximowicziana-relative birch, which is associated with other deciduous broadleaf Betulaceae species, as well as Acer spp. and an evergreen conifer, Picea sp. The compositions of these floras, ecologies of their contemporary counterparts, and results of quantitative climate analysis based on CLAMP (the Climate Leaf Analysis Multivariate Program) indicate that the floras represent a combination of lakeside, slope, and subalpine vegetation types under humid and cool temperate climate conditions. Although the Taushubetsu flora represents a more modern species composition than the Tokachihoroka flora, the physiognomies of both floras reflect volcanic influences under similar humid and cool temperate climatic conditions.

To better understand how ground motion in the Tokyo Lowland is affected by the geological conditions in the shallow subsurface, we analyzed borehole logs and conducted microtremor observations along the Ueno-Koiwa survey line, which crosses the buried valley beneath the Tokyo Lowland. Remarkable peaks in the H/V spectra at ~1 Hz were found in the area of the lower buried terrace (buried flat surface 2), whereas the peaks at ~1 Hz are small in the area of the buried valley bottom with the thickest valley-filling post-Last Glacial Maximum (LGM) deposits. The sharp peaks around buried terrace 2 are generated by the large contrast in the physical properties of the soft, muddy post-LGM deposits and the underlying gravel bed, which suggests larger ground-motion amplification during an earthquake. The variation of the ground motion characteristics along the survey line obtained by microtremor observation is consistent with the distribution of seismic intensity during the 1923 Kanto Earthquake. It is, therefore, important to consider not only the thickness and physical properties of the post-LGM deposits during seismic hazard assessment, but also the total geological composition, including the Pleistocene strata below the post-LGM deposits.

Spherical Fe- oxide concretions are found in the Navajo Sandstone Formation in Utah, USA, which range in size from a few millimeters to a few centimeters. The interior of the concretions is filled with sand and the surface is covered with an Fe oxide rind. The process that formed the Fe rinds, the timescales of formation, and the effect of pores in the concretions and the dissolved oxygen concentration on the rind formation were studied experimentally.

Fe oxide concretions were artificially prepared in a petri dish. An experimental system was established to capture images of the forming Fe rind (brown band). The chemical distribution was investigated by X-ray fluorescence analysis. The results suggest the following two points about the formation of natural Fe oxide concretions. (1) In the early stages of Fe rind formation, there is a rapid increase in the width of the rind. The Fe rind grows rapidly there are many pores in the concretion. (2) Fe oxide concretions with clear rinds were formed at lower dissolved oxygen concentrations.

We propose a new stratigraphic unit, the Nagasaki Kitaura Formation, for the Upper Cretaceous sedimentary rocks on the coast of Kitaura, Nagasaki City, Nagasaki Peninsula, northwestern Kyushu, Japan, to replace the previously named Kitaura Formation. The Nagasaki Kitaura Formation is divided into two lithostratigraphic units that are in fault contact: the Akasakino-hana Sandstone and Mudstone Member (ASMM), the lower, thin unit (>13 m thick), and the Zatobama Gravelly Sandstone and Mudstone Member (ZGSMM), the upper, thicker unit (>140 m). The ASMM consists of shallow marine deposits yielding ammonoid (Polyptychoceras obatai and cf. Phylloceras sp.) and bivalve fossils including an inoceramid (Platyceramus japonicus), and an incomplete femur of a hadrosauroid dinosaur was unearthed from the fluvial ZGSMM. Based on the biostratigraphic range of Platyceramus japonicus (late Santonian? to early Campanian), Polyptychoceras obatai (late Santonian), and the ²⁰⁶Pb/²³⁸U dates of the detrital zircon from the ASMM (the youngest concordant date = 83.6±5.0 Ma; the weighted mean age of the youngest date cluster = 85.74±0.75 Ma; 95% confidence level), the Nagasaki Kitaura Formation is no older than the late Santonian and potentially extends to the Campanian in age. The main body of the formation, the ZGSMM, is correlated with the lower part of the Mitsuse Formation (middle Campanian) on the western Nagasaki Peninsula. The stratigraphy of the Nagasaki Kitaura Formation can be assessed in association with the depositional environments of the lower half of the Upper Cretaceous Himenoura Group in western Kyushu.

The lower Miocene strata in the San’in region were presumed to be a graben-fill deposit based on their distribution and the extensional setting. However, previous research has presented little evidence for grabens; only a few syndepositional faults have been found, and the regional stress has been called into question. To collect more basic data that can improve our understanding of the origin of the Miocene basins, we present geological data for the Tajima Mihonoura area, eastern San’in region, Southwest Japan, including the structure of the base of the lower Miocene Yoka Formation, the zircon U‒Pb age of the formation, and the paleostress during its deposition. There is talus or basal breccia at the contact between the basement and the Yoka Formation, and no faults were found along the contact. These observations indicate that the Yoka Formation unconformably overlies the basement. Although the thickness of the lower Miocene strata was used to estimate the shape of the grabens in the San’in region, we show that the thickness in the study area was dependent on the paleogeography during the early Miocene. Zircon from a felsic pumice tuff from the Yoka Formation was dated, yielding a weighted mean ²³⁸U‒²⁰⁶Pb age of 19.6±0.15 Ma (2σ) from the grains with concordant Miocene ages. This mean age is consistent with other chronological constraints on the formation obtained in the Tango Peninsula and the Tajima-Myokensan area, which form its eastern and southern margins, respectively. Paleostress inversion from the orientation of dikes related to the Yoka Formation suggests that the study area was subject to NE-SW extension with a low stress ratio. This stress probably represents the regional stress in the eastern San’in region, given the similarity of paleostresses reported recently from other areas of Hokutan.

Spherical Fe-oxide concretions have been recognized in both terrestrial and Martian strata and are thought to record a variety of past environmental and alteration conditions. This paper presents a comprehensive review of the occurrence and elemental composition of spherical Fe-oxide concretions on Earth and Mars and their proposed mechanisms of formation. On the basis of geological evidence from Utah and Mongolia, Fe-oxide concretions are considered to form by pH-buffering reactions between Fe-rich acidic water and precursor calcite concretions. By comparing the characteristics of hematite spherules in Meridiani Planum and spherical nodules in Gale Crater, we propose that Martian concretions may also have been formed by interaction between pre-existing carbonates and sulfuric acidic water that infiltrated the rocks early in Martian history. The abundant hematite spherules in Meridiani Planum and spherical nodules in Gale Crater can be considered as relicts of the widespread deposition of carbonate that occurred during the late Noachian-early Hesperian (c. 3.8 to 3.7 Ga) and its dissolution during the late Hesperian (c. 3.5 to 3.2 Ga).

Ocean acidification (OA) is a decrease in seawater pH caused by an increase in the dissolved carbon dioxide concentration in seawater and is an ongoing environmental issue. It is a threat to marine organisms with a calcified skeleton. Decreases in the populations and diversity of these marine organisms may change the carbon and nutrient cycles and cause the depletion of marine biological resources. Predicting the long-term (over a decadal scale) change in seawater pH is difficult. Long-term OA has been identified in geological records. The Paleocene-Eocene thermal maximum (PETM; ~56 Ma) was accompanied by benthic foraminifer and ostracod extinction events and is an ideal target for studying OA over geological time. We review previous studies on OA during the PETM. Many studies report a decrease in the carbonate content of deep-sea sediments, suggesting a shallowing of the carbonate compensation depth (CCD) and lysocline during the PETM. Carbonate ion concentrations on the Pacific seafloor were greater than those in the Atlantic, in contrast to the Holocene. Studies using boron isotopic compositions of planktic foraminifer shells estimate a decrease in sea-surface water pH of 0.2-0.5 within 60 ky of the onset of the PETM. The estimated pH values are associated with measurement and calculation uncertainties. The uptake of CO₂ into the ocean and its emission into the atmosphere and ocean circulation affect the geographic pattern of seawater pH and are still debated.

During the back-arc opening of the Japan Sea between 21 and 15 Ma, volcanic activity increased in range to the oceanic side, erupting a variety of magma types with different origins. We obtained a new K‒Ar age of 16.40±0.10 Ma for an aphyric volcanic rock intruding Jurassic sedimentary rocks in Shirosato Town, Ibaraki Prefecture, which indicates that this rock is a product of Early Miocene fore-arc volcanism. Samples of this volcanic rock show intermediate whole-rock geochemical compositions with high Fe and low Al. Trace-element compositions and Sr‒Nd isotopic ratios indicate that the volcanic rocks were derived from a residual melt generated by crystal fractionation of a mafic magma similar in composition to the nearby Motokosawa Basalt. This basalt may have been derived from lithospheric mantle melted by the injection of upwelling high-temperature asthenospheric material involved in the opening of the Japan Sea.

The Upper Miocene to Lower Pleistocene Shimajiri Group, composed of muddy sediments, and the Lower to Upper Pleistocene Ryukyu Group, consisting of reef-complex deposits, are widely distributed throughout the Ryukyu Islands. The Lower Pleistocene Chinen Formation, which has an intermediate lithofacies, is sporadically distributed between both groups in the central and southern parts of Okinawa-jima. The Chinen Formation was previously believed to be limited to Okinawa-jima, but correlated outcrops, aged between 1.71 and 1.39 Ma, have recently been discovered in Kikai-jima, Kagoshima Prefecture. The outcrops consist of calcareous mudstone and sandstone, or sandy limestone rich in bryozoan fragments, with clear contacts between the underlying and overlying groups. The Chinen Formation overlies the So-machi Formation of the Shimajiri Group across a clearly defined angular unconformity, indicating post-depositional tilting and erosion of the Shimajiri Group. In contrast, there are no structural differences to indicate tilting during the period between the deposition of the Chinen Formation and that of the overlying Ryukyu Group. Therefore, Kikai-jima emerged as a result of relative sea-level fall after the deposition of the Chinen Formation, following which the supply of terrigenous sediment decreased.

Carbonate concretions occur in sedimentary rocks of widely varying geological ages throughout the world. Recently, more than 100 gigantic carbonate concretions with diameters ranging from 1 to 9 m have been identified along the Unosaki coast of Oga Peninsula, Akita Prefecture, Japan. The formation process of such gigantic concretions, some of which along the Unosaki coast contain whale bones, remains uncertain. A mineral composition analysis reveals that the major mineral of the concretions is dolomite. Considering the location of dolomite precipitation, their composition implies that the concretions were formed in a reducing environment in which sulfate ions were removed. Stable carbon and oxygen isotopic analysis reveals that the CaCO₃ of whale bone and concretions contains light δ¹³C and heavy δ¹⁸O, suggesting that whale organic matter contributed to the formation of the concretions. The gigantic carbonate concretions were presumably formed by the accumulation and burial of whale carcasses with high sedimentation rates, and subsequent reaction of carbon decomposed by benthic and microbial activity with seawater.

There should be a lot of supernova explosions near the Solar System since its formation. They have affected the Earth through strong electromagnetic waves, cosmic rays, and blasts. The ionization of the atmosphere by the strong cosmic rays varies the concentrations of ozone and oxides of nitrogen, probably resulting into climate changes. The strong cosmic rays may introduce the evolution and the extinctions of life on the earth. The cosmic rays also generate various radioactive elements through the collisions with the atoms in the atmosphere. Other radioactive elements such as 60Fe may be delivered directly from the supernovae. These elements likely preserved in geological samples of sediments and ice cores.

A bed containing large ammonoids (mostly Mesopuzosia yubarensis, 40-60 cm in diameter) and an underlying bed containing huge calcareous concretions in the middle part of the Obisagawa Member (lower Coniacian), Ashizawa Formation, Futaba Group, are exposed in the Iwaki City Ammonite Center. This study investigated these beds to reconstruct their formation on the basis of sedimentary facies and taphonomy, as well as geochemical analyses of the concretions, including major elements, mineral components, and carbon and oxygen isotopic compositions. Numerous shells of M. yubarensis lacking soft tissues may have been transported into the littoral region through postmortem drift from the initial offshore habitat. Subsequently, these shells were partially destroyed (especially body chambers and umbilical whorls), sorted in size, accumulated, and transported offshore by a series of storm waves and storm-induced currents. Finally, the remains were scattered on mounds of hummocky cross-stratification and rapidly buried within amalgamated hummocky cross-stratified very fine sandstone on the offshore side of a lower-shoreface sedimentary environment. Abundant calcareous concretions of 15-194 cm in diameter and with prolate to oblate spheroid shapes are densely and uniformly distributed under the ammonoid bed. Considering the spatial positioning of the ammonoid shells and concretions within the beds, and isotopic values of δ¹³C = −6‰ to −1‰ and δ¹⁸O = −11‰ to −6‰ for 21 concretion samples, the concretions are interpreted to have begun to form in association with the decomposition of organic matter that had accumulated under the influence of storm waves and storm-induced currents, and carcasses of prolific meiobenthos organisms within shallow substrata. Subsequently, the concretions were buried more deeply and enlarged through further filling of calcium carbonate involving bicarbonate ions generated by the methanogenetic decomposition of organic matter.

This study investigated the mode of occurrence, petrography and geochemistry of basaltic rocks of the Upper Cretaceous accretionary complex (Matoya Group) in the Shimanto Belt in the Kii Naga-shima-Taiki area, eastern part of the Kii Peninsula (Mie Prefecture) to understand their genesis. The Matoya Group in this study area is classified into several stratigraphic units that are distinguished by lithologic assemblage and age. Basaltic rocks included in two of these units; most of which are stratigraphically and closely associated with chert and/or siliceous mudstone, but the remainder occurs as an isolated block in fault contact with the host clastic rocks. Major and trace elements of the basaltic rocks (one sample from the lower unit and five from the upper unit) were analyzed by X-ray fluorescence spectrometry. On the basis of geochemical discrimination diagrams and primitive mantle-normalized incompatible element plots, it is inferred that most of the basaltic rocks have a geochemical affinity to mid-oceanic ridge basalt (MORB) and one sample possibly to oceanic island basalt (OIB). The field observations and petrogenetic pro-perties indicate that the basaltic rocks in the study area formed at depths greater than the carbonate compensation depth in a pelagic environment.

The Gomura fault zone in the Tango Peninsula, southwestern Japan, comprises the Chuzenji (CZJ) and Gomura (GMR) faults and also includes the Go-seihou (GS) fault, which is shorter but has a similar strike to the CZJ and GMR faults. We conducted an audio-frequency magnetotelluric survey at 27 stations along a survey line crossing all of these faults and constructed a two-dimensional resistivity model (GMR2019 model) extending to a depth of 1.5 km. The GMR2019 model can be divided into three areas (Areas 1 to 3). Area 1 is located in the northeastern part of the survey line and shows a typical resistivity structure of the Miyazu granite body, which is almost unaffected by active faulting, and represents the background resistivity structure of the survey area. Area 2 is located in the central part of the survey line and contains the CZJ and GMR faults at its northeastern and southwestern ends, respectively. A highly conductive and subvertical zone is identified just beneath the surface trace of the GMR fault up to ~1 km depth and is interpreted as a fault zone conductor (FZC) formed by fault activity. In contrast, no pronounced FZC is found below the surface trace of the CZJ fault. As both faults have developed in the same granite body under the same tectonic conditions, this difference in FZC can be ascribed to the difference in elapsed time since the last earthquake along each fault; namely, ~100 yr for the GMR fault and 12,000-18,000 yr for the CZJ fault. This shows the possible temporal change in an FZC over a prolonged period of ~10,000 yr. Area 3 is located in the southwestern part of the survey line and contains the GS fault. The resistivity structure and surface displacement related to fault movement of the GS fault are both obscure, suggesting that this fault is likely a secondary fault associated with the adjacent GMR fault.

We investigated the chronology and magma system of the Shiobara caldera-forming eruption at Takahara volcano in Tochigi Prefecture, using geologic investigation, chemical analyses of juvenile materials, and U-Pb dating of zircon grains. The Shiobara caldera-forming eruption deposits consist of three ignimbrite units: So-KT (KT), So-TN (TN), and So-OT (OT) (in ascending stratigraphic order). Two exotic tephra layers characteristically containing biotite are recognized in thick volcanic ash soils just below KT and TN, respectively. On the basis of their glass chemistry, Fe-Ti oxide compositions, and U-Pb ages, the lower tephra layer correlates with the Kaisho-Kamitakara Tephra (KMT: 620 ka), whereas the upper tephra layer correlates with one of the members of the Omachi APm Tephra Beds (A₁Pm to A₅Pm: 410-337 ka). In addition to these tephrochronologic results, loess chronometric calculations suggest that KT formed at ~596 ka, whereas TN and OT (OT/TN) are younger than 380 ka. Magma mixing was a common magmatic process in the production of the three ignimbrite units, with each ignimbrite having a different felsic end-member. The considerable geochemical gap between KT and OT/TN is interpreted to mean that crustal melting beneath Takahara volcano changed from wet to dry conditions after a long period of dormancy (> ca. 200 ky) following the KT eruption.

The Miocene Tottori Group in southwestern Japan was formed in association with the expansion of the Japan Sea as a back-arc basin along the margin of East Asia. Strata of this group record processes involved in the opening of this back-arc basin. However, despite previous stratigraphic studies, the geochronology of the Tottori Group is uncertain, and the sedimentology of conglomerate strata of the group exposed along the Hakuto Coast in eastern Tottori Prefecture has not been examined.

Here, we present results of geological investigation and K-Ar dating of andesite from the Kawabara Volcanic Member of the Yazu Formation, Tottori Group, exposed along Cape Keta, as well as sedimentary characteristics of unclassified conglomerate strata of the Iwami Formation, Tottori Group, exposed on Okinoshima Island off the Hakuto Coast. Plagioclase in the groundmass of two-pyroxene quartz andesite of the Kawabara Volcanic Member has a K-Ar age of 18.3±0.6 Ma, supporting the interpretation of previous studies that the Kawabara Volcanic Member is correlated with the Yoka Formation of the Yabu Subgroup, Hokutan Group. The unclassified conglomerate strata contain sediments that record a series of environmental changes in a fluvial system, including sedimentation due to intense volcanic activity and subsequent slope deformation caused by riverine downcutting, followed by Gilbert-type fan-delta deposition and finally alluvial-fan deposition. Paleo-current directions of the fan-delta and alluvial-fan sediments indicate a northeasterly to southwesterly orientation, implying the existence of land to the northeast of the study area during the sedimentary period. Findings of the study will be useful for reconstructing the paleogeography of the Sea of Japan during the Miocene.

We identified six Kuroko-type deposits in the Izu collision zone, central Japan, which formed as seafloor massive sulfides (SMS) in the Paleo-Izu Arc before its collision with the Honshū Arc during the middle Miocene. These deposits are found in the same stratigraphic horizon (~15 Ma) in the Nishiyatsushiro and Koma groups, between the basaltic volcanic sequence of the Furusekigawa Formation (or its equivalent) and the hanging-wall mudstone of the Tokiwa Formation of the Nishiyatsushiro Group (or the equivalent sedimentary unit in the Koma Group).

The most remarkable difference between the Kuroko-type deposits in this region and typical Kuroko deposits in the back-arc troughs of the Honshū Arc is the close association of the former with basalt, in contrast to the common association of the latter with rhyolite- or dacite-dominant bimodal volcanism. We interpret the deposits in this region as Kuroko-type deposits because they are the products of arc volcanism and related hydrothermal activity. This conclusion is supported by the sulfur isotopic compositions [δ34S vs. Canyon Diablo Troilite (‰)] of gypsum ores from the Takara and Mogura deposits, which fall within a narrow range of values (+21.9‰ to +22.5‰ and +20.1‰ to +22.0‰, respectively) that are consistent with those of middle Miocene seawater sulfate.

Recent exploration in the present-day Izu-Bonin arc indicates that SMS deposits occur exclusively at the summit or within the summit crater or caldera of submarine volcanoes where high-temperature hydrothermal activity could be focused. Therefore, it is highly likely that the footwall basaltic lava and pyroclastic units of these Kuroko deposits are components of the volcanic edifices that hosted the mineralization. The SMS deposits collided as parts of the thin-skinned uppermost crust of the Paleo-Izu Arc and accumulated near major faults, including the Itoigawa-Shizuoka Tectonic Line and Tonoki-Aikawa Tectonic Line.

Spherical concretions found in sedimentary rocks are fascinating natural objet trouvés because of their rounded shapes and distinct boundaries. They consist of several minerals, including carbonate minerals, silicate minerals, and iron oxides. Well-preserved fossils are often found in concretions, particularly those composed of calcium carbonate. Concretions are thought to form by diffusion and the development of a syn-depositional reaction front that travels rapidly from the center of the concretion toward its outer margins. Based on the examination of several hundred spherical calcium carbonate concretions, we developed a diffusion-based model to represent the generalized growth conditions of spherical concretions. This model shows that spherical concretions grow rapidly during the first few years of diagenesis. In particular, carbonate concretions consist mainly of CaCO₃, and their permeability is greatly reduced by cementation and sealing by calcite. As a result, any fossils inside the concretion are well preserved, as water is prevented from penetrating the concretion after its formation. This sealing can provide strong resistance to weathering for more than a million years. Based on this model, we have developed synthetic concretion-forming solvents. To test the effectiveness of these solvents in sealing groundwater flow paths, we conducted an in situ experiment in an underground laboratory in Horonobe, Hokkaido. In the experiment, groundwater flow paths in the excavation damaged zone around an underground gallery were successfully sealed. The experiment showed a decrease in permeability by a factor of 1/100 to 1/1,000 over one year. Here we present a detailed model of the concretion formation process and our conclusions about the sealing process. This sealing process can be applied to activities that require long-term containment of material underground; for example, the geological disposal of nuclear waste and underground carbon dioxide storage. These applications will become increasingly important in the near future.