Bed-thickness frequency distributions of sediment-gravity-flow deposits, especially turbidites, are one of the major interests of sedimentology. Lognormal, power-law, exponential, and truncated normal distributions have all been proposed for their frequency distributions. Although these frequency distributions have been obtained from many field observations and estimated from statistical models, problems associated with the complexity of sedimentary processes have remained. In this study, bed-thickness frequency distributions and the recurrence intervals of sediment-gravity-flow deposits intercalated in the Pleistocene lacustrine varved diatomite in southwest Japan were analyzed. The results reveal that the bed thicknesses of sediment-gravity-flow deposits induced by different mechanisms show different types of frequency distribution. For example, flood-induced sediment-gravity-flow deposits show power-law-like distributions, whereas such deposits caused by lake-slope-failure show lognormal distributions. The suggestion is that flood-induced types are deposited from floods having a power-law scale. However, the bed thicknesses of the deposits induced by lake-slope-failure do not purely reflect the event scale, because the lateral variation of their thicknesses reflects the depositional processes. The recurrence intervals of both types of event show Poisson-like distributions except for lake-slope-failure deposits at the slope-base section. Despite observed ranges, the distributions of lake-slope-failure deposits at the slope-base section have a high amount of zero value and the recurrence interval show exponentially decreasing. These results suggest that both events were generated randomly, despite different origins. In addition, the incompleteness of the records was also suggested from sediment bypass of a lake-slope-failure event at the slope-base section.

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<p>Fluorescent annual layers with thicknesses of 0.01–0.1 mm occur frequently in stalagmites around the world. Aggradational variations of fluorescence intensity expressing those annual layers have been postulated as being caused by seasonal fluctuations of the supply of fulvic acid from the surface. The variation patterns of fluorescence intensity in annual layers can be classified into symmetric, gradually increasing, and gradually decreasing types. Numerical simulation of fluorescent annual-layer patterns based on the stalagmite-formation model suggests that various patterns of fluorescence intensity in annual layers can form by time lags between a growth season and the fulvic acid supply peak on a stalagmite. However, verification of those fluorescence patterns requires long-term cave climate monitoringin caves. In this study, we simulated fluorescence intensity variations in a modeled stalagmite based on cave climate monitoring data from a cave in a humid-temperature climate and validated annual layer formations.</p><p>Cave climate monitoring was performed at point A (40 m inside the entrance), point B (90 m inside the entrance), and other points in Koumori-ana Cave, Mine City, Yamaguchi Prefecture, southwest Japan, from the end of 2016. The monitoring data included cave air temperatures, CO<sub>2</sub> concentrations, and drip rates. Ca<sup>2+</sup> concentrations and relative fluorescence intensities to quantify fulvic-acid concentrations were measured monthly from drip-water samples.</p><p>The monitoring data showed that cave temperatures decrease in winter near the entrance and increase in summer near the upper vent. Drip rates at point A corresponded to rainfall amounts at the meteorological station in Akiyoshi-dai, whereas drip rates at point B were constant throughout the years monitored. CO<sub>2</sub> concentrations in the cave, closed to outside air values from November to March, became greater from April and reached maximum values in September. Ca<sup>2+</sup> concentration had gradual seasonal variations, showing a maximum in October and a minimum in March. The relative fluorescence intensities, showing fulvic acid concentration, at both points revealed a change range of about four times the minimum.</p><p>The stalagmite-growth simulations based on the monitoring data showed different growth patterns at the two monitored points: continuous growth at one and hiatus at the other. The calculated fluorescent annual layer at point A was the symmetric or gradually increasing type, with high concentration of fulvic acid in August. The growth rate varied in the range of 0.45 (Jan–Apr) to 6.2 (May–Oct) µm/month. Because the relative fluorescence intensity of fulvic acid had small variations throughout the years, the simulated fluorescent annual layer at point A is suggested to be affected by the growth rate of stalagmite. At point B, decreased saturation indices of calcite from April to June and September to October suggest no precipitation of calcite. Although the simulated annual thickness of precipitation at point B is around 28 µm, half of the thickness is precipitated in July. Point B stalagmite growth is stopped by a high concentration of CO<sub>2</sub>, low Ca<sup>2+</sup> concentration, and low drip rate. This study suggests that specific seasonal paleoenvironmental changes recorded in stalagmites can be estimated by using fluorescence patterns of annual layers.</p>

<p>Stalagmites can provide long, accurate, and continuous palaeoenvironmental records of the Earth’s surface. However, insufficient or biased information on stalagmites has also been derived from some observed data, such as fluorescent annual-layer patterns and cave-climate monitoring data, which indicate sub-annual stalagmite growth rates can change with seasonal cave environments. Observations of stalagmite growth processes compared with cave-climate monitoring data provide an estimate of changes in growth rate. However, this method is considered unreliable as growth rates of normal stalagmites (~ 0.001 – 0.1 mm yr<sup>-1</sup>) cannot provide sufficient data for validation. Many caves developed in uplifted Quaternary coral-limestones of subtropical islands in the Northeastern Pacific region.</p><p>The Gyokusen-do Cave in the southern part of Okinawa Island, southwest Japan, is famous for frequent and massive speleothems and as a tourist destination. This cave has stalagmites with a high growth rate (~ 1 mm yr<sup>-1</sup>) along a pathway laid in 1987. The cave climate (temperature, carbon dioxide concentration, drop rates, and water chemistry) has been monitored since the summer of 2017. Distinctive seasonal changes in the cave environment are apparent in the data. In this study, we sampled sub-annual layer patterns collected in January 2019 from a stalagmite (~ 20 mm in length) on a stone wall in the cave and compared them with the cave-climate monitoring data and climate records near the study site, thus verifying the formation of annual layers. About 31 or 32 years are reflected in the (0.63 – 0.65 mm yr<sup>-1</sup>) in the stalagmite record, because the stone wall was constructed in 1987. From base to top, the stalagmite has about 30 couplets of a transparent layer and a coarsely crystalline zone. The uppermost 5 mm has continuous layers without any hiatus, whereas concave points such as the drop position have thick layers of large crystals still in development. The stalagmite surface is covered with relatively large crystals that developed in the winter of 2018, which suggests that the winter climate produces coarse-grained layers precipitated during the winter season. The cave-climate monitoring data, collected about 150 m from the stalagmite, shows calcium ion concentrations of around 1 – 1.5 mol m<sup>-3</sup>, temperature around 24 – 25 °C, and drastically different carbon dioxide concentrations in summer and winter seasons (around 400 – 500 ppm from the end of October to the beginning of May and around 2500 ppm from the middle of May to the middle of October). Precipitation and drop rates are highest in summer as compared to other seasons. Stalagmite growth simulations based on the monitoring data showed that the growth rate during the summer season was about five times that in winter. These results suggest that alternation between the transparent layer precipitated in summer and the coarse-grained layer precipitated in winter make annual layers that were strongly affected by drop rates and carbon dioxide concentrations. As some seasonal layers have significantly different thicknesses, more precise comparisons with cave-climate data are required to fully understand on the processes that occur in cave environments.</p>

The Middle Pleistocene Hiruzenbara Formation is distributed in Hiruzenbara Highland, Maniwa City, Okayama Prefecture. The formation comprises the upper fluvial gravel (Fig. 1) and the lower lacustrine banded diatomite units (Fig. 2). Lateral continuity and stratigraphy of the lower unit can be clearly observed in the mining pits of Showa Chemical Co., Ltd. The banded diatomite includes varves (1 to 2 mm in thickness) composed of a set of white and light gray colored seasonal sub -layers with slope failure induced-and flood-induced sediment gravity flow deposits ( Fig. 3 ; Sasaki et al., in press). Deformation structures of various scales corresponding to the disappearance of Paleo-Hiruzenbara Lake can also be seen in the pits ( Fig. 4 ; Cover Photo). On the cover：Varved diatomite including flood-induced sediment gravity flow deposits (in middle) deformed by small faults. The width of the picture is about 40 cm. (Fig.1)と下部の湖成縞状珪藻土(Fig.2)からなる．蒜山原層下 部は，珪藻土採掘ピットで連続的に観察できる．縞状珪藻土は厚さ 1～2 mm の濃淡の葉理のセットからなる年縞をなし，しばしば 崩壊や洪水による重力流堆積物を含む( Fig.3 ; Sasaki et al., in press) ．珪藻土中には，古蒜山原湖の消滅にともなって形成された と考えられる様々な変形構造も認められる (Fig.4，Cover Photo) ． References：Sasaki, H., Sasaki, Y., Saito-Kato, M., Naruse, H., Yumi, M. and Ishihara, Y., in press, Lacustrine sediment gravity-flow deposits and stratigraphic changes intercalated in varved diatomite : an example from the Hiruzenbara Formation, Okayama Prefecture, southwest Japan, Quaternary International, doi: 10.1016 / j.quaint.2015.08.032 中部更新統蒜山原層の湖成年縞珪藻土と変形構造(石原与四郎・佐々木 華，福岡大学理学部)岡山県真庭市の蒜山原高原には， 中部更新統蒜山原層が分布する．蒜山原層は上部の河川成礫層