Precipitation history of the Lake Biwa area in central Japan over the last 145 ka

The fluvial quartz flux (FQF, g cm ^-2  ka ^-1 ) to Lake Biwa of central Japan is developed as a proxy of variations in palaeoprecipitation over the lake catchment. Lake Biwa sediments spanning the last c. 145 ka are characterized by 4 main intervals when the FQF values were significantly greater than 2 g cm ^-2  ka ^-1 , and 5 main periods during which FQF values were lower. Three of the intervals with high FQF values occur from c. 128 to 78 ka BP, with peak values at c. 122, 101 and 82 ka BP; the fourth of two narrow peaks exists between c. 48 and 35 ka BP. Three main periods with lower FQF values intervene between intervals of high FQF values, and two others lie before c. 128 ka BP and after c. 35 ka BP. The data imply that palaeoprecipitation over the lake catchment increased during the intervals of high FQF values, and decreased during the periods of lower FQF values. High FQF values between c. 48 and 35 ka BP are interpreted to reflect an effective runoff of meltwater from the surrounding mountains during the interstade of the last glaciation. Relatively low FQF values during the early Holocene are interpreted to reveal a sluggish northward retreat of the polar front in the North Pacific Ocean that suppressed the northward advance of the summer monsoonal front and regional precipitation. During the last interglaciation, the increasing trend of FQF values is interpreted to indicate a progressive expansion of the Sea of Japan related to the rise in global sea level, which increased moisture advection to, and precipitation within, the Lake Biwa region.     

Interrelations between framework-building and encrusting skeletal organisms and microbes: more-refined growth history of Lower Devonian bindstones

The framework‐building stromatoporoid Stachyodes, the encrusting calcimicrobe Rothpletzella and encrusting Graticula‐like red algae are major contributors to red algal–calcimicrobial–stromatoporoid bindstones in the Lower Devonian Elmside Formation of the Yass Basin, New South Wales, Australia. The distribution and accumulation patterns of encrusting organisms within the red algal–calcimicrobial–stromatoporoid bindstones observed by optical microscopy and SEM imply a biotic interrelationship between skeletal organisms and microbes that reflects environmental changes. Rothpletzella is characterized by prostrate filaments with frequent branching and a high angle of bifurcation. Filaments of Graticula‐like red algae exhibit rare branching and a relatively low angle of bifurcation. In addition, they are prostrate at the base before becoming erect. Both Rothpletzella and the red algae successively encrust the surfaces of skeletal frameworks, but exhibit different distributions. Rothpletzella and other calcimicrobes cover both the lower and upper surfaces of frameworks, whereas red algae are limited to the upper surfaces. Their individual distributions are thus significantly influenced by the frameworks formed by the thin, laminar stromatoporoid Stachyodes, which create different microenvironments as by‐products. The limited distribution of the red algae was probably related to light levels or phototropism. Upper framework surfaces are variously encrusted by calcimicrobes and the red algae to form thick crusts with varying accumulation patterns. Micritization around the algal thalli, covering of calcimicrobes such as Wetheredella, and microbial micrites between algal thalli all suggest interruptions of algal growth that correspond to episodes of harsh environmental conditions. Transitions from Graticula‐like red algae to Rothpletzella reflect periods of deteriorating environmental change for skeletal organisms, which resulted in the predominance of microbial growth. In contrast, a resurgence of red algae on calcimicrobes suggests improved environmental change. Repeated accumulation patterns between Graticula‐like red algae and Rothpletzella indicate changing habitat environments and competitive relations within skeletal organisms and microbes. These relationships provide insight into understanding how skeletal organisms and microbes utilized space and how they interrelated with each other to produce Devonian reefal limestones.