Redox control in arsenic accumulation with organic matter derived from a varved lacustrine deposit in the Jurassic accretionary complexes.

Oxidation states and distribution of arsenic (As) in annually laminated (varved) lacustrine deposits were analyzed with a seasonal resolution. This deposit was formed in the mid-Holocene landslide-dammed paleolake in the upper reaches of the Ane River, central Japan and the paleolake watershed consists of the Jurassic accretionary complexes (Mino-Tamba belt) including sedimentary and igneous rocks. In the outcrop, centimeter-to-decimeter-scale silty clay layers alternating with laminated layers are well developed.

Geochemistry and C dating of guano deposits in the Karaftu Cave, Kurdistan, Iran: implication for paleoenvironment.

Karaftu Cave in the northwest of Divandareh includes four floors plus an underground area. The bat hall and its underground area are covered with guano deposits. C dating indicates the onset of guano deposition is about 14,260±50 BP years, and its average accumulation rate is about 4.

Syngenetic rapid growth of ellipsoidal silica concretions with bitumen cores.

Isolated silica concretions in calcareous sediments have unique shapes and distinct sharp boundaries and are considered to form by diagenesis of biogenic siliceous grains. However, the details and rates of syngenetic formation of these spherical concretions are still not fully clear. Here we present a model for concretion growth by diffusion, with chemical buffering involving decomposition of organic matter leading to a pH change in the pore-water and preservation of residual bitumen cores in the concretions.

Publisher Correction: Sr/Sr age determination by rapidly formed spherical carbonate concretions.

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Sr/Sr age determination by rapidly formed spherical carbonate concretions.

Isolated spherical carbonate concretions are frequently observed in finer grained marine sediments of widely varying geological age. Recent studies on various kinds of spherical carbonate (CaCO) concretions revealed that they formed very rapidly under tightly constrained conditions. However, the formation ages of the isolated spherical carbonate concretions have never been determined.

Generalized conditions of spherical carbonate concretion formation around decaying organic matter in early diagenesis.

Isolated spherical carbonate concretions observed in marine sediments are fascinating natural objet trouve because of their rounded shapes and distinct sharp boundaries. They occur in varied matrices and often contain well preserved fossils. The formation process of such concretions has been explained by diffusion and rapid syn-depositional reactions with organic solutes and other pore water constituents.

Early post-mortem formation of carbonate concretions around tusk-shells over week-month timescales.

Carbonate concretions occur in sedimentary rocks of widely varying geological ages throughout the world. Many of these concretions are isolated spheres, centered on fossils. The formation of such concretions has been variously explained by diffusion of inorganic carbon and organic matter in buried marine sediments.

Difference in radiocarbon ages of carbonized material from the inner and outer surfaces of pottery from a wetland archaeological site.

AMS (Accelerator Mass Spectrometry) radiocarbon dates for eight potsherds from a single piece of pottery from a wetland archaeological site indicated that charred material from the inner pottery surfaces (5052 ± 12 BP; N = 5) is about 90 (14)C years older than that from the outer surfaces (4961 ± 22 BP; N = 7). We considered three possible causes of this difference: the old wood effect, reservoir effects, and diagenesis. We concluded that differences in the radiocarbon ages between materials from the inner and outer surfaces of the same pot were caused either by the freshwater reservoir effect or by diagenesis.