A semi-quantitative calculation to estimate siderite proportion (siderite/[siderite + chukanovite]) in the precipitates was carried out using peak intensity ratios of siderite (d104 [2θ = 32.02 ...

Here, we propose a new model for the formation of Fe-oxide concretions based on field evidence that preexisting calcite concretions were precursors of Fe-oxide concretions at two localities: the Jurassic Navajo Sandstone, Utah, and the Cretaceous Djadokhta Formation, Mongolia (Fig. 1, A and B, and Table 1).In this new model, Fe-oxide …

41 rowsInvestigation into the formation of siderite concretions and the complex …

There are two phases of siderite concretion growth within the sediment, as there are distinct changes in the carbon isotopic composition and mineralogy across the concretions, and the lack of dissolved iron is the limiting factor for sidersite formation if microbial sulfate reduction is the dominant microbial metabolism.

The second model of Loope et al. (2011 Loope et al. (, 2012 assumes siderite concretions that were oxidized with microbial consumption of some siderite to leave iron oxide rinds. The third model ...

The septarian carbonate concretions from the Boom Clay (Belgium) consist mainly of authigenic minerals such as micrite (≤ 70% bulk volume) and pyrite framboids (∼ 3%). These mineral phases occur between detrital grains and fossils. The septarian cracks are lined with calcite, which is sometimes covered with pyrite. The preservation of delicate …

Siderite from bioturbations shows d18O values between 2.5xand 3.5x 20.5x. and has an average d13C composition of This stable isotope composition can be the result of a variety of microbial processes, but the fact that the siderite from the bioturbations is slightly more depleted that the concretionary calcite and siderite may point to a ...

Fe (III) reduction is a key component of the global iron cycle, and an important control on carbon mineralization. However, little is known about the relative roles and rates of microbial (biotic) iron reduction, which utilizes organic matter, versus abiotic iron reduction, which occurs without carbon mineralization.

1 INTRODUCTION. Carbonate minerals are one of the major components of the sedimentary rock record. While the vast majority of carbonate rocks comprise the minerals calcite (CaCO 3), aragonite (CaCO 3), and dolomite (CaMg(CO 3) 2), other carbonate minerals, such as siderite (FeCO 3) can also be common (Baker, Kassan, & …

The Gammon member of the Pierre shale of the northern Great Plains, USA, contains abundant siderite concretions. The relative depth and time of siderite precipitation can be inferred from the structure, mineralogy and isotopic composition of these concretions. Concretions that formed at shallow depths, early in the history of the sediment, contain …

Authigenic vivianite and siderite microconcretions were found, respectively, in hemipelagic and deltaic facies of 600-m-long BDP-98 sediment section from Lake Baikal. Textural investigations of these microconcretions show that they are typically <1 mm in size, irregular in shape and composed of aggregated crystallites. Dissimilar orientation of …

Sandstone adjacent to spherical concretions is stained locally producing an apparent streaming effect adjacent to the concretion referred to as a "comet tail" (e.g., Fig. 8 of Chan et al., 2000). The concretions in the area around Escalante UT (Fig. 1) have been the subject of the bulk of recent research on the origin of iron oxide concretions.

Les concrétions sont des corps durs qui se forment dans les sédiments avant de devenir des roches sédimentaires. Des changements chimiques lents, peut-être liés à l'activité microbienne, font que les minéraux sortent des eaux souterraines et scellent les sédiments ensemble. Le plus souvent, le minéral de cimentation est la calcite ...

Carbonate concretions occur commonly in organic-rich clastic sediments of ancient coastal floodplains and deltas. They consist of calcite, dolomite, or siderite or combinations of these. The influence of marine, mixed or non-marine depositional waters is seen in early cements; solute sources from decomposition of unstable detrital minerals ...

Siderite Fe2+CO3 c 2001-2005 Mineral Data Publishing, version 1 Crystal Data: Hexagonal. Point Group: 32/m. Commonly crystallized, typically rhombohedral {1011} to steep scalenohedral {2131}, prismatic {1010}, {0001}, with additional minor forms, to 25 cm; fibrous, stalactitic, spherulitic, cleavable, fine-grained massive.

Gedenk, R.; Zimmerle, W. 1982: Bitumenimprägnation in Siderit-Konkretionen des Ober-Apt (Clansayes) von Lohne bei Hannover - Imprégnation de bitume dans des concrétions de sidérite de l'Aptien supérieur (Clansayesien) de Lohne près de Hanovre - Bituminous impregnation in siderite concretions in the Upper Aptian (Clansayesian) from Lohne ...

Siderite concretions in the Glen Afton Claystone are rarely larger than 40 cm across, finer-grained, and develop a yellow-brown goethite coating upon weathering. Septarian siderite concretions in the Waikato Coal Measures (Class 4) are confined to beds immediately above major coal seams and are most commonly subspherical to …

The δ¹³C values of the Gams siderite concretions (-11.1 to -7.5%) point to microbial respiration of organic carbon and the d18O values (-3.5 to +2.2%) are in accordance with a marine ...

A concretion is a hard mass found within layers of sedimentary stone. They're generally round in shape, and each type tends towards one form or another. You shouldn't confuse a concretion with a nodule. Nodules occur as minerals different from the surrounding layers, while concretions are … See more

Back-scattered electron microscopy has been used to examine the microstructure of nonmarine-shale-hosted siderite concretions. The concretions are composed of 50-100 mu m, zoned crystallites ...

This microtextural and geochemical investigation posits siderite as a derivate of biological processes at the sediment–water interface. Bacteria cell walls denoted by …

The Upper Cretaceous Gammon Shale in the northern Great Plains contains abundant siderite concretions that formed during the early compactional history of the fine-grained, marine sediments. The relative depth of siderite precipitation can be estimated on the basis of textural, mineralogical, and isotopic evidence. Siderite concretions that formed at …

Septarian concretions are abundant in many Phanerozoic marine and marginal-marine shales and mudstones. They range from a few centimetres to several …

Investigation into the formation of siderite concretions and the complex taphonomic processes controlling soft-bodied preservation are still continuing but are reviewed in …

The most common iron carbonate is siderite (FeCO3), a frequent constituent of carbonate sediments and rocks on Earth. Siderite has a low-temperature transition at 30–35 K ( Housen et al., 1996), distinctively different from that of pyrrhotite (Section 5.08.3.9). Siderite is paramagnetic at ordinary temperatures and carries no NRM.

Ancient sedimentary iron formations (IFs) are composed of diverse iron oxides, silicates, and carbonates that are thought to form through diagenesis and subsequent metamorphism of primary ferric-ferrous (Fe 3+ -Fe 2+) iron (oxyhydr)oxide precipitates ( Gole, 1980; Raiswell et al., 2011 ). Yet iron carbonate minerals such as …

Fossilised true ferns (Pecopteris sp.) preserved in siderite concretions from the Mazon Creek Lagerstätte (Illinois) presented a unique opportunity to characterise the organic signatures of these ...

δ13C values of the Gams siderite concretions (-11.1 to -7.5‰) point to microbial respiration of organic carbon and the δ18O values (-3.5 to +2.2‰) are in accordance with a marine ...

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 ...

Mineralogical, geochemical, and stable-isotope data were collected from 80 siderite samples and their immediate non-siderite-bearing regions. Geometrically, siderite mineralization occurs in the form of concretions or bands, with the latter being the most common textural type and occurring solely in mudstone, whereas the former is found in ...

North Dakota, especially in the wondrously sculpted badland areas of the west, has a fantastic variety of concretions and nodules. Some are the size and shape of petrified logs, while others, perched atop pedestals of softer sediments that they shield from erosion, have lens or disk shapes. Some - like the classic cannonballs - are perfectly ...

Concretions in rapidly deposited sediments formed at shallow depths (<10 m), whereas siderite concretions in sediments that accumulated slowly formed at greater depths …

Rinded concretions with mud-rich cores are very abundant at the bases of large to medium- scale cross-bed sets of the study site (Fig-ures 1 and 2). The concretions range from spheroids less than 10 mm in diameter to platter-shaped masses up to 8 cm thick and 50 cm across. Most concretions are ovoids or spheroids (Fig. 3A to C), but Fig. 1.