Evans, D.A.D., and R.N. The evidence comprises the deflected laminae wrapping the concretions (Fig. Calcite samples digested by 5% acetic acid show REE concentrations of 35133g/g. Trocine. In outcrops, where they have acquired the name "doggers", they are typically only a few meters across, but in the subsurface they can be seen to penetrate up to tens of meters of along-hole dimension. 31). Hendry, J.P., M.J. Pearson, N.H. Trewin, and A.E. Liang, H.M., X. Chen, C.S. Wang, D.K. The availability of oxidants for biochemical reactions during early diagenesis is profoundly influenced by the overlying seawater chemistry. a and d were collected from Huangtugang section; the others were collected from Jizhentun section. Hendry et al. Correspondence to In recent years, multiple approaches have been used to decipher the potential of microbial processes for their formation, of which analysis of mineralogy, CS isotopes and REE are principal aspects (e.g. In local brickyards, they were called "clay-dogs" either because of their animal-like forms or the concretions were nuisances in molding bricks. The calcite crystals away from the geodes are commonly small, <20100m in diameter (Fig. Geologically young concretions of the Errol Beds of Scotland show texture consistent with formation from flocculated sediments containing organic matter, whose decay left tiny gas bubbles (30 to 35 microns in diameter) and a soap of calcium fatty acids salts. Concretions are formed from mineral precipitation around some kind of nucleus while a nodule is a replacement body. As shown in Table1 and illustrated in Fig. Provided by the Springer Nature SharedIt content-sharing initiative. Element concentrations of micron-sized spots were quantitatively analyzed by an Oxford X-act energy dispersive X-ray spectrometer (EDS) connected to the FESEM, operated at 20kV with a working distance of ~15mm and a beam diameter of ~2m. 2017a. Growth mechanisms and environmental implications of carbonate concretions from the ~1.4Ga Xiamaling Formation, North China, https://doi.org/10.1186/s42501-019-0036-4, http://creativecommons.org/licenses/by/4.0/. Complex compositional zonation in concretionary siderite: Implications for geochemical studies. 2022 BioMed Central Ltd unless otherwise stated. For example, a middle-REE (MREE) enriched pattern commonly occurs in a Fe-reduction zone (Haley et al. This is consistent with the suggestion that the atmospheric oxygen level was likely higher than 4% PAL during the deposition of the Member IV of Xiamaling Formation. 2017a). Organic matter preserved in the Xiamaling Formation is ranked as immature to early thermal mature, with burial temperatures of 90C (Zhang et al. About 150400g of powder was placed in a 10mL Na-glass vial, sealed with a butyl rubber septum, and reacted with 100% phosphoric acid at 72C after flushing with helium. Nowicki. 8; e.g. 2012. Jurassic septarian concretions from NW Scotland record interdependent bacterial, physical and chemical processes of marine mudrock diagenesis. Biogeosciences 14 (8): 21332149. 2012), and possible growth model for the carbonate concretions of Xiamaling Formation. 3e and f). Geology 44 (7): 555558. 1993. Journal of Palaeogeography Their development in the Member IV of the Xiamaling Formation likely indicates that high Mn-hydroxide content and an expanded Mn reduction zone existed in the sediments. The authors declare that they have no competing interests. Yttrium and lanthanides in eastern Mediterranean seawater and their fractionation during redox-cycling. All the tested samples show no obvious Eu anomalies (1.031.12, calculated as Eu/Eu*=EuSN/(0.66SmSN+0.33TbSN)). 4). 2004; Gutjahr et al. This concretionary cement often makes the concretion harder and more resistant to weathering than the host stratum. a Major tectonic subdivisions of China (modified from Tang et al. 2016). Wang, M.M. The REEs of calcites from 9 carbonate concretions of Xiamaling Formation (Huangtugang section) are listed in Table2 and shown in Fig. Sedimentology 63 (3): 662698. Hu, H. Huang, and W.C. Yu. 7ae, calcite crystals commonly have an irregular nucleusrim structure, with low MnFe contents in the nuclei, and relatively high MnFe contents in the rims. 7g, selected 21 carbonate concretions show 13Ccarb values around 0.4 (1.7 to +1.5), and 18Ocarb values around 7.5 (10 to 4.8). Following the method described in Tang et al. 2018). Day-Stirrat, R.J., R.G. Unlike limestone beds, however, it is impossible to consistently correlate them between even closely spaced wells. Huggett, J.M., A.S. Gale, and S. Evans. Carbonate concretions are widespread in the organic-poor green silty shales from the Member IV of Xiamaling Formation (1.401.35Ga) in the North China Platform. [60] Somewhat weathered and eroded giant cannonball concretions, as large as 6 meters (20 feet) in diameter, occur in abundance at "Rock City" in Ottawa County, Kansas. In Handbook on the Physics and Chemistry of Rare Earths 23, 497593. pyrite and marcasite, or in some cases jarosite, which are found in outcrops of the Smoky Hill Chalk Member of the Niobrara Formation within Gove County, Kansas. 2017, 2018). Yang, Z.F. Based on the integration of petrographic, mineralogical, carbon isotopic and elemental geochemical data, the carbonate concretions of Xiamaling Formation are best interpreted as early diagenetic products that may have been formed largely in nitrate to Mn reduction zones, with some of them also extending into the iron reduction zone below the Mn reduction zone via displacive growth (Fig. Loyd, S.J., J.A.D. Methane-derived authigenic carbonates of mid-Cretaceous age in southern Tibet: Types of carbonate concretions, carbon sources, and formation processes. Trefry et al. Iron sulfide concretions, such as the Kansas Pop rocks, consisting of either pyrite and marcasite, are nonmagnetic. A shale-hosted Cr isotope record of low atmospheric oxygen during the Proterozoic. In most of the samples, calcite in D-horizons exhibits dull orange or black color under CL (Fig. Sedimentary Geology 208 (12): 2735. Frank. These are found along the Cannonball River within Morton and Sioux Counties, North Dakota, and can reach 3m (9.8ft) in diameter. 3b). [76] Instead, all of these iron sulfide concretions were created by the precipitation of iron sulfides within anoxic marine calcareous ooze after it had accumulated and before it had lithified into chalk. Zhang, S.H., Y. Zhao, Z.Y. 2; Zhang et al. 1991; Bau et al. 5c and d) has been interpreted as a primary depositional feature, and their preservation could be ascribed to passive porefilling carbonate growth prior to the significant compaction of clays (e.g. 2012; Dong et al. 3a) but dense in other layers (Fig. [28] Other concretions, which formed as a result of microbial sulfate reduction, consist of a mixture of calcite, barite, and pyrite. Geology 26 (6): 555558. Pathways of carbon oxidation in continental margin sediments off central Chile. -30 to +15) have been identified as the mark of methanogenesis (Raiswell and Fisher 2000). Thus, the positive Ce anomalies and low Y/Ho ratios in the carbonate concretions of Xiamaling Formation (Huangtugang section) (Fig. Evidence for surface reaction-controlled growth of carbonate concretions in shales. Kah, J.H. Isotopic constraints on growth conditions of multiphase calcitepyritebarite concretions in Carboniferous mudstones. [36][34] Shrinkage of a still-wet matrix may also take place through syneresis, in which the particles of colloidal material in the interior of the concretion become gradually more tightly bound while expelling water. 1989; German and Elderfield 1990; Johnson et al. Zhao, H.Y. 2014. 1998. 2013). 1986; Raiswell and Fisher 2000; Hendry et al. He, and H. Wu. The calcite crystals are commonly small, <100m in size, but in geodes they become larger and rod-shape in morphology (length and width up to 50m and 200m, respectively; Fig. The radiating cracks sometimes intersect a second set of concentric cracks. Rates of carbonate cementation associated with sulphate reduction in DSDP/ODP sediments: Implications for the formation of concretions. Chemical Geology 155 (12): 7790. Curtis et al. Depending on the environmental conditions present at the time of their formation, concretions can be created by either concentric or pervasive growth. Tripati, J.M. Geochimica et Cosmochimica Acta 74 (22): 63876405. De Carlo, E.H., and W.J. 2) and can be approximately estimated as ~1.36Ga in age. This deduction is in good consistence with the frequent occurrence of seafloor precipitations (e.g. This could crack the interior at depths as shallow as 10 meters (33ft). Wang, L. Ma, and M. Li. Coley, V.A. 3e and f). Large spherical rocks, which are found on the shore of Lake Huron near Kettle Point, Ontario, and locally known as "kettles", are typical cannonball concretions. [18] They appear in nodular patches, concentrated along bedding planes,[18] or protruding from weathered cliffsides. 1986; Loyd et al. The decay of these substances, together with syneresis of the host mud, produced stresses that fractured the interiors of the concretions while still at shallow burial depth. McKenzie, T.W. Even so, the primary carbonates were not directly formed on the seafloor, suggesting that the bicarbonate from degraded organic matter and the nucleation sites provided by degraded organic matters may have played significant roles in triggering the initial carbonate precipitation as well. 1988. 2013. 2017, 2018; Wang et al. In fact, metamorphic rocks are completely absent from the Smoky Hill Chalk Member. 2006; Loyd et al. 2), and is the focus of this study. The carbonate concretions were mainly induced by Mn reduction in host silty shale. Keeney-Kennicutt, and R.P. 1 and 2). 1986; Raiswell and Fisher 2000; Hendry et al. 7af) likely indicate that the rims were formed in a Mn reduction zone (Curtis et al. Manganese, iron and sulfur cycling in a coastal marine sediment, Aarhus bay, Denmark. 6ce). Science 257 (5074): 12421245. These data suggest a significantly less contribution of organic matter to the growth of carbonate concretions of Xiamaling Formation than that of typical carbonate concretions formed in organic-rich mudstones (e.g. They typically show an internal structure of polyhedral blocks (the matrix) separated by mineral-filled radiating cracks (the septaria) which taper towards the rim of the concretion. Consequently, 13C values of concretion carbonates are often used as fingerprints for specific microbial pathways that may have triggered and maintained concretion growth (e.g. Towards a consistent classification scheme for geochemical environments, or, why we wish the term 'suboxic' would go away. For example, in modern oceans the average sulfate concentration is as high as 28mM (Lowenstein et al. They can vary in length from 2in (5.1cm) to over 22in (56cm) and often exhibit concentric grooves on their surfaces. 5e) reveal that the carbonate matrix grew freely within the mudstone beds, pushing clay grains aside and disrupting the primary depositional fabric (Gaines and Vorhies 2016). If this deduction is the case, many similar concretions formed in nitrate and Mn reduction zones with seawater-like carbon isotope composition should exist in the Mesoproterozoic strata and further studies are required to test this explanation. Dickson, J.R. Boles, and A.K. EDS analysis results confirm that the black area contains low concentrations of Mn and Fe, while the dull orange area has relatively high Mn and Fe concentrations. Dong-Jie Tang. The studied interval (marked with red bar in Fig. Prominence of Mn reduction in the porewater likely indicates that there was sufficient oxygen to support active Mn-redox cycling in the overlying seawater. All of the 13Ccarb values fall into the typical range of Boring Billion (Brasier and Lindsay 1998) carbonate values (e.g. Ernst, and Z.Y. 2008). (2017) and Zhang et al. 5a), and are mainly composed of clay minerals, fine detrital quartz and authigenic carbonate minerals (Fig. The D-horizons of concretions commonly have homogeneous textures, with almost all calcites having nucleusrim structures, likely indicating that the concretions mainly grew pervasively rather than concentrically (Raiswell and Fisher 2000). For example, great numbers of strikingly symmetrical concretions have been found eroding out of outcrops of Quaternary proglacial lake sediments along and in the gravels of the Connecticut River and its tributaries in Massachusetts and Vermont. In the study area, the Xiamaling Formation is dominated by dark siltstone and black shales, and can be subdivided into four members (Member I to IV) in an ascending order, which constitutes a large transgressiveregressive cycle with its largest depositional water-depth (below storm wave base) in the Member III (Fig. 1989. Palaeomagnetic study suggested that the North China Platform was most likely located in between 10N and 30N during the deposition of the Xiamaling Formation (Evans and Mitchell 2011; Zhang et al. van der Pluijm. There is an important distinction to draw between concretions and nodules. Sedimentology 53 (3): 537565. They are found where submarine erosion has concentrated early diagenetic concretions as lag surfaces by washing away surrounding fine-grained sediments. Rouxel, B. Kamber, A. Hofmann, A. Knudsen, and T.W. Geodes, with diameter around 1mm, are abundant in the D-horizons. Carbon and hydrogen isotope systematics of bacterial formation and oxidation of methane. 2000; Feldmann et al. If this is the case, most mid-Proterozoic carbonate concretions would record far less prominent BSR process with seldom authigenic pyrites. 2017; Zhang et al. [68][60][69][70] In addition to providing information about the orientation of past fluid flow in the host rock, elongate concretions can provide insight into local permeability trends (i.e., permeability correlation structure; variation in groundwater velocity,[71] and the types of geological features that influence flow. Geochimica et Cosmochimica Acta 50 (10): 23212334. 1). For example, carbonate concretions, which form in response to the reduction of sulfates by bacteria, often contain minor percentages of pyrite. R-horizons are typically separated by portions of concretionary framework that grew displacively (Fig. Raiswell and Fisher 2000; Day-Stirrat et al. Dean, J.D. Nature 431 (7010): 834838. [39] Another possibility is that early cementation reduces the permeability of the concretion, trapping pore fluids and creating excess pore pressure during continued burial. Bjerrum, E.U. Dale, A., C.M. However, the evidence is ambiguous, and many or most concretions may have formed by pervasive cementation of the entire volume of the concretion at the same time. Authigenic apatite also occurs within R-horizons. These concretions range in size from a few millimeters to as much as 0.7m (2.3ft) in length and 12cm (0.39ft) in thickness. Hammarlund, M.M. Descriptions dating from the 18th century attest to the fact that concretions have long been regarded as geological curiosities. Loyd, S.J., W.M. Earth and Planetary Science Letters 231 (34): 263277. Curtis et al. EDS analysis of 93 points reveal that the dolomitization is rather weak, with MgO content commonly less than 1wt% and Mg/Ca molar ratio lower than 0.04 (Additionalfile1: Table S1). 5c and d). [17], Concretions are commonly composed of a mineral present as a minor component of the host rock. Bjerrum, E.U. They are composed mainly of displacive growth horizons with a small portion of replacive growth horizons. Johnson, K.S., W.M. Pathways of organic carbon oxidation in three continental margin sediments. In contrast, in the host silty shale these phenomena are not seen (Fig. Zhang, S.C., X.M. 1991. a A green-yellow replacive layer (marked by R) interbedded in displacive layers (marked by D); b A BSE image showing that the replacive layer is composed of siliciclastic illite (Ill), chamosite (Ch), quartz (Q), K-feldspar (Kfs) and iron oxides (IO), and authigenic dolomite (Dol) and apatite (Ap); c and d Cardhouse structures (arrows) in the replacive layer; e SEM image of replaced mudstone horizon in a concretion, showing laminar clay minerals bended around an authigenic dolomite grain (dash line); f Green-yellow silty shale matrix adjacent to a concretion; g SEM image of panel f showing horizontal clay lamination (arrow); h SEM image with high magnification, showing horizontally distributed laminar clay minerals (arrow). Septarian concretions (or septarian nodules) are carbonate-rich concretions containing angular cavities or cracks (septaria; sg. Halliday. Saager, P.M., H.J.W. Waugh. 2013). Loucks, K.L. DJT designed the study. 2009, 2012, 2017b; Tang et al. The carbon isotope compositions of the concretions (1.7 to +1.5) are stable and close to or slightly lower than that of the contemporaneous seawater, indicating that the bicarbonates required for the concretion formation were mainly sourced from seawater by diffusion rather than produced by methanogenesis or anoxic oxidation of methane (AOM); the rare occurrence of authigenic pyrite grains in the concretions likely indicates that bacterial sulfate reduction (BSR) did not play a significant role in their formation either. Canfield. The REE+Y patterns of the carbonate concretions of Xiamaling Formation provide further support for their early diagenetic origin mainly through Mn reduction process. Hammarlund, J. Su, Y. Wang, and D.E. Decho, D.H. Buckley, J.R. When the iron-bearing groundwater came into contact with more oxygen-rich groundwater, the reduced iron was converted back to insoluble iron oxide, which formed the concretions. Mozley and Burns 1993; Raiswell and Fisher 2000). Microfabrics were examined on thin sections with a Zeiss Stereo Discovery V20 microscope for large scope and a Zeiss Axio Scope A1 microscope for high magnification. Light-microscope observation shows that the carbonate concretions analyzed in this study have not suffered intensive recrystallization, with the component microspar commonly less than 50m (Fig. McLennan, S.M. Comparing yttrium and rare earths in hydrothermal fluids from the Mid-Atlantic Ridge: Implications for Y and REE behaviour during near-vent mixing and for the Y/Ho ratio of Proterozoic seawater. 2012). 2004; Meyer et al. In the middle part of the Member IV of the Xiamaling Formation (ca. 1984; Saager et al. Geology 32 (2): 129132. Tripati. This evidence suggests that Mn reduction is the dominant process responsible for the formation of calcite rims while nitrate reduction probably triggered the precipitation of calcite nuclei. Science in China Series D: Earth Sciences 51 (9): 13301339. For prolonged growth, zoned crystals (Raiswell 1988; Mozley 1989; Raiswell and Fisher 2000) and multiple generations of cements with distinct chemical and isotopic properties are commonly present (e.g. This likely implies that parts of the rigid framework of the concretions were formed rather rapidly and considerably earlier than the significant compaction of host sediments. Extremely low oxygen concentration in mid-Proterozoic shallow seawaters. Dong, J., S.H. In fine-siliciclastic settings, they preferentially form in organic-rich mudstones, owing to a significant fraction of the bicarbonate required for carbonate precipitation resulted from the decomposition of organic matter in sediments. Zhang, G.Q. 2012). PAAS (Post-Archean Australian Shale)-normalized REE distribution patterns (REESN) of the calcites show prominent positive Ce anomalies (calculated as Ce/Ce*=CeSN/(PrSN2/NdSN)) and moderate enrichment of middle REE (MREE) (Table 2, Fig. The growth process of the concretion is probably as follows. Schweitzer, and D.A. Geochimica et Cosmochimica Acta 52 (5): 12031219. 1993; Thamdrup and Canfield 1996; Raiswell and Fisher 2000; Loyd et al. 2004; Hendry et al. Pore water evolution during sediment burial from isotopic and mineral chemistry of calcite, dolomite and siderite concretions. Precambrian Research 276: 145157. 2016). Marshall, A. Carr, and D. Hatfield. Geochimica et Cosmochimica Acta 55 (12): 35533558. 1994. Cookies policy. 2016. Lyons, T.W., C.T. Connelly, B.M. Tang, D.J., X.Y. 2015; Tang et al. J. Palaeogeogr. 2016). Surrounding the cardhouse structures, there are no rigid grains such as detrital quartz to support the voids from being compacted. 2001), therefore, during early diagenetic stage BSR is commonly the predominant process in sediments (e.g. Gogottes have fetched high prices at auction due to their sculpture-like quality. A few of these concretions enclose, at least in part, large flattened valves of inoceramid bivalves. Clarkson. Disc concretions composed of calcium carbonate are often found eroding out of exposures of interlaminated silt and clay, varved, proglacial lake deposits. Light-microscope and BSE images reveal that the centers of some geodes were filled with siliciclastic chamosite, illite, and later diagenetic euhedral carbonate minerals that have dolomite nucleus and ankerite rim, and minor amount of pyrite grains (Fig. 7h). a and b BSE images, showing a calcite crystal with dark nucleus (low MnFe contents) and light rim (high MnFe contents) (Zhaojiashan section); c and d EDS spectrums showing that the MnFe contents of the nucleus are lower than the detection limits of EDS, while the rim has higher MnFe contents; e A cross plot showing that the nuclei of calcite crystals have low Mn and Fe concentrations, while the rims have high Mn and Fe concentrations; f Average Mn/Fe ratios under different redox conditions. 2017a). 2004; Meyer et al. Field emission scanning electron microscope, Inductively Coupled Plasma Mass Spectrometry. Jrgensen. Jrgensen, H. Fossing, R. Glud, J. Gundersen, N.B. 2016. Visscher. The carbonate-free residue was then rinsed by deionized water and centrifuged several times until pH test gives a neutral value. Privacy [3][4][5][6][7][8] They typically form when a mineral precipitates and cements sediment around a nucleus, which is often organic, such as a leaf, tooth, piece of shell or fossil. The duration of this formation is constrained between ~1.40Ga and ~1.35Ga according to the high-precision zircon/baddeleyite ages of 1384.41.4Ma and 1392.21.0Ma from its middle part (Zhang et al. Meyer, R.L., N. Risgaard-Petersen, and D.E. 2015. 4c). This is mainly based on the observation that in modern oceans active Mn redox cycling could only occur when the oxygen concentration is at least higher than 10M (e.g. Distribution and chemistry of manganese, iron, and suspended particulates in Orca Basin. [38], Septarian concretions are found in many kinds of mudstone, including lacustrine siltstones such as the Beaufort Group of northwest Mozambique,[39] but are most commonly found in marine shales, such as the Staffin Shale Formation of Skye,[38] the Kimmeridge Clay of England,[40][41] or the Mancos Group of North America. Zhou. [64] Their significance for stratigraphy, sedimentology and paleontology was first noted by Voigt who referred to them as Hiatus-Konkretionen. Vertically, the abundance of concretions in the ~6-m-thick interval varies dramatically. 3). [79][80][81] Similar disc-shaped calcium carbonate concretions have also been found in the Harricana River valley in the Abitibi-Tmiscamingue administrative region of Quebec, and in stergtland county, Sweden. Formation mechanisms of carbonate concretions of the Monterey Formation: Analyses of clumped isotopes, iron, sulfur and carbon. Costa, J.N. The 13C and 18O of these two laboratory standards are +1.61 and11.59, and6.06 and24.12, respectively. The upper and lower contacts of concretions with host silty shale are sharp (Fig. Reinhard, and N.J. Planavsky. 
In fact, both nitrate reduction (5C2H3O2+8NO3+3H+ 4N2+10HCO3+4H2O) and manganese reduction (C2H3O2+4MnO2+7H+ 2HCO3+4Mn2+ + 4H2O) could facilitate the precipitation of calcite during early diagenesis by increasing environmental alkalinity and pH (Fig. [84], Compact mass formed by precipitation of mineral cement between particles, "Septaria" redirects here. Applied and Environmental Microbiology 71 (10): 61426149. Liu. Samples analyzed in this study were collected from the Member IV of the Xiamaling Formation, along road cuts at the Zhaojiashan (40284.76N, 115245.74E), Jizhentun (402743.10N, 1151629.48E), and Huangtugang sections (40278.62N, 1151255.74E), Hebei Province, North China (Fig. 
In fact, both nitrate reduction (5C2H3O2+8NO3+3H+ 4N2+10HCO3+4H2O) and manganese reduction (C2H3O2+4MnO2+7H+ 2HCO3+4Mn2+ + 4H2O) could facilitate the precipitation of calcite during early diagenesis by increasing environmental alkalinity and pH (Fig. [84], Compact mass formed by precipitation of mineral cement between particles, "Septaria" redirects here. Applied and Environmental Microbiology 71 (10): 61426149. Liu. Samples analyzed in this study were collected from the Member IV of the Xiamaling Formation, along road cuts at the Zhaojiashan (40284.76N, 115245.74E), Jizhentun (402743.10N, 1151629.48E), and Huangtugang sections (40278.62N, 1151255.74E), Hebei Province, North China (Fig.