Precipitation Of Authigenic Calcite Research Articles

Limnogeology of the Agua de la Zorra Formation (Middle–Upper Triassic), Cuyana Basin, NW Argentina: Emphasising lacustrine carbonates

Lacustrine systems are complex and highly sensitive in responding to allogenic factors like tectonics, climate and volcanism but also present within lake processes that are difficult to disentangle. The Agua de la Zorra Formation (Middle–Upper Triassic) outcropping in the Paramillos de Uspallata sub-basin, Cuyana rift Basin (SW Gondwana), is composed of deltaic–fluvial–lacustrine–volcaniclastic deposits. The lacustrine system presents carbonate deposits, as almost every other sub-basin within the Cuyana rift. This makes it an exceptional case for analysing limnogeological questions in an extensional tectonic regime linked to volcanism (basalt flow and tuff deposits) and studying lacustrine carbonate in that particular setting. This study focuses on a high-resolution stratigraphic, sedimentologic, petrographic and limnogeological investigation of the Agua de la Zorra depositional system to understand its evolution through space and time; and to reconstruct the development of the carbonate factory within the palaeolake. Stratigraphic correlation of five sedimentary logs across the sub-basin allowed the identification of a deltaic–lacustrine facies association and a progradational–retrogradational stacking pattern interpreting the palaeolake as an overfilled lake basin type. Five facies associations represent a delta front, prodelta, lake margin, lake centre and volcanic episodes. The stratigraphic analysis allowed interpreting that volcanic episodes were diachronous during the evolution of the Agua de la Zorra system; the development of a well-established axial fluvial system upsection and the coeval migration of the highest accommodation point and lake centre northwards. Carbonate deposits are part of the lake margin subenvironment and immediately overlie volcanic basalts and are laterally linked to altered sandstones in contact with basalts. Their microfabric is characterised by fibro-radial spar mosaics and laminated carbonate, interpreted as inorganic authigenic calcite precipitation. This and their restricted extent support that alkaline lava flows in contact with the palaeolake water column triggered carbonate precipitation. Stratigraphic, sedimentologic, limnogeological and petrographic analyses strongly support volcanism and tectonics as the main allogenic factors controlling the Agua de La Zorra lacustrine system evolution.

Microbially promoted calcite precipitation in the pelagic redoxcline: Elucidating the formation of the turbid layer.

Large bell-shaped calcite formations called "Hells Bells" were discovered underwater in the stratified cenote El Zapote on the Yucatán Peninsula, Mexico. Together with these extraordinary speleothems, divers found a white, cloudy turbid layer into which some Hells Bells partially extend. Here, we address the central question if the formation of the turbid layer could be based on microbial activity, more specifically, on microbially induced calcite precipitation. Metagenomic and metatranscriptomic profiling of the microbial community in the turbid layer, which overlaps with the pelagic redoxcline in the cenote, revealed chemolithoautotrophic Hydrogenophilales and unclassified β-Proteobacteria as the metabolic key players. Bioinformatic and hydrogeochemical data suggest chemolithoautotrophic oxidation of sulfide to zero-valent sulfur catalyzed by denitrifying organisms due to oxygen deficiency. Incomplete sulfide oxidation via nitrate reduction and chemolithoautotrophy are both proton-consuming processes, which increase the pH in the redoxcline favoring authigenic calcite precipitation and may contribute to Hells Bells growth. The observed mechanism of microbially induced calcite precipitation is potentially applicable to many other stagnant sulfate-rich water bodies.

Changes in the geochemical parameters of karst lakes over the past three decades – The case of Plitvice Lakes, Croatia

One of the major reasons for the increase in global air temperature since the early 20th century is considered to be the increase in the atmospheric CO2 concentration. Karst relief is considered an important carbon sink, but it can also be a natural source of carbon and CO2 emission. Aquatic systems in karst areas facilitate carbon exchange between the karst and the atmosphere, often through groundwater geochemical carbonate rock dissolution (carbon sink) and in the form of secondary calcium carbonate precipitation (possible carbon source).The protected area of Plitvice Lakes National Park, located in the karst region of Croatia, was chosen as a case study on karst geochemical processes. The lakes are also specific for their authigenic calcite precipitation in the form of tufa barriers and lake sediment. Physical and chemical data (temperature, pH, Ca2+, HCO3−, Mg2+ and CO2 concentrations, calcite saturation index (SIcalc), calcite dissolution ionic ratio (IRcalc), and Mg/Ca ratio) from water samples collected at 8 locations (2 springs, 2 rivers, and 4 lakes) from 1981 to 2014 were studied.The data were not collected systematically, so long-term changes have been mostly assessed through comparison between parameters from two selected periods (1981–1986 and 2010–2014) and through temporal correlations for each observed parameter in each calendar month.For the 33 years studied, an increase in air and water temperature, Ca2+ and HCO3− concentrations, calcite saturation index (SIcalc), calcite dissolution ionic ratio (IRcalc), and a decrease in the Mg/Ca ratio were observed. No statistically significant change was observed for pH or CO2 and Mg2+ concentrations. Average discharge rates did not display any significant change over the past three decades, however there was a change in their seasonal distribution.The significant increase in Ca2+ and HCO3− concentrations at lake locations were primarily caused by an increase in Ca2+ and HCO3− values in the water of the springs. Simultaneously, Mg2+ concentrations remained constant, which indicates higher levels of limestone (calcite) dissolution than dolomite dissolution. One of the reasons for this could be higher air/soil temperatures, resulting in higher soil CO2 production, which appears to result in the higher dissolution of calcite exclusively. An increase in HCO3− concentrations at the springs implies that karst groundwater is a carbon sink. Furthermore, the fact that the spatial decrease in HCO3− concentration in downstream waters was the same during the 1981–1986 and 2010–2014 periods implies that the entire observed karst lake system itself is a carbon sink.Temporal and spatial changes in SIcalc and IRcalc values in surface waters were mainly attributed to an increase in the intensity of bioactivity, which is in turn connected with an increase in water temperature.

Precipitation of Calcite during the Deposition of Paleogene Sangkarewang Oil Shale, Ombilin Basin, West Sumatra, Indonesia

DOI: 10.17014/ijog.2.3.185-197Geochemical and petrographical analyses were carried out to investigate the occurrence of calcite in theformer Ombilin lacustrine lake. The study involves eight samples taken from a 56 m long drill core of Sangkarewangoil shale. Geochemical investigation showed that the samples consist of varied terrigenous input represented by Si, Al, K, and Ti, and autochthonous input represented by S, total organic carbon (TOC), and d13C of bulk organic matter. Along the drill core profile the abundance of autochthonous input decreases upwards, while that of terrigenous input oppositely increases upwards. Petrographical analysis revealed that calcite is a major mineral in the samples. In this study, the abundance of calcite could be represented by the abundance of Ca, as calcite is the only significant Ca containing mineral. Ca is abundant in the samples (8.4% in average) and its concentration varies similarly with those of S, TOC, and d13C, suggesting that the element as well as calcite incorporates the autochthonous input. Thevariation of calcite abundance in the drill core profile is considered to be related with primary productivity changes during the development of the former lake. Higher primary productivity represented by more positive of d13C value(-24.8‰) during the deposition of the lower part of the drill core profile promoted the higher amount of deposited organic matter. In such environment, the supersaturation of carbonate ion in lake water was also reached and significant precipitation of authigenic calcite occurred. As the lake developed, the primary productivity decreased as indicated by more negative of d13C value (eventually -26.8‰). This condition led to the decreases of deposited organic matterand calcite in the lake sediments.

First microbialites associated to organic-rich facies of the Oceanic Anoxic Event 2 (Northern Tunisia, Cenomanian–Turonian transition)

From northern Tunisia, small-scale well-preserved microbialites, contemporaneous to the global oceanic anoxic event 2 (OAE 2) are first reported on the southern Tethyan Margin. These microbialites are encased within the pelagic organic-rich black shales of the Bahloul Formation (Cenomanian–Turonian transition). Biostratigraphic, petrographic, and geochemical investigations carried out to constrain their biogenicity and genesis character led to consider them as thrombolites and stromatolites occurring in lenticular bioherms/biostromes and columnar bodies co-relatable to the global ‘filament event’ of the authors, close to the base of the Watinoceras ammonite zone. Abundant clotted micrite, cyanobacterial filaments, and algal tissues point to the key process of microbial carbonate precipitation and to a major role played by microbes in the stabilisation and subsequent lithification, which in turn favoured the preservation of the original structure of the microbialites. These microbially induced carbonate formations are considered as favoured by chemosynthetic fauna of bivalve molluscs and lithistid sponges which were able to host symbiotic microbial communities. The latter contributed to the precipitation of authigenic calcite and non-carbonate minerals (e.g. pyrite) fuelled by microbial activity under sulphate-reducing conditions. The carbonate body onset is considered to be initiated by seafloor instability due to syndepositional fault acting that induced the appraisal of uplifted tilted blocks within oxygenated waters but near the anoxic water masses. Generated depressions allowed the development of chemosynthetic-based communities. Deep faults related to Triassic salt domes acted as conducts for hydrocarbon and salt brine expulsion to the seafloor and the microbialite growth was enhanced by an abrupt uprising sea level under warmer conditions.

Influence of diagenesis on the stable isotopic composition of biogenic carbonates from the Gulf of Tehuantepec oxygen minimum zone

In order to evaluate the influence of diagenetic and post‐sampling processes on the stable oxygen and carbon isotope compositions of biogenic carbonates, we conducted a multiproxy study of organic‐rich sediments from the eastern Pacific oxygen minimum zone. Core MD02‐2520, which was retrieved from the Gulf of Tehuantepec (Mexico), has seasonal laminations and covers the last 40 kyr. Together with the presence of gypsum crystals and inorganic calcite aggregates, the occurrence of large excursions in the stable oxygen and carbon isotope records of both planktonic and benthic foraminifera (as large as +3‰ in δ18O and −5‰ in δ13C) point to significant secondary transformations. Storage‐related gypsum precipitation was ruled out since it implies sulfide reoxidation by oxygen that triggers biogenic calcite dissolution, which proved to be of minor importance here. Instead, precipitation of authigenic calcite during early diagenesis appears to be the most likely process responsible for the observed isotopic excursions. The δ13C composition for inorganic calcite aggregates (−5 to −7‰) suggests a major contribution from anaerobic oxidation of organic matter. The δ34S composition for gypsum crystals (−10 to +15‰) suggests a major contribution from anaerobic reoxidation of authigenic sulfides, potentially involving reactions with metal oxides and sulfur disproportionation. A minor part of the gypsum might possibly have formed as a result of local pore water salinity increases induced by gas hydrate formation.

Controls on ostracod valve geochemistry, Part 1: Variations of environmental parameters in ostracod (micro-)habitats

The variations of environmental conditions ( T°, pH, δ 13C DIC, [DIC], δ 18O, Mg/Ca, and Sr/Ca) of ostracod habitats were examined to determine the controls of environmental parameters on the chemical and isotopic composition of ostracod valves. Results of a one-year monitoring of environmental parameters at five sites, with depths of between 2 and 70 m, in Lake Geneva indicate that in littoral to sub-littoral zones (2, 5, and 13 m), the chemical composition of bottom water varies seasonally in concert with changes in temperature and photosynthetic activity. An increase of temperature and photosynthetic activity leads to an increase in δ 13C values of DIC and to precipitation of authigenic calcite, which results in a concomitant increase of Mg/Ca and Sr/Ca ratios of water. In deeper sites (33 and 70 m), the composition of bottom water remains constant throughout the year and isotopic values and trace element contents are similar to those of deep water within the lake. The chemical composition of interstitial pore water also does not reflect seasonal variations but is controlled by calcite dissolution, aerobic respiration, anaerobic respiration with reduction of sulphate and/or nitrate, and methanogenesis that may occur in the sediment pores. Relative influence of each of these factors on the pore water geochemistry depends on sediment thickness and texture, oxygen content in bottom as well as pore water. Variations of chemical compositions of the ostracod valves of this study vary according to the specific ecology of the ostracod species analysed, that is its life-cycle and its (micro-)habitat. Littoral species have compositions that are related to the seasonal variations of temperature, δ 13C values of DIC, and of Mg/Ca and Sr/Ca ratios of water. In contrast, the compositions of profundal species are largely controlled by variations of pore fluids along sediment depth profiles according to the specific depth preference of the species. The control on the geochemistry of sub-littoral species is a combination of controls for the littoral and profundal species as well as the specific ecology of the species.

Origin of CO2 in natural gas from the Triassic Feixianguan Formation of Northeast Sichuan Basin

The natural gas from the Triassic Feixianguan Formation of Northeast Sichuan Basin contains high H2S whereas relatively low CO2 concentrations and the CO2 display high δ13C values (ranging from −5.81‰ to 3.3‰ (PDB)). This seems to contradict the conventional wisdom that TSR should be a primary source of CO2 in natural gas from the Feixianguan Formation. In contrast, many authigenic calcite samples from these sites display very low δ13C values (ranging from −18.4‰ to −10.3‰ (PDB)). This suggests that the carbon from TSR source dominated the formation of calcite whereas the carbon from inorganic source came into CO2 in natural gas. In order to assess the origin of CO2 from these H2S-rich sites, we have calculated the relative contributions of organic and inorganic carbon sources to the CO2 and authigenic calcite. The organic carbon source possibly originated from TSR, whereas the inorganic one might be generated from marine carbonates dissolution. This calculation is based on the carbon isotopic compositions of CO2 and authigenic calcite as well as an isotopic mass balance. The results show that the contribution of organic carbon source to the CO2 is only 2%, whereas that to authigenic calcite is as high as 43% on average. Such results combined with thermodynamic evidence indicate that the isotopically light CO2 produced by TSR process may contribute to authigenic calcite precipitation during burial diagenesis. Distinguishable from Ordovician reservoir of Tarim Basin, Feixianguan reservoir of Northeast Sichuan Basin experienced rapid tectonic uplift due to Yanshanian movement after TSR occurred. Such tectonic event could induce temperature decrease and further promote carbonates dissolution. During these processes, secondary porosity has developed in Feixianguan carbonate reservoirs. Therefore, much attention should be paid to the structural highs in search of high quality carbonate reservoirs.

Late glacial to Holocene climate and sedimentation history in the NW Black Sea

Gravity cores from the continental slope in the northwestern Black Sea were studied using high-resolution stable isotope, grain size and XRF-scanning data. The measurements provide a 30 000 years AMS 14C-dated record of variations in the hydrological regime of the Black Sea and give insight into changing paleoenvironments in the surrounding areas. Stable climatic conditions during the Last Glacial Maximum were followed by a series of meltwater pulses most likely originating from the Scandinavian ice sheet between 18 000 and 15 500 yr BP. 1 1 All dates are calibrated to calendar years B.P. (yr BP). This meltwater input rose the level of the Caspian Sea to a point that Caspian water could spill into the Black Sea via the Manych-depression north of the Caucasian mountains. High-frequency oscillations in the XRF-data during this period suggest a probable link to the arctic climate regime. Later, during the Bølling/Allerød and the early Holocene, prevailing high temperatures led to authigenic calcite precipitation through increased phytoplankton activity, interrupted by the Younger Dryas and the “8200 yr BP cold event” with dominant clastic sedimentation.

Tracing calcite precipitation with specific conductance in a hard water alpine lake (Lake Bourget)

The authors discuss the reliability of a new method used to depict precisely the authigenic calcite precipitation process in the water column of a mesotrophic alpine lake (Lake Bourget, Savoie, France). Complete chemical analysis of dissolved major elements shows that, in the epilimnion, calcium concentration and alkalinity are the only chemical species presenting large variations. The behaviour of these two parameters is only related to calcite precipitation. The method is based on in situ specific conductance measurements ( C 25). Experimental values were compared with theoretical calculations. The results demonstrate clearly that dissolved calcium concentration can be directly related to measured specific conductance. Hence, a mathematical relationship was developed to compute calcium concentration profiles in the water column with a centimetre spatial resolution through the whole water column. Finally, authigenic calcite production can be observed and quantified on a time scale covering two years of experimental data. Calcite production is estimated to 4.8 mol m −2 yr −1. Extrapolation to the whole lake surface leads to 16,000±2000 tons yr −1 as CaCO 3. Specific conductance is an easy-to-measure in situ parameter which could be used to trace authigenic calcite production in other hard water alpine lakes.

The labile fraction of suspended matter in the Loire River (France): multi-element chemistry and isotopic (Rb–Sr and C–O) systematics

Suspended particulate matter transported by the Loire River (France) comprises mainly quartz and K-feldspar during periods of high river flow, with an increase in calcite contents during periods of low flow. We studied the labile fraction (leached by HCl 0.2 N) associated with the suspended matter transported by the upper Loire River. The acid extractable matter (AEM) concentrations in the Loire exhibit a wide range from 8% during high-flow conditions in the river to 47% during the low-flow conditions. The dispersion of AEM data differentiates two fields; one related to a domain where CaCO 3 precipitation is possible, and the other related to a domain where erosion is dominant. The concentrations of trace elements and REE fluctuate widely and generally decrease with increasing AEM concentrations. A middle REE (MREE) enrichment over the LREE and HREE is observed which can be related to Fe–Mn oxide coatings developed on the clastic particles. The 87Sr/ 86Sr ratio varies from 0.710582 to 0.711472 and displays two different trends when plotted against AEM abundance, again reflecting varying contributions from two main end-members. The hydrous Fe–Mn oxides have the lowest 87Sr/ 86Sr ratio (≈0.7105) and the carbonates have the highest 87Sr/ 86Sr ratio (≈0.7115). The highest 87Sr/ 86Sr ratios of AEM, obtained during the period of authigenic calcite precipitation, agree with values measured for the dissolved Sr over the same period. During the period where erosion dominates, the 87Sr/ 86Sr ratio of the hydrous Fe–Mn oxide end-member diverges from the mean value of the dissolved load of the Loire River. This implies that the oxides were formed in water with a lower 87Sr/ 86Sr ratio, suggesting that (i) the location of oxide precipitation is upland, and (ii) the oxides conserve their Sr isotope signature during transport by the river and do not re-equilibrate with local waters during transport. Stable carbon and oxygen isotope compositions of the carbonate fraction of the AEM during low-flow conditions are consistent with authigenic calcite formation in isotopic equilibrium with Loire River water. At high-flow conditions we observe an isotopic enrichment that may reflect a higher proportion of atmospheric CO 2 within the river waters at this time, or a contribution of detrital carbonate material from marine sediments exposed in the watershed, or secondary calcite derived from eroded soils.

Evidence for Dedolomitization and Mixing in Paleozoic Carbonates Near Oak Ridge, Tennessee

AbstractMultiport ground‐water sampling systems in five deep core holes near DOE's Y‐12 facility at Oak Ridge, Tennessee provide data on the three‐dimensional distribution of ground‐water types and chemical evolution processes. Interpretation of ground‐water chemistry, coupled with data on the primary and authigenic mineralogy from drill core, indicates the ground water evolves chemically by three main processes: (1) open system dissolution of calcite and dolomite at shallow depths to produce Ca‐Mg‐HCO3 waters; (2) irreversible dissolution of gypsum, which causes dedolomitization and leads to the formation of Ca‐Mg‐SO4 waters at deeper levels; and (3) mixing with deep brines to form saline Na‐Ca‐Cl waters. Evidence for dedolomitization included the precipitation of authigenic calcite in gypsum dissolution cavities, decrease in ground‐water pH, and increases in dissolved Ca, Mg, and SO4. In this study, we document the dedolomitization process along a relatively short (< 2000 ft) flow path in low permeability Paleozoic carbonates. Mixing of the shallower ground water with an Na‐Ca‐Cl brine thought to be present at depth can account for the progressive increase in salinity of ground water with depth and the precipitation of authigenic barite and celestite. The mixing process could be a combination of diffusion from below, diffusion from older matrix water into fractures, or advective mixing.

Geological evidence for mud diapirism on the Mediterranean Ridge accretionary complex

A mud breccia has been repeatedly cored from four mud diapir fields located on the crest of the Mediterranean Ridge.This breccia is composed of subrounded clasts supported by a clay-rich matrix and ranges in age from Cretaceous to early Miocene. Sedimentological analysis allows identification of a “primitive” intrusive and a “reworked” mud breccia, the latter being formed by mud extrusion and gravitational reworking of the former. Homogeneous mud, sorted by grain size, which occurs at the top of the diapirs has been interpreted as a lake deposit.Based on composition and carbon isotopic ratios, gases present within the diapiric material suggest a partial thermogenic origin, and gas escape structures have been identified in the mud breccia and host sediments. Carbonate crusts occurring in the host sediments are not related to bacterial oxidation of methane and consequent authigenic calcite precipitation. Their carbon and oxygen isotopic ratios reveal that they are characteristic of early deep-sea lithification in the Mediterranean Sea.The presence of a marker bed composed of Mn nodules and bacterial colonies, the mud lake deposits showing lower carbonate content than primitive mud breccia, and the gas escape structures suggest the presence of active fluid vents in the vicinity of the diapiric structures.Evidence of active mud diapirism can be found from about 300,000 yrs B.P. to the present.

Ostracod shell chemistry: A new palaeoenvironmental indicator applied to a regressive/transgressive record from the gulf of Carpentaria, Australia

We demonstrate the feasibility of determining a continuous record of chemical changes occurring during marine transgressive/regressive phases, using the Mg/Ca and Sr/Ca ratios measured in some 300 single valves of the euryhaline ostracod Cyprideis from two cores from the Gulf of Carpentaria, Australia. The molar Mg and Sr distribution coefficients K d [Mg] and K D[Sr] for modern Australian Cyprideis specimens (Chivas et al. 1986b), K D[ Mg] at 25°C=( Mg/Ca) shell /( Mg/Ca) water =0.00458±0.00072 K D[ Sr]=( Sr/Ca) water /( Sr/Ca) water =0.475±0.057 are used here to reconstruct the palaeoenvironmental record of the gulf. The two cores studied show similar patterns during the past 40,000 yr for equivalent hydrologic phases recognized in the cores. The Mg/Ca ratios of the water inferred from ostracod shell chemistry indicate that Carpentaria was a fresh or slightly saline lake between ≈ 40,000 and ≈ 13,000 yr B.P., before being transgressed by the sea during sea level rise. Around 26,000 yr B.P., a phase of substantial precipitation of authigenic calcite caused a dramatic increase in the Sr/Ca and Mg/Ca ratios of the lake water, and this was registered by the ostracod shell chemistry. From ≈ 26,000 to ≈ 13,000 yr B.P., the lake remained fresh or slightly saline despite the Ca depletion of the water which caused the Sr/Ca and Mg/Ca of the ostracods to be unusually high.