Loss of calcareous microfossils from sediments through gypsum formation

doi:10.1016/0025-3227(80)90085-7

Marine Geology

Volume 36, Issues 3–4, July 1980, Pages M35-M44

https://doi.org/10.1016/0025-3227(80)90085-7 Get rights and content

Abstract

Laboratory experiments with fresh marine sediments demonstrate the dissolution of calcareous microfossils (foraminifers) and the production of “authigenic” gypsum. Slow oxidation of iron sulfide in the presence of oxygen drives the following reactions:

1.
(1) 4FeS + 9O₂ + 6H₂O = 4FeO(OH) + 4SO²⁻₄ + 8H⁺ or $2 FeS_{2} + 7 12 O_{2} + 5 H_{2} O = 2 FeO (OH) + 4 SO^{2−}_{4} + 8 H^{+}$
2.
(2) H⁺ + CaCO₃ = Ca²⁺ + HCO⁻₃
3.
(3) Ca²⁺ + SO²⁻₄ + 2H₂O = CaSO₄·2H₂O

Three-month experiments resulted in minor to total dissolution of different species from estuarine and open ocean sediments. Elphidium ustilatum was the most resistant to dissolution whereas Elphidium subarcticum was the first species to disappear completely. Agglutinated foraminifers are nearly completely destroyed largely because of bacterial decay of the test binding agent.

Loss or partial loss of species may occur either in conditions of storage after collection or because of changing environmental conditions (primarily oxygen levels) at the sediment—water interface.

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There are more references available in the full text version of this article.

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Solution pores were filled by albite and ferrodolomite/dolomite, indicating that dissolution occurred after the devitrification and argillization of tuff and before the appearance of albite (Fig. 10). Both bacterial sulfate reduction (BSR) (Berner and Raiswell, 1983) and thermochemical sulfate reduction (TSR) (Toland, 1960) can cause organic matter in sediments to react to form pyrite, and cause carbonate minerals to dissolve and form autogenous gypsum (Schnitker et al., 1980; Muza and Wise, 1983). Albite, as a diagnostic mineral in hot water deposition, is commonly seen in submarine hydrothermal diagenesis and is the product of submarine hydrotherm mixed with seawater (Mills and Elderfield, 1995).
Based on thin section identification, scanning electron microscope (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) analysis of samples from cuttings and cores in drillings, tuffaceous deposits were identified to intercalate in marine carbonate rocks and mudstones in the upper part of Maokou Formation and the middle to lower part of the Wujiaping Formation in Guangyuan area, northern Sichuan basin, China. These tuffaceous deposits are of significance to understand the influence range of magmatic activity of the Emeishan Large Igneous Provinces (ELIP), and explore and exploit oil and gas reservoirs in Permian strata in the Sichuan basin. The research results indicated that tuffs formed 0.1–10 mm-thick laminae, and they formed lamellar interbedding with organic mudstones and carbonaceous mudstones, which were sandwiched among bioclast limestones and marls. Tuffaceous deposits in the study area include tuff, sedimentary tuff and tuffaceous sedimentary rock. Under the influence of sulfate reduction, acidic hydrotherm and alkaline fluid, tuffaceous deposits were altered by diagenesis such as dolomitization, argillization, pyritization and dissolution, and formed a variety of secondary rocks and pores which characterized by the micron-scale solution pores in tuff components and the nanometer-scale intercrystal pores among authigenic clay minerals. In addition, the primary directional sedimentary structure of tuffs and sedimentary tuffs and developed laminae in the rocks are conducive to the formation of fissures parallel to laminae, and effectively improve the reservoir property of rocks. The tuffaceous deposits in the study area are mainly the products of subaqueous pyroclastic flow that were dominated by acidic magmatism and indicated that they may not be directly related to the ELIP, which is located in the southwest Sichuan-Yunnan provinces and dominated by continental eruption of basalt.
An effective method to distinguish between artificial and authigenic gypsum in marine sediments
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For fresh sediments with preformed ferric (hydr)oxides and no authigenic gypsum, the molar ratios of gypsum sulfur and ferric (hydr)oxide iron (i.e., atomic S/Fe ratios above) should be lower than 2 after artificial oxidation of pyrite. However, Schnitker et al. (1980) suggested that the aerobic oxidation of pyrite may also happen in deep-water marine environments. For example, dissolved oxygen can penetrate into the anoxic zone from overlying aerobic bottom seawater by infaunal activities, giving rise to the elevated sulfate concentrations in the subsurface sediments (e.g., Iversen and Jørgensen, 1985; Fossing et al., 2000; Claypool et al., 2006).
Gypsum often occurs in marine sediments as an authigenic mineral, but it may also be produced artificially through oxidation of sulfide during sample storage and preparation. Therefore, the origin of the gypsum should be carefully checked, especially for those DSDP, ODP and IODP samples that have stored for a long time. It is nearly impossible to distinguish between gypsum formed by these two processes based on the mineral morphology or the sulfur and oxygen isotope methods currently used. In this study, we proposed a simple, quantitative scheme based on chemical extractions of iron and sulfur to distinguish whether the gypsum in marine sediment samples is an authigenic mineral or an artificial product formed after sample collection. The new method was tested on two suites of deep-water sediment cores sampled from Hydrate Ridge and Kaoping Slope, in which the origins of gypsum were known beforehand, and was successfully validated. Finally, the potential influence of artificial productions of elemental sulfur and jarosite on the application of this new method was evaluated and the corresponding solutions were given.
Nonevaporative origin for gypsum in mud sediments from the East China Sea shelf
2018, Marine Chemistry
Citation Excerpt :
Nonetheless, authigenic gypsum crystals have already been reported in sediments in the absence of evaporative or volcanogenic materials. For example, gypsum occurs, in association with pyrite, in fine-grained sediments of the South West African continental slope (Siesser and Rogers, 1976) and is usually accompanied by carbonate dissolution (Briskin and Schreiber, 1978; Schnitker et al., 1980). On the basis of their isotopic compositions, gypsum crystals have been explained to be the result of pyrite oxidation, as observed in cold-water carbonate mounds in the Porcupine Seabight, off Ireland (Pirlet et al., 2010), and in the eastern Pacific oxygen minimum zone (Blanchet et al., 2012).
Gypsum (CaSO₄∙2H₂O) precipitated in nonevaporative marine environments is rarely reported, and the related diagenetic process and its implications for the sulfur cycle (e.g., sulfide reoxidation) are still not well known. We employ coupled sulfur and oxygen isotopes of authigenic gypsum, as well as sulfur isotopic compositions of pyrite, from core EC2005, which is drilled on the inner shelf of the East China Sea, to constrain the sulfur and oxygen sources for gypsum precipitation. The δ³⁴S_gypsum values range from −24.8 to −12.2‰, which are much more depleted in ³⁴S than modern seawater sulfate, suggesting additional ³⁴S-depleted sulfur sources, i.e., co-existing pyrites produced by microbial sulfate reduction. According to a mixing model for paired sulfur isotopes of gypsum and pyrite, >70% of gypsum sulfur is derived from pyrite reoxidation. The δ¹⁸O_gypsum values, ranging from 1.1 to 4.6‰, suggest that the oxygen isotopes of porewater sulfate should fall between −2.4 and 1.1‰, which are more depleted than seawater sulfate in ¹⁸O. Two mechanisms are proposed to explain the reoxidation of pyrite at different depths: in the lower section (10–4 m; Unit II), pyrite is oxidized by metal oxides under anaerobic conditions, producing ¹⁸O-depleted oxygen from seawater; while in the upper section (4–0 m; Unit I), pyrite reoxidation may occur under aerobic conditions, involving atmospheric oxygen. Either the aerobic or anaerobic mechanisms could cause drops in the porewater pH, leading to carbonate dissolution. These processes could therefore elevate the concentrations of sulfate and calcium ions in porewater, in which authigenic gypsum crystals are precipitated. In addition, both sulfur and oxygen isotopic signals of gypsum indicate a possible influence of methane on sulfate reduction in the mud sediments of core EC2005, which may be related to biogenic gas (dominated by CH₄) in this region. Our new findings thus indicate that sulfide reoxidation in marine sediments plays an important role in the biogeochemical sulfur cycle on the continental margin.
Comparison of living and dead benthic foraminifera on the Portuguese margin: Understanding the taphonomical processes
2018, Marine Micropaleontology
Dead benthic foraminifera (> 150 μm) were studied in 23 sediment cores from the Portuguese Margin at water depths between 20 and 2000 m and located on 4 transects off the Douro, Mondego, Tagus and Sado river mouths and 1 transect in the Estremadura. For 10 stations, the dead faunal vertical distribution (0–8 cm) was first investigated in 4 different sediment horizons per core to evaluate the sampling effort necessary to have a representation of the dead fauna deposited under different environmental areas. As a result, it appears that the faunal vertical distribution is constant, except for the deepest environments where fragile taxa were identified in the top layers only. Dead foraminiferal assemblages in the 4–5 cm layer for all stations were then compared to previously published living foraminiferal assemblages (of March 2011) from the same cores to evaluate the taphonomical processes affecting major species. This improves the knowledge of the faunal distribution for a better benthic foraminiferal proxy for paleostudies. There was a considerable loss of some species in the dead fauna. Firstly, this concerns the fragile organic-cemented agglutinated taxa such as Reophax spp., Glomospira charoides, or Bathysiphon spp. Secondly, some calcitic species such as Nonion scaphum, Cancris auriculus, Ammonia beccarii or Bulimina aculeata that were particularly abundant in the living fauna on the inner shelf under the late winter high river discharge conditions, were also far less dominant in the dead fauna. Lastly, other species like Cassidulina carinata, Valvulineria bradyana, and Bulimina marginata systematically showed higher abundance in the dead fauna at the mid shelf. These species, related to eutrophic conditions occurring in summer during the upwelling activity, were therefore not well represented in the living fauna, collected in March. Transport of allochthonous specimens may also account for higher contribution in the dead community of some species like Cibicides lobatulus, Asterigerinata mamilla or Haynesina depressula, especially in coastal environments where hydrodynamic processes (river flood, winter storm, coastal drift) are more vigorous. Several species (U. mediterranea, U. bifurcata, T. agglutinans, H. balthica or B. costata), however, show little or no difference in both abundance and spatial occurrence between the living and dead faunas and provide a stable signal for paleoclimatic investigations.
Formation mechanism of authigenic gypsum in marine methane hydrate settings: Evidence from the northern South China Sea
2016, Deep-Sea Research Part I: Oceanographic Research Papers
Citation Excerpt :
Elevated porewater Ca2+ concentrations also favor precipitation of authigenic gypsum crystals. Laboratory experiments with fresh marine sediments demonstrate that the dissolution of biogenic carbonates can play an important role in the formation of gypsum (Schnitker et al., 1980). For example, oxidation of sedimentary sulfide can strongly enhance the production of H+, leading to porewater acidification and dissolution of carbonate sediment (e.g., Z.Y. Lin et al., 2016; Pierre et al., 2012; 2014; Pirlet et al., 2010, 2012).
During the last decade, gypsum has been discovered widely in marine methane hydrate-bearing sediments. However, whether this gypsum is an in-situ authigenic precipitate remains controversial. The GMGS2 expedition carried out in 2013 by the Guangzhou Marine Geological Survey (GMGS) in the northern South China Sea provided an excellent opportunity for investigating the formation of authigenic minerals and, in particular, the relationship between gypsum and methane hydrate. In this contribution, we analyzed the morphology and sulfur isotope composition of gypsum and authigenic pyrite as well as the carbon and oxygen isotopic compositions of authigenic carbonate in a drillcore from Site GMGS2–08. These methane-derived carbonates have characteristic carbon and oxygen isotopic compositions (δ¹³C: −57.9‰ to −27.3‰ VPDB; δ¹⁸O: +1.0‰ to +3.8‰ VPDB) related to upward seepage of methane following dissociation of underlying methane hydrates since the Late Pleistocene. Our data suggest that gypsum in the sulfate-methane transition zone (SMTZ) of this core precipitated as in-situ authigenic mineral. Based on its sulfur isotopic composition, the gypsum sulfur is a mixture of sulfate derived from seawater and from partial oxidation of authigenic pyrite. Porewater Ca²⁺ ions for authigenic gypsum were likely generated from carbonate dissolution through acidification produced by oxidation of authigenic pyrite and ion exclusion during methane hydrate formation. This study thus links the formation mechanism of authigenic gypsum with the oxidation of authigenic pyrite and evolution of underlying methane hydrates. These findings suggest that authigenic gypsum may be a useful proxy for recognition of SMTZs and methane hydrate zones in modern and ancient marine methane hydrate geo-systems.
Multi-year life spans of high salt marsh agglutinated foraminifera from New Zealand
2014, Marine Micropaleontology
Citation Excerpt :
The calcareous tests dissolve because of the low pH of the porewater as a result of the sulphate reduction reactions that decay dead plant detritus near the surface and dying roots beneath the surface (e.g., Howarth and Teal, 1979). In some salt marsh core sequences that are now above tide levels and above ground water level for long periods of time, all the agglutinated foraminiferal tests have also disappeared (e.g., Big Lagoon, Hayward et al., 2010) through oxidation and bacterial degradation of organic cements (e.g., Schnitker et al., 1980; Goldstein and Watkins, 1999; Berkeley et al., 2007). Where exposure to oxygen has been less, the more fragile agglutinated tests (e.g., E. tetrastomella, Miliammina spp.) are preferentially lost by organic cement breakdown with consequent enhanced relative abundance of more robust tests (e.g., T. inflata, T. salsa).
The depth-related density profiles of live and dead foraminiferal tests were studied in eleven cores (four with replicate cores) from above mean high water spring level in four high salt marshes in the temperate South Island of New Zealand. The species most tolerant of high elevation and low salinity in New Zealand, Trochamminita salsa, was strongly dominant in most cores but two other species, Haplophragmoides wilberti and Trochammina inflata, occurred in sufficient numbers in several cores to allow analysis. We found that the highest salt marsh foraminifera live at variable depths, sometimes in low numbers down to 30 cm at least. T. salsa appears to occur at greater depths (maximum densities between 5 and 13 cm) than H. wilberti and T. inflata (maximum densities in upper 5 cm). No strong evidence was observed for significant seasonal blooms of these agglutinated species in these highest marsh cores that are only inundated by the tide for a matter of hours a few times per year.
Using the size of the total live stock in each core, the downcore density profile of dead tests and the relatively constant sediment accumulation rates we calculated estimates for the mean life spans of these high marsh foraminiferal species by two slightly different methods. Before accepting these life span estimates we compared the actual depth profiles of dead test density in each core with modelled downcore test density profiles based on ideal conditions of constant sedimentation rates, constant livestock numbers, constant live depth distributions and no taphonomic loss. Estimates from three of our cores are rejected because their dead test profiles suggest significant taphonomic loss in the intervals of interest. Estimates from the remaining eight cores indicate that the highest salt marsh foraminifera in temperate New Zealand have mean life spans of 1.3–13 years, with means of 5.5 years for T. salsa, 4.5 years for T. inflata and 3 years for H. wilberti – showing progressively shorter life spans at lower elevations in less stressful environments. These life span estimates are considerably longer than the majority reported for foraminifera from less harsh conditions but help explain how highest marsh foraminifera survive and grow in this extreme environment.

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Letter sectionLoss of calcareous microfossils from sediments through gypsum formation

Abstract

Deep-Sea Res.

Mar. Geol.

Deep-Sea Res.

Pelagic sediments

Sedimentary pyrite formation

Am. J. Sci.

Letter section
Loss of calcareous microfossils from sediments through gypsum formation