Carbonate concretions in Miocene mudrocks in NW Algeria: types, geochemistry, and origins

Nemra, Abdelkrim; Mehadji, Abdelkader Ouali; Munnecke, Axel; Belkhedim, Salim; Belkebir, Lahcen

doi:10.1007/s10347-019-0559-2

Cited by 6 publications

(2 citation statements)

References 53 publications

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“…While many such analyses have been published, with a wide range of early diagenetic concretion data compiled by Mozley & Burns (1993), these early compilations were based on low‐resolution bulk‐sampled carbon and oxygen isotope analysis (δ 13 C and δ 18 O) rather than examining high‐resolution, centre‐to‐edge, profiles. Several more recent studies have presented higher resolution analysis within concretions (Lash & Blood, 2004; Woo & Khim, 2006; Lash, 2018; Liu et al ., 2019; Nemra et al ., 2019). The vast majority of carbonate concretions record negative δ 13 C values and in some cases δ 13 C values as low as −40‰ (Mozley & Burns, 1993).…”

Section: Introductionmentioning

confidence: 99%

Internal isotopic variability of Neogene carbonate concretions: Constraining formational growth mechanisms and isotopic disequilibrium

et al. 2023

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Carbonate concretions collected from the Dominican Republic present a valuable opportunity to evaluate the internal isotopic variations within concretions that have never been exposed to deep burial or structural deformation. Here, three concretions from the Neogene (Late Miocene-Early Pliocene) Cibao Basin are investigated, utilizing a multi-isotope (δ 13 C, δ 18 O, δ 34 S CAS and Δ 47 values) high-resolution approach, to constrain the microenvironmental conditions associated with multiple stages of concretion growth. Isotopic variability and potential disequilibrium effects, which can influence geological interpretations utilizing concretions, are also considered. The petrographic characteristics and geochemical profiles indicate internal differences relating to concretion growth mechanisms and environmental changes, driven by sea-level fluctuations. The δ 34 S values of carbonate-associated sulphate indicate a closed system environment; however, the overall values are influenced by sulphide oxidation within the sediments, resulting in a complex signal. The Δ 47 -derived temperatures of the concretions range between 29 to 55°C, indicating significantly warmer temperatures than are measured from the host sediments, which average 24°C. This indicates that carbonate concretion Δ 47 values are in disequilibrium with their environments of formation, likely related to ion diffusion in the pore fluids or isotopic fractionation associated with microbial processes. Here geochemical variations within concretions are utilized to assess the environmental conditions and microbial interactions after sediment deposition. However, for future studies, caution should be taken when using concretions for making environmental assessments as the signals can be influenced by a multitude of processes, even prior to diagenetic alteration.

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Section: Introductionmentioning

confidence: 99%

Internal isotopic variability of Neogene carbonate concretions: Constraining formational growth mechanisms and isotopic disequilibrium

et al. 2023

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“…Mineral concretions in sedimentary rocks, including ferromanganese (Fe-Mn), Co-rich, siderite and phosphorite ones, contain potential important (non)-metallic resources [1][2][3][4][5][6] and record many important diagenetic and paleoenvironmental information [5][6][7][8]. Although increasing studies tend to divide concretions into three main types, that is, syngenetic, diagenetic and epigenetic [9][10][11], all of them record the composition and conditions of the surrounding sediment layers [5,6]. Pyrite concretions record the sedimentary formation processes [7,8], the subsequent metasomatic growth and/or alteration [12,13], microbial sulphate reducing pyrite formation versus later-formed (metasomatic or hydrothermal related) pyrite formation [12,13] and thus determine the mineral and geochemical characteristics of pyrite concretions are highly important [8].…”

Section: Introductionmentioning

confidence: 99%

Genesis of Pyrite Concretions: Constraints from Mineral and Geochemical Features of Longtan Formation in Anhui Province, Eastern China

Sun

et al. 2019

Minerals

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The occurrence of pyrite concretions in the Permian Longtan Formation sheds light on the paragenesis, formation conditions and regional paleoenvironment. We analyzed the mineral and geochemical characteristics of pyrite concretions using scanning electron microscopy-energy dispersive spectrometer (SEM-EDS), X-ray diffraction (XRD) and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) from the Longtan Formation shales in Anhui, Eastern China. These pyrite concretions consist of two types, each with a distinct nucleus and outer layer: The former is mainly made up of quartz, bivalve fragments and minor gypsum, ankerite, siderite and pyrite, the latter consists of pyrite (FeS 2 ) in the voids of quartz. Based on the correlation matrix and geochemical/mineralogical affinity, trace elements in the pyrite concretions fall into three groups, that is, I (Sr, Ba, Rb and K) in calcic minerals from bivalve-bearing nucleus, II (Nb, Ta, Zr and Hf) in certain heavy minerals and III (V, Cr, Co and Ni) in pyrites. Mineral assemblage and paragenetic analysis show that the formation of pyrite concretions can be divided into three stages: (1) deposition of bivalve-bearing nucleus, (2) lithification of diatoms and (3) diagenesis of pyrite. Mineral and geochemical indicators suggest that the formation environment of pyrite concretions has undergone a major shift from lagoon with intense evaporation, to strong reducing marsh. and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) analyses [16][17][18], we identified the composition of nucleus and rims of pyrite concretions and proposed that pyrite concretions were formed in multiple stages of diagenesis and metasomatism. This paper offers new insight into the sedimentary conditions of the Longtan Formation.

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Middle Miocene trace fossils from the Tenes area (NW Algeria) and their palaeoenvironmental implications

Nemra,

Tellal,

Knaust

et al. 2023

Palaeobio Palaeoenv

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Carbonate concretions in Miocene mudrocks in NW Algeria: types, geochemistry, and origins

Cited by 6 publications

References 53 publications

Internal isotopic variability of Neogene carbonate concretions: Constraining formational growth mechanisms and isotopic disequilibrium

Internal isotopic variability of Neogene carbonate concretions: Constraining formational growth mechanisms and isotopic disequilibrium

Genesis of Pyrite Concretions: Constraints from Mineral and Geochemical Features of Longtan Formation in Anhui Province, Eastern China

Middle Miocene trace fossils from the Tenes area (NW Algeria) and their palaeoenvironmental implications

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