DOI: 10.1016/j.earscirev.2021.103502
论文题名: Carbonate-hosted clay minerals: A critical re-evaluation of extraction methods and their possible bias on palaeoenvironmental information
作者: Coimbra R. ; Rocha F. ; Immenhauser A. ; Olóriz F. ; Terroso D. ; Horikx M.
刊名: Earth Science Reviews
ISSN: 00128252
出版年: 2021
卷: 214 语种: 英语
中文关键词: Carbonate rocks
; Clay minerals
; Decarbonatation
; Palaeoenvironmental interpretation
英文关键词: carbonate rock
; clay mineral
; depositional environment
; dolostone
; host rock
; paleoenvironment
; qualitative analysis
; quantitative analysis
英文摘要: The qualitative and quantitative investigation of non-carbonate minerals—such as clay minerals—in ancient limestones and dolostones is a widely applied tool in palaeoenvironmental analysis. In order to exploit clay minerals as palaeoenvironmental proxies, these must be extracted from their host carbonate prior to analysis. Over the last decades, efforts to optimize experimental procedures for the extraction of carbonate-hosted clay minerals resulted in a wide range of laboratory protocols (e.g., hydrochloric acid, acetic acid, formic acid or cation-exchange resins). Specifically, the risk that the extraction procedures damage the clay fraction merits attention. Standard decarbonatation procedures established for clay-lean, pelagic carbonates may provide redundant or unsatisfactory results when applied to terrigenous shallow-water carbonates. Here, we focus on mineralogically complex shallow-water carbonate materials and review, test and discuss different decarbonatation procedures in a process-oriented context. By exploring the significance of clay minerals for palaeoenvironmental and diagenetic interpretations, the relevance of the clay fraction as a key proxy is highlighted. Selected case studies are presented and by this, we intend to test and discus the most commonly reported decarbonatation procedures using representative cases of natural mixed carbonate-siliciclastic facies including a variable degree of dolomitization. These experiments show a differential behaviour when applied to pure and mixed natural materials. For mixed carbonate-clastic facies, the relative increase in quartz and dolomite intensity peaks (where present) obscured further identification of non-carbonate minerals. This pattern is observed despite the effective dissolution of calcite at higher acetic acid concentration (2N). Dolomitized limestone samples were addressed, but remained largely unresponsive to all tested pre-treatment procedures. Due to complexities inherent to the presence of dolomite in polymineralic natural samples, further work is necessary to clarify their resilience to decarbonatation procedures, as well as to the impact of dolomitization as such with regard to the clay fraction. For calcite dominated lithologies (here oolitic limestone), the use of acetic acid at higher concentration (2N) resulted in the most efficient decarbonatation. With reference to >95% carbonate-bearing limestones and dolostones, the application of elevated fluid temperatures (50°C) improved the reaction rates and the efficiency of the dissolution steps. With regard to mixed carbonate-clastic facies, elevated fluid temperatures of up to 50°C imposed considerable damage to the clay fraction, showing significantly reduced intensity peaks when compared to room temperature conditions at similar acid concentration. Moreover, it was demonstrated that: (i) bulk and insoluble residues show no major differences regarding their mineralogical composition; and that (ii) acetic acid at 2N is the best approach to ensure the preservation of the clay fraction. Conversely, the application of hydrochloric acid tests, a commonly used chemical in many published protocols, resulted in the least satisfactorily results. The potential bias induced by various clay-extraction methods is put to the test in the form of a representative case study, reflecting a series of distinct paleoenvironmental scenarios. © 2021 Elsevier B.V. Citation statistics:
资源类型: 期刊论文
标识符: http://119.78.100.158/handle/2HF3EXSE/166362
Appears in Collections: 气候变化与战略
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作者单位: GeoBioTec, Department of Geosciences, University of Aveiro, Portugal; Institute for Geology, Mineralogy and Geophysics, Ruhr-Universität Bochum, Germany; Departamento de Estratigrafia y Palaeontologia, Universidad de Granada - RNM 178, Spain; Institute of Geology, Leibniz University Hannover, Germany
Recommended Citation:
Coimbra R.,Rocha F.,Immenhauser A.,et al. Carbonate-hosted clay minerals: A critical re-evaluation of extraction methods and their possible bias on palaeoenvironmental information[J]. Earth Science Reviews,2021-01-01,214