Integrated Facies Analysis
To understand the formation and diagenesis of carbonate rocks mineralogical and geochemical data derived from the study of non-carbonate constituents, trace elements, and stable isotopes must be integrated. Other indicators for depositional and diagenetic
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To understand the formation and diagenesis of carbonate rocks mineralogical and geochemical data derived from the study of non-carbonate constituents, trace elements, and stable isotopes must be integrated. Other indicators for depositional and diagenetic conditions are organic matter and organic carbon. The following shows how these data can be successfully combined with data based on microfacies analyses. The first section deals with acid-insoluble residues in carbonate rocks and with authigenic minerals (oxides, silicates, sulfides, sulfates and phosphorites) formed after the deposition of the sediment. The second section discusses the value of trace elements in tracing the depositional and diagenetic history of limestones, and the importance of stable isotopes studied in the context of microfacies analyses. The third section gives a brief overview of organic matter in carbonate rocks.
13.1 Non-Carbonate Constituents Non-carbonate constituents oflimestones and dolomites include clastic terrigenaus minerals as well as authigenic minerals. The study of clay minerals in acidinsoluble residues has a high potential for recognizing changes in erosion, climate changes and sea level and estimating the influx of siliciclastic material into shallow and deep-marine carbonate basins. Authigenic minerals grow after sediment deposition during diagenesis. They describe the course of diagenesis and are proxies for varying chemical and physical conditions.
13.1.1 Insoluble Residues (IR): Clay Minerals and Detrital Quartz The input of terrigenaus material into carbonate environments takes place by eolian transport, fluvial transpoft (e.g. during flash-floods from wadis), or by erosion ofunderlying rocks (e.g. in tidal zones). E. Flügel, Microfacies of Carbonate Rocks © Springer-Verlag Berlin Heidelberg 2004
Common clay minerals in mudstones and also in Iimestones are those of the smectite group, kaolinite, illite and mixed-layer illite/smectites and chlorite. Kaolinite and other clay minerals are often used as paleoclimatic proxies, but the post-depositional diagenetic alteration of clays related to the depth of burial and the pore-water geochemistry must be thoroughly considered (see review by Ruffell et al. 2002). As a consequence of different transpoft behavior clay minerals are deposited in the ocean at different distances from the coast. The relative abundance of kaolinite as a detrital mineral may reflect proximity to the sediment source and deposition in relatively nearshore settings, whereas smectite may be deposited in deeper more offshore settings. The relative proportians of illite/kaolinite to smectite in marine deposits have been used to infer shallowing/regressive and deepening/transgressive episodes. Techniques: The use of IR as paleoenvironmental indicators requires data on the amount of non-carbonate constituents and the mineralogical composition. The non-carbonate fraction of carbonate rocks is commonly extracted by acid digestion with a variety of acids and chelating agents (Müller 1967), or by the use of ac
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