Calcitization/dedolomitization of Jurassic dolostones (Lebanon): results from petrographic and sequential geochemical analyses

Abstract

Calcitized Jurassic dolostones from central Mount Lebanon (Kesrouane Formation) are discussed utilizing petrographic, mineralogical and geochemical data. In particular, two sequential extraction methods for both major/trace elements and stable isotope analyses provide results that support and refine conventional bulk analyses data. The new data demonstrate that the major dedolomitization phase of the investigated Jurassic carbonates occurred as a result of the migration of karst‐related meteoric waters (characterized by soil‐derived carbon, and estimated δ18OV‐SMOW composition between −7·2‰ and −3·4‰) into previously dolomitized horizons within the limestone rock, during the final uplift and emergence of Mount Lebanon, after Palaeogene time. The study demonstrates that, in this case, the mechanisms of dedolomitization and their resulting fabrics are controlled primarily by the texture of the original dolomite rock. Pervasively dolomitized rocks, where the micritic matrix is entirely dolomitized, show calcitization mainly through dissolution/precipitation. By contrast, the rock textures that still include a considerable amount of limey micritic matrix – spared from dolomitization – are more prone to mole per mole and mimic replacement of the dolomite crystals by calcite.

Influence of climate and dolomite composition on dedolomitization: insights from a multi-proxy study in the central Oman Mountains

“…13 C of about 26 to 28% VPDB as in Cantrell et al 2007;Nader et al 2008). Stable isotope results here show two clusters of data, one for the goethite-calcite fabric and one for the goethite-dolomite fabric.…”

“…Similarly to previous studies that suggested that dedolomitization is driven by surface meteoric fluids (e.g. Sanz-Rubio et al 2001;Cantrell et al 2007;Nader et al 2008), calcite resulting from pseudomorphic replacement of D2 (indicated as ''calcitized D2'' in Fig. 13) has a signature of both depleted d…”

“…Evidence for burial dedolomitization is present only in D1, whereas the alteration of D2 testifies to a second and major alteration and dedolomitization phase that is interpreted as a late post-uplift surface weathering process based on the depleted stable isotope signature (both d 18 O and d 13 C) of calcitized D2 typical of rain-water oxygen and soilrelated carbon (e.g., Sanz-Rubio et al 2001;Cantrell et al 2007;Nader et al 2008; see more extensive discussion in the next section). This phase of weathering and dedolomitization affected D2 extensively but spared some D1 in all lithologies (i.e., limestone, SBD as well as FRD).…”

Extended chronologies of aqueous alteration in the CM2 carbonaceous chondrites: Evidence from carbonates in Queen Alexandra Range 93005

“…The replacement of dolomite by calcite is termed 'dedolomitisation' if the reaction is true replacement, or calcitisation if calcite crystallises within pores formed by dissolution of dolomite (Lee and Harwood, 1989;Nader et al, 2008). The principal evidence for dedolomitisation is the presence of corroded relicts of dolomite within calcite-rich bimineralic grains (Fig.…”

Hydrothermal Dolomites in the Early Albian (Cretaceous) Platform Carbonates (NW Spain): Nature and Origin of Dolomites and Dolomitising Fluids

“…Dedolomitisation, as an example of diagenetic processes, is also favored by nonstoichiometric dolomites (Dorobek et al, 1993;Nader et al, 2008). For this purpose, initially X-ray diffractometry was used to determine the stoichiometry of the selected dolomite phases.…”