Abstract
AbstractEarly marine diagenetic dolomite is a rather thermodynamically‐stable carbonate phase and has potential to act as an archive of marine porewater properties. However, the variety of early to late diagenetic dolomite phases that can coexist within a single sample can result in extensive complexity. Here, the archive potential of early marine dolomites exposed to extreme post‐depositional processes is tested using various types of analyses, including: petrography, fluid inclusion data, stable δ13C and δ18O isotopes, 87Sr/86Sr ratios, and U‐Pb age dating of various dolomite phases. In this example, a Triassic carbonate platform was dissected and overprinted (diagenetic temperatures of 50 to 430°C) in a strike‐slip zone in Southern Spain. Eight episodes of dolomitization, a dolostone cataclasite and late stage meteoric/vadose cementation were recognized. The following processes were found to be diagenetically relevant: (i) protolith deposition and fabric‐preservation, and marine dolomitization of precursor aragonite and calcite during the Middle–Late Triassic; (ii) intermediate burial and formation of zebra saddle dolomite and precipitation of various dolomite cements in a Proto‐Atlantic opening stress regime (T ca 250°C) during the Early–Middle Jurassic; (iii) dolomite cement precipitation during early Alpine tectonism, rapid burial to ca 15 km, and high‐grade anchizone overprint during Alpine tectonic evolution in the Early Eocene to Early Miocene; (iv) brecciation of dolostones to cataclasite during the onset of the Carboneras Fault Zone activity during the Middle Miocene; and (v) late‐stage regression and subsequent meteoric overprint. Data shown here document that, under favourable conditions, early diagenetic marine dolomites and their archive data may resist petrographic and geochemical resetting over time intervals of 108 or more years. Evidence for this preservation includes preserved Late Triassic seawater δ13CDIC values and primary fluid inclusion data. Data also indicate that oversimplified statements based on bulk data from other petrographically‐complex dolomite archives must be considered with caution.
Highlights
Stoichiometric dolomites are the most thermodynamically-stable carbonate phase, surpassing even low-Mg calcites, which have been referred to as the most reliable archives of their depositional environment (Nordeng & Sibley, 1994)
The aims of this paper are three-fold; (i) to identify the complex diagenetic pathways of allochthonous Triassic dolostones in the Neogene Carboneras Fault Zone in Southern Spain by mineralogy, petrology and geochemistry; (ii) to place these findings into context of hydrothermal fluid properties reconstructed from fluid inclusion data and geochemical fingerprints; and (iii) to test the resistance of a suite of early diagenetic dolostones to mechanical and hydrothermal alteration culminating in cataclastic fault gouge formation
Zebra dolomite is common in the Alpujarride dolostones, and known from other localities in the Betic Cordilleras (e.g. Sanz de Galdeano & Lopez Garrido, 2014)
Summary
Stoichiometric dolomites (dolostones) are the most thermodynamically-stable carbonate phase, surpassing even low-Mg calcites, which have been referred to as the most reliable archives of their depositional environment (Nordeng & Sibley, 1994). Previous studies have exploited these carbonates as archives of their palaeo-porewater properties (Geske et al, 2012), often with reference to replacement dolostones or primary dolomite precipitates in modern sabkha and peritidal–supratidal settings (Land, 1980; Patterson & Kinsman, 1982) or in various ancient carbonate deposits (Mazumdar & Strauss, 2006; Johnston et al, 2010; Kasemann et al, 2014). These authors argued that fabric-preserving, early diagenetic marine dolomites may largely escape subsequent alteration. Other research questions included the redox state of past oceans (Kamber & Webb, 2001; Hood et al, 2018), element fluxes between oceans and continents (Tipper et al, 2006), and the geochemical cycles of C, Ca and Mg through time (Arvidson et al, 2006; Farkas et al, 2007; Arvidson et al, 2011)
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
