<p>Jurassic successions of the northern part of the Friuli (a.k.a. Dinaric or Adriatic) Carbonate Platform (hereinafter FAD) are best exposed along the Trnovski Gozd Plateau in SW Slovenia. A major stratigraphic unit, known as the Trnovo (Ternowaner) oolite has been considered as a classical, textbook example of a highly productive carbonate platform system exporting oolite sediments to the adjacent deep water depositional settings, producing massive bodies of resedimented oolite, such as the Vajont Limestone of the Belluno Basin. Whereas the stratigraphy of the basinal units in the eastern southern Alps and NW Dinarides is well constrained, coeval shallow marine depositional sequences of FAD Carbonate Platform lack a reliable chronostratigraphic framework.</p><p>We performed Sr isotope analysis of brachiopod shells and belemnite rostra from two stratigraphic levels at the base and above the Trnovo oolite unit (TOU). Suitability of the fossil material was controlled by selecting skeletal parts without fractures and lacking evidence of alteration due to diagenesis and weathering. The ultrastructure of specimens was inspected in resin-embedded polished thin sections under a petrographic microscope, supported by cathodoluminescence and SEM examination, including EDS semi-quantitative elemental analysis of skeletal parts in thin sections and slabs. For chemical analysis, powdered samples were drilled from thin section wafers and analysed for <sup>87</sup>Sr/<sup>86</sup>Sr (stratigraphy), d<sup>13</sup>C, d<sup>18</sup>O, Ca, Mg, Sr, Fe, Mn and Rb (diagenetic alteration control).</p><p>The elemental quantification was performed at Jo&#382;ef Stefan Institute on an Agilent 8800 Triple-Quad Mass Spectrometer and Sr isotopic analysis on a Nu plasma II Multi-Collector MS. Additional <sup>87</sup>Sr/<sup>86</sup>Sr measurements were performed at UCM Madrid on a IsotopX TIMS. The numerical values were calculated from published Sr curves.</p><p>Brachiopod species from a lumachelle directly overlying a condensed interval in the base of TOU have been considered indicative for the early Toarcian. However, <sup>87</sup>Sr/<sup>86</sup>Sr values obtained from rynchonellid brachipod shells ranged from 0.707109 to 0.707122, corresponding to numerical ages of either 184.7 &#177; 0.4 Ma (late Pliensbachian) or 181.8 &#177; 0.5 Ma (early Toarcian). Belemnites from the Limestone with chert, an informal unit overlying TOU, yielded <sup>87</sup>Sr/<sup>86</sup>Sr values from 0.706838 to 0.706862, that fit two intervals of the Sr isotope curve, i.e., 162.5 &#177; 1.9 Ma (latest Callovian-early Oxfordian) and 159.4 &#177; 1.7 Ma (middle to late Oxfordian), respectively. In both cases, the duality in results is caused by their proximity to the Sr curve minima.</p><p>These ages open several important questions about the geometry and depositional history of the northern FAD platform system. Despite of a limited accuracy of our results, the age range for TOU clearly spans (at least) late Toarcian and almost whole middle Jurassic, while the age of the supposedly time-equivalent basinal unit, the Vajont Limestone, falls into the late Bajocian-Bathonian interval. Furthermore, our sedimentological re-examination of the classical TOU localities has not shown characteristics of in-situ oolite production environments but, on contrary, evidence of deeper marine deposition marked by beds of carbonate mudstone, including most typical rosso-ammonitico-type facies, associated with (resedimented) oolite and crinoidal facies, similar to parts of the succession of the Vajont Limestone.</p>
<p>Biomonitoring of mercury (Hg) in the air using transplanted and <em>in-situ</em> lichens were studied at three locations in Slovenia: 1) the former Hg mine Idrija, with known Hg contamination; 2) vicinity of a Hg point source of pollution near the cement production plant in Anhovo, and 3) a noncontaminated reference site at Pokljuka. Total Hg concentrations and Hg isotopic composition were measured. Lichens were transplanted from Pokljuka, exposed at different sites in three locations and sampled four times, once per season. Lichens were exposed under tree branches, on fences and also under cover, allowing them different exposure to natural light. Additionally, the <em>in situ</em> lichens were sampled at the beginning and the end of the one year sampling period. As expected, the trend of concentrations in transplanted lichens increased over time, especially in the area of Idrija, and significantly less in the area of Anhovo, which is consistent with previous research. Significant mass dependent fractionation has been observed in transplanted lichens. <em>&#948;</em><sup>202</sup>Hg changed from winter to summer from -2.5 to -0.5 &#8240; and dropped again to -2.5 in autumn/winter of the following year. The most likely mechanism for this is Hg reduction (biotic or abiotic) and / or Hg evaporation in summer due to elevated temperatures, leaving heavier isotopes on the lichen thalli. The <em>in situ</em> lichens that were sampled one year apart show no major changes in isotopic composition. Such a trend has been observed in all of the samples apart from the ones from the most polluted Idrija sampling site directly above the former smelting plant. This is probably due to the new Hg constantly being deposited to the lichen with local isotopic fingerprint. Small mass independent fractionation was observed, likely due to photo-reduction as was concluded in similar foliage studies, but no trends in its change over time were seen.</p>
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply.
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.