Ocena kratkotrajnega raztapljanja in izločanja karbonata z uporabo vrstičnega elektronskega mikroskopa: metodološki postopki in preliminarni rezultati iz Postojnske jame

Carbonate dissolution and precipitation are important geological processes whose rates often require quantification. In natural settings, these processes may be taking place at a slow rate, and thus, it may not be easily visible which of these processes is occurring. Alternatively, if the effects of precipitation/dissolution are visible, it may not be clear if they are still underway or an artefact of past conditions. Moreover, these two opposing processes may flip states depending on the environmental conditions, such as, on a seasonal basis. Here, we present the technical details and preliminary results of a method using carbonate tablets and Scanning Electron Microscopy (SEM) to evaluate which process (carbonate dissolution or precipitation) is occurring, using as an example, a cave environment. Our method involves making tablets by encasing blocks of carbonate rock into resin and polishing these to form a completely flat and smooth “zero surface”. These tablets are observed under SEM in exactly the same points both before and after exposure to the field environment, using a system of marking lines at specific locations on the resin. Our results show significant differences in the before and after images of the tablet surface after just six weeks in the cave. Furthermore, the use of the insoluble resin zero surface permits a comparison of the starting height with the new dissolved/precipitated surface that can be used to quantitatively estimate the rate of dissolution/precipitation happening at a field location in a relatively short time-frame (weeks/months). This method could be used in numerous natural and industrial settings to identify these processes that can be caused purely geochemically, but also through microbialmediation and physical weathering.Raztapljanje in izločanje karbonatnih mineralov spadata med geološke procese, katerih hitrost pogosto želimo kvantitativno ovrednotiti. V naravnih okoljih so ti procesi počasni, zato običajno ni enostavno oceniti, kateri proces trenutno poteka na določeni točki, niti tega, ali so vidni učinki raztapljanja ali izločanja posledica aktivnih pogojev in procesov ali dogajanj v preteklosti. Poleg tega se nasprotujoča si procesa lahko hitro izmenjujeta zaradi sprememb v jamskem okolju, na primer sezonsko. V članku prikazujemo metodologijo in preliminarne rezultate preiskave apnenčevih ploščic (tablet), izpostavljenih pogojem raztapljanja in/ali izločanja v jamskem okolju, pod vrstičnim elektronskim mikroskopom (SEM). Metodologija obsega izdelavo testnih ploščic iz apnenca, ki smo jih zalili v epoksidno smolo, izravnali in spolirali do ravne in gladke referenčne površine. Preden smo jih izpostavili naravnim pogojem, smo ploščice označili z referenčnimi lokacijskimi točkami na meji med smolnim obodom in kamnino ter referenčna področja fotografirali pod SEM v grobovakuumskih pogojih. Nadaljne analize z SEM so pokazale znatne razlike na površini ploščic že po šestih tednih izpostavljenosti jamskim pogojem: s primerjavo z nivojem netopne epoksidne smole smo lahko neposredno ugotovili, ali je na apnenčevi ploščici prišlo do raztapljanja ali do izločanja. Referenčna mejna področja na ploščicah smo nato pod SEM analizirali v tedenskih in mesečnih intervalih z uporabo stereoskopske topografske rekonstrukcije, s katero smo kvantitativno ocenili hitrost raztapljanja oziroma izločanja karbonata. Metoda je potencialno uporabna za proučevanje geokemijskih, mikrobno induciranih in mehanskih prosesov na mikroskopski ravni v naravnih in laboratorijskih (industrijskih) pogojih

Dolomite in speleothems of Snežna Jama cave

In Snežna Jama cave, Slovenia, extensive speleothems composed of dolomite, aragonite and hydromagnesite have been found, occurring as 5 cm thick globular crusts coating the host rock. Arborescent aragonite constitutes the skeleton of the crust, whereas dolomite is cementing, coating and replacing the aragonite. The dolomite displays two distinctive fabrics: coarse rounded to spheroidal crystals, frequently showing fibrous-radial and concentric patterns, and microcrystalline aggregates. Dissolution of the dolostone host rock has provided Mg, which is the main control on the precipitation of aragonite, dolomite and hydromagnesite. Dolomite precipitation could be promoted by increased Mg/Ca ratios due to the prior precipitation of calcite and aragonite and by forced degassing due to ventilation caused by the existence of shafts cutting the main cave passage and a former entrance to the cave. However, in many caves such conditions do not lead to the formation of dolomite and so we discuss other mechanisms which might promote dolomite precipitation, like the possible contribution of microbes, or the transformation of precursor phases such as amorphous Ca-Mg carbonates, or hydromagnesite

First dinosaur from the Shan–Thai Block of SE Asia: a Jurassic sauropod from the southern peninsula of Thailand

International audienceA vertebra collected from the Jurassic non-marine Khlong Min Formation of southern Thailand is referred to the family Euhelopodidae, a group of sauropod dinosaurs that apparently was endemic to eastern Asia during the Jurassic and Early Cretaceous, at a time when that part of the world was isolated from other land masses. The occurrence of a euhelopodid in the Jurassic of the Shan–Thai Block supports the idea of a collision of the Shan–Thai Block with the Indochina Block, thus establishing connections with ‘mainland Asia', early in the Mesozoic, probably before the Jurassic

The Paleocene-Eocene thermal maximum (PETM) in shallow-marine successions of the Adriatic carbonate platform (SW Slovenia)

The Paleocene-Eocene thermal maximum represents one of the most rapid and extreme warming events in the Cenozoic. Shallow-water stratigraphic sections from the Adriatic carbonate platform offer a rare opportunity to learn about the nature of Paleocene-Eocene thermal maximum and the effects on shallow-water ecosystems. We use carbon and oxygen isotope stratigraphy, in conjunction with detailed larger benthic foraminiferal biostratigraphy, to establish a high-resolution paleoclimatic record for the Paleocene-Eocene thermal maximum. A prominent negative excursion in 13C curves of bulk-rock (~1‰-3‰), matrix (~4‰), and foraminifera (~6‰) is interpreted as the carbon isotope excursion during the Paleocene-Eocene thermal maximum. The strongly 13C-depleted 13C record of our shallow-marine carbonates compared to open-marine records could result from organic matter oxidation, suggesting intensified weathering, runoff, and organic matter flux. The Ilerdian larger benthic foraminiferal turnover is documented in detail based on high-resolution correlation with the carbon isotopic excursion. The turnover is described as a two-step process, with the first step (early Ilerdian) marked by a rapid diversifi-cation of small alveolinids and nummulitids with weak adult dimorphism, possibly as adaptations to fluctuating Paleocene-Eocene thermal maximum nutrient levels, and a second step (middle Ilerdian) characterized by a further specific diversification, increase of shell size, and well-developed adult dimorphism. Within an evolutionary scheme controlled by long-term biological processes, we argue that high seawater temperatures could have stimulated the early Ilerdian rapid specific diversification. Together, these data help elucidate the effects of global warming and associated feedbacks in shallow-water ecosystems, and by inference, could serve as an assessment analog for future changes. © 2012 Geological Society of America

Vodnik po ekskurziji

This brochure was published for the 50th anniversary of the Institute of Paleontology and contains three contributions. The first and the second contribution describe two paleontological sites (of Upper Cretaceous dinosaurs and Upper Jurassic corals, respectively), that were visited during a field-trip organized on this occasion. The third contribution is a brief history of the institute.Brošura, izdana ob polstoletnici Paleontološkega inštituta, vsebuje tri kratke sestavke. Prvi z naslovom »Prvi dinozavri v Sloveniji« prinaša kratko poročilo o nahajališču kosti zgornjekrednih dinozavrov na gradbišču avtoceste pri Kozini. Drugi sestavek govori o zgornjejurskem koralno-spongijskem grebenskem kompleksu v Sloveniji, konkretno o nahajališču grebenskih apnencev pri Selovcu v Trnovskem gozdu. Tretji in zadnji sestavek pa podaja kratko zgodovino inštituta

The Buzet Thrust Fault in Istria and overturned carbonate megabeds in

Detailed geological mapping undertaken in the framework of monitoring of the motorway construction works in SW Slovenia has revealed the existence of a large-scale thrust fault between Buzet and Koper (termed the Buzet Thrust Fault) and extensive thrust-related fold structure which is clearly expressed by overturned carbonate megabeds in the thrust footwall in the eastern part of the Dragonja River basin. The Buzet Thrust Fault represents the southeastern margin of the structurally complex Kras Thrust Edge

Discontinuity Surfaces in Upper Cretaceous to Paleogene Carbonates of Central Dalmatia (Croatia): Glossifungites Ichnofacies, Biogenic Calcretes, and Stratigraphic Implications

Substrate-controlled ichnofacies and biogenic calcretes represent key features for identification and interpretation of discontinuities in the carbonate rock record, which are of great significance for stratigraphic interpretations and correlations. Intraformational firmground and composite surfaces, as well as a regional Cretaceous to Paleogene (K-Pg) subaerial unconformity, developed in Upper Cretaceous to Paleogene intra-platform peritidal successions in central Dalmatia, Croatia (Adriatic-Dinaridic Carbonate Platform, ADCP), were analyzed for their trace fossil and subaerial exposure features. Thalassinoides (probably T. paradoxicus) box-work burrow systems of the substrate-controlled Glossifungites ichnofacies characterize the two documented firmgrounds and one composite (polygenic) surface. Rhizogenic laminar calcretes developed subsequently inside burrows of the composite surface through diagenetic overprint of marine sediment that passively infilled the burrows. While the formation of the two firmgrounds was probably caused by cessation of precipitation and/or deposition of calcium carbonate due to relative sea-level fall, the recorded trace fossils associated with the composite surface indicate that this surface developed through both submarine firmground and subaerial exposure stages probably caused by several episodes of regression and transgression, and exemplifies the general complexity of hiatal surfaces in shallow-marine carbonate successions. The regional K-Pg subaerial unconformity is characterized by biogenic (beta microfabric) calcretes with rhizoliths including Microcodium aggregates, root tubules, as well as alveolar-septal structures. Laminar calcretes and pisoids, together with in situ and resedimented speleothems, and bauxitic deposits, were also recorded. The unconformity developed due to formation of a forebulge in front of the approaching Dinaridic orogen. Ichnological and subaerial exposure features, together with stratigraphic implications derived from the analyzed discontinuities, serve as examples that can be applied to discontinuities present in carbonate successions elsewhere

A Jurassic amber deposit in Southern Thailand

International audiencePublished reports of amber predating the Aptian are rare and mention only amber pieces the size of millimetric marbles. Mid Cretaceous amber records, however, show a dramatic increase in number as well as in the size of the pieces, a phenomenon which is still poorly understood. The discovery of the first Jurassic deposit with comparatively large centimetric sized pieces of amber, in southern Thailand, is significant. Taphonomy and palaeobotany indicate a dense forest surrounding a coastal lake dominated by the resin-producing Agathoxylon tree. Since the palaeoecology of other amber-producing Jurassic and Cretaceous deposits is very similar a new hypothesis needs to be sought to explain the mid Cretaceous amber boom. It is suggested here that it was the result of a geological or taphonomic bias because coastal lacustrine environments are much better preserved after the Aptian on a worldwide scale