INVESTIGATION METHODS IN KARST DINARIDES

We have started with the initial investigations of the presumed Permian/Triassic boundary (PTB) areas in the central and Southern part of the Velebit Mt., and have made the detailed geological columns of the investigated parts. Samples are collected for palaeontological and sedimentological analyses, and for isotope and geochemical analyses. After the initial sampling and preliminary analyses, which have given us the first clues on the problem of the Permian/Triassic Boundary, additional samples were taken at the most important parts of the columns.

Preparation techniques
Preparation of the sedimentological samples. Structural and textural features of carbonate and clastic rocks were observed already in the field. Additional analyses were made on the basis of thin-sections. Cathodoluminescence method was applied to carbonate samples.
Preparation of  the palaeontological samples. The thin sections are made out of hard rocks to see the facies and palaeontological communities. For the conodont analyses, the bigger amount of samples (2-5 kg) were crushed and milled, and then dissolved in the formic acid. After washing and sieving, we have picked up the fossils under the stereomicroscope in search for the conodonts and other interesting microfossils and minerals, of which some were observed in detail by Scanning electrone microscope (SEM).
Preparation for  the chemical analyses. Samples were prepared for Major, Minor, Trace and Rare Earth elements (REE) analyses: cca. 3 g of the powdered sample is heated in an oven at 1050°C for 1,5h. After that, 1.2 g of cooled sample is mixed with 6 g of tetraborate, and such homogenous mixture is melted into pastilles at 1300 °C. 12 g of the sample powdered in agate mill is mixed with 30 drops of "glue", after which the gained homogenous matter gets compressed to tablets and dried for 1 day in the oven. The results for the REE are gained by the LA-ICPMS (Laser Ablation - Inductively Coupled Plasma Mass Spectrometer).
Preparation for the stable isotope and organic geochemical analyses. For the bitumen extraction, samples were cut with the diamond saw and cleaned with deionized water (in the ultrasonic bath), distilled ethanol and dichloromethane, and dried for 24 hours at 50°. After that, samples were crashed, and milled in agate mill. Powdered samples were then weighed and set into pear-shaped beakers mixed with dichloromethane (DCM). Process of "boiling" takes place 6-7 days, with exchange of DCM after 2 days. After filtration of the samples, we put them to evaporate for some time. To clean the samples from the elemental sulphur we then do the desulphurization with the activated cooper. After that samples are left to evaporize near dryness at the room temperature, and the extracted bitumen is then stored for further analyses.  To separate saturated, aromatic and polar hydrocarbons, the silica-alumina liquid chromatography is done. Kerogen extraction: For extraction of insoluble organic matter, powdered sample is treated with HCl (to eliminate the carbonate component) and with HF (for silicate component). After the neutralization of the acid, samples are filtered and the residue is dried in the oven. Elemental analyses of C and N, as well as ?13Cker and ?14Nker, are performed with Elemental Analyser (EA) connected to Isotope Ratio Mass Spectrometer (IRMS).