Paleontological and biostratigraphical characteristics of the Badenian deposits on the Srebrenik-Donja Orahovica profile (Bosnia and Herzegovina)

This paper describes the biostratigraphic and paleontological research conducted on the geological section of SrebrenikDonja Orahovica (Northern Bosnia and Herzegovina). The samples for micropaleontological research were taken from the exploration works (eight wells and nine excavations). Based on the presence of microforaminifera, the stratigraphic level of Lower Badenian was defined. According to micropaleontological and biostratigraphic analyses within this stratigraphic level, one local foraminiferal zone was identified: zone with Trilobatus trilobus and Orbulina suturalis which represents the upper parts of the Lower Badenian. This zone is characterized by a rich microfossil community with a dominance of planktonic forms over benthic ones, normal salinity, warm sea, and basic character of the environment.


Introduction
Marine Miocene sediments in Bosnia and Herzegovina are present only in the area of northern Bosnia, which in the Miocene represented the southern rim of the Central Paratethys (see Figure 1). In many parts, these sediments are covered with younger deposits so data on lithofacial and biofacial features are lacking. For these reasons, an insufficient number of paleogeographic analyses of Miocene sediments have been performed. A significant contribution to the knowledge of facial, biostratigraphic, tectonic and other features of marine Miocene sediments in Bosnia and Herzegovina has been made by numerous researchers: Katzer, 1903; Steva nović and Eremija 1960; Soklić, 1964Soklić, , 1982Soklić, , 1988Soklić, , 2001Soklić and Vrabac, 1995;Čičić, 1964, 2002Čičić and Jovanović, 1987;Kranjec, 1969;Eremia, 1970;Atanacković, 1977Atanacković, , 1981Stojčić et al., 1978;Petrović, 1979/80;Pantić et al., 1988;Petrović et al., 1990;Vrabac, 1986Vrabac, , 1987Vrabac, , 1989Vrabac, , 1991Vrabac, , 1999Vrabac, , 2005Vrabac, , 2007 According to the Basic Geological map of former Yugoslavia in scale 1:100 000, sheet Doboj (Laušević and Jovanović, 1983) Middle Miocene sediments have a large distribution and are represented by typical marine sediments. In the examined area, Middle Miocene sediments are characterized by significant lithological diversity, which is probably due to the fragmented paleorelief and coastal sedimentation regime . Badenian in northern Bosnia is characterized by significant paleogeographic changes (coastal disintegration and bottom relief, mostly normal salinity, favorable gas regime, water temperature identical to tropical to subtropical seas, shallow sea, etc.) (Pantić et al., 1988;. The fossil faunal association is characterized by numerous microfauna and pteropods. At the lowest level are mostly numerous planktonic foraminifera where globigerinoid and orbitolinoid taxa are the most abundant. They are typical for the Lower Badenian foraminiferal zone Trilobatus trilobus and Orbitolina suturalis. Benthic forms are represented by buliminas and uvigerinas. In addition to numerous pteropods, there are also mollusks: Pycnodonta cochlear, Chenopus pespelicani, Tellina ottnangensis, Conus sp., and others. The geological profile Srebrenik -Donja Orahovica (see Figure 2) represents an insufficiently known area, especially from a micropaleontological point of view. According to the current information, Badenian and Sar-  istics of this area were the main issues to be addressed, based on the data collected during the research. The research was performed using geological mapping, laboratory, and cabinet methods. Micropaleontological analyses were performed to assess the presence of foraminifera in certain stratigraphic levels and more accurately define the boundaries of different biostratigraphic units.
The terrain is quite covered with soil and vegetation with very rare rock outcrops along the examined section. The study of microforaminifera was performed on 12 samples (see Figures 511) that were taken from investigative boreholes and excavations (B-boreholes., R-excavations). The coordinates of sampling points are shown in Table 1.
The samples after the collection were packed in special bags and marked. After that, they were wet-sieved at the Faculty of Mining, Geology, and Civil Engineering in Tuzla, using laboratory sieves with a diameter of 0.8, 0.5, 0.25, and 0.15mm (see Figure 12). The sieve fraction of 0.15 mm was dried and analyzed using a Leica EZ4D stereomicroscope. For each sample with the association of microforaminifera, a photograph was taken using a digital camera built into the microscope.

Methods for the micropaleontological examination
Micropaleontology has become especially important in petroleum engineering. During this study, rock particles up to 1 cm in size were caught in a sieve. The same amount of sample was taken from each piece (the weight of the piece is 6 grams). Samples were washed with tap water, dried, labeled, and stored in bags. For micropaleontological research, the method of wet -sieving was applied, whereby the clay rocks were immersed in water with the addition of baking soda or a 15% hydrogen peroxide solution. Glauber's salt was applied to compact marls. After rinsing with a jet of water (see Figure 13) on sieves with openings of 0.8, 0.5, 0.25, and 0.15mm, the microfossil material remains, which is then dried and examined under a binocular Leica EZ4D microscope. Foraminifera were determined according to Cicha et al. (1998).

Results
Microscopic determination of foraminifera was performed using a Leica EZ4D microscope with the appro-priate software package (see Figure 14). Separate samples were carefully analyzed in detail and all fossils were extracted from them. Based on the association of fossils in individual samples, the stratigraphic level was defined. All fossil names were checked by relevant bases (World Register of Marine Species) and revised. Table 2 shows sampling points and samples and Table  3 shows the determination of fossils in individual samples. Some species of foraminifera are shown in the

Discussion
In Bosnia and Herzegovina, marine Miocene deposits are present in northern Bosnia and are covered with younger deposits, an aggravating circumstance for performing paleogeographic reconstructions. In addition, data on the lithofacial and biofacial characteristics of the Miocene sediments are not available in the parts where these sediments are covered leaving many questions unresolved. Geological characteristics have been studied in detail on numerous outcrops of the Miocene sediments, while a very small number of published papers present paleogeographic reconstructions or sedimentological analyses. A detailed analysis of the sedimentation conditions of the Badenian and Sarmatian facies of northern Bosnia was performed by Vrabac, S. (1989). Geological        (Cushman & Jarvis, 1936) 2008) and reef limestones indicate that the seawater was warm during the lower Badenian in the investigated area. The presence of a large number of echinoid remains, known as stenohaline organisms, indicates that the sea in this area in the Lower Badenian had normal salinity. Numerous planktonic foraminifera indicates the wide connection of this sedimentary basin with the open sea. Based on the number of planktonic forms with carbonate shells and the richness of oxygen, it can be concluded that the character of the environment was basic, not acidic.

Conclusions
Based on the performed geological, micropaleontological, and biostratigraphic analyses, it is proven that the Lower Badenian sediments are present along the whole research area. The Lower Badenian sediments are lithologically represented by grey and layered marls, limestones, and platy siltstones of a yellowish-brown to grey colour. Based on index microfossils, one local foraminiferal zone has been determined: zone with Trilobatus trilobus and Orbulina suturalis, representing the upper part of the Lower Badenian. Trilobatus trilobus (REUSS), Orbulina suturalis Brönimann and Globigerina bulloides d`Orbigny appear as dominant and leading fossils. Some other planktonic taxa e.g. Globigerinella regularis (d'Orbigny), Globigerina diplostoma Reuss, Dentoglobigerina altispira (Cushman & Jarvis), also occur in the samples. Benthic forms are scarce and are mainly represented by the genera Bulimina, Nonion, and Cibicidoides. Analysis and synthesis of data obtained from this study will be the foundation for preparing detailed geological maps, paleogeographic reconstructions, structural-tectonic analyses, and other specialistic studies.