Lithostratigraphic units in the Drava Depression (Croatian and Hungarian parts) – a correlation T. Malviæ and M. Cvetkoviæ ORIGINAL SCIENTIFIC PAPER The lithostratigraphic division and correlation is one of the most common stratigraphic divisions. It is strictly connected with lithological content of the rocks or deposits. Sometimes lithostratigraphic units, especially in rank of formations and members, can be approximately correlated with particular chronostratigraphic units in range of stages or sub-stages, i.e. lithosratigraphic units have synchronous borders. In other cases, the borders are asynchronous. Croatian and Hungarian lithostratigraphic units in the Drava Depression are analysed here as well as the possibility of their correlation. Such correlation scheme can be useful in comparison of different units, especially because the Croatian part is based on approximately synchronous, and Hungarian on asynchronous borders between units. Moreover, the Drava Depression in this region is an important hydrocarbon production province where lithostratigraphic correlation is widely used, even across state borders. The presented lithostratigraphic scheme, it's lithological descriptions and correlation could help in any geological research or evaluation in the entire analysed depression. Key words: lithostratigraphy, Drava Depression, Croatia, Hungary 1. Introduction The analysed chronostratigraphic and lithostrati- The entire Drava Depression covers the surface area of graphic units of the Drava Depression are based on nu- about 12 000 square km, where approximately 9 100 be- merous well and seismic data. There are several regional long to the Croatia (Figure 1). Generally, the Neogene and papers where ranks and lithostratigraphic units are de- Quaternary rocks and deposits defined the subsurface fined. In Croatian part the most famous source is ref.43 volume known as the Drava Depression. The total thick- internal study and later dissertation34 where he pro- ness can reach more than 7 000 m in the central part of posed the formal lithostratigraphic nomenclature in the that depression.38 In Ng-Q complex a sporadic occur- Drava Depression. The most available and reliable rences of volcanic rocks of Middle Miocene stage as well source of the Croatian lithostratigraphic nomenclature as fluvial and lacustric sediments of Lower Miocene can in the Croatian part of the Pannonian Basin System be found. However, the most part consists of Middle Mio- cene, Upper Miocene and Plio- cene clastic and biogenic sediments and Pleistocene and Holocene sediments and de- posits. The basement of the Drava Depression is represented with rocks of significantly dif- ferent lithology assemblage and chronostratigraphic as- semblage. Those are mostly carbonates (limestone and do- lomite), metamorphites (am- phibolite, schist and gneiss) and magmatites (granite, gab- bro) from Mesozoic and Palaeozoic eras. However, that basement is not part of Cro- atian lithostratigraphy nomen- Fig. 1. Area that approximately covers the Drava Depression clature of the Drava Depres- Sl. 1. Priblino podruèje prostiranja Dravske depresije sion. NAFTA 64 (1) 27-33 (2013) 27 T.MALVIÆ AND M. CVETKOVIÆ LITHOSTRATIGRAPHIC UNITS IN THE DRAVA... (CPBS) is given in ref.38. In Hungarian part, several Those are mostly granite, gabbro as well as cataclised sources were used here (refs.11,12,33) with lithostrati- and hydrothermal altered metamorphites, mostly of graphical columns and correlation through several geo- amphibolitic and greenschist facies (Figure 2). The age is logical provinces in the Hungarian part of the Pannonian often only approximated, due to numerous orogeneses Basin System (HPBS). This analysis is based on time in- that masked or destroyed characteristic mineral tervals that encompassed particular serie, stages and paragenesis. Some metamorphic periods had been dated sub-stages during Neogene and Quaternary, and that are from4 using samples from the Moslavaèka gora Mt., who 5,18 given in refs. described granite as younger than metamorphic rocks, Moreover, in the Croatian part of the western Drava De- i.e. on 90±5, 64 and 62 Ma. Furthermore, in ref.25 are de- pression the lithostratigraphic division had been made scribed several magmatic and metamorphic complexes according with lithostratigraphy of the Sava Depression, and ofiolitic rocks in the CPBS as Mesozoic. Other au- which are both corresponding. Those two areas together thor7 dated gabbro and serpentinite on NW sides of the represented the most southern (south-western) part of Majevica and Trebovac Mts as Upper Cretaceous. When the PBS and shared similar depositional processes and Mesozoic carbonate sediments are present between the environments. magmatic and metamorphic rocks and Neogene-Quater- nary infill they are called “podloga tercijara” what means 2. Lithological description of “Tertiary basement” – a name that is a relic of an older pre-Neogene basement rocks stratigraphical division. Those in the CPBS are mainly Magmatic and metamorphic rocks in Croatian part are limestones and dolomites (Figure 2), often cataclised and named as “temeljno gorje” what means “the basement”. weathered into breccias and conglomerates. Their Mid- Fig. 2. A schematic representation of the correlation of units between Croatian and Hungarian parts of the Drava Depression, modified after refs.11,12,34,38 (thicknesses are not in scale). Sl. 2. Shematski prikaz litološkog sastava i korelacije jedinica izmeðu hrvatskog i maðarskog dijela Dravske depresije, modificiran prema11,12,34,38 (debljine nisu u mjerilu). 28 NAFTA 64 (1) 27-33 (2013) LITHOSTRATIGRAPHIC UNITS IN THE DRAVA... T.MALVIÆ AND M. CVETKOVIÆ dle Triassic (i.e., Ladinic) age is often proven from algae Sarmatian and Lower Pannonian. Those periods are also genus Dasicladacea, i.e. Diplopora annulata characterised with pelitic, dominantly calcitic rocks like SCHAFHÄUTL and Teutloporella sp. and correlation (marlitic) limestones and marl, mostly deposited over with Mesozoic outcrops on present-day mountain like lithoral areas. Consequently, it is very hard to distinguish Papuk (refs.9,10). borders between stages of Badenian, Sarmatian and Pannonian, so the only EL-marker Rs5 is recognised 3. Lithostratigraphic units of onto resistivity curves as border between Lower and Up- approximately Middle Miocene to per Pannonian. Sporadically EL-marker Rs7 can be dis- Lower Pannonian serie/substage tinguished but not in the whole part of this segment. Locally Lower Pannonian can include several sequences Sediments of Middle Miocene (and very locally Lower of marlitic sandstones or, rarely, sandstones, what indi- Miocene) represent the period of overall marine trans- cate on changes in dominant depositional mechanism. gression in the entire PBS. They are deposited over The Mosti Member is mostly represented with sand- Palaeozoic or Mesozoic unconformities. Lower Miocene stone, breccia and breccia-conglomerate, and locally extension locally started in Ottnangian and Karpatian tuffite or tuffitic sandstones. In Sarmatian entire area is (ref.30) with development of smaller fluvial and lacustric covered with calcitic marl. The Krievci Member (also environments, where some sporomorphs taxons are named as Croatica-deposits after characteristic fossil characteristic just for Central Paratethys (e.g.20,29). How- shell Radix croatica) is lithologically marl and clayey ever, overall marine transgression and forming of the limestone in different ratios. The Koprivnica Sandstones Central Paratethys (e.g.17,18,31,32,39) started in Badenian are a lateral equivalent of the Krievci Member but only when present-day mountains in Northern Croatia, like with the dominant lithology being sandstones. Sporadi- Medvednica and Psunj Mts., were isolated islands. Nu- cally effusive rocks of Badenian to Lower Pannonian age merous smaller rhomboidal (pull-apart) basins were reg- are present and as named as the Æeralije Member. ularly created onto sea bottom, and the largest was the 15,16 Bjelovar Subdepression (e.g. ). The sediment thick- In Croatian part of the Drava Depression, eastern part, 19 nesses reached several hundred meters . The weather- Miocene sediments up to Lower Pannonian can be di- ing and cataclising were especially strong into shallow vided into two formations. These are THE VUKOVAR and sea and inland, where the main siliciclastic and carbon- THE VALPOVO FORMATIONS (Figure 2). As in western ate (Coralinacea and Briozoa reefs) detritus sources part the border with pre-Neogene basement is defined by were located. The dominant depositional mechanisms EL-border “Tg” or “Pt” and Rs5 separates the Valpovo were alluvial fans. The Late Badenian sea-level rise, re- Formation from younger, Upper Pannonian one. Border 31 sulted from re-opening of the Indo-pacific seaway , between Vukovar and Valpovo formation is defined by caused flooding of uplifted blocks on many places in the EL-border Rs7. THE VUKOVAR FORMATION is repre- Drava Depression. The boundary in the base of Upper sented by coarse grained sediments (breccias and con- Badenian deposits may be compared with the acknowl- glomerates) at its base with sandstones and limestone in edged Middle Badenian unconformity, and is considered its upper part which approximately belongs to 8,26 as a syn-rift/post-rift boundary .The disintegration of Sarmatian. THE VALPOVO FORMATION is similar to the the Central Paratethys started in the Uppermost Krievci Member and is mostly comprised of clayey Badenian, when this large palaeo-sea lost connections limestone.