| Abstract | U ovom doktorskom radu analizirane su gornjomiocenske i pliocenske naslage istočne Dravske depresije. Cilj istraživanja je određivanje klinoformi i parasekvencija na temelju interpretacije površinskih seizmičkih mjerenja i podataka iz dubokih bušotina te određivanje starosti naslaga korištenjem metode datiranja autigenih nuklida 10Be/9Be. Pretpostavka je da se sintezom ovih rezultata može dobiti uvid u dinamiku i razvoj okoliša taloženja. Na seizmičkim podacima provedene su seizmostratigrafske analize, analize seizmičke geomorfologije te strukturna interpretacija. Na bušotinskim geološkim podacima provedene su sedimentološke analize, odredbe starosti geokronološkim i biostratigrafskim metodama, a na karotažnim podacima su interpretirane parasekvencije. Zajedničkom interpretacijom svih izvora podataka određene su četiri litostratigrafske jedinice: formacija Medvedski breg (duboko do otvoreno jezero), formacija Andraševec (dubokovodni turbiditi), formacija Nova Gradiška (delta i plitkovodni jezerski okoliši) i formacija Pluska (aluvijalni i fluvijalni). U analiziranim naslagama određeno je pet sekvencija III. reda, koje su sastavljene od osam sekvencija IV. reda. Radiometrijskim datiranjem naslaga utvrđeno je da su jezerski okoliši prevladavali od 11,089 ± 0,549 do 6,713 ± 0,272 mil. god., a kopneni okoliši i prije 4,987 ± 0,161 mil. god. Rezultati analiza pokazuju da je uslijed promjenjivih smjerova taloženja dinamika taloženja bila kompleksna, što je utjecalo na složenu raspodjelu litofacijesa i različite stratigrafske granice između jedinica. Posljedica toga je otežana korelacija manjih sedimentnih tijela i jedinica viših redova na većim udaljenostima ili korištenjem samo jednog izvora podataka. Na dugoročni razvoj taložnog sustava, odnosno razvijanje sekvencija III. reda, dominantno je utjecala klima, subsidencija i tektonika, odnosno strukturni sklop o kojem je ovisila morfologija depresije. Na razvoj sekvencija IV. reda utjecale su periodične izmjene vlažne i suhe klime te unutarnji mehanizmi taložnog sustava. Rezultati i metode istraživanja primjenjivi su u analizama geoenergetskih resursa, od još neotkrivenih akumulacija nafte i plina, geotermalnog potencijala, mogućnosti skladištenja ugljikovog dioksida do skladištenja energije ili vodika u dubokom podzemlju. |
| Abstract (english) | The focus of this research is on the Upper Miocene and Pliocene sedimentary infill in the eastern part of the Drava Basin. The mentioned area has been continuously subjected to oil and gas exploration for more than 70 years; however, the ages of the final sedimentary filling, disappearance of the lacustrine environments, and subsequent development of delta plain and terrestrial environments have not been precisely estimated. In light of the proposed theme, the research aims to determine the clinoforms and parasequences in analyzed deposits because such units can most adequately depict the most important palaeogeograpy and depositional environments. Furthermore, the absolute age of deposits can be resolved using the authigenic nuclides 10Be/9Be dating method, while biostratigraphic analyses determine the relative age and facies. Through the data synthesis and interpretation, an attempt will be made to reconstruct the development of paleoenvironments and paleogeography in as much detail as possible, as well as to distinguish the main external and internal factors that influenced the dynamics of the Late Miocene and Pliocene sedimentation in the study area. For this purpose, seismic reflection and borehole data were used. Specifically, the deposits were analyzed by seismostratigraphic approach; seismic geomorphology and structural analyses which were performed on the seismic data. Sedimentological analyses and absolute age determinations were performed using geochronological and biostratigraphic methods on the well-core data. The cycles and parasequences were interpreted on the well-log data, from which the schematic geological columns were made. Data integration enables the separation of environments, lithostratigraphic units, inside which sequences were interpreted. The depth, structure, and thickness maps were made for each sequence. The analyzed sequence is composed of four lithostratigraphic units: Medvedski breg fm. (shallow to the deep open lake), Andraševec fm. (deep-water and slope-toe turbidite system), Nova Gradiška fm. (deltaic to shallow water lacustrine) and Pluska fm. (alluvial and fluvial). Three phases of third-order sequences inside the Lake Pannon lacustrine deposits were distinguished. The development of the third-order sequences was generally controlled by the ratio of accommodation and sediment supply, or more precisely, the interplay between the subsidence, climate variations, and possibly tectonics. Each unit is composed of fourth-order vi sequences or parasequences sets that can also be interpreted as regressive and transgressive system tracts in classical sequence stratigraphic terms. The results show that the deposition dynamics were rather complex due to changing sedimentary system directions affecting the complex lithofacies distribution and the stratal stacking patterns. This is especially emphasized in the evolution of the third sequence of the overfilled lake, where sediment input direction was frequent due to lateral switching of deltaic lobes. The authigenic nuclides 10Be/9Be dating method results reveal that the lacustrine environments prevailed from at least 11,089 ± 0,549 Ma to 6,713 ± 0,272 Ma. The subsequent terrestrial environments were developed well before 4,987 ± 0,161 Ma. The long-term, third-order evolution of the depositional system was dominantly influenced by climate, subsidence, and tectonics, and especially the structural relations that influenced the morphology of the depression. Periodic changes in wet and dry climates and internal mechanisms (e.g., frequent avulsion) controlled the development of fourth-order sequences. As a result, it is challenging to correlate smaller-scale sedimentary bodies or units of higher orders at greater distances or using a single data source (e.g., well data). The results and research methods are applicable in analyzing various geo-energy resources, especially in understanding the role of the strike variability in reservoir correlation. |
