Paleogeographic evolution of the Southern Pannonian Basin: 40Ar/39Ar age constraints on the Miocene continental series of notthern Croatia

The Pannonian Basin, originating during the Early Miocene, is a large extensional basin incorporated between Alpine, Carpathian and Dinaride fold-thrust belts. Back-arc extensional tectonics triggered deposition of up to 500-m-thick continental fluvio-lacustrine deposits distributed in numerous sub-basins of the Southern Pannonian Basin. Extensive andesitic and dacitic volcanism accompanied the syn-rift deposition and caused a number of pyroclastic intercalations. Here, we analyze two volcanic ash layers located at the base and top of the continental series. The lowermost ash from Mt. Kalnik yielded an 40Ar/39Ar age of 18.07 ± 0.07 Ma. This indicates that the marine-continental transition in the Slovenia-Zagorje Basin, coinciding with the onset of rifting tectonics in the Southern Pannonian Basin, occurs roughly at the Eggenburgian/ Ottnangian boundary of the regional Paratethys time scale. This age proves the synchronicity of initial rifting in the Southern Pannonian Basin with the beginning of sedimentation in the Dinaride Lake System. Beside geodynamic evolution, the two regions also share a biotic evolutionary history: both belong to the same ecoregion, which we designate here as the Illyrian Bioprovince. The youngest volcanic ash level is sampled at the Glina and Karlovac sub-depressions, and both sites yield the same 40Ar/39Ar age of 15.91 ± 0.06 and 16.03 ± 0.06 Ma, respectively. This indicates that lacustrine sedimentation in the Southern Pannonian Basin continued at least until the earliest Badenian. The present results provide not only important bench marks on duration of initial synrift in the Pannonian Basin System, but also deliver substantial backbone data for paleogeographic reconstructions in Central and Southeastern Europe around the Early–Middle Miocene transition

A chronostratigraphy for the Dinaride Lake System deposits of the Livno-Tomislavgrad Basin: the rise and fall of a long-lived lacustrine environment

The Dinarides are an integral part of the Alpine orogenic belt and stretch over large parts of Slovenia, Croatia, Bosnia-Herzegovina, Monte Negro and Serbia. A great number of intra-montane basins formed in the interior of this Late Eocene to EarlyOligocene orogen during the Miocene. These basins harbored a suite of long-lived lakes, collectively called the Dinaride Lake System (DLS). Lake Livno, with its 600km2 of preserved surface, was the second largest of these Dinaride Lakes. At present, its deposits are divided between the Livno and Tomislavgrad basins, which were part of a single basin when Lake Livno first formed. High resolution age constraints for the over 2km basin infill have been lacking up to now, partly due to the endemic nature of its lacustrine fauna. This severely hampered geodynamic as well as paleoenvironmental reconstructions. Here, we present a chronostratigraphy based on radioisotopic and magnetostratigraphic data. 40Ar/39Ar measurements reveal that the Tušnica volcanic ash, found in between the Gomphoteriumbearing coal seams at the base of the basin infill, is 17.00±0.17 Ma old. 40Ar/39Ar dating of the Mandek ash, correlative to the uppermost sedimentary unit, provides an age of 14.68±0.16 Ma. Correlation of the composite magnetostratigraphy for the main lacustrine depositional phase to the Astronomically Tuned Neogene Time Scale is straightforward and reveals that the majority of the deposits of Lake Livno accumulated between 17 Ma and approximately 13 Ma. The disappearance of Lake Livno is most likely attributable to a change in tectonic regime. Calcarenites and breccias, derived from the basin margins, first entered the lake around 14.8 Ma and subsequently coarsened and thickened upwards. The basinmargins were apparently gradually uplifted before subsidence stalled. Comparison with chronostratigraphic data for other constituents of the DLS leads to the conclusion that their lifetimes largely coincide. Finally, we calibrate the most important marker fossils of the various Dinaride basins to the geological time scale and we present a new biochronological scheme for the DLS

Methane and hydrogen in hyperalkaline groundwaters of the serpentinized Dinaride ophiolite belt, Bosnia and Herzegovina

Methane (CH4) in continental serpentinized peridotites (MSP) has been documented in numerous hyperalkaline (pH > 9) springs and gas seeps worldwide. With a dominantly abiotic origin, MSP is often associated with considerable amounts of hydrogen (H2), produced by serpentinization. Both gases may fuel microbial activity in igneous rocks and may have played roles in the origin of life. MSP is also a natural CH4 source for the atmosphere, not included in the global greenhouse-gas budget, yet. Here we document a new and major case of MSP, in the Dinaride ophiolite belt in Bosnia and Herzegovina. CH4 is dissolved (83-2706 mM) in low temperature (13-30 °C), hyperalkaline (pH 10 to 12.8) waters in six sites, sampled through springs and boreholes. Four sites (Slanac, Vlajici, Kulasi and Ljesljani) show CH4 isotopic signatures typical of abiotic MSP (d13C: -18.5 to -35.7‰; d2H: -221 to -335.4‰); two sites (Vaiceva and Kiseljak) show a dominantly biotic signature (d13C: -58.8 and -65.1‰; d2H: -310.8 and -226.8‰), probably due to mixing with gas from coal-beds adjacent to the ultramafic rocks. H2 concentration is highly variable (up to 348 mM), ethane, propane and butane reach 0.13 vol.% in total, and helium isotopic composition (R/Ra: 0.12 to 0.48) reflects a dominant crustal signature. The Ljesljani site features the highest pH (12.8) and CH4 emission (~9 ton y-1) in peridotite-hosted hyperalkaline groundwater documented so far. Geological and geochemical data converge towards the hypothesis that, as proposed in similar cases, CH4 was mainly generated by Sabatier reaction between H2 (from serpentinization) and CO2 (from C-bearing rocks, in tectonic contact with the ophiolite, or other CO2 sources). CH4-H2-H2O disequilibria and Sabatier reaction constraints suggest that CH4 is not formed in the hyperalkaline water, but in water-free or unsaturated rocks hosting opportune metal catalysts (e.g., chromitites). The amount of methane released to the atmosphere from individual springs is comparable to that of conventional biotic gas seeps/springs in sedimentary basins.Published286-2966A. Geochimica per l'ambienteJCR Journa

Magneto-biostratigraphy and paleoenvironments of the Miocene freshwater sediments of the Sarajevo-Zenica Basin

The Sarajevo-Zenica Basin of Bosnia-Herzegovina was part of the Dinaride Lake System, a large network of Miocene long-lived freshwater basins in southeastern Europe. The basin contains a thick sedimentary succession of carbonates, coals and mixed siliciclastic deposits that reflects the paleoclimatic and tectonic evolution of the region. In this study, we present novel integrated (magneto-bio)stratigraphic and sedimentological data and reconstruct the paleoenvironmental evolution of the Sarajevo-Zenica Basin during its two main evolutionary phases (thrusting and extension). The basal “Oligo-Miocene” freshwater paleoenvironments are characterized by alternating palustrine, shallow lacustrine and distal fluvial phases. The base level fluctuations are largely controlled by syn-sedimentary pulses of tectonic loading during the final phase of thrusting in the Internal Dinarides. The majority of this succession is considered early Miocene in age, which contrasts with previous Oligocene age estimates. The subsequent extensional phase initiated not later than ~18.4 Ma. This coarsening upward sequence of lacustrine carbonates, silts, sands and conglomerates is correlated between 17.2 and 15 Ma (C5Cr-C5Br) by means of integrated bio-magnetostratigraphy. During this upper extensional phase, subsidence and sediment influx was generally controlled by activity along the basin bounding normal fault, overruling smaller scale climatic influences. We conclude that the existence of the long-lived Sarajevo lake is coeval with other Dinaric and southern Pannonian lakes, and overlaps in time with the Miocene Climatic Optimum. Sedimentation in the Sarajevo-Zenica basin terminated at ~15–14 Ma which concurs with both the end of the climatic optimum as well as the cessation of extension in the Dinarides. These results will help to better quantify the paleoclimatic changes in the Dinaride Lake System as well as the regional tectono-sedimentary events, such as potential migrations of deformation across the Dinarides

The link between tectonics and sedimentation in asymmetric extensional basins : Inferences from the study of the Sarajevo-Zenica Basin

Abstract The coupled tectonic and depositional history of extensional basins is usually described in terms of stratigraphic sequences linked with the activity of normal faults. This depositional-kinematic interplay is less understood in basins bounded by major extensional detachments or normal fault systems associated with significant exhumation of footwalls. Of particular interest is the link between tectonics and sedimentation during the migration of normal faulting in time and space across the basin. One area where such coupled depositional-kinematic history can be optimally studied is the Late Oligocene - Miocene Sarajevo-Zenica Basin, located in the Dinarides Mountains of Bosnia and Herzegovina. This intra-montane basin recorded Oligocene – Pliocene sedimentation in an endemic and isolated lake environment. We use field kinematic and sedimentological mapping in outcrops correlated with existing local and regional studies to derive a high-resolution evolutionary model of the basin. The novel results demonstrate a close correlation between moments of normal faulting and high-order sedimentological cycles, while the overall extensional basin was filled by a largely uni-directional sediment supply from the neighbouring mountain chain. The migration in time and space of listric NE-dipping normal faults was associated with a gradual shift of the sedimentological environment. Transgressive-regressive cycles reflect sequential displacements on normal faults and their footwall exhumation, defining a new sedimentological model for such basins. This Early - Middle Miocene extension affected the central part of the Dinarides and was associated with the larger opening of the neighbouring Pannonian Basin. The extension was preceded and followed by two phases of contraction. The Oligocene - Early Miocene thrusting took place during the final stages of the Dinarides collision, while the post-Middle Miocene contraction is correlated with the regional indentation of the Adriatic continental unit. This latter phase inverted the extensional basin by reactivating the inherited basal listric detachment

The link between tectonics and sedimentation in asymmetric extensional basins : Inferences from the study of the Sarajevo-Zenica Basin

Abstract The coupled tectonic and depositional history of extensional basins is usually described in terms of stratigraphic sequences linked with the activity of normal faults. This depositional-kinematic interplay is less understood in basins bounded by major extensional detachments or normal fault systems associated with significant exhumation of footwalls. Of particular interest is the link between tectonics and sedimentation during the migration of normal faulting in time and space across the basin. One area where such coupled depositional-kinematic history can be optimally studied is the Late Oligocene - Miocene Sarajevo-Zenica Basin, located in the Dinarides Mountains of Bosnia and Herzegovina. This intra-montane basin recorded Oligocene – Pliocene sedimentation in an endemic and isolated lake environment. We use field kinematic and sedimentological mapping in outcrops correlated with existing local and regional studies to derive a high-resolution evolutionary model of the basin. The novel results demonstrate a close correlation between moments of normal faulting and high-order sedimentological cycles, while the overall extensional basin was filled by a largely uni-directional sediment supply from the neighbouring mountain chain. The migration in time and space of listric NE-dipping normal faults was associated with a gradual shift of the sedimentological environment. Transgressive-regressive cycles reflect sequential displacements on normal faults and their footwall exhumation, defining a new sedimentological model for such basins. This Early - Middle Miocene extension affected the central part of the Dinarides and was associated with the larger opening of the neighbouring Pannonian Basin. The extension was preceded and followed by two phases of contraction. The Oligocene - Early Miocene thrusting took place during the final stages of the Dinarides collision, while the post-Middle Miocene contraction is correlated with the regional indentation of the Adriatic continental unit. This latter phase inverted the extensional basin by reactivating the inherited basal listric detachment

Magneto-biostratigraphy and paleoenvironments of the Miocene freshwater sediments of the Sarajevo-Zenica Basin

The Sarajevo-Zenica Basin of Bosnia-Herzegovina was part of the Dinaride Lake System, a large network of Miocene long-lived freshwater basins in southeastern Europe. The basin contains a thick sedimentary succession of carbonates, coals and mixed siliciclastic deposits that reflects the paleoclimatic and tectonic evolution of the region. In this study, we present novel integrated (magneto-bio)stratigraphic and sedimentological data and reconstruct the paleoenvironmental evolution of the Sarajevo-Zenica Basin during its two main evolutionary phases (thrusting and extension). The basal “Oligo-Miocene” freshwater paleoenvironments are characterized by alternating palustrine, shallow lacustrine and distal fluvial phases. The base level fluctuations are largely controlled by syn-sedimentary pulses of tectonic loading during the final phase of thrusting in the Internal Dinarides. The majority of this succession is considered early Miocene in age, which contrasts with previous Oligocene age estimates. The subsequent extensional phase initiated not later than ~18.4 Ma. This coarsening upward sequence of lacustrine carbonates, silts, sands and conglomerates is correlated between 17.2 and 15 Ma (C5Cr-C5Br) by means of integrated bio-magnetostratigraphy. During this upper extensional phase, subsidence and sediment influx was generally controlled by activity along the basin bounding normal fault, overruling smaller scale climatic influences. We conclude that the existence of the long-lived Sarajevo lake is coeval with other Dinaric and southern Pannonian lakes, and overlaps in time with the Miocene Climatic Optimum. Sedimentation in the Sarajevo-Zenica basin terminated at ~15–14 Ma which concurs with both the end of the climatic optimum as well as the cessation of extension in the Dinarides. These results will help to better quantify the paleoclimatic changes in the Dinaride Lake System as well as the regional tectono-sedimentary events, such as potential migrations of deformation across the Dinarides