Upper Triassic to Lower Cretaceous stratigraphic successions deposited on the passive continental margin of Adria microplate facing the Neotethys Ocean were investigated on Ivanščica Mt. (NW ...Croatia). This area represents a transitional area between the Alps and the Dinarides. After a short Middle Triassic pelagic episode related to the rifting of the Neotethys, progradation of the carbonate platform over newly formed grabens resulted in formation of stable shallow-water depositional environment during the Late Triassic. Tectonically induced subsidence pulse at the Triassic/Jurassic boundary affected SE part of the investigated area resulting in the deposition of pelagic limestones, shale, marls, and calcarenites above Upper Triassic platform carbonates. At the same time, NW part of the investigated area was still characterized by shallow-water sedimentation until the Pliensbachian. This second subsidence phase was manifested by formation of neptunian dykes within Lower Jurassic platform limestones and deposition of the Middle Jurassic pelagic limestones. These two Early Jurassic subsidence events are likely related to the rifting of the Alpine Tethys. Radiolarian cherts were deposited in both areas in the late Middle and Late Jurassic. Radiolarians from the SW Ivanščica Mt. indicate late Bathonian to Early Tithonian age of the radiolarian cherts. Uppermost Jurassic to Lower Cretaceous Aptychus limestone is found across the entire investigated area. These limestones were deposited from the Late Tithonian to the Valanginian when synorogenic mixed carbonate–siliciclastic turbidites started to fill the basin indicating a prominent compressional tectonic phase widely recorded in the Alps and the Dinarides.
We show crucial evidence for the Cretaceous–Palaeogene (K–Pg) boundary event recorded within a rare succession deposited in an inner‐platform lagoon on top of a Mesozoic, tropical, intra‐oceanic ...(western Tethys) Adriatic carbonate platform, which is exposed at Likva cove on the island of Brač (Croatia). The last terminal Maastrichtian fossils appear within a distinct 10–12 cm thick event bed that is characterised by soft‐sediment bioturbation and rare shocked‐quartz grains, and is interpreted as a distal tsunamite. Directly overlying this is a 2 cm thick reddish‐brown clayey mudstone containing planktonic foraminifera typical of the basal Danian, and with elevated platinum‐group elements in chondritic proportions indicating a clear link to the Chicxulub asteroid impact. These results strongly support the first discovery of a “potential” K–Pg boundary tsunamite on the neighbouring island of Hvar, and these two complementary sections represent probably the most complete record of the event among known distal shallow‐marine successions.
Active tectonics in long-lived orogenic belts usually manifests on the preexisting inherited structures. In the Kvarner region of the External Dinarides, an area with low-to-moderate seismicity ...related to the Adriatic microplate (Adria) northward movement, we deal with faults in predominantly carbonate rocks within tectonically complex NW-SE striking fold-and-thrust belt, which makes the identification and parametrization of the active structures challenging. Moreover, anthropogenic modifications greatly complicate access to the surface geological and geomorphological data. This paper demonstrates results of focused multidisciplinary research, from surface geological mapping and offshore shallow seismic surveys to earthquake focal mechanisms, as an active fault identification and parametrization kit, with a final goal to produce an across-methodological integrated model of the identified features in the future. Reverse, normal, and strike-slip orogen-parallel (longitudinal) to transverse faults were identified during geological mapping, but there is no clear evidence of their mutual relations and possible recent activity. The focal mechanisms calculated from the instrumental record include weak-to-moderate earthquakes and show solutions for all faulting types in the upper crust, compatible with the NE-SW oriented principal stress direction, with the stronger events favoring reverse and strike-slip faulting. The 3D spatial and temporal distribution of recent earthquake hypocenters indicate their clustering along predominantly subvertical transversal and steeply NE-dipping longitudinal planes. High-resolution shallow seismic geoacoustical survey (subbottom profiler) of the Quaternary sediments in the Rijeka Bay revealed local tectonic deformations of the stratified Late Pleistocene deposits that, along with overlaying mass-transport deposits, could imply prehistorical strong earthquake effects. Neotectonic faults onshore are tentatively recognized as highly fractured zones characterized by enhanced weathering, but there is no evidence for its recent activity. Thus, it seems that the active faults are blind and situated below the thin-skinned and highly deformed early-orogenic tectonic cover of the Adria. A strain accumulating deeper in the crust is probably irregularly redistributed near the surface along the preexisting fault network formed during the earlier phases of the Dinaric orogenesis. The results indicate a need for further multidisciplinary research that will contribute to a better seismic hazard assessment in the densely populated region that is also covered by strategic infrastructure.
Maastrichtian to Palaeocene pelagic carbonates on the central Adriatic island of Svetac (Sveti Andrija) are the only outcrops reported to date that document pelagic deposition during the ...Cretaceous-Palaeogene (K-Pg) transition within the Adriatic Basin. An approximately 3 m thick succession at the Smokvica locality contains a rich and diverse planktonic foraminiferal assemblage which allows dating of the succession and the recognition of some biostratigraphic zones. The lower part of the Smokvica section consists of 1.5 m thick pelagic biomicrite characterized by the abundance of late Maastrichtian planktonic foraminifera that indicate the Abathomphalus mayaroensis Zone. An intercalation of intraclastic floatstone <0.5 m in thickness occurring on top of Maastrichtian pelagic biomicrite is characterized by unsorted pelagic intraclasts floating within the pelagic matrix, and both components only contain Maastrichtian planktonic foraminifera. The floatstone is overlain by another <0.5 m thick intraclastic-bioclastic floatstone characterized by rounded pelagic intraclasts (plasticlasts) containing Maastrichtian planktonic foraminifera floating in the pelagic matrix. The matrix of the later floatstone contains Maastrichtian and Palaeocene planktonic foraminifera mixed together. Thus, the transition from the Maastrichtian to the Palaeocene is not continuous but is characterized by amalgamated debrites that are related to at least two separated re-depositional events within the basin. The overlying pure pelagic biomicrite is rich in planktonic foraminifera that indicates the Palaeocene P3 Zone. A few metres apart, after the covered interval, there are also Eocene pelagic biomicrites with planktonic foraminifera which indicate the Eocene E9 Zone, characterized by the co-appearance of benthic foraminifera (Discocyclina) floating within the pelagic matrix. It is assumed that a Maastrichtian opening of the deep-water environment connected to the Adriatic Basin within the former Adriatic Carbonate Platform west of the island of Vis could be related to a re-activation of an inherited transverse fault zone.
The area of the Vinodol Valley and Bakar Bay represents a NW-SE oriented valley in the NW Adriatic characterised by prominent historical and instrumentally recorded seismicity. As part of the greater ...geodynamic domain including the Ilirska Bistrica-Rijeka-Senj seismogenic fault zone, new geological and structural data addressing the tectonic evolution of the area were collected in order to better understand the focal mechanisms of previous earthquakes and to enable identification of potential seismogenic sources. Mapped informal lithostratigraphic units mostly correspond to the Upper Cretaceous, Palaeogene and Quaternary successions described in other parts of the External Dinarides. However, a shorter stratigraphic range of the Gornji Humac fm., the youngest Cretaceous unit in the study area, was determined and suggests that the uplifted area in the central NW part of the Adriatic Carbonate Platform already comprised several thousand km2 (from W and NW Istria to Krk and Vinodol area) at the end of the Turonian. Structural measurements of the fault planes in the study area generally correspond to the existing structural model of the tectonic evolution of the Dinarides. However, in contrast to the SW vergences typical of the Dinarides, NE-vergent reverse structures are common, especially along the SW margin of the Vinodol Valley. Cross-cutting relationships suggest that transpressional (NW-SE and NE-SW striking dextral and sinistral faults) and extensional features (NW-SE and NE-SW striking normal faults) are structurally concurrent or younger than the reverse faults, suggesting a change in the palaeostress field during the Neogene-Quaternary, with prevalent transpression and radial extension. Comparison of results of the palaeostress field analysis and the constructed synthetic focal mechanisms on one side, with available focal mechanism solutions for earthquakes within the Ilirska Bistrica-Rijeka-Senj seismogenic fault zone on the other, shows a favourable orientation of the observed NW-SE and NE-SW striking faults with respect to the recent compressional/transpressional stress field (N-S oriented P-axis), indicating these as potential seismogenic sources within the study area.
Cretaceous shallow-marine carbonate rocks of SW Slovenia were deposited in the northern part of the Adriatic Carbonate Platform. A 560-m-thick continuous Upper Cenomanian to Santonian carbonate ...succession has been studied near Hrušica Village in Matarsko Podolje. With regard to lithological, sedimentological, and stratigraphical characteristics, the succession has been divided into nine lithostratigraphic units, mainly reflecting regressive and transgressive intervals of larger scale. During the latest Cenomanian and Early Turonian, hemipelagic limestones were deposited on top of shallow-marine lagoon and peritidal Upper Cenomanian deposits indicating relative sea-level rise. Subsequently, the deeper marine depositional setting was gradually filled by clinoform bioclastic sand bodies overlain by peritidal and shallow-marine low-energy mainly lagoonal lithofacies. Similar lithofacies of predominately inner ramp/shelf depositional settings prevail over the upper part (i.e., Coniacian to Santonian) of the succession. In the area, the Upper Cetaceous carbonate rocks are separated from the overlying Lower Eocene (Upper Paleocene?) carbonate sequence by regional unconformity denoted by distinct paleokarstic features. On the Adriatic Carbonate Platform the deeper marine carbonate setting, developed at the Cenomanian/Turonian boundary, is usually correlated with OAE2 and related eustatic sea-level rise. Similarly, subsequent reestablished shallow-marine conditions are related to Late Turonian long- and short-term sea-level fall. However, we are suggesting that deeper marine deposits were deposited in a tectonically induced intraplatform basin formed simultaneously with the uplift of the northern and northeastern marginal parts of the Adriatic Carbonate Platform.
On the NE slopes of Ćićarija Mt. (N Istria) a 120-150 m thick complex composed of dolomite-limestone breccia crops out between the Lower and Upper Cretaceous deposits. This studied breccia sequence ...is of post-sedimentary, tectogenic-diagenetic origin. It was formed bypoly phase tectonic fracture of the Upper Albian to Lower Cenomanian early- and late-diagenetic dolomite succession with relics of recrystallized limestone, which enabled very important subsequent diagenetic alteration. This included partial dissolution, dedolomitization,recrystallization and calcitization of the fine-grained, crushed dolomite matrix, and centripetal dissolution of dolomite fragments and their cementation by calcite and ferroan calcite cements, as wellas the partial collapse of fragments from the roofs of dissolution cavities and limited late-diagenetic silicification (the silica surplus originating from layers of diagenetic quartz from underlying Upper Albian deposits). Such a complex pattern of different events resulted in the high variability of breccia characteristics over relatively small distances, especially near more intensively tectonized zones. The contemporaneous stratigraphic level (Lower to Upper Cretaceous transition) in other parts of the Adriatic Carbonate Platform is also characterised by predominantly late-diagenetic dolomites with relics of limestones (including local occurrences of early-diagenetic dolomites) which are, in more tectonized areas, late-diagenetically altered into tectogenic-diagenetic breccias.
Twelve lithostratigraphic units, representing a 5 km thick succession,have been determined from the Senj -Ogulin profile through theVelika Kapela Mt. This 45 km long sequence lies approximately ...normalto the Dinaric strike. Carbonate deposits ranging from the MiddleLiassic to the Albian include laterally variable environments duringthe Kimmeridgian and Lower Tithonian. The deposits were deformedby compressive tectonics during the Tertiary tectonic cycle, and wereconsequently reshaped by weaker Neotectonic transpression. Thereforestructures with the N-S strike, which are different to the commonDinaric strike (NW-SE), are interpreted as a consequence of syngenetic bending during the Tertiary cycle, rather than rotation during theNeotectonic cycle.
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