Geological and structural setting of the Vinodol Valley (NW Adriatic, Croatia): insights into its tectonic evolution based on structural investigations

Abstract

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 km 2 (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.

Types and Distribution of Quaternary Deposits Originating From Carbonate Rock Slopes in the Vinodol Valley, Croatia – New Insight Using Airborne Lidar Data

“…Quaternary sediments identified in the NW part of the Vinodol Valley mostly represent the engineering soils deposited by multiple debris flow events (e.g., Figure 13g), and not only the carbonate breccias formed by the intensive structural deformation of carbonate rocks along the north-eastern margin (Blašković, 1999). However, despite certain differences in the spatial distribution, the engineering formations identified in this study can be correlated with informal lithostratigraphic units determined by Palenik et al (2019), where the older talus (B s1 ), recent talus (B s2 ) and boulders and olistoliths (B,Ol) correspond to the rockfall deposits, the proximal proluvium (GS pr ) and distal proluvium (GS-SG pr ) correspond to the deluvialproluvial deposits, and the breccia (Br) corresponds to the rockfall breccias. Taking into account the prominent historical and instrumentally recorded seismicity of the study area (Palenik et al, 2019), and the upcoming climate changes, the stratigraphy, sedimentology and origin of Quaternary deposits in the Vinodol Valley need to be further investigated in more detail, partly because of the question whether similar landslide events could occur in the present age, given that morphological features indicative of rock slope deformations (Hungr et al, 2014) are in places visible along the carbonate cliffs (marked with purple arrows in Figure 13a, f).…”

“…The geological map of the Vinodol Valley at a scale 1:25.000 published by Palenik et al (2019) shows that the informal lithostratigraphic unit of the Quaternary rockfall breccias is distributed only in a small area along the north-eastern part of the flysch slopes in the central part of the Vinodol Valley, i.e., in the wider area of the Blaškovići settlement located at the foot slope of the carbonate cliffs. Flysch bedrock is mostly covered by the Quaternary deluvial-proluvial deposits, composed of unsorted angular to sub-rounded carbonate rock fragments ranging in size from gravel to boulder mixed with fine-grained reddish soil.…”

“…The inner parts and the bottom of the valley are formed of Palaeogene flysch deposits, predominantly composed of alternations of sandstones and marls (Šušnjar et al, 1970). Highly fractured carbonate rock slopes in both valley flanks are separated from the inner flysch slopes by predominantly reverse fault contacts (Blašković, 1999;Palenik et al, 2019). Carbonate rocks that separate the Vinodol Valley from the Adriatic coast are in the form of a brachianticline with a more steeply inclined north-eastern flank, whereas carbonates in the north-eastern valley flank exhibit a more complex tectonic structure.…”

“…57-77, DOI: 10.17794/rgn.2020.4.6 movements of carbonate detritus to the hypsometrically lower portions of the Vinodol Valley (Blašković, 1999). Considering falls to be the only type or predominant type of movement, different types of superficial deposits consisting of carbonate rock fragments have been commonly designated by the term rockfall, added to the name of the identified material: for example, Quaternary rockfall breccia (Blašković, 1999), or Quaternary rockfall deposits (Palenik et al, 2019). Although gravitational mass movements were probably initiated predominantly by rockfalls triggered by strong earthquakes, the shapes, sizes and hypsometric positions of certain sedimentary bodies suggest that some other types of mass movements were also involved in their accumulation (Đomlija et al, 2019b).…”

Active Tectonics in the Kvarner Region (External Dinarides, Croatia)—An Alternative Approach Based on Focused Geological Mapping, 3D Seismological, and Shallow Seismic Imaging Data

“…The earthquake hypocenters lie mostly at depths of up to 20 km, within the seismogenic tectonic zone striking in the NW-SE direction along the coastline. The Ilirska Bistrica-Rijeka-Vinodol-Senj zone is interpreted as an obliquely reverse fault system that accommodates oblique subduction of the Adriatic microplate and the compression in the Dinarides (Kuk et al, 2000;Palenik et al, 2019), along the NE Adriatic fault zone.…”