engleski

Recurrent events of dinoturbation in the Early Cretaceous deposits, Cape Gustinja, Istria.

Cape Gustinja is located on the western coast of Istria, near the Kolone Bay. The outcrops with footprints are located near the shore on the southern side of Cape Gustinja, and the exposed location contributes to destruction and decay of the footprints (both by nature and tourists). The investigated succession on the Cape Gustinja consists of well-bedded limestones with an average thickness of 20 cm. Since the tracksite is situated at the seaside, during normal tide the water covers some layers that include recognized footprints. Due to the susceptibility of limestone to erosion and seawater corrosion, almost all dinosaur footprints at this site are at least partially damaged, and some are almost unrecognizable. A continuous 20m-thick section of shallow-water platform carbonates was studied to determine biostratigraphy of microfossil assemblage (benthic foraminifera and calcareous algae) and microfacies. Studied succession indicates deposition within very shallow inner platform environments occasionally interrupted by short lasting subaerial exposures (occasionally short lasting emergent horizon). The main horizon with the dinosaur footprints is composed of wackestone with bioclasts and fenestral laminites deposited in the intertidal environments (Fig. 1). Bioclasts of bivalves, gastropods, ostracods, benthic foraminifers and green algae prevail. The Late Valanginian – Early Hauterivian age of these deposits is based on their microfossil content, which is dominated by ostracods, benthic foraminifera and calacareous green algae (Dasycladales). The Cape Gustinja site is unique among the Croatian tracksites characterized by a relatively small area with abundant track horizons in a short time sequence. Track horizons include fossilized dinosaur footprints and dinoturbated layers with dinoturbation in several stratigraphical horizons, sometimes located directly below each other. Layers with dinoturbation are extremely disturbed, the individual footprints and their movement directions are almost impossible to discern, so whole ichnotaxonomic interpretation is based on horizons without dinoturbation. Although the Gustinja site is relatively close (about 900m) to another dinosaur footprint site (the Palud locality ; MEZGA et al., 2015), a fault zone located at the tip of Cape Gustinja separates the two localities and disable the correlation. In the Gustinja Cape carbonate succession eight different horizons with dinosaur footprints and dinoturbation have been identified. More than 50 individual footprints and several trackways are recognized. Two types of tracks can be discerned ; circular-elliptical and semi-circular to half-moon forms. Because of this characteristic appearance, and without any apparent more detailed morphology, the footprints are attributed to the sauropod dinosaur, which is in line with earlier research (DALLA VECCHIA et al., 2000). The main trackbearing layer is split into two separate outcrops with a fault between. Dinoturbated layers are placed above the main layer with the footprints, what in the undisturbed sediment sequence means that they are stratigraphically younger. The length of the footprints varies between 30 and 60 cm indicating individuals of different length (up to 20 meters).

Dinosaur footprints, Dinoturbation, Sauropods, Early Cretaceous, Istria

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