Naslov
Bioeroded rocky-shores and calcareous plankton stratigraphy of the Middle Miocene (Badenian) transgressive successions in the North Croatian Basin (Central Paratethys)

Autori
Brlek, Mihovil ; Ćorić, Stjepan ; Iveša, Ljiljana ; Santos, Ana ; Špišić, Monika ; Brčić, Vlatko ; Devescovi, Massimo ; Mišur, Ivan ; Avanić, Radovan ; Johnson, Markes

Vrsta, podvrsta i kategorija rada
Sažeci sa skupova, sažetak, ostalo

Izvornik
7th international workshop Neogene of Central and south-eastern Europe, abstracts book / Horvat, Marija ; Wacha, Lara - Zagreb : Hrvatski geološki institut, 2017, 16-18

ISBN
978-953-59036-4-2

Skup
7th international workshop Neogene of Central and south-eastern Europe

Mjesto i datum
Velika, Hrvatska, 28.05.2017. - 31.05.2017

Vrsta sudjelovanja
Predavanje

Vrsta recenzije
Nije recenziran

Ključne riječi
Gastrochaenolites-Entobia ichnoassemblage · Trypanites ichnofacies · Rocky shore · Badenian · North Croatian

Sažetak
Mesozoic (Upper Cretaceous and Triassic) basement limestone lithoclasts occurring in basal conglomerates (overlain by rhodolith-bearing and maërl deposits) of the Middle Miocene transgressive deepening-upward successions of northeast Mt. Medvednica (North Croatian Basin, Central Paratethys ; BRLEK et al., 2016) show abundant Gastrochaenolites and Entobia borings (represented by an in situ rocky substrate community of bivalves and sponges, respectively), with Gastrochaenolites being the dominant ichnogenus and together with Entobia often occurring on all sides of limestone clasts. Gastrochaenolites torpedo and Gastrochaenolites lapidicus are the two most commonly recorded ichnospecies of bivalve borings (with possible occurrence of G. dijugus, G. cluniformis, and G. orbicularis). Gastrochaenolites-Entobia ichnofossil assemblage related to the Entobia subichnofacies and in turn assignable to the Trypanites Ichnofacies, is very typical of Neogene rocky shores (DE GIBERT et al., 2012). This ichnoassociation characterizes littoral rockground environments indicating wave-cut platforms and marine flooding surfaces (transgressive surfaces) with a low or null rate of sedimentation (BROMLEY & ASGAARD, 1993). Actualistic comparison was made in order to make more accurate palaeoecological and palaeoenvironmental interpretations (based on e.g., ecology of possible tracemakers, as well as recorded trace fossil assemblages, orientation, preservation, and succession of ichnocoenosis with possible cross-cutting relationships) of the basal Middle Miocene conglomerates. Modern Northern Adriatic rocky coast endoliths (Lithophaga lithophaga, Rocellaria/Gastrochaena dubia, clinoid sponges) and their bioerosion trace fossils (Gastrochaenolites torpedo, Gastrochaenolites dijugus, ? G. lapidicus, Entobia sp.) were analysed from breakwater limestone boulders of the west Istrian coast (DEVESCOVI & IVEŠA, 2008). The Badenian, regarded as Middle Miocene regional stage of the Central Paratethys, has recently been subdivided by HOHENEGGER et al. (2014) based on paleoclimatic events (e.g., MMCO and MMCT), sea-level changes and biostratigraphic data. According to ĆORIĆ et al. (2009), the initial Middle Miocene marine flooding of the North Croatian Basin corresponds to Middle Badenian transgressive pulse (NN5 Zone, TB 2.4) of the Central Paratethys (HOHENEGGER et al., 2014). The co-occurrence of calcareous nannoplankton Sphenolithus heteromorphus and Helicosphaera waltrans (with absence of Helicosphaera ampliaperta) in some marl intervals (which represent the uppermost part of the Middle Miocene trangressive deepeningupward successions on northeast Mt. Medvednica) analysed here, points to the lower part of nannoplankton Zone NN5. HOHENEGGER et al. (2014) correlated this part of NN5 with Orbulina suturalis Plankton Zone of the Middle Badenian (TB 2.4 – main Badenian transgressive pulse of the Central Paratethys), which is also supported by the recorded co-occurrence of planktonic foraminifera Orbulina suturalis and Praeorbulina glomerosa circularis. Somewhat younger age (the upper part of NN5 Zone) of some successions is suggested by the occurence of Orbulina universa, supported also by recorded nannoplankton assemblage with Reticulfenestra minuta, Coccolithus pelagicus and Helicosphaera carteri. Besides the Badenian transgressive pulse(s) of the Central Paratethys being the probable cause for the development of Mt. Medvednica transgressive successions, possible local tectonic influence must also be taken in consideration due to possible age difference and stratigraphic position of closely spaced Mt. Medvednica outcrops on the Badenian sea-level curve.

Izvorni jezik
Engleski

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