Shallow-water benthic foraminiferal assemblages and their response to the palaeoenvironmental changes — example from the Middle Miocene of Medvednica Mt. (Croatia, Central Paratethys)

Abstract

During the Middle Miocene, the northern Croatian Medvednica Mt. was an island within the Pannonian Basin System, situated on the SW margin of the Central Paratethys Sea. Miocene sedimentary rocks (the Late Badenian Bulimina-Bolivina Zone and Ammonia beccarii ecozone), from the SW slopes of Medvednica Mt. clearly reflect a transgressive-regressive cycle with emersion during the Badenian/Sarmatian boundary. After the initial phase of transgression, the pioneer Elphidium-Asterigerinata-Ammonia benthic foraminiferal assemblage is present in bioclastic limestones, such as those at the Borovnjak locality. This marginal marine assemblage from a highly energetic, normally saline environment is characterized by poor preservation of foraminiferal tests, low diversity and strong domination. Advanced transgression is followed by establishment of the Elphidium-Asterigerinata assemblage, which is found in biocalcsiltites from the laterally deeper and more sheltered environment at Gornje Vrapče. This diverse assemblage is typical for inner/middle shelf environment with sufficient oxygen content. A general shallowing upward trend can be recognized at both localities, followed by visible interchange of different sedimentological and biotic features. Successive and oscillatory regression in the marginal marine environment was followed by salinity fluctuations and final brackish conditions with Ammonia-Elphidium assemblage. The laterally deeper environment reacted to regressive trends on finer scale with almost regular changes of benthic foraminiferal assemblages in the laminae (Heterolepa-Bolivina assemblage/Bolivina-Cassidulina assemblage/Elphidium-Asterigerinata assemblage). It might reflect sea-level oscillations with periodically increased siliciclastic and nutrient input from land or influence of seasonality on benthic assemblages, which occurred in the advanced phase of the regression near the Badenian/Sarmatian boundary.

Facies analyses, biostratigraphy and radiometric dating of the Lower-Middle Miocene succession near Zajecar (Dacian basin, eastern Serbia)

“…RTK-1501, RTK-1502a) there is an in-dication about the late Badenian transgressive event. It could be correlative with global 3 rd order cycle TB 2.5 of sea-level fluctation that is already known form Central Paratethys (ćoRIć et al, 2009;PEZELj et al, 2016). Species such as Ammonia ex gr.…”

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“…Determination was corrected according to the up-to-date WORMS database (World Register of Marine Species, 2019) to exclude invalid names and synonyms. The ecological/palaeoecological preference of each benthic species was taken from MURRAY (1991,2006), BÁLDI (2006); PEZELJ et al (2013PEZELJ et al ( , 2016, including all references therein), and others referred to later in the text.…”

The evolution of the Carpathian Foredeep Basin during the latest Badenian and Sarmatian (Middle Miocene): inferences from micropalaeontological data

“…As sem blage IX (Figs. 2 and 3) of the Up per Sarmatian, com posed of high abundant infaunal spe cies be long ing to Bulimina and Bolivina, in dicates deeper sea depths (mid dle neritic) with gen er ally normal-sa lin ity and low ox y gen-con tent at the sea-floor (Murray, 1991;Sen Gupta and Machain-Castillo, 1993;Jorissen et al, 1995;Dubicka et al, 2014;Drinia et al, 2016;Pezelj et al, 2016). Sim i lar con di tions can be pos tu lated for the de pos its of the up per most part of the Costeºti sec tion, rep re sented by As sem blage XI, which is en tirely com posed of rep re sen ta tives of Fissurina (Silye, 2015).…”