engleski

Reconstruction of the Sarmatian paleoenvironments based on benthic foraminifera, case study: Bukova glava section.

The section Bukova glava, located within the quarry Našicecement d.d., on the northern slope of Krndija Mt., belongs to the North Croatian Basin. During the Middle Miocene, the basin situated on the southwestern margin of the Central Paratethys Sea, was a part of Pannonian Basin System (PAVELIĆ & KOVAČIĆ, 2018). Previous studies revealed the continuity of sedimentation from the Badenian to Sarmatian (KOVAČIĆ et al., 2015 ; KOVAČIĆ et al., 2017). The Upper Badenian Bulimina – Bolivina was identified in the section based on smaller benthic foraminifera, whereas the top of the section was attributed to the Anomalinoides dividens zone of the Lower Sarmatian. Due to recent work in quarry, the upper part of the sections became available for study and consequently high-resolution sampling and logging took place in April 2019. This abstract contains preliminary results of study of smaller benthic foraminifera from newly exposed dark and light marly beds. Samples submitted standard treatment in laboratory (wet sieving and standardization into aliquots of about 300 specimens per sieve-residue). The analysis included quantification of planktonic vs benthic foraminifera (P/B ratio), generic interpretation of benthics and study of taphonomic conditions of foraminiferal tests. All studied tests are well preserved. The low values of P/B ratio are characteristic for shallow-water settings, inner shelf zone, whereas greater values of the ratio, found in some parts of the section, suggest possible deepening of the Sarmatian paleoenvironment. Two foraminiferal assemblages were described, Elphidium assemblage confined to the light marls and Bolivina assemblage to the dark beds. Elphidium assemblage is composed of large individuals of epifaunal forms among which representatives of Elphidium sp. with well- developed keel prevail. These characteristics suggest an oxic environment, with phytal covers where herbivores thrived (according to MURRAY, 2006). The dark marly samples depict that changes in the environments took place. The Bolivina assemblage is made of smaller individuals where Bolivina representatives dominate. Infaunal mode of life, dysoxic conditions (MURRAY, 2006) and detritus feeders are characteristics of bolivinas, implying possible reduction in oxygen concertation. The local sea-level changes or changes in terrigeous input caused by different rate of weathering could provoked such alteration of foraminiferal assemblages.

Elphidium sp. ; Bolivina sp. ; Sarmatian ; Central Paratethys ; Bukova Glava

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