Sedimentology and biostratigraphy of the Early-Middle Miocene transition in NW Transylvanian Basin (Pâglişa and Dej sections)

• Published in: Studia Universitatis Babes-Bolyai, Geologia
• Main Authors: Beldean, Claudia, Bercea, Răzvan, Filipescu, Sorin
• Format: Report
• Language: unknown
• Published: Digital Commons @ University of South Florida 2013
• Subjects: Early-Middle Miocene boundary; Transylvanian Basin; planktonic foraminifera; sedimentology; progradation; Geology; Planktonic foraminifera
• Online Access: https://digitalcommons.usf.edu/geologia/vol58/iss1/art5; https://doi.org/10.5038/1937-8602.58.1.5; https://digitalcommons.usf.edu/context/geologia/article/1265/viewcontent/Vol58_1_5_Beldean_20130805.pdf

The Early - Middle Miocene transition can be studied in several sections from the north-western Transylvanian Basin, across the boundary between the Hida and Dej Formations. The Pâglişa and Râpa Dracului (Dej locally outcrop) sections offer a very good record of the changes in the sedimentary facies and micropaleontological content across the boundary. The lower parts of the sections display the upper Hida Formation with prodelta fine grained sediments covered by coarser grained sediments related to a delta front progradation. Four sedimentary facies associations have been separated based on grain size and associated sedimentary structures. Micropaleontological assemblages are moderately to poorly preserved, with a low abundance and diversity. Planktonic Streptochilus pristinum is the main taxon associated with rare (< 10%) calcareous benthic foraminifera (Bulimina, Bolivina, Cibibicidoides). The Dej Formation consists of stacked channel lag deposits associated with lateral accretion bars and crevasse splays followed by fall-out tuffs and redeposited low density tuffites interbedded with low density fine siliciclastics. The deposits of Dej Formation from the investigated areas were separated in four facies associations based on grain size/petrography and primary sedimentary structures. Micropaleontological assemblages contain typical early Badenian planktonic foraminifera (species of Orbulina, Praeorbulina, Globigerinoides, and Globorotalia) associated to the main phase of the marine transgresion from the beginning of the Middle Miocene.